Gene Summary

Gene:COL4A6; collagen type IV alpha 6 chain
Aliases: DFNX6, DELXq22.3, CXDELq22.3
Summary:This gene encodes one of the six subunits of type IV collagen, the major structural component of basement membranes. Like the other members of the type IV collagen gene family, this gene is organized in a head-to-head conformation with another type IV collagen gene, alpha 5 type IV collagen, so that the gene pair shares a common promoter. Deletions in the alpha 5 gene that extend into the alpha 6 gene result in diffuse leiomyomatosis accompanying the X-linked Alport syndrome caused by the deletion in the alpha 5 gene. Alternative splicing results in multiple transcript variants encoding different isoforms. [provided by RefSeq, Dec 2013]
Databases:OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:collagen alpha-6(IV) chain
Source:NCBIAccessed: 29 August, 2019


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1994-2019)
Graph generated 29 August 2019 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Mediator Complex
  • Leiomyomatosis
  • Immunohistochemistry
  • Sequence Homology, Nucleic Acid
  • Vulva
  • Molecular Sequence Data
  • Sex Chromosome Aberrations
  • Urinary Bladder
  • Muscle, Smooth
  • Young Adult
  • Sequence Deletion
  • Exome
  • Stomach Cancer
  • DNA Mutational Analysis
  • X-Ray Computed Tomography
  • Exons
  • Messenger RNA
  • Mutation
  • Genome-Wide Association Study
  • Leiomyoma
  • Childhood Cancer
  • Base Sequence
  • Basement Membrane
  • Biomarkers, Tumor
  • Gene Deletion
  • Phenotype
  • Esophageal Cancer
  • Collagen Type IV
  • Esophagus
  • Restriction Mapping
  • Gene Expression Profiling
  • Collagen
  • Point Mutation
  • Cancer RNA
  • Polymerase Chain Reaction
  • X Chromosome
  • Viscera
  • Cancer Gene Expression Regulation
  • Nephritis, Hereditary
Tag cloud generated 29 August, 2019 using data from PubMed, MeSH and CancerIndex

Specific Cancers (2)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: COL4A6 (cancer-related)

Mello JBH, Barros-Filho MC, Abreu FB, et al.
MicroRNAs involved in the HMGA2 deregulation and its co-occurrence with MED12 mutation in uterine leiomyoma.
Mol Hum Reprod. 2018; 24(11):556-563 [PubMed] Related Publications
STUDY QUESTION: Can the mediator complex subunit 12 (MED12) mutation and high mobility group AT-hook 2 (HMGA2) overexpression co-occurrence be explained by the alternative mechanism of HMGA2 dysregulation in uterine leiomyomas (UL)?
SUMMARY ANSWER: The co-occurrence of MED12 mutation and HMGA2 overexpression, and a negative correlation of five validated or predicted microRNAs that target HMGA2 were reported.
WHAT IS KNOWN ALREADY: The recent stratification of UL, according to recurrent and mutually exclusive genomic alterations affecting HMGA2, MED12, fumarate hydratase (FH) and collagen type IV alpha 5-alpha 6 (COL4A5-COL4A6) pointed out the involvement of distinct molecular pathways. However, the mechanisms of regulation involving these drivers are poorly explored.
STUDY DESIGN, SIZE, DURATION: A total of 78 UL and 34 adjacent normal myometrium (NM) tissues was collected from 56 patients who underwent hysterectomies at a single institution. The patients were treated at the Department of Gynecology and Obstetrics, School of Medicine, Sao Paulo State University, Botucatu, SP, Brazil, from October 1995 to February 2004.
PARTICIPANTS/MATERIALS, SETTING, METHODS: Gene expression profiling was evaluated from fresh frozen tissues and compared with MED12 mutations at exon 2. In addition, RT-qPCR was applied to evaluate the expression levels of HMGA2 and their predictive miRNA regulators: hsa-let-7a, miR-26a, miR-26b, mir-93 and mir-106b.
MAIN RESULTS AND THE ROLE OF CHANCE: An unsupervised hierarchical clustering analysis revealed two main clusters with one of them (26 of 42 UL) showing an enrichment of MED12 mutated cases (18 of 26 UL). Increased expression levels of HMGA2 were observed in both clusters, including cases with MED12 mutation (cluster 1:18 UL). A significant HMGA2 overexpression (P < 0.001) in UL in comparison with NM was found. Five miRNAs predicted to regulate HMGA2 were significantly downregulated (P < 0.001) and negatively correlated to HMGA2 expression levels (P < 0.05) in UL.
LIMITATIONS REASONS FOR CAUTION: An in vivo functional study was not performed to validate the microRNAs and HMGA2 interaction due to technical limitations.
WIDER IMPLICATIONS OF THE FINDINGS: HMGA2 overexpression was detected in a significant number of MED12 mutated ULs, suggesting that these alterations coexist. Furthermore, five miRNAs were described as potential regulators of HMGA2 expression in UL.
LARGE-SCALE DATA: Data available in the Gene Expression Omnibus GSE42939.
STUDY FUNDING AND COMPETING INTEREST(S): This study was supported by grants from Fundação de Amparo a Pesquisa do Estado de São Paulo (# 2008/58835-2) and Conselho Nacional de Pesquisa (# 485032/2007-4), Brazil. The authors declared having no conflicts of interest.

Nozu K, Minamikawa S, Yamada S, et al.
Characterization of contiguous gene deletions in COL4A6 and COL4A5 in Alport syndrome-diffuse leiomyomatosis.
J Hum Genet. 2017; 62(7):733-735 [PubMed] Related Publications
Alport syndrome-diffuse leiomyomatosis (AS-DL, OMIM: 308940) is a rare variant of the X-linked Alport syndrome that shows overgrowth of visceral smooth muscles in the gastrointestinal, respiratory and female reproductive tracts in addition to renal symptoms. AS-DL results from deletions that encompass the 5' ends of the COL4A5 and COL4A6 genes, but deletion breakpoints between COL4A5 and COL4A6 have been determined in only four cases. Here, we characterize deletion breakpoints in five AS-DL patients and show a contiguous COL4A6/COL4A5 deletion in each case. We also demonstrate that eight out of nine deletion alleles involved sequences homologous between COL4A5 and COL4A6. Most breakpoints took place in recognizable transposed elements, including long and short interspersed repeats, DNA transposons and long-terminal repeat retrotransposons. Because deletions involved the bidirectional promoter region in each case, we suggest that the occurrence of leiomyomatosis in AS-DL requires inactivation of both genes. Altogether, our study highlights the importance of homologous recombination involving multiple transposed elements for the development of this continuous gene syndrome and other atypical loss-of-function phenotypes.

Ryu D, Lee C
Expression quantitative trait loci for PI3K/AKT pathway.
Medicine (Baltimore). 2017; 96(1):e5817 [PubMed] Free Access to Full Article Related Publications
A genome-wide association study (GWAS) was conducted to identify expression quantitative trait loci (eQTLs) for the genes involved in phosphatidylinositol-3-kinase/v-akt murine thymoma viral oncogene homolog (PI3K/AKT) pathway.Data on mRNA expression of 341 genes in lymphoblastoid cell lines of 373 Europeans recruited by the 1000 Genomes Project using Illumina HiSeq2000 were utilized. We used their genotypes at 5,941,815 nucleotide variants obtained by Genome Analyzer II and SOLiD.The association analysis revealed 4166 nucleotide variants associated with expression of 85 genes (P < 5 × 10). A total of 73 eQTLs were identified as association signals for the expression of multiple genes. They included 9 eQTLs for both of the genes encoding collagen type I alpha 1 (COL1A1) and integrin alpha 11 (ITGA11), which synthesize a major complex of plasma membrane. They also included eQTLs for type IV collagen molecules; 13 eQTLs for both collagen type IV alpha 1 (COL4A1) and collagen type IV alpha 2 (COL4A2) and 18 eQTLs for both collagen type IV alpha 5 (COL4A5) and collagen type IV alpha 6 (COL4A6). Some genes expressed by the eQTLs might induce expression of the genes encoding type IV collagen. One eQTL (rs16871986) was located in the promoter of palladin (PALLD) gene which might synthesize collagen by activating fibroblasts through the PI3K/AKT pathway. Another eQTL (rs34845474) was located in an enhancer of cadherin related family member 3 (CDHR3) gene which can mediate cell adhesion.This study showed a profile of eQTLs for the genes involved in the PI3K/AKT pathway using a healthy population, revealing 73 eQTLs associated with expression of multiple genes. They might be candidates of common variants in predicting genetic susceptibility to cancer and in targeting cancer therapy. Further studies are required to examine their underlying mechanisms for regulating expression of the genes.

Strand SH, Switnicki M, Moller M, et al.
RHCG and TCAF1 promoter hypermethylation predicts biochemical recurrence in prostate cancer patients treated by radical prostatectomy.
Oncotarget. 2017; 8(4):5774-5788 [PubMed] Free Access to Full Article Related Publications
PURPOSE: The lack of biomarkers that can distinguish aggressive from indolent prostate cancer has caused substantial overtreatment of clinically insignificant disease. Here, by genome-wide DNA methylome profiling, we sought to identify new biomarkers to improve the accuracy of prostate cancer diagnosis and prognosis.
EXPERIMENTAL DESIGN: Eight novel candidate markers, COL4A6, CYBA, TCAF1 (FAM115A), HLF, LINC01341 (LOC149134), LRRC4, PROM1, and RHCG, were selected from Illumina Infinium HumanMethylation450 BeadChip analysis of 21 tumor (T) and 21 non-malignant (NM) prostate specimens. Diagnostic potential was further investigated by methylation-specific qPCR analysis of 80 NM vs. 228 T tissue samples. Prognostic potential was assessed by Kaplan-Meier, uni- and multivariate Cox regression analysis in 203 Danish radical prostatectomy (RP) patients (cohort 1), and validated in an independent cohort of 286 RP patients from Switzerland and the U.S. (cohort 2).
RESULTS: Hypermethylation of the 8 candidates was highly cancer-specific (area under the curves: 0.79-1.00). Furthermore, high methylation of the 2-gene panel RHCG-TCAF1 was predictive of biochemical recurrence (BCR) in cohort 1, independent of the established clinicopathological parameters Gleason score, pathological tumor stage, and pre-operative PSA (HR (95% confidence interval (CI)): 2.09 (1.26 - 3.46); P = 0.004), and this was successfully validated in cohort 2 (HR (95% CI): 1.81 (1.05 - 3.12); P = 0.032).
CONCLUSION: Methylation of the RHCG-TCAF1 panel adds significant independent prognostic value to established prognostic parameters for prostate cancer and thus may help to guide treatment decisions in the future. Further investigation in large independent cohorts is necessary before translation into clinical utility.

Yatsenko SA, Mittal P, Wood-Trageser MA, et al.
Highly heterogeneous genomic landscape of uterine leiomyomas by whole exome sequencing and genome-wide arrays.
Fertil Steril. 2017; 107(2):457-466.e9 [PubMed] Related Publications
OBJECTIVE: To determine the genomic signatures of human uterine leiomyomas and prevalence of MED12 mutations in human uterine leiomyosarcomas.
DESIGN: Retrospective cohort study.
SETTING: Not applicable.
PATIENT(S): This study included a set of 16 fresh frozen leiomyoma and corresponding unaffected myometrium specimens as well as 153 leiomyosarcomas collected from women diagnosed with uterine leiomyomas or leiomyosarcomas who underwent clinically indicated abdominal hysterectomy.
MAIN OUTCOME MEASURE(S): Whole exome sequencing and high-resolution X-chromosome and whole genome single nucleotide polymorphism microarray analyses were performed on leiomyoma samples negative for the known MED12 mutations and compared with their corresponding myometrium. Leiomyosarcoma specimens were examined for exon 2 MED12 mutations to evaluate the frequency of MED12 mutated leiomyosarcomas.
RESULT(S): Our results indicate remarkable genomic heterogeneity of leiomyoma lesions. MED12-negative leiomyomas contain copy number alterations involving the Mediator complex subunits such as MED8, MED18, CDK8, and long intergenic nonprotein coding RNA340 (CASC15), which may affect the Mediator architecture and/or its transcriptional activity. We also identified mutations in a number of genes that were implicated in leiomyomagenesis such as COL4A6, DCN, and AHR, as well as novel genes: NRG1, ADAM18, HUWE1, FBXW4, FBXL13, and CAPRIN1.
CONCLUSION(S): Mutations in genes implicated in cell-to-cell interactions and remodeling of the extracellular matrix and genomic aberrations involving genes coding for the Mediator complex subunits were identified in uterine leiomyomas. Additionally, we discovered that ∼4.6% of leiomyosarcomas harbored MED12 exon 2 mutations, but the relevance of this association with molecular pathogenesis of leiomyosarcoma remains unknown.

