Abstract
The beta(1) integrin, functioning as a mechanoreceptor, senses a mechanical stimulus generated during collagen matrix contraction and down-regulates the phosphatidylinositol 3-kinase (PI3K)/Akt survival signal triggering apoptosis. The identities of integrin-associated signal molecules in the focal adhesion complex that are responsible for propagating beta(1) integrin viability signals in response to collagen matrix contraction are not known. Here we show that in response to collagen contraction focal adhesion kinase (FAK) is dephosphorylated. In contrast, enforced activation of beta(1) integrin by anti-beta(1) integrin antibody, which protects fibroblasts from apoptosis, preserves FAK phosphorylation. We demonstrate that ligation of beta(1) integrin by type I collagen or by enforced activation of beta(1) integrin by antibody promotes phosphorylation of FAK, p85 subunit of PI3K, and serine 473 of Akt. Wortmannin inhibited Akt but not FAK phosphorylation in response to enforced activation of beta(1) integrin by antibody. Blocking FAK by pharmacologic inhibition or by dominant negative FAK attenuated phosphorylation of p85 subunit of PI3K and Akt. Dominant negative FAK augmented fibroblast apoptosis during collagen contraction, and this was associated with diminished Akt activity. Constitutively active FAK augmented levels of p85 subunit of PI3K and Akt phosphorylation, and fibroblasts were protected from apoptosis. Our data identify a novel role for FAK, functioning upstream of PI3K/Akt, in transducing a beta(1) integrin viability signal in collagen matrices.
Highlights
Fibroblast survival in type I collagen matrices is regulated by integrin-extracellular matrix interactions [6]
In conjunction with our previous finding that Akt becomes dephosphorylated during matrix contraction, these data suggested a link between Focal adhesion kinase (FAK) and Akt activity and regulation of fibroblast viability in collagen matrices
Activity by enforced activation of 1 integrin by anti-1 integrin antibody or by using constitutively active FAK promoted increases in phosphatidylinositol 3-kinase (PI3K) and Akt activity and promoted protection against collagen contraction-induced apoptosis. These results suggested that FAK was functioning upstream of PI3K in regulating Akt activity and fibroblast viability. To extend these findings and confirm that FAK is upstream of PI3K in regulating fibroblast survival, we examined the effect of blocking PI3K activity with wortmannin on 1) the ability of enforced activation of 1 integrin by anti-1 integrin antibody to increase Akt activity and 2) the survival of fibroblasts expressing constitutively active FAK
Summary
3-Kinase/Akt in Regulating Fibroblast Survival in Response to Contraction of Type I Collagen Matrices via a 1 Integrin Viability Signaling Pathway*. Data supporting a role for FAK in the 1 integrin/PI3K/Akt viability pathway include the finding that integrin-extracellular matrix interaction recruits FAK to the focal adhesion complex and activates it. We demonstrate that ligation of 1 integrin with type I collagen or enforced activation of 1 integrin by anti-1 integrin antibody promotes the phosphorylation of FAK, the p85 subunit of PI3K, and serine 473 of Akt. Blocking FAK function by pharmacologic inhibition or by dominant negative FAK inhibits both the phosphorylation of the p85 subunit of PI3K and serine 473 of Akt. dominant negative FAK promotes fibroblast apoptosis in both anoikis and collagen gel assays. Our data identify a novel role for FAK functioning upstream of PI3K and Akt in mediating 1 integrin viability signaling of fibroblasts in collagen matrices
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