Summary Epidermal growth factor receptor (EGFR) regulates many crucial cellular programs, with seven different activating ligands shaping cell signaling in distinct ways. Using crystallography and other approaches, we show how the EGFR ligands epiregulin (EREG) and epigen (EPGN) stabilize different dimeric conformations of the EGFR extracellular region. As a consequence, EREG or EPGN induce less stable EGFR dimers than EGF – making them partial agonists of EGFR dimerization. Unexpectedly, this weakened dimerization elicits more sustained EGFR signaling than seen with EGF, provoking responses in breast cancer cells associated with differentiation rather than proliferation. Our results reveal how responses to different EGFR ligands are defined by receptor dimerization strength and signaling dynamics. These findings have broad implications for understanding receptor tyrosine kinase (RTK) signaling specificity. Our results also suggest parallels between partial and/or biased agonism in RTKs and G protein-coupled receptors, as well as new therapeutic opportunities for correcting RTK signaling output.

Multicellular organisms have co-evolved with complex consortia of viruses, bacteria, fungi and parasites, collectively referred to as the microbiota. In mammals, changes in the composition of the microbiota can influence a wide range of physiologic processes (including development, metabolism, and immune cell function) and are associated with susceptibility to multiple diseases. Alterations in the microbiota can also modulate host behaviors such as social activity, stress, and anxiety-related responses that are linked to diverse neuropsychiatric disorders. However, the mechanisms through which the microbiota influence neuronal activity and host behavior remain poorly defined. Here we demonstrate that manipulation of the microbiota in either antibiotictreated or germ-free adult mice results in significant deficits in fear extinction learning. Single nucleus RNA-sequencing of the medial prefrontal cortex of the brain revealed significant alterations in gene expression in multiple cell types including excitatory neurons and glial cells. Transcranial two-photon imaging following deliberate manipulation of the microbiota demonstrated that extinction learning deficits were associated with defective learning-related remodeling of postsynaptic dendritic spines and reduced activity in cue-encoding neurons in the medial prefrontal cortex. In addition to effects of manipulating the microbiota on behavior in adult mice, selective re-establishment of the microbiota revealed a limited neonatal developmental window in which microbiota-derived signals can restore normal extinction learning in adulthood. Lastly, unbiased metabolomic analysis identified four metabolites that were significantly downregulated in germ-free mice and were previous reported to be related to human and mouse models of neuropsychiatric disorders, suggesting that microbiota-derived compounds may directly affect brain function and behavior. Together, these data indicate that fear extinction learning requires microbiota-derived signals during both early postnatal neurodevelopment and in adult mice, with implications for our understanding of how diet, infection, and lifestyle influence brain health and subsequent susceptibility to neuropsychiatric disorders.

Retention of Golgi-resident integral membrane proteins depends on the supply of PI(4)P.

Interleukin (IL)-2 is a pleiotropic cytokine that is necessary to prevent chronic inflammation in the gastrointestinal tract 1 – 4 . The protective effects of IL-2 involve the generation, maintenance and function of regulatory T cells (Tregs) 4 – 8 , and low-dose IL-2 has emerged as a potential therapeutic strategy in inflammatory bowel disease (IBD) patients 9 . However, the cellular and molecular pathways that control the production of IL-2 in the context of intestinal health are undefined. Here we identify that IL-2 is acutely required to maintain Tregs and immunologic homeostasis throughout the gastrointestinal tract. Strikingly, lineage-specific deletion of IL-2 in T cells did not recapitulate these phenotypes in the small intestine. Unbiased analyses revealed that group 3 innate lymphoid cells (ILC3) are the dominant cellular source of IL-2 in the small intestine, which is selectively induced by IL-1β. Macrophages produce IL-1β in the small intestine and activation of this pathway involves MyD88- and Nod2-dependent sensing of the microbiota. Loss-of-function studies defined that ILC3-derived IL-2 is essential to maintain Tregs, immunologic homeostasis and oral tolerance to dietary antigens uniquely in the small intestine. Furthermore, ILC3 production of IL-2 was significantly reduced in the small intestine of Crohn’s disease patients, and this correlated with diminished Tregs. Collectively, these results reveal a previously unappreciated pathway whereby a microbiota- and IL-1β-dependent axis promotes ILC3 production of IL-2 to orchestrate immune regulation in the intestine.

No abstract

Summary Physical separation between the mammalian immune system and commensal bacteria is necessary to limit chronic inflammation. However, selective species of commensal bacteria can reside within intestinal-associated lymphoid tissues of healthy mammals. Here, we demonstrate that lymphoid tissue-resident commensal bacteria (LRC) colonized murine dendritic cells and modulate their cytokine production. In germ-free and antibiotic-treated mice, LRCs colonized intestinal-associated lymphoid tissues and induced multiple members of the IL-10 cytokine family, including dendritic cell-derived IL-10 and group 3 innate lymphoid cell (ILC3)-derived IL-22. Notably, IL-10 limited the development of pro-inflammatory Th17 cell responses, and IL-22 production enhanced LRC colonization in the steady state. Furthermore, LRC colonization protected mice from lethal intestinal damage in an IL-10-IL-10R-dependent manner. Collectively, our data reveal a unique host-commensal bacteria dialogue whereby selective subsets of commensal bacteria interact with dendritic cells to facilitate tissue-specific responses that are mutually beneficial for both the host and the microbe.

Group 2 innate lymphoid cells (ILC2s) regulate immunity, inflammation, and tissue homeostasis. Two distinct subsets of ILC2s have been described: steady-state natural ILC2s and inflammatory ILC2s, which are elicited following helminth infection. However, how tissue-specific cues regulate these two subsets of ILC2s and their effector functions remains elusive. Here, we report that interleukin-33 (IL-33) promotes the generation of inflammatory ILC2s (ILC2 INFLAM ) via induction of the enzyme tryptophan hydroxylase 1 (Tph1). Tph1 expression was upregulated in ILC2s upon activation with IL-33 or following helminth infection in an IL-33-dependent manner. Conditional deletion of Tph1 in lymphocytes resulted in selective impairment of ILC2 INFLAM responses and increased susceptibility to helminth infection. Further, RNA sequencing analysis revealed altered gene expression in Tph1 deficient ILC2s including inducible T cell co-stimulator (Icos). Collectively, these data reveal a previously unrecognized function for IL-33, Tph1, and ICOS in promoting inflammatory ILC2 responses and type 2 immunity at mucosal barriers.

Bleeding and altered iron distribution occur in multiple gastrointestinal diseases, but the importance and regulation of these changes remain unclear. We found that hepcidin, the master regulator of systemic iron homeostasis, is required for tissue repair in the mouse intestine after experimental damage. This effect was independent of hepatocyte-derived hepcidin or systemic iron levels. Rather, we identified conventional dendritic cells (cDCs) as a source of hepcidin that is induced by microbial stimulation in mice, prominent in the inflamed intestine of humans, and essential for tissue repair. cDC-derived hepcidin acted on ferroportin-expressing phagocytes to promote local iron sequestration, which regulated the microbiota and consequently facilitated intestinal repair. Collectively, these results identify a pathway whereby cDC-derived hepcidin promotes mucosal healing in the intestine through means of nutritional immunity.