Direct activation of protein kinase C by 1 alpha,25-dihydroxyvitamin D3.
The key metabolite of vitamin D3, 1 alpha,25-dihydroxyvitamin D3 (1,25-D3), induces rapid cellular responses that constitute a so-called "non-genomic" response. This effect is distinguished from its "classic" genomic role in calcium homeostasis involving the nuclear 1,25-D3 receptor. Evidence is presented that protein kinase C (PKC) is directly activated by 1,25-D3 at physiological concentrations (EC50 = 16 +/- 1 nM). The effect was demonstrable with single PKC-alpha, -gamma, and -epsilon isoform preparations, assayed in a system containing only purified enzyme, substrate, co-factors, and lipid vesicles, from which it is inferred that a direct interaction with the enzyme is involved. The finding that calcium-independent isoform PKC-epsilon was also activated by 1,25-D3 shows that the calcium binding C2 domain is not required. The level of 1,25-D3-induced activation, paired with either diacylglycerol or 4 beta-12-O-tetradecanoylphorbol-13-acetate, was greater than that achievable by any individual activator alone, each at a saturating concentration, a result that implies two distinct activator sites on the PKC molecule. Phosphatidylethanolamine present in the lipid vesicles potentiated 4 beta-12-O-tetradecanoylphorbol-13-acetate- and diacylglycerol-induced PKC activities, whereas 1,25-D3-induced activity decreased, consistent with 1,25-D3-activated PKC possessing a distinct conformation. The results suggest that PKC is a "membrane-bound receptor" for 1,25-D3 and that it could be important in the control of non-genomic cellular responses to the hormone.
Slater
S J
SJ
Department of Pathology and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Kelly
M B
MB
Taddeo
F J
FJ
Larkin
J D
JD
Yeager
M D
MD
McLane
J A
JA
Ho
C
C
Stubbs
C D
CD
D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D010714:Phosphatidylethanolamines / Q000494:pharmacology; D011487:Protein Conformation; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004075:Diglycerides; D010714:Phosphatidylethanolamines; D011493:Protein Kinase C; D002117:Calcitriol; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium