Novel Gene C17ORF37 in Prostate Cancer Progression and Metastasis

C17orf37 also known as MGC14832, C35, Rdx12, a novel gene located on human chromosome 17q12 in the ERBB2 amplicon, is abundantly expressed in different forms of human cancer. C17orf37 expression has been reported to positively correlate with grade and stage of cancer progression; however the functional significance of C17orf37 overexpression in cancer biology is not known. Here, we show that C17orf37 is highly expressed in prostate cancer cell lines and tumors, compared to minimal expression in normal prostate cells and tissues. RNA interference mediated downregulation of C17orf37 resulted in decreased migration and invasion of DU-145 prostate cancer cells, and suppressed the DNA binding activity of NF-κB transcription factor resulting in reduced expression of downstream target genes MMP-9, uPA and VEGF. Phosphorylation of PKB/Akt was also reduced upon C17orf37 downregulation, suggesting C17orf37 acts as a signaling molecule that increases invasive potential of prostate cancer cells by NF-κB mediated downstream target genes. Cellular localization studies by confocal and total internal reflection (TIRF) microscopy revealed expression of C17orf37 protein in the cytosol predominantly surrounding the membrane of prostate cancer cells. We identified that C17orf37 has a functional prenylation motif and is posttranslationally modified by geranylgeranyl transferase-I (GGTase-I) enzyme. Prenylated proteins (often referred to as CAAX family of proteins) contain a CAAX motif (C denotes cysteine, A represents aliphatic amino acids, and X any amino acid) at the carboxyl terminal which serves as a substrate for a series of post-translational modifications converting otherwise hydrophilic to lipidated proteins with hydrophobic domain, facilitating membrane localization. Geranylgeranylation of C17orf37 at the ‘CVIL’ motif translocates the protein to the inner leaflet of plasma membrane, enhances migratory phenotype of cells by inducing increased filopodia formation and potentiates directional migration. The prenylation-deficient C17orf37 mutant is functionally inactive and fails to disseminate injected cells in the mouse model of metastasis. This implies that prenylation activates the C17orf37 protein in cancer cells and functionally regulates metastatic progression of the disease. Our data strongly suggest C17orf37 overexpression in prostate cancer functionally enhances migration and invasion facilitating metastatic dissemination of tumor cells, and is an important target for cancer therapy.