Intestinal epithelial cells (IECs) are the first to encounter luminal antigens and may be involved in intestinal immune responses. Fungi are important components of the intestinal microflora. The potential role of fungi, and in particular their cell wall component β-glucan, in modulating human intestinal epithelial responses is still unclear. Here we examined whether human IECs are capable of recognizing and responding to β-glucans, and the potential mechanisms of their activation. We show that human IECs freshly isolated from surgical specimens, and the human IEC lines HT-29 and SW480, express the β-glucan receptor Dectin-1. The β-glucan-consisting glycans curdlan and zymosan stimulated IL-8 and CCL2 secretion by IEC lines. This was significantly inhibited by a Dectin-1 blockade using its soluble antagonist laminarin. Spleen tyrosine kinase (Syk), a signaling mediator of Dectin-1 activation, is expressed in human IECs. β-glucans and Candida albicans induced Syk phosphorylation, and Syk inhibition significantly decreased β-glucan-induced chemokine secretion from IECs. Thus, IECs may respond to β-glucans by the secretion of pro-inflammatory chemokines in a Dectin-1- and Syk-dependent pathway, via receptors and a signaling pathway described to date only for myeloid cells. These findings highlight the importance of fungi-IEC interactions in intestinal inflammation.
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spleen tyrosine kinase (SYK) was recently identified as a new target in acute myeloid leukemia (AML); however, its mechanistic role in this disease is poorly understood. Based on the known interaction between SYK and mammalian target of rapamycin (mTOR) signaling in lymphoma, we hypothesized that SYK may regulate mTOR signaling in AML. Both small-molecule inhibition of SYK and SYK-directed shRNA suppressed mTOR and its downstream signaling effectors, as well as its upstream activator, AKT. Moreover, the inhibition of multiple nodes of the phosphatidylinositol 3'-kinase (PI3K) signaling pathway enhanced the effects of SYK suppression on AML cell viability and differentiation. Evaluation of the collateral mitogen-activated protein kinase (MAPK) pathway revealed a heterogeneous response to SYK inhibition in AML with downregulation of MEK and extracellular signal-regulated kinase (ERK) phosphorylation in some AML cell lines but a paradoxical increase in MEK/ERK phosphorylation in RAS-mutated AML. These studies reveal SYK as a regulator of mTOR and MAPK signaling in AML and demonstrate that inhibition of PI3K pathway activity enhances the effects of SYK inhibition on AML cell viability and differentiation.

We report preclinical proof of principle for effective treatment of B-precursor acute lymphoblastic leukemia (ALL) by targeting the spleen tyrosine kinase (SYK)-dependent antiapoptotic blast cell survival machinery with a unique nanoscale pharmaceutical composition. This nanoscale liposomal formulation (NLF) contains the pentapeptide mimic 1,4-Bis (9-O dihydroquinidinyl) phthalazine/hydroquinidine 1,4-phathalazinediyl diether (C61) as the first and only selective inhibitor of the substrate binding P-site of SYK. The C61 NLF exhibited a very favorable pharmacokinetic and safety profile in mice, induced apoptosis in primary B-precursor ALL blast cells taken directly from patients as well as in vivo clonogenic ALL xenograft cells, destroyed the in vivo clonogenic fraction of ALL blast cells, and, at nontoxic dose levels, exhibited potent in vivo antileukemic activity against patient-derived ALL cells in xenograft models of aggressive B-precursor ALL. Our findings establish SYK as an attractive molecular target for therapy of B-precursor ALL. Further development of the C61 NLF may provide the foundation for therapeutic innovation against therapy-refractory B-precursor ALL.