The promoting molecular mechanism of alphafetoprotein on the growth of human hepatoma Bel 7402 cell line

AIM: The goal of this study was to characterize the AlPreceptor, its possible signal transduction pathway and itsproliferative functions in human hepatoma cell line Bel 7402.METHODS: Cell proliferation enhanced by AFlP was detectedby MTT assay, 3H-thymidine incorporation and S-stsgepercentage of cell cycle analysis. With radioactive labeled 125 I-AFP for receptor binding assay; cAMP acctmuation, ProteinKinase A activity were detected by radioactive immunosorbentassay and the change of intracellular free calcium ([Ca2+ ], )was monitored by scanning fluorescence intensity under TCS-NT confocal microscope. The expression of oncxgenes N- ras,p53, and p21ras in the cultured cells in vitro were detected byNorthem blotting and Western blotting respectively.RESULTS: It was demonstrated that AFP enhanced theproliferation of human hepatoma Bel 7402 cell in a dosedependlent fashion asshown in MTT assay, 3H-thymidineincorporation and S-phase percentage up to 2-fold. Twosubtypes of AFP receptors were identified in the cells withKds of 1.3 x 10-9 mol. L-1 and 9.9 x 10-8 mol. L-1 respectively.Pretreatnent of cells with AFP resulted-in a significantincrease (625 %) in cAMP accumulation. The activity ofprotein kinase A activity were increased up to 37.5, 122.6,73.7 and 61.2 % at treatment time point 2, 6, 12 and 24hours. The level of intracellular calcium were elevated afterthe treatment of alpha-fetoprotsin and achieved to 204 % at 4min. The results also showed that AFP (20 mg. L-1 ) couldupregulate the expression of N-ras oncogenes and p53 andp21ras in Bel 7402 cells. In the later case, the alteration ware 81.1%(12 h) and 97.3 %(12 h) respectively compared with control.CONCLUSION: These results demonstrate that AFP is apotential growth factor to promote the proliferation of humanhepatoma Bel 7402 cells. Its growth-regulatory effects aremediated by its specific plasma membrane receptorscoupled with its transmembrane signaling transductionthrough the pathway of cAMP-PKA and intracellular calciumto regulate the expression of oncog