REGULATION OF N-ACETYLGLUCOSAMINYLTRANSFERASE-V BY PROTEIN-KINASES

When 7721 human hepatocarcinoma cells were treated with 100 nM phorbol -12-myristate-13-acetate (PMA), the activity of N-acetylglucosaminyltr ansferase V(GnT-V) in the cells varied in accordance with the activity of membranous protein kinase C (PKC), but not with that of cytosolic PKC. Quercetin, a non-specific inhibitor of Ser/Thr protein kinase, an d D-sphingosine and staurosporine, two specific inhibitors of PKC, blo cked the activation of membranous PKC and GnT-V by PMA. Among the thre e inhibitors, quercetin was least effective. The inhibitory rates of q uercetin and staurosporine toward membranous PKC and GnTV were proport ional to the concentrations of the two inhibitors. The activities of G nTV and membranous protein kinase A (PKA) were also induced in paralle l by dibutyryl cAMP (db-cAMP) and this induction was blocked by a spec ific PKA inhibitor. When cell free preparations of 7721 cells and huma n kidney were treated with alkaline phosphatase (ALP) to remove the ph osphate groups, the GnTV activities were decreased. These results sugg est that GnTV may be activated by membranous PKC or PKA, indirectly or directly, via phosphorylation of Ser/Thr residues.