Increasing cAMP attenuates activation of mitogen-activated protein kinase.

Abstract

Activation of the mitogen-activated protein kinase (MAP kinase) isoforms ERK1 and ERK2 was investigated in rat adipocytes. Kinase activities were measured by using myelin basic protein as substrate after the isoforms were resolved by Mono Q chromatography or by immunoprecipitation with specific antibodies. Insulin increased the activity of both isoforms by 3-to 4-fold. The 3-adrenergic agonist isoproterenol was without effect in the absence of insulin but markedly reduced the increases in ERK1 and ERK2 activities produced by the hormone. MAP kinase activation was also attenuated by forskolin and glucagon, which increase intracellular cAMP, and by dibutyryl-cAMP, and 8-(4-chlorophenylthio)-cAMP. Thus, increasing cAMP is associated with decreased activation of MAP kinase by insulin. Forskolin also inhibited activation of MAP kinase by several agents (epidermal growth factor, phorbol 12-myristate 13-acetate, and okadaic acid) that act independently of insulin receptors. Moreover, forskolin did not inhibit insulinstimulated tyrosine phosphorylation of the insulin receptor substrate IRS-1. Therefore, the inhibitory effect on MAP kinase did not result from compromised functioning of the insulin receptor. The inhibitory effect was not confined to adipocytes, as forskolin and dibutyryl-cAMP inhibited the increase in MAP kinase activity by phorbol 12-myristate 13-acetate in wild-type CHO cells. In contrast, these agents did not inhibit MAP kinase activity in mutant CHO cells (line 10248) that express a cAMP-dependent protein kinase resistant to activation by cAMP. Our results suggest that activation of cAMP-dependent protein kinase represents a general counterregulatory mechanism for opposing MAP kinase activation.Mitogen-activated protein kinase (MAP kinase) was first described as a microtubule-associated protein 2 kinase that was rapidly activated by insulin (1). cDNA cloning of MAP kinase led to the identification of three isoforms, ERK1, ERK2, and ERK3 (2), and to the discovery that the MAP kinases are homologous to KSS1 and FUS3 (3), two kinases that are intermediates in the response of Saccharomyces cerevisiae to a mating factor. Phosphorylation of ERK1 and ERK2 in two sites (one a threonine and one a tyrosine residue) is necessary for kinase activity (4, 5). Relatively little is known about the properties of ERK3.MAP kinase is now known to be activated in response to a large number of mitogenic stimuli, and the enzyme is believed to be a key participant in the response to growth factors (see refs. 6-8). The kinase phosphorylates the transcription factors c-Myc (9) and c-Jun (10) and activates the protein-serine/threonine kinase Rsk-2 (11). In skeletal muscle the protein phosphatase that activates glycogen synthase, PP1G, is phosphorylated and apparently activated in response to insulin (12). The kinase catalyzing phosphorylationThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §17...

A chemical biology approach identifies a beta-2 adrenergic receptor agonist that causes human tumor regression by blocking the Raf-1/Mek-1/Erk1/2 pathway

“…Therefore, tumors that express two or more of these growth factors may require a cocktail of anticancer drugs. In contrast, b2AR stimulation will block activation of the Raf-1/Mek-1/Erk1/2 pathway when it is driven by several growth factors as they all require Mek to activate Erk1/2 (Graves et al, 1993;Sevetson et al, 1993;Wu et al, 1993;Sebolt-Leopold, 2000;Dumaz and Marais, 2005). For example, we have shown that growth factor (i.e., EGF) stimulation of P-Erk1/2 is blocked by ARA-211 in MDA-MB-231 cells (data not shown).…”

“…In normal cells, it has been shown that adrenergic stimulation can either stimulate or inhibit P-Erk1/2 and proliferation (Sevetson et al, 1993;Maudsley et al, 2000;Stork and Schmitt, 2002). However, in tumor cells, it is not known if stimulation of the b2AR can stimulate tumorigenesis.…”

Role of Janus kinase-2 in insulin-mediated phosphorylation and inactivation of protein phosphatase-2A and its impact on upstream insulin signalling components

“…In addition, cAMP also inhibits insulin and growth-factor-stimulated MAPK signalling in most cell types [25,[37][38][39][40], with the exception of Swiss 3T3 and PC12 cells (reviewed in [25]). Our previous studies have shown that SpcAMP counter-regulates insulin's effect on PP-2A inactivation by decreasing the tyrosine phosphorylation of PP-2A and restoring its catalytic activity [25].…”

Activation of mitogen-activated protein kinase couples neurotensin receptor stimulation to induction of the primary response gene Krox-24

“…We indeed found that NT increased cAMP levels in CHO-hNTR cells (results not shown). Because hydrolysis-resistant cAMP analogues such as dibutyryl cAMP or 8-Br-cAMP, which maintain high cellular levels of cAMP, are able either to prevent or to increase the MAPK level, depending on the cell type [34], we examined whether MAPK activation could be related to cAMP metabolism. In CHO-hNTR cells, cAMP analogues alone did not significantly affect this activity.…”