Degree of Tissue Differentiation Dictates Susceptibility to BRAF-driven Colorectal Cancer
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ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE106330 | GEO | 2017/12/26
SECONDARY ACCESSION(S): PRJNA416320
REPOSITORIES: GEO
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Project description:It is not known why cancers arising in anatomically distinct locations but within the same tissue type can exhibit stark differences in molecular, pathological and clinical features. Cancers arising in proximal and distal sites of the colon are emblematic of these above differences as the proximal and distal colon cancers harbor differences in key molecular features, with BRAFV600E oncogene predominantly occurring in proximal colon cancers in the context of the increased promoter DNA methylation phenotype (CIMP-high), while distal colon cancers lack these molecular features. We determined the molecular basis of tissue-location specificity of driver mutations using normal mouse derived organoid models for colon cancer initiation. We show that the homeobox transcription factor, Cdx2, which is downregulated by DNA methylation in proximal colon cancers, plays distinct roles in regulating stem cell and differentiation in proximal compared to distal colon stem cells. Loss of Cdx2 altered the differentiation and stem cell programs and result in transformation by BRAFV600E specifically in the proximal but not distal colon stem cells. Analyses of RNA expression and Cdx2-binding to target genomic regions revealed that Cdx2 was a key effector of the transcriptional response to differentiation cues in proximal colon cells. This proximal colon-specific transcriptional program concurrently is tumor suppressive, and its loss sufficiently creates permissive state for oncogenic-BRAF mutations. The transcriptional program associated with Cdx2 loss in mouse proximal organoids matches that of human proximal colon cancers with downregulated CDX2 expression due to epigenetic silencing. Our analyses reveal that developmental and lineage-restricted transcription factors maintain tissue-location specific transcriptional programs which create critical dependencies for tumor initiation.
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Project description:Degree of Tissue Differentiation Dictates Susceptibility to BRAF-driven Colorectal Cancer
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Project description:The objective of this study was to elucidate the molecular background of sessile serrated adenoma/polyp (SSA/P) endoscopically resected with comprehensive gene expression analysis. Gene expression profiling was performed for 10 tumor-normal pairs of SSA/P. Cluster analysis, gene set enrichment analysis (GSEA), and consensus molecular subtype (CMS) classification of colorectal cancer (CRC) were applied to our transcriptome analysis. Unsupervised cluster analysis showed that the gene expression profile of SSA/Ps is different from that of adjacent normal epithelial cells, even in the very early stage of tumorigenesis. According to the CMS classification, our microarray data indicated that SSA/Ps were classified as CMS1. GSEA demonstrated a strong association between SSA/P and microsatellite instability-high (MSI-H) CRC (p < 10-5). Transcriptome analysis of five MSI-related genes (MSH2, MSH6, MLH1, PMS1, and PMS2) and five CRC-related genes (BRAF, KRAS, APC, TP53, and CDX2) showed that CDX2 expression was most severely decreased in SSA/P. Immunohistochemical staining confirmed that CDX2 protein was reduced compared with the surrounding mucosa. Direct sequencing of the BRAF gene showed that the BRAF V600E mutation was detected in only nine of 36 cases. In an mouse model, BRAF, APC, or CDX2 deficiency indicated that the gene expression pattern with loss of CDX2 is more similar to our SSA/Ps compared with those induced by BRAF or APC mutation. Transcriptome analysis of SSA/Ps showed characteristic gene expression with a strong resemblance to MSI-H CRC. Downregulation of CDX2 expression is an essential molecular mechanism involved in the initial stage of SSA/P tumorigenesis. All samples were obtained prior to treatment in order to minimize effects of cauterization, and immediately fresh-frozen.
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