Roles of protein tyrosine kinase Syk in nasal polyps.

The non-receptor protein tyrosine kinase Syk is widely expressed and plays an important role in intracellular signal transduction in haematopoietic cells including B cells, mast cells, eosinophils, platelets, macrophages, neutrophils and T cells. We found that Syk is expressed in human nasal polyp tissue-derived fibroblasts and plays a critical role in chemokine production and activation of c-Jun N-terminal kinase 1 stimulated with lipopolysaccharide or IL-1. In mast cells, cross-linking FcℇRI via IgE bound to multivalent antigen induces tyrosine phosphorylation of immunoreceptor tyrosine-based activation motifs, and binds and modifies the activity of Syk, thereby initiating downstream signalling. In eosinophils, Syk is essential for activating the antiapoptotic pathway and generating reactive oxygen intermediates in response to Fcγ receptor engagement. In nasal polyps, Syk inhibition might influence the levels and function of specific IgE to Staphylococcus aureus enterotoxins that are thought to drive local eosinophilic inflammation therein. The regulation of Syk expression may prove to be a useful strategy in the treatment of airway diseases. [ABSTRACT FROM AUTHOR]