Metastatic spread of the cancer is usually the consequence of the activation of signaling pathways that generate cell motility and tissue invasion. Metastasis involves the reorganization of cytoskeleton and cell shape for the swift movement of the cells through extracellular matrix. Previously, we have described the invasive and metastatic role played by one of the members (Toca-1) of CIP4 subfamily of F-BAR proteins. In the present study, we address the role of another member (FBP17) of same family in the invasion breast cancer cells. Here, we report that the formin-binding protein 17 (FBP17) is highly expressed at both mRNA and protein levels in breast cancer cells. The study showed the association of FBP17 with cytoskeletal actin regulatory proteins like dynamin and cortactin. To determine its role in extracellular matrix (ECM) degradation, we achieved stable knockdown of FBP17 in MDA-MB-231 cells. FBP17 knockdown cells showed a defect and were found to be compromised in the degradation of ECM indicating the role of FBP17 in the invasion of breast cancer cells. Our results suggest that FBP17 is highly expressed in breast cancer cells and facilitates the invasion of breast cancer cells.

BACKGROUND: Molecular lesions in T-cell acute lymphoblastic leukemias affect regulators of cell cycle, proliferation, differentiation, survival and apoptosis in multi-step pathogenic pathways. Full genetic characterization is needed to identify events concurring in the development of these leukemias.
DESIGN AND METHODS: We designed a combined interphase fluorescence in situ hybridization strategy to study 25 oncogenes/tumor suppressor genes in T-cell acute lymphoblastic leukemias and applied it in 23 adult patients for whom immunophenotyping, karyotyping, molecular studies, and gene expression profiling data were available. The results were confirmed and integrated with those of multiplex-polymerase chain reaction analysis and gene expression profiling in another 129 adults with T-cell acute lymphoblastic leukemias.
RESULTS: The combined hybridization was abnormal in 21/23 patients (91%), and revealed multiple genomic changes in 13 (56%). It found abnormalities known to be associated with T-cell acute lymphoblastic leukemias, i.e. CDKN2A-B/9p21 and GRIK2/6q16 deletions, TCR and TLX3 rearrangements, SIL-TAL1, CALM-AF10, MLL-translocations, del(17)(q12)/NF1 and other cryptic genomic imbalances, i.e. 9q34, 11p, 12p, and 17q11 duplication, del(5)(q35), del(7)(q34), del(9)(q34), del(12)(p13), and del(14)(q11). It revealed new cytogenetic mechanisms for TCRB-driven oncogene activation and C-MYB duplication. In two cases with cryptic del(9)(q34), fluorescence in situ hybridization and reverse transcriptase polymerase chain reaction detected the TAF_INUP214 fusion and gene expression profiling identified a signature characterized by HOXA and NUP214 upregulation and TAF_I, FNBP1, C9orf78, and USP20 down-regulation. Multiplex-polymerase chain reaction analysis and gene expression profiling of 129 further cases found five additional cases of TAF_I-NUP214-positive T-cell acute lymphoblastic leukemia.
CONCLUSIONS: Our combined interphase fluorescence in situ hybridization strategy greatly improved the detection of genetic abnormalities in adult T-cell acute lymphoblastic leukemias. It identified new tumor suppressor genes/oncogenes involved in leukemogenesis and highlighted concurrent involvement of genes. The estimated incidence of TAF_I-NUP214, a new recurrent fusion in adult T-cell acute lymphoblastic leukemias, was 4.6% (7/152).

