c-Rel plays a key role in deficient activation of B cells from a non–X-linked hyper-IgM patient

Abstract

Our previous results demonstrated that B cells from a patient (pt1) with non-X-linked hyper-IgM syndrome (HIGM) possess an atypical CD23(lo) phenotype that is unaffected by CD40-mediated activation. To investigate the molecular mechanism underlying defective CD23 expression in pt1 B cells, we used lymphoblastoid cell lines that express LMP1 under the control of a tetracycline-inducible promoter (LCL(tet)). Our analysis revealed that the CD23(lo) phenotype in the pt1-LCL(tet) cells is a direct consequence of diminished CD23 transcription. We demonstrate a marked decrease in c-Rel-containing complexes that bind to the proximal CD23a/b promoters in pt1-LCL(tet) extracts, resulting from an overall lower expression of c-Rel in pt1-LCL(tet) cells. Analysis of c-Rel mRNA revealed relatively equal amounts in pt1-LCL(tet) and control LCL(tet) cells, indicating that diminished c-Rel protein expression is unrelated to decreased transcription. Finally, a critical role for c-Rel in CD23 regulation was demonstrated by effectively altering c-Rel expression that resulted in the direct modulation of CD23 surface expression. Collectively, these findings demonstrate that low levels of c-Rel are the underlying cause of aberrant CD23 expression in pt1 B cells and are likely to play a critical role in the pathophysiology of this form of HIGM.

REL, encoding a member of the NF-κB family of transcription factors, is a newly defined risk locus for rheumatoid arthritis

“…Interestingly, rescue from Fas induced apoptosis is normal in these cells, demonstrating the existence of distinct CD40 signaling pathways that are at least in part distinguished by the involvement of c-rel. A similar c-rel associated difference in CD40 signaling has been seen in patients with ectodermal dysplasia and hyperIgM syndrome due to mutations in the NF-κB essential modulator, NEMO, where c-Rel dependent IL4 responses are also impaired19. C-Rel is the only NF-kappaB family member with oncogenic activity and the gene is amplified in some B cell lymphomas.…”

c-Rel Deficiency Increases Caspase-4 Expression and Leads to ER Stress and Necrosis in EBV-Transformed Cells

“…Of the 27,000 genes assessed, 764 (p = 0.05) displayed differential expression of 1.6-fold or higher. Importantly, we were able to show that both the expression of c-Rel and CD23 ( FCER2 ), which had been previously identified as a bona fide c-Rel target, were decreased on the array [32]. However, there was no difference in the expression of pro-survival genes including Bcl-xL and thus the difference observed at the protein level was likely independent of a direct, c-Rel-specific affect on transcription (see Figure 1C).…”

“…Our previous analysis of c-Rel expression in Pt1 and control cells suggested that reduced c-Rel expression was due to translational or post-translational differences [32] . However, additional analyses using multiple primer pairs that targeted both the 5′ and 3′untranslated regions revealed that reduced c-Rel corresponded to a transcriptional defect that resulted in an approximate 3.5-fold decrease in RNA ( Figure 1A ).…”

“…Importantly, the Pt1-LCL tet cells retained a subset of characteristics found in the primary B cells including reduced levels of surface CD23. These defects were not complemented by LMP1 and were directly linked to decreased c-Rel expression [32] .…”

PTIP chromatin regulator controls development and activation of B cell subsets to license humoral immunity in mice

“…Although the precise molecular targets by which PTIP mediates its function in B cell signaling remain to be elucidated, we provide multiple lines of evidence in PTIP-deficient B-1a cells and activated B-2 B cells for deregulation of the classical NF-κB pathway. In addition to decreased cREL and increased IκBα at steady state and in response to anti-IgM, we find protein levels of a handful of NF-κB target genes to be decreased in PTIP-deficient B cells, including BCL2, BCLXL ( 27 , 28 ), NFATc1 ( 29 ), uPA, IRF4 ( 30 ), and CD23 ( 31 ). These findings indicate a requirement for PTIP in the classical NF-κB pathway and are in line with ( i ) the established role of the NF-κB pathway in B-1 cell development ( 15 , 24 , 25 , 32 ), ( ii ) evidence for a role of NF-κB downstream of pre-BCR signaling in small pre-B cells ( 28 , 33 – 36 ), and ( iii ) FO B-2 cell functionality including activation-induced proliferation, survival, antibody production, GC differentiation, and CSR ( 24 – 26 , 37 ).…”