beta-adrenergic activation of p38 MAP kinase in adipocytes - cAMP induction of the uncoupling protein 1 (UCP1) gene requires p38 MAP kinase

Because of increasing evidence that G protein-coupled receptors activate mu ltiple signaling pathways, it becomes important to determine the coordinati on of these pathways and their physiological significance. Here we show tha t the beta (3)-adrenergic receptor (beta (3)AR) stimulates p38 mitogen-acti vated protein kinase (p38 MAPK) via PKA in adipocytes and that cAMP-depende nt transcription of the mitochondrial uncoupling protein 1 (UCP1) promoter by beta (3)AR requires p38 MAPK. The selective beta (3)AR agonist CL316,243 (CL) stimulates phosphorylation of MAP kinase kinase 3/6 and p38 MAPK in a time- and dose-dependent manner in both white and brown adipocytes, Isopro terenol and forskolin mimicked the effect of CL on p38 MAPK. In all cases a ctivation was blocked by the specific p38 MAPK inhibitor SB202190 (SB; 1-10 muM). The involvement of PKA in beta (3)AR-dependent p38 MAPK activation w as confirmed by the ability of the PKA inhibitors H89 (20 muM) and (R-p)-cA MP-S (1 mM) to block phosphorylation of p38 MAPK. Treatment of primary brow n adipocytes with CL or forskolin induced the expression of UCP1 mRNA level s (6.8- +/- 0.8-fold), and this response was eliminated by PKA inhibitors a nd SB202190. A similar stimulation of a 3.7-kilobase UCP1 promoter by CL an d forskolin was also completely inhibited by PKA inhibitors and SB202190, i ndicating that these effects on UCP1 expression are transcriptional. Moreov er, the PKA-dependent transactivation of the UCP1 promoter, as well as its sensitivity to SB202190, was fully reproduced by a 220-nucleotide enhancer element from the UCP1 gene. We similarly observed that increased phosphoryl ation of ATF-2 by CL was sensitive to both H89 and SB202190, while phosphor ylation of cAMP-response element-binding protein was inhibited only by H89. Together, these studies illustrate that p38 MAPK is an important downstrea m target of the beta -adrenergic/cAMP/PKA signaling pathway in adipocytes, and one of the functional consequences of this cascade is stimulation of UC P1 gene expression in brown adipocytes.