Abstract 242: Analyses of novel genes encoding secreted and transmembrane proteins identified by CAST method: CDON is highly expressed in prostate cancer

Abstract Prostate cancer (PCa) is one of the most common human cancers. Identification of novel genes that encode membrane-spanning or secreted proteins expressed specifically in PCa has a great advantage to develop of ideal biomarkers for cancer diagnosis and therapeutics. Escherichia coli Ampicillin Secretion Trap (CAST) is a signal sequence trap method to identify genes encoding cell surface and secreted proteins. In this study, to identify novel diagnostic and therapeutic targets of PCa, CAST method was used. We generated cDNA libraries from normal prostate and two PCa cell lines, LNCaP and DU145. These CAST libraries were ligated into the pCAST which was plasmid with a mutant beta-lactamase lacking the endogenous signal peptide. Survival on ampicillin was observed only when various cDNA fragments encoding a signal sequence were inserted. We sequenced 960 ampicillin-resistant colonies for normal prostate CAST library, 1344 colonies for LNCaP CAST library and 960 colonies for DU145 CAST library. By comparing these sequences to those deposited in the public databases using BLAST (NCBI), 223 genes from normal prostate CAST library, 234 genes from LNCaP and 228 genes from DU145 were identified. To extract highly expressed genes in PCa, the genes expressed in normal prostate were excluded. Quantitative RT-PCR analyses of 64 candidate genes were performed and compared mRNA levels in 9 PCa tissues, 2 normal prostate tissues and 14 kinds of normal tissues. Quantitative RT-PCR analyses revealed that CDON was highly expressed in PCa. Overexpression of CDON (tumor/normal ratio > 2) was observed in 8 (89%) of 9 PCa tissues. CDON is a cell surface receptor of the immunoglobulin /fibronectin type III repeat family. By western blot analysis, low to moderate CDON expression was noted in LNCaP cell extracts and moderate to high CDON expression was noted in DU145 cell extracts. The expression of CDON in LNCaP and DU145 was suppressed by treatment with CDON specific siRNA. Cell invasion assay and MTT assay revealed that knockdown of CDON in LNCaP cells did not inhibit both cell growth and invasion ability, but knockdown of CDON in DU145 cells inhibited both cell growth and invasion ability. In conculusion, CAST is a robust and rapid method to identify cell surface and secreted proteins. CDON was up-regulated in PCa and participated in cell growth and invasion. These finding suggest that CDON may be a good therapeutic target. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 242.