Mitogen-activated Protein Kinase Kinase Inhibition Does Not Block the Stimulation of Glucose Utilization by Insulin

Abstract

Insulin stimulates the activity of mitogen-activated protein kinase (MAPK) via its upstream activator, MAPK kinase (MEK), a dual specificity kinase that phosphorylates MAPK on threonine and tyrosine. The potential role of MAPK activation in insulin action was investigated with the specific MEK inhibitor PD98059. Insulin stimulation of MAPK activity in 3T3-L1 adipocytes (2.7-fold) and L6 myotubes (1.4-fold) was completely abolished by pretreatment of cells with the MEK inhibitor, as was the phosphorylation of MAPK and pp90Rsk, and the transcriptional activation of c-fos. Insulin receptor autophosphorylation on tyrosine residues and activation of phosphatidylinositol 3'-kinase were unaffected. Pretreatment of cells with PD98059 had no effect on basal and insulin-stimulated glucose uptake, lipogenesis, and glycogen synthesis. Glycogen synthase activity in extracts from 3T3-L1 adipocytes and L6 myotubes was increased 3-fold and 1.7-fold, respectively, by insulin. Pretreatment with 10 microM PD98059 was without effect. Similarly, the 2-fold activation of protein phosphatase 1 by insulin was insensitive to PD98059. These results indicate that stimulation of the MAPK pathway by insulin is not required for many of the metabolic activities of the hormone in cultured fat and muscle cells.

Inhibition of MAP kinase kinase (MEK) blocks endothelial PGI2 release but has no effect on von Willebrand factor secretion or E‐selectin expression

“…We also observed marginal tyrosine phosphorylation of a =44 kDa protein in thrombin-stimulated cells which was also inhibited by PD98059. This protein may well correspond to p44 mapk which is known to be activated in response to thrombin in other cell types, including smooth muscle [22]; inhibition by PD98059 would be consistent with previous observations that PD98059 totally blocks all measurable in vitro MAP kinase activity in adipocytes [8]. However, unlike the phosphorylation of the 42 kDa protein (p42m~pk), tyrosine phosphorylation of the 44 kDa substrate was not consistently observed in our experiments and, if present, (Fig.…”

“…In the present study we have employed a highly specific, non-competitive inhibitor of MEK (PD98059 [6][7][8]) to address directly the role of p42 mapk in thrombin-induced PGI2 generation and in E-selectin expression evoked by IL-la or TNFa.…”

Molecular Mechanisms of Insulin Resistance: Serine Phosphorylation of Insulin Receptor Substrate-1 and Increased Expression of p85α

“…Most, if not all, of the metabolic and antiapoptotic effects of insulin are mediated by the signaling pathway involving IRS proteins, phosphorylation, and activation of phosphatidylinositol (PI) 3-kinase, Akt (also known as protein kinase B), molecular target of rapamycin (mTOR), and p70 S6 kinase (21)(22)(23)(24). Activation of PI 3-kinase, Akt, and atypical protein kinase C (PKC) via the phosphoinositide-dependent protein kinase (25) appears to be critical in the mechanism of insulin action on GLUT-4 translocation and glucose transport.…”

Inhibition of the MAP kinase cascade blocks heregulin-induced cell cycle progression in T-47D human breast cancer cells

“…Recently, a synthetic compound, PD98059, has been described that acts in vivo as a selective inhibitor of MEK and the MAP kinase cascade (Alessi et al, 1995;Dudley et al, 1995;Pang et al, 1995). PD98059 binds to the inactive form of MEK, blocking its activation by Raf and has been tested in vitro and in vivo on more than 25 closely related kinases, none of which show signi®cant inhibition (Alessi et al, 1995;Dudley et al, 1995;Lazar et al, 1995).…”