Differential microRNA regulation of HLA-C expression and its association with HIV control.

The HLA-C locus is distinct relative to the other classical HLA class I loci in that it has relatively limited polymorphism, lower expression on the cell surface, and more extensive ligand-receptor interactions with killer-cell immunoglobulin-like receptors. A single nucleotide polymorphism (SNP) 35 kb upstream of HLA-C (rs9264942; termed -35) associates with control of HIV, and with levels of HLA-C messenger RNA transcripts and cell-surface expression, but the mechanism underlying its varied expression is unknown. We proposed that the -35 SNP is not the causal variant for differential HLA-C expression, but rather is marking another polymorphism that directly affects levels of HLA-C. Here we show that variation within the 3' untranslated region (UTR) of HLA-C regulates binding of the microRNA hsa-miR-148 to its target site, resulting in relatively low surface expression of alleles that bind this microRNA and high expression of HLA-C alleles that escape post-transcriptional regulation. The 3' UTR variant associates strongly with control of HIV, potentially adding to the effects of genetic variation encoding the peptide-binding region of the HLA class I loci. Variation in HLA-C expression adds another layer of diversity to this highly polymorphic locus that must be considered when deciphering the function of these molecules in health and disease.

Genetic modifiers of neurofibromatosis type 1-associated café-au-lait macule count identified using multi-platform analysis.

Neurofibromatosis type 1 (NF1) is an autosomal dominant, monogenic disorder of dysregulated neurocutaneous tissue growth. Pleiotropy, variable expressivity and few NF1 genotype-phenotype correlates limit clinical prognostication in NF1. Phenotype complexity in NF1 is hypothesized to derive in part from genetic modifiers unlinked to the NF1 locus. In this study, we hypothesized that normal variation in germline gene expression confers risk for certain phenotypes in NF1. In a set of 79 individuals with NF1, we examined the association between gene expression in lymphoblastoid cell lines with NF1-associated phenotypes and sequenced select genes with significant phenotype/expression correlations. In a discovery cohort of 89 self-reported European-Americans with NF1 we examined the association between germline sequence variants of these genes with café-au-lait macule (CALM) count, a tractable, tumor-like phenotype in NF1. Two correlated, common SNPs (rs4660761 and rs7161) between DPH2 and ATP6V0B were significantly associated with the CALM count. Analysis with tiled regression also identified SNP rs4660761 as significantly associated with CALM count. SNP rs1800934 and 12 rare variants in the mismatch repair gene MSH6 were also associated with CALM count. Both SNPs rs7161 and rs4660761 (DPH2 and ATP6V0B) were highly significant in a mega-analysis in a combined cohort of 180 self-reported European-Americans; SNP rs1800934 (MSH6) was near-significant in a meta-analysis assuming dominant effect of the minor allele. SNP rs4660761 is predicted to regulate ATP6V0B, a gene associated with melanosome biology. Individuals with homozygous mutations in MSH6 can develop an NF1-like phenotype, including multiple CALMs. Through a multi-platform approach, we identified variants that influence NF1 CALM count.

Novel dithiolethione-modified nonsteroidal anti-inflammatory drugs in human hepatoma HepG2 and colon LS180 cells.

PURPOSE: Nonsteroidal anti-inflammatory drugs (NSAID) are promising chemopreventive agents against colon and other cancers. However, the molecular basis mediated by NSAIDs for chemoprevention has not been fully elucidated. Environmental carcinogens induce DNA mutation and cellular transformation; therefore, we examined the effect of NSAIDs on carcinogenesis mediated by the aryl hydrocarbon receptor signaling pathway. In this study, we investigated the activities of a new class of NSAIDs containing dithiolethione moieties (S-NSAID) on both arms of carcinogenesis. EXPERIMENTAL DESIGN: We investigated the effects of the S-NSAIDs, S-diclofenac and S-sulindac, on carcinogen activation and detoxification mechanisms in human hepatoma HepG2 and human colonic adenocarcinoma LS180 cells. RESULTS: We found that S-diclofenac and S-sulindac inhibited the activity and expression of the carcinogen activating enzymes, cytochromes P-450 (CYP) CYP1A1, CYP1B1, and CYP1A2. Inhibition was mediated by transcriptional regulation of the aryl hydrocarbon receptor (AhR) pathway. The S-NSAIDs down-regulated carcinogen-induced expression of CYP1A1 heterogeneous nuclear RNA, a measure of transcription rate. Both compounds blocked carcinogen-activated AhR from binding to the xenobiotic responsive element as shown by chromatin immunoprecipitation. S-diclofenac and S-sulindac inhibited carcinogen-induced CYP enzyme activity through direct inhibition as well as through decreased transcriptional activation of the AhR. S-sulindac induced expression of several carcinogen detoxification enzymes of the glutathione cycle including glutathione S-transferase A2, glutamate cysteine ligase catalytic subunit, glutamate cysteine ligase modifier subunit, and glutathione reductase. CONCLUSIONS: These results indicate that S-diclofenac and S-sulindac may serve as effective chemoprevention agents by favorably balancing the equation of carcinogen activation and detoxification mechanisms.

