Proliferation of Pulmonary Interstitial Fibroblasts Is Mediated by Transforming Growth Factor- beta 1-induced Release of Extracellular Fibroblast Growth Factor-2 and Phosphorylation of p38 MAPK and JNK

Idiopathic pulmonary fibrosis (IPF; a progressive lung disease) is characterized by parenchymal remodeling with enlarged air spaces called honeycomb cysts and palisades of fibroblasts called fibroblast foci. In IPF, lung epithelial cells covering honeycomb cysts and fibroblast foci aberrantly express the active conformation of the potent fibrogenic cytokine transforming growth factor- beta 1 (TGF- beta 1). Using explanted rat lung slices, we transfected alveolar epithelial cells with the retrovirus pMX containing a site-directed mutation in which Cys super(223) and Cys super(225) were substituted with serines, resulting in release of biologically active TGF- beta 1 and fibroblast proliferation and remodeling that resembled IPF. Fibroblasts obtained from transfected explants and in culture for 6 weeks incorporated 6.59 plus or minus 1.55-fold more [ super(3)H]thymidine compared with control fibroblasts without transfection or fibroblasts obtained from transfected explants cultured with antibody to fibroblast growth factor-2 (FGF-2). Primary lung fibroblasts obtained from normal rat lungs cultured with TGF- beta 1 expressed increased levels of phosphorylated p38 MAPK and JNK, but not ERK1/2. The presence of TGF- beta 1 caused an immediate release of extracellular FGF-2 from primary pulmonary fibroblasts; and in the presence of anti-FGF-2 antibody, phosphorylated p38 MAPK and JNK were abrogated. TGF- beta inhibits cell proliferation by suppression of c-Myc and induction of p15 super(INK46), p21 super(CIP1), or p27 super(KIP). Fibroblasts cultured with TGF- beta 1 showed no regulation of c-Myc or induction of p15 super(INK46), p21 super(CIP1),or p27 super(KIP). These findings suggest that pulmonary fibroblasts may not respond to the anti-proliferative effects of TGF- beta 1, but proliferate in response to TGF- beta 1 indirectly by the release of FGF-2, which induces phosphorylation of p38 MAPK and JNK.