Protein Tyrosine Phosphatase Shp-1 Modulates Microtubule Organization In Later Stages Of Mast Cell Activation

Abstract Antigen-mediated activation of mast cells initiates signaling events leading to degranulation and release of inflammatory mediators. Although rapid and transient microtubule reorganization during activation has been described, the molecular mechanisms that control their rearrangement are largely unknown. Important role in microtubule nucleation from centrosomes play γ-tubulin complexes. Here we report on the regulation of microtubule organization in bone marrow-derived mast cells (BMMCs) by Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 1 (SHP-1). Reciprocal immunoprecipitation experiments revealed that SHP-1 is present in complexes containing γ-tubulin complex proteins and protein tyrosine kinase Syk. Pull-down experiments with truncated forms of γ-tubulin and SHP-1 unveiled corresponding interaction domains. When compared to controls, activated BMMCs without SHP-1 had more protrusions containing microtubules, higher level of tyrosine phosphorylation, enhanced activity of Syk kinase, as well as increased expression of cytokines and prostaglandins. Intracellular calcium mobilization and degranulation also increased. Microtubule regrowth experiments in cells lacking SHP-1 revealed stimulation of microtubule nucleation, and phenotypic rescue experiments confirmed that SHP-1 represents a negative regulator of microtubule nucleation in BMMCs. Moreover, inhibition of the SHP-1 activity by inhibitors TPI-1 and NSC87877 also augmented microtubule nucleation. The regulation was due to changes of γ-tubulin accumulation in centrosomes. Our data suggest a novel SHP-1 dependent mechanism for the suppression of microtubule formation in later stages of mast cell activation.