Restoration of PPP2CA expression reverses epithelial-to-mesenchymal transition and suppresses prostate tumour growth and metastasis in an orthotopic mouse model

Background: Emergence of castration-resistance in prostate cancer (PCa) is invariably associated with aggressive and metastatic disease. Previously, we reported promotion of castration-resistance upon downregulation of PPP2CA (encoding catalytic subunit of protein phosphatase 2A (PP2A), alpha-isoform); however, its role in PCa growth and metastasis remained undetermined. Methods: PPP2CA was overexpressed/silenced in PCa cells by stable transfection. Gene expression was examined by reverse transcription polymerase chain reaction, immunoblot and immunofluorescence analyses, and transcriptional activity measured by luciferase-based promoter-reporter assay. Effect on PCa phenotype was studied in vitro and in orthotopic mouse model, and immunohistochemical/histological analyses performed to assess proliferation/apoptosis and confirm metastatic lesions. Results: An inverse association of PPP2CA expression was observed with epithelial-to-mesenchymal transition (EMT) and aggressive PCa phenotype. PPP2CA restoration resulted in decreased nuclear accumulation and transcriptional activity of beta-catenin/NF-kappa B, and restitution of their activity abrogated PPP2CA-induced EMT reversal and suppression of PCa invasiveness. Akt mediated PPP2CA loss-induced nuclear accumulation of beta-catenin/NF-kappa B through inactivation of Gsk3-beta and I kappa B-alpha, respectively. Animal studies revealed a suppressive effect of PPP2CA expression on PCa growth and metastasis. Conclusions: Our findings suggest that PPP2CA downregulation serves as a molecular link between gain of castration-resistance and aggressive PCa phenotype, and its restoration could be an effective preventive/therapeutic approach against the advanced disease.