Protein tyrosine phosphatase activity associates with the high affinity IgE receptor and dephosphorylates the receptor subunits, but not Lyn or Syk.

Protein tyrosine phosphorylation is an early event in the high affinity IgE receptor (Fc epsilon RI)-mediated signaling cascade leading to secretion in mast cells. Numerous proteins, including the beta- and gamma-subunits of Fc epsilon RI, become tyrosine phosphorylated after receptor aggregation. Dephosphorylation of these proteins may be important to reverse and limit transmembrane signaling. RBL-2H3 mast cell lysates were found to contain protein tyrosine phosphatase activity that dephosphorylated the tyrosine-phosphorylated beta- and gamma-subunits of Fc epsilon RI. The protein tyrosine phosphatase activity associated with Fc epsilon RI and was equally present with receptors from nonactivated and stimulated cells. Moreover, the phosphatase eluted from the immunoprecipitates and, when added back, dephosphorylated both tyrosine-phosphorylated beta- and gamma-subunits, but not tyrosine-phosphorylated Lyn or Syk. These results strongly suggest that the IgE receptor-associated protein tyrosine phosphatase may regulate the steady state level of tyrosylphosphate of the beta- and gamma-subunits and, therefore, may modulate the interaction of these subunits with other downstream molecules, such as Syk.