TGF beta 1 regulation of vimentin gene expression during differentiation of the C2C12 skeletal myogenic cell line requires Smads, AP-1 and Sp1 family members

摘要

Vimentin exhibits a complex pattern of developmental and tissue-specific expression regulated by such growth factors as TGF beta 1, PDGF, FGF, EGF and cytokines. Vimentin is expressed in the more migratory, mesetichymal cell and its expression is often down-regulated to make way for tissue-specific intermediate filaments proteins such as desmin in muscle. Here, we suggest a mechanism to explain how TGF beta 1 contributes to the up-regulation of vimentin expression while blocking myogenesis. TGF beta 1 binds to serine/threonine kinase receptors resulting in the phosphorylation of Smad2 and Smad3, followed by formation of a heteromeric complex with Smad4. The translocation of this complex to the nucleus modulates transcription of selected genes such as vimentin. However, the vimentin gene lacks a consensus TGFP beta 1 response element. By transient transfection analysis of vimentin's various promoter elements fused to the CAT reporter gene, we have determined that tandem AP-1 sites surrounded by GC-boxes are required for TGF beta 1 induction. Mutations within this region eliminated the ability of Smad3 to induce reporter gene expression.. DNA precipitation and ChIP assays suggest that c-Jun, c-Fos, Smad3 and Sp1/Sp3 interact over this region, but this interaction changes during myogenesis with TGF beta 1 induction. (c) 2006 Elsevier B.V. All rights reserved.