Protein kinase C is regulated in vivo by three functionally distinct phosphorylations

Abstract

Structural and biochemical analyses of native and phosphatase-treated protein kinase C indicate that protein kinase C is processed by three phosphorylations. Firstly, trans-phosphorylation on the activation loop (T500) renders it catalytically competent to autophosphorylate. Secondly, a subsequent autophosphorylation on the carboxyl terminus (T641) maintains catalytic competence. Thirdly, a second autophosphorylation on the carboxyl terminus (S660) regulates the enzyme's subcellular localization. The conservation of each of these residues (or an acidic residue) in conventional, novel and atypical protein kinase Cs underscores the essential role for each in regulating the protein kinase C family.

Activation of protein kinase C by tyrosine phosphorylation in response to H 2 O 2

“…However, it cannot be ruled out that some other serine and threonine protein kinases take part in PKC activation. Thr 500 in subdomain VIII of PKC ␤ has been shown to be phosphorylated nearly stoichiometrically in vivo (28,29). If Thr 505 in PKC ␦, which is equivalent to Thr 500 in PKC ␤, is constitutively phosphorylated, PKC ␦ could be phosphorylated on both threonine and tyrosine residues in subdomain VIII upon H 2 O 2 stimulation.…”

Regulation of Protein Kinase C function by phosphorylation on conserved and non-conserved sites

“…While it had been demonstrated that PKC family members underwent a posttranslational modification shortly after synthesis that was later shown to involve phosphorylation [22], it was not until studies involving mutational analysis of predicted phosphorylation sites [23,24] and mass spectrometry [25,26] that three key phosphorylation sites were identified on the C-terminus that were important for PKC function. These sites are known as the activation-loop (A-loop), the turn-motif (TM) and the hydrophobic-motif (HM).…”

“…This theme developed because it was demonstrated that PKCs (predominantly cPKCs) are phosphorylated at these sites shortly after synthesis [83,42] and are often highly phosphorylated at these sites in many types of cells grown in culture, even under quiescent conditions [26,66,84]. In the absence of phosphorylation at one or more of these sites, catalytic activation of these isoforms is impaired or enzyme stability is compromised.…”

“…As an example, Newton and colleagues have shown that mature cPKCs that are isolated from cells are quantitatively phosphorylated at the TM and HM sites, while only ~ 50% of this species retains phosphate at the A-loop [26].…”

Loss of protein kinase C function induces an apoptotic response

“…It has become clear recently, that PKC isotypes (speci®cally PKCa and PKCb which have been analysed in detail) are subject to functional control through the phosphorylation of at least three sites (see Parker, 1996, 1997;Keranen et al, 1995). The evidence to date implies that the accumulation of these phosphates is constitutive and thus the proteins are fully active albeit in a latent, e ectordependent state.…”