Abstract 1924: Thrombospondin-2 expression is down-regulated in prostate cancer and is associated with inhibition of prostate cancer progression.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Introduction: Thrombospondin 2 (THBS2 or TSP2) is a secreted glycoprotein associated with tumor growth and angiogenesis inhibition. TSP2 expression levels are altered in many tumors, but, to date, there is no detailed analysis of TSP2 expression and function in prostate cancer (PCa). Objectives: The aim of this work was to characterize TSP2 expression levels in PCa and its potential usefulness for the differential diagnosis between PCa and benign prostatic hyperplasia (BPH), besides characterizing TSP2 functions in PCa. Methods: TSP2 transcript expression levels were analyzed by quantitative real time PCR, in PCa and BPH tissue samples and tumor and non-tumor cell lines. TSP2 protein expression levels were assessed by immunohistochemistry in a tissue microarray platform, containing 204 PCa and 66 BPH tissue samples, using a semi-automated image analysis system. To investigate TSP2 functions in PCa cells, PC3 and DU145 cell lines, were treated with recombinant TSP2 protein (rTSP2) (50 ug/ml) and were subjected to proliferation end point assays and cell cycle analysis. PC3 cells were also subjected to phosphoproteomic analysis using a phospho-antibody array. Results: Our data showed that TSP2 transcript expression levels are down-regulated in PCa tissue samples and cell lines, compared to BPH and non-tumoral samples (p<0.01). Receiving Operating Curve (ROC) analysis demonstrated that TSP2 transcript levels could better distinguish PCa from BPH tissue samples (p<0.01) than serum PSA levels (p=0.299). TSP2 protein expression was observed in the cytoplasm of both PCa and BPH epithelial and stromal cell compartments. TSP2 stromal staining scores were significantly lower in PCa than in BPH tissues (p<0.01), while similar TSP2 epithelial staining patterns were observed. Notably, TSP2 epithelial staining score was positively correlated to vascular invasion and biochemical recurrence in PCa (p<0.05). Treatment of PC3 and DU145 cells with rTSP2 significantly decreased the proliferation rate of these cells, while increased the percentage of cells in sub-G1 phase of the cell cycle. The phosphoproteomic analysis of PC3 cells treated with rTSP2 showed significantly lower phosphorylation levels of ERK and JNK proteins, in contrast to the higher phosphorylation status of p53, p27, paxillin and RSK. Conclusions: Our data indicate that lower TSP2 expression levels in PCa has potential application for the differential diagnosis of PCa and BPH, and suggests possible stromal and epithelial cross talks modulating PCa progression. Additionally, our results point to a putative role of TSP2 on negatively modulating PCa cell proliferation and survival, which could be partially associated with modulation of phosphorylation levels of proteins involved in the MAPK pathway and controlling the cell cycle. Citation Format: Aline R. Matos, Claudia M. Coutinho-Camillo, Eloisio A. Silva, Francisco P. Fonseca, Luiz C S Thuler, Fernando A. Soares, Etel R P Gimba. Thrombospondin-2 expression is down-regulated in prostate cancer and is associated with inhibition of prostate cancer progression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1924. doi:10.1158/1538-7445.AM2013-1924