Integrin alpha8beta1 mediates adhesion to LAP-TGFbeta1.
The development of fibrosis is a common response to a variety of injuries and results in the net accumulation of matrix proteins and impairment of normal organ function. We previously reported that the integrin alpha8beta1 is expressed by alveolar interstitial cells in normal lung and is upregulated during the development of fibrosis. TGFbeta1 is an important mediator of the inflammatory response in pulmonary fibrosis. TGFbeta1 is secreted as a latent protein that is non-covalently associated with latency-associated peptide (LAP) and requires activation to exert its effects. LAP-TGFbeta1 and LAP-TGFbeta3 contain the tripeptide sequence, arginine-glycine-aspartic acid (RGD), a known integrin recognition motif. The integrin alpha8beta1 binds to several ligands such as fibronectin and vitronectin through the RGD sequence. Recent reports demonstrate that the integrins alphavbeta1, alphavbeta6 and alphavbeta8 adhere to LAP-TGFbeta1 through the RGD site. Therefore, we asked whether LAP-TGFbeta1 might be a ligand for alpha8beta1 and whether this may be important in the development of fibrosis. We found that cell lines transfected with alpha8 subunit were able to spread on and adhere to recombinant LAP-TGFbeta1 significantly better than mock transfected cell lines. alpha8-transfected cells were also able to adhere to LAP-TGFbeta3 significantly better than mock transfected cells. Adhesion to LAP-TGFbeta1 was enhanced by activation of alpha8beta1 by Mn(2+), or 8A2, an integrin beta1 activating antibody. Furthermore, cell adhesion was abolished when we used a recombinant LAP-TGFbeta1 protein in which the RGD site was mutated to RGE. alpha8beta1 binding to LAP-TGFbeta1 increased cell proliferation and phosphorylation of FAK and ERK, but did not activate of TGFbeta1. These data strongly suggest that LAP-TGFbeta1 is a ligand of alpha8beta1 and interaction of alpha8beta1 with LAP-TGFbeta1 may influence cell behavior.
Lu
Min
M
Pulmonary and Critical Care Medicine, Department of Medicine, Mount Sinai School of Medicine, New York, NY 10029, USA.
Munger
John S
JS
Steadele
Melissa
M
Busald
Christina
C
Tellier
Marinka
M
Schnapp
Lynn M
LM
D000818:Animals; D002448:Cell Adhesion; D002455:Cell Division; D002460:Cell Line; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D008168:Lung / Q000378:metabolism; D051379:Mice; D008907:Mink; D010446:Peptide Fragments / Q000378:metabolism*; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism*; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D014407:Tumor Cells, Cultured
D016023:Integrins; D010446:Peptide Fragments; D011498:Protein Precursors; C508960:TGFB1 protein, human; C508961:Tgfb1 protein, mouse; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C094866:integrin alpha8beta1