BACKGROUND: Signal regulatory protein (Sirp) is a recently isolated, cloned and identified inhibitor receptor distributed in the membrane of hematopoietic and nonhematopoietic cells. Sirp alpha1 (Sirpα1) is a member of Sirp families. Sirpα1 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 Sirpα1 in liver cancer.
METHODS: pLXSN, Sirpα1 and Sirpα1Δ4Y2 plasmids were respectively transfected into Sk-Hep1 liver cancer cell line, and various stable Sk-Hep1 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 cytometry 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 cytometry 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 Sirpα1 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: Sirpα1 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.