Abstract 2695: Olfactomedin 4 gene is associated with progression of prostate cancer: Evidence from an OLFM4 knockout mouse model

Abstract

Abstract The olfactomedin 4 gene (OLFM4) encodes an olfactomedin-related glycoprotein whose physiological and pathological functions are largely unknown. We have previously reported that expression of OLFM4 is down regulated during the progression of human prostate cancer, and that reduced expression is due to gene deletions of OLFM4 (36.7%) and/or hyper-methlytion of CpG sites in the promoter region. We also demonstrated that ectopic expression of OLFM4 in several human prostate cancer cell lines inhibits proliferation, invasion and metastatic potential. In this study, we further investigated the potential role of OLFM4 in the carcinogenesis of prostate cancer utilizing an OLFM4 knock out mouse model. Histopathological analysis revealed that homozygous OLFM4 mutant mice develop prostatic epithelial lesions in an age-dependent manner. The prostatic epithelial hyperplasia was seen at 6 months of age, prostatic intraepithelial neoplasia (PIN) was found at 10-12 months of age, and prostate adenoma was observed from 18-24 months of ages in the both anterior prostate (AP) and dorsal-lateral prostate (DLP) of OLFM4-null mice. The frequency of PIN lesions at the AP and DLP was 0 % (0/20) at 3-6 months, 38% (5/13) at 10-12 months and 44% (11/25) at 18-24 months. The frequency of prostatic adenoma was 28% (7/25), and 8% (2/25) of OLFM4-null mice developed lung metastases at 18-24 months of age. To determine whether OLFM4 affects proliferation or apoptosis of prostatic epithelial cells in the OLFM4-null mice, we carried out Ki-67 immunohistochemical staining and TUNEL assays. The ratio of Ki-67 positive cells was significantly higher at 3-6 months (p=0.04180), 10-12 months (P=0.002) and 18-20 months (p=0.0038) compared to age-matched controls, OLFM4 wild type mice, or heterozygous mice, thus indicating an increase in proliferation in OLFM4-null prostate tissues. There was no difference in the number of apoptotic cells in the control versus null mice. Since we have previously found that OLFM4 blocks CXCL12 induced AKT activity in the human prostate cancer cell PC-3, and inhibits cell invasion, we studied the phosphorylation of AKT and downstream signaling pathway components by Western blot analysis of prostate samples from 3-4 month old mice. Compared with OLFM4 wild type mice, pAKT, pGSK3β, β-catenin, cyclin D1 and c-Myc were increased in the OLFM4-null mice tissue even in the absence of morphological abnormalities. Elevated β-catenin protein in OLFM4-null mice prostate epithelial cells was also observed in PIN and tumor cells at 18 months of age, and positive staining with Cyclin D1 in OLFM4-null tumor was also detected. Taken together, the data show OLFM4-null prostatic epithelial cells exhibit higher levels of AKT and β-catenin, suggesting this is the mechanism leading to their enhanced cellular proliferation and carcinogenetic potential. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2695. doi:1538-7445.AM2012-2695