AGENTS THAT ACTIVATE CYCLIC AMP-DEPENDENT PROTEIN-KINASE INHIBIT EXPLANT CULTURE-GROWTH AND MITOTIC-ACTIVITY

[摘要] Epidermal cells contain 4 separate surface receptors which are linked to adenylate cyclase. Activation of any one of these receptors leds to the accumulation of cAMP within the cell which in turn leads to the activation of cAMP-dependent protein kinase. The levels of cAMP accumulation within the cell caused by the 4 activators are not the same. Epinephrine, histamine, adenosine, and prostaglandins of the E series cause easily measurable concentrations of cAMP within 5 min of exposure. Prostaglandin F2.alpha. cause only a small nonsignificant increase. Similarly, 2 phosphodiesterase inhibitors, which inhibit the breakdown of cAMP formed within the cell, differ in their ability to accumulate cAMP when cells are exposed to these agents alone. Isobutylmethylxanthine causes a measurable increase in cAMP, while theophylline, a weak inhibitor of phosphodiesterase, gives a nonsignificant increase in cAMP. Recently, experiments have shown that agents that give only slight increaess in cAMP by biochemical measurements, that is, prostaglandins F2.alpha. and theophylline, are equally able to activate protein kinase within the cell. Since activation of protein kinase is the only mechanism for an increase in cAMP to have a physiologic effect, all of these agents that do activate protein kinase should cause physiologic effects. An explant culture system using pig skin was developed. All agents that activate protein kinase inhibited mitotic activity regardless of whether or not they are able to raise cAMP to a level significantly different from the baseline value.