Intestinal epithelial cells (IECs

Spleen Tyrosine Kinase (SYK) is a critical immune signaling molecule and therapeutic target. We identified damaging monoallelic SYK variants in six patients with immune deficiency, systemic disease such as colitis, arthritis and skin inflammation, and diffuse large B cell lymphomas. The SYK variants increased phosphorylation and enhanced downstream signaling indicating gain-of-function. A knock-in (SYK S544Y ) mouse model of a patient variant (p.S550Y) recapitulated aspects of the human disease that could be partially treated with a SYK inhibitor or transplantation of bone marrow from wildtype mice. Our studies demonstrate that SYK gain-of-function variants result in a potentially treatable form of inflammatory disease.

Autophagy, a process of self-digestion of cellular constituents, regulates the balance between protein synthesis and protein degradation. Beclin 1 represents an important component of the autophagic machinery. It interacts with proteins that positively regulate autophagy, such as Vps34, UVRAG, and Ambra1, as well as with anti-apoptotic proteins such as Bcl-2 via its BH3-like domain to negatively regulate autophagy. Thus, Beclin 1 interactions with several proteins may regulate autophagy. To identify novel Beclin 1 interacting proteins, we utilized a GST-Beclin 1 fusion protein. Using mass spectroscopic analysis, we identified Beclin 1 as a protein that interacts with GST-Beclin 1. Further examination by cross linking and co-immunoprecipitation experiments confirmed that Beclin 1 self-interacts and that the coiled coil and the N-terminal region of Beclin 1 contribute to its oligomerization. Importantly, overexpression of vps34, UVRAG, or Bcl-x(L), had no effect on Beclin 1 self-interaction. Moreover, this self-interaction was independent of autophagy induction by amino acid deprivation or rapamycin treatment. These results suggest that full-length Beclin 1 is a stable oligomer under various conditions. Such an oligomer may provide a platform for further protein-protein interactions.

Intestinal epithelial cells (IECs) are the first to encounter luminal antigens and play an active role in intestinal immune responses. We previously reported that β‐glucans, major fungal cell‐wall glycans, induced chemokine secretion by IEC lines in a Dectin‐1‐ and Syk‐dependent manner. Here, we show that in contrast to β‐glucans, stimulation of IEC lines with Candida albicans and Saccharomyces cerevisiae did not induce secretion of any of the proinflammatory cytokines IL‐8, CCL2, CXCL1, and GM‐CSF. Commensal fungi and β‐glucans activated Syk and ERK in IEC lines. However, only β‐glucans activated p38, JNK, and the transcription factors NF‐κB p65 and c‐JUN, which were necessary for cytokine secretion. Furthermore, costimulation of IEC lines with β‐glucans and C. albicans yielded decreased cytokine secretion compared to stimulation with β‐glucans alone. Finally, ex vivo stimulation of human colonic mucosal explants with zymosan and C. albicans, leads to epithelial Syk and ERK phosphorylation, implying recognition of fungi and similar initial signaling pathways as in IEC lines. Lack of cytokine secretion in response to commensal fungi may reflect IECs’ response to fungal glycans, other than β‐glucans, that contribute to mucosal tolerance. Skewed epithelial response to commensal fungi may impair homeostasis and contribute to intestinal inflammation.