miR-34a-mediated regulations in the micro-environment of colorectal cancer

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Inflammatory processes and tumor formation have been linked since Virchow, however the underlying mechanisms have not been fully understood. We have shown that the microRNA miR-34a, which is induced by the prototypic tumor suppressor p53, is an integral component of the response of epithelial cells to inflammation mediated by the cytokine IL-6 (Rokavec et al. (2014) JCI): miR-34a functions in the context of a positive feedback-loop consisting of the IL-6 receptor (IL-6R), the transcription factor STAT3 and miR-34a. This loop is activated in human CRCs and associated with distant metastases and poor survival. We recently determined that miR-34a and p53 cooperate in the suppression of invasion and metastasis in a sporadic CRC mouse model and that their combined inactivation is associated with poorer survival than their singular inactivation in human CRCs (Öner et al., 2018, Gastroenterology). In this proposal we aim to further characterize components of the IL-6R/STAT3/miR-34a feed-back loop and downstream effectors using genetic approaches and mouse models of CRC and colitis-associated colon cancer (CAC). Since we obtained evidence for a role of miR-34a expression in tumor associated macrophages (TAMs) for the invasive phenotype of CACs we will characterize the role of miR-34a and two of its targets, that we found to be directly regulated by miR-34a, in TAMs and bone marrow derived macrophages (BMDMs) in detail. One of them is CSF1R, the receptor for colony-stimulating factor 1 (CSF1) and the other IL4R, the receptor for interleukin 4. Both cytokine/receptor pairs are known, central regulators of TAM M1/M2 polarization, which is central for the anti- or pro-tumorigenic potential of TAMs. Therefore, we will analyze mice with macrophage-specific deletion of CSF1R or IL4R combined with miR-34a deletion. We will evaluate the influence of miR-34a on inflammatory signalling, mRNA expression and polarization in BMDMs and TAMs derived from these mice, as well as their effects on the invasiveness of co-cultured CRC cells. Furthermore, we will determine the relevance of macrophage miR-34a for suppression of invasiveness in mouse models of CAC. In addition, we plan to interrogate the therapeutic relevance of CSF1R and IL4R activation by genetically and therapeutically inhibiting these receptors in miR-34a-deficient mice in mouse models of CAC and sporadic CRC. In addition, we will determine the relevance of miR-34a for the ability of myeloid p53 to suppress the formation of adenomas in the APCmin mouse model. In summary, the planned analyses represent an important contribution to understanding the role of miR-34a as a mediator of tumor suppression. In the future, the clinical translation of these results may be relevant for the treatment and prognostication of sporadic colon and colitis-associated cancer.