Notch Ankyrin Repeat Domain Variation Influences Leukemogenesis and Myc Transactivation

, cell-based and structural analyses to compare the abilities of activated Notch1-4 to support T cell development, induce T cell acute lymphoblastic leukemia/lymphoma (T-ALL), and maintain T-ALL cell growth and survival., a direct Notch target that has an important role in Notch-associated T-ALL.We conclude that the leukemogenic potentials of Notch receptors vary, and that this functional difference stems in part from divergence among the highly conserved ankyrin repeats, which influence the transactivation of specific target genes involved in leukemogenesis

Developmental-associated differences in membrane cholesterol content play a defining role in the response of transitional immature and mature B cells upon B cell receptor engagement

The immature B cell represents an important window in B lymphocyte development, for it is at this stage that cells expressing B cell antigen receptors (BCRs) specific for endogenous or “self” antigens can be identified and eliminated, inactivated, or undergo alterations in their receptor specificity in processes collectively referred to as B cell tolerance. The long-term objective of this project is to define the molecular basis for differences in the responsiveness of immature and follicular mature B cells to BCR signaling. Although multiple mechanisms of tolerance affect the ultimate fate of the B cell, we have determined that intrinsic or “hard-wired” differences in BCR-induced signal transduction dictate B cell fate decisions. Transitional B cells fail to sustain BCR triggered pathways linked to survival, proliferation, and cytoskeletal re-organization and maintain lower levels of unesterified cholesterol in their plasma membrane relative to mature B cells. We have recently shown that this latter phenotype accounts for their inability to localize their BCR into cholesterol-enriched membrane compartments following BCR aggregation. As repletion of membrane cholesterol in transitional B cells reverses proximal signaling differences, we hypothesize that developmental differences in cholesterol levels represent the defining difference between immature and mature B cells that dictates their cell fate following BCR engagement. Therefore, we have utilized several different approaches to specifically manipulate cholesterol levels in transitional B cells and evaluate potential links between cholesterol content and differential BCR-induced signal transduction and cell fate. My studies in this thesis demonstrate that developmentally regulated or cell type-specific differences in membrane cholesterol levels can have significant physiologic impact on tolerance induction in B cells in vivo