The c-jun N-terminal kinase (JNK) proteins are encoded by three genes (Jnk1-3), giving rise to 10 isoforms in the mammalian brain. The differential roles of JNK isoforms in neuronal cell death and development have been noticed in several pathological and physiological contexts. However, the mechanisms underlying the regulation of different JNK isoforms to fulfill their specific roles are poorly understood. Here, we report an isoform-specific regulation of JNK3 by palmitoylation, a posttranslational modification, and the involvement of JNK3 palmitoylation in axonal development and morphogenesis. Two cysteine residues at the COOH-terminus of JNK3 are required for dynamic palmitoylation, which regulates JNK3's distribution on the actin cytoskeleton. Expression of palmitoylation-deficient JNK3 increases axonal branching and the motility of axonal filopodia in cultured hippocampal neurons. The Wnt family member Wnt7a, a known modulator of axonal branching and remodelling, regulates the palmitoylation and distribution of JNK3. Palmitoylation-deficient JNK3 mimics the effect of Wnt7a application on axonal branching, whereas constitutively palmitoylated JNK3 results in reduced axonal branches and blocked Wnt7a induction. Our results demonstrate that protein palmitoylation is a novel mechanism for isoform-specific regulation of JNK3 and suggests a potential role of JNK3 palmitoylation in modulating axonal branching. The c-jun N-terminal kinase (JNK) family consists of JNK1, JNK2 and JNK3 subgroups, which participate in diverse biological and pathological processes. 1,2 At least 10 JNK isoforms of varied sizes, with most between 46 and 54 kDa, are produced from the Jnk1-3 genes, giving rise to JNK isoforms. 1 In the nervous system, JNKs (particularly isoform JNK3) have been extensively studied as the key players in apoptosis and neurodegeneration. [3][4][5][6] However, accumulating evidence supports a physiological role of JNK in regulating neurite formation and morphogenesis. 7-12 Pharmacological inhibition of JNK activity blocks axogenesis in hippocampal neurons, arguing for an essential role of JNK in neurite development. 13 Growth factors and signalling molecules, including secreted proteins of the Wnt family, have also been found to activate JNK for remodelling dendrites and axons, a process that relies on cytoskeletal rearrangement. 11,[14][15][16] This has led to the identification of several actin-or microtubule-associated proteins as JNK substrates that modulate different aspects of cytoskeletal activity. 17 However, all the 10 JNK isoforms share the same kinase domain and activation mechanism. 17 The differential roles of JNK isoforms in neurite development and the mechanisms underlying isoform-specific regulation are poorly understood.Analysis of animals null for particular JNK isoforms provides the first evidence to support isoform-specific roles of JNKs in the brain. Mice with Jnk1 À/À show abnormalities in neurite development, 7 whereas mice null for Jnk1 and Jnk2 show embryonic lethality due to severe neuro...

20S-protopanaxadiol (aPPD) is a metabolite of ginseng saponins, which is reported to be pro-apoptotic in some cells but anti-apoptotic in neuronal cells by regulating Akt signaling. Owing to its cholesterol-like structure, we hypothesized that aPPD may regulate Akt signaling by interacting with lipid rafts. Here, we compared Akt signaling in glioblastoma U87MG and neuroblastoma Neuro-2a cells treated with aPPD. aPPD did not change Akt activity in the total plasma membranes of each cell type, but drastically altered the activity of raft-associated Akt. Strikingly, Akt activity was decreased in the rafts of U87MG cells but increased in N2a cells by aPPD through regulating raft-associated dephosphorylation. The bidirectional regulation of raft-associated Akt signaling by aPPD enhanced the chemotoxicity of Paclitaxel or Vinblastine in U87MG cells but attenuated the excitotoxicity of N-methyl--aspartate in N2a cells. Our results demonstrated that the activity of raft-associated but not total membrane Akt determines its cellular functions. Lipid rafts differ in different types of cells, which allows for the possibility of cell-type-specific targeting for which aPPD might prove to be a useful agent.

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