Protein Kinase C-θ Participates in NF-κB Activation Induced by CD3-CD28 Costimulation through Selective Activation of IκB Kinase β

Abstract

The NF-κB/Rel family of eukaryotic transcription factors plays an essential role in the regulation of inflammatory, antiapoptotic, and immune responses. NF-κB is activated by many stimuli including costimulation of T cells with ligands specific for the T-cell receptor (TCR)-CD3 complex and CD28 receptors. However, the signaling intermediates that transduce these costimulatory signals from the TCR-CD3 and CD28 surface receptors leading to nuclear NF-κB expression are not well defined. We now show that protein kinase C-θ (PKC-θ), a novel PKC isoform, plays a central role in a signaling pathway induced by CD3-CD28 costimulation leading to activation of NF-κB in Jurkat T cells. We find that expression of a constitutively active mutant of PKC-θ potently induces NF-κB activation and stimulates the RE/AP composite enhancer from the interleukin-2 gene. Conversely, expression of a kinase-deficient mutant or antisense PKC-θ selectively inhibits CD3-CD28 costimulation, but not tumor necrosis factor alpha-induced activation of NF-κB in Jurkat T cells. The induction of NF-κB by PKC-θ is mediated through the activation of IκB kinase β (IKKβ) in the absence of detectable IKKα stimulation. PKC-θ acts directly or indirectly to stimulate phosphorylation of IKKβ, leading to activation of this enzyme. Together, these results implicate PKC-θ in one pathway of CD3-CD28 costimulation leading to NF-κB activation that is apparently distinct from that involving Cot and NF-κB-inducing kinase (NIK). PKC-θ activation of NF-κB is mediated through the selective induction of IKKβ, while the Cot- and NIK-dependent pathway involves induction of both IKKα and IKKβ.

ACKNOWLEDGMENTS

We thank Amnon Altman and Peter Parker for PKC expression plasmids.

This work was supported by grants from the UCSF Center for AIDS Research (MH 59037) and from Pfizer.