REGULATION OF THE ALPHA-2(I) COLLAGEN GENE-TRANSCRIPTION IN FAT-STORING CELLS DERIVED FROM A CIRRHOTIC LIVER

Fat-storing cells (FSC) are the main producers of type I collagen in b oth normal and fibrotic livers. In order to elucidate the molecular me chanisms controlling collagen expression in FSC, we examined the trans cription of the alpha 2(I) collagen gene (COL1A2) in two distinct FSC clones, CFSC-2G and CFSC-5H, derived from a single CCl4-induced cirrho tic liver. The phenotype of CFSC-2G resembles freshly isolated FSC, wh ereas that of CFSC-5H mimics activated myofibroblasts. Cell transfecti on experiments showed that the upstream sequence between nucleotides - 378 and -183 is essential for COL1A2 transcription in both FSC clones. This is the same promoter region that is transcriptionally active and contains the binding site of a multimeric protein complex that mediat es TGF-beta stimulation of COL1A2 expression in dermal fibroblasts. We therefore examined the relative levels of endogenous and transfected COL1A2 transcription and their response to TGF-beta treatment in the t wo FSC clones. The results showed that CFSC-5H expresses a significant ly higher level of the COL1A2 mRNA than CFSC-2G. They also showed that TGF-beta treatment increases both endogenous and transfected COL1A2 t ranscription in CFSC-2G but not in CFSC-5H. Interestingly, nuclear pro teins from both FSC clones bind to the TGF-beta-responsive element mor e strongly than those from dermal fibroblasts. Altogether, the data su ggest that collagen production in CFSC-5H cells has been already activ ated by the autocrine stimulation of TGF-beta. In contrast, CFSC-2G ce lls are only partially activated but can be easily recruited to produc e collagen when stimulated by exogenous TGF-beta. Thus, we conclude th at FSC activation during hepatofibrogenesis is probably a multistep pr ocess that involves autocrine and paracrine stimulation by TGF-beta.