Massively parallel reporter assays combined with cell-type specific eQTL identified a functional melanoma risk variant in HIV-1 restriction gene, MX2 [MPRA NGS]
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ABSTRACT: Genome-wide association studies (GWAS) have identified twenty melanoma susceptibility loci. To identify susceptibility genes and variants simultaneously from multiple GWAS loci, we integrated massively-parallel reporter assays (MPRA) with melanocyte-specific expression quantitative trait locus (eQTL) profiling. We identified thirty-nine candidate functional variants displaying allelic transcriptional activity, of which nine from four loci were also correlated with local gene expression in melanocytes (CTSS, CASP8, MX2, and MAFF). Among these, we further characterized the locus in MX2 gene on chromosome band Chr21q22.3 and validated a functional variant, rs398206. The functional variant mediates allelic transcriptional activity via binding of the transcription factor, YY1. This allelic transcriptional regulation largely accounts for a significant cis-eQTL of the HIV-1 restriction gene, MX2, in primary melanocytes, where the melanoma risk-associated A allele is correlated with higher MX2 levels. Melanocyte-specific transgenic expression of human MX2 in a zebrafish model demonstrated an accelerated melanoma formation in a BRAFV600E background. Thus, using an efficient scalable approach to streamline GWAS follow-up functional studies, we uncovered a pleiotropic function of MX2 in melanoma susceptibility.
Project description:Genome-wide association studies (GWAS) have identified twenty melanoma susceptibility loci. To identify susceptibility genes and variants simultaneously from multiple GWAS loci, we integrated massively-parallel reporter assays (MPRA) with melanocyte-specific expression quantitative trait locus (eQTL) profiling. We identified thirty-nine candidate functional variants displaying allelic transcriptional activity, of which nine from four loci were also correlated with local gene expression in melanocytes (CTSS, CASP8, MX2, and MAFF). Among these, we further characterized the locus in MX2 gene on chromosome band Chr21q22.3 and validated a functional variant, rs398206. The functional variant mediates allelic transcriptional activity via binding of the transcription factor, YY1. This allelic transcriptional regulation largely accounts for a significant cis-eQTL of the HIV-1 restriction gene, MX2, in primary melanocytes, where the melanoma risk-associated A allele is correlated with higher MX2 levels. Melanocyte-specific transgenic expression of human MX2 in a zebrafish model demonstrated an accelerated melanoma formation in a BRAFV600E background. Thus, using an efficient scalable approach to streamline GWAS follow-up functional studies, we uncovered a pleiotropic function of MX2 in melanoma susceptibility.
Project description:Genome-wide association studies (GWAS) have identified twenty melanoma susceptibility loci. To identify susceptibility genes and variants simultaneously from multiple GWAS loci, we integrated massively-parallel reporter assays (MPRA) with melanocyte-specific expression quantitative trait locus (eQTL) profiling. We identified thirty-nine candidate functional variants displaying allelic transcriptional activity, of which nine from four loci were also correlated with local gene expression in melanocytes (CTSS, CASP8, MX2, and MAFF). Among these, we further characterized the locus in MX2 gene on chromosome band Chr21q22.3 and validated a functional variant, rs398206. The functional variant mediates allelic transcriptional activity via binding of the transcription factor, YY1. This allelic transcriptional regulation largely accounts for a significant cis-eQTL of the HIV-1 restriction gene, MX2, in primary melanocytes, where the melanoma risk-associated A allele is correlated with higher MX2 levels. Melanocyte-specific transgenic expression of human MX2 in a zebrafish model demonstrated an accelerated melanoma formation in a BRAFV600E background. Thus, using an efficient scalable approach to streamline GWAS follow-up functional studies, we uncovered a pleiotropic function of MX2 in melanoma susceptibility.