Chen X, Wu R, Wang S, et al.
RNA-Seq analysis for the potential targets and molecular mechanisms of 17 β-estradiol in squamous cell lung carcinoma.
Neoplasma. 2016; 63(3):394-401 [PubMed] Related Publications
The efficacy of 17 β-estradiol (E2) was valid in some cancers, while its effects on squamous cell lung carcinoma (SCLC) were still unclear. The aim of our study was to investigate the potential targets and molecular mechanisms of E2 in SCLC cells.Two RNA libraries from human lung carcinoma cells (SK-MES-1) with and without E2 treatment were constructed and sequenced. The differentially expressed genes (DEGs) between cells with or without E2 treatment were identified by cuffdiff software. Hierarchical Clustering Analysis (HCA) was performed for displaying gene expression changes and classification. Furthermore, enrichment analyses of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and Gene Ontology Biological Process (GO BP) terms were performed through DAVID. The protein-protein interaction (PPI) network was constructed through STRING. Additionally, differentially expressed lncRNAs were also selected by cuffdiff software.Total 129 DEGs including 58 up- and 71 down- regulated genes were obtained. Cancer-related pathways including small cell lung cancer, hypertrophic cardiomyopathy (HCM) and pathways in cancer and biological processes including regulation of phosphorus metabolic process, protein localization and nucleus organization were enriched. The PPI network with 113 nodes and 312 edges was constructed. CASP3, ITGA2, COL4A6, PML and CDC25B were identified as hub nodes which had more interactions with others in the PPI network. Furthermore, eight up-regulated and ten down-regulated lncRNAs were selected.CASP3, ITGA2 and Lnc-DLK1-4:31 (one of down-regulated lncRNAs) might play pivotal roles in E2 treated SCNC cells by influencing cell apoptosis, angiogenesis and cell invasion respectively.

Lim B, Kim C, Kim JH, et al.
Genetic alterations and their clinical implications in gastric cancer peritoneal carcinomatosis revealed by whole-exome sequencing of malignant ascites.
Oncotarget. 2016; 7(7):8055-66 [PubMed] Free Access to Full Article Related Publications
Peritoneal carcinomatosis accompanied by malignant ascites is a major cause of death of advanced gastric cancer (GC). To comprehensively characterize the underlying genomic events involved in GC peritoneal carcinomatosis, we analyzed whole-exome sequences of normal gastric tissues, primary tumors, and malignant ascites from eight GC patients. We identified a unique mutational signature biased toward C-to-A substitutions in malignant ascites. In contrast, the patients who received treatment of adjuvant chemotherapy showed a high rate of C-to-T substitutions along with hypermutation in malignant ascites. Comparative analysis revealed several candidate mutations for GC peritoneal carcinomatosis: recurrent mutations in COL4A6, INTS2, and PTPN13; mutations in druggable genes including TEP1, PRKCD, BRAF, ERBB4, PIK3CA, HDAC9, FYN, FASN, BIRC2, FLT3, ROCK1, CD22, and PIK3C2B; and mutations in metastasis-associated genes including TNFSF12, L1CAM, DIAPH3, ROCK1, TGFBR1, MYO9B, NR4A1, and RHOA. Notably, gene ontology analysis revealed the significant enrichment of mutations in the Rho-ROCK signaling pathway-associated biological processes in malignant ascites. At least four of the eight patients acquired somatic mutations in the Rho-ROCK pathway components, suggesting the possible relevance of this pathway to GC peritoneal carcinomatosis. These results provide a genome-wide molecular understanding of GC peritoneal carcinomatosis and its clinical implications, thereby facilitating the development of effective therapeutics.

Mehine M, Kaasinen E, Heinonen HR, et al.
Integrated data analysis reveals uterine leiomyoma subtypes with distinct driver pathways and biomarkers.
Proc Natl Acad Sci U S A. 2016; 113(5):1315-20 [PubMed] Free Access to Full Article Related Publications
Uterine leiomyomas are common benign smooth muscle tumors that impose a major burden on women's health. Recent sequencing studies have revealed recurrent and mutually exclusive mutations in leiomyomas, suggesting the involvement of molecularly distinct pathways. In this study, we explored transcriptional differences among leiomyomas harboring different genetic drivers, including high mobility group AT-hook 2 (HMGA2) rearrangements, mediator complex subunit 12 (MED12) mutations, biallelic inactivation of fumarate hydratase (FH), and collagen, type IV, alpha 5 and collagen, type IV, alpha 6 (COL4A5-COL4A6) deletions. We also explored the transcriptional consequences of 7q22, 22q, and 1p deletions, aiming to identify possible target genes. We investigated 94 leiomyomas and 60 corresponding myometrial tissues using exon arrays, whole genome sequencing, and SNP arrays. This integrative approach revealed subtype-specific expression changes in key driver pathways, including Wnt/β-catenin, Prolactin, and insulin-like growth factor (IGF)1 signaling. Leiomyomas with HMGA2 aberrations displayed highly significant up-regulation of the proto-oncogene pleomorphic adenoma gene 1 (PLAG1), suggesting that HMGA2 promotes tumorigenesis through PLAG1 activation. This was supported by the identification of genetic PLAG1 alterations resulting in expression signatures as seen in leiomyomas with HMGA2 aberrations. RAD51 paralog B (RAD51B), the preferential translocation partner of HMGA2, was up-regulated in MED12 mutant lesions, suggesting a role for this gene in the genesis of leiomyomas. FH-deficient leiomyomas were uniquely characterized by activation of nuclear factor erythroid 2-related factor 2 (NRF2) target genes, supporting the hypothesis that accumulation of fumarate leads to activation of the oncogenic transcription factor NRF2. This study emphasizes the need for molecular stratification in leiomyoma research and possibly in clinical practice as well. Further research is needed to determine whether the candidate biomarkers presented herein can provide guidance for managing the millions of patients affected by these lesions.

Ordulu Z
Fibroids: Genotype and Phenotype.
Clin Obstet Gynecol. 2016; 59(1):25-9 [PubMed] Free Access to Full Article Related Publications
Fibroids represent a major public health care problem as the most prevalent pelvic tumors in women of reproductive age and as the leading cause of gynecologic surgeries in the United States. The recent advances in the genomic technologies including genome-wide association studies and high-throughput sequencing provide insight into their pathogenesis and molecular classification. Understanding the molecular basis of fibroids may facilitate development of effective targeted treatment options of this very common disease.

