CD45-DEFICIENT RBL-2H3 CELLS - CELLULAR-RESPONSE TO FC-EPSILON-R AND IONOPHORE-INDUCED STIMULATION

The CD45 protein is a transmembrane tyrosine phosphatase that is requi red for normal T and B cell receptor-mediated signaling. In order to s tudy the function of this phosphatase in mast cells, we have isolated a CD45-deficient variant from the rat basophilic leukemia cell line (R BL-2H3), a tumor analog of mucosal mast cells. The secretory response as well as the inositol 1,4,5-triphosphate (InSP3) formation to Fcepsi lonRI and ionophore stimuli were similar in the RBL-2H3 cell line and its derived CD45-deficient subpopulation. However, pretreatment with t he phorbol ester TPA, which directly activates protein kinase C (PKC), caused a marked increase in mediator release and InSP3 production in the CD45-deficient variant compared to the parental RBL-2H3 cells. The se findings suggest that CD45 might directly or indirectly modify the activity of PKC or the InSP3-dephosphorylating phosphatase.