Abstract 4465: Glypican-1: A tumor suppressor or an oncogene in human bone metastatic prostate cancer cells

Abstract

Abstract Glypican-1 (GPC-1) is a cell surface heparan sulfate proteoglycan that mediates cell proliferation, differentiation and migration. It also possess oncogenic functions in breast, pancreatic and lung cancer cells, and is a proposed biomarker for prostate cancer. Despite these data the function of GPC-1 in prostate cancer is not fully known. We addressed this gap-in-knowledge using in vitro and in vivo mouse models. We first showed that GPC-1 was overexpressed in bone metastatic prostate cancer cells (PC-3) but was not detected in lymph node metastatic cancer cells (LNCaP) and non-cancerous prostate cells (RWPE-1). Next, we inhibited GPC-1 expression using shRNA in bone metastatic cancer cells (PC-3), and verified inhibition using western blot analysis and qRT-PCR. Crystal violet staining, trans-well assays, matrigel colony cultures and adhesion assays were used to determine the effect of GPC-1 inhibition on cancer cell growth, migration, spheroid formation and cell adhesion. Inhibition of GPC-1 reduced prostate cancer cell growth, migration and spheroid formation; however, there were no changes in cell adhesion. These in vitro data suggested that GPC-1 played a role in prostate cancer progression by acting as an oncogene. We further investigated this possibility in vivo using athymic (NCr) mice xenografts. Interestingly, inhibition of GPC-1 in PC-3 cells appeared to increase tumor size as compared to scrambled controls. Further analysis showed that that inhibition of GPC-1 increased the tumor expression of MMP-9 and N-cadherin, but not E-cadherin. We hypothesized that the discrepancy between the in vitro and in vivo results may be mediated by interaction of PC-3 cells with the tumor microenvironment. We addressed this hypothesis by testing the effect of tumor conditioned media (TCM) from control and GPC-1 knockdown cells on human bone marrow derived mesenchymal stem cells (hMSC) and fibroblast (HS-27). Treatment of both hMSC and HS-27 cells with TCM from GPC-1 knockdown PC-3 cells increased MMP-9 and interestingly MMP-2 expression and activity as compared to control cells. We also detected increases in the expression of N-Cadherin in a co-culture model. Collectively, these data suggest that GPC-1 acts as an oncogene to enhance prostate cancer cell growth in vitro; however, these data also suggest the GPC-1 may act as a tumor suppressor in vivo. This discrepancy may be due to the interaction off GPC-1 with the tumor microenvironment, which would not be detected in single-cell culture models. Citation Format: Nhat D. Quach, Matthew Eggert, Deepraj Ghosh, Michelle R. Dawson, Robert Arnold, Brian S. Cummings. Glypican-1: A tumor suppressor or an oncogene in human bone metastatic prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4465. doi:10.1158/1538-7445.AM2017-4465