Novel Mechanisms of Calcium-Dependent NF-kappaB Activation in Lymphocytes
Thursday, May 26, 2016
2:00 PM-4:00 PM
BIOMED PhD Research Proposal
Title:
Novel Mechanisms of Calcium-Dependent NF-kappaB Activation in Lymphocytes
Speaker:
Corbett T. Berry, MD/PhD Candidate, School of Biomedical Engineering, Science and Health Systems
Advisors:
Uri Hershberg, PhD, Assistant Professor, School of Biomedical Engineering, Science and Health Systems
Bruce Freedman, VMD, PhD, Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania
Abstract:
T cell fates initiated by engagement of the TCR and costimulatory molecules are encoded, in part, by intracellular calcium (Ca2+) signals. However, how Ca2+ encodes differences in antigen avidity and costimulatory influences and how these signals are decoded into unique transcriptional programs controlling distinct T cell fates and functions is unknown. The significance of this signal is evident in human patients with deficient TCR-induced Ca2+ entry due to functional defects in the ER transmembrane Ca2+-sensing STIM proteins. These individuals suffer from devastating immune dysfunctions including defects in T cell activation and a severe reduction in natural regulatory T cells (nTregs). Similarly, mice whose T cell progenitors lack STIM1/2 exhibit a selective defect in nTreg induction, including reduced CD4+ CD25+ Foxp3- and CD4+ CD25+ Foxp3+ T cells. Interestingly, a similar selective reduction in nTregs is observed in NF-κB p65 and c-Rel deficient mice raising important questions about the role of Ca2+ signaling in NF-κB signaling and thymocyte differentiation. Despite extensive efforts to unravel the molecular and biochemical mechanisms controlling TCR-induced Ca2+ signaling and NF-κB activation, we know virtually nothing about how Ca2+ controls NF-κB activation and NF-κB dependent transcriptional specificity.
At rest, NF-κB hetero-/homo-dimers of c-Rel and p65 are sequestered in the cytoplasm by inhibitory kappa-B (IκB) proteins and, following TCR engagement, NF-κB release from IκB proteins is initiated by protein kinase Cθ (PKCθ). While IκBα degradation is necessary, it is not sufficient for full transcriptional activation of NF-κB. Rather, post-translational modifications on p65 and c-Rel critically regulate their activity. Indeed, we recently established a novel mechanism of Ca2+-induced p65 Ser536 phosphorylation that critically regulates it nuclear localization and transcriptional activation and preliminary studies have revealed two additional novel Ca2+ depependent phospho-acceptors, Ser316 on p65 and Ser34 on c-Rel. Published studies support the idea that quantitatively distinct Ca2+ waveforms can initiate distinct NF-κB-dependent transcriptional programs through p65 and c-Rel dependent transcriptional activation. Thus, the overarching hypothesis of this proposal is that dynamic Ca2+ signals and distinct kinases tuned to these dynamics control the phosphorylation landscape of p65 and c-Rel and thereby the patterns of NF-κB-dependent gene expression and cell fate. To address this hypothesis, I will define how dynamic Ca2+ signals control the phosphorylation of specific serines on p65 and c-Rel to initiate transcription in T lymphocytes. These efforts will establish a mechanistic framework for developing new approaches to pharmacologically modulate Ca2+ signals and their targets to tune immune activation or prevent pathophysiological immune dysfunction.
Contact Information
Ken Barbee
215-895-1335
barbee@drexel.ed