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Effect of Sirpalpha1 on the expression of nuclear factor-kappa B in hepatocellular carcinoma.

BACKGROUND
Signal regulatory protein alpha1 (Sirpalpha1) is a member of Sirps families containing four immunoreceptor tyrosine-based inhibitory motifs (ITIMs) domains in the cytoplasm of and an activated substrate of receptor tyrosine kinase (RTK), that negatively regulates the RTK-dependent cell proliferating signal transduction pathway. Previously we found that Sirpalpha1 was closely associated with the occurrence and development of hepatocellular carcinoma (HCC) as well as liver regeneration. Since it is unclear about the regulatory mechanisms, we established the cell line transfected Sirpalpha1 gene and preliminarily clarified the mechanisms by which Sirpalpha1 negatively regulates the carcinogenesis and development of HCC.


METHODS
Liver cancer Sk-Hep1 cell was respectively transfected with plasmids of pLXSN, pLXSN-Sirpalpha1 and pLXSN-Sirpalpha1delta4Y2, screened with the drug of G418 (1200 microg/ml), and various transfected Sk-Hep1 cell lines were obtained. The protein expressions of P65, P50, IkappaBalpha, cyclin D1 and Fas in various Sk-Hep1 cell lines were determined by Western blotting, and P65 and P50 were localized by the immunofluorescence technique.


RESULTS
Sirpalpha1 could significantly upregulate the protein expression of IkappaBalpha (vs. other cell lines, P<0.05) in the Sk-Hep1 cell, and downregulate the protein expressions of P65, P50 and cyclin D1 (vs. other cell lines, P<0.05) in the Sk-Hep1 cell. P65 protein expression was mainly localized in the cytoplasm in the pLXSN Sk-Hep1 cell, and in the nucleus of the Sk-Hep1 cell with mutant Sirpalpha1delta4Y2, but in nucleus of the Sk-Hep1 cell with wild Sirpalpha1. P50 protein expression was localized in the cytoplasm and nucleus of the pLXSN Sk-Hep1 cell, but in the nucleus of the Sk-Hep1 cell with wild Sirpalpha1 and mutant Sirpalpha1delta4Y2 plasmid.


CONCLUSIONS
Sirpalpha1 might negatively regulate and control the abnormal proliferation of liver cancer cells by influencing the protein content and localization of nuclear factor-kappa B, then influence the expression of cyclins such as cyclin D1 in the signal transduction pathway. It may be one of the important mechanisms by which Sirpalpha1 negatively regulates the carcinogenesis and development of HCC.