All ETDs from UAB

Advisory Committee Chair

Robert P Kimberly

Advisory Committee Members

Susan Bellis

Robin Lorenz

Selvarangan Ponnazhagan

Alexander Szalai

Document Type

Dissertation

Date of Award

2013

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Fc receptors provide an interface between humoral immunity and cellular immunity by binding to the Fc portion of immunoglobulin and mediating effector functions. Cells expressing Fc receptors play a major role in immune complex clearance via phagocytosis, leading to a context dependent pro- or anti-inflammatory environment. Signaling by multi-chain Fc receptor complexes, including FcgRI, FcgRIII, FceRI and FcaRI is mediated by the ITAM-containing common FceRIg (g-chain) subunit. However, despite the use of a common g-chain, different Fc receptor complexes elicit specific cellular programs, suggesting additional layers of regulation of tyrosine based signaling by g-chain. We hypothesized that the unique g-chain cytoplasmic domains differentially modulate Fc receptor complex functions. In order to test our hypothesis, we established P388D1 and RBL-2H3 cell lines stably expressing either WT or Tail minus (TL) mutant FcgRI g-chains. Data from these systems suggest that g-chain cytoplasmic domain (CY) indeed influences certain Fc receptor signaling pathways such as phagocytosis, degranulation and IL-6 production, but not others such as TNF-a and IL-1b production. Furthermore, serine and threonine residues in the g-chain are reportedly phosphorylated after Fc receptor stimulation. We hypothesized that putative phosphorylation of serine/threonine sites fine-tune Fc receptor signaling, and provide the additional layer of regulation. To test this hypothesis, we stably transfected WT human g-chain or mutants carrying serine/threonine to alanine changes into RBL-2H3 cells lacking the endogenous g-chain expression. Using these cells, we observed that serine/threonine residues in the g-chain ITAM influence g-chain signaling pathways such as IL-4 production and intracellular calcium flux. Additionally, using mass spectrometry, we observed that Serine 51 in the ITAM is phosphorylated in stimulated samples. Studies with Serine 51 to Alanine and Aspartic Acid mutants suggest an inhibitory role for Serine 51 phosphorylation in g-chain signaling. Taken together, our data identified two layers of regulation of signaling by Fc receptors that utilizefnthe commonfng-chain. Identification of these regulators and, more importantly, identification of their interacting proteins, will provide attractive therapeutic targets for pharmacological interventions in Fc receptor mediated diseases.

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