Activation of the isotypes of protein kinase C and other kinases by phorbol esters of different biological activities
1993
Evans, F.J. | Hassan, N.M.
The Ca2+- and phospholipid-dependent protein kinase C (PKC) has been recognised as the major receptor of the toxic plant compounds known as the phorbol esters. PKC exists as a number of related isotypes which are variously distributed in tissues. The abilities of a number of phorbol esters of different biological activities to stimulate these isotypes were investigated. The tumour-promoting agent, tetradecanoylphorbolacetate (TPA), activated the purified PKC isotypes alpha, beta 1, gamma in a Ca2+-dependent manner, but was also capable of the activation of PKC-delta and epsilon in a Ca2+-independent manner. The non-promotor, sapintoxin-A (SAPA), failed to activate PKC-delta, whilst 12-deoxyphorbol-phenylacetate-20-acetate (DOPPA) only stimulated PKC-beta 1 in a Ca2+-dependent manner. A tissue screen of the responsiveness to TPA using rat brain PKC as separated by hydroxyapatite chromatography produced seven peaks of kinase activity, of which immunological analysis by Western blotting confirmed that peaks 2 to 4 (in order of elution) consisted of PKC-alpha, beta 1, gamma, delta and epsilon. Peaks 1, 5, 6 and 7 failed to respond to these antibodies and may represent new phorbol-kinase receptors. Similarly, a screen of human mononuclear cells, human neutrophils and mouse macrophages using resiniferatoxin (Rx) produced a late peak of activity. This peak, known as Rx-kinase, was immunologically distinct from PKC and was shown to be Ca2+ inhibited.
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