Colorectal cancer cells utilize autophagy to maintain mitochondrial metabolism for cell proliferation under nutrient stress.

Cancer cells reprogram cellular metabolism to maintain adequate nutrient pools to sustain proliferation. Moreover, autophagy is a regulated mechanism to break down dysfunctional cellular components and recycle cellular nutrients. However, the requirement for autophagy and the integration in cancer cell metabolism is not clear in colon cancer. Here, we show a cell-autonomous dependency of autophagy for cell growth in colorectal cancer. Loss of epithelial autophagy inhibits tumor growth in both sporadic and colitis-associated cancer models. Genetic and pharmacological inhibition of autophagy inhibits cell growth in colon cancer-derived cell lines and patient-derived enteroid models. Importantly, normal colon epithelium and patient-derived normal enteroid growth were not decreased following autophagy inhibition. To couple the role of autophagy to cellular metabolism, a cell culture screen in conjunction with metabolomic analysis was performed. We identified a critical role of autophagy to maintain mitochondrial metabolites for growth. Loss of mitochondrial recycling through inhibition of mitophagy hinders colon cancer cell growth. These findings have revealed a cell-autonomous role of autophagy that plays a critical role in regulating nutrient pools in vivo and in cell models, and it provides therapeutic targets for colon cancer.

Functions and Implications of Autophagy in Colon Cancer.

Autophagy is an essential function to breakdown cellular proteins and organelles to recycle for new nutrient building blocks. In colorectal cancer, the importance of autophagy is becoming widely recognized as it demonstrates both pro- and anti-tumorigenic functions. In colon cancer, cell autonomous and non-autonomous roles for autophagy are essential in growth and progression. However, the mechanisms downstream of autophagy (to reduce or enhance tumor growth) are not well known. Additionally, the signals that activate and coordinate autophagy for tumor cell growth and survival are not clear. Here, we highlight the context- and cargo-dependent role of autophagy in proliferation, cell death, and cargo breakdown.

Temporal induction of intestinal epithelial hypoxia-inducible factor-2α is sufficient to drive colitis.

Hypoxia is a notable feature of inflammatory bowel disease and chronic induction of hypoxia-inducible factor (HIF)-1α and HIF-2α (endothelial PAS domain protein 1, EPAS1) play important, but opposing, roles in its pathogenesis. While activation of HIF-1α decreases intestinal inflammation and is beneficial in colitis, activation of HIF-2α exacerbates colitis and increases colon carcinogenesis in animal models, primarily due to the role of epithelial HIF-2α in mounting a potent inflammatory response. Previous work from our laboratory showed that mice overexpressing intestinal epithelial HIF-2α led to massive intestinal inflammation and decreased survival. As oxygen homeostasis and HIFs are critical in embryonic development, it is not clear whether the observed intestinal inflammatory response was secondary to developmental defects. To address this question, the present study used a mouse model to temporally modulate expression of intestinal epithelial HIF-2α to assess its role in mediating inflammatory response. Remarkably, activation of HIF-2α in intestinal epithelial cells in adult mice increased expression of proinflammatory mediators; however, no decrease in survival was observed. Furthermore, in an acute model of colitis, activation of HIF-2α was sufficient to exacerbate colitis. These data confirm our previous finding that epithelial HIF-2α mediates inflammatory response and demonstrates that activation of HIF-2α is sufficient to exacerbate colitis.NEW & NOTEWORTHY Inflammatory bowel disease (IBD) is a chronic relapsing inflammatory disease of the intestinal tract. Hypoxia and activation of its downstream transcription factors hypoxia-inducible factor (HIF)-1α and HIF-2α are notable features of IBD. HIF-1α has well-characterized protective roles in IBD; however, the role of HIF-2α has been less studied. Using novel HIF-2α mouse models, we show that activation of HIF-2α in intestinal epithelial cells is sufficient to exacerbate colitis.

Intestinal non-canonical NFκB signaling shapes the local and systemic immune response.

