c-Rel deficiency and its effect on proliferation and survival in immunodeficient lymphoblastic B cells.

摘要

The analysis of lymphocytes from immunodeficient patients has provided valuable insights into understanding the development and function of the immune system. In particular, studies of patients with Hyper IgM syndrome, a rare immunodeficiency resulting from defects in both CD40L in activated CD4+ T cells and components of the CD40 signaling pathway in B cells have been crucial for the elucidation of molecular pathways involved in the activation, proliferation and differentiation of B lymphocytes. Previously our lab generated EBV transformed lymphoblastic cells with inducible LMP1 from a female patient diagnosed with non-X-linked HIGM (Pt1-LCLtet cells, Pt1). Analysis of these cells revealed a CD40-specific activation defect associated with low c-Rel levels. To broaden our understanding of the Pt1 phenotype we analyzed c-Rel expression and found that low c-Rel levels were the outcome of depressed transcriptional activation of the c-rel promoter. In-vivo analysis revealed that low transcription was coincident with increased p65 activity at the c- rel promoter although this was insufficient to induce normal c-Rel expression. Further investigations of the Pt1-LCLtet cells uncovered a proliferation and survival defect characterized by reduced c-Myc transcription and increased levels of caspase-4. This defect was complemented after c-Rel overexpression, supporting a causative role for c-Rel deficiency in the observed phenotype of the Pt1-LCLtet cells. The LCL tet cells were further utilized as a model system for the independent analysis of LMP1 and CD40 signaling. These studies revealed several outcomes of LMP1 signaling in the biology and function of CD40. Specifically, LMP1 signaling induced a unique pattern of CD40 phosphorylation as well as the expression of several novel CD40 isoforms. Moreover, when CD40 and LMP1 were activated simultaneously a synergistic effect was observed towards p65 and p38 phosphorylation suggesting a functional interaction that might occur during early stages of EBV infection or malignant transformation where both LMP1 and CD40 are co-expressed in the infected cell. Collectively, our results demonstrate that a majority of the defects displayed in the Pt1-LCL tet cells are a result of reduced c-Rel expression. Importantly, these results ascribe c-Rel a novel function as a negative regulator of caspase-4 expression and a putative key player in the control of cell survival in EBV-immortalized B cells.