Functional characterization of two potential breast cancer related genes

Thesis Type: Doctorate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Arts and Sciences, Department of Biology, Turkey

Approval Date: 2012




Cancer may arise as a result of deregulation of oncogenes and/or tumor suppressors. Although much progress has been made for the identification of such cancer related genes, our understanding of the complex tumorigenesis pathways is still not complete. Therefore, to improve our understanding of how certain basic mechanisms work in normal and in cancer cells, we aimed to characterize two different breast cancer related genes. First part of the study focused on subcellular localization USP32 (Ubiquitin Specific Protease 32) to help understand the function of this uncharacterized gene. USP32 is a member of deubiquitinating enzymes (DUBs) and the gene maps to a gene rich region on 17q23. Genes on 17q23 are known to undergo amplification and overexpression in a subset of breast cancer cells and tumors. DUBs are known to be implicated in a variety of cellular functions including protein degradation, receptor endocytosis and vesicle trafficking. Therefore to elucidate the function of USP32, we localized the full length USP32 protein fused to GFP, in HeLa cells, using Fluorescence Protease Protection (FPP) assay and confocal microscopy. Results suggested a Golgi localization for USP32 as confirmed by co-localization study via BODIPY-TR, a Golgi specific marker. Additional investigations to find the role of USP32 in Golgi will further clarify the function of this candidate oncogene. Second part of the study focused on a potential tumor suppressor. For this purpose, we functionally characterized miR-125b, a microRNA gene as a potential tumor suppressor in breast cancer. microRNAs are regulators of gene expression and their deregulation is detected in cancer cells. miR-125b is reported as a down regulated microRNA in breast cancers. In this study, we investigated the expression, function and possible targets of miR-125b in breast cancer cell lines (BCCLs). Our results revealed a dramatic down regulation of miR-125b in a panel of BCCLs. Restoring the expression of miR-125b in low miR-125b expressing cells decreased the cell proliferation and migration as well as cytoplasmic protrusions, detected by staining of actin filaments. While connection of miR-125b and cell motility based on ERBB2 targeting has been reported earlier, here we present data on ERBB2 independent effects of miR-125b on cell migration in non-ERBB2 overexpressing breast cancer cells. Our results showed involvement of a miR-125b target, ARID3B, in cell motility and migration. Our findings showed miR-125b to be an important regulator of cell proliferation and migration in ERBB2 negative breast cancer cells, possibly through regulating multiple targets.