SIPA1

Gene Summary

Gene:SIPA1; signal-induced proliferation-associated 1
Aliases: SPA1
Location:11q13
Summary:The product of this gene is a mitogen induced GTPase activating protein (GAP). It exhibits a specific GAP activity for Ras-related regulatory proteins Rap1 and Rap2, but not for Ran or other small GTPases. This protein may also hamper mitogen-induced cell cycle progression when abnormally or prematurely expressed. It is localized to the perinuclear region. Two alternatively spliced variants encoding the same isoform have been characterized to date. [provided by RefSeq, Jul 2008]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:signal-induced proliferation-associated protein 1
HPRD
Source:NCBIAccessed: 27 February, 2015

Ontology:

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 (1990-2015)
Graph generated 27 February 2015 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.

  • Disease Progression
  • siRNA
  • Single Nucleotide Polymorphism
  • RNA, Catalytic
  • Base Sequence
  • rap1 GTP-Binding Proteins
  • Neoplasm Proteins
  • Gene Expression Profiling
  • Cervical Cancer
  • Quantitative Trait Loci
  • Genetic Predisposition
  • Extracellular Matrix
  • Nuclear Proteins
  • Xenograft Models
  • Alleles
  • Signal Transduction
  • Neoplasm Metastasis
  • Up-Regulation
  • Cohort Studies
  • GTPase-Activating Proteins
  • Treatment Failure
  • Genotype
  • Transcription Factors
  • Lymphatic Metastasis
  • Chromosome 11
  • Polymorphism
  • Leukemia, Myelomonocytic, Juvenile
  • Cancer Gene Expression Regulation
  • T-Lymphocytes
  • Estrogen Receptors
  • Staging
  • Mutation
  • Case-Control Studies
  • Tissue Distribution
  • Germ-Line Mutation
  • Risk Factors
  • Lymph Nodes
  • Tumor Markers
  • Breast Cancer
  • rap GTP-Binding Proteins
Tag cloud generated 27 February, 2015 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: SIPA1 (cancer-related)

Yi SM, Li GY
The association of SIPA1 gene polymorphisms with breast cancer risk: evidence from published studies.
Tumour Biol. 2014; 35(1):441-5 [PubMed] Related Publications
Previous studies have focused on the association of signal-induced proliferation associated 1 gene (SIPA1) with carcinogenesis of many cancers, including breast cancer. It has been suggested that SIPA1 polymorphisms are associated with susceptibility to breast cancer. In the present study, we performed a meta-analysis to systematically summarize the possible association between SIPA1 and the risk for breast cancer. We conducted a search of case-control studies on the associations of SPIA1 with susceptibility to breast cancer in PubMed, Embase, International Statistical Institute Web of Science, Wanfang Database in China, and Chinese National Knowledge Infrastructure databases. Data from eligible studies were extracted for meta-analysis. Breast cancer risk associated with SIPA1 was estimated by pooled odds ratios and 95% confidence intervals. Four studies on SIPA1 and breast cancer were included in our meta-analysis. Our results showed that rs746429 was associated with the risk of breast cancer. However, rs931127 and rs3741378 were not found to be associated with breast cancer in our analysis. This meta-analysis suggests that rs746429 is associated with the risk of breast cancer. Well-designed studies with larger sample size and more ethnic groups are required to further validate the results.

Roberts MR, Hong CC, Edge SB, et al.
Case-only analyses of the associations between polymorphisms in the metastasis-modifying genes BRMS1 and SIPA1 and breast tumor characteristics, lymph node metastasis, and survival.
Breast Cancer Res Treat. 2013; 139(3):873-85 [PubMed] Free Access to Full Article Related Publications
Lymph node metastases and tumor characteristics predict breast cancer prognosis but correlate imperfectly with likelihood of metastatic relapse. Discovery of genetic polymorphisms affecting metastasis may improve identification of patients requiring aggressive adjuvant therapy to prevent recurrence. We investigated associations between several variants in the BRMS1 and SIPA1 metastasis-modifying genes and lymph node metastases, tumor subtype and grade, recurrence, disease-free survival, and overall survival. This cross-sectional and prospective prognostic analysis included 859 patients who received surgery for incident breast cancer at Roswell Park Cancer Institute, participated in the DataBank and BioRepository shared resource, and had DNA, clinical, and pathology data available for analysis. Genotyping for BRMS1 (rs11537993, rs3116068, and rs1052566) and SIPA1 (rs75894763, rs746429, rs3741378, and rs2306364) polymorphisms was performed using Sequenom(®) iPLEX Gold and Taqman(®) real-time PCR assays. Logistic and Cox proportional hazards regressions were used to estimate odds ratios (OR) and hazard ratios (HR), respectively. BRMS1 rs1052566 heterozygous individuals were more likely to have node-positive tumors (OR = 1.58, 95 % CI 1.13-2.23), although there was no dose-response relationship, and those with at least one variant allele were less likely to have the luminal B subtype (AG + AA: OR = 0.59, 95 % CI 0.36-0.98). BRMS1 rs3116068 was associated with increased likelihood of having the luminal B and the HER2-enriched tumor subtype (P trend = 0.03). Two SIPA1 SNPs, rs746429 and rs2306364, were associated with decreased risk of triple-negative tumors (P trend = 0.04 and 0.07, respectively). Presence of 8 or more risk alleles was associated with an increased likelihood of having a node-positive tumor (OR = 2.14, 95 % CI 1.18-3.36, P trend = 0.002). There were no significant associations with survival. Polymorphisms in metastasis-associated genes may be related to tumor characteristics and lymph node metastasis, but not survival. Future evaluation of metastasis-modifying gene variants is necessary to better understand the biology of metastasis.

