Role of inflammation, innate resistance, and immunity in carcinogenesis

Division Of Basic Sciences - Nci

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Abstract

Tristetraprolin expression by keratinocytes protects against skin carcinogenesis: Multiple genes associated with the initiation and development of tumors are also regulated at the level of mRNA decay, through the recruitment of RNA-binding proteins to AU-rich elements (AREs) located in their 3'-untranslated regions. One of these ARE-binding proteins, tristetraprolin (TTP; encoded by Zfp36), is consistently dysregulated in many human malignancies. Herein, using regulated overexpression or conditional ablation in the context of cutaneous chemical carcinogenesis, we show that TTP represents a critical regulator of skin tumorigenesis. TTP controlled both tumor-associated inflammation and key oncogenic pathways in neoplastic epidermal cells. We identify Areg as a direct target of TTP in keratinocytes and show that EGFR signaling potentially contributed to exacerbated tumor formation. Finally, single-cell RNA-Seq analysis indicated that ZFP36 was downregulated in human malignant keratinocytes. We conclude that TTP expression by epidermal cells played a major role in the control of skin tumorigenesis. Distinct contributions of cathelin-related antimicrobial peptide (CRAMP) derived from epithelial cells and macrophages to colon mucosal homeostasis: CRAMP protects the mouse colon from inflammation, inflammation-associated carcinogenesis, and disrupted microbiome balance, as shown in systemic Cnlp(-/-) mice (also known as Camp(-/-) mice). However, the mechanistic basis for the role and the cellular source of CRAMP in colon pathophysiology are ill defined. This study, using either epithelial or myeloid conditional Cnlp(-/-) mice, demonstrated that epithelial cell-derived CRAMP played a major role in supporting normal development of colon crypts, mucus production, and repair of injured mucosa. On the other hand, myeloid cell-derived CRAMP potently supported colon epithelial resistance to bacterial invasion during acute inflammation with exacerbated mucosal damage and higher rate of mouse mortality. Therefore, a well concerted cooperation of epithelial- and myeloid-derived CRAMP is essential for colon mucosal homeostasis. We also reported that normal (wild-type, WT) mouse macrophages increased their expression of cathelin-related antimicrobial peptide (CRAMP, encoded by Camp) after infection by viable E. coli or stimulation with inactivated E. coli and its product lipopolysaccharide (LPS), a process involving activation of NF-kB followed by protease-dependent conversion of CRAMP from an inactive precursor to an active form. The active CRAMP was required by WT macrophages for elimination of phagocytosed E. coli, with participation of autophagy-related proteins ATG5, LC3-II and LAMP-1, as well as for aggregation of the bacteria with p62 (also known as SQSTM1). This process was impaired in CRAMP(-/-) macrophages, resulting in retention of intracellular bacteria and fragmentation of macrophages. These results indicate that CRAMP is a critical component in autophagy-mediated clearance of intracellular E. coli by mouse macrophages. Formyl peptide receptor 2 (Fpr2) plays a crucial role in colon homeostasis and microbiota balance: Commensal E. coli is known to promote the regeneration of damaged colon epithelial cells. The deficiency of Fpr2 was associated with impaired integrity of the colon mucosa and an imbalance of microbiota, characterized by the enrichment of Proteobacteria in the colon. Two serotypes of E. coli, O22:H8 and O91:H21, were identified in the mouse colon through complete genome sequencing. E. coli O22:H8 was found to be prevalent in the gut of mice and exhibited lower virulence compared to O91:H21. Germ-free (GF) mice orally inoculated with E. coli O22:H8 showed reduced susceptibility to chemically induced colitis, increased proliferation of epithelial cells, and improved mouse survival. Following infection with E. coli O22:H8, the expression of Fpr2 in colon epithelial cells was upregulated, and the products derived from E. coli O22:H8 induced migration and proliferation of colon epithelial cells through Fpr2. Fpr2 deficiency increased susceptibility to chemically induced colitis, delayed the repair of damaged colon epithelial cells, and heightened inflammatory responses. Additionally, the population of E. coli was observed to increase in the colons of Fpr2-/- mice with colitis. Thus, commensal E. coli O22:H8 stimulated the upregulation of Fpr2 expression in colon epithelial cells, and the products from E. coli induced migration and proliferation of colon epithelial cells through Fpr2. Fpr2 deficiency led to an increased E. coli population in the colon and delayed recovery of damaged colon epithelial cells in mice with colitis. Therefore, Fpr2 is essential for the effects of commensal E. coli on colon epithelial cell recovery. Myd88 in Cd11b+ cells protect from colitis-associated colon cancer through intestinal microbial homeostasis: These cells are an important component of the innate immune system which maintains homeostasis in the gut by maintaining a balance between pro- and anti-inflammatory responses and by promoting the integrity of the barrier function of the epithelium. Armed with an arsenal of pattern-recognition receptors, these cells can respond to the multitudes of microbial antigens on the mucosal surface. Myeloid differentiation factor 88 (Myd88) is an important signaling molecule which contributes to signal transduction triggered by microbial products via recognition mediated by members of the Toll-like receptor and IL-1 receptor families. Using the azoxymethane (AOM)/DSS model of colitis-associated colorectal cancer, we previously showed that Myd88-/- mice are unable to heal colonic ulcers thereby increasing perpetuating the inflammatory microenvironment and fostering the dramatic increase in adenoma and adenocarcinoma formation in the colon. In this study, we decipher the compartment responsible for driving the anti-tumorigenic effects of MyD88. We hypothesized that MyD88 signaling from Cd11b+ myeloid cells mediates anti-tumor responses in the colon by reducing myeloid cell infiltration into the lamina propria and by preventing the expansion of GUS-type beta-glucuronidase- and invasin-containing microbes. Indeed, deletion of Myd88 in Cd11b+ cells (Myd88CD11b-/- mice) increased the number of adenomas formed relative to their corresponding floxed littermate controls. Remarkably, wild type mice co-housed with Myd88CD11b-/- animals or recipients of microbial transfer from these animals developed greater polyps in quantity and size. Taken together, MyD88 signaling in myeloid cells favors the development of a protective anti-tumoral response from the host and the gut microbiota. We also showed that enterochromaffin (EC) cells, which function as chemosensors on the gut epithelium, are known to translate environmental cues into serotonin (5-HT) production, contributing to intestinal physiology. However, how immune signals participate in gut sensation and neuroendocrine response remains unclear. Interleukin-33 (IL-33) acts as an alarmin cytokine by alerting the system of potential environmental stresses. We here demonstrate that IL-33 induced instantaneous peristaltic movement and facilitated Trichuris muris expulsion. We found that IL-33 could be sensed by EC cells, inducing release of 5-HT. IL-33-mediated 5-HT release activated enteric neurons, subsequently promoting gut motility. Mechanistically, IL-33 triggered calcium influx via a non-canonical signaling pathway specifically in EC cells to induce 5-HT secretion. Our data establish an immune-neuroendocrine axis in calibrating rapid 5-HT release for intestinal homeostasis. .