Cellular localization of hepatic cytochrome 1B1 expression and its regulation by aromatic hydrocarbons and inflammatory cytokines

Cytochrome P450 1B1 (CYP1B1) is an activator of several xenobiotics and is induced in the liver upon experimental exposure to aromatic hydrocarbons. S ince its cellular localization and regulation are incompletely clarified, C yp1B1 expression and inducibility by 9,10-dimethyl-1,2-benzanthracene (DMBA ) and inflammatory cytokines were investigated in different rat liver cell populations in vitro and in the liver during hepatocellular injury. Express ion of Cyp1B1 was studied by Northern blot analysis in hepatic stellate cel ls (HSCs), myofibroblasts (MFs), Kupffer cells (KCs), and hepatocytes at va rious time points of primary cultures and in acutely damaged rat liver (car bon tetrachloride model). Enzyme inducibility was assessed by incubation of cells with DMBA as well as, in the case of HSCs, with tumor necrosis facto r-alpha (TNF-alpha) and transforming growth factor beta 1 (TGF beta 1). Cyp 1B1 messengers were expressed at high levels by HSCs and MFs, whereas const itutive expression was not detectable in KCs or in hepatocytes. Cyp1B1-spec ific mRNA were expressed at highest levels in HSCs at an early stage of act ivation (2 days after plating) and were diminished upon further activation. DMBA strongly enhanced Cyp1B1 gene expression in HSCs, MFs, and in hepatoc ytes at day 3 of primary cultures, but not in hepatocytes at day 1, or in K Cs. The inflammatory cytokine TNF-alpha enhanced the Cyp1B1 gene expression in HSCs, either when administered alone or in addition to DMBA, while TGF beta 1 did not affect Cyp1B1 expression, even after DMBA induction. We conc lude that HSCs and MFs seem to be the major cellular sources of hepatic CyP 1B1 expression and that the constitutive expression of the Cyp1B1 gene and the responsiveness to DMBA stimulation differ between mesenchymal and paren chymal liver cells, indicating a cell-specific regulation of Cyp1B1 gene ex pression. Interestingly, TNF-alpha is a potent stimulator of the Cyp1B1 gen e in HSCs and acts in concert with DMBA. BIOCHEM PHARMACOL 58;1:157-165, 19 99. (C) 1999 Elsevier Science Inc.