Liu W, Wong JK, He Q, et al.
Chinese family with diffuse oesophageal leiomyomatosis: a new COL4A5/COL4A6 deletion and a case of gonosomal mosaicism.
BMC Med Genet. 2015; 16:49 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Diffuse oesophageal leiomyomatosis (DOL) is a rare disorder characterized by tumorous overgrowth of the muscular wall of the oesophagus. DOL is present in 5 % of Alport syndrome (AS) patients. AS is a rare hereditary disease that involves varying degrees of hearing impairment, ocular changes and progressive glomerulonephritis leading to renal failure. In DOL-AS patients, the genetic defect consists of a deletion involving the COL4A5 and COL4A6 genes on the X chromosome.
CASE PRESENTATION: We report a two-generation family (4 individuals; parents and two children, one male and one female) with two members (mother and son) affected with oesophageal leiomyomatosis. Signs of potential renal failure, which characterizes AS, were only apparent in the index patient (son) 2 years and three months after the initial diagnosis of DOL. Blood DNA from the four family members were submitted to exome sequencing and array genotyping to perform a genome wide screening for disease causal single nucleotide (SN) and copy number (CN) variations. Analyses revealed a new 40kb deletion encompassing from intron 2 of COL4A5 to intron 1 of COL4A6 at Xq22.3. The breakpoints were also identified. Possible confounding pathogenic exonic variants in genes known to be involved in other extracellular matrices disorders were also shared by the two affected individuals. Meticulous analysis of the maternal DNA revealed a case of gonosomal mosaicism.
CONCLUSIONS: This is the first report of gonadosomal mosaicism associated to DOL-AS.

Mehine M, Mäkinen N, Heinonen HR, et al.
Genomics of uterine leiomyomas: insights from high-throughput sequencing.
Fertil Steril. 2014; 102(3):621-9 [PubMed] Related Publications
Uterine leiomyomas are benign smooth-muscle tumors of extremely low malignant potential. Early work utilizing classical cytogenetics revealed that a subset of uterine leiomyomas harbor recurrent chromosomal rearrangements, such as translocations affecting the HMGA2 gene. Our understanding of the genetics of many tumor types has deepened remarkably with the emergence of next-generation sequencing technologies. Exome sequencing identified that the majority of leiomyomas display highly specific MED12 mutations. Further studies suggest that these MED12 hotspot mutations are also frequent in breast fibroadenomas, but not in other human tumors. Whole-genome sequencing showed that a subset of leiomyomas display complex chromosomal rearrangements resembling chromothripsis. These were formed in a single event of chromosomal breakage and random reassembly involving one or a limited number of chromosomes. Although most leiomyomas have been shown to arise independently, these studies also revealed that distinct nodules within a uterus may display identical genetic changes indicating a common clonal origin. A minority of leiomyomas were also found to display deletions within the COL4A5-COL4A6 genes, leading to upregulation of the adjacent gene IRS4. The findings derived from high-throughput sequencing combined with previous knowledge have led to an emerging molecular classification of leiomyomas, suggesting that there are several distinct pathogenic pathways involved in leiomyoma formation. The evidence points to at least 4 molecular subclasses: leiomyomas with MED12 mutation, FH inactivation, HMGA2 overexpression, and COL4A6-COL4A5 deletion. Elucidating the molecular pathogenesis of leiomyomas should be relevant for developing treatments for this very common disease.

Sá MJ, Fieremans N, de Brouwer AP, et al.
Deletion of the 5'exons of COL4A6 is not needed for the development of diffuse leiomyomatosis in patients with Alport syndrome.
J Med Genet. 2013; 50(11):745-53 [PubMed] Related Publications
BACKGROUND: Alport syndrome (AS), a hereditary type IV collagen nephropathy, is a major cause of end-stage renal disease in young people. About 85% of the cases are X-linked (ATS), due to mutations in the COL4A5 gene. Rarely, families have a contiguous gene deletion comprising at least exon 1 of COL4A5 and the first exons of COL4A6, associated with the development of diffuse leiomyomatosis (ATS-DL). We report three novel deletions identified in families with AS, one of which challenges the current concepts on genotype-phenotype correlations of ATS/ATS-DL.
METHODS: In the setting of a multicentric study aiming to describe the genetic epidemiology and molecular pathology of AS in Portugal, three novel COL4A5 deletions were identified in two families with x-linked Alport syndrome (ATS) and in one family with ATS-DL. These mutations were initially detected by PCR and Multiplex Ligation-dependent Probe Amplification, and further mapped by high-resolution X chromosome-specific oligo-array and PCR.
RESULTS: In the ATS-DL family, a COL4A5 deletion spanning exons 2 through 51, extending distally beyond COL4A5 but proximally not into COL4A6, segregated with the disease phenotype. A COL4A5 deletion encompassing exons 2 through 29 was identified in one of the ATS families. In the second ATS family, a deletion of exon 13 of COL4A5 through exon 3 of COL4A6 was detected.
CONCLUSIONS: These observations suggest that deletion of the 5' exons of COL4A6 and of the common promoter of the COL4A5 and COL4A6 genes is not essential for the development of leiomyomatosis in patients with ATS, and that COL4A5_COL4A6 deletions extending into COL4A6 exon 3 may not result in ATS-DL.

Sousa RG, Figueiredo PC, Pinto-Marques P, et al.
An unusual cause of pseudoachalasia: the Alport syndrome-diffuse leiomyomatosis association.
Eur J Gastroenterol Hepatol. 2013; 25(11):1352-7 [PubMed] Related Publications
Alport syndrome (AS) is a hereditary disease characterized by glomerular nephropathy progressing to end-stage renal disease, frequently associated with sensorineural deafness and ocular abnormalities. Rarely, AS coexists with diffuse leiomyomatosis, a benign proliferation of smooth muscle in the gastrointestinal tract, mostly of the oesophagus, but also of the tracheobronchial tree and the female genital tract. Patients with this association have been shown to have contiguous gene deletion involving both COL4A5 and COL4A6 genes. The authors report the case of a 25-year-old man with AS and long-standing dysphagia. The patient received a renal transplant at the age of 23 because of end-stage renal disease. Clinical assessment as well as endoscopic, manometric and radiologic studies suggested the diagnosis of achalasia, which was treated by Heller's myotomy with Dor fundoplication. Postprocedure dysphagia led to an endoscopic ultrasound that showed diffuse thickening of the second layer, resulting in the hypothesis of oesophageal leiomyomatosis. The diagnosis was confirmed through histological study of endoscopic biopsies and genetic analysis.

