Mechanism of inhibition of protein kinase C by 14-3-3 isoforms. 14-3-3 isoforms do not have phospholipase A2 activity

The ability of individual members of the 14-3-3 protein family to inhibit protein kinase C (PKC) has been studied by using a synthetic peptide based on the specific 80 kDa substrate for PKC (MARCKS protein) in two different assay systems. Recombinant 14-3-3 and isoforms renatured by a novel method after separation by reverse-phase h.p.l.c. were studied. The detailed effects of diacylglycerol and the phorbol ester phorbol 12-myristate 13-acetate on the inhibition were also investigated. This suggests that one of the sites of interaction of 14-3-3 may be the cysteine-rich (C1) domain in PKC. Since a region in secreted phospholipase A 2 (PLA 2 ) shares similarity with this domain, the ability of 14-3-3 to interact with mammalian PLA 2 was studied. Cytosolic PLA 2 has some similarity to the C2 region of PKC, and the effect of 14-3-3 on this class of PLA 2 was also analysed. In contrast with a previous report, no PLA 2 activity was found in brain 14-3-3, nor in any of the recombinant proteins tested. These include ξ 14-3-3 isoform, on which the original observation was made.