T Cell Receptor induced Nuclear Factor kB (NF kB) Signaling and Transcriptional Activation Are Regulated by STIM1 and Orai1 mediated Calcium Entry*
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 kB. The mechanism of NFAT activation by Ca2+ has been determined. However, the role of Ca2+ in controlling NF kB signaling is poorly understood, and the source of Ca2+ required for NF kB activation is unknown. We demonstrate that TCR but not TNF induced NF kB signaling upstream of IkB kinase activation absolutely requires the influx of extracellular Ca2+ via STIM1 dependent Ca2+ release activated Ca2+/Orai channels. We further show that Ca2+ influx controls phosphorylation of the NF kB protein p65 on Ser 536 and that this posttranslational modification controls its nuclear localization and transcriptional activation. Notably, our data reveal that this role for Ca2+ is entirely separate from its upstream control of IkBa degradation, thereby identifying a novel Ca2+ dependent distal step in TCR induced NF kB activation. Finally, we demonstrate that this control of distal signaling occurs via Ca2+ dependent PKCa mediated phosphorylation of p65. Thus, we establish the source of Ca2+ required for TCR induced NF kB activation and define a new distal Ca2+ dependent checkpoint in TCR induced NF kB signaling that has broad implications for the control of immune cell development and T cell functional specificity.
The Journal of Biological Chemistry