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J. Cell Biol.,
Volume 143, Number 5, November 30, 1998 1375-1383
Craniofacial Developmental Biology and Regeneration Branch, National Institute of Dental and Craniofacial Research,
National Institutes of Health, Bethesda, Maryland 20892-4370
The tumor suppressor PTEN dephosphorylates focal adhesion kinase (FAK) and inhibits integrin-mediated cell spreading and cell migration. We demonstrate here that expression of PTEN selectively inhibits
activation of the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK)
pathway. PTEN expression in glioblastoma cells lacking the protein resulted in inhibition of integrin-mediated MAP kinase activation. Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF)-
induced MAPK activation were also blocked. To determine the specific point of inhibition in the Ras/Raf/
MEK/ERK pathway, we examined these components
after stimulation by fibronectin or growth factors. Shc
phosphorylation and Ras activity were inhibited by expression of PTEN, whereas EGF receptor autophosphorylation was unaffected. The ability of cells to
spread at normal rates was partially rescued by coexpression of constitutively activated MEK1, a downstream component of the pathway. In addition, focal
contact formation was enhanced as indicated by paxillin staining. The phosphatase domain of PTEN was essential for all of these functions, because PTEN with an
inactive phosphatase domain did not suppress MAP kinase or Ras activity. In contrast to its effects on ERK,
PTEN expression did not affect c-Jun NH2-terminal kinase (JNK) or PDGF-stimulated Akt. Our data suggest
that a general function of PTEN is to down-regulate FAK and Shc phosphorylation, Ras activity, downstream MAP kinase activation, and associated focal
contact formation and cell spreading.
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