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Mol. Cell. Biol., Mar 1997, 1595-1606, Vol 17, No. 3
G Kulik, A Klippel and MJ Weber
We have found that insulin-like growth factor I (IGF-I) can protect
fibroblasts from apoptosis induced by UV-B light. Antiapoptotic signalling
by the IGF-I receptor depended on receptor kinase activity, as cells
overexpressing kinase-defective receptor mutants could not be protected by
IGF-I. Overexpression of a kinase-defective receptor which contained a
mutation in the ATP binding loop functioned as a dominant negative and
sensitized cells to apoptosis. The antiapoptotic capacity of the IGF-I
receptor was not shared by other growth factors tested, including epidermal
growth factor (EGF) and thrombin, although the cells expressed functional
receptors for all the agonists. However, EGF was antiapoptotic for cells
overexpressing the EGF receptor, and expression of activated pp60v-src also
was protective. There was no correlation between protection from apoptosis
and activation of mitogen- activated protein kinase, p38/HOG1, or p70S6
kinase. On the other hand, protection by any of the tyrosine kinases
against UV-induced apoptosis was blocked by wortmannin, implying a role for
phosphatidylinositol 3- kinase (PI3 kinase). To test this, we transiently
expressed constitutively active or kinase-dead PI3 kinase and found that
overexpression of activated phosphatidylinositol 3-kinase (PI3 kinase) was
sufficient to provide protection against apoptosis. Because Akt/PKB is
believed to be a downstream effector for PI3 kinase, we also examined the
role of this serine/threonine protein kinase in antiapoptotic signalling.
We found that membrane-targeted Akt was sufficient to protect against
apoptosis but that kinase-dead Akt was not. We conclude that the endogenous
IGF-I receptor has a specific antiapoptotic signalling capacity, that
overexpression of other tyrosine kinases can allow them also to be
antiapoptotic, and that activation of PI3 kinase and Akt is sufficient for
antiapoptotic signalling.
Copyright © 1997, American Society for Microbiology
Antiapoptotic signalling by the insulin-like growth factor I receptor, phosphatidylinositol 3-kinase, and Akt
Department of Microbiology and Cancer Center, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
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