A Novel Histone-stimulated Protein Kinase in Normal and Psoriatic Epidermis

During the course of studies on protein kinases in psoriatic epidermis, a novel histone-activated protein kinase activity was identified. This activity (referred to as PK-II because it was the second peak of protein kinase activity eluted from a DEAE column) was partially purified from the supernatant of an epidermal homogenate by DEAE-cellulose column chromatography. Although histone was not a substrate for phosphorylation, in the presence of histone, endogenous proteins of Mr 105 and 95kDa were phosphorylated. Activity was not affected by Ca2+/phospholipid, cAMP, cGMP, cAMP-dependent kinase inhibitor, spermine, spermidine, calmodulin, EGF, or phorbol ester. Pbosphorylation was specific for serine and threonine residues. A major peak of PK-II activity eluted from sepharose 6B with an apparent Mr of 100kDa, suggesting that histone may stimulate autophosphorylation. The properties of PK-II resemble those recently described for a class of polypeptide-dependent protein kinases isolated from placenta, Ehrlich ascites tumor cells, and bakers' yeast. PK-II was significantly higher in psoriatic involved epidermis (32.6 ± 11.6 pmol/min/mg protein) compared to psoriatic uninvolved epidermis (5.7 ± 0.6 pmol/min/mg; p = 0.03) and normal epidermis (9.5 ± 2.2 pmol/min/mg; p = 0.05).The function of histone stimulated protein kinase in epidermal function and its role in the pathophysiology of psoriasis remain to be explored