Activation of PRK1 by phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate. A comparison with protein kinase C isotypes.
As potential targets for polyphosphoinositides, activation of protein kinase C (PKC) isotypes (beta 1, epsilon, zeta, nu) and a member of the PKC-related kinase (PRK) family, PRK1, has been compared in vitro. PRK1 is shown to be activated by both phosphatidylinositol 4,5-bisphosphate (PtdIns 4,5-P2) as well as phosphatidylinositol 3,4,5-trisphosphate (PtdIns-3,4,5-P3) either as pure sonicated lipids or in detergent mixed micelles. When presented as sonicated lipids, PtdIns-4,5-P2 and PtdIns-3,4,5-P3 were equipotent in activating PRK1, and, furthermore, sonicated phosphatidylinositol (PtdIns) and phosphatidylserine (PtdSer) were equally effective. In detergent mixed micelles, PtdIns-4,5-P2 and PtdIns-3,4,5-P3 also showed a similar potency, but PtdIns and PtdSer were 10-fold less effective in this assay. Similarly, PKC-beta 1, -epsilon, and -nu were all activated by PtdIns-4,5-P2 and PtdIns-3,4,5-P3 in detergent mixed micelles. The activation constants for PtdIns-4,5-P2 and PtdIns-3,4,5-P3 were essentially the same for all the kinases tested, implying no specificity in this in vitro analysis. Consistent with this conclusion, the effects of PtdIns-4,5-P2 and PtdIns-3,4,5-P3 were found to be inhibited at 10 mM Mg2+ and mimicked by high concentrations of inositol hexaphosphate and inositol hexasulfate. The similar responses of these two classes of lipid-activated protein kinase to these phosphoinositides are discussed in light of their potential roles as second messengers.
Palmer
R H
RH
Protein Phosphorylation Laboratory, Imperial Cancer Research Fund, London, United Kingdom.
Dekker
L V
LV
Woscholski
R
R
Le Good
J A
JA
Gigg
R
R
Parker
P J
PJ
D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000494:pharmacology*; D008823:Micelles; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D011994:Recombinant Proteins; D017384:Sequence Deletion; D013329:Structure-Activity Relationship
D007295:Inositol Phosphates; D008823:Micelles; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D011994:Recombinant Proteins; D015544:Inositol 1,4,5-Trisphosphate; C061570:protein kinase N; D011493:Protein Kinase C