The tumor microenvironment is a complex community consisting of neoplastic cells, surrounding stromal cells, a broad array of immune cells, and a microbiota. By sheer numbers, the microbiota has its greatest manifestation in colorectal cancer (CRC) because the colon contains up to 100 trillion bacteria, outnumbering human cells by a factor of 10 and encoding a gene-content that is 100-fold larger than that of the human genome. Indeed, previous studies using germ-free mice in a variety of genetic backgrounds have demonstrated that the microbiota can impact colorectal tumorigenesis. In addition, specific strains of enterotoxigenic bacteria have been shown to promote colitis-associated cancer in mice. Here, we explore the composition of the tissue-associated microbiota in human CRC and evaluate the role of tumor-enriched microbes in potentiating colorectal tumorigenesis in mice. Advances in DNA sequencing technology have fueled a renaissance in the microbiome field. Deep sequencing metagenomics enables rapid, culture-independent characterization of a microbial community. We present PathSeq, a highly scalable software tool that performs computational subtraction on high-throughput sequencing data to identify nonhuman nucleic acids. PathSeq makes it possible to analyze sequence datasets as large as human whole-genomes for the purpose of metagenomics and also to discover previously unsequenced microorganisms. We used PathSeq to characterize the composition of the microbiota in human CRCusing whole-genome sequencing on nine tumor/normal pairs and 16S rDNA sequencing on an additional 95 pairs. The genus Fusobacterium was highly enriched in tumors, while the Bacteroidetes and Firmicutes phyla were depleted.We show that in the \(Apc^{Min/+}\) mouse model of intestinal tumorigenesis, Fusobacterium nucleatum increases tumor multiplicity, selectively recruits tumor-infiltrating myeloid cells, and is associated with a pro-inflammatory expression signature that is shared with human fusobacteria-positive colorectal carcinomas. We find that Fusobacterium spp. are enriched in human colonic adenomas relative to surrounding tissues and fusobacterial abundance is increased in stool samples from patients with colorectal adenomas and carcinomas, compared to healthy subjects. Collectively, these data support that fusobacteria may be involved in early stages of intestinal tumorigenesis and, through recruitment of tumor-infiltrating immune cells, may generate a pro-inflammatory tissue microenvironment conducive to colorectal neoplasia progression.
| Identifer | oai:union.ndltd.org:harvard.edu/oai:dash.harvard.edu:1/11129202 |
| Date | 08 June 2015 |
| Creators | Kostic, Aleksandar David |
| Contributors | Meyerson, Matthew Langer |
| Publisher | Harvard University |
| Source Sets | Harvard University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Rights | open |
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