This study examined the effect of 8-[2-(2-pentylcyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA), a newly synthesized linoleic acid derivative with cyclopropane rings instead of cis -double bonds, on protein kinase C (PKC) activity. In the in situ PKC assay with reverse-phase highperformance liquid chromatography, DCP-LA significantly activated PKC in PC-12 cells in a concentration-dependent (10 nM-100 mM) manner, with the maximal effect at 100 nM, and the DCP-LA effect was blocked by GF109203X, a PKC inhibitor, or a selective inhibitor peptide of the novel PKC isozyme PKC-e. Furthermore, DCP-LA activated PKC in HEK-293 cells that was inhibited by the small, interfering RNA against PKC-e. In the cell-free PKC assay, of the nine isozymes examined here, DCP-LA most strongly activated PKC-e, with .7-fold potency over other PKC isozymes, in the absence of dioleoyl-phosphatidylserine and 1,2-dioleoyl-snglycerol; instead, the DCP-LA action was inhibited by dioleoyl-phosphatidylserine. DCP-LA also activated PKC-g, a conventional PKC, but to a much lesser extent compared with that for PKC-e, by a mechanism distinct from PKC-e activation. Thus, DCP-LA serves as a selective activator of PKC-e, possibly by binding to the phosphatidylserine binding site on PKC-e. These results may provide fresh insight into lipid signaling in PKC activation.-Kanno, T., H. Yamamoto, T. Yaguchi, R. Hi, T. Mukasa, H. Fujikawa, T. Nagata, S. Yamamoto, A. Tanaka, and T. Nishizaki. The linoleic acid derivative DCP-LA selectively activates PKC-e, possibly binding to the phosphatidylserine binding site. J. Lipid Res. 2006Res. . 47: 1146Res. -1156 Supplementary key words 8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid . protein kinase C-e . protein kinase C-g Protein kinase C (PKC) is linked to lipid signaling pathways and participates in a wide range of signal transduction pathways. PKC isozymes are classified as conventional PKCs, such as PKC-a, -bI, -bII, and -g; novel PKCs, such as PKC-d, -e, -h, -u, and -m; and atypical PKCs, such as PKC-l/L for mouse/human, -z, and -r. PKCs are activated via several pathways mediated by phospholipase C, phospholipase A 2 , phospholipase D, and phosphatidylcholine-specific phospholipase C (1-3). Phospholipase C hydrolyzes phosphatidylinositol 4,5-bisphosphate into diacylglycerol and inositol 1,4,5-trisphosphate, the latter activating inositol 1,4,5-trisphosphate receptors to release Ca 21 from intracellular calcium stores, and conventional PKCs are activated by diacylglycerol and intracellular Ca 21 increase (1, 2). Phosphatidylcholine-specific phospholipase C produces diacylglycerol by hydrolysis of phosphatidylcholine, thereby activating PKC (3). Cis-unsaturated free fatty acids, such as arachidonic, oleic, linoleic, linolenic, and docosahexaenoic acid, that are produced by phospholipase A 2 -catalyzed hydrolysis of phosphatidylcholine activate novel PKCs in a Ca 21 -independent manner (1, 2). The free fatty acids, alternatively, may synergistically activate conventional PKCs or ...

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P19 embryonal carcinoma (EC) cells undergo apoptosis during neuronal differentiation induced by all-trans retinoic acid (RA). Caspase-3-like proteases are activated and involved in the apoptosis of P19 EC cells during neuronal differentiation. 1 Recently it has been shown that growth factor signals protect against apoptosis by phosphorylation of Bad. Phosphorylated Bad, an apoptotic member of the Bcl-2 family, cannot bind to Bcl-x L and results in Bcl-x L homodimer formation and subsequent antiapoptotic activity. In the present study, we demonstrate that this system is used generally to protect against apoptosis during neuronal differentiation. Bcl-x L inhibited the activation of caspase-3-like proteases. Basic fibroblast growth factor (bFGF) inhibited more than 90% of the caspase-3-like activity, inhibited processing of caspase-3 into its active form, and inhibited DNA fragmentation. bFGF activated phosphatidyl-inositol-3-kinase (PI3K) and stimulated the phosphorylation of Bad. Phosphorylation was inhibited by wortmannin, an inhibitor of PI3K and its downstream target Akt. Thus, Bad is a target of the FGF receptor-mediated signals involved in the protection against activation of caspase-3.

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