PHACTR4 regulates proliferation, migration and invasion of human hepatocellular carcinoma by inhibiting IL-6/Stat3 pathway

OBJECTIVE: Phosphatase and actin regulator 4 (PHACTR4) is one member of the largely uncharacterized PHACTR family of protein phosphatase 1 (PP1)-and actin-binding proteins. PHACTR4 is significantly deleted or mutant in many tumor subtypes, such as breast, colorectal, lung, neural, ovarian, and renal cancers. However, the role of PHACTR4 in human hepatocellular carcinoma (HCC) is completely unknown. MATERIALS AND METHODS: Ten paired HCC tissues and adjacent non-cancerous tissues were used to detect the expression PHACTR4. Real-time PCR was used to detect the mRNA level of PHACTR4 in clinic samples. The protein level of PHACTR4 was determined by Western blot. Retrovirus-based gene transduction was used to generate Flag-tagged PHACTR4 HepG2 stable cell line. BrdU assay was used to determine the cell growth of HepG2 cells. The cell cycle distribution was detected by flow cytometry assay. In vitro scratch wounding and Matrigel invasion assays were used to test the migration and invasion ability of HepG2 cells. RESULTS: The expression of PHACTR4 was noticeably decreased in clinical HCC tissues, compared to the non-tumoral tissues. Overexpression of PHACTR4 inhibited HCC cells proliferation, colony formation, migration and invasion, and resulted in significant cycle arrest. PHACTR4 attenuated both constitutive and IL-6-induced phosphorylation of signal transducer and activator of transcription 3 (Stat3), and inhibited Stat3 downstream genes expression. CONCLUSIONS: Overall, our results suggest that PHACTR4 is a tumor suppressor in HCC by inhibiting IL-6/Stat3 pathway.