Abstract 3997: TUSC3 (N33) affects protein N-glycosylation and proliferation of prostate cancer cells

Prostate cancer is the most prevalent cancer in males in developed countries. Molecular aberrations in the pathogenesis of this disease are numerous, though losses on the short arm of chromosome 8 are highly prevalent. In our previous studies, hypermethylation and diminished TUSC3 expression turned out to be significantly associated with poor progression free and overall survival in ovarian cancer. Additionally, expression profiling of TUSC3 negative cancer cell lines revealed deregulation of genes involved in ‘cell structure and motility’ and ‘development processes’, further supporting our hypothesis of TUSC3 as a tumor suppressor. In silico prediction of TUSC3 shows a high homology of TUSC3 to the Ost3p subunit of the oligosaccharyltransferase (OST) complex in yeast, hinting to its role in protein glycosylation. In this project, we characterized TUSC3 (N33), a putative tumor suppressor gene on 8p, in prostate cancer. To study the prognostic role of TUSC3 in prostate cancer we used a comprehensive prostate cancer tissue microarray, comprised of samples from 143 prostate cancer patients. Serum DNA methylation was studied in an additional cohort of 67 prostate cancer patients. Statistical analysis demonstrated low or missing TUSC3 protein expression in 56.6% of prostate cancer patients based on immunohistochemical staining. Methylation of the TUSC3 promoter was observed in 38.8% of prostate cancer patients’ serum DNA, confirming our previous findings of TUSC3 promoter hypermethylation as a possible epigenetic regulatory mechanism. In our prostate cancer cohorts, however, neither expression nor hypermethylation of TUSC3 had a significant effect on overall survival, possibly due to the relatively short follow-up period. Next, we studied the function of TUSC3 in N-glycosylation and in particular its influence on carcinogenesis using a cell culture model. We downregulated TUSC3 expression in prostate cancer cell lines DU145 and PC3 using shRNA mediated knockdown and analyzed them for their proliferative and carcinogenic properties in vitro. We could show that loss of TUSC3 expression confers growth advantage of prostate cancer cell lines, in particular under conditions of serum starvation. We also observed increased migratory properties of prostate cancer cell lines upon TUSC3 knockdown. Further, influence of TUSC3 downregulation on several putative targets of N-linked glycosylation has been analyzed in vitro. In our study, we characterized TUSC3 expression and