Probes for MTOR

Deregulated expression of MYC is a driver of colorectal carcinogenesis, suggesting that inhibiting MYC may have significant therapeutic value. The PI3-kinase and mTOR pathways control MYC turnover and translation, respectively, providing a rationale to target both pathways to inhibit MYC. Surprisingly, inhibition of PI3-kinase does not promote MYC turnover in colon carcinoma cells, but enhances MYC expression since it promotes FOXO-dependent expression of growth factor receptors and MAPkinase-dependent transcription of MYC. Inhibition of mTOR fails to inhibit translation of MYC, since levels of 4E-BPs are insufficient to fully sequester eIF4E and since an IRES-element in the 5'-UTR of the MYC permits translation independent of eIF4E. A small molecule inhibitor of the translation factor, eIF4A, silvestrol, bypasses the signaling feedbacks, reduces MYC translation and inhibits tumor growth in a mouse model of colorectal tumorigenesis. We propose that targeting translation initiation is a promising strategy to limit MYC expression in colorectal tumors.

The small intestinal epithelial barrier inputs signals from the gut microbiota in order to balance physiological inflammation and tolerance, and to promote homeostasis. Understanding the dynamic relationship between microbes and intestinal epithelial cells has been a challenge given the cellular heterogeneity associated with the epithelium and the inherent difficulty of isolating and identifying individual cell types. Here, we used single-cell RNA sequencing of small intestinal epithelial cells from germ-free and specific pathogen-free mice to study microbe-epithelium crosstalk at the single-cell resolution. The presence of microbiota did not impact overall cellular composition of the epithelium, except for an increase in Paneth cell numbers. Contrary to expectations, pattern recognition receptors and their adaptors were not induced by the microbiota but showed concentrated expression in a small proportion of epithelial cell subsets. The presence of the microbiota induced the expression of host defense- and glycosylation-associated genes in distinct epithelial cell compartments. Moreover, the microbiota altered the metabolic gene expression profile of epithelial cells, consequently inducing mTOR signaling thereby suggesting microbe-derived metabolites directly activate and regulate mTOR signaling. Altogether, these findings present a resource of the homeostatic transcriptional and cellular impact of the microbiota on the small intestinal epithelium.