More than one application of the potent Tumorpromoting agent, 12-O-tetradecanoylphorbol-13-acetate (TPA), to mouse skin at intervals of more than 48 h led to a larger induction of ornithine decarboxylase (EC 126.96.36.199; ODC) than did a single application. In contrast, at intervals of less than 24 h, the first application of TPA appeared to induce a refractory state; the second application of TPA did not induce ODC. The extent of the inhibitory effect caused by the first application of TPA was dependent on the dose. The abilities of a series of phorbol esters to induce the refractory state correlated with their promoting abilities. However, both mezerein and ethylphenylpropiolate, potent hyperplastic agents with little or no promoting properties, induced the refractory state. On the other hand, pretreatment with TPA caused a refractory effect on ODC induction by mezerein but potentiated ODC induction by ethylphenylpropiolate. The epidermal cells escaped from the refractory state by repeated application of TPA at intervals of 24 h as well as at intervals of twice a week; that is, there was a full induction of ODC activity following a second application within 24 h of a prior application. TPA did not elicit production of detectable ODC-antizyme activity in mouse epidermis. Mixing of a soluble extract from mouse epidermis in the refractory state with that from TPA-stimulated epidermis gave essentially additive ODC activity. Elimination of ODC induction by topical application of retinoic acid or injection of cycloheximide concurrent with the first application of TPA did not restore the ability of a second application of TPA to induce ODC. These results suggest that the refractory effect on ODC induction by TPA does not result from feedback regulation of ODC.
|出版ステータス||Published - 1月 1 1986|
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