| Summary: | Mast cells (MCs) play a crucial role in the induction of allergic asthma by secreting inflammatory mediators in response to allergens. In addition to MC activation via the antigen/IgE receptor FcεR1, MC tissue recruitment and responsiveness is greatly enhanced by co-stimulation with the stem cell factor (SCF). Levels of SCF are elevated in the asthmatic lung, where it stimulates the c-Kit receptor on MCs. Sufficient signaling through c-Kit and FcεR1 requires the activation of Src family kinases, which can be regulated by protein tyrosine phosphatase alpha (PTPα). Our lab has previously demonstrated that PTPα exerts positive regulatory effects on SCF-stimulated c-Kit phosphorylation and MC migration. In contrast, PTPα negatively regulates antigen-induced mast cell activation and the release of inflammatory mediators. To determine the role of PTPα in the integrated c-Kit and FcεR1 signaling that is believed to facilitate allergic inflammation, mouse bone marrow-derived WT and PTPα-KO MCs were treated with combinations of antigen and SCF, and analyzed for secretory and migratory responses as well as for the activation of key signaling proteins. However, the expected MC hyper-responsiveness due to the lack of PTPα was not observed, which may have arisen from intrinsic changes in the cultured mast cells and not from testing methodologies. Co-treatment with antigen and SCF produced synergistic degranulation and cytokine release that was similar between WT and PTPα-KO MCs. Yet, PTPα was required for the full phosphorylation of Akt and p38 after 15 min co-treatment with antigen and SCF. PTPα itself was found to be dephosphorylated at tyrosine 789, especially upon treatment with antigen. During fibronectin-aided Transwell migration towards SCF, the addition of antigen significantly reduced the number of PTPα-KO but not WT MCs that remained attached to fibronectin. Interestingly, in the presence of fibronectin, the SCF-mediated migration of WT and PTPα-KO MCs was not significantly affected by the addition of antigen, whereas fibronectin-independent MC migration was synergistically enhanced by antigen and SCF. Taken together, despite effects on the FcεRI/c-Kit integrated activation of downstream signaling proteins, the overall SCF-enhanced mediator release and migration of mast cells were found to be independent of PTPα.
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