Effects of cell surface receptor-altering agents on the binding and biological activity of 12-O-tetradecanoylphorbol-13-acetate in isolated epidermal cells

Abstract

Isolated epidermal cells were incubated with a variety of compounds known to interfere with or alter the ultrastructure of cell surface receptors, and the ability of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) to bind to these cells and induce epidermal ornithine decarboxylase (ODC) activity was investigated. The α- and β-adrenergic antagonists, phentolamine and propranolol, and the cholinergic antagonist, atropine, which competed effectively for the binding receptors of [ ³ H]dihydro-α-ergocryptine, [ ³ H]dihydroalprenolol, and [ ¹⁴ C]acetylcholine, did not inhibit the induction of ODC activity by TPA or the specific binding of [ ³ H]TPA to the cells. Neuraminidase treatments caused a time- and dose- related release of sialic acid from the cells and enhanced the stimulatory effect of cholera toxin on basal and TPA-induced ODC activities as much as the monosialoganglioside GM ₁ . Neuraminidase and the other membrane-altering agents, fucosidase, galactosidase, galactose oxidase, phospholipases A2 and C, and NaIO ₄ , were used alone and/or in various combinations in our studies. All treatments tested inhibited the specific binding of several ¹²⁵ I-labeled hormones and epidermal growth factor to the cells. In contrast, none of these treatments was able, in the same cell system, to affect either the binding or the biological activity of TPA. Therefore, these results suggest that the primary interaction of TPA at the plasma membrane level as well as its biological effect in the intact cell do not proceed through adrenergic or cholinergic receptors and do not require the integrity of the cell surface glycoconjugates and phospholipids. In addition, the inhibitory effect of retinoic acid on TPA-induced ODC activity remained unaffected by some of the above treatments, suggesting that retinoic add is unlikely to interfere with TPA interactions at the plasma membrane level.