Xie C, Yang L, Yang X, et al.
Sipa1 promoter polymorphism predicts risk and metastasis of lung cancer in Chinese.
Mol Carcinog. 2013; 52 Suppl 1:E110-7 [PubMed] Related Publications
Signal-induced proliferation associated gene 1 (Sipa1) is a signal transducer to activate the Ras-related proteins and modulate cell progression, differentiation, adhesion and cancer metastasis. In this study, we tested the hypothesis that single nucleotide polymorphisms (SNPs) in Sipa1 are associated with lung cancer risk and metastasis. Three common SNPs (rs931127A > G, rs2448490G > A, and rs3741379G > T) were genotyped in a discovery set of southern Chinese population and then validated the promising SNPs in a validation set of an eastern Chinese population in a total of 1559 lung cancer patients and 1679 cancer-free controls. The results from the two sets were consistent, the rs931127GG variant genotype had an increased risk of lung cancer compared to the rs931127AA/GA genotypes (OR = 1.27; 95% CI = 1.09-1.49) after combination of the two populations, and the rs931127GG interacted with pack-year smoked on increasing lung cancer risk (P = 0.037); this SNP also had an effect on patients' clinical stages (P = 0.012) that those patients with the rs931127GG genotype had a significant higher metastasis rate and been advanced N, M stages at diagnosis. However, these associations were not observed for rs2448490G > A and rs3741379G > T in the discovery set. Our data suggest that the SNP rs931127A > G in the promoter of Sipa1 was significantly associated with lung cancer risk and metastasis, which may be a biomarker to predict the risk and metastasis of lung cancer.

Minato N
Rap G protein signal in normal and disordered lymphohematopoiesis.
Exp Cell Res. 2013; 319(15):2323-8 [PubMed] Related Publications
Rap proteins (Rap1, Rap2a, b, c) are small molecular weight GTPases of the Ras family. Rap G proteins mediate diverse cellular events such as cell adhesion, proliferation, and gene activation through various signaling pathways. Activation of Rap signal is regulated tightly by several specific regulatory proteins including guanine nucleotide exchange factors and GTPase-activating proteins. Beyond cell biological studies, increasing attempts have been made in the past decade to define the roles of Rap signal in specific functions of normal tissue systems as well as in cancer. In the immune and hematopoietic systems, Rap signal plays crucial roles in the development and function of essentially all lineages of lymphocytes and hematopoietic cells, and importantly, deregulated Rap signal may lead to unique pathological conditions depending on the affected cell types, including various types of leukemia and autoimmunity. The phenotypical studies have unveiled novel, even unexpected functional aspects of Rap signal in cells from a variety of tissues, providing potentially important clues for controlling human diseases, including malignancy.

