Stimulation of MAPK cascades by insulin and osmotic shock: lack of an involvement of p38 mitogen-activated protein kinase in glucose transport in 3T3-L1 adipocytes.

Abstract

Osmotic shock and insulin stimulate GLUT4 translocation and glucose transport via mechanisms that are for the most part distinct yet convergent. In this article, we investigated the effect of osmotic shock and insulin on the activation of the mitogen-activated protein kinase (MAPK) cascades in differentiated 3T3-L1 adipocytes. The MAPKs are activated by phosphorylation on conserved tyrosine and threonine residues. Both sorbitol and insulin strongly stimulated extracellular regulated kinase (ERK) 1 and 2 phosphorylation (8-and 18-fold, respectively). In contrast, c-jun-NH 2 -terminal kinase (JNK)/stress-activated protein kinase (SAPK) phosphorylation was stimulated only by sorbitol (sevenfold) and not by insulin. Phosphorylation of p38 MAPK was stimulated strongly by sorbitol (22-fold) but weakly by insulin (2.7-fold). Measurement of intrinsic JNK and p38 MAPK activity confirmed the phosphorylation studies. JNK and p38 MAPK were activated only significantly by sorbitol. (1-3). The ERKs are strongly activated by polypeptide growth factors and phorbol esters but are weakly activated by environmental stresses, such as osmotic or heat shock, UV light, and inhibitors of protein synthesis. In contrast, JNK and p38 MAPKs are strongly activated by cytokines and adverse stimuli, but are poorly activated by growth factors.All MAPKs are activated by phosphorylation on both threonine and tyrosine residues within the motif Thr-Xaa-Tyr. The Xaa represents Glu in the ERK subfamily, Pro in the JNK subfamily, and Gly in the p38 MAPK subfamily. Both the threonine and tyrosine residues are phosphorylated by a dualspecificity kinase or MAPK (mitogen-activated ERK-activating kinase [MEK] or MAPK kinase [MKK]). The central residue in the Thr-Xaa-Tyr motif allows for selective activation by different MKKs, such that MEK1 and MEK2 selectively phosphorylate and activate the ERKs; MKK4/SAPK kinase (SEK) 1 and MKK7 phosphorylate and activate JNK; MKK3 and MKK6 phosphorylate and activate p38 MAPK (4-9). Despite the prevailing view of the selectivity of these kinases, a growing body of evidence indicates that these pathways overlap. In a study examining interleukin-1␤-induced cyclooxygenase-2 expression in rat renal mesangial cells, Guan et al. (10) have found that overexpressing the dominant negative form of MKK4 inhibited both JNK and p38 MAPK phosphorylation in their system. This finding indicates that MKK4 can act upstream of p38 in certain systems (10). In another study, the investigators coexpressed p38␦ and MKK3, MKK4, and MKK6 in 293 cells and found that, although MKK3 and MKK6 were the dominant regulators, MKK4 could also phosphorylate p38␦ (11).

Activation of JNK/p38 Pathway is Responsible for α-Methyl-n-butylshikonin Induced Mitochondria-Dependent Apoptosis in SW620 Human Colorectal Cancer Cells

“…Both of JNK and p38 inhibitors (SP600125 and SB203580) could attenuate MBS-induced apoptosis. The JNK and p38 inhibitors (SP600125 and SB203580) specifically inhibit JNK and p38 catalytic activity respectively by binding to the ATPbinding pocket preventing the activation of downstream factors, but p38 inhibitor SB203580 does not result in the decreased phosphorylation levels of p38 (Kayali et al, 2000;Bennett et al, 2001). Here, we also found that SP600125 (a specific inhibitor of JNK) inhibited JNK activation, but SB203580 (a specific inhibitor of p38) had no effect on p38 activation.…”

Analysis of 3-phosphoinositide-dependent kinase-1 signaling and function in ES cells

“…This occurred concomitant with an increase in phosphorylation of the ERK-dependent phosphorylation site S380 of RSK as well as an increase in ERK phosphorylation. Although ERK has previously been shown to be phosphorylated in response to osmotic shock in some cells [42], p90RSK is normally not thought to participate in this response [43]. This may therefore represent a cell type specific response to ES cells and it will be interesting to determine the significance of this.…”

Insulin-induced myocardial protection in isolated ischemic rat hearts requires p38 MAPK phosphorylation of Hsp27

“…The MAPK pathway is activated by many stimulatory agents and phosphorylates downstream signaling molecules (16). Insulin also activates MAPK (24,32,49), and MAPK activation leads to Hsp27 phosphorylation (1,25,35,39,63). Thus, in the present study, we used phosphospecific antibodies to detect phosphorylated isoforms of Hsp27.…”

“…Once insulin activates the insulin receptor, the PI3K/Akt and MAPK pathways are activated (55). Recent evidence indicates that insulin activates ERK1/2 and p38 MAPK (3,25,35,41). p38 MAPK, in turn, activates MAPKAPK-2 that directly regulates the phosphorylation of Hsp27 (1,39,69).…”