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Regulation of uridine diphosphate-glucuronosyltransferase 1A3 activity by protein phosphorylation
Yongsheng Xiao1, Yan Yao1, Huidi Jiang1
1Laboratory of Pharmaceutical Analysis and Drug Metabolism, Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, China.
Abstract:
Protein phosphorylation is a vital post-translational modification. This study investigated the effect of phosphorylation on human uridine diphosphate (UDP)-glucuronosyltransferase 1A3 (UGT1A3) activity. Curcumin and calphostin C suppressed the activity and phosphorylation of recombinant UGT1A3 expressed in Sf9 cells. These results indicate that UGT1A3 undergoes phosphorylation, which is required for its catalytic activity. Calphostin C is a highly specific protein kinase C (PKC) inhibitor, so three predicted PKC phosphorylation sites in UGT1A3 were examined. Site-directed mutation analysis at residues 28, 43 and 436 (from serine to glycine) was conducted. Compared with the wild-type, the S43G-mutant showed significantly decreased UGT1A3 catalytic activity. Furthermore, the UGT1A3 activity of wild-type and S43G-mutant was down-regulated by calphostin C, whereas the calphostin C inhibitory effect was much weaker on the S43G-mutant than the wild-type. In conclusion, phosphorylation plays an important role in UGT1A3 activity, and the serine at site 43 in UGT1A3 is most likely a phosphorylation site.
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