PKCθ cooperates with atypical PKCζ and PKCι in NF-κB transactivation of T lymphocytes

Using yeast two-hybrid, we isolated atypical PKCζ as a PKCθ-interacting kinase and demonstrated that it selectively interacted with, and was phosphorylated by, PKCθ. Importantly, however, both atypical PKCζ and PKCι were functionally required in TCR/CD28-mediated activation of NF-κB downstream of PKCθ in Jurkat T cells albeit, activation responses of PKCζ-deficient CD3+ T cells were comparable with wildtype controls. This normal activation thresholds of PKCζ−/− T cells suggested that PKCι, the closest structural relative, might play a compensatory role in TCR/CD28-induced signalling. Consistently, both PKCζ and PKCι resided in the plasma membrane lipid raft microdomains of Jurkat as well as primary mouse CD3+ T cells. Thus, PKCθ, the established constituent of the immunological synapse, physically and functionally interacted with PKCζ and PKCι. Together, these data demonstrate that atypical PKCζ/ι isotypes serve as direct downstream targets of PKCθ in the signalling pathway leading to NF-κB activation in T lymphocytes.