Two splice variants of protein kinase B gamma have different regulatory capacity depending on the presence or absence of the regulatory phosphorylation site serine 472 in the carboxyl-terminal hydrophobic domain.

Abstract We have reported previously the cloning and characterization of human and mouse protein kinase Bγ (PKBγ), the third member of the PKB family of second messenger-regulated serine/threonine kinases (Brodbeck, D., Cron, P., and Hemmings, B. A. (1999) J. Biol. Chem. 274, 9133–9136). Here we report the isolation of human and mouse PKBγ1, a splice variant lacking the second regulatory phosphorylation site Ser-472 in the hydrophobic C-terminal domain. Expression of PKBγ1 is low compared with PKBγ, and it is regulated in different human tissues. We show that PKBγ and PKBγ1 differ in their response to stimulation by insulin, pervanadate, peroxide, or okadaic acid. Activation of PKBγ1 requires phosphorylation at a single regulatory site Thr-305. Interestingly, this site is phosphorylated to a higher extent in PKBγ compared with PKBγ1 upon maximal stimulation by pervanadate, and this is reflected in the respective specific kinase activities. Furthermore, upon insulin stimulation of transfected cells, PKBγ1 translocates to the plasma membrane to a lesser extent than PKBγ. Taken together, these results suggest that phosphorylation of the hydrophobic motif at the extreme C terminus of PKBγ may facilitate translocation of the kinase to the membrane and/or its phosphorylation on the activation loop site by phosphoinositide-dependent protein kinase-1.