We previously isolated and characterized the novel human gene MOST-1 (C8orf17) that is ubiquitously expressed in all cancer cell lines tested but differentially expressed in normal adult tissues. MOST-1 maps to chromosome region 8q24.2 whose amplification is frequently associated with breast and prostate cancers. RT-PCR analyses of breast and prostatic biopsies revealed MOST-1 overexpression and/or amplification in high-grade carcinomas. We raised and characterized a polyclonal antibody against a MOST-1-specific synthetic peptide. in vitro expression of MOST-1 protein revealed a tendency to exist as high molecular mass isoforms which are SDS-insoluble upon thermal stress. MOST-1 displayed cytoplasmic localization in four human cell lines (hTERT-HME1 normal mammary epithelial, MCF7 breast adenocarcinoma, PrEC normal prostate epithelial and DU145 prostate carcinoma), with polar expression during cell division. Knockdown of MOST-1 expression in DU145 cells resulted in reduced cell proliferation but enhanced apoptosis implying a putative mitogenic role of MOST-1. Yeast two-hybrid analyses demonstrated interaction with seven human proteins, most of which are overexpressed in tumors or involved in metabolic pathways. The interacting proteins were creatine kinase, Gardner feline sarcoma v-FGR oncogene product, telethonin, SNC73 protein, ferritin light chain, peripheral benzodiazepine receptor, and immunoglobulin C (μ) and C (δ) heavy chain. Co-immunoprecipitation assays validated the interactions of MOST-1 with the latter three proteins. Our results suggest that MOST-1 is associated with cell survival, proliferation and progression of cancer cells.

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