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

We investigated the role of protein kinase C theta (PKC theta) in the activ ation of the NF-kappaB cascade in primary human CD4(+) lymphocytes, Among s ix or so PKC isoforms expressed in T cells, only PKC theta participates in the assembly of the supramolecular activation dusters at the contact site o f the TCR with Ag, Signaling via both the TCR and CD28 is required for opti mal activation of the multisubunit I kappaB kinase (IKK) complex in primary human T lymphocytes; this activation could be inhibited by a Ca2+-independ ent PKC isoform inhibitor, rottlerin, Moreover, endogenous PKC theta physic ally associates with activated IKK complexes in CD3/CD28-costimulated prima ry CD4(+) T cells. The same set of stimuli also induced relocation of endog enous PKC theta and IKKs to a GM1 ganglioside-enriched, detergent-insoluble membrane compartment in primary T cells. IKKs recruited to these lipid raf ts were capable of phosphorylating a recombinant I kappaB alpha sustrate. C onfocal microscopy further demonstrated that exogenously expressed PKC thet a and IKK beta colocalize in the membrane of CD3/CD28-costimulated Jurkat T cells. Constitutively active but not kinase-inactive PKC theta activated I KK 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. Tak en together, these data show that the activation of PKC theta by the TCR an d CD28 plays an important role In the assembly and activation of IKK comple xes in the T cell membrane.