Negatively regulating mechanism of Sirpal in hepatocellular carcinoma:an experimental study

BACKGROUND: Signal regulatory protein ( Sirp) is a recently isolated, cloned and identified inhibitor receptor distributed in the membrane of hematopoietic and nonhema-topoietic cells. Sirp alphal ( Sirpα1) is a member of Sirp families. Sirpal can bind SHP-2 in the form of tyrosine phosphorylation by SH2 effect and negatively regulate growth factor, oncogene, or insulin-induced responses as its substrate. This study aimed to preliminarily clarify the negatively regulating proliferation mechanism of Sirpal in liver cancer. METHODS: pLXSN, Sirpα1 and Sirpα1Δ4Y2 plasmids were respectively transfected into Sk-Hepl liver cancer cell line, and various stable Sk-Hepl cell lines were obtained with screening agent of G418 (1200 μg/ml). The expressing levels of cyclin D1, CDK4, Fas, β-catenin and gankyrin in various cell lines were determined with Western blotting. Cell cycles were determined at 0, 12 and 24 hours with flow cytotnetry after various synchronous cell lines were cultured without serum for 72. Cell apoptosis induced with agent of TNF-α (50 ng/ml) was determined with flow cytotnetry at 0,0.5,1,3,6 and 12 hours. RESULTS: Sirpα1 could significantly decrease the expression of cyclin D1, β-catenin and gankyrin, but it couldn't affect the expression level of CDK4 and Fas. When synchronous cells were cultured for 12 hours, S phase Sk-Hep1 cell transfected with Sirpal plasmid was the lowest [(31.92 ± 0.22)% vs. other cell lines, P <0.05], and the cell line was highly sensitive to TNF-α agent for 1 hour. (59.31 ±0.59)% of apoptotic cells occurred (vs. the other time points, P < 0.05). CONCLUSIONS: Sirpal might block the cell cycle of liver cancer, inhibit cell proliferation, promote cell apoptosis by decreasing the expression of cyclin D1, β-catenin and gankyrin. It is one of the important mechanisms inhibiting the occurrence and development of hepatocellular carcinoma.