ABSTRACT:Patients with chronic hepatitis C viral infection underwent liver biopsies and laboratory studies for evaluation and to determine subsequent treatment. Changes in status of drug metabolism and disposition may vary with chronic hepatitis C stage and should be assessed. Total RNA was extracted from liver biopsy specimens (n ‫؍‬ 63) and reverse transcribed to yield cDNA. Relative mRNA levels of drug-metabolizing enzymes, transporters, nuclear receptors, and proinflammatory cytokines were analyzed with normalization to glyceraldehyde 3-phosphate dehydrogenase expression. mRNAs encoding cytochromes P450 1A2, 2E1, and 3A4, and drug transporters, Na ؉ -taurocholate-cotransporting polypeptide, organic anion-transporting peptide-C, and organic cation transporter 1 showed remarkable decreases, and tumor necrosis factor-␣ showed an increase according to fibrosis stage progression. HepG2 cells and primary hepatocytes of two human individuals were treated with interleukin 1␤, interleukin 6, or tumor necrosis factor-␣. CYP1A2 and Na ؉ -taurocholate-cotransporting polypeptide mRNA levels significantly decreased in HepG2 cells with interleukin 1␤ and interleukin 6 treatments. CYP2E1 and organic cation transporter 1 mRNA levels significantly decreased with tumor necrosis factor-␣ treatment only in HepG2. These results suggested that down-regulation of CYP1A2, 2E1, and 3A4, and drug transporters, Na ؉ -taurocholate-cotransporting polypeptide, organic anion-transporting peptide-C, and organic cation transporter 1, manifested in livers of patients with chronic hepatitis C viral infection, was associated, at least in part, with the elevated production of proinflammatory cytokines, including tumor necrosis factor-␣.Infection and inflammation generally cause a decrease in hepatic capacity for drug metabolism and disposition. Using lipopolysaccharide models of hepatic inflammation, a number of investigators have demonstrated decreases in the expression of various drug-metabolizing enzymes (Iber et al., 1999;Renton, 2004). Bacterial and viral infections are associated with the induction of various cytokines, including interleukins (ILs) 1␤ and 6, tumor necrosis factor (TNF)-␣, and interferon-␥, which decrease the level of hepatic drug-metabolizing enzymes (Iber et al., 1999;Renton, 2004). Hepatitis C virus (HCV) infection was reported to cause changes in levels of drugmetabolizing enzymes cytochrome P450 2E1 (Gochee et al., 2003), an oxidative stress-related enzyme, and glutathione peroxidase (Levent et al., 2006); and nuclear receptors, including peroxisome proliferator-

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The SGS1 gene of Saccharomyces cerevisiae is a homologue for the Bloom's syndrome and Werner's syndrome genes. The disruption of the SGS1 gene resulted in very poor sporulation, and the majority of the cells were arrested at the mononucleated stage. The recombination frequency measured by a return-to-growth assay was reduced considerably in sgs1 disruptants. However, double-strand break formation, which is a key event in the initiation of meiotic DNA recombination, occurred; crossover and noncrossover products were observed in the disruptants, although the amounts of these products were slightly decreased compared with those in wild-type cells. The spores produced by sgs1 disruptants showed relatively high viability. The sgs1 spo13 double disruptants sporulated poorly, like the sgs1 disruptants, but spore viability was reduced much more than with either sgs1 or spo13 single disruptants. Disruption of the RED1 or RAD17 gene partially alleviated the poorsporulation phenotype of sgs1 disruptants, indicating that portions of the population of sgs1 disruptants are blocked by the meiotic checkpoint. The poor sporulation of sgs1 disruptants was complemented with a mutated SGS1 gene encoding a protein lacking DNA helicase activity; however, the mutated gene could suppress neither the sensitivity of sgs1 disruptants to methyl methanesulfonate and hydroxyurea nor the mitotic hyperrecombination phenotype of sgs1 disruptants.Proteins having DNA helicase activity play important roles in many processes involving DNA, such as replication, repair, and recombination. The product of the Escherichia coli recQ gene, which has DNA helicase activity, is a member of the RecF pathway of recombination. The recF mutants lack conjugal recombination proficiency and UV resistance in the background of recBCD (lacking active endonuclease V) and sbcBC (lacking active exonuclease I), and recQ deletion mutants in the background of recBC sbcBC display UV and methyl methanesulfonate (MMS) sensitivity (22,30).We (38) and Puranam and Blackshear (32) cloned cDNAs encoding a RecQ homologue of human cells, DNA helicase Q1 and RECQL, respectively. Since these are the same gene, we tentatively designated this gene RECQL1. We also cloned a gene of Saccharomyces cerevisiae encoding a protein having DNA helicase motifs with high homology to those of E. coli RecQ and human ATPase RECQL1. This gene soon was found to be identical to the SGS1 (slow growth suppressor 1) gene.A mutant allele of the SGS1 gene was identified as a suppressor of the slow-growth phenotype of top3 mutants (11). Two-hybrid experiments indicated that the yeast Sgs1 protein interacts with DNA topoisomerase III (Top3) (11) as well as DNA topoisomerase II (50). The protein encoded by the SGS1 gene has seven conserved helicase motifs, and Sgs1 was shown to actually have DNA helicase activity (3, 23). Deletion mutants of the SGS1 gene showed a reduction in the fidelity of chromosome segregation during mitosis and meiosis (50, 51); mitotic hyperrecombination phenotypes in interchromosomal homo...

