Activation of fibroblast procollagen α1(I) transcription by mechanical strain is transforming growth factor-β-dependent and involves increased binding of CCAAT-binding factor (CBF/NF-Y) at the proximal promoter

Abstract

During normal developmental tissue growth and in a number of diseases of the cardiopulmonary system, adventitial and interstitial fibroblasts are subjected to increased mechanical strain. This leads to fibroblast activation and enhanced collagen synthesis, but the underlying mechanisms involved remain poorly understood. In this study, we have begun to identify and characterize mechanical strain-responsive elements in the rat procollagen α1(I) (COL1A1) gene and show that the activity of COL1A1 promoter constructs, transiently transfected into cardiac fibroblasts, was increased between 2- and 4-fold by continuous cyclic mechanical strain. This was accompanied by a ∼3-fold increase in the levels of total active transforming growth factor-β (TGF-β) released into the medium. Inclusion of a panspecific TGF-β neutralizing antibody inhibited straininduced COL1A1 promoter activation. Deletion analysis revealed the presence of two potential strain response regions within the proximal promoter, one of which contains an inverted CCAAT-box overlapping a GC-rich element. Both mechanical strain and exogenously added TGF-β1 enhanced the binding activity of CCAAT-binding factor, CBF/NF-Y, at this site. Moreover, this element was sufficient to confer strain-responsiveness to an otherwise unresponsive SV40 promoter. In summary, this study demonstrates that strain-induced COL1A1 promoter activation in cardiac fibroblasts is TGF-β-dependent and involves increased binding of CCAAT-binding factor at the proximal promoter. Furthermore, these findings suggest a novel and potentially important TGF-β response element in the rat COL1A1 gene.