All ETDs from UAB

Advisory Committee Chair

Christopher A Klug

Advisory Committee Members

Peter D Burrows

Peter J Detloff

Louis B Justement

Thomas M Ryan

Document Type

Dissertation

Date of Award

2014

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

B-lymphocyte commitment from common lymphoid progenitors (CLP) is orchestrated by a number of transcription factors and extracellular developmental cues. Most prominently, IL-7 signaling acts as a critical factor for promotion of B cell differentiation through its role in upregulation of the B-cell commitment factor, Ebf1, by activation of Jak-Stat5 signaling. Other cytokines and growth factors secreted by bone marrow stromal cells, such as Flt3 ligand, are known to modulate developmental outcomes by regulating the IL-7R-Jak-Stat5 pathway. The role of stem cell factor (SCF), the ligand of the receptor tyrosine kinase (RTK) c-Kit, and the mechanism by which it affects cell fate decisions in the B-lymphoid lineage remains unclear. In our studies, we demonstrate that increasing the concentration of SCF in the presence of IL-7 leads to dose-dependent inhibition of B cell differentiation from c-Kit+Lin-Sca-1+ (KLS) cells in the OP9 co-culture system. Similarly, overexpression of a constitutively active form of c-Kit, c-KitD814V, in the bone marrow cells completely inhibits B-lymphoid commitment in vivo, and stimulates expansion of Mac-1+Gr-1+ myeloid cells. Stimulation of c-Kit receptor with SCF was sufficient to inhibit IL-7-dependent upregulation of Ebf1 expression, as well as expression of other STAT5-dependent target genes including Socs3, Cis, and Osm in CLP cells ex vivo. Furthermore, phosphorylation of STAT5 in response to IL-7 signaling was also inhibited in presence of SCF. In this work, we demonstrate that Y567F/Y569F mutations within the SH2 docking site of the juxtamembrane region of c-KitD814V reduce expansion of myeloid lineage cells, but pro-vide only partial rescue of B cell development. In contrast, overexpression c-KitD814V harboring I570A and L937A substitution mutations in residues critical for activation of the E3 ubiquitin ligase c-Cbl, completely suppressed the ability of c-KitD814V to inhibit normal B lymphopoiesis in the bone marrow. Additionally, in contrast to IL-7-deficient cells, co-stimulation of CLP isolated from IL-7-/-Cbl-/- mice with IL-7 and SCF did not inhibit IL-7-dependent accumulation of STAT5, which suggests a critical role for c-Cbl in regulation of STAT5 in response to c-Kit activation. Overall, these results suggest that c-Kit signaling functions as a major mechanism for maintaining the oligopotent differentiation potential of CLP by inhibiting IL-7-dependent commitment to the B cell fate.

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