Fli-1 inhibits collagen type I production in dermal fibroblasts via an Sp1-dependent pathway

Fibrosis is characterized by the excessive deposition of extracellular matr ix (ECM), especially collagen. Because Ets factors are implicated in physio logical and pathological ECM remodeling, the aim of this study was to inves tigate the role of Ets factors in collagen production. We demonstrate that the expression of collagenous proteins and collagen alpha2(I) (COL1A2) mRNA was inhibited following stable transfection of Fli-1 in dermal fibroblasts , Subsequent analysis of the COL1A2 promoter identified a critical Ets bind ing site that mediates Fli-1 inhibition. In contrast, Ets-1 stimulates COL1 A2 promoter activity. In vitro binding assays demonstrate that both Fli-1 a nd Ets-1 form DNA-protein complexes with sequences present in COL1A2 promot er. Furthermore, Fli-1 binding to the COL1A2 is enhanced via Sp1-dependent interaction. Studies using Fli-1 dominant interference and DNA binding muta nts indicate that Fli-1 inhibition is mediated by both direct (DNA binding) and indirect (via protein-protein interaction) mechanisms and that Spl is an important mediator of the Fli-1 function. Furthermore, experiments using the Gal4 system in the context of different cell types as well as experime nts with the COL1A2 promoter in different cell lines demonstrate that the d irection and magnitude of the effect of Fli-1 is promoter- and cell context -specific. We propose that Fli-1 inhibits COL1A2 promoter activity by compe tition with Ets-1, In addition, we postulate that another factor (co-repres sor) may be required for maximal inhibition after recruitment to the Fli-1- Sp1 complex. We conclude that the ratio of Fli-1 to Ets-1 and the presence of co-regulatory proteins ultimately control ECM production in fibroblasts.