NTAL phosphorylation is a pivotal link between the signaling cascades leading to human mast cell degranulation following kit activation and FcεRI aggregation

Aggregation of high-affinity receptors for immunoglobulin E (FcepsilonRI) on the surface of mast cells results in degranulation, a response that is potentiated by binding of stem cell factor (SCF) to its receptor Kit. We observed that one of the major initial signaling events associated with FcepsilonRI-mediated activation of human mast cells (HuMCs) is the rapid tyrosine phosphorylation of a protein of 25 to 30 kDa. The phosphorylation of this protein was also observed in response to SCF. This protein was identified as non-T-cell activation linker (NTAL), an adaptor molecule similar to linker for activated T cells (LAT). Unlike the FcepsilonRI response, SCF induced NTAL phosphorylation in the absence of detectable LAT phosphorylation. When SCF and antigen were added concurrently, there was a marked synergistic effect on NTAL phosphorylation, however, SCF did not enhance the phosphorylation of LAT induced by FcepsilonRI aggregation. FcepsilonRI- and SCF-mediated NTAL phosphorylation appear to be differentially regulated by Src kinases and/or Kit kinase, respectively. Diminution of NTAL expression by silencing RNA oligonucleotides in HuMCs resulted in a reduction of both Kit- and FcepsilonRI-mediated degranulation. NTAL, thus, appears to,be an important link between the signaling Pathways that are initiated by these receptors, culminating in mast cell degranulation.