Dedicator of cytokinesis 8 regulates signal transducer and activator of transcription 3 activation and promotes T_H17 cell differentiation.

Abstract

The autosomal recessive hyper-IgE syndrome (HIES) caused by dedicator of cytokinesis 8 (DOCK8) deficiency shares clinical features with autosomal dominant HIES because of signal transducer and activator of transcription 3 (STAT3) mutations, including recurrent infections and mucocutaneous candidiasis, which are suggestive of T_H17 cell dysfunction. The mechanisms underlying this phenotypic overlap are unclear. We sought to elucidate common mechanisms operating in the different forms of HIES. We analyzed the differentiation of CD4⁺ T_H cell subsets in control and DOCK8-deficient subjects. We also examined the role of DOCK8 in regulating STAT3 activation in T cells. T_H cell differentiation was analyzed by ELISA, flow cytometry, and real-time PCR measurements of cytokines and T_H cell transcription factors. The interaction of DOCK8 and STAT3 signaling pathways was examined by using flow cytometry, immunofluorescence, coimmunoprecipitation, and gene expression analysis. There was a profound block in the differentiation of DOCK8-deficient naive CD4⁺ T cells into T_H17 cells. A missense mutation that disrupts DOCK8 guanine nucleotide exchange factor (GEF) activity while sparing protein expression also impaired T_H17 cell differentiation. DOCK8 constitutively associated with STAT3 independent of GEF activity, whereas it regulated STAT3 phosphorylation in a GEF activity-dependent manner. DOCK8 also promoted STAT3 translocation to the nucleus and induction of STAT3-dependent gene expression. DOCK8 interacts with STAT3 and regulates its activation and the outcome of STAT3-dependent T_H17 differentiation. These findings might explain the phenotypic overlap between DOCK8 deficiency and autosomal dominant HIES.