DIRECT INTERACTION BETWEEN PROTEIN-KINASE C-THETA (PKC-THETA) AND 14-3-3-TAU IN T-CELLS - 14-3-3 OVEREXPRESSION RESULTS IN INHIBITION OF PKC-THETA TRANSLOCATION AND FUNCTION

Recent studies have documented direct interactions between 14-3-3 prot eins and several oncogene and proto-oncogene products involved in sign al transduction pathways, Studies on the effects of 14-3-3 proteins on protein kinase C (PKC) activity in vitro have reported conflicting re sults, and previous attempts to demonstrate a direct association betwe en PKC and 14-3-3 were unsuccessful. sere, we examined potential physi cal and functional interactions between PKC theta, a Ca2+-independent PKC enzyme which is expressed selectively in T lymphocytes, and the 14 -3-3 tau isoform in vitro and in intact T cells. PKC theta and 14-3-3 tau coimmunoprecipitated from Jurkat T cells, and recombinant 14-3-3 t au interacted directly with purified PKC theta in vitro, Transient ove rexpression of 14-3-3 tau suppressed stimulation of the interleukin 2 (IL-2) promoter mediated by cotransfected wild-type or constitutively active PKC theta, as well as by endogenous PKC in ionomycin- and/or ph orboI ester-stimulated cells, This did not represent a general inhibit ion of activation events, since PBC-independent (but Ca2+-dependent) a ctivation of an IL-4 promoter element was not inhibited by 14-3-3 tau under similar conditions, Overexpression of wild-type 14-3-3 tau also inhibited phorbol ester-induced PKC theta translocation from the cytos ol to the membrane in Jurkat cells, while a membrane-targeted form of 14-3-3 tau caused increased localization of PKC theta in the particula te fraction in unstimulated tells, Membrane-targeted 14-3-3 tau was mo re effective than wild-type 14-3-3 tau in suppressing PKC theta-depend ent IL-2 promoter activity, suggesting that 14-3-3 tau inhibits the fu nction of PKC theta not only by preventing its translocation to the me mbrane but also by associating with it, The interaction between 14-3-3 and PKC theta may represent an important general mechanism for regula ting PKC-dependent signals and, more specifically, PKC theta-mediated functions during T-cell activation.