The physical association of protein kinase Cθ with a lipid raft-associated inhibitor of κB factor kinase (IKK) complex plays a role in the activation of the NF-κB cascade by TCR and CD28

We investigated the role of protein kinase C theta (PKC theta) in the activation of the NF-kappaB cascade in primary human CD4(+) lymphocytes, Among six or so PKC isoforms expressed in T cells, only PKC theta participates in the assembly of the supramolecular activation dusters at the contact site of the TCR with Ag, Signaling via both the TCR and CD28 is required for optimal activation of the multisubunit I kappaB kinase (IKK) complex in primary human T lymphocytes; this activation could be inhibited by a Ca2+-independent PKC isoform inhibitor, rottlerin, Moreover, endogenous PKC theta physically associates with activated IKK complexes in CD3/CD28-costimulated primary CD4(+) T cells. The same set of stimuli also induced relocation of endogenous PKC theta and IKKs to a GM1 ganglioside-enriched, detergent-insoluble membrane compartment in primary T cells. IKKs recruited to these lipid rafts were capable of phosphorylating a recombinant I kappaB alpha sustrate. Confocal microscopy further demonstrated that exogenously expressed PKC theta and IKK beta colocalize in the membrane of CD3/CD28-costimulated Jurkat T cells. Constitutively active but not kinase-inactive PKC theta activated IKK beta in Jurkat T cells, Expression of dominant-active PKC theta also had stimulatory effects on the CD28 response element of the IL-2 promoter. Taken together, these data show that the activation of PKC theta by the TCR and CD28 plays an important role In the assembly and activation of IKK complexes in the T cell membrane.