All ETDs from UAB

Advisory Committee Chair

Louis B Justement

Advisory Committee Members

Peter D Burrows

Randall S Davis

John F Kearney

Chandar Raman

Harry W Schroeder, Jr

Document Type

Dissertation

Date of Award

2017

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

This dissertation research describes two independent characterizations of molecular pathways involved in the manufacture of class-switched antibodies and differentiation of B cells involving the adaptor protein Hematopoietic SRC Homology 2 Domain-containing protein (HSH2) and the surface molecule CD19. HSH2 is dynamically expressed in different subsets of B cells, showing high expression in B1 and MZ B cells and low expression in GC B cells. Experiments involving HSH2 transgenic mice have determined that HSH2 may act as a rheostat regulating the production of class-switched antibodies. Various factors that stimulate B cell activation and differentiation induce HSH2 expression, although regulation of HSH2 has not been characterized. Here we describe a novel mechanism by which NF-B regulates HSH2 at the level of protein turnover by negatively regulating a short-lived labile protease. HSH2 is dependent on NF-B activity for maintenance and upregulation, while inhibition of NF-B leads to rapid degradation of HSH2. CD19 is a 97kD protein that interacts with the B cell receptor to amplify downstream signaling through its cytosolic phosphorylated tyrosines. CD19 knock-out studies have demonstrated the importance of CD19 signaling in an effective BCR-dependent immune response to both T-dependent and T-independent antigens. CD19-/- mice develop few B1 B cells, MZ B cells or GC B cells. CD19 contains several cytosolic tyrosine residues that when phosphorylated allow binding of effector proteins, thus mediating downstream signaling events. Mice with point mutations replacing tyrosines with phenylalanine at Y482 and Y513 on the cytosolic side of CD19 exhibit a similar phenotype to CD19-/- mice in terms of B cell development and antibody response against T-dependent and T-independent antigens. However, the importance of CD19-mediated signaling via upstream tyrosines, or whether CD19 Y482/Y513-mediated signaling is sufficient to retain a wild-type B cell subset phenotype and antigen-specific antibody response against T-dependent and T-independent antigens are not well understood. Using mice with tyrosine to phenylalanine point mutations at all positions in CD19 except 482 and 513, we demonstrate that CD19 Y82 and Y513 are sufficient for MZ and B1 B cell development but confer a skewed antigen-specific antibody response against T-dependent and T-independent antigens.

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