Project description:The most recent genome-wide association study (GWAS) of cutaneous melanoma identified 54 risk-associated loci, but functional variants and their target genes for most have not been established. Here, we performed massively parallel reporter assays (MPRA) using malignant melanoma and normal melanocyte cells and further integrated multi-layer annotation to systematically prioritize functional variants and susceptibility genes from these GWAS loci. Of 1,992 risk-associated variants tested in MPRA, we identified 285 from 42 loci (78% of the known loci) displaying significant allelic transcriptional activities in either cell type (FDR < 1%). We further characterized MPRA-significant variants by motif prediction, epigenomic annotation, and statistical/functional fine-mapping to create integrative variant scores, which prioritized one to six plausible candidate variants per locus for the 42 loci and nominated a single variant for 43% of these loci. Overlaying the MPRA-significant variants with genome-wide significant expression or methylation quantitative trait loci (QTLs) from melanocytes or melanomas identified candidate susceptibility genes for 60% of variants (172 of 285 variants). CRISPRi of top-scoring variants validated their cis-regulatory effect on the eQTL target genes, MAFF (22q13.1) and GPRC5A (12p13.1). Finally, we identified 36 melanoma-specific and 45 melanocyte-specific MPRA-significant variants, a subset of which are linked to cell-type-specific target genes. Analyses of transcription factor availability in MPRA datasets and variant-transcription factor interaction in eQTL datasets highlighted the roles of transcription factors in cell-type-specific variant functionality. In conclusion, MPRA along with variant scoring effectively prioritized plausible candidates for most melanoma GWAS loci and highlighted cellular contexts where the susceptibility variants are functional.
Project description:The most recent genome-wide association study (GWAS) of cutaneous melanoma identified 54 risk-associated loci, but functional variants and their target genes for most have not been established. Here, we performed massively parallel reporter assays (MPRA) using malignant melanoma and normal melanocyte cells and further integrated multi-layer annotation to systematically prioritize functional variants and susceptibility genes from these GWAS loci. Of 1,992 risk-associated variants tested in MPRA, we identified 285 from 42 loci (78% of the known loci) displaying significant allelic transcriptional activities in either cell type (FDR < 1%). We further characterized MPRA-significant variants by motif prediction, epigenomic annotation, and statistical/functional fine-mapping to create integrative variant scores, which prioritized one to six plausible candidate variants per locus for the 42 loci and nominated a single variant for 43% of these loci. Overlaying the MPRA-significant variants with genome-wide significant expression or methylation quantitative trait loci (QTLs) from melanocytes or melanomas identified candidate susceptibility genes for 60% of variants (172 of 285 variants). CRISPRi of top-scoring variants validated their cis-regulatory effect on the eQTL target genes, MAFF (22q13.1) and GPRC5A (12p13.1). Finally, we identified 36 melanoma-specific and 45 melanocyte-specific MPRA-significant variants, a subset of which are linked to cell-type-specific target genes. Analyses of transcription factor availability in MPRA datasets and variant-transcription factor interaction in eQTL datasets highlighted the roles of transcription factors in cell-type-specific variant functionality. In conclusion, MPRA along with variant scoring effectively prioritized plausible candidates for most melanoma GWAS loci and highlighted cellular contexts where the susceptibility variants are functional.
Project description:Most loci contributing to breast cancer susceptibility identified by the recent genome-wide association studies (GWAS) are predicted to have a regulatory function. Additionally, the early phases of the GWAS studies have generated long lists of possible candidates that need to be prioritised for follow-up studies. Integration of allelic expression mapping and disease association data should enable the identification of those GWAS hits with higher cis-regulatory potential. Our aims are (1) to assess how well functional data and disease risk are correlated and (2) to help prioritise and select the strongest candidates from the GWAS scan for further follow-up and functional analysis. We are performing genome-wide differential allelic expression (DAE) analysis to identify loci with cis-regulatory potential in sixty-four normal breast tissue samples. Using the Illumina Exon510S-Duo BeadChips, we have identified 34K informative SNPs of which approximately 8K (23.5%) displayed DAE. Two SNPs showed monoallelic expression suggesting possible new imprinted loci. We are mapping the cis-regulatory loci by fitting a linear regression model with permutations to DAE ratios vs genotype at SNPs within ±250kb of the RefSeq gene corresponding to the DAE SNP. We will combine our data with the UK GWAS1 and GWAS2 studies for breast cancer susceptibility, to generate a list of genes that show regulatory variation for further evaluation as candidates. This is the first genome-wide differential allelic expression study in normal breast tissue, and one of the first in a primary tissue. We predict that this will be a powerful approach to validate/identify susceptibility loci and to unravel some of the biology underlying breast cancer susceptibility. Allelic gene expression of normal breast sample from healthy controls.
Project description:To explore the roles of cell-type specific methylation QTL (meQTL) for melanoma GWAS annotation, we generated DNA methylation data from the same sample set as our previouse eQTL study including 106 primary melanocyte cultures. The Illumina Infinium 450k Human DNA methylation Beadchip v1.2 was used to obtain DNA methylation profiles across approximately 480,000 CpGs in 106 primary melanocyte cultures. To be able to identify the DNA methylation probes whose methylation levels are correlated with germline genetic variants including the ones associated with melanoma, meQTL analysis was performed in these 106 primary melanocyte cultures using the same method as we did for eQTL study.
