Role of Salt-Inducible Kinase 1 in the Activation of MEF2-Dependent Transcription by BDNF

Abstract

Substantial evidence supports a role for myocyte enhancer factor 2 (MEF2)-mediated transcription in neuronal survival, differentiation and synaptic function. In developing neurons, it has been shown that MEF2-dependent transcription is regulated by neurotrophins. Despite these observations, little is known about the cellular mechanisms by which neurotrophins activate MEF2 transcriptional activity. In this study, we examined the role of salt-inducible kinase 1 (SIK1), a member of the AMP-activated protein kinase (AMPK) family, in the regulation of MEF2-mediated transcription by the neurotrophin brain-derived neurotrophic factor (BDNF). We show that BDNF increases the expression of SIK1 in primary cultures of rat cortical neurons through the extracellular signal-regulated kinase 1/2 (ERK1/2)-signaling pathway. In addition to inducing SIK1 expression, BDNF triggers the phosphorylation of SIK1 at Thr182 and its translocation from the cytoplasm to the nucleus of cortical neurons. The effects of BDNF on the expression, phosphorylation and, translocation of SIK1 are followed by the phosphorylation and nuclear export of histone deacetylase 5 (HDAC5). Blockade of SIK activity with a low concentration of staurosporine abolished BDNF-induced phosphorylation and nuclear export of HDAC5 in cortical neurons. Importantly, stimulation of HDAC5 phosphorylation and nuclear export by BDNF is accompanied by the activation of MEF2-mediated transcription, an effect that is suppressed by staurosporine. Consistent with these data, BDNF induces the expression of the MEF2 target genes Arc and Nur77, in a staurosporine-sensitive manner. In further support of the role of SIK1 in the regulation of MEF2-dependent transcription by BDNF, we found that expression of wild-type SIK1 or S577A SIK1, a mutated form of SIK1 which is retained in the nucleus of transfected cells, is sufficient to enhance MEF2 transcriptional activity in cortical neurons. Together, these data identify a previously unrecognized mechanism by which SIK1 mediates the activation of MEF2-dependent transcription by BDNF.

De Novo Mutations in SIK1 Cause a Spectrum of Developmental Epilepsies

“…25 Phosphorylation of HDAC5 allows MEF2C transcriptional activity to proceed. 26 MEF2C is a transcription factor important in both dorsal and ventral neuronal developmental pathways 17 and its expression is decreased with deficiency of the early forebrain transcription factor ARX. 27 Loss-of-function mutations in both ARX and MEF2C cause developmental epilepsies including infantile spasms.…”

“…Using immunoprecipitation-kinase assays, we evaluated both autophosphorylation of SIK1 and phosphorylation of HDAC5, a well-characterized substrate of SIK1. 26,34 We used recombinant fragments of HDAC5 expressed as GST fusion proteins that contained SIK1 phosphorylation sites Ser359 and Ser498. A kinase-dead form of SIK1 (p.Lys56Met) was used as a negative control in our activity assays.…”

Oleanolic Acid Promotes Neuronal Differentiation and Histone Deacetylase 5 Phosphorylation in Rat Hippocampal Neurons

“…Whole-cell proteins were extracted, and Western blot analysis was performed, as previously described ( Finsterwald et al, 2013 ), with the following antibodies: mouse anti-neuron-specific class III β-tubulin (Tuj1, 1:1000, Covance, USA), mouse anti-MAP2 (1:1000, Sigma Aldrich), rabbit anti-postsynaptic density protein 95 (PSD95, 1:1000, Cell Signaling, USA), rabbit anti-synapsin1 (SYN1, 1:1000, Cell Signaling), rabbit antisynaptophysin (SYP, 1:1000, Abcam), rabbit anti-HDAC5 (1:1000, Abcam), rabbit anti-phosphorylated HDAC5 (Ser259) (1:1000, Sigma Aldrich), rabbit anti-phosphorylated HDAC5 (Ser498) (1:1000, Abcam) rabbit anti-phosphorylated CaMKII (Thr286) (1:1000, Cell Signaling), rabbit anti-CaMKII (1:1000, Cell Signaling), rabbit anti-phosphorylated PKD (Ser744/748) (1:1000, Cell Signaling), rabbit anti-PKD (1:1000, Cell Signaling), mouse anti-myocyte enhancer factor-2 (MEF2D, 1:1000, BD Bioscience, USA), rabbit anti-brain-derived neurotrophic factor (BDNF, 1:1000, Santa Cruz, USA), rabbit anti-krüppel-like factor 6 (KLF6, 1:1000, Santa Cruz), mouse anti-β-actin (1:1000, Santa Cruz), and rabbit anti-lamin B1 (1:1000, Abcam) antibodies. The blots were then treated with anti-mouse or anti-rabbit IgG conjugated with peroxidase (1:2000, Santa Cruz) and bands were visualized using an enhanced chemi-luminescence (ECL) detection kit (Neuronex, Korea).…”

Long Non-coding RNA in Neurons: New Players in Early Response to BDNF Stimulation

“…Some BDNF-induced IEGs involved in synaptic plasticity have been identified. Among them, activity-regulated cytoskeleton-associated protein ( ARC ), salt-inducible kinase 1 ( SIK1 ), and transcription factor NR4A1 ( Nur77 ), have been shown to be up-regulated early by BDNF stimulation of neurons ( Ying et al, 2002 ; Rao et al, 2006 ; Zheng et al, 2009 ; Finsterwald et al, 2013 ). Beyond the classical protein-coding IEGs, micro-RNAs (miRNAs) have also been singled out in the early response to BDNF stimulation.…”