Low α(2)β(1) integrin function enhances the proliferation of fibroblasts from patients with idiopathic pulmonary fibrosis by activation of the β-catenin pathway.
Idiopathic pulmonary fibrosis (IPF) is a progressive and incurable fibroproliferative disorder characterized by unrelenting proliferation of fibroblasts and their deposition of collagen within alveoli, resulting in permanently scarred, nonfunctional airspaces. Normally, polymerized collagen suppresses fibroblast proliferation and serves as a physiological restraint to limit fibroproliferation after tissue injury. The IPF fibroblast, however, is a pathologically altered cell that has acquired the capacity to elude the proliferation-suppressive effects of polymerized collagen. The mechanism for this phenomenon remains incompletely understood. Here, we demonstrate that expression of α(2)β(1) integrin, a major collagen receptor, is pathologically low in IPF fibroblasts interacting with polymerized collagen. Low integrin expression in IPF fibroblasts is associated with a failure to induce PP2A phosphatase activity, resulting in abnormally high levels of phosphorylated (inactive) GSK-3β and high levels of active β-catenin in the nucleus. Knockdown of β-catenin in IPF fibroblasts inhibits their ability to proliferate on collagen. Interdiction of α(2)β(1) integrin in control fibroblasts reproduces the IPF phenotype and leads to the inability of these cells to activate PP2A, resulting in high levels of phosphorylated GSK-3β and active β-catenin and in enhanced proliferation on collagen. Our findings indicate that the IPF fibroblast phenotype is characterized by low α(2)β(1) integrin expression, resulting in a failure of integrin to activate PP2A phosphatase, which permits inappropriate activation of the β-catenin pathway.
Department of Medicine, University of Minnesota, Minneapolis, MN 55455, USA.
Hong
H
Xia
Jeremy
J
Seeman
Jian
J
Hong
Polla
P
Hergert
Vidya
V
Bodem
Jose
J
Jessurun
Karen
K
Smith
Richard
R
Nho
Judy
J
Kahm
Philippe
P
Gaillard
Craig
C
Henke
D049109:Cell Proliferation; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology*; D055785:Gene Knockdown Techniques; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D054990:Idiopathic Pulmonary Fibrosis / Q000378:metabolism* / Q000473:pathology; D038982:Integrin alpha2beta1 / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D019012:Integrin beta1 / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D051176:beta Catenin / Q000378:metabolism*
D024042:Collagen Type I; D038982:Integrin alpha2beta1; D019012:Integrin beta1; D051176:beta Catenin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; D054648:Protein Phosphatase 2