Molecular and Cellular Biology, March 2000, p. 1526-1536, Vol. 20, No. 5
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
andDepartment of Biochemistry and Molecular Biology and Walther Oncology Center, Indiana University School of Medicine and Walther Cancer Institute, Indianapolis, Indiana 46202-5254,1 and Departments of Medicine, Oncology, and Biochemistry, Molecular Oncology Group, Royal Victoria Hospital, McGill University, Montreal, Quebec, Canada H3A 1A12
Received 13 August 1999/Returned for modification 15 September 1999/Accepted 23 November 1999
We have previously shown that activation of extracellular
signal-regulated kinase (Erk) by epidermal growth factor (EGF)
treatment was significantly decreased in mouse fibroblast cells
expressing a mutant Shp-2 molecule lacking 65 amino acids in the SH2-N
domain, Shp-2
46-110. To address the molecular mechanism
for the positive role of Shp-2 in mediating Erk induction, we evaluated
the activation of signaling components upstream of Erk in Shp-2 mutant
cells. EGF-stimulated Ras, Raf, and Mek activation was significantly attenuated in Shp-2 mutant cells, suggesting that Shp-2 acts to promote
Ras activation or to suppress the down-regulation of activated Ras.
Biochemical analyses indicate that upon EGF stimulation, Shp-2 is
recruited into a multiprotein complex assembled on the Gab1 docking
molecule and that Shp-2 seems to exert its biological function by
specifically dephosphorylating an unidentified molecule of 90 kDa in
the complex. The mutant Shp-2
46-110 molecule failed to
participate in the Gab1-organized complex for dephosphorylation of p90,
correlating with a defective activation of the Ras-Raf-Mek-Erk cascade
in EGF-treated Shp-2 mutant cells. Evidence is also presented that
Shp-2 does not appear to modulate the signal relay from EGF receptor to
Ras through the Shc, Grb2, and Sos proteins. These results begin to
elucidate the mechanism of Shp-2 function downstream of a receptor
tyrosine kinase to promote the activation of the Ras-Erk pathway, with
potential therapeutic applications in cancer treatment.
Present address: Lilly Research Laboratories, Indianapolis, IN 46285.
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