Overexpression of the prolyl isomerase PIN1 promotes cell growth in osteosarcoma cells

PIN1 was recently identified as a peptidyl-prolyl cis-trans isomerase (PPIase). It binds to and isomerizes specific pSer/Thr-Pro motifs and catalytically induces conformational changes after phosphorylation. PIN1 plays an important role in several cellular events, such as cell cycle progression, transcriptional regulation, RNA processing, cell proliferation and differentiation. The relationship between PIN1 and osteosarcoma has not been previously studied. In the present study, we investigated the expression pattern of PIN1 in human osteosarcoma tissues and the role of PIN1 in osteosarcoma generation and development. The expression levels of PIN1 were detected by immunohistochemistry and western blotting. Results demonstrated that the expression of PIN1, cyclin D1 and β-catenin were significantly higher in human osteosarcoma tissues compared to normal tissues. The in vitro effects of PIN1 overexpression were studied in human osteosarcoma cell lines. Adenovirus-mediated PIN1 overexpression significantly stimulated the proliferation of MG-63 and U2-OS osteosarcoma cells by 148±10.5 and 187±21.5%, respectively. In FACS analysis, U2-OS cells displayed significant levels of arrest in cell cycle progression at the G0/G1 phase. Consistent with increased cell growth, levels of cyclin D1 and cyclin E and their associated cyclin-dependent kinases, CDK4 and CDK6, were enhanced in PIN1-overexpressed cells compared with the control virus-transfected cells. When the PIN1 inhibitor juglone was added to the cells, the proliferative effects of PIN1 were abolished. These results suggest that PIN1 may play an important role in tumorigenesis and tumor progression of osteosarcoma and therefore, provide a new target for gene therapy.