In the development and progression of cancer, tumor suppressor genes may be silenced by mechanisms such as methylation. Thus the discovery of new genes silenced by methylation may uncover new tumor suppressor genes, and improve our understanding of cancer biology. In this study we investigated the methylation of 19 genes in esophageal squamous cell carcinoma. Methylation was measured in 10 of these genes in esophageal squamous cell carcinoma cell lines: CDH13, CLDN6, C16orf62, FBN2, FNBP1, ID4, RBP1, RBP4, TFPI2 and TMEFF2. To determine if there was a correlation between DNA methylation and gene silencing, each cell line was cultured with or without the demethylating drug 5-aza-2'-deoxycytidine (aza-dC). For 6 genes (CLDN6, FBN2, RBP1, RBP4, TFPI2 and TMEFF2) there was an association between reduction of methylation and increase in mRNA expression in the demethylated cell lines. The frequency of the methylation of these 6 genes in esophageal squamous cell carcinoma resection specimens was also investigated. All 6 genes showed more frequent methylation in the tumor than the matched proximal resection margin of uninvolved esophagus. There was a significant difference in the frequency of methylation and in the extent of the methylation between the cancer and the margin tissues for CLDN6, FBN2, TFPI2 and TMEFF2 (P=0.0007, P=0.0048 P=0.0002 and P<0.0001, respectively). This is the first report of gene silencing by methylation of CLDN6, FBN2, RBP4, TFPI2 and TMEFF2 in esophageal squamous cell carcinoma.

The t(9;11) has been described in patients with acute myeloid leukemia (AML), and two genes [AF9 (at 9p21) and FBP17 (at 9q34)] have been cloned as fusion partners of the MLL gene. From an AML-M5 with a t(9;11)(q34;q23), we identified a novel MLL fusion partner, AF9Q34. The AF9Q34 protein shows high homology with nGAP, a RAS GTPase-activating protein (RASGAP), and contains the highly conserved GRD and FLR motifs characteristic of RASGAPs. Recently, the rat homologue (DAB2IP) also was identified and reported to act as a RASGAP both in vivo and in vitro. RASGAPs negatively regulate the activity of RAS proteins that modulate diverse cellular processes by cycling between an inactive GDP-bound and an active GTP-bound state. In addition, the NH(2) terminus harbors an amino acid stretch with homology to the pleckstrin homology (PH) domain implicated in regulating the interaction between RAS and the catalytic domain of RASGAP. As a result of the breakpoint in the AF9Q34-MLL fusion protein, this PH domain is disrupted. This suggests that because of the translocation, the normal function of the AF9Q34 gene is aborted. Thus, AF9Q34 encodes a novel RASGAP gene that appears to be deregulated as a result of the translocation. The identification of this RASGAP protein in a novel MLL fusion implies that an indirect RAS-deregulating mechanism could be involved in leukemic transformation.

We have cloned a fusion partner of the MLL gene at 11q23 and identified it as the gene encoding the human formin-binding protein 17, FBP17. It maps to chromosome 9q34 centromeric to ABL. The gene fusion results from a complex chromosome rearrangement that was resolved by fluorescence in situ hybridization with various probes on chromosomes 9 and 11 as an ins(11;9)(q23;q34)inv(11)(q13q23). The rearrangement resulted in a 5'-MLL/FBP17-3' fusion mRNA. We retrovirally transduced murine-myeloid progenitor cells with MLL/FBP17 to test its transforming ability. In contrast to MLL/ENL, MLL/ELL and other MLL-fusion genes, MLL/FBP17 did not give a positive readout in a serial replating assay. Therefore, we assume that additional cooperating genetic abnormalities might be needed to establish a full malignant phenotype. FBP17 consists of a C-terminal Src homology 3 domain and an N-terminal region that is homologous to the cell division cycle protein, cdc15, a regulator of the actin cytoskeleton in Schizosaccharomyces pombe. Both domains are separated by a consensus Rho-binding motif that has been identified in different Rho-interaction partners such as Rhotekin and Rhophilin. We evaluated whether FBP17 and members of the Rho family interact in vivo with a yeast two-hybrid assay. None of the various Rho proteins tested, however, interacted with FBP17. We screened a human kidney library and identified a sorting nexin, SNX2, as a protein interaction partner of FBP17. These data provide a link between the epidermal growth factor receptor pathway and an MLL fusion protein.