Immunological trigger of mast cells by monomeric IgE: effect on microphthalmia transcription factor, STAT3 network of interactions.

Microphthalmia transcription factor (MITF) and STAT3 are two transcription factors that play a major role in the regulation of growth and function of mast cells and melanocytes. We have previously provided experimental evidence regarding the functional cross-talk between MITF, protein inhibitor of activated STAT3, and STAT3 in response to cytokine activation of mast cells. Recent studies have demonstrated that binding of different IgE molecules to their FcepsilonRI induces a spectrum of intracellular events in the absence of specific Ag. In this work, we show for the first time that, in mouse bone marrow-derived mast cells and in rat basophilic leukemia cells, monomeric IgE alone can induce the MITF-protein inhibitor of activated STAT3-STAT3 network of interactions and leads to phosphorylation of MITF at S73 and of STAT3 at both tyrosine 705 and S727. This phosphorylation increases the transcriptional activity of MITF and STAT3 as indicated by mRNA accumulation of their target genes such as Bcl-2, granzyme B, and c-Myc. Interestingly, MITF and STAT3 were not found to be obligatory factors in the anti-apoptotic response induced by IgE. Thus, the phenomenon that IgE alone was able to induce transcription factors that are essential for mast cell function could contribute to our understanding of the pathogenesis of allergy and its associated diseases.