title: Role of integrin-linked kinase in regulating phosphorylation of Akt and fibroblast survival in type I collagen matrices through a beta1 integrin viability signaling pathway.
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.
authors.affiliation: Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Richard Seonghun
authors.initials: RS
authors.lastname: Nho
authors.forename: Hong
authors.initials: H
authors.lastname: Xia
authors.forename: Judy
authors.initials: J
authors.lastname: Kahm
authors.forename: Jill
authors.initials: J
authors.lastname: Kleidon
authors.forename: Deanna
authors.initials: D
authors.lastname: Diebold
authors.forename: Craig A
authors.initials: CA
authors.lastname: Henke
mesh_terms: D017209:Apoptosis; D015153:Blotting, Western; D002448:Cell Adhesion; D002460:Cell Line; D002470:Cell Survival; D002478:Cells, Cultured; D003094:Collagen / Q000737:chemistry; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D020287:In Situ Nick-End Labeling; D019012:Integrin beta1 / Q000378:metabolism*; D008168:Lung / Q000166:cytology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D000099200:Scaffold Protein ILK
chemical_list: D003094:Collagen; D019012:Integrin beta1; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D012694:Serine; D000099200:Scaffold Protein ILK; C494918:AKT1 protein, human