Title

Distinct roles of the ERK and the NFkappaB signaling pathways in dendritic cell differentiation of human progenitor cell line

Date of Award

2005

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Microbiology and Immunology

First Committee Member

Kelvin P. Lee, Committee Chair

Abstract

Dendritic cells (DC) play a unique role in immune response in that they perform contrasting functions such as immune stimulation and tolerance induction. There are currently two models (the functional plasticity model and the specialized lineage model) explaining the mechanism behind the generation of functionally distinct DC. Our findings that the ERK and the NFkappaB pathways play distinct roles during DC differentiation support the idea that early developmental divergences at the precursor level predispose the resulting DC to carry out specialized functions. The regulation of signaling pathways at the initiation of differentiation has clear biological relevance as several studies have shown that NFkappaB inhibition in DC precursors during tumorogenesis is associated with immunosuppression. To bypass proximal events triggered by exogenous cytokine-mediated receptor engagement, we use PKC activation (shown to be downstream of cytokine-driven DC differentiation of monocytes and CD34 + progenitors) by phorbol ester PMA as a direct intracellular signal to drive DC differentiation. In a multipotent hematopoietic cell line K562 we find that PMA preferentially triggers the activation of protein kinase CbetaII(PKCbetaII), and that the ERK and the NFkappaB pathways are both activated downstream. These studies are confirmed using cytokine-induced DC differentiation of human monocytes. Furthermore, we demonstrate that pathogens such as Yersinia pestis may target these pathways in progenitors as a strategy to inhibit DC differentiation and consequently subvert immunological response. Interestingly, the NFkappaB and the ERK pathways regulate distinct features of DC differentiation and their selective inactivation results in the development of qualitatively different DC. While the NFkappaB pathway mediates DC survival and causes the upregulation of DC surface and molecular markers (CD40 and Rel B), the induction of the MAPK/ERK pathway is associated with differentiation-induced growth arrest (possibly due to BCR-ABL downregulation). Functionally, while both pathways are required for efficient T cell stimulation, the selective inhibition of the MAPK/ERK results in less immunostimulatory DC, while the NFkappaB-inhibited DC induce T cell anergy. We speculate that our results have biological relevance to both peripheral homeostasis and immune dysfunctions where selective inactivation of NFkappaB during DC differentiation potentially predisposes precursors to become tolerogenic DC.

Keywords

Biology, Neuroscience; Biology, Microbiology; Health Sciences, Immunology

Link to Full Text

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