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: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:BRAF mutations occur early in serrated colorectal cancers, but their long-term influence on tissue homeostasis are poorly characterized. We investigated the impact of short-term (3 days) and long-term (6 months) expression of BrafV600E in the intestinal tissue of an inducible mouse model. We show that BrafV600E perturbs the homeostasis of intestinal epithelial cells, with impaired differentiation of enterocytes emerging after prolonged expression of the oncogene. Moreover, BrafV600E leads to a persistent transcriptional reprogramming with enrichment of numerous gene signatures indicative of proliferation and tumorigenesis, and signatures suggestive of metabolic rewiring. We focused on the top-ranking cholesterol biosynthesis signature and confirmed its increased expression in human serrated lesions. Functionally, the cholesterol lowering drug atorvastatin prevents the establishment of intestinal crypt hyperplasia in BrafV600E-mutant mice. Overall, our work unveils the long-term impact of BrafV600E expression in intestinal tissue and suggests that colorectal cancers with mutations in BRAF might be prevented by statins.
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Project description:BRAF mutations occur early in serrated colorectal cancers, but their long-term influence on tissue homeostasis are poorly characterized. We investigated the impact of short-term (3 days) and long-term (6 months) expression of BrafV600E in the intestinal tissue of an inducible mouse model. We show that BrafV600E perturbs the homeostasis of intestinal epithelial cells, with impaired differentiation of enterocytes emerging after prolonged expression of the oncogene. Moreover, BrafV600E leads to a persistent transcriptional reprogramming with enrichment of numerous gene signatures indicative of proliferation and tumorigenesis, and signatures suggestive of metabolic rewiring. We focused on the top-ranking cholesterol biosynthesis signature and confirmed its increased expression in human serrated lesions. Functionally, the cholesterol lowering drug atorvastatin prevents the establishment of intestinal crypt hyperplasia in BrafV600E-mutant mice. Overall, our work unveils the long-term impact of BrafV600E expression in intestinal tissue and suggests that colorectal cancers with mutations in BRAF might be prevented by statins.
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Project description:We tamoxifen treated 8-12 week old mice that had floxed alleles of the following: 1) both Apc alleles (giving rise to Apc truncation/inactivation); 2) both Cdx2 alleles (giving rise to Cdx2 inactivation; 3) one Braf allele, that upon Cre-mediated recombination gives a Braf V600E mutant allele (details below), and 4) the combination of both the Cdx2 alleles and the BrafV600E allele. All four of those groups also had a CDX2P-CreERT2 transgene that expresses Cre recombinase fused to a tamoxifen-regulated fragment of the estrogen receptor ligand binding domain. CreERT2 expression occurs only in tissues where the Cdx2 gene is expressed, which is almost exclusively in adult mouse cecum and colon epithelium. A fifth group of mice had the floxed Cdx2 alleles, but no CDX2P-CreERT2 gene. Treating the mice having CDX2P-CreERT2 with tamoxifen permits the Cre recombinase to enter the cell nucleus and recombine the Apc, Braf, and/or Cdx2 alleles containing loxP sequence elements. Mice were treated with intraperitoneal injection of tamoxifen dissolved in corn oil. Three mice per group were used. The control mice did not develop tumors or any morphological or histological changes in their epithelium, but their colons were used to create the 3 control samples. To obtain the BrafV600E allele we used a genetically engineered mouse line previously described by Dankort et al. (Genes Dev 2007, 21:379-84) that can express the BrafV600E mutant protein following Cre-mediated recombination. The Braf(CA) (Braf-Cre-activated) allele mice carry a gene-targeted allele of Braf, where Braf sequences from exons 15-18 are present in the normal mouse Braf intron 14, followed by a mutated exon 15 (carrying the V600E mutation). The exon 15-18 sequence element is flanked by loxP sites. In the absence of Cre-mediated recombination, the Braf(CA) allele expresses a wild type Braf protein. Following Cre-mediated recombination, the Braf exon 15-18 element is removed, and the Braf(CA) allele then encodes the Braf V600E protein (from the introduced mutated exon 15). RNA was purified from tumor or normal tissue, and targets for Affymetrix arrays were synthesized from the mRNAs. We used Affymetrix Mouse Gene 2.1 ST arrays, which hold 41345 probe-sets, but we largely analyzed just those 25216 probe-sets that were mapped to Entrez gene IDs. Raw data was processed with the Robust Multi-array Average algorithm (RMA). Data is log2-transformed transcript abundance estimates. We fit a one-way ANOVA model to the five groups of samples. We supply a supplementary excel workbook that holds the same data as the data matrix file, but also holds the probe-set annotation at the time we analyzed the data, and some simple statistical calculations, which selects subsets of the probe-sets as differentially expressed between pairs of groups, as well as significant Cdx2-/- by Braf V600E interactions. It also gives the homologous human gene IDs we used for enrichment testing, which were 1-to-1 best homologs according to build 68 of NCBI's Homologene. A second supplementary sheet shows the data we enrichment tested after collapsing to distinct human homologs, joins of the results of tests with GSE4045 data and of tests with TCGA data to the mouse genes, and the intersections of selected genes in those data set with our gene selections in mouse. Consumers should consider obtaining more up-to-date probe-set annotation for the array platform.