Mehine M, Kaasinen E, Mäkinen N, et al.
Characterization of uterine leiomyomas by whole-genome sequencing.
N Engl J Med. 2013; 369(1):43-53 [PubMed] Related Publications
BACKGROUND: Uterine leiomyomas are benign but affect the health of millions of women. A better understanding of the molecular mechanisms involved may provide clues to the prevention and treatment of these lesions.
METHODS: We performed whole-genome sequencing and gene-expression profiling of 38 uterine leiomyomas and the corresponding myometrium from 30 women.
RESULTS: Identical variants observed in some separate tumor nodules suggested that these nodules have a common origin. Complex chromosomal rearrangements resembling chromothripsis were a common feature of leiomyomas. These rearrangements are best explained by a single event of multiple chromosomal breaks and random reassembly. The rearrangements created tissue-specific changes consistent with a role in the initiation of leiomyoma, such as translocations of the HMGA2 and RAD51B loci and aberrations at the COL4A5-COL4A6 locus, and occurred in the presence of normal TP53 alleles. In some cases, separate events had occurred more than once in single tumor-cell lineages.
CONCLUSIONS: Chromosome shattering and reassembly resembling chromothripsis (a single genomic event that results in focal losses and rearrangements in multiple genomic regions) is a major cause of chromosomal abnormalities in uterine leiomyomas; we propose that tumorigenesis occurs when tissue-specific tumor-promoting changes are formed through these events. Chromothripsis has previously been associated with aggressive cancer; its common occurrence in leiomyomas suggests that it also has a role in the genesis and progression of benign tumors. We observed that multiple separate tumors could be seeded from a single lineage of uterine leiomyoma cells. (Funded by the Academy of Finland Center of Excellence program and others.).

Varisli L
Identification of new genes downregulated in prostate cancer and investigation of their effects on prognosis.
Genet Test Mol Biomarkers. 2013; 17(7):562-6 [PubMed] Related Publications
Prostate cancer is the most common noncutaneous malignant neoplasm in men in the Western countries. It is well established that genetic and epigenetic alterations are common events in prostate cancer, which may lead to aberrant expression of critical genes. Most of the studies are focused on the overexpressed or duplicated genes in prostate cancer. However, it is known that some of the differentially expressed genes in prostate cancer are downregulated. Since the inventory of downregulated genes is incomplete, we performed in silico approaches to reveal the novel prostate cancer downregulated genes. Moreover, we also investigated for a possible link between the expression of the downregulated genes and tumor grade, recurrence, metastasis, or survival status in prostate cancer. Our results showed that the expression of GSTP1 and AOX1 are downregulated in prostate cancer, in concordance with previous reports. Moreover, we showed that TPM2, CLU, and COL4A6 mRNA levels are downregulated in prostate cancer. Further, we found a significant negative correlation between the expression of the above-mentioned genes and the prognosis of prostate cancer.

Zhou D, Yang L, Zheng L, et al.
Exome capture sequencing of adenoma reveals genetic alterations in multiple cellular pathways at the early stage of colorectal tumorigenesis.
PLoS One. 2013; 8(1):e53310 [PubMed] Free Access to Full Article Related Publications
Most of colorectal adenocarcinomas are believed to arise from adenomas, which are premalignant lesions. Sequencing the whole exome of the adenoma will help identifying molecular biomarkers that can predict the occurrence of adenocarcinoma more precisely and help understanding the molecular pathways underlying the initial stage of colorectal tumorigenesis. We performed the exome capture sequencing of the normal mucosa, adenoma and adenocarcinoma tissues from the same patient and sequenced the identified mutations in additional 73 adenomas and 288 adenocarcinomas. Somatic single nucleotide variations (SNVs) were identified in both the adenoma and adenocarcinoma by comparing with the normal control from the same patient. We identified 12 nonsynonymous somatic SNVs in the adenoma and 42 nonsynonymous somatic SNVs in the adenocarcinoma. Most of these mutations including OR6X1, SLC15A3, KRTHB4, RBFOX1, LAMA3, CDH20, BIRC6, NMBR, GLCCI1, EFR3A, and FTHL17 were newly reported in colorectal adenomas. Functional annotation of these mutated genes showed that multiple cellular pathways including Wnt, cell adhesion and ubiquitin mediated proteolysis pathways were altered genetically in the adenoma and that the genetic alterations in the same pathways persist in the adenocarcinoma. CDH20 and LAMA3 were mutated in the adenoma while NRXN3 and COL4A6 were mutated in the adenocarcinoma from the same patient, suggesting for the first time that genetic alterations in the cell adhesion pathway occur as early as in the adenoma. Thus, the comparison of genomic mutations between adenoma and adenocarcinoma provides us a new insight into the molecular events governing the early step of colorectal tumorigenesis.

Hirashima K, Iyama K, Baba Y, et al.
Differential expression of basement membrane type IV collagen α2 and α6 chains as a prognostic factor in patients with extrahepatic bile duct carcinoma.
J Surg Oncol. 2013; 107(4):402-7 [PubMed] Related Publications
BACKGROUND: The destruction of the basement membrane (BM) is the first step in cancer invasion and metastasis. Type IV collagen is a major component of the BM, and is composed of six genetically distinct α(IV) chains; α1(IV) to α6(IV). The loss of α5(IV) and α6(IV) chains from the epithelial BM at the early stage of cancer invasion has been reported in several types of cancers. However, the expression of α5(IV) and α6(IV) chains in extrahepatic bile duct carcinoma (EBDC) remains unclear.
METHODS: We examined the expression of α(IV) chains by immunohistochemistry using 71 resected EBDC specimens. Prognostic significance of α(IV) chains was examined by Cox regression and Kaplan-Meier analyses.
RESULTS: In the invasive cancer, the expression of α6(IV) chain in the BM was lost partially or completely preceded by the loss of α2(IV) chain. The loss of α6(IV) chain in the BM of the invasive cancer was related to the tumor classification, TNM stages, and the expression of α2(IV) chain. The patients with α2(IV)-negative and α6(IV)-negative chains had significantly poorer prognosis than those with α2(IV)-positive and α6(IV)-positive/negative chains (P = 0.04).
CONCLUSIONS: The loss of α2(IV) and α6(IV) chains might be a useful prognostic factor in patients with EBDC.

Uliana V, Marcocci E, Mucciolo M, et al.
Alport syndrome and leiomyomatosis: the first deletion extending beyond COL4A6 intron 2.
Pediatr Nephrol. 2011; 26(5):717-24 [PubMed] Related Publications
Alport syndrome (ATS) is a nephropathy characterized by the association of progressive hematuric nephritis with ultrastructural changes of the glomerular basement membrane (thinning, thickening, and splitting), sensorineural deafness, and variable ocular abnormalities (anterior lenticonus, macular flecks, and cataracts). The most common mode of transmission is X-linked inheritance, due to COL4A5 mutations. X-linked ATS is rarely associated with diffuse leiomyomatosis (DL), a benign hypertrophy of the visceral smooth muscle in gastrointestinal, respiratory, and female reproductive tracts. The ATS-DL complex is due to deletions that encompass the 5' ends of the COL4A5 and COL4A6 genes and include the bidirectional promoter. In this paper, we described 3 ATS-DL cases, 2 familial and 1 sporadic bearing a deletion encompassing the 5'-end of both the COL4A5 and COL4A6 genes, as identified by multiplex ligation-dependent probe amplification (MLPA) analysis. The array-CGH technique allowed a better definition of deletion size, confirming that the proximal breakpoint was within COL4A6 intron 2 in 2 cases. Surprisingly, 1 case had a deletion extending proximally beyond exon 3 of COL4A6, as confirmed by qPCR analysis. This is the largest deletion reported to date that has been associated with ATS-DL and this case should lead us to reconsider the mechanisms that might be involved in the development of diffuse leiomyomatosis.

