Studies On The Biological Functions And Regulation Of CPS1 In AFB₁ Hepatocarcinogenesis

Carbamyl phosphate synthetase I(CPS1)is the first and rate-limiting enzyme of urea cycle,which is important for ammonia detoxification.It is always down-regulated in hepatocellular carcinoma(HCC).The level of urea was decreased in HCC and AFB1 treated liver cell and tissue.But no evidence revealed that AFB1 down regulated CPS1.In this study,the expression of CPS1 was analyzed in different tissues of mice and human cells.CPS1 was shown to mainly express in liver and litter in small intestine and was high conserved in different species.And the expression of CPS1 was down-regulated by AFB1 in a time-and dose-dependent manner.And then,two potential pathways:DNA methylation and Y-boxing binding protein up regulation were not shown to regulate CPS1.At the meantime,knock-down of CPS1 inhibited cell proliferation and induced cell apoptosis while overexpression of CPS1 had no obvious function,indicating that CPS 1 was an important protein in cells.The regulation mechanism was analyzed through searching the interacting proteins of CPS1 by endogenous co-immunoprecipitation(CO-IP).Five potential interacting proteins(DSP,HSJUP,KRT1,ALB and UBC)were identified by MS/MS.By analyzing the interaction with CPS1 and AFB1,keratin I was the most potent one.Both CPS1 and cytokeratins play critical roles in differentiation and tissue specialization.This interaction may offer an increased understanding that CPS1 might have functions in cell differentiation and tumor formation.