Abstract
This study identifies signaling pathways activated by the β2-/β3-adrenoceptor (AR) agonist zinterol, the selective β3-AR agonist L755507, and the selective β3-AR antagonist L748337 in CHO-K1 cells expressing human β3-adrenoceptors. Zinterol and L755507 caused a robust concentration-dependent increase in cAMP accumulation (pEC50 values of 8.5 and 12.3, respectively), whereas L748337 had low efficacy. Maximal cAMP accumulation with zinterol and L755507 was increased after pretreatment with pertussis toxin, indicating that the human β3-AR couples to Gi and to Gs. In contrast to cAMP, zinterol, L755507 and L748337 increased phosphorylation of extracellular signal-regulated kinase 1/2 (Erk1/2) with very high potency (pEC50 values of 10.9, 11.7, and 11.6). These compounds also stimulated phosphorylation of p38 mitogen-activated protein kinase (MAPK) but with much lower potency than Erk1/2 (pEC50 values of 5.9, 5.5, and 5.7, respectively). Pertussis toxin completely blocked Erk1/2 and p38 MAPK phosphorylation in response to L748337, demonstrating a requirement for Gi/o coupling, whereas L755507-stimulated p38 MAPK phosphorylation was not inhibited by pertussis toxin, and Erk1/2 phosphorylation was inhibited by only 30%. We found that high levels of cAMP interfered with agonist-activated p38 MAPK phosphorylation. L748337 increased extracellular acidification rate (ECAR) in the cytosensor microphysiometer with efficacy similar to zinterol and L755507, albeit with lower potency (pEC50 value of 7.2 compared with zinterol, 8.1, and L755507, 8.6). The ECAR response to L748337 was largely via activation of p38 MAPK, demonstrated by 65% inhibition with 4-[4-(4-fluorophenyl)-1-(3-phenylpropyl)-5-(4-pyridinyl)-1H-imidazol-2-yl]-3-butyn-1-ol (RWJ67657). We conclude that the β3-AR agonist L755507 couples to both Gs and Gi to activate adenylate cyclase and MAPK signaling, whereas the β3-AR antagonist L748337 couples predominantly to Gi to activate MAPK signaling.
Footnotes
-
This work was supported by National Health and Medical Research Council (NHMRC) of Australia Project grants 236884 and 491190 (to R.J.S. and B.A.E.). D.S.H. is an NHMRC CJ Martin Fellow, and M.S. is a Monash University Research Scholar.
-
ABBREVIATIONS: AR, adrenoceptor; CHO, Chinese hamster ovary; ECAR, extracellular acidification rate; MAPK, mitogen-activated protein kinase; Erk1/2, extracellular signal-regulated protein kinase 1/2; PTX, pertussis toxin; ISO, (-)-isoproterenol; DMEM, Dulbecco's modified Eagle's medium; FBS, fetal bovine serum; ICYP, 125I-(-)-cyanopindolol; BSA, bovine serum albumin; DDA, 2′,3′-dideoxyadenosine; 8-Br-cAMP, 8-bromoadenosine 3′,5′-cAMP; PKA, protein kinase A; LDS, ligand-directed signaling; RWJ67657, 4-[4-(4-fluorophenyl)-1-(3-phenylpropyl)-5-(4-pyridinyl)-1H-imidazol-2-yl]-3-butyn-1-ol; L755507, 4-[[(hexylamino)carbonyl]amino]-N-[4-[2-[[(2S)-2-hydroxy-3-(4-hydroxyphenoxy)propyl] amino]-ethyl]phenyl]-benzenesulfonamide; L748337, (S)-N-[4-[2-[[3-[3-(acetamidomethyl)phenoxy]-2-hydroxypropyl]amino]ethyl]phenyl]benzenesulfonamide; LY294002, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; PP2, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine; PD98059, 2′-amino-3′-methoxyflavone; H-89, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride; SR59230A, 3-(2-ethylphenoxy)-1-[(1,S)-1,2,3,4-tetrahydronapth-1-yl[amino]-(2S)-2-propanol oxalate; CL316243, disodium 5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate; CGP12177A, (±)-4[3-[(1,1-dimethyl)amino]-2-hydroxypropoxy]1,3-dihydro-2H-benzimidazol-2-one hydrochloride.
- Received March 17, 2008.
- Accepted August 6, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|