Oohashi T, Naito I, Ueki Y, et al.
Clonal overgrowth of esophageal smooth muscle cells in diffuse leiomyomatosis-Alport syndrome caused by partial deletion in COL4A5 and COL4A6 genes.
Matrix Biol. 2011; 30(1):3-8 [PubMed] Related Publications
This is a study of a patient who manifests all of the features of a diffuse leiomyomatosis-Alport syndrome (DL-ATS), and her two-year-old son who has already been diagnosed with Alport syndrome. Fourteen years ago, the patient underwent a partial esophageal resection followed by a replacement with jejunum. Recently, she underwent a surgical resection of the esophagus due to esophageal dysfunction. Genetic analyses of COL4A5 and COL4A6 on the X-chromosome were efficiently performed using the genomic DNA of her son. We have identified a novel deletion of 194-kb in length, encompassing COL4A5-COL4A6 promoters as well as nearly the entire large intron 1 of COL4A5 and intron 2 of COL4A6. To uncover the relationship of the esophagus-specific occurrence of the tumor and the expression of those genes, immunohistochemical analyses of type IV collagen α chains were conducted in the non-affected individuals. The esophageal smooth muscle-specific expression of α5(IV) and α6(IV) chains in the gastrointestinal tract was observed. Moreover, CAG repeat analysis of the androgen receptor gene and an immunohistochemical analysis in the leiomyoma revealed clonal overgrowth of the cells which received X-inactivation on the non-affected allele. These results may suggest that the dominant effect was caused by the partial deletion of the esophageal smooth muscle-specific genes, COL4A5 and COL4A6.

Prenzel KL, Schäfer E, Stippel D, et al.
Multiple giant leiomyomas of the esophagus and stomach.
Dis Esophagus. 2006; 19(6):504-8 [PubMed] Related Publications
Leiomyomas are rare esophageal disorders, although among the benign esophageal neoplasms, they are the most common. Multiple leiomyomas are distinguished from esophageal leiomyomatosis, an extremely rare condition, which is associated with Alport syndrome, showing deletions and rearrangements of the COL4A5/COL4A6 gene. There are only a few reports of diffuse multilocular lesions. A 19-year-old man presented with upper gastrointestinal bleeding and diffuse abdominal pain. On endoscopy multiple nodules covered with intact mucosa were present, the largest tumor arising from the gastro-esophageal border infiltrating the cardia. Barium swallow demonstrated narrowing of the middle and lower esophagus with the upper third of the stomach filled by the tumor. Thorax and abdominal CT scans revealed infiltration of almost the total aboral esophagus by the tumor with compression of left and right bronchi. The infiltration reached the whole lesser curvature of the stomach. Endosonography showed multiple encapsulated nodules. Due to the extended tumor growth with infiltration of the upper third of the stomach, a total esophago-gastrectomy with reconstruction by colon interposition was performed. On histopathological examination multiple esophageal leiomyomas with infiltration of the proximal third of the stomach was shown. Immunohistochemically the tumor stained positive for desmin and sm-actin and negative for CD34 and c-kit. Genetic analysis ruled out a deletion of the COL4A5/COL4A6 locus on chromosome X that is linked with Alport syndrome-diffuse leiomyomatosis. Extended mutations in the COL4A5 gene, associated with Alport syndrome, to the COL4A6 gene, are required for the development of leiomyomatosis. In young patients with diffuse multinodular infiltration by encapsulated tumors, esophageal leiomyomatosis should be considered. If the proximal third of the stomach is infiltrated by the tumor an extended resection is necessary. Reconstruction procedures include colon interposition.

Ikeda K, Iyama K, Ishikawa N, et al.
Loss of expression of type IV collagen alpha5 and alpha6 chains in colorectal cancer associated with the hypermethylation of their promoter region.
Am J Pathol. 2006; 168(3):856-65 [PubMed] Free Access to Full Article Related Publications
Type IV collagen, a major component of the basement membrane (BM), is composed of six genetically distinct alpha(IV) chains, alpha1(IV) to alpha6(IV). Their genes are paired on three different chromosomes in a head-to-head arrangement. The alpha5(IV) gene (COL4A5) and the alpha6(IV) gene (COL4A6) are on chromosome Xq22 and are regulated by a bidirectional promoter. Loss of the alpha5(IV)/alpha6(IV) chains in epithelial BM occur in the early stage of cancer invasion. However, the regulatory mechanism of the specific loss of the alpha5(IV)/alpha6(IV) chains during cancer cell invasion is still undetermined. In the present study, we examined the expression of the alpha5(IV)/alpha6(IV) chains and the methylation profiles of the bidirectional promoter region of COL4A5/COL4A6 in colon cancer cell lines and colorectal tumor tissues. The expression of the alpha5(IV)/alpha6(IV) chains was down-regulated in colorectal cancer, and the loss of expression of the alpha5(IV)/alpha6(IV) chains was associated with the hypermethylation of their promoter region. In conclusion, the hypermethylation of the bidirectional promoter region of COL4A5/COL4A6 is one of the events that is responsible for the loss of expression of the alpha5(IV)/alpha6(IV) chains and the remodeling of the epithelial BM during cancer cell invasion.

Sugimoto K, Yanagida H, Yagi K, et al.
A Japanese family with Alport syndrome associated with esophageal leiomyomatosis: genetic analysis of COL4A5 to COL4A6 and immunostaining for type IV collagen subtypes.
Clin Nephrol. 2005; 64(2):144-50 [PubMed] Related Publications
BACKGROUND: In some families, X-linked Alport syndrome (AS) is associated with diffuse leiomyomatosis. We describe clinical, pathologic and molecular-genetic findings in a Japanese family with this inheritance mode of AS in association with leiomyomatosis.
PATIENT: AS was diagnosed in a one-year-old boy with recurrent aspiration pneumonia caused by esophageal stenosis from leiomyomatosis. Diagnosis was confirmed by electron microscopy coupled with type IV collagen chain subtype staining in a renal biopsy specimen. His mother, who exhibited esophageal leiomyomatosis and is heterozygous for AS, showed a discontinuous staining pattern for collagen alpha5(IV) chain along the epidermal basement membrane in a skin biopsy specimen. Genetic analysis in the boy revealed the deletion of the first two exons of COL4A6 together with deletion of the 5' end of COL4A5. Despite administration of cyclosporin A, massive proteinuria has persisted in the boy, although renal function otherwise remains normal.
CONCLUSION: Identification of an AS patient during infancy is extremely rare. Clinical manifestations, including macroscopic hematuria, cataracts and leiomyomatosis caused by the large deletion involving COL4A5 to COL4A6, led to early presentation with AS.

