Previous Article | Next Article ![]()
Mol. Cell. Biol., Feb 1996, 577-583, Vol 16, No. 2
KH Holt, BG Kasson and JE Pessin
The Ras guanylnucleotide exchange protein SOS undergoes feedback
phosphorylation and dissociation from Grb2 following insulin receptor
kinase activation of Ras. To determine the serine/threonine kinase(s)
responsible for SOS phosphorylation in vivo, we assessed the role of
mitogen-activated, extracellular-signal-regulated protein kinase kinase
(MEK), extracellular-signal-regulated protein kinase (ERK), and the c- JUN
protein kinase (JNK) in this phosphorylation event. Expression of a
dominant-interfering MEK mutant, in which lysine 97 was replaced with
arginine (MEK/K97R), resulted in an inhibition of insulin-stimulated SOS
and ERK phosphorylation, whereas expression of a constitutively active MEK
mutant, in which serines 218 and 222 were replaced with glutamic acid
(MEK/EE), induced basal phosphorylation of both SOS and ERK. Although
expression of the mitogen-activated protein kinase- specific phosphatase
(MKP-1) completely inhibited the insulin stimulation of ERK activity both
in vitro and in vivo, SOS phosphorylation and the dissociation of the
Grb2-SOS complex were unaffected. In addition, insulin did not activate the
related protein kinase JNK, demonstrating the specificity of insulin for
the ERK pathway. The insulin-stimulated and MKP-1-insensitive SOS-
phosphorylating activity was reconstituted in whole-cell extracts and did
not bind to a MonoQ anion-exchange column. In contrast, ERK1/2 protein was
retained by the MonoQ column, eluted with approximately 200 mM NaCl, and
was MKP-1 sensitive. Although MEK also does not bind to MonoQ,
immunodepletion analysis demonstrated that MEK is not the
insulin-stimulated SOS-phosphorylating activity. Together, these data
demonstrate that at least one of the kinases responsible for SOS
phosphorylation and functional dissociation of the Grb2-SOS complex is an
ERK-independent but MEK-dependent insulin-stimulated protein kinase.
Copyright © 1996, American Society for Microbiology
Insulin stimulation of a MEK-dependent but ERK-independent SOS protein kinase
Department of Physiology & Biophysics, University of Iowa, Iowa City 52242-1109, USA.
This article has been cited by other articles:
| J. Bacteriol. | J. Virol. | Eukaryot. Cell |
|---|
| Microbiol. Mol. Biol. Rev. | Clin. Vaccine Immunol. | All ASM Journals |
|---|