Pei R, Xu Y, Wei Y, et al.
Association of SIPA1 545 C > T polymorphism with survival in Chinese women with metastatic breast cancer.
Front Med. 2013; 7(1):138-42 [PubMed] Related Publications
It has been demonstrated that single nucleotide polymorphisms (SNPs) of SIPA1 (signal-induced proliferation associated gene 1) are associated with metastatic efficiency in both human and rodents. The purpose of this study was to determine whether SIPA1 545 C > T polymorphism was associated with overall survival in patients with metastatic breast cancer. In this study, SIPA1 545 C > T polymorphism was detected in 185 metastatic breast cancer patients using polymerase chain reaction-restriction fragment length polymorphism assay (PCR-RFLP). Survival curves for patients with SIPA1 545 C > T polymorphism was compared using the Kaplan-Meier method with log-rank tests. We found that SIPA1 545 C > T polymorphism was significantly associated with survival in 185 patients with metastatic breast cancer. Patients with SIPA1 545 T/T genotype had a significantly worse overall survival (OS) than did patients with C/T or C/C genotype (50.0% vs. 62.9%, P = 0.042). Moreover, in multivariate analysis, as compared with the C/C or C/T genotype, the T/T genotype remained an independent unfavorable prognostic marker of OS in this cohort (hazard ratio [HR] = 2.16; 95% CI = 1.12-4.15; P = 0.022). Our findings indicate that metastatic breast cancer patients with SIPA1 545 T/T genotype have a poorer survival compared to patients with C/C or C/T genotype.

Ji K, Ye L, Toms AM, et al.
Expression of signal-induced proliferation-associated gene 1 (SIPA1), a RapGTPase-activating protein, is increased in colorectal cancer and has diverse effects on functions of colorectal cancer cells.
Cancer Genomics Proteomics. 2012 Sep-Oct; 9(5):321-7 [PubMed] Related Publications
BACKGROUND: Signal-induced proliferation-associated gene 1 (SIPA1) codes for a GTPase-activating protein, known to be a negative regulator of Ras-related Protein (RAP) which belongs to the Ras superfamily. It has been implicated in certain malignancies, including leukemia, cervical cancer and breast cancer. However the role of this molecule in colorectal cancer remains unknown. The current study aimed to investigate the expression of SIPA1 in colorectal tumour tissues and its impact on the function of colorectal cancer cells.
MATERIALS AND METHODS: A total of 94 colorectal cancer tissues together with 80 normal background tissues were used to examine the expression of SIPA1 transcript and protein using real-time quantitative Polymerase Chain Reaction (PCR) and immunohistochemical methods, respectively. Any association with clinical and histopathological characteristics was then identified. Ribozyme transgenes targeting SIPA1 were prepared to knockdown the expression of SIPA1 in colorectal cancer cells. The impact on their functions was subsequently determined, using respective in vitro function assays.
RESULTS: An increased expression of SIPA1 was evident in colorectal cancer tissues compared with its expression in normal background tissues (p<0.001). In colorectal tumours, its expression appeared to be lower in poorly-differentiated samples and in patients who had lymphatic metastasis. Knockdown of SIPA1 in colorectal cancer cells resulted in reduced cell growth in vitro. The knockdown exhibited a contrasting effect on invasion and migration, both of which were increased in SIPA1-knockdown cells compared with the controls.
CONCLUSION: SIPA1 is up-regulated in colorectal cancer. This suggests that SIPA1 plays diverse roles during disease progression as has contrasting effects on growth and motility of colorectal cancer cells.

Mathieu V, Pirker C, Schmidt WM, et al.
Aggressiveness of human melanoma xenograft models is promoted by aneuploidy-driven gene expression deregulation.
Oncotarget. 2012; 3(4):399-413 [PubMed] Free Access to Full Article Related Publications
Melanoma is a devastating skin cancer characterized by distinct biological subtypes. Besides frequent mutations in growth- and survival-promoting genes like BRAF and NRAS, melanomas additionally harbor complex non-random genomic alterations. Using an integrative approach, we have analysed genomic and gene expression changes in human melanoma cell lines (N=32) derived from primary tumors and various metastatic sites and investigated the relation to local growth aggressiveness as xenografts in immuno-compromised mice (N=22). Although the vast majority >90% of melanoma models harbored mutations in either BRAF or NRAS, significant differences in subcutaneous growth aggressiveness became obvious. Unsupervised clustering revealed that genomic alterations rather than gene expression data reflected this aggressive phenotype, while no association with histology, stage or metastatic site of the original melanoma was found. Genomic clustering allowed separation of melanoma models into two subgroups with differing local growth aggressiveness in vivo. Regarding genes expressed at significantly altered levels between these subgroups, a surprising correlation with the respective gene doses (>85% accordance) was found. Genes deregulated at the DNA and mRNA level included well-known cancer genes partly already linked to melanoma (RAS genes, PTEN, AURKA, MAPK inhibitors Sprouty/Spred), but also novel candidates like SIPA1 (a Rap1GAP). Pathway mining further supported deregulation of Rap1 signaling in the aggressive subgroup e.g. by additional repression of two Rap1GEFs. Accordingly, siRNA-mediated down-regulation of SIPA1 exerted significant effects on clonogenicity, adherence and migration in aggressive melanoma models. Together our data suggest that an aneuploidy-driven gene expression deregulation drives local aggressiveness in human melanoma.

