PR55α Subunit of Protein Phosphatase 2A Supports the Tumorigenic and Metastatic Potential of Pancreatic Cancer Cells by Sustaining Hyperactive Oncogenic Signaling

The protein phosphatase 2 (PP2A) holoenzyme consists of a catalytic subunit, a scaffold subunit, and a regulatory subunit. Based on loss-of-function analysis using PP2A catalytic inhibitors or inhibition via tumor viral antigens, limited studies suggest that PP2A is a putative tumor suppressor. However, PP2A has also been shown to facilitate the activation of oncogenic signaling pathways when associated with specific regulatory subunits. In this study, we investigated the possible oncogenic role of PP2A in pancreatic cancer. We found a striking increase in the expression of PR55 alpha (PPP2R2A), a PP2A regulatory subunit, in pancreatic cancer cells compared with normal pancreatic epithelial cells. Consistently, PR55 alpha expression was markedly elevated in pancreatic ductal adenocarcinoma tissues compared with adjacent normal pancreatic tissues (P < 0.0001) and correlated with poor survival of pancreatic cancer patients (P < 0.0003). RNAi-mediated depletion of PR55 alpha in pancreatic cancer cell lines resulted in diminished phosphorylation of both AKT and ERK1/2 (MAPK3/1) and decreased protein levels of beta-catenin (CTNNB1). Accordingly, pancreatic cancer cells with reduced PR55 alpha expression exhibited significantly impaired properties of transformation, including attenuated cell growth, clonogenicity, mobility, and anchorage-independent growth. Moreover, orthotopic implantation of PR55 alpha-depleted pancreatic cancer cells into nude mice resulted in markedly reduced tumorigenicity (P < 0.001) and distant metastases. Together, these results suggest that PR55 alpha promotes pancreatic cancer development by sustaining hyperactivity of multiple oncogenic signaling pathways, including AKT, ERK, and Wnt. These studies also provide a basis for exploring PR55 alpha as a diagnostic or therapeutic target in pancreatic cancer. (C) 2016 AACR.