Recent studies have documented direct interaction between 14-3-3 proteins a
nd 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 wi
th protein kinase C theta and to negatively regulate interleukin-2 secretio
n, 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 ac
tivation mechanisms. Specific interaction of PKC mu and 14-3-3 tau can be s
hown in the T cell line Jurkat by immunocoprecipitiation and by pulldown as
says of either endogenous or overexpressed proteins using PKC mu-specific a
ntibodies and GST-14-3-3 fusion proteins, respectively. Using PKC mu, delet
ion 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 p
horbol ester stimulation of PKC mu kinase activity in Jurkat cells and occu
rs 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 sig
nificantly reduced phorbol ester induced activation of PKC mu kinase activi
ty in intact cells. We therefore conclude that 14-3-3 tau is a negative reg
ulator of PKC mu in T cells.