A 3-phosphoinositide-dependent protein kinase-1 (PDK1) docking site is required for the phosphorylation of protein kinase C zeta (PKC zeta) and PKC-related kinase 2 by PDK1

Members of the AGC subfamily of protein kinases including protein kinase B, p70 S6 kinase, and protein kinase C (PKC) isoforms are activated and/or st abilized by phosphorylation of two residues, one that resides in the T-loop of the kinase domain and the other that is located C-terminal to the kinas e domain in a region known as the hydrophobic motif. Atypical PKC isoforms, such as PKC zeta, and the PKC-related kinases, like PRK2, are also activat ed by phosphorylation of their T-loop site but, instead of possessing a pho sphorylatable Ser/Thr in their hydrophobic motif, contain an acidic residue . The 3-phosphoinositide-dependent protein kinase (PDK1) activates many mem bers of the AGC subfamily of kinases in vitro, including PKC zeta and PRK2 by phosphorylating the T-loop residue. In the present study we demonstrate that the hydrophobic motifs of PKC zeta and PKC iota, as well as PRK1 and P RK2, interact with the kinase domain of PDK1. Mutation of the conserved res idues of the hydrophobic motif of full-length PKC zeta, fulllength PRK2, or PRK2 lacking its N-terminal regulatory domain abolishes or significantly r educes the ability of these kinases to interact with PDK1 and to become pho sphorylated at their T-loop sites in rtiao. Furthermore, overexpression of the hydrophobic motif of PRK2 in cells prevents the T-loop phosphorylation and thus inhibits the activation of PRK2 and PKC zeta. These findings indic ate that the hydrophobic motif of PRK2 and PKC zeta acts as a "docking site " enabling the recruitment of PDK1 to these substrates. This is essential f or their phosphorylation by PDK1 in cells.