2 DISTINCT PATHWAYS FOR CAMP-MEDIATED DOWN-REGULATION OF THE BETA-2-ADRENERGIC RECEPTOR - PHOSPHORYLATION OF THE RECEPTOR AND REGULATION OF ITS MESSENGER-RNA LEVEL
- 5 October 1989
- journal article
- research article
- Vol. 264 (28) , 16786-16792
Abstract
We have studied cyclic AMP-mediated regulation of the .beta.2-adrenergic receptor (.beta.2AR). The effects of cAMP were assessed in Chinese hamster fibroblast (CHW) cells expressing either the wild type human .beta.2AR receptor (CH-.beta.2) or mutated forms of the receptor lacking the consensus sequences for phosphorylation by the cAMP-dependent protein kinase. Treatment of the CH-.beta.2 cells with the cAMP analogue dibutyryl cAMP (Bt2cAMP) induces a time-dependent "down-regulation" of the number of .beta.2AR. This down-regulation of the receptors is accompanied by a decline in the steady state level of .beta.2AR mRNA. Moreover, the treatment with Bt2cAMP induces an increase in the phosphorylation level of the membrane-associated .beta.2AR. Both the reduction in .beta.2AR mRNA and the enhanced phosphorylation of the receptor are rapid and precede the loss of receptor. The down-regulation of .beta.2AR induced by Bt2cAMP is concentration-dependent and mimicked by the other biologically active cyclic nucleotide analogue, 8-Br-cAMP, by forskolin, and by the phosphodiesterase inhibitor, isobutylmethylxanthine. In the CHW cell lines expressing receptors lacking the putative protein kinase A phosphorylation sites, the Bt2cAMP-induced phosphorylation of .beta.2AR is completely abolished. In these cells the down-regulation of .beta.2AR receptor number produced by cAMP is significantly slowed, whereas the reduction in .beta.2AR mRNA level is equivalent to that observed in CH-.beta.2 cells. These data indicate that there are at least two pathways by which cAMP may decrease the number of .beta.2AR in cells: one involves phosphorylation of the receptor by the cAMP-dependent protein kinase and the other leads to a reduction in steady state .beta.2AR mRNA levels.This publication has 29 references indexed in Scilit:
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