Characterization of Protein Kinase C θ Activation Loop Autophosphorylation and the Kinase Domain Catalytic Mechanism

Dominant negative properties are conferred on protein kinase (PK) Cα by mutation of the phosphorylation site in the activation loop of the kinase domain. To address the universality and/or specificity of such mutations, analogous alterations were introduced in other members of the PKC family and tested for their effects on the function of co-transfected activated PKC. For all three subclasses of the PKC family, mutations of the predicted activation loop phosphorylation sites resulted in dominant negative properties. These properties were not restricted to the cognate PKC isotypes, but were effective across the different subclasses. For example, two PKCζ mutants (atypical isotype) inhibited both PKCα (classical isotype) and PKCε (novel isotype). For all these mutants, inhibition correlated with an ability to prevent the accumulation of phosphorylated PKCα, consistent with the expected mode of action. In the case of the PKCα mutant, it was shown that inhibition required the full-length mutant protein. The results provide evidence for the involvement of a common step in the phosphorylation of all PKC isotypes.

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Regulation of novel protein kinase C ε by phosphorylation

Biochemical Journal ◽

10.1042/bj3630537 ◽

2002 ◽

Vol 363 (3) ◽

pp. 537-545 ◽

Cited By ~ 71

Author(s):

Vittoria CENNI ◽

Heike DÖPPLER ◽

Erica D. SONNENBURG ◽

Nadir MARALDI ◽

Alexandra C. NEWTON ◽

...

Keyword(s):

Protein Kinase C ◽

Protein Kinase ◽

Intracellular Localization ◽

Kinase Domain ◽

Activation Loop ◽

3T3 Fibroblasts ◽

Kinase C ◽

Hydrophobic Motif ◽

Nih 3T3

The activity and intracellular localization of protein kinase C (PKC) family members are controlled by phosphorylation at three highly conserved sites in the catalytic kinase domain. In the case of the novel PKC∊ isoform, these are Thr566 in the activation loop, Thr710 in the turn motif and Ser729 in the C-terminal hydrophobic motif. In the present study, we analysed the contribution of the phosphoinositide-dependent kinase 1 (PDK-1) and PKC∊ kinase activity in controlling the phosphorylation of Thr566 and Ser729. In NIH 3T3 fibroblasts, PKC∊ migrated as a single band, and stimulation with platelet-derived growth factor resulted in the appearance of a second band with a slower electrophoretic mobility, concomitant with an increase in phosphorylation of Thr566 and Ser729. Cells transfected with an active PDK-1 allele also resulted in increased PKC∊ Thr566 and Ser729 phosphorylation, whereas an active myristoylated PKC∊ mutant was constitutively phosphorylated at these sites. Protein kinase-inactive mutants of PKC∊ were not phosphorylated at Ser729 in cells, and phosphorylation of this site leads to dephosphorylation of the activation-loop Thr566, an effect which can be reversed with either okadaic acid or co-transfection with active PDK-1. In vitro, PDK-1 catalysed the phosphorylation of purified PKC∊ in the presence of mixed micelles containing either diacylglycerol or PtdIns(3,4,5)P3, concomitant with an increase in Ser729 phosphorylation. These studies reveal that the mechanism of phosphorylation of a novel PKC is the same as that for conventional PKCs: PDK-1 phosphorylation of the activation loop triggers autophosphorylation of the hydrophobic motif. However, the regulation of this phosphorylation is different for novel and conventional PKCs. Specifically, the phosphorylation of novel PKCs is regulated rather than constitutive.

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