Regulation of uridine diphosphate‐glucuronosyltransferase 1A3 activity by protein phosphorylation

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.

Pseudomonas aeruginosa Activates PKC-Alpha to Invade Middle Ear Epithelial Cells

“…Myristoylation of PKC inhibitory peptide makes it cell permeable and facilitates the entry inside cells. Calphostin C is a perylenequinone metabolite that targets classical and novel PKC isoforms and inhibits both phorbol ester binding and phosphotransferase activity of PKC through binding to the regulatory domain ( Kobayashi et al, 1989 ; Xiao et al, 2015 ). Chelerythrine is a benzophenanthridine that is a potent and selective antagonist of classical as well as novel PKCs that targets the catalytic domain ( Li SJ et al, 2015 ).…”