Sulindac and its metabolites induce carcinogen metabolizing enzymes in human colon cancer cells.

Sulindac is a nonsteroidal antiinflammatory drug that has been demonstrated to be a potent chemopreventive agent against colorectal cancer in both human and animal models. In vivo, sulindac may be reversibly reduced to the active antiinflammatory compound, sulindac sulfide, or irreversibly oxidized to sulindac sulfone. Sulindac has also been shown to inhibit polycyclic aromatic hydrocarbon (PAH)-induced cancer, but the molecular mechanisms of its antitumor effect remain unclear. In this study, we investigated the effects of sulindac and its metabolites on the expression of enzymes that metabolize and detoxify PAHs in 2 human colon cancer cell lines, LS180 and Caco-2. Sulindac and sulindac sulfide induced a sustained, concentration-dependent increase in CYP enzyme activity as well as an increase in the mRNA levels of CYP1A1, CYP1A2 and CYP1B1. Sulindac and sulindac sulfide induced the transcription of the CYP1A1 gene, as measured by the level of heterogeneous nuclear CYP1A1 RNA and verified by the use of actinomycin D as a transcription inhibitor. Chromatin immunoprecipitation assays demonstrated that sulindac and sulindac sulfide also increased the nuclear level of activated aryl hydrocarbon receptor, the transcription factor which mediates CYP expression. Additionally, sulindac and both metabolites increased the activity and mRNA expression of the carcinogen detoxification enzyme NAD(P)H:quinone oxidoreductase, as well as the expression of UDP-glucuronosyltransferase mRNA. These results show an overall upregulation of carcinogen metabolizing enzymes in colon cancer cells treated with sulindac, sulindac sulfide and sulindac sulfone that may contribute to the established chemoprotective effects of these compounds.

Sulindac regulates the aryl hydrocarbon receptor-mediated expression of Phase 1 metabolic enzymes in vivo and in vitro.

Sulindac, a widely used non-steroidal anti-inflammatory drug (NSAID), has been shown to inhibit chemically induced carcinogenesis in animal models. In the present study, we have investigated the molecular mechanism by which sulindac affects the activity and expression of the enzymes that mediate the initial detoxification steps of many environmental carcinogens, the cytochromes P450 1A1, 1A2 and 1B1. Sulindac treatment of Sprague-Dawley rats resulted in a dose-dependent increase in hepatic cytochrome P450 (CYP) enzyme activity and in the expression of hepatic CYPs 1A1 and 1B1 mRNA. In the HepG2 human liver cancer cell line, sulindac caused a sustained, dose-dependent increase in CYP enzyme activity. Sulindac treatment resulted in a profound, dose-dependent increase in CYP 1A1 mRNA and a modest increase in 1A2 mRNA. The increase in CYP 1A1 mRNA induced by sulindac was, like enzyme activity, sustained for several days after the initial treatment. Sulindac induced the transcription of the CYP1A1 gene, as measured by the level of heterogeneous nuclear 1A1 RNA and by actinomycin D chase experiment. Since the transcription of CYP1A1 is under the control of the aryl hydrocarbon receptor (AhR), we examined the ability of sulindac to activate the receptor. Sulindac bound to the AhR, as measured by ligand-binding assay, and induced the binding of the AhR with the xenobiotic-responsive element present in the promoter region of the CYP1A1 gene. These results are the first demonstration that NSAIDs modulate carcinogen metabolic enzymes and provide a novel mechanism to explain the established chemopreventive activity of sulindac.