Thielen BK, Barker DF, Nelson RD, et al.
Deletion mapping in Alport syndrome and Alport syndrome-diffuse leiomyomatosis reveals potential mechanisms of visceral smooth muscle overgrowth.
Hum Mutat. 2003; 22(5):419 [PubMed] Related Publications
Diffuse leiomyomatosis is associated with the inherited kidney disease Alport syndrome, and characterized by visceral smooth muscle overgrowth within the respiratory, gastrointestinal and female reproductive tracts. Although partial deletions of the type IV collagen genes COL4A5 and COL4A6, paired head-to-head on chromosome Xq22, are known to cause diffuse leiomyomatosis, loss of function for type IV collagen does not explain smooth muscle overgrowth. To further clarify pathogenic mechanisms, we have characterized novel deletions in patients with Alport syndrome-diffuse leiomyomatosis or Alport syndrome alone. A 27.6-kb deletion, in a female with Alport syndrome-diffuse leiomyomatosis, is marked by the most proximal, i.e. most 5', COL4A5 breakpoint described to date. By comparing this deletion to others described here and previously, we have defined a minimal overlap region, only 4.2 kb in length and containing the COL4A5-COL4A6 proximal promoters, loss of which contributes to smooth muscle overgrowth. A novel deletion in a male with Alport syndrome alone is>1.4 Mb in length, encompassing COL4A5 and COL4A6 entirely, as well as neighboring genes. We postulate that loss of the 4.2-kb region in diffuse leiomyomatosis causes misregulation of neighboring genes, contributing to smooth muscle overgrowth. Deletion of the neighboring genes themselves may afford protection from this condition.

Anker MC, Arnemann J, Neumann K, et al.
Alport syndrome with diffuse leiomyomatosis.
Am J Med Genet A. 2003; 119A(3):381-5 [PubMed] Related Publications
Alport syndrome (AS) is a hereditary nephropathy with hematuria progressing to end-stage renal failure (ESRF), sensorineural deafness, and specific eye signs (lenticonus, macular flecks, and congenital cataracts). Inheritance is X-linked in about 85% of the cases, caused by different mutations in the COL4A5 gene. Rarely AS is seen in combination with diffuse leiomyomatosis (DL). DL is a tumorous process involving smooth muscle cells, mostly of the esophagus, but also of the tracheobronchial tree and the female genital tract. Characteristically, the patients have deletions of the 5'-end of both the COL4A5 and the COL4A6 genes, respectively. We here present a 9-year-old boy who was admitted because of a newly diagnosed sensorineural deafness. He was born with cataracts and presented symptoms of dysphagia and bronchial irritation in the first year of life. Macroscopic hematuria was first noticed at 2 years during a febrile infection. Since early childhood the boy suffered from severe constipation. Taking together these symptoms, the diagnosis of Alport syndrome with diffuse leiomyomatosis (AS-DL) has to be considered. Genetic analysis demonstrated the predicted deletion of the COL4A5/COL4A6 genes.

Mothes H, Heidet L, Arrondel C, et al.
Alport syndrome associated with diffuse leiomyomatosis: COL4A5-COL4A6 deletion associated with a mild form of Alport nephropathy.
Nephrol Dial Transplant. 2002; 17(1):70-4 [PubMed] Related Publications
BACKGROUND: The X-linked Alport syndrome (AS) is an inherited nephropathy due to mutations in the COL4A5 gene, encoding the alpha5 chain of type IV collagen, a major component of the glomerular basement membrane (GBM). Here, we report a new kindred with the rare association of X-linked AS and diffuse leiomyomatosis (DL), which is a tumourous process involving smooth muscle cells of the oesophagus, the tracheobronchial tree and, in females, the genital tract. For this syndrome, an almost constant association of large COL4A5 rearrangements with a severe juvenile form of nephropathy has been described for male patients.
METHODS: DNA rearrangement at the COL4A5-COL4A6 locus was studied in several members of this family using polymerase chain reaction and pulsed field gel electrophoresis. Furthermore, immunohistochemical staining of tumour and skin samples was performed.
RESULTS: The affected patients in this family carry a 120 kb deletion by which the COL4A5 exon 1 and COL4A6 exons 1, 1', and 2 are removed. Immunohistochemical investigation of a skin biopsy of an affected male patient confirmed the absence of both the alpha5 and the alpha6 chains of type IV collagen in the basement membrane of the skin. Surprisingly, both affected male patients had a rather mild renal phenotype.
CONCLUSIONS: This report shows that, contrary to what has been reported to date, patients suffering from AS associated with DL can be associated with a late onset renal failure (adult) form of nephropathy.

Guillem P, Delcambre F, Cohen-Solal L, et al.
Diffuse esophageal leiomyomatosis with perirectal involvement mimicking Hirschsprung disease.
Gastroenterology. 2001; 120(1):216-20 [PubMed] Related Publications
We describe a 25-year-old woman with diffuse esophageal leiomyomatosis. During childhood, achalasia was mistakenly diagnosed in this patient. Subsequently, she underwent cardiomyotomy and developed symptoms of Hirschsprung disease. These symptoms were caused by infiltration of the esophageal and rectal walls by benign muscular hypertrophy. The pseudo-Hirschsprung disorder was manifested by chronic severe constipation, with consistent manometric findings. Clitoral hypertrophy and vulvar and periurethral leiomyoma were also present. Genetic analysis demonstrating deletion of the COL4A5/COL4A6 locus and the discovery of microscopic hematuria implied that the patient could transmit both diffuse leiomyomatosis and the Alport syndrome.

