Roles of the alpha1A-adrenergic receptor carboxyl tail in protein kinase C-induced phosphorylation and desensitization.

摘要

Noradrenaline- and tetradecanoyl phorbol acetate (TPA)-induced phosphorylation and functional desensitization of the following receptors were studied: (1) wild-type bovine alpha(1A)- and hamster alpha(1B)-adrenergic receptors (ARs), (2) chimeric ARs in which the carboxyl terminus tails were exchanged (alpha(1AB)- and alpha(1BA)-ARs), and (3) carboxyl terminus-truncated alpha(1A)-ARs fussed to enhanced green fluorescent protein. Noradrenaline and TPA pronouncedly increased alpha(1B)-AR phosphorylation while TPA markedly desensitized these receptors. In contrast, TPA-induced desensitization and TPA- and noradrenaline-induced phosphorylation of alpha(1A)-ARs were clearly of lesser magnitude. Chimeric ARs with exchanged carboxyl terminus tails showed that the extent of phosphorylation reflected the carboxyl domain rather than the receptor core. Surprisingly, there was no correlation between phosphorylation and functional desensitization, i.e., activation of protein kinase C clearly desensitized both chimeric receptors to a similar extent. Interestingly, TPA and noradrenaline increased carboxyl terminus-truncated alpha(1A)-AR phosphorylation and TPA also induced receptor desensitization. We were unable to detect carboxyl terminus-truncated alpha(1A)-AR internalization after 5-min stimulations with noradrenaline or TPA. Our results suggest the following: (a) the alpha(1A)-AR carboxyl terminus tail was not essential for signaling or desensitization; (b) carboxyl terminus tail exchange "transplanted" the phosphorylation pattern of the receptors, but the functional consequences of such a transplant were very limited; (c) alpha(1A)-AR desensitization was not associated to receptor internalization.