Overexpression of Protein Phosphatase 1γ (PP1γ) Is Associated with Enhanced Cell Proliferation and Poor Prognosis in Hepatocellular Carcinoma.

Abstract

Protein phosphatase1γ (PP1γ), as a member of the protein phosphatase1 family, may be involved in regulation of multiple cellular processes, such as mitosis, cell survival, and apoptosis. However, little is known about the underlying mechanisms by which PP1γ regulates hepatocellular carcinoma development. We investigated the expression profile of PP1γ in hepatocellular carcinoma (HCC) cell lines and human HCC specimens, as well as its potential prognostic significance in HCC. PP1γ expression profile was detected in 94 HCC specimens using immunohistochemistry. PP1γ levels in HCC cells were downregulated by small interfering RNA (siRNA) transfection. Cell cycle progression and proliferation status of HCC cells and the effectiveness of doxorubicin were evaluated by flow cytometry and CCK-8 assay. The levels ofPP1γ, CyclinD1, PCNA, Mdmx, p53, p21, and active caspase-3 were evaluated by Western blot analysis. PP1γ was upregulated in tumorous specimens, compared with adjacent nontumorous tissues. Univariate and multivariate survival analyses were conducted to determine the prognostic significance of PP1γ in HCC. The expression pattern of PP1γ was positively correlated with tumor size, histological grade, Ki-67 expression, and poor prognosis in HCC. In addition, depletion of PP1γ by siRNA could inhibit cell proliferation, resulted in G1 phase arrest, and attenuated resistance to doxorubicin in Huh7 cells. PP1γ is upregulated in HCC cell lines and HCC specimens, promotes cancer cell proliferation through regulation of p53, and may be a potential target for treatment of HCC.