Garcia-Torres R, Cruz D, Orozco L, et al.
Alport syndrome and diffuse leiomyomatosis. Clinical aspects, pathology, molecular biology and extracellular matrix studies. A synthesis.
Nephrologie. 2000; 21(1):9-12 [PubMed] Related Publications
The Alport syndrome-diffuse leiomyomatosis association can be defined as a hereditary disease of type IV collagen combining features of Alport syndrome (hematuric nephropathy, deafness and ocular abnormalities: anterior lenticonus, maculopathy) and leiomyomatosis involving oesophagus (diffuse type), tracheobronchial tree, and genitals (only in women). This entity is transmitted as an X-linked dominant trait. Mutations of both the COL4A5 and COL4A6 genes, located head to head in Xq22 encoding the alpha 5 and alpha 6(IV) chains are responsible for the abnormalities. Molecular studies have shown deletions of the 5' end of both COL4A5 and COL4A6 including the intergenic region. The breakpoint in COL4A6 is always located within intron 2. Immunohistochemistry has shown significant alterations of basement membranes in the kidney and esophageal leiomyomas. Leiomyomas lack alpha 5 and alpha 6(IV) chains, fibronectin and laminin beta 1 chains in the muscle basement membranes where they are normally expressed. The tumors also show myocyte anomalies: irregular expression of the alpha 5 integrin subunits, and disorganization of actin and desmin filaments. It is hypothesized that a third as yet unknown gene, situated within the large intron 2 in a critical 90 kb region, is responsible for the smooth muscle proliferation. Abnormalities of the basement membranes could destabilize interactions between muscular cells and the extracellular matrix.

Kashtan CE
Alport syndrome. An inherited disorder of renal, ocular, and cochlear basement membranes.
Medicine (Baltimore). 1999; 78(5):338-60 [PubMed] Related Publications
Alport syndrome (AS) is a genetically heterogeneous disease arising from mutations in genes coding for basement membrane type IV collagen. About 80% of AS is X-linked, due to mutations in COL4A5, the gene encoding the alpha 5 chain of type IV collagen (alpha 5[IV]). A subtype of X-linked Alport syndrome (XLAS) in which diffuse leiomyomatosis is an associated feature reflects deletion mutations involving the adjacent COL4A5 and COL4A6 genes. Most other patients have autosomal recessive Alport syndrome (ARAS) due to mutations in COL4A3 or COL4A4, which encode the alpha 3(IV) and alpha 4(IV) chains, respectively. Autosomal dominant AS has been mapped to chromosome 2 in the region of COL4A3 and COL4A4. The features of AS reflect derangements of basement membrane structure and function resulting from changes in type IV collagen expression. The primary pathologic event appears to be the loss from basement membranes of a type IV collagen network composed of alpha 3, alpha 4, and alpha 5(IV) chains. While this network is not critical for normal glomerulogenesis, its absence appears to provoke the overexpression of other extracellular matrix proteins, such as the alpha 1 and alpha 2(IV) chains, in glomerular basement membranes, leading to glomerulosclerosis. The diagnosis of AS still relies heavily on histologic studies, although routine application of molecular genetic diagnosis will probably be available in the future. Absence of epidermal basement membrane expression of alpha 5(IV) is diagnostic of XLAS, so in some cases kidney biopsy may not be necessary for diagnosis. Analysis of renal expression of alpha 3(IV)-alpha 5(IV) chains may be a useful adjunct to routine renal biopsy studies, especially when ultrastructural changes in the GBM are ambiguous. There are no specific therapies for AS. Spontaneous and engineered animal models are being used to study genetic and pharmacologic therapies. Renal transplantation for AS is usually very successful. Occasional patients develop anti-GBM nephritis of the allograft, almost always resulting in graft loss.

Zheng K, Harvey S, Sado Y, et al.
Absence of the alpha6(IV) chain of collagen type IV in Alport syndrome is related to a failure at the protein assembly level and does not result in diffuse leiomyomatosis.
Am J Pathol. 1999; 154(6):1883-91 [PubMed] Free Access to Full Article Related Publications
X-linked Alport syndrome is a progressive nephropathy associated with mutations in the COL4A5 gene. The kidney usually lacks the alpha3-alpha6 chains of collagen type IV, although each is coded by a separate gene. The molecular basis for this loss remains unclear. In canine X-linked hereditary nephritis, a model for X-linked Alport syndrome, a COL4A5 mutation results in reduced mRNA levels for the alpha3, alpha4, and alpha5 chains in the kidney, implying a mechanism coordinating the production of these 3 chains. To examine whether production of alpha6 chain is under the same control, we studied smooth muscle cells from this animal model. We determined the canine COL4A5 and COL4A6 genes are separated by 435 bp, with two first exons for COL4A6 separated by 978 bp. These two regions are >/= 78% identical to the human sequences that have promoter activity. Despite this potential basis for coordinated transcription of the COL4A5 and COL4A6 genes, the alpha6 mRNA level remained normal in affected male dog smooth muscle while the alpha5 mRNA level was markedly reduced. However, both alpha5 and alpha6 chains were absent at the protein level. Our results suggest that production of the alpha6 chain is under a control mechanism separate from that coordinating the alpha3-alpha5 chains and that the lack of the alpha6 chain in Alport syndrome is related to a failure at the protein assembly level, raising the possibility that the alpha5 and alpha6 chains are present in the same network. The lack of the alpha6 chain does not obviously result in disease, in particular leiomyomatosis, as is seen in Alport patients with deletions involving the COL4A5 and COL4A6 genes.

Sado Y, Kagawa M, Naito I, et al.
Organization and expression of basement membrane collagen IV genes and their roles in human disorders.
J Biochem. 1998; 123(5):767-76 [PubMed] Related Publications
Six distinct genes have been identified as belonging to the type IV collagen gene family. They can be organized into three sets, i.e., COL4A1/COL4A2, COL4A3/COL4A4, and COL4A5/COL4A6, which are localized on three different chromosomes in humans, 13, 2, and X, respectively. Within each set the genes are aligned head-to-head and their expression is regulated by bidirectional promoters between the genes. Transcriptional regulation of the COL4A1/COL4A2 set has been well characterized. The transcription of COL4A6 seems to be controlled by two alternative promoters. While collagen IV molecules composed of alpha1 and alpha2 chains are broadly distributed, molecules comprising combinations of the other four chains, alpha3-alpha6, are important components of specialized basement membranes. The precise chain composition of triple-helical molecules assembled from the alpha3-alpha6 chains is not entirely clear, but it is hypothesized that alpha3-alpha5 chains and alpha5 and alpha6 chains form heterotrimeric molecules. Several pieces of evidence indicate that alpha3/alpha4/alpha5 molecules and alpha5/alpha6 molecules are components of the basement membrane network. This helps explain the observation that the kidney and skin basement membranes from patients with Alport syndrome caused by mutations in the alpha5 coding gene, COL4A5, are defective in the alpha3, alpha4, and alpha6 chains together with the alpha5 chain. Large deletions involving the COL4A5 and COL4A6 genes have been found in rare cases of diffuse leiomyomatosis associated with Alport syndrome.

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