Shimizu Y, Hamazaki Y, Hattori M, et al.
SPA-1 controls the invasion and metastasis of human prostate cancer.
Cancer Sci. 2011; 102(4):828-36 [PubMed] Related Publications
Recent studies suggest that SIPA1 encoding a Rap GTPase-activating protein SPA-1 is a candidate metastasis efficiency-modifying gene in human breast cancer. In this study, we investigated the expression and function of SPA-1 in human prostate cancer (CaP). Immunohistochemical studies of tumor specimens from CaP patients revealed a positive correlation of SPA-1 expression with disease progression and metastasis. The correlation was recapitulated in human CaP cell lines; LNCaP that rarely showed metastasis in SCID mice expressed an undetectable level of SPA-1, whereas highly metastatic PC3 showed abundant SPA-1 expression. Moreover, SIPA1 transduction in LNCaP caused prominent abdominal lymph node metastasis without affecting primary tumor size, whereas shRNA-mediated SIPA1 knockdown or expression of a dominant-active Rap1 mutant (Rap1V12) in PC3 suppressed metastasis. LNCaP transduced with SPA-1 (LNCaP/SPA-1) showed attenuated adhesion to the precoated extracellular matrices (ECM) including collagens and fibronectin, due to defective ECM-medicated Rap1 activation. In addition, LNCaP/SPA-1 showed a diminished level of nuclear Brd4, which is known to bind SPA-1, resulting in reduced expression of a series of ECM-related genes. These results suggest that SPA-1 plays an important role in controlling metastasis efficiency of human CaP by regulating the expression of and interaction with ECM in the primary sites.

Brooks R, Kizer N, Nguyen L, et al.
Polymorphisms in MMP9 and SIPA1 are associated with increased risk of nodal metastases in early-stage cervical cancer.
Gynecol Oncol. 2010; 116(3):539-43 [PubMed] Free Access to Full Article Related Publications
OBJECTIVE: Heritable polymorphisms modulate metastatic efficiency in Cancer Single nucleotide polymorphisms (SNPs) in MMP9 (rs17576) and SIPA1 (rs746429, rs931127) have been associated with nodal metastases in multiple cancers. We investigated the association of these SNPs with nodal metastases in early-stage cervical cancer.
METHODS: Consecutive patients with stage IB cervical cancer who underwent a pelvic lymph node (LN) dissection were included. Cases (>1 positive LN, n=101) were compared with controls (negative LN pathology, n=273). Genotyping was performed on genomic DNA in the 3 SNPs using a TaqMan assay and correlated with clinical variables.
RESULTS: The G allele at SIPA1 rs931127 was associated with an increased risk of nodal disease (OR 1.9, P=0.03) and approached significance at SIPA 1 rs746429 (OR 2.2, P=0.09) and MMP9 rs17576 (OR 1.5, 0.08). In patients with stage Ib1 lesions (n=304), the G allele at both SIPA1 SNPs was associated with LN metastases (rs746429 OR 10.1, P=0.01; rs931127 OR 2.4, P=0.01). In patients with no lymph vascular space invasion, SIPA1 SNPs were again associated with LN metastases, and all patients with nodal disease had at least one G allele at SIPA1 rs746429.
CONCLUSIONS: In this case-control study, SNPs in SIPA1 varied statistically in cervical cancer patients with and without nodal metastases and in MMP9 after controlling for stage and lymphvascular space invasion. Further work is needed to characterize inherited polymorphisms that provide a permissive background for the metastatic cascade.

