PKCtheta cooperates with atypical PKCzeta and PKCiota in NF-kappaB transactivation of T lymphocytes.

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