Project description:Changes in chromatin organization are associated with resistance to anti-cancer drugs, such as platinum-based chemotherapy used as the primary treatment of ovarian cancer. We have examined the genomic distribution of chromatin accessibility changes, and relationship to gene expression changes, occurring during acquisition of resistance in vivo of high grade serous ovarian cancer (HGSOC) patients and whether this associates with genomic DNA damage distribution. Using matched chemo-sensitive and chemo-resistant ovarian cell lines isolated from HGSOC patients before and following acquisition of clinical resistance to platinum-based chemotherapy, we have examined the relationship between chromatin accessibility by ATAC-seq, platinum-DNA adduct distribution by Pt-Exo-seq and gene expression by RNA-seq. We have correlated chromatin changes between the lines at gene promoters, CpG islands, enhancer sequences and other genomic regions with changes in gene expression and platinum-DNA adduct distribution. We observe chromatin conformation differences following acquisition of platinum-resistance, with the HGSOC resistant lines clustering together, separately from their respective sensitive counterparts. Resistant lines show altered chromatin accessibility at intergenic regions, but less so at gene promoters. Super-enhancers, as defined by clusters of cis-regulatory elements, at these intergenic regions show chromatin changes that are associated with altered expression of linked genes, with enrichment for genes involved in the Fanconi anemia/BRCA DNA damage response pathway. Genome-wide distribution of platinum adducts associates with the chromatin changes and distinguish sensitive from resistant lines. Regions incurring fewer platinum-adducts showed a significant reduction in accessibility the resistant HGSOC cell line PEO4 compared to the sensitive PEO1 counterpart. Surprisingly, regions showing increased damage in PEO4 had an even greater reduction in accessibility. In the resistant line, we observe fewer adducts around gene promoters and more adducts at intergenic regions. In cell lines derived from patients following acquisition of clinical resistance to platinum-based chemotherapy, chromatin changes at super-enhancers correlate with gene expression changes in DNA repair pathways known to influence platinum sensitivity. Although cisplatin is a relatively non-specific DNA damaging agent, there are consistent differences in distribution of adducts between the matched sensitive and resistant ovarian cell lines, which is independent of the overall level of adducts formed.

Project description:Administration of tamoxifen (TAM) as breast cancer adjuvant therapy is associated with a 50% reduction in breast cancer risk and an increase in endometrial cancer risk. To investigate underlying mechanisms, we documented TAM-induced gene expression changes in cultured normal human mammary epithelial cell (NHMEC) strains (numbered 5, 16 and 40) established from tissue taken at reduction mammoplasty from three different individuals. Cells exposed to 0 and 10 uM TAM for 48 hours were evaluated for survival, TAM-DNA adduct formation by TAM-DNA chemiluminescence immunoassay (CIA), and gene expression changes using DNA-oligonucleotide microarray and real time reverse transcriptase-PCR (RT-PCR). At 48 hr, cells exposed to 10 uM TAM were 78% viable, respectively, and there were no measurable TAM-DNA adducts (limit of detection [LOD] = 0.3 adducts/10^8 nucleotides). For microarray analysis, RNA was extracted from cells exposed on three occasions to 10 uM TAM and the corresponding oligonucleotide probes were labeled with fluorescent dyes and hybridized to NCI microarrays (>20,000 human genes). Expression changes of > 3-fold were considered significant, and by these criteria, thirteen genes were up-regulated and one was down-related in NHMEC strain 16, seventeen genes were up-regulated in strain 05, and eleven genes were up-regulated in strain and 40. Elements that were up-regulated in all three cell strains included several interferon-induced genes (IFITM1, IFIT1, IFNA1, MXI and GIP3), and a potassium ion channel (KCNJ1). No significant expression changes were found for genes related to estrogen or xenobiotic metabolism. RT-PCR revealed TAM-induced up-regulation of the five genes of interest, and interferon á (IFNA1), in all three NHMEC strains, with the exception of GIP3 and MX1, which were unchanged in strain 40. The magnitude of TAM-induced up-regulation ranked: strain 16 > strain 05> strain 40. The consistent induction of interferon-related genes in all three NHMEC strains suggests that, in addition to hormonal effects, TAM exposure may enhance immune response, through interferon induction, in normal breast tissue. RNA was extracted from three cell strains (NHMEC 98016, 98040 and 99005) and exposed on three separate occasions to 10 uM TAM. Comparisons were made using 16 arrays with 8 dye swaps for cell strain NHMEC 99005, 9 arrays with 4 dye swaps for NHMEC 98016, and 12 arrays with 6 dye swaps for NHMEC 98040.

Dataset Information

Discovery and visualization of uncharacterized drug-protein adducts using mass spectrometry

Publications

Discovery and Visualization of Uncharacterized Drug-Protein Adducts Using Mass Spectrometry.

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