Hsieh SM, Look MP, Sieuwerts AM, et al.
Distinct inherited metastasis susceptibility exists for different breast cancer subtypes: a prognosis study.
Breast Cancer Res. 2009; 11(5):R75 [PubMed] Free Access to Full Article Related Publications
INTRODUCTION: Previous studies in mouse models and pilot epidemiology studies have demonstrated that inherited polymorphisms are associated with inherited risk of tumor progression and poor outcome in human breast cancer. To extend these studies and gain better understanding of the function of inherited polymorphism in breast cancer progression, a validation prognosis study was performed in a large independent breast cancer patient population.
METHODS: The study population consisted of 1863 Dutch patients with operable primary breast cancer from Rotterdam, The Netherlands. Genomic DNA was genotyped for the missense Pro436Leu RRP1B single nucleotide polymorphism (SNP) rs9306160 and the intronic SIPA1 SNP rs2448490 by SNP-specific PCR.
RESULTS: A significant association of variants in RRP1B with metastasis-free survival was observed (P = 0.012), validating the role of RRP1B with inherited metastatic susceptibility. Stratification of patients revealed that association with patients' survival was found to be specifically restricted to estrogen receptor positive, lymph node-negative (ER+/LN-) patients (P = 0.011). The specific association with metastasis-free survival only in ER+/LN- patients was replicated for SIPA1, a second metastasis susceptibility gene known to physically interact with RRP1B (P = 0.006). Combining the genotypes of these two genes resulted in the significant ability to discriminate patients with poor metastasis-free survival (HR: 0.40, 95% CI: 0.24 to 0.68, P = 0.001).
CONCLUSIONS: These results validate SIPA1 and RRP1B as metastasis susceptibility genes and suggest that genotyping assays may be a useful supplement to other clinical and molecular indicators of prognosis. The results also suggest that lymphatic and hematogeneous metastases are genetically distinct that may involve different mechanisms. If true, these results suggest that metastatic disease, like primary breast cancer, may be multiple diseases and that stratification of late stage patients may therefore be required to fully understand breast cancer progression and metastasis.

Hsieh SM, Smith RA, Lintell NA, et al.
Polymorphisms of the SIPA1 gene and sporadic breast cancer susceptibility.
BMC Cancer. 2009; 9:331 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The novel breast cancer metastasis modulator gene signal-induced proliferation-associated 1 (Sipa1) underlies the breast cancer metastasis efficiency modifier locus Mtes 1 and has been shown to influence mammary tumour metastatic efficiency in the mouse, with an ectopically expressing Sipa1 cell line developing 1.5 to 2 fold more surface pulmonary metastases. Sipa1 encodes a mitogen-inducible GTPase activating (GAP) protein for members of the Ras-related proteins; participates in cell adhesion and modulates mitogen-induced cell cycle progression. Germline SIPA1 SNPs showed association with positive lymph node metastasis and hormonal receptor status in a Caucasian cohort. We hypothesized that SIPA1 may also be correlated to breast carcinoma incidence as well as prognosis. Therefore, this study investigated the potential relationship of SIPA1 and human breast cancer incidence by a germline SNP genotype frequency association study in a case-control Caucasian cohort in Queensland, Australia.
METHODS: The SNPs genotyped in this study were identified in a previous study and the genotyping assays were carried out using TaqMan SNP Genotyping Assays. The data were analysed with chi-square method and the Monte Carlo style CLUMP analysis program.
RESULTS: Results indicated significance with SIPA1 SNP rs3741378; the CC genotype was more frequently observed in the breast cancer group compared to the disease-free control group, indicating the variant C allele was associated with increased breast cancer incidence.
CONCLUSION: This observation indicates SNP rs3741378 as a novel potential sporadic breast cancer predisposition SNP. While it showed association with hormonal receptor status in breast cancer group in a previous pilot study, this exonic missense SNP (Ser (S) to Phe (F)) changes a hydrophilic residue (S) to a hydrophobic residue (F) and may significantly alter the protein functions of SIPA1 in breast tumourgenesis. SIPA1 SNPs rs931127 (5' near gene), and rs746429 (synonymous (Ala (A) to Ala (A)), did not show significant associations with breast cancer incidence, yet were associated with lymph node metastasis in the previous study. This suggests that SIPA1 may be involved in different stages of breast carcinogenesis and since this study replicates a previous study of the associated SNP, it implicates variants of the SIPA1 gene as playing a potential role in breast cancer.

Gaudet MM, Hunter K, Pharoah P, et al.
Genetic variation in SIPA1 in relation to breast cancer risk and survival after breast cancer diagnosis.
Int J Cancer. 2009; 124(7):1716-20 [PubMed] Free Access to Full Article Related Publications
Genetic variation in SIPA1, signal-induced proliferation-associated gene 1, has been proposed to be associated with aggressive breast tumor characteristics related to metastasis and worse prognosis in humans and rodents. To test this hypothesis, we genotyped 3 single nucleotide polymorphisms (SNP) located at -3092 (AT, rs3741378), and exon 14 + 14 (C>T, rs746429), and examined them in relation to breast cancer risk and overall survival, stratified by tumor characteristics in 2 independent case-control studies conducted in Poland (1,995 cases, 2,296 controls) and in Britain (2,142 cases, 2,257 controls). Vital status (n = 396 deaths) was available for 911 Polish and 1,919 British breast cancer cases with an average follow-up time of 5.5 years. Overall, we found no significant associations between genetic variants of SIPA1 SNPs and breast cancer risk (per allele odds ratios, 95% confidence intervals (CI): rs931127-0.99, 0.93-1.06; rs3741378-1.03, 0.94-1.13; and, rs74642-0.98, 0.92-1.04). In both studies, SIPA1 polymorphisms were not related to overall mortality (per allele hazard ratios, 95% CI: 1.02, 0.88-1.17; 0.90, 0.72-1.11; 1.04, 0.90-1.21, respectively). Our results do not support a relationship between SIPA1 polymorphisms and breast cancer risk or subsequent survival.

