Protein kinase C μ is negatively regulated by 14-3-3 signal transduction proteins

Recent studies have documented direct interaction between 14-3-3 proteins and hey molecules in signal transduction pathways like Ras, Cbl, and protein kinases, In T cells, the 14-3-3 tau isoform has been shown to associate with protein kinase C theta and to negatively regulate interleukin-2 secretion, Here we present data that 14-3-3 tau interacts with protein kinase C mu (PKC mu), a subtype that differs from other PKC members in structure and activation mechanisms. Specific interaction of PKC mu and 14-3-3 tau can be shown in the T cell line Jurkat by immunocoprecipitiation and by pulldown assays of either endogenous or overexpressed proteins using PKC mu-specific antibodies and GST-14-3-3 fusion proteins, respectively. Using PKC mu, deletion mutants, the 14-3-3 tau binding region is mapped within the regulatory C1 domain. Binding of 14-3-3 tau to PKC mu is significantly enhanced upon phorbol ester stimulation of PKC mu kinase activity in Jurkat cells and occurs via a Cbl-like serine containing consensus motif, However, 14-3-3 tau is not a substrate of PKC mu, In contrast 14-3-3 tau strongly down-regulates PKC mu kinase activity in vitro. Moreover, overexpression of 14-3-3 tau significantly reduced phorbol ester induced activation of PKC mu kinase activity in intact cells. We therefore conclude that 14-3-3 tau is a negative regulator of PKC mu in T cells.