Palmitoylation controls DLK localization, interactions and activity to ensure effective axonal injury signaling

Abstract

Dual leucine-zipper kinase (DLK) is critical for axon-to-soma retrograde signaling following nerve injury. However, it is unknown how DLK, a predicted soluble kinase, conveys long-distance signals and why homologous kinases cannot compensate for loss of DLK. Here, we report that DLK, but not homologous kinases, is palmitoylated at a conserved site adjacent to its kinase domain. Using short-hairpin RNA knockdown/rescue, we find that palmitoylation is critical for DLK-dependent retrograde signaling in sensory axons. This functional importance is because of three novel cellular and molecular roles of palmitoylation, which targets DLK to trafficking vesicles, is required to assemble DLK signaling complexes and, unexpectedly, is essential for DLK's kinase activity. By simultaneously controlling DLK localization, interactions, and activity, palmitoylation ensures that only vesiclebound DLK is active in neurons. These findings explain how DLK specifically mediates nerve injury responses and reveal a novel cellular mechanism that ensures the specificity of neuronal kinase signaling.

Slippery signaling: Palmitoylation-dependent control of neuronal kinase localization and activity

“…In peripheral neurons JNK3 plays key roles in retrograde responses to axonal injury and was previously reported to colocalize with JIP3 on axonal vesicles (Keramaris et al, 2005, Cavalli et al, 2005). It is thus tempting to speculate that palmitoylation accounts for this vesicular targeting of JNK3 and that these JNK3-JIP3-positive vesicles are similar, or perhaps identical, to the recently reported DLK-JIP3 positive vesicles (Holland et al, 2016). If so, then palmitoylation would play a key role in modifying multiple DLK-JNK pathway components to ensure the specificity and transport of neuronal injury signals.…”

“…However, it had been unknown how DLK, a predicted soluble kinase, conveys these long-distance signals. Recently, DLK was found to be palmitoylated at a conserved site adjacent to its kinase domain (Holland et al, 2016). ShRNA knockdown/rescue experiments, in which endogenous DLK in sensory neurons was replaced with a palmitoyl-site mutant, revealed that palmitoylation at this site is critical for DLK-dependent retrograde injury signaling (Holland et al, 2016) (Figure 3).…”

“…In addition to this clear effect on trafficking, though, palmitoylation also impacts DLK at the molecular level. In particular, palmitoyl-site mutation prevents DLK's ability to form multiprotein complexes that contain the scaffold protein JNK-interacting Protein-3 (JIP3) and the downstream kinases MAP Kinase Kinase-4 (MKK4) and MKK7 (Holland et al, 2016). Both MKK4 and JIP3 can co-traffic with wild type (i.e.…”

“…palmitoylated) DLK in axons, suggesting that palmitoylation of DLK may be critical for the assembly and/or stability of axonal complexes that contain multiple JNK pathway signaling components. Finally, palmitoylation is also critical for DLK's ability to phosphorylate its direct substrates MKK4 and MKK7, both in vitro and in transfected cells (Holland et al, 2016). These findings strongly suggest that palmitoylation plays an additional role to control DLK-dependent signaling and raise the exciting possibility that palmitoylation directly controls DLK's kinase activity.…”

EZH2 Palmitoylation Mediated by ZDHHC5 in p53-Mutant Glioma Drives Malignant Development and Progression

“…Palmitoylation is required for EZH2 targeting to the Golgi apparatus, where phosphorylation occurs. ZDHHC5 is localized to detergent-resistant microdomains of the plasma membrane (18); palmitoylation is necessary for vesicle trafficking and for the formation of EZH2 multiprotein complexes (40).…”