Crawford NP, Alsarraj J, Lukes L, et al.
Bromodomain 4 activation predicts breast cancer survival.
Proc Natl Acad Sci U S A. 2008; 105(17):6380-5 [PubMed] Free Access to Full Article Related Publications
Previous work identified the Rap1 GTPase-activating protein Sipa1 as a germ-line-encoded metastasis modifier. The bromodomain protein Brd4 physically interacts with and modulates the enzymatic activity of Sipa1. In vitro analysis of a highly metastatic mouse mammary tumor cell line ectopically expressing Brd4 demonstrates significant reduction of invasiveness without altering intrinsic growth rate. However, a dramatic reduction of tumor growth and pulmonary metastasis was observed after s.c. implantation into mice, implying that activation of Brd4 may somehow be manipulating response to tumor microenvironment in the in vivo setting. Further in vitro analysis shows that Brd4 modulates extracellular matrix gene expression, a class of genes frequently present in metastasis-predictive gene signatures. Microarray analysis of the mammary tumor cell lines identified a Brd4 activation signature that robustly predicted progression and/or survival in multiple human breast cancer datasets analyzed on different microarray platforms. Intriguingly, the Brd4 signature also almost perfectly matches a molecular classifier of low-grade tumors. Taken together, these data suggest that dysregulation of Brd4-associated pathways may play an important role in breast cancer progression and underlies multiple common prognostic signatures.

Crawford NP, Walker RC, Lukes L, et al.
The Diasporin Pathway: a tumor progression-related transcriptional network that predicts breast cancer survival.
Clin Exp Metastasis. 2008; 25(4):357-69 [PubMed] Free Access to Full Article Related Publications
Microarray expression signature analyses have suggested that extracellular matrix (ECM) gene dysregulation is predictive of metastasis in both mouse mammary tumorigenesis and human breast cancer. We have previously demonstrated that such ECM dysregulation is influenced by hereditary germline-encoded variation. To identify novel metastasis efficiency modifiers, we performed expression QTL (eQTL) mapping in recombinant inbred mice by characterizing genetic loci modulating metastasis-predictive ECM gene expression. Three reproducible eQTLs were observed on chromosomes 7, 17 and 18. Candidate genes were identified by correlation analyses and known associations with metastasis. Seven candidates were identified (Ndn, Pi16, Luc7l, Rrp1b, Brd4, Centd3 and Csf1r). Stable transfection of the highly metastatic Mvt-1 mouse mammary tumor cell line with expression vectors encoding each candidate modulated metastasis-predictive ECM gene expression. Implantation of these cells into mice demonstrated that candidate gene ectopic expression impacts tumor progression. Gene expression analyses facilitated the construction of a transcriptional network that we have termed the 'Diasporin Pathway'. This pathway contains the seven candidates, as well as metastasis-predictive ECM genes and metastasis suppressors. Brd4 and Rrp1b appear to form a central node within this network, which likely is a consequence of their physical interaction with the metastasis efficiency modifier Sipa1. Furthermore, we demonstrate that the microarray gene expression signatures induced by activation of ECM eQTL genes in the Mvt-1 cell line can be used to accurately predict survival in a human breast cancer cohort. These data imply that the Diasporin Pathway may be an important nexus in tumor progression in both mice and humans.

