MODULATION OF HUMAN ALPHA-1(I) PROCOLLAGEN GENE ACTIVITY BY INTER-ACTION WITH SP1 AND SP3 TRANSCRIPTION FACTORS IN-VITRO

In previous work, we delineated a proximal region of the human al(I) c ollagen gene (COL1A1) promoter necessary to direct its basal transcrip tion in fibroblasts. This region has potential recognition sites for a variety of DNA-binding proteins. Here, we show that the - 129/- 107-b p sequence in this region of the promoter, which harbors an inverted C CAAT moth closely linked to a GC-rich direct repeat and is perfectly c onserved between mouse and human, specifically bound the transcription factors Sp1, Sp3, and CTF/NF-1 in nuclear extracts from human skin an d lung fibroblasts. Drosophila Schneider L2 cells lacking endogenous S p activity were used to investigate the effect of expression of Sp or CTF/NF-1 transcription factors on COL1A1 promoter activity. Expression of Sp1 caused potent trans-activation of a COL1A1 promoter (-174 to 42 bp). In contrast, expression of Sp3, which binds to the same recogn ition sites as Sp1, and CTF/NF-1 stimulated COL1A1 promoter activity o nly at higher concentrations, and Sp2 did not transactivate. Expressio n of a 10-fold excess of Sp3, but not CTF/NF-1 or Sp2, abrogated the s timulation of COL1A1 promoter activity induced by Sp1. TGF-beta at con centrations previously shown to increase COL1A1 transcription caused a decrease in the relative amount of Sp3 in fibroblast nuclear extracts . These results suggest that both Sp1 and Sp3 bind to the proximal COL 1A1 promoter and stimulate its activity; however, their interaction wi th each other may result in repression of Sp1-induced COL1A1 transcrip tion. Alterations in the relative amounts or DNA-binding activities of these transcription factors in a cell- or signal-specific manner may contribute to the control of transcription from the COL1A1 promoter. T he present findings, and recent observations implicating Sp1 and its h omologs in regulating the expression of several collagen genes, sugges t that the family of Sp1 transcription factors play a role in physiolo gical and pathological modulation of connective tissue accumulation. ( C) 1998 Elsevier Science B.V. All rights reserved.