Novel Mechanism for FcϵRI-mediated Signal Transducer and Activator of Transcription 5 (STAT5) Tyrosine Phosphorylation and the Selective Influence of STAT5B over Mast Cell Cytokine Production

Nicholas A Pullen,Brian O Barnstein,Yves T Falanga,Zhengqi Wang,Ryo Suzuki,Tenchee D Lama Tamang,Michele C Khurana,Emily A Harry,Petr Draber,Kevin D Bunting,Kazuya Mizuno,Bridget S Wilson,John J Ryan

doi:10.1074/jbc.m111.311142

Abstract

Previous studies indicate that STAT5 expression is required for mast cell development, survival, and IgE-mediated function. STAT5 tyrosine phosphorylation is swiftly and transiently induced by activation of the high affinity IgE receptor, FcεRI. However, the mechanism for this mode of activation remains unknown. In this study we observed that STAT5 co-localizes with FcεRI in antigen-stimulated mast cells. This localization was supported by cholesterol depletion of membranes, which ablated STAT5 tyrosine phosphorylation. Through the use of various pharmacological inhibitors and murine knock-out models, we found that IgE-mediated STAT5 activation is dependent upon Fyn kinase, independent of Syk, PI3K, Akt, Bruton's tyrosine kinase, and JAK2, and enhanced in the context of Lyn kinase deficiency. STAT5 immunoprecipitation revealed that unphosphorylated protein preassociates with Fyn and that this association diminishes significantly during mast cell activation. SHP-1 tyrosine phosphatase deficiency modestly enhanced STAT5 phosphorylation. This effect was more apparent in the absence of Gab2, a scaffolding protein that docks with multiple negative regulators, including SHP-1, SHP-2, and Lyn. Targeting of STAT5A or B with specific siRNA pools revealed that IgE-mediated mast cell cytokine production is selectively dependent upon the STAT5B isoform. Altogether, these data implicate Fyn as the major positive mediator of STAT5 after FcεRI engagement and demonstrate importantly distinct roles for STAT5A and STAT5B in mast cell function.

Highlights

STAT5 is a transcription factor that is vital for mast cell function
Through the use of various pharmacological inhibitors and murine knock-out models, we found that IgE-mediated STAT5 activation is dependent upon Fyn kinase, independent of Syk, PI3K, Akt, Bruton’s tyrosine kinase, and JAK2, and enhanced in the context of Lyn kinase deficiency
The electron-dense quantum dot (QD) appear as small rods in the transmission electron microscopy image in Fig. 1A, where their distribution is clearly segregated from the 5-nm gold label for STAT5

Summary

Background

Results: Loss of Fyn kinase prevents, whereas loss of Lyn, Gab, or SHP-1 enhances, Fc⑀RI-mediated STAT5 tyrosine phosphorylation. SHP-1 tyrosine phosphatase deficiency modestly enhanced STAT5 phosphorylation This effect was more apparent in the absence of Gab, a scaffolding protein that docks with multiple negative regulators, including SHP-1, SHP-2, and Lyn. Targeting of STAT5A or B with specific siRNA pools revealed that IgE-mediated mast cell cytokine production is selectively. These data implicate Fyn as the major positive mediator of STAT5 after Fc⑀RI engagement and demonstrate importantly distinct roles for STAT5A and STAT5B in mast cell function. Studies utilizing STAT5A- or B-specific RNA interference demonstrated that STAT5B is the central and selective mediator of cytokine induction, independent of STAT5A These studies offer a novel mechanistic view of a central pathway controlling allergic disease

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION