Glycogen synthase kinase-3β is a crucial mediator of signal-induced RelB degradation

Abstract

The immediate early transcription factor nuclear factor (IjBs) kappa B (NF-jB) is crucially involved in the regulation of numerous physiological or pathophysiological processes such as inflammation and tumourigenesis. Therefore, the control of NF-jB activity, which is mainly regulated by signal-induced degradation of cytoplasmic inhibitors of NF-jB (IjBs), is of high relevance. One known alternative pathway of NF-jB regulation is the stimulus-induced proteasomal degradation of RelB, a component of the NF-jB dimer. Here, we identified the serine/threonine protein kinase glycogen synthase kinase-3b (GSK-3b) as a critical signalling component leading to RelB degradation. In Jurkat leukaemic T cells as well as in primary human T cells, tetradecanoylphorbolacetate/ionomycinand CD3/CD28-induced RelB degradation were impaired by a GSK-3b-specific pharmacological inhibitor, an ectopically expressed dominant-negative GSK-3b mutant and by small-interfering RNA-mediated silencing of GSK-3b expression. Furthermore, a physical interaction between RelB and GSK-3b was shown by co-immunoprecipitation, which was already notable in unstimulated cells. Most importantly, as demonstrated by in vitro kinase assays, human RelB is inducibly phosphorylated by GSK-3b, indicating a direct substrate-enzyme relationship. The serine residue 552 is a target of GSK-3b-mediated phosphorylation in vitro and in vivo. We conclude that GSK-3b is a crucial regulator of RelB degradation, stressing the relevant linkage between the NF-jB system and GSK-3b.

Hypercapnia Induces Cleavage and Nuclear Localization of RelB Protein, Giving Insight into CO2 Sensing and Signaling

“…RelB cleavage/degradation is an important control mechanism of NF-B activity and is sensitive to the proteasome inhibitor MG-132. RelB processing has also been reported to involve glycogen synthase kinase 3␤ (GSK3␤) (23) and MALT-1 (24). In this study, we demonstrate that under conditions of elevated CO 2 , RelB is cleaved to a low molecular weight form that translocates to the nucleus, where it impacts upon the expression of proinflammatory genes.…”

“…This modification of RelB was partially reversible by treatment with MG-132 (a proteasome inhibitor that also has anti-secretase activity (30)) and completely reversible by mutation of two key phosphoacceptor sites, Thr-84 and Ser-552. Recently, GSK3␤ was identified as the kinase involved in regulating these events (23). Thus, we investigated whether elevated CO 2 was driving RelB processing through this pathway.…”

Transcriptional repression by the HDAC4–RelB–p52 complex regulates multiple myeloma survival and growth

“…Importantly, the physiological significance of RelB-phosphorylation has been elusive especially because a previous study based on analysis of T-cells reported that similar to the IkB molecules, the consequence of RelB-S573 phosphorylation is its degradation suggesting an inhibitory role for RelB 44,55 . On the contrary our results presented here indicate that phospho-RelB-S573 in MM In MM cells RelB and ERK1 constitutively interact with each other.…”

“…The physiological importance of RelB-phosphorylation has not been well studied especially in the context of tumour growth and the only known kinase for RelB at Ser-573 to date is GSK3b (ref. 44). It has been previously shown that GSK3b-dependent RelB-phosphorylation results in the degradation of the latter 44 .…”

“…44). It has been previously shown that GSK3b-dependent RelB-phosphorylation results in the degradation of the latter 44 . However, we found that RelB is phosphorylated in a GSK3b-independent manner (Supplementary Fig.…”