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Project description:Most cancer genomics papers to date have focused on aberrations in genomic DNA and protein-coding transcripts. However, around 50% of transcripts have no coding potential and may exist as non-coding RNA. We performed RNA-seq in BRAFv600e melanoma skin cancer and on melanocytes over-expressing oncogenic BRAF to catalog transcriptome remodeling. We discovered that BRAF regulates expression of 1027 protein coding transcripts, 39 annotated lncRNAs and 70 novel transcripts. Many of the novel transcripts are lncRNAs. We used an indepenedent dataset to interrogate our novel transcripts and found that the novel lncRNA BANCR is a BRAF-regulated lncRNA recurrently upregulated in melanoma. Knockdown of BANCR impairs melanoma cell migration. Whole transcriptome RNA-seq followed assembly to Refseq/Gencode and de novo transcript assembly. RNA-seq performed on: 2 BRAFv600e melanomas, melanocytes+RFP control and melanocytes + BRAFv600e. We discovered protein-coding transcripts, annotated ncRNAs and novel transcripts (including lncRNAs) regulated by BRAFv600e also coordinately expressed in melanoma.
2012-04-28 | E-GEOD-33092 | biostudies-arrayexpress
Project description:Degree of Tissue Differentiation Dictates Susceptibility to BRAF-driven Colorectal Cancer
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Project description:Abnormal promoter DNA hypermethylation arises early during tumorigenesis and yet its role in cancer initiation has remained underexplored. An important scenario for examining this is, BRAFV600E-mutant colon adenocarcinomas (COAD) which most often arise in the proximal colon and harbor extensive, abnormal gene promoter CpG-island methylation or the methylator phenotype (CIMP). How CIMP and BRAF-mutations specifically interact for COAD initiation has remained unclear. Using mouse colon-derived organoids, we show promoter hypermethylation spontaneously arises in wild type cells mimicking “aging like” phenotype. The silenced genes sufficiently activate the Wnt pathway, causing a stem–like state and profound differentiation block. This phenotype renders long-term cultured organoids to be rapidly susceptible to transformation by BRAFV600E with features of typical right-sided COAD. Our studies tightly link epigenetic abnormalities, suggested to arise with aging, to intestinal cell fate changes and define an “epi-driver” role for multiple abnormally silenced genes that predispose to BRAFV600E-driven colon tumorigenesis.
2019-01-01 | GSE121672 | GEO
Project description:Abnormal promoter DNA hypermethylation arises early during tumorigenesis and yet its role in cancer initiation has remained underexplored. An important scenario for examining this is, BRAFV600E-mutant colon adenocarcinomas (COAD) which most often arise in the proximal colon and harbor extensive, abnormal gene promoter CpG-island methylation or the methylator phenotype (CIMP). How CIMP and BRAF-mutations specifically interact for COAD initiation has remained unclear. Using mouse colon-derived organoids, we show promoter hypermethylation spontaneously arises in wild type cells mimicking “aging like” phenotype. The silenced genes sufficiently activate the Wnt pathway, causing a stem–like state and profound differentiation block. This phenotype renders long-term cultured organoids to be rapidly susceptible to transformation by BRAFV600E with features of typical right-sided COAD. Our studies tightly link epigenetic abnormalities, suggested to arise with aging, to intestinal cell fate changes and define an “epi-driver” role for multiple abnormally silenced genes that predispose to BRAFV600E-driven colon tumorigenesis.
2019-01-01 | GSE114800 | GEO