Agonist regulation of beta-adrenergic receptor mRNA. Analysis in S49 mouse lymphoma mutants.
Agonist-promoted down-regulation of beta-adrenergic receptor mRNA was investigated in S49 mouse lymphoma variants with mutations in elements of hormone-sensitive adenylate cyclase. In wild-type cells steady-state levels of beta-adrenergic receptor mRNA were established by DNA-excess solution hybridization to be 1.72 +/- 0.08 (n = 8) amol/microgram total cellular RNA. Receptor mRNA levels declined 35-45% in response to stimulation by the beta-adrenergic agonist (-)isoproterenol or forskolin as described previously in DDT1 MF-2 cells (Hadcock, J. R., and Malbon, C. C. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 5021-5025). Agonist-promoted cAMP accumulation and down-regulation of receptor mRNA were analyzed in three variants with mutations in Gs alpha (H21a, unc, cyc-) and a single variant lacking cAMP-dependent protein kinase activity (kin-). H21a (Gs alpha coupled to receptor, but not to adenylate cyclase), unc (Gs alpha uncoupled from receptor), and cyc- (lacking Gs alpha) variants accumulated cAMP and down-regulated beta AR mRNA in response to forskolin. In unc and cyc- cells isoproterenol failed to stimulate cAMP; accumulation and down-regulation of receptor mRNA was not observed. H21a cells, in contrast, displayed agonist-promoted regulation of beta-adrenergic receptor mRNA but only basal levels of cAMP accumulation in response to isoproterenol. The kin- cells displayed cAMP accumulation in response to forskolin as well as to isoproterenol but no down-regulation of receptor mRNA or receptor expression. Taken together these data demonstrate several features of agonist-promoted down-regulation of mRNA: (i) cAMP-dependent protein kinase activity is required for down-regulation of mRNA (kin-), although elevated cAMP accumulation is not (H21a); (ii) functional receptor-Gs coupling is required (H21a), and clones lacking Gs alpha (cyc-) or receptor Gs coupling (unc) lack the capacity to down-regulate mRNA in response to agonist; and (iii) in the presence of basal levels of cAMP and cAMP-dependent protein kinase activity, functional receptor-Gs coupling (H21a) to some other effector other than adenylate cyclase may be propagating the signal.
Hadcock
J R
JR
Department of Pharmacological Sciences, School of Medicine, State University of New York, Stony Brook 11794-8651.
Ros
M
M
Malbon
C C
CC
D000818:Animals; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D005796:Genes / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology*; D008223:Lymphoma; D051379:Mice; D009154:Mutation; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics*; D011943:Receptors, Adrenergic, beta / Q000235:genetics*
D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D007545:Isoproterenol