Tiirikainen, Maarit

Abstract Alterations in the expression of microRNAs (miRNAs) contribute to the development and progression of colon cancer, which arises from the accumulation of genetic and epigenetic alterations in the colon tissue. With the advent of next-generation sequencing (NGS), new depths can be reached, allowing for comprehensive profiling of known and novel miRNAs. To profile the miRNAs and their associated target genes in colon cancer, we examined differential expression of miRNAs and predicted target genes between tumor and normal tissue of microsatellite stable (MSS) and CpG island methylator phenotype (CIMP)-negative colon cancer. Ten fresh-frozen colon tumors and 10 adjacent normal mucosa were profiled for miRNAs using the SOLiD NGS platform and mRNA expression analysis was conducted using Affymetrix arrays. To identify differentially expressed miRNAs in tumor versus normal tissue, analysis of variance was conducted that included Bonferroni correction. Integrated expression analysis of miRNAs and their target mRNAs was conducted using Pearson's correlation and the Benjamini and Hochberg's false discovery rate. Both analyses were done using Partek Genomics Suite software. Nineteen miRNAs were significantly differentially expressed in tumor versus normal tissue (fold change ≥ ±2 and p<0.05). Six of these 19 miRNAs have previously been associated with colon cancer (miR-30a, miR-31, miR-135b, miR-182, miR-183 and miR-202). Integrated analysis of miRNA and predicted target mRNA expression yielded 97 significantly correlated miRNA::mRNA pairs for 14 miRNAs with 92 genes (absolute r = 0.71–0.88, q<0.05). Within these miRNA::mRNA pairs, expression levels of the 6 colon cancer-associated miRNAs were correlated with 33 target genes and 8 miRNAs newly identified to be differentially expressed in colon cancer were correlated with 57 target genes. The top functional Ingenuity Pathway Analysis gene ontology categories (p<0.05) for the 92 genes were gastrointestinal disease (18 genes), genetic disorder (21genes), inflammatory disease (15 genes) and cancer (21 genes). The correlated target genes included several genes implicated in colon cancer such as CDH3, NKD1, RGS2, TCFL5 and ZEB2. In summary, deep miRNA sequencing among MSS/CIMP-negative colon tumors confirmed differential expression of 6 colon cancer-associated miRNAs and identified 13 miRNAs not previously reported in colon cancer. Differential expression of most of the discovered miRNAs was correlated with the expression of genes potentially relevant for colon cancer. If confirmed, these miRNAs may serve as new biomarkers for colon cancer and may further our understanding of the epigenetic changes and pathways involved in the development of colon cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-348. doi:10.1158/1538-7445.AM2011-LB-348

Abstract Introduction: Genome-wide association studies of colorectal cancer have identified 18 risk variants that explain ∼25% of the hereditable risk of colorectal cancer. These variants are located in intronic, inter-genic or gene-desert regions. To uncover whether some of these variants may have a regulatory function on the expression of near-by genes, we conducted expression quantitative trait loci (eQTL) analyses of these 18 regions. Methods: DNA and RNA were extracted from 40 fresh-frozen paired colon tumor (microsatellite stable and CpG island methylator phenotype-negative) and adjacent normal tissue samples collected by the Colon Cancer Family Registry. Whole genome gene expression assessment was performed in the tumors and adjacent normal tissue with the Affymetrix GeneChip Human Exon 1.0 ST array. Genome-wide SNP data was generated with DNA extracted from the same normal tissue samples using the Affymetrix Genome-Wide Human SNP 6.0 array. Partek software was used to compare the expression levels by genotype for each gene spanning a 2 Mb region up- and down- stream of each of the 18 established risk variants for colorectal cancer. Results: Three of the 18 risk variants (rs10795668, rs4444235, rs9929218) demonstrated significant cis-eQTLs (FDR q-values<0.05). Specifically, differential gene expression was observed in genes neighboring rs10795668 at 10p14 (ATP5C1, q=0.024), rs4444235 at 14q22.2 (DLGAP5, q=0.041), and rs9929218 at 16q22.1 (NOL3, q=0.017; DDX28, q=0.046). In particular, DLGAP5 (discs, large (Drosophila) homolog-associated protein 5) at 14q22.2 and NOL3 (nucleolar protein 3) at 16q22 are interesting candidate genes for colorectal cancer. DLGAP5 encodes for a microtubule-associated protein and functions as a mitotic regulator that has been reported to be overexpressed in colon tumors. NOL3 (nucleolar protein 3) encodes for an anti-apoptotic protein that down-regulates the expression of caspase 2 and 8, and p53. NOL3 also appears to be overexpressed in colorectal tumors. Conclusion: In summary, these findings suggest putative functional activities for three established colorectal risk variants and highlight potentially interesting candidate genes for this malignancy. If confirmed, these results may help explain the total genetic risk of the disease, as well as further our understanding of the underlying biology of colorectal cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4732. doi:10.1158/1538-7445.AM2011-4732

