Latent transforming growth factor-beta-binding protein-4 regulates transforming growth factor-beta1 bioavailability for activation by fibrogenic lung fibroblasts in response to bleomycin.
Recent evidence suggests that subsets of lung fibroblasts differentially contribute to fibrogenic progression. We have previously shown that a subset of rat lung fibroblasts with fibrogenic characteristics [Thy-1 (-) fibroblasts] responds to stimuli (bleomycin, interleukin-4, etc) with increased latent transforming growth factor (TGF)-beta activation, whereas non-fibrogenic Thy-1-expressing [Thy-1 (+)] fibroblasts do not. Activation of latent TGF-beta1 by interstitial lung fibroblasts is critical for fibrogenic responses. To better understand the susceptibility of fibrogenic fibroblasts to the stimulation of TGF-beta activation, we examined the role of latent TGF-beta-binding proteins (LTBPs), key regulators of TGF-beta bioavailability and activation, in TGF-beta1 activation by these fibroblasts. Treatment of fibroblasts with bleomycin up-regulated LTBP-4 mRNA, protein, and soluble LTBP-4-bound large latent TGF-beta1 complexes in Thy-1 (-) fibroblasts to significantly higher levels than in Thy-1 (+) fibroblasts. Bleomycin-induced TGF-beta1 activation required LTBP-4, since lung fibroblasts deficient in LTBP-4 did not activate TGF-beta1. Expression of LTBP-4 restored TGF-beta1 activation in response to bleomycin, but expression either of LTBP-4 lacking the TGF-beta-binding site or only the TGF-beta-binding domain did not. Bleomycin treatment of mice increased LTBP-4 expression in the lung. Thy-1 knockout mice had increased levels of both LTBP-4 expression and TGF-beta activation, as well as enhanced Smad3 phosphorylation compared with wild-type mice. Together, these data identify a critical role for LTBP-4 in the regulation of latent TGF-beta1 activation in bleomycin-induced lung fibrosis.
Zhou
Yong
Y
Department of Pathology, Division of Molecular and Cellular Pathology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
Koli
Katri
K
Hagood
James S
JS
Miao
Mi
M
Mavalli
Mahendra
M
Rifkin
Daniel B
DB
Murphy-Ullrich
Joanne E
JE
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000633:toxicity; D001761:Bleomycin / Q000633:toxicity; D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D053779:Latent TGF-beta Binding Proteins / Q000378:metabolism*; D008168:Lung / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D011658:Pulmonary Fibrosis / Q000139:chemically induced / Q000378:metabolism*; D051381:Rats; D018800:Thy-1 Antigens / Q000235:genetics / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
D000903:Antibiotics, Antineoplastic; D053779:Latent TGF-beta Binding Proteins; C509034:Ltbp1 protein, rat; D018800:Thy-1 Antigens; D053773:Transforming Growth Factor beta1; D001761:Bleomycin