Global Methylome Scores Correlate with Histological Subtypes of Colorectal Carcinoma and Show Different Associations with Common Clinical and Molecular Features.

BACKGROUND: The typical methylation patterns associated with cancer are hypermethylation at gene promoters and global genome hypomethylation. Aberrant CpG island hypermethylation at promoter regions and global genome hypomethylation have not been associated with histological colorectal carcinomas (CRC) subsets. Using Illumina's 450 k Infinium Human Methylation beadchip, the methylome of 82 CRCs were analyzed, comprising different histological subtypes: 40 serrated adenocarcinomas (SAC), 32 conventional carcinomas (CC) and 10 CRCs showing histological and molecular features of microsatellite instability (hmMSI-H), and, additionally, 35 normal adjacent mucosae. Scores reflecting the overall methylation at 250 bp, 1 kb and 2 kb from the transcription starting site (TSS) were studied. RESULTS: SAC has an intermediate methylation pattern between CC and hmMSI-H for the three genome locations. In addition, the shift from promoter hypermethylation to genomic hypomethylation occurs at a small sequence between 250 bp and 1 Kb from the gene TSS, and an asymmetric distribution of methylation was observed between both sides of the CpG islands (N vs. S shores). CONCLUSION: These findings show that different histological subtypes of CRC have a particular global methylation pattern depending on sequence distance to TSS and highlight the so far underestimated importance of CpGs aberrantly hypomethylated in the clinical phenotype of CRCs.

Differences in gene expression profiling and biomarkers between histological colorectal carcinoma subsets from the serrated pathway.

AIMS: To discern the differences in expression profiling of two histological subtypes of colorectal carcinoma (CRC) arising from the serrated route (serrated adenocarcinoma (SAC) and CRC showing histological and molecular features of a high level of microsatellite instability (hmMSI-H) both sharing common features (female gender, right-sided location, mucinous histology, and altered CpG methylation), but dramatically differing in terms of prognosis, development of an immune response, and treatment options. METHODS AND RESULTS: Molecular signatures of SAC and hmMSI-H were obtained by the use of transcriptomic arrays; quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC) were used to validate differentially expressed genes. An over-representation of innate immunity functions (granulomonocytic recruitment, chemokine production, Toll-like receptor signalling, and antigen processing and presentation) was obtained from this comparison, and intercellular cell adhesion molecule-1 (ICAM1) was more highly expressed in hmMSI-H, whereas two genes [those encoding calcitonin gene-related peptide-receptor component protein and C-X-C motif chemokine ligand 14 (CXCL14)] were more highly expressed in SAC. These array results were subsequently validated by qPCR, and by IHC for CXCL14 and ICAM1. Information retrieved from public databanks confirmed our findings. CONCLUSIONS: Our findings highlight specific functions and genes that provide a better understanding of the role of the immune response in the serrated pathological route and may be of help in identifying actionable molecules.