[Studies of calcium-activated, phospholipid-dependent protein kinase in pig epidermis]

Calcium-activated, phospholipid-dependent protein kinase (C kinase) is activated by diacylglycerol which is produced in the signal-induced turnover of inositol phospholipid. C kinase has a important role in the transduction of extracellular signals of cellular function, proliferation and differentiation. C kinase in pig epidermis was investigated. Pig epidermal homogenates were centrifuged at 30,000 g for 30 min, and the supernatant was applied on a DEAE-cellulose column for purification. The partially purified enzyme was stimulated by simultaneous addition of Ca2+ and phosphatidylserine. Small amount of diolein or 12-o-tetradecanoylphorbol-13-acetate (TPA) further activated the enzyme activity. Polyprenoic acid (E5166) which is a newly-synthesized retinoic acid derivative inhibited the TPA activation of C kinase. This inhibition may explain the mechanism in which retinoids inhibit TPA-induced tumor promotion. C kinase preferentially phosphorylated seryl and threonyl residues of lysine-rich histone. Endogenous C kinase phosphorylated 97kD pig epidermal soluble protein. This protein was phosphorylated immediately. With two dimensional polyacrylamide gel electrophoresis, it was shown to be a basic protein.