Identification of Palmitoyltransferase and Thioesterase Enzymes That Control the Subcellular Localization of Axon Survival Factor Nicotinamide Mononucleotide Adenylyltransferase 2 (NMNAT2)*

Abstract

Background: Axon survival factor nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) is targeted to Golgi membranes through palmitoylation, resulting in its rapid turnover and axon degeneration.

Results: Thioesterases APT1/APT2 depalmitoylate NMNAT2 and zDHHC17 is the strongest candidate palmitoyltransferase for NMNAT2.

Conclusion: Depalmitoylation is insufficient to release NMNAT2 from membranes, suggesting palmitoylation-independent mechanisms contribute to membrane association.

Significance: Modulation of NMNAT2 subcellular localization could delay axon degeneration in neurodegenerative disease.

Abstract

The NAD-synthesizing enzyme nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) is a critical survival factor for axons and its constant supply from neuronal cell bodies into axons is required for axon survival in primary culture neurites and axon extension in vivo. Recently, we showed that palmitoylation is necessary to target NMNAT2 to post-Golgi vesicles, thereby influencing its protein turnover and axon protective capacity. Here we find that NMNAT2 is a substrate for cytosolic thioesterases APT1 and APT2 and that palmitoylation/depalmitoylation dynamics are on a time scale similar to its short half-life. Interestingly, however, depalmitoylation does not release NMNAT2 from membranes. The mechanism of palmitoylation-independent membrane attachment appears to be mediated by the same minimal domain required for palmitoylation itself. Furthermore, we identify several zDHHC palmitoyltransferases that influence NMNAT2 palmitoylation and subcellular localization, among which a role for zDHHC17 (HIP14) in neuronal NMNAT2 palmitoylation is best supported by our data. These findings shed light on the enzymatic regulation of NMNAT2 palmitoylation and highlight individual thioesterases and palmitoyltransferases as potential targets to modulate NMNAT2-dependent axon survival.