FAK-dependent regulation of myofibroblast differentiation.
Fibroblasts and myofibroblasts both participate in wound healing. Transforming growth factor beta (TGFbeta) induces fibroblasts to differentiate into myofibroblasts, whereas fibroblast growth factor and heparin (FGF/h) induce myofibroblasts to "de-differentiate" into fibroblasts. TGFbeta induces expression of smooth muscle alpha actin (SMalphaA) and incorporation into in stress fibers, a phenotype of differentiated myofibroblasts. Additionally, TGFbeta induces the expression of fibronectin and fibronectin integrins. Fibronectin-generated signals contribute to the TGFbeta-mediated myofibroblast differentiation. Because fibronectin signals are transmitted through focal adhesion kinase (FAK), it was predicted that FAK would be essential to TGFbeta-mediated myofibroblast differentiation. To determine whether the FAK signaling pathway is required for myofibroblast differentiation, we used two approaches to decrease FAK in mouse embryo fibroblasts (MEFs): 1) FAK +/+ MEFs, in which FAK protein expression was greatly decreased by short hairpin RNA (shRNA), and 2) FAK -/- MEFs, which lack FAK. In both cases, the majority of cells were myofibroblasts, expressing SMalphaA in stress fibers even after treatment with FGF/h. Furthermore, both the surface expression of FGFRs and FGF signaling were greatly reduced in FAK -/- [corrected]MEFs. We conclude that FAK does not contribute to TGFbeta-dependent myofibroblast differentiation. Instead, FAK was necessary for FGF/h signaling in down-regulating expression of SMalphaA, which is synonymous with myofibroblast differentiation. FAK activation could contribute to regulating myofibroblast differentiation, thereby ameliorating fibrosis.
Department of Ophthalmology, Box 1183, Mount Sinai School of Medicine, 1 Gustave Levy Pl., New York, New York 10029-6574, USA. roseanne.greenberg@mssm.edu
Roseanne S
RS
Greenberg
Audrey M
AM
Bernstein
Miriam
M
Benezra
Irwin H
IH
Gelman
Lavinia
L
Taliana
Sandra K
SK
Masur
D000199:Actins / Q000378:metabolism; D002454:Cell Differentiation; D002478:Cells, Cultured; D015536:Down-Regulation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1 / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D005786:Gene Expression Regulation; D034622:RNA Interference; D017468:Receptors, Fibroblast Growth Factor / Q000378:metabolism; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000378:metabolism
D000199:Actins; D017468:Receptors, Fibroblast Growth Factor; D016212:Transforming Growth Factor beta; D005346:Fibroblast Growth Factors; D051417:Focal Adhesion Kinase 1; C496051:Ptk2 protein, mouse; D048049:Extracellular Signal-Regulated MAP Kinases