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Mol. Cell. Biol., 04 1997, 1824-1831, Vol 17, No. 4
N Gotoh, M Toyoda and M Shibuya
Epidermal growth factor (EGF) induces tyrosine phosphorylation of the Shc
adapter protein, which plays an important role in EGF-stimulated
mitogenesis. Shc stimulates Ras/mitogen-activated protein kinase (MAPK)
through forming a complex with Grb2 at the phosphorylated tyrosine (Y)
residue 317. In this study, we identified novel phosphorylation sites of
Shc, at Y239 and Y240. To define the Shc pathway further, we used NIH 3T3
cells expressing the previously characterized mutant EGF receptor (EGF-R)
which lacks all known autophosphorylation sites but retains EGF-stimulated
mitogenesis with selective phosphorylation of Shc. We constructed wild-type
(WT) or mutant Shc cDNAs in which Y317 or/and Y239 and Y240 are replaced
with phenylalanine (F) and introduced them into NIH 3T3 cells expressing WT
or mutant EGF-R. In the WT EGF-R- expressing cells, the Y239/240/317F Shc,
but not Y317F or Y239/240F Shc, decreased EGF-stimulated cell growth. In
the mutant EGF-R- expressing cells, Y317F Shc or Y239/240F Shc decreased
EGF-stimulated cell growth significantly, though Y317F was a little more
potent than Y239/240F. Although cells expressing the Y317F Shc hardly
activated MAPK in response to EGF, cells expressing the Y239/240F Shc fully
activated MAPK. In contrast, Y239/240F Shc, but not Y317F Shc, reduced the
EGF-induced c-myc message. These results suggest that Shc activates two
distinct signaling pathways, Y317 to Ras/MAPK and Y239 and Y240 to another
pathway including Myc, and that both are involved in EGF- induced mitogenic
signaling.
Copyright © 1997, American Society for Microbiology
Tyrosine phosphorylation sites at amino acids 239 and 240 of Shc are involved in epidermal growth factor-induced mitogenic signaling that is distinct from Ras/mitogen-activated protein kinase activation
Department of Genetics, Institute of Medical Science, University of Tokyo, Japan.
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