SMAD-independent down-regulation of caveolin-1 by TGF-β: effects on proliferation and survival of myofibroblasts.

Yan Y Sanders,Zongbin Cui,Jeffrey C Horowitz,Claude Jourdan Le Saux,Victor J Thannickal,Veena B Antony,Ashish Kurundkar,Sunad Rangarajan,Rajasingh Johnson

doi:10.1371/journal.pone.0116995

Abstract

Transforming growth factor-β (TGF-β) mediates growth-inhibitory effects on most target cells via activation of the canonical SMAD signaling pathway. This growth-inhibitory activity may be coupled with cellular differentiation. Our studies demonstrate that TGF-β1 inhibits proliferation of primary, non-transformed human lung fibroblasts in association with the induction of myofibroblast differentiation. Differentiated myofibroblasts maintain the capacity to proliferate in response to exogenous mitogenic stimuli and are resistant to serum deprivation-induced apoptosis. These proliferative and anti-apoptotic properties of myofibroblasts are related, in part, to the down-regulation of caveolin-1 (Cav-1) by TGF-β1. Cav-1 down-regulation is mediated by early activation of p38 MAPK and does not require SMAD signaling. In contrast, myofibroblast differentiation is dependent on activation of the SMAD pathway, but not on p38 MAPK. Thus, combinatorial signaling by TGF-β1 of myofibroblast differentiation and down-regulation of Cav-1 by SMAD and p38 MAPK pathways, respectively, confer proliferative and apoptosis-resistant properties to myofibroblasts. Selective targeting of this SMAD-independent, p38-MAPK/Cav-1-dependent pathway is likely to be effective in the treatment of pathological conditions characterized by TGF-β signaling and myofibroblast activation.

Highlights

Transforming growth factor-β1 (TGF-β1) regulates cell growth, differentiation and apoptosis in a cell- and context-specific manner; both tumor-promoter and tumor-suppressive actions have been described [1,2]
We examined the effect of TGF-β1 on the proliferative responses of early passage non-transformed human lung fibroblasts (IMR-90)
Our studies show that TGF-β1 (2 ng/ml) consistently inhibits the proliferation of IMR-90 fibroblasts grown in the presence of serum (10% FBS) as assessed by cell number/Coulter counter (Fig. 1A) and by BrdU incorporation at 48 h following TGF-β1 stimulation (Fig. 1B)

Summary

INTRODUCTION

Transforming growth factor-β1 (TGF-β1) regulates cell growth, differentiation and apoptosis in a cell- and context-specific manner; both tumor-promoter and tumor-suppressive actions have been described [1,2]. Caveolin-1 Regulation by TGF-β several studies have demonstrated the ability of TGF-β1 to promote mesenchymal cell proliferation, an effect that appears to be mediated primarily by indirect mechanisms involving the autocrine production of mitogenic growth factors [8,9,10] and/or their receptor(s) up-regulation [11,12]. Exogenous receptor tyrosine kinases (RTKs)-activating fibroblast growth factors mediate enhanced mitogenic responses in TGF-β1-differentiated myofibroblasts [12]. We examined the regulation of Cav-1 expression in non-transformed human lung fibroblasts that undergo myofibroblast differentiation in response to TGFβ1 stimulation. For the first time, a novel action of TGF-β1 to down-regulate Cav expression via SMAD-independent and p38 MAPK-dependent mechanisms; this occurs concomitantly with the induction of myofibroblast differentiation via canonical SMAD signaling. We explore potential role(s) of Cav-1 in the regulation of myofibroblast proliferation and apoptosis resistance

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION