Protein tyrosine kinase Syk is involved in Thy‐1 signaling in rat basophilic leukemia cells

Publisher Website
Google Scholar
Abstract
Thy‐1, a glycosyl‐phosphatidylinositol‐anchored surface glycoprotein, has been shown to possess transmembrane signaling capacity. In rat mast cells and rat basophilic leukemia cells (RBL) aggregation of surface Thy‐1 with antibodies triggers a series of intracellular events, resembling those induced by aggregation of the high‐affinity receptor for IgE (FcεRI), including tyrosine phosphorylation of multiple proteins and release of secretory components. Unlike the FcεRI‐mediated activation, where both the membrane‐associated protein tyrosine kinase (PTK) Lyn and the cytoplasmic PTK Syk are responsible for initiating the signaling cascade, only Lyn has been implicated in Thy‐1‐mediated activation in RBL cells. Here we report that Syk is also rapidly tyrosine phosphorylated upon Thy‐1 cross‐linking. Increased Syk tyrosine phosphorylation is observed only in cells in which extensive aggregation of Thy‐1 is induced by two layers of cross‐linking reagents. RBL‐derived mutant cells deficient in the expression of surface Thy‐1 and transfectants re‐expressing surface Thy‐1 were used to exclude the possibility that Syk activation reflects an interaction of the cross‐linking reagents with surface molecules other than Thy‐1. As FcεRI γ subunits are well known to promote activation of Syk and its recruitment to membrane complexes, we also investigated the role of these subunits in Thy‐1‐mediated Syk activation, using RBL‐derived mutant cells deficient in the expression of FcεRI γ subunits and their revertants. Consistent with the lack of FcεRI expression, no IgE‐induced response could be elicited, while Thy‐1‐inducible Syk phosphorylation was preserved. Our results suggest that Syk might be one of the kinases responsible for signal propagation upon Thy‐1 cross‐linking in a FcεRI‐independent pathway.

This publication has 52 references indexed in Scilit: