Suppressor of Cytokine Signaling (SOCS)1 Regulates Interleukin-4 (IL-4)-activated Insulin Receptor Substrate (IRS)-2 Tyrosine Phosphorylation in Monocytes and Macrophages via the Proteasome.

Allergic asthma is a chronic lung disease initiated and driven by Th2 cytokines IL-4/-13. In macrophages, IL-4/-13 bind IL-4 receptors, which signal through insulin receptor substrate (IRS)-2, inducing M2 macrophage differentiation. M2 macrophages correlate with disease severity and poor lung function, although the mechanisms that regulate M2 polarization are not understood. Following IL-4 exposure, suppressor of cytokine signaling (SOCS)1 is highly induced in human monocytes. We found that siRNA knockdown of SOCS1 prolonged IRS-2 tyrosine phosphorylation and enhanced M2 differentiation, although siRNA knockdown of SOCS3 did not affect either. By co-immunoprecipitation, we found that SOCS1 complexes with IRS-2 at baseline, and this association increased after IL-4 stimulation. Because SOCS1 is an E3 ubiquitin ligase, we examined the effect of proteasome inhibitors on IL-4-induced IRS-2 phosphorylation. Proteasomal inhibition prolonged IRS-2 tyrosine phosphorylation, increased ubiquitination of IRS-2, and enhanced M2 gene expression. siRNA knockdown of SOCS1 inhibited ubiquitin accumulation on IRS-2, although siRNA knockdown of SOCS3 had no effect on ubiquitination of IRS-2. Monocytes from healthy and allergic individuals revealed that SOCS1 is induced by IL-4 in healthy monocytes but not allergic cells, whereas SOCS3 is highly induced in allergic monocytes. Healthy monocytes displayed greater ubiquitination of IRS-2 and lower M2 polarization than allergic monocytes in response to IL-4 stimulation. Here, we identify SOCS1 as a key negative regulator of IL-4-induced IRS-2 signaling and M2 differentiation. Our findings provide novel insight into how dysregulated expression of SOCS increases IL-4 responses in allergic monocytes, and this may represent a new therapeutic avenue for managing allergic disease.

ß-Catenin is required for the differentiation of iNKT2 and iNKT17 cells that augment IL-25-dependent lung inflammation.

BACKGROUND: Invariant Natural Killer T (iNKT) cells have been implicated in lung inflammation in humans and also shown to be a key cell type in inducing allergic lung inflammation in mouse models. iNKT cells differentiate and acquire functional characteristics during development in the thymus. However, the correlation between development of iNKT cells in the thymus and role in lung inflammation remains unknown. In addition, transcriptional control of differentiation of iNKT cells into iNKT cell effector subsets in the thymus during development is also unclear. In this report we show that ß-catenin dependent mechanisms direct differentiation of iNKT2 and iNKT17 subsets but not iNKT1 cells. METHODS: To study the role for ß-catenin in lung inflammation we utilize mice with conditional deletion and enforced expression of ß-catenin in a well-established mouse model for IL-25-dependen lung inflammation. RESULTS: Specifically, we demonstrate that conditional deletion of ß-catenin permitted development of mature iNKT1 cells while impeding maturation of iNKT2 and 17 cells. A role for ß-catenin expression in promoting iNKT2 and iNKT17 subsets was confirmed when we noted that enforced transgenic expression of ß-catenin in iNKT cell precursors enhanced the frequency and number of iNKT2 and iNKT17 cells at the cost of iNKT1 cells. This effect of expression of ß-catenin in iNKT cell precursors was cell autonomous. Furthermore, iNKT2 cells acquired greater capability to produce type-2 cytokines when ß-catenin expression was enhanced. DISCUSSION: This report shows that ß-catenin deficiency resulted in a profound decrease in iNKT2 and iNKT17 subsets of iNKT cells whereas iNKT1 cells developed normally. By contrast, enforced expression of ß-catenin promoted the development of iNKT2 and iNKT17 cells. It was important to note that the majority of iNKT cells in the thymus of C57BL/6 mice were iNKT1 cells and enforced expression of ß-catenin altered the pattern to iNKT2 and iNKT17 cells suggesting that ß-catenin may be a major factor in the distinct pathways that critically direct differentiation of iNKT effector subsets. CONCLUSIONS: Thus, we demonstrate that ß-catenin expression in iNKT cell precursors promotes differentiation toward iNKT2 and iNKT17 effector subsets and supports enhanced capacity to produce type 2 and 17 cytokines which in turn augment lung inflammation in mice.