T Cell Receptor-induced Nuclear Factor κB (NF-κB) Signaling and Transcriptional Activation Are Regulated by STIM1- and Orai1-mediated Calcium Entry

Abstract

T cell activation following antigen binding to the T cell receptor (TCR) involves the mobilization of intracellular Ca2؉ to activate the key transcription factors nuclear factor of activated T lymphocytes (NFAT) and NF-B. 2؉ -dependent checkpoint in TCR-induced NF-B signaling that has broad implications for the control of immune cell development and T cell functional specificity. Activation of T cells following antigen binding to the T cell antigen receptor (TCR)3 induces diverse lineage-and fate-specific proinflammatory and immune-modulatory responses. Central to these responses is the induction of quantitatively distinct intracellular Ca 2ϩ signals and their selective activation of the key transcription factors NFAT and NF-B (1-6). The mechanism by which Ca 2ϩ controls NFAT activation in lymphocytes is well established (7). In contrast, although Ca 2ϩ has been implicated in TCR-induced NF-B signaling (8 -10), how Ca 2ϩ regulates NF-B activity is largely unexplored and represents a significant gap in our understanding of transcriptional control of T cell development, activation, and functional specificity.In resting T cells, classical NF-B consists of heterodimers of p50/p65 or p50/c-Rel that are retained in the cytosol by members of the inhibitory family of IB proteins (11, 12). Following TCR engagement, IB kinase (IKK)-mediated phosphorylation triggers the ubiquitination and proteasomal degradation of IB␣, releasing p50/p65 and p50/c-Rel, which localize to the nucleus to initiate transcription of crucial immune-regulatory, proinflammatory, and proproliferative genes (13-30). Although TCR-mediated Ca 2ϩ mobilization has been implicated in proximal steps of NF-B activation (8 -10), the precise mechanisms and source of Ca 2ϩ that regulate nuclear localization and transcriptional activation of NF-B are poorly defined. It is well established that TCR signaling induces inositol 1,4,5-trisphosphate-mediated depletion of Ca 2ϩ from the endoplasmic reticulum (ER). A resulting Ca 2ϩ dissociation from the ER membrane protein stromal interaction molecule 1 (STIM1) triggers its oligomerization and relocalization to ER membrane domains juxtaposed to the plasma membrane (31-33), where STIM1 physically gates Orai (also known as Ca 2ϩ release-activated Ca 2ϩ ) channels, allowing extracellular Ca 2ϩ to enter the cell (34,35). However, it is not known whether Ca 2ϩ control of TCR-induced NF-B signaling requires STIM1-and Orai1-mediated Ca 2ϩ influx or whether the initial release of Ca 2ϩ from the ER is sufficient for classical NF-B activation.In this study, we sought to determine both the source and mechanism of Ca 2ϩ control of antigen receptor-induced NF-B activation in T cells. We show that influx of extracellular Ca 2ϩ via STIM1 and Orai is critical for TCR-but not TNFinduced IB␣ degradation and NF-B activation. Importantly, we also demonstrate that Ca 2ϩ -dependent, PKC␣-mediated phosphorylation of p65 critically regulates its nuclear localization and transcriptional activation following TCR engagement. Thus, our findings ...

STIM- and Orai-mediated calcium entry controls NF-κB activity and function in lymphocytes

“…Interestingly, expression of a constitutively active catalytic subunit of CaN or calcineurin A (CnA) in T cells, in the absence of any other signals, activates NF-κB upstream of the IKKβ but not IKKα of the IKK complex [51–53]. Moreover, in T lymphocytes with defective Ca 2+ entry, constitutively active CnA rescues the block in NF-κB activation [51, 54] indicative of a role for Ca 2+ /CaN in efficient CBM complex formation [55]. Thus, PKC-mediated phosphorylation of CARMA1 regulates its membrane association while Ca 2+ /CaN-dependent de-phosphorylation of MALT1-associated BCL10 promotes its interaction with CARMA1 leading to assembly and activation of the CBM complex [55].…”

“…A multitude of studies have established that stimulus specific phosphorylation of serine and threonine residues in p65 and c-Rel regulate their activity. Phosphorylation critically regulates the kinetics, extent of nuclear localization [54, 75, 76], nuclear DNA interactions [77, 78], transcriptional activation [79–82] and the specificity of gene expression [83]. Additional modifications including acetylation, methylation and O-GlcNAcylation also control transcriptional competency, promoter accessibility, and specificity [78, 79, 84–88].…”

EGR-mediated control of STIM expression and function

“…For example, the C-terminal region of zinc finger III in EGR4 directly interacts with the NF-κB family member p65, leading to robust activation of the IL-2 promoter [89]. There is also growing evidence of a Ca 2+ -dependent feedback loop between NF-κB and STIM1/Orai1 expression in which 1) SOCE drives IκB degradation [90], 2) Ca 2+ regulates NF-κB nuclear localization via p65 S536 phosphorylation [90] and 3) NF-κB is recruited to binding sites in the promoters of STIM1 and Orai1 [91-93]. Since both EGR and NF-κB both regulate STIM1 expression and yet are themselves regulated by Ca 2+ , their co-activation would be expected to be relatively common.…”

The Role of Mitochondria in the Regulation of Lymphocyte Calcium Signaling

“…Отве-том активированных лимфоцитов является индукция активности тирозинкиназ и семейства киназ ZAP70, которые стимулируют факторы транскрипции NFkB и AP1, а также Ca 2+ /кальцинейрин -зависимую фосфатазу, мобилизующую фактор активации Т лимфоцитов NFAT [7,24]. Процесс инициации транс-крипции генов, обеспечивающих долгосрочную про-лиферацию активированных клеток, опосредован механизмами кальциевой сигнализации, в частности, фосфоинозитол-3-фосфат-зависимым опустошением депо (эндоплазматического ретикулума -ЭПР), ко-торое приводит к стимуляции митохондрий, кальций -селективных каналов и взаимодействию с мембра-ной ЭПР.…”

“…Лимфоциты экспрессируют широ-кий спектр молекул, способных к специфической модуляции амплитуды, кинетики и субклеточному распространению кальциевых сигналов. В свою очередь ионы Ca 2+ опосредуют их дифференциацию, пролиферацию и образование провоспалительных цитокинов [24]. Иммунореактивность лимфоцитов обеспечивается интеграцией митохондрий и механиз-мов кальциевой сигнализации.…”