The high affinity IgE receptor, FcepsilonRI, is comprised of an IgE-binding alpha chain and betagamma2 signaling subunits. FcepsilonRI controls allergic mediator secretion in mast cells. FcepsilonRIbeta topology and function are unique among human antigen receptors. Dr. Kinet and his colleagues have found that beta acts as an amplifier at two levels: 1) beta amplifies FcepsilonRI regulated signaling events in vitro and in vivo . 2) beta potentiates FcepsilonRI surface expression. They have identified a novel beta splice variant (betaT), which is co-expressed with wild-type (WT) beta, has a short half-life, and negatively regulates of FcepsilonRI surface expression. They will explore the molecular mechanisms behind the signaling and expression amplification functions of beta, and the receptor down regulation due to betaT. First, they will elucidate the signal amplification mechanism of beta. They will test the hypothesis that the signal amplifier function is due to the protein-protein interactions of the beta N- and C-termini. They will study whether the atypical structure of the ITAM signaling motif in the beta C-terminus, bears upon this role of beta, and test the hypothesis that beta N-terminus contributes to Lyn kinase activation/deactivation. Second, Dr. Kinet will elucidate the mechanism of expression amplification function by beta. They hypothesize that this amplification depends on interactions between alpha and beta in the ER. They will characterize the regions in alpha and beta that interact, and assay whether these interactions participate in beta expression amplifier function. Third, they will address the mechanism of action of betaT, which, in contrast to WT beta, is a negative regulator of FcepsilonRI. They will address 1) how betaT, affects levels of intracellular and mature FcepsilonRI subunits, 2) whether betaT and betaWT compete for nascent alpha chains in the ER, and 3) whether the short half-life of betaT reflects targeting of betaT and associated proteins to the proteasome. Finally, Dr. Kinet hypothesizes that the relative expression levels of betaT and WT beta may alter the allergic status of an individual, since expression of betaT severely alters FcepsilonRI expression on cells, and will change the intensity of their antigen responses. He will investigate 1) whether there are differences between individuals in the betaWT/betaT ratio, and 2) whether these differences correlate with allergic status.