Abstract Colon cancer is the result of a multi-step process involving the accumulation of genetic and epigenetic alterations leading to the transformation of normal colon epithelium to adenocarcinoma. Identification of characteristic genetic alterations is of critical importance to increase our understanding of the transformation process. We focused our analysis on the most common molecular sub-type of colon cancers, microsatellite stable (MSS) and CpG island methylator phenotype (CIMP)-negative, to identify characteristic copy number alteration (CNA) events and associated gene expression profiles using high-resolution genome-wide microarrays. DNA and RNA were extracted from 41 fresh-frozen paired colon tumors and adjacent normal tissue collected by the Colon Cancer Family Registry. Genomic profiles, such as CNAs and loss of heterozygosity (LOH), were identified with the Affymetrix Genome-Wide Human SNP 6.0 array for both tumor and adjacent normal tissue. Gene expression profiles of tumors and adjacent normal tissue were identified with the Affymetrix GeneChip Human Exon 1.0 ST array. Partek Genomics Suite software was used for analysis and data integration. We identified recurrent (>25%) CNAs in several chromosomal regions: gain in 1q, 7p, 7q, 8q, 13q, 20p, 20q, Xp, Xq and loss in 5q, 8p, 14q, 16p, 17p, 18p, and 18q. In addition, based on the allele information from the SNP arrays, we found a subset of these recurrent CNAs were associated with LOH. Preliminary results from the integration of CNA and gene expression data in tumors indicate that a subset of these recurrent CNAs is associated with the disruption of gene expression. For example, we observed recurrent copy number gain in 8q24.21, the genomic region containing the c-MYC gene, and associated up-regulation of c-MYC gene expression in tumors compared to adjacent normal tissue. In another example, recurrent copy number loss at 5q22.2 was associated with down-regulation of APC gene expression; loss of function of this tumor suppressor is associated with both hereditary and sporadic colon cancer. This genome-wide characterization of both genomic alterations and gene expression may help identify key genes and pathways that are disrupted in this common molecular subtype of colon cancer. We will present detailed results from this integrated and comprehensive genetic profiling of MSS and CIMP-negative colon cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2145.

Abstract Recent publications have reported that common variants on 8q24 are associated with both prostate and colorectal cancers (CRC). In addition, one of these studies (the ARCTIC study) initially observed an association with a single nucleotide polymorphism (SNP) on 9p24 that was not confirmed in some of their validation data sets. In the research described here, we conducted a case-unaffected sibling analysis using population- and clinic-based discordant sibships (N = 1,567 sibships) from the Colon Cancer Family Registry (Colon CFR) to investigate the associations between common variants at 9p24 and 8q24 and risk of CRC. We also evaluated whether these associations differed by age, family history, and tumor characteristics, including microsatellite instability and tumor site. Associations were estimated using conditional logistic regression, treating sibship as the matching factor. Analyses were adjusted for age and sex, and stratified by ascertainment source (population versus clinic). We observed an association between a SNP on 9p24 (rs719725) and risk of CRC in the population-based series (AA versus CC: odds ratios, 1.46; 95% confidence interval, 1.06–2.02; AC versus CC: odds ratios, 1.50; 95% confidence interval, 1.14–1.98; P = 0.011 on 2 df). In the population-based series, we also detected statistically significant associations between two SNPs on 8q24, rs10505477 and rs6983267, and risk of CRC (P = 0.005 and P = 0.002, respectively). There was no evidence of statistically significant heterogeneity by age at diagnosis, family history of CRC, microsatellite instability, or tumor site at either locus and no evidence of interaction between SNPs on 8q24 and 9p24. These data suggest that common variants may play important roles in the risk of CRC. [Cancer Res 2007;67(23):11128–32]