The SGS1 gene of Saccharomyces cerevisiae is homologous to the genes that are mutated in Bloom's syndrome and Werner's syndrome in humans. Disruption of SGS1 results in high sensitivity to methyl methanesulfonate (MMS), poor sporulation, and a hyper-recombination phenotype including recombination between heteroalleles. In this study, we found that SGS1 forms part of the RAD52 epistasis group when cells are exposed to MMS. Exposure to DNA-damaging agents causes a striking, Rad52-dependent, increase in heteroallelic recombination in wild-type cells, but not in sgs1 disruptants. However, in the absence of DNA damage, the frequency of heteroallelic recombination in sgs1 disruptants was several-fold higher than in wild-type cells, as described previously. These results imply a function for Sgs1: it acts to suppress spontaneous heteroallelic recombination, and to promote DNA damage-induced heteroallelic recombination.

The SGS1 gene of Saccharomyces (cerevisiae is a homologue of the genes affected in Bloom's syndrome, Werner's syndrome, and Rothmund-Thomson's syndrome. Disruption of the SGS1 gene is associated with high sensitivity to methyl methanesulfonate (MMS) and hydroxyurea (HU), and with hyper-recombination phenotypes, including interchromosomal recombination between heteroalleles. SGS1 encodes a protein which has a helicase domain similar to that of Escherichia coli RecQ. A comparison of amino acid sequences among helicases of the RecQ family reveals that Sgs1,WRN, and BLM share a conserved region adjacent to the C-terminal part of the helicase domain (C-terminal conserved region). In addition, Sgs1 contains two highly charged acidic regions in its N-terminal region and the HRDC (helicase and RNaseD C-terminal) domain at its C-terminal end. These regions were also found in BLM and WRN, and in Rqh1 from Schizosaccharomyces pombe. In this study, we demonstrate that the C-terminal conserved region, as well as the helicase motifs, of Sgs1 are essential for complementation of MMS sensitivity and suppression of hyper-recombination in sgs1 mutants. In contrast, the highly charged acidic regions, the HRDC domain, and the C-terminal 252 amino acids were dispensable for the complementation of these phenotypes. Surprisingly, the N-terminal 45 amino acids of Sgs1 were absolutely required for the suppression of the above phenotypes. Introduction of missense mutations into the region encoding amino acids 4-13 abolished the ability of Sgsl to complement MMS sensitivity and suppress hyper-recombination in sgs1 mutants, and also prevented its interaction with Top3, indicating that interaction with Top3 via the N-terminal region of Sgs1 is involved in the complementation of MMS sensitivity and the suppression of hyper-recombination.