Project description:Most loci contributing to breast cancer susceptibility identified by the recent genome-wide association studies (GWAS) are predicted to have a regulatory function. Additionally, the early phases of the GWAS studies have generated long lists of possible candidates that need to be prioritised for follow-up studies. Integration of allelic expression mapping and disease association data should enable the identification of those GWAS hits with higher cis-regulatory potential. Our aims are (1) to assess how well functional data and disease risk are correlated and (2) to help prioritise and select the strongest candidates from the GWAS scan for further follow-up and functional analysis. We are performing genome-wide differential allelic expression (DAE) analysis to identify loci with cis-regulatory potential in sixty-four normal breast tissue samples. Using the Illumina Exon510S-Duo BeadChips, we have identified 34K informative SNPs of which approximately 8K (23.5%) displayed DAE. Two SNPs showed monoallelic expression suggesting possible new imprinted loci. We are mapping the cis-regulatory loci by fitting a linear regression model with permutations to DAE ratios vs genotype at SNPs within ±250kb of the RefSeq gene corresponding to the DAE SNP. We will combine our data with the UK GWAS1 and GWAS2 studies for breast cancer susceptibility, to generate a list of genes that show regulatory variation for further evaluation as candidates. This is the first genome-wide differential allelic expression study in normal breast tissue, and one of the first in a primary tissue. We predict that this will be a powerful approach to validate/identify susceptibility loci and to unravel some of the biology underlying breast cancer susceptibility.
Project description:Genome-wide association studies (GWAS) have identified over 300 loci associated with the inflammatory bowel diseases (IBD), but putative causal genes for most are unknown. We conducted the largest disease-focused expression quantitative trait loci (eQTL) analysis using colon tissue from 252 IBD patients to determine genetic effects on gene expression and potential contribution to IBD. Combined with two non-IBD colon eQTL studies, we identified 194 potential target genes for 108 GWAS loci. eQTL in IBD tissue were enriched for IBD GWAS loci colocalizations, provided novel evidence for IBD-associated genes such as ABO and TNFRSF14, and identified additional target genes compared to non-IBD tissue eQTL. IBD-associated eQTL unique to diseased tissue had distinct regulatory and functional characteristics with increased effect sizes. Together, these highlight the importance of eQTL studies in diseased tissue for understanding functional consequences of genetic variants, and elucidating molecular mechanisms and regulation of key genes involved in IBD.
Project description:Genome-wide association studies (GWAS) have identified multiple lung cancer risk loci including those that are distinct in the major histological types. However, most of these loci have not been functionally characterized. Here we employed massively parallel reporter assays (MPRA) to assess allelic transcriptional activity of risk-associated variants en masse. We tested 2,245 variants in 42 loci from 3 recent GWASs of East Asian and European populations in the context of lung adenocarcinoma and squamous cell carcinoma cells while incorporating exposure to a tobacco-smoke carcinogen, benzo[a]pyrene. At FDR < 0.01, we identified 844 MPRA-significant variants with allelic transcriptional activity across 88% of lung cancer loci. Further variant scoring using lung-specific epigenomic annotation demonstrated that 63% of the loci harbored multiple equally functional variants in linkage disequilibrium. Cell-type-specific variants were observed in 72% of the loci, a subset of which aligned with histology-specific association in the GWAS. Distinct subsets of transcription factors were predicted to bind to cell-type-specific variants and those affecting multiple GWAS loci in trans. Linking MPRA-significant variants to target genes based on four different approaches identified candidate susceptibility genes including essential genes for lung cancer cell growth. CRISPR-interference of a high-scoring MPRA-significant variant validated multiple variant-gene connections from different datasets, including RTEL1, SOX18, and ARFRP1. Our data provide a comprehensive catalog of functional characterization of lung cancer GWAS loci and the molecular basis of heterogeneity and polygenicity of lung cancer susceptibility.
Project description:Using ChIP-seq for p300 and H3K4me1, we identified 2,489 putative melanocyte enhancer loci in the mouse genome. We demonstrated that these putative enhancers are evolutionarily constrained, enriched for sequence motifs predicted to bind key melanocyte transcription factors, located near genes relevant to melanocyte biology, and capable of driving reporter gene expression with high frequency in cultured melanocytes and in melanocytes of transgenic zebrafish. ChIP-seq for EP300 and H3K4me1 in the mouse melanocyte cell line melan-a.