Abstract
A beta1 integrin phosphatidylinositol 3-kinase/Akt pathway regulates fibroblast survival in collagen matrices. When fibroblasts attach to collagen, Akt becomes phosphorylated, providing a survival signal. In contrast, in response to mechanical forces generated during collagen contraction, Akt is dephosphorylated and fibroblasts undergo apoptosis. The kinase(s) responsible for regulating Akt phosphorylation in response to matrix-derived mechanical signals are unclear. Integrin-linked kinase (ILK) is associated with the beta1 integrin in the focal adhesion complex and as such is a candidate kinase that may regulate Akt phosphorylation and fibroblast viability. Nevertheless, there is no direct evidence that matrix-derived mechanical forces regulate cell viability by modulating ILK activity. Here, we show that ILK activity decreased in response to collagen matrix contraction, which correlated with Akt dephosphorylation and induction of fibroblast apoptosis. In contrast, enforced activation of beta1 integrin by activating antibody preserved ILK and Akt activity during collagen matrix contraction, and this is associated with protection from collagen contraction-induced apoptosis. Knock-down of ILK by small, interfering RNA (siRNA) attenuated Akt phosphorylation in response to ligation of beta1 integrin by collagen or activating antibody and enhanced fibroblast apoptosis in response to collagen contraction. Kinase dead ILK attenuated Akt phosphorylation and enhanced fibroblast apoptosis, whereas hyperactive and wild type ILK augmented Akt phosphorylation and protected fibroblasts from apoptosis. Constitutively active Akt preserved Akt activity and rescued ILK siRNA-treated fibroblasts from collagen contraction-induced apoptosis. These data establish that matrix-derived mechanical forces sensed by beta1 integrin are capable of modulating ILK activity which regulates fibroblast viability via an Akt-dependent mechanism.
Highlights
During tissue development and repair, cells respond to cues derived from the extracellular matrix (ECM),1 and in the process such cellular functions as cell viability may be modulated
These data establish that matrix-derived mechanical forces sensed by 1 integrin are capable of modulating Integrin-linked kinase (ILK) activity which regulates fibroblast viability via an Akt-dependent mechanism
We present data establishing that collagen matrix contraction-derived mechanical signals sensed by 1 integrin are capable of modulating ILK activity, which regulates fibroblast viability through an Akt-dependent mechanism
Summary
During tissue development and repair, cells respond to cues derived from the extracellular matrix (ECM), and in the process such cellular functions as cell viability may be modulated. We have found that in response to mechanical forces generated during collagen matrix contraction, a 1 integrin/PI 3-kinase/ Akt signal pathway regulates fibroblast viability [3, 11]. Multiple exogenous stimuli have been shown to activate ILK; these include direct integrin ligation by the ECM and growth factor and chemokine activation [20, 21] These data suggest a possible link between ILK activity and the regulation of Akt phosphorylation, currently there is no direct evidence that matrix-derived mechanical forces sensed by integrin receptors modulate ILK activity and cell viability in an Akt-dependent manner. We present data establishing that collagen matrix contraction-derived mechanical signals sensed by 1 integrin are capable of modulating ILK activity, which regulates fibroblast viability through an Akt-dependent mechanism
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