THE JOURNAL OF BlOLOGICAL CHEMISTRY

Regulation of the procollagen type I (Proal) gene in cultured Ito cells by diverse cytokines was studied. Specifically, we have examined the effect of interleukin-1/3 (IL-lf¡), tumor necrosis factor a (TNFa), and transforming growth factor /3 (TGF/3) on collagen biosynthesis, levéis of Proal(I) mRNA, and rate of transcription of Proa 1(1) gene. TGF/? stimulated procollagen synthesis at least 2-fold at every concentration tested (5-20 ng/ml), whereas TNFa inhibited it at the same concentrations. In contrast to what occurs in dermal fibroblasts, IL-1(8 (5—20 units/ml) preferentially inhibited procollagen production as measured by I^HIproline incorporation. A similar pattern was obtained when total protein synthesis was analyzed by [25S]methionine radiolabeling. Interestingly, while TGF/3-treated cells exhibited greater than 3-fold increase in steady-state levéis of Proal(I) mRNA, the treatment with IL-1 had no effect on procollagen mRNA levéis. TNFa treatment resulted in a 2-fold decrease in the amount of collagen mRNA. The treatment with combinations of cytokines indicated that collagen gene expression in Ito cells is differentially regulated by these cytokines. Furthermore, nuclear run-off transcription experiments were performed. The results obtained suggest that TGF/3 regulates increasing collagen type I gene expression at transcriptional levéis, and TNFa inhibits the transcriptional rate of Proal(I) gene. It is noteworthy that IL-1/? acts on collagen type I gene regulation by a sepárate mechanism at a posttranscriptional level. inflammation (5), and it has been suggested that lipocytes might be involved in capillarization of the sinusoids (6). Regardiess of the etiology, the deposition of interstitial type I and type III collagens into the subendothelial space of Disse is a salient feature and appears to be a critical early event. This process (7), referred to as "capillarization" ofthe sinusoids, is associated with deterioration of liver function in patients with hepatic cirrhosis (8) and contributes significantly to hepatic failure in CCLrtreated rats (9). Because of the strategic location of lipocytes in the space of Disse and the observations that activated lipocytes may be the primary collagen producing cells in damaged liver, it is thought that Ito cells play a central role in the development of hepatic fibrosis (6, 10). Enhanced lipocyte collagen formation is likely to occur not oniy by a direct stimulation of collagen production per cell, but aiso by an increase in the cell number via enhanced proliferation or directed migration. Thus, the rate of biosynthesis of collagen by Ito cells may be regulated by: (a) cytokines, such as TGFft,1 TNFa, IL-1,8 (11, 12), retinoids (13), and acetaldehyde (14), and (b) extracellular matrix itself, which depending on its composition, maintains quiescence or promotes activation (4). Despite existing information regarding the effect of soluble factors on lipocyte collagen production, littie is known about the molecular mechanisms and the levéis of gene regulation involved in the process of lipocyte activation. We summarize experiments which demónstrate the involvement of complex transcriptional and posttranscriptional mechanisms by which collagen type I gene expression is modulated by IL-1,8, TNFo-, and TGF|8 in cultured lipocytes.