Microfold cells (M-cells) are specialized cells of the intestine that sample luminal microbiota and dietary antigens to educate the immune cells of the intestinal lymphoid follicles. The function of M-cells in systemic inflammatory responses are still unclear. Here we show that epithelial non-canonical NFkB signaling mediated by NFkB-inducing kinase (NIK) is highly active in intestinal lymphoid follicles, and is required for M-cell maintenance. Intestinal NIK signaling modulates M-cell differentiation and elicits both local and systemic IL-17A and IgA production. Importantly, intestinal NIK signaling is active in mouse models of colitis and patients with inflammatory bowel diseases; meanwhile, constitutive NIK signaling increases the susceptibility to inflammatory injury by inducing ectopic M-cell differentiation and a chronic increase of IL-17A. Our work thus defines an important function of non-canonical NFkB and M-cells in immune homeostasis, inflammation and polymicrobial sepsis.

Neutrophils Restrict Tumor-Associated Microbiota to Reduce Growth and Invasion of Colon Tumors in Mice.

BACKGROUND & AIMS: Neutrophils are among the most prevalent immune cells in the microenvironment of colon tumors; they are believed to promote growth of colon tumors, and their numbers correlate with outcomes of patients with colon cancer. Trials of inhibitors of neutrophil trafficking are underway in patients with cancer, but it is not clear how neutrophils contribute to colon tumorigenesis. METHODS: Colitis-associated colon cancer was induced in mice with conditional deletion of neutrophils (LysMCre;Mcl1fl/fl) and wild-type littermates (LysMCre;Mcl1wt/wt, control mice) by administration of azoxythmethane and/or dextran sulfate sodium. Sporadic colon tumorigenesis was assessed in neutrophil-deficient and neutrophil-replete mice with conditional deletion of colon epithelial Apc (Cdx2-CreERT2;Apcfl/fl). Primary colon tumor tissues from these mice were assessed by histology, RNA sequencing, quantitative polymerase chain reaction, and fluorescence in situ hybridization analyses. Fecal and tumor-associated microbiota were assessed by 16s ribosomal RNA sequencing. RESULTS: In mice with inflammation-induced and sporadic colon tumors, depletion of neutrophils increased the growth, proliferation, and invasiveness of the tumors. RNA sequencing analysis identified genes that regulate antimicrobial and inflammatory processes that were dysregulated in neutrophil-deficient colon tumors compared with colon tumors from control mice. Neutrophil depletion correlated with increased numbers of bacteria in tumors and proliferation of tumor cells, tumor-cell DNA damage, and an inflammatory response mediated by interleukin 17 (IL17). The 16s ribosomal RNA sequencing identified significant differences in the composition of the microbiota between colon tumors from neutrophil-deficient vs control mice. Administration of antibiotics or a neutralizing antibody against IL17 to neutrophil-deficient mice resulted in development of less-invasive tumors compared with mice given vehicle. We found bacteria in tumors to induce production of IL17, which promotes influx of intratumor B cells that promote tumor growth and progression. CONCLUSIONS: In comparisons of mice with vs without neutrophils, we found neutrophils to slow colon tumor growth and progression by restricting numbers of bacteria and tumor-associated inflammatory responses.

The genomic landscape of UM-SCC oral cavity squamous cell carcinoma cell lines.

OBJECTIVES: We sought to describe the genetic complexity of 14 UM-SCC oral cavity cancer cell lines that have remained uncharacterized despite being used as model systems for decades. MATERIALS AND METHODS: We performed exome sequencing on 14 oral cavity UM-SCC cell lines and denote the mutational profile of each line. We used a SNP array to profile the multiple copy number variations of each cell line and use immunoblotting to compare alterations to protein expression of commonly amplified genes (EGFR, PIK3CA, etc.). RNA sequencing was performed to characterize the expression of genes with copy number alterations. RESULTS: The cell lines displayed a highly complex network of genetic aberrations that was consistent with alterations identified in the HNSCC TCGA project including PIK3CA amplification, CDKN2A deletion, as well as TP53 and CASP8 mutations, enabling genetic stratification of each cell line in the panel. Copy number FISH and spectral karyotyping analysis demonstrate that cell lines retain chromosomal heterogeneity. CONCLUSIONS: Collectively, we developed an important resource for future oral cavity HNSCC cell line studies and highlight the complexity of genomic aberrations in cell lines.