Further evidence that 3-phosphoinositide-dependent protein kinase-1 (PDK1)is required for the stability and phosphorylation of protein kinase C (PKC) isoforms
A. Balendran et al., Further evidence that 3-phosphoinositide-dependent protein kinase-1 (PDK1)is required for the stability and phosphorylation of protein kinase C (PKC) isoforms, FEBS LETTER, 484(3), 2000, pp. 217-223
The multi-site phosphorylation of the protein kinase C (PKC) superfamily pl
ays an important role in the regulation of these enzymes. One of the key ph
osphorylation sites required for the activation of all PKC isoforms lies in
the T-loop of the kinase domain. Recent in vitro and transfection experime
nts indicate that phosphorylation of this residue can be mediated by the 3-
phosphoinositide-dependent protein kinase-1 (PDK1), In this study, we demon
strate that in embryonic stem (ES) cells lacking PDK1 (PDK1 -/- cells), the
intracellular levels of endogenously expressed PKC alpha, PKC betaI, PKC g
amma, PKC delta, PKC epsilon, and PKC-related kinase-1 (PRK1) are vastly re
duced compared to control ES cells (PDK1 +/+ cells). The levels of PKC zeta
and PRK2 protein are only moderately reduced in the PDK1 -/- ES cells. We
demonstrate that in contrast to PKC zeta expressed PDK1 +/+ ES cells, PKC z
eta in ES cells lacking PDK1 is not phosphorylated at its T-loop residue. T
his provides the first genetic evidence that PKC zeta is a physiological su
bstrate for PDK1, In contrast, PRK2 is still partially phosphorylated at it
s T-loop in PDK1 -/- cells, indicating the existence of a PDK1-independent
mechanism for the phosphorylation of PRK2 at this residue. (C) 2000 Federat
ion of European Biochemical Societies. Published by Elsevier Science B,V, A
ll rights reserved.