Investigation of the Presence and Implications of S‐Palmitoylation on Norepinephrine and Serotonin Transporters

Abstract

The dopamine, norepinephrine and serotonin transporters (DAT, NET and SERT, respectively) are plasma membrane proteins belonging to the SLC6 family of secondary active transporters and are responsible for clearance of their corresponding substrates dopamine (DA), norepinephrine (NE) and serotonin (5‐HT) from the extraneuronal space during neurotransmission. Each monoamine controls distinct behavioral and physiological functions in the nervous system. DA controls motor functions, mood, reward and cognition. NE regulates arousal, mood, attention, stress‐responsiveness and 5‐HT modulates mood, aggression, motivation, appetite, sleep, cognition and sexual function. Extraneuronal monoamine levels are controlled spatially and temporally by transporter mediated reuptake of released transmitter into presynaptic neurons. Abnormalities in transmitter levels and subsequent neurotransmission are linked to neurological disorders including major depression, schizophrenia, bipolar disorder, attention deficit hyperactivity disorder, Tourette syndrome, and Parkinson disease, through mechanisms that are incompletely understood. The transporters are sites of action for therapeutic drugs such as methylphenidate, bupropion, selective serotonin and serotonin‐norepinephrine reuptake inhibitors, used to treat these disorders, and are also targets for addictive drugs including cocaine, amphetamine (AMPH), and methylenedioxy methamphetamine (MDMA) that elevate transmitter levels. Several lines of evidence indicate that modulation of transporter phosphorylation, ubiquitylation, and palmitoylation regulate their cell surface expression, activity, trafficking and degradation. We previously reported that rat, mouse and human DATs are modified by S‐palmitoylation, a post‐translational modification in which C16 saturated palmitic acid is added via a thioester linkage to cysteine. These results indicated that DAT palmitoylation has the capacity to impact dopaminergic signaling acutely by regulating DA transport kinetics independent of surface losses and chronically by opposing DAT degradation. We have extended our examination of transporter palmitoylation using acyl‐biotinyl exchange to include SERT and NET finding both transporters are palmitoylated proteins, suggesting potential palmitoylation regulatory mechanisms for NET and SERT analogous to DAT. Furthermore, treatment with the palmitoyl acyltransferase inhibitor 2‐bromopalmitate (2BP), in a heterologous cell system, resulted in decreased overall palmitoylation of these proteins. Inhibition of palmitoylation by 2BP also revealed acute and long‐term differences between SERT and NET stability where loss of palmitoylation is accompanied by a loss of total transporter protein. Collectively, these results indicate that S‐palmitoylation may serve as a potential regulator for NET and SERT properties, sharing some functional consequences as demonstrated with DAT.Support or Funding InformationSupported by the National Institute on Drug Abuse Grant DA 031991 JDF, P20 RR017699 (to U.N.D.) from the COBRE program of the National Center for Research Resources, and P20 RR016741 (to U.N.D.) from the INBRE program of the National Center for Research Resources.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Palmitoylation Regulates Human Serotonin Transporter Activity, Trafficking, and Expression and Is Modulated by Escitalopram

“…Ultimately, our findings provide the first report of SERT as a palmitoyl protein 57,58 and contribute a novel component to an already extensive pool of existing literature on post-translational modifications of monoamine transporters. The regulatory nature of post-translational modifications, including palmitoylation, is critical in maintaining physiologic homeostasis in response to cellular demands and environmental challenges.…”