TNF-ALPHA INHIBITS LIVER COLLAGEN-ALPHA(1)(I) GENE-EXPRESSION THROUGHA TISSUE-SPECIFIC REGULATORY REGION

Although tumor necrosis factor-alpha (TNF-alpha) inhibits collagen-alp ha(1)(I) gene expression in cultured hepatic stellate cells, assessmen t of its effects on hepatic collagen expression is complicated by the confounding variables of tissue necrosis and inflammation. Therefore, we analyzed whether chronically elevated serum TNF-alpha affects const itutive hepatic collagen metabolism in vivo by inoculating nude mice w ith Chinese hamster ovary (CHO) cells secreting TNF-alpha (TnF-alpha m ice) or with control CHO cells (control mice). Before the onset of wei ght loss, collagen synthesis and collagen gene expression were inhibit ed in the liver of TNF-alpha mice. In transgenic mice, after 8 h, TNF- alpha (500 ng at 0 and 5 h) inhibited the liver expression of the coll agen-alpha(1)(I)-human growth hormone (hGH) transgene containing the f irst intron and -440 bp of the 5' region. Similarly, in cultured hepat ic stellate cells isolated from these transgenic animals, the -440 bp collagen-alpha(1)(I)-hGH transgene was responsive to TNF-alpha treatme nt independent of the activation of these cells. Transfection studies in stellate cells allowed further characterization of this TNF-alpha-r esponsive segment to -220 bp of the 5' region. Because in the skin the inhibitory effect of TNF-alpha involves a regulatory region of the co llagen-alpha(1)(I) gene beyond -440 bp, we herein identify a novel tis sue-specific regulation of collagen-alpha(1)(I) gene by TNF-alpha.