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

Isolated epidermal cells were incubated with a variety of compoundsknown to interfere with or alter the ultrastructure of cellsurface receptors, and the ability of 12-O-tetradecanoyl-phorbol-13-acetate(TPA) to bind to these cells and induce epidermal ornithinedecarboxylase (ODC) activity was investigated. The - and ß-adrenergicantagonists, phentolamine and propranolol, and the cholinergicantagonist, atropine, which competed effectively for the bindingreceptors of [³H]dihydro--ergocryptine, [³H]dihydroalprenolol,and [¹⁴C]acetylcholine, did not inhibit the induction of ODCactivity by TPA or the specific binding of [³H]TPA to the cells.Neuraminidase treatments caused a time- and dose- related releaseof sialic acid from the cells and enhanced the stimulatory effectof cholera toxin on basal and TPA-induced ODC activities asmuch as the monosialoganglioside GM₁. Neuraminidase and theother membrane-altering agents, fucosidase, galactosidase, galactoseoxidase, phospholipases A2 and C, and NaIO₄, were used aloneand/or in various combinations in our studies. All treatmentstested inhibited the specific binding of several ¹²⁵I-labeledhormones 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 interactionof TPA at the plasma membrane level as well as its biologicaleffect in the intact cell do not proceed through adrenergicor cholinergic receptors and do not require the integrity ofthe cell surface glycoconjugates and phospholipids. In addition,the inhibitory effect of retinoic acid on TPA-induced ODC activityremained unaffected by some of the above treatments, suggestingthat retinoic add is unlikely to interfere with TPA interactionsat the plasma membrane level.