Transmembrane Adaptor Protein PAG/CBP Is Involved in both Positive and Negative Regulation of Mast Cell Signaling

Abstract

The transmembrane adaptor protein PAG/CBP (here, PAG) is expressed in multiple cell types. Tyrosine-phosphorylated PAG serves as an anchor for C-terminal SRC kinase, an inhibitor of SRC-family kinases. The role of PAG as a negative regulator of immunoreceptor signaling has been examined in several model systems, but no functions in vivo have been determined. Here, we examined the activation of bone marrow-derived mast cells (BMMCs) with PAG knockout and PAG knockdown and the corresponding controls. Our data show that PAG-deficient BMMCs exhibit impaired antigen-induced degranulation, extracellular calcium uptake, tyrosine phosphorylation of several key signaling proteins (including the high-affinity IgE receptor subunits, spleen tyrosine kinase, and phospholipase C), production of several cytokines and chemokines, and chemotaxis. The enzymatic activities of the LYN and FYN kinases were increased in nonactivated cells, suggesting the involvement of a LYN- and/or a FYN-dependent negative regulatory loop. When BMMCs from PAG-knockout mice were activated via the KIT receptor, enhanced degranulation and tyrosine phosphorylation of the receptor were observed. In vivo experiments showed that PAG is a positive regulator of passive systemic anaphylaxis. The combined data indicate that PAG can function as both a positive and a negative regulator of mast cell signaling, depending upon the signaling pathway involved.

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ACKNOWLEDGMENTS

We thank H. Mrazova, L. Kocanda, and R. Budovicova for technical assistance.

This work was supported by projects 301/09/1826, P302/10/1759, P302-14-09807S, P302/12/G101, P305-14-00703S, and 204/09/H084 from the Czech Science Foundation, by Action BM1007 from European Cooperation in Science and Technology, by project LD12073 COST-CZ-MAST from the Ministry of Education, Youth, and Sports of the Czech Republic, and by the Institute of Molecular Genetics of the Academy of Sciences of the Czech Republic (RVO 68378050). L.P., M.B., and I.P. were supported in part by the Faculty of Science, Charles University, Prague, Czech Republic.

We have no conflicting financial interests.