Crawford NP, Qian X, Ziogas A, et al.
Rrp1b, a new candidate susceptibility gene for breast cancer progression and metastasis.
PLoS Genet. 2007; 3(11):e214 [PubMed] Free Access to Full Article Related Publications
A novel candidate metastasis modifier, ribosomal RNA processing 1 homolog B (Rrp1b), was identified through two independent approaches. First, yeast two-hybrid, immunoprecipitation, and functional assays demonstrated a physical and functional interaction between Rrp1b and the previous identified metastasis modifier Sipa1. In parallel, using mouse and human metastasis gene expression data it was observed that extracellular matrix (ECM) genes are common components of metastasis predictive signatures, suggesting that ECM genes are either important markers or causal factors in metastasis. To investigate the relationship between ECM genes and poor prognosis in breast cancer, expression quantitative trait locus analysis of polyoma middle-T transgene-induced mammary tumor was performed. ECM gene expression was found to be consistently associated with Rrp1b expression. In vitro expression of Rrp1b significantly altered ECM gene expression, tumor growth, and dissemination in metastasis assays. Furthermore, a gene signature induced by ectopic expression of Rrp1b in tumor cells predicted survival in a human breast cancer gene expression dataset. Finally, constitutional polymorphism within RRP1B was found to be significantly associated with tumor progression in two independent breast cancer cohorts. These data suggest that RRP1B may be a novel susceptibility gene for breast cancer progression and metastasis.

Hsieh SM, Lintell NA, Hunter KW
Germline polymorphisms are potential metastasis risk and prognosis markers in breast cancer.
Breast Dis. 2006-2007; 26:157-62 [PubMed] Related Publications
A number of theories have been proposed to account for the origins of metastasis, although none as yet have adequately explained all of its characteristics. With approximately 90% of cancer-related deaths due to the effects of disseminated tumors, improved understanding of this process is critical for reducing cancer-associated morbidity and mortality. Extensive research to investigate the molecular basis of this process has been conducted, and our lab has focused on the role of germline polymorphism in this complex process. Simple breeding experiments using a highly metastatic mouse model showed that germline polymorphisms significantly contribute to metastasis susceptibility. Genetic mapping studies revealed that a number of genomic regions are linked to metastasis susceptibility, including a metastasis modifier on mouse chromosome 19. Subsequent analysis identified Sipa1 as the most likely candidate for the observed linkage on Chr 19. Evaluation of SNPs in SIPA1 in a pilot association study in a human breast cancer cohort supported this possibility and demonstrated that SIPA1 polymorphisms are associated with various markers of poor prognosis including differential sentinel lymph node status. Taken together, these data suggest that germline polymorphism is an important modulating component in metastatic progression that needs to be investigated if we are to fully understand the metastatic process.

Crawford NP, Ziogas A, Peel DJ, et al.
Germline polymorphisms in SIPA1 are associated with metastasis and other indicators of poor prognosis in breast cancer.
Breast Cancer Res. 2006; 8(2):R16 [PubMed] Free Access to Full Article Related Publications
INTRODUCTION: There is growing evidence that heritable genetic variation modulates metastatic efficiency. Our previous work using a mouse mammary tumor model has shown that metastatic efficiency is modulated by the GTPase-activating protein encoded by Sipa1 ('signal-induced proliferation-associated gene 1'). The aim of this study was to determine whether single nucleotide polymorphisms (SNPs) within the human SIPA1 gene are associated with metastasis and other disease characteristics in breast cancer.
METHOD: The study population (n = 300) consisted of randomly selected non-Hispanic Caucasian breast cancer patients identified from a larger population-based series. Genomic DNA was extracted from peripheral leukocytes. Three previously described SNPs within SIPA1 (one within the promoter [-313G>A] and two exonic [545C>T and 2760G>A]) were characterized using SNP-specific PCR.
RESULTS: The variant 2760G>A and the -313G>A allele were associated with lymph node involvement (P = 0.0062 and P = 0.0083, respectively), and the variant 545C>T was associated with estrogen receptor negative tumors (P = 0.0012) and with progesterone negative tumors (P = 0.0339). Associations were identified between haplotypes defined by the three SNPs and disease progression. Haplotype 3 defined by variants -313G>A and 2760G>A was associated with positive lymph node involvement (P = 0.0051), and haplotype 4 defined by variant 545C>T was associated with estrogen receptor and progesterone receptor negative status (P = 0.0053 and P = 0.0199, respectively).
CONCLUSION: Our findings imply that SIPA1 germline polymorphisms are associated with aggressive disease behavior in the cohort examined. If these results hold true in other populations, then knowledge of SIPA1 SNP genotypes could potentially enhance current staging protocols.

Park YG, Zhao X, Lesueur F, et al.
Sipa1 is a candidate for underlying the metastasis efficiency modifier locus Mtes1.
Nat Genet. 2005; 37(10):1055-62 [PubMed] Free Access to Full Article Related Publications
We previously identified loci in the mouse genome that substantially influence the metastatic efficiency of mammary tumors. Here, we present data supporting the idea that the signal transduction molecule, Sipa1, is a candidate for underlying the metastasis efficiency modifier locus Mtes1. Analysis of candidate genes identified a nonsynonymous amino acid polymorphism in Sipa1 that affects the Sipa1 Rap-GAP function. Spontaneous metastasis assays using cells ectopically expressing Sipa1 or cells with knocked-down Sipa1 expression showed that metastatic capacity was correlated with cellular Sipa1 levels. We examined human expression data and found that they were consistent with the idea that Sipa1 concentration has a role in metastasis. Taken together, these data suggest that the Sipa1 polymorphism is one of the genetic polymorphisms underlying the Mtes1 locus. This report is also the first demonstration, to our knowledge, of a constitutional genetic polymorphism affecting tumor metastasis.

Kometani K, Ishida D, Hattori M, Minato N
Rap1 and SPA-1 in hematologic malignancy.
Trends Mol Med. 2004; 10(8):401-8 [PubMed] Related Publications
Rap1 is a member of the Ras family of GTPases and, depending on the cellular context, has an important role in the regulation of proliferation or cell adhesion. In lymphohematopoietic tissues, SPA-1 is a principal Rap1 GTPase-activating protein. Mice that are deficient for the SPA-1 gene develop age-dependent progression of T-cell immunodeficiency followed by a spectrum of late onset myeloproliferative disorders, mimicking human chronic myeloid leukemia. Recent studies reveal that deregulated Rap1 activation in SPA-1-deficient mice causes enhanced expansion of the bone marrow hematopoietic progenitors, but induces progressive unresponsiveness or anergy in T cells. Rap1 and its regulator, SPA-1, could, therefore, provide unique molecular targets for the control of human hematologic malignancy.

Ishida D, Kometani K, Yang H, et al.
Myeloproliferative stem cell disorders by deregulated Rap1 activation in SPA-1-deficient mice.
Cancer Cell. 2003; 4(1):55-65 [PubMed] Related Publications
SPA-1 (signal-induced proliferation-associated gene-1) is a principal Rap1 GTPase-activating protein in hematopoietic progenitors. SPA-1-deficient mice developed a spectrum of myeloid disorders that resembled human chronic myelogenous leukemia (CML) in chronic phase, CML in blast crisis, and myelodysplastic syndrome as well as anemia. Preleukemic SPA-1-deficient mice revealed selective expansion of marrow pluripotential hematopoietic progenitors, which showed abnormal Rap1GTP accumulation. Overexpression of an active form of Rap1 promoted the proliferation of normal hematopoietic progenitors, while SPA-1 overexpression markedly suppressed it. Furthermore, restoring SPA-1 gene in a SPA-1-deficient leukemic blast cell line resulted in the dissolution of Rap1GTP accumulation and concomitant loss of the leukemogenicity in vivo. These results unveiled a role of Rap1 in myeloproliferative stem cell disorders and a tumor suppressor function of SPA-1.

Largaespada DA
A bad rap: Rap1 signaling and oncogenesis.
Cancer Cell. 2003; 4(1):3-4 [PubMed] Related Publications
In the paper by Ishida et al. in this issue of Cancer Cell, the authors report the results of targeted inactivation of a Rap1-specific GTPase-activating protein (GAP) gene, called SPA-1, in mice. Rap1 hyperactivation was observed in hematopoietic cells, which led over time to features associated with symptoms typical of human myeloid dyslastic and myeloid proliferative diseases. The authors present additional data showing that the level of Rap1 activation is important for regulating myelopoiesis and that, in the right context, can deliver an oncogenic signal.

Ebrahimi S, Wang E, Udar N, et al.
Genomic organization and cloning of the human homologue of murine Sipa-1.
Gene. 1998; 214(1-2):215-21 [PubMed] Related Publications
Murine Sipa-1 (signal-induced proliferation associated protein) is a mitogen induced GTPase activating protein (GAP). While mapping candidate genes for multiple endocrine neoplasia type 1 (MEN1) at 11q13, we cloned the human homologue of Sipa-1. Herein, we report the complete cDNA sequence, expression, and genomic organization of SIPA-1. SIPA-1 consists of 16 exons with highly conserved exon-intron boundaries. The predicted SIPA-1 protein is highly homologous to the mouse protein, particularly in the region of the GAP-related domain at the amino terminus and the leucine zipper at the carboxy terminus. It is widely expressed, including in fetal tissues, but is most highly expressed in lymphoid organs. During the course of cloning SIPA-1, the MEN1 gene was identified, thus excluding human SIPA-1 as a candidate for this disease.

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