S-Nitrosylation-Mediated Redox Transcriptional Switch Modulates Neurogenesis and Neuronal Cell Death

Abstract

SUMMARY Redox-mediated posttranslational modifications represent a molecular switch that controls major mechanisms of cell function. Nitric oxide (NO) can mediate redox reactions via S-nitrosylation, representing transfer of an NO group to a critical protein thiol. NO is known to modulate neurogenesis and neuronal survival in various brain regions in disparate neurodegenerative conditions. However, a unifying molecular mechanism linking these phenomena remains unknown. Here we report that S-nitrosylation of myocyte enhancer factor 2 (MEF2) transcription factors acts as a redox switch to inhibit both neurogenesis and neuronal survival. Structure-based analysis reveals that MEF2 dimerization creates a pocket, facilitating S-nitrosylation at an evolutionally conserved cysteine residue in the DNA binding domain. S-Nitrosylation disrupts MEF2-DNA binding and transcriptional activity, leading to impaired neurogenesis and survival in vitro and in vivo. Our data define a novel molecular switch whereby redox-mediated posttranslational modification controls both neurogenesis and neurodegeneration via a single transcriptional signaling cascade.

The Expanding List of Redox-Sensing Transcription Factors in Mammalian Cells

“…A thiol-disulfide redox switch in the Rev-erbβ molecule appears to control the interaction between heme and the ligandbinding domain, with the reduced form exhibiting an affinity which is 5-fold higher than that of the oxidized form [9]. Moreover, Okamoto et al have demonstrated that the muscle-specific transcription factor myocyte enhancer factor 2 (MEF2) can undergo NO-induced nitrosylation, which disrupts MEF2-DNA binding and the transcriptional activity [10]. Specifically, MEF2 dimerization creates a pocket that facilitates S-nitrosylation of an evolutionally conserved cysteine residue in the DNA binding domain.…”

“…Specifically, MEF2 dimerization creates a pocket that facilitates S-nitrosylation of an evolutionally conserved cysteine residue in the DNA binding domain. This redox switch inhibits neurogenesis and neuronal survival, and it is suggested that this may be an important molecular mechanism to explain the effects of NO in neurodegenerative diseases [10].…”

“…Specifically, MEF2 dimerization creates a pocket that facilitates S-nitrosylation of an evolutionally conserved cysteine residue in the DNA binding domain. This redox switch inhibits neurogenesis and neuronal survival, and it is suggested that this may be an important molecular mechanism to explain the effects of NO in neurodegenerative diseases [10].Sensing redox changes by a binding partner/regulator of a transcription factor is also an important fashion of redox-dependent transcriptional regulation in cell biology. For example, the redoxsensitive multifunctional protein APE1/Ref-1 is thought to be a critical redox-dependent regulator of multiple transcription factors, including AP-1, nuclear factor κB, p53, activating transcription factor/cAMPresponse element-binding protein (ATF/CREB), and hypoxiainducible factor-1α [11].…”

MEF2D haploinsufficiency downregulates the NRF2 pathway and renders photoreceptors susceptible to light-induced oxidative stress

“…2 E and F). Our group has previously shown-via reporter gene assays, chromatin immunoprecipitation (ChIP), and electrophoretic mobility shift assay-that posttranslational redox modification of Cys39 inhibits MEF2 transcriptional activity by interfering with DNA binding (27,28,35,36). Hence, it might be expected that excessive ROS exposure would lead to the formation of SO X H-MEF2D (x = 1-3), thereby impairing transcription of MEF2 target genes.…”

“…Mechanistically, we show that excessive ROS in this LIRD model leads to decreased MEF2 activity via a posttranslational modification of MEF2 at cysteine 39 (causing a sulfonation adduct). The presence of this adduct interferes with the ability of the transcription factor to bind to DNA (27,28), thus preventing activation of its downstream targets. We show that heterozygosity for Mef2d partially decreases MEF2D transcriptional activity, rendering photoreceptors more susceptible to an oxidizing light insult.…”