A TAT–DEF–Elk-1 Peptide Regulates the Cytonuclear Trafficking of Elk-1 and Controls Cytoskeleton Dynamics

Abstract

The transcription factor Elk-1 plays a key role in cell differentiation, proliferation and apoptosis. This role is thought to arise from its phosphorylation by activated extracellular signal-regulated kinases (ERKs), a critical posttranslational event for the transcriptional activity of the ternary complex composed of Elk-1 and a dimer of serum response factor (SRF) at the serum response element (SRE) regulatory site of transcription. In addition to its nuclear localization, Elk-1 is found in the dendrites and soma of neuronal cells and recent evidence implicate a cytoplasmic proapoptotic function of Elk-1, via its association with the mitochondrial permeability transition pore complex. Thus, the nuclear versus cytoplasmic localization of Elk-1 seems to be crucial for its biological function. In this study we show that the excitatory neurotransmitter, glutamate, induces an ERK-dependent Elk-1 activation and nuclear relocalization. We demonstrate that Elk-1 phosphorylation on Ser383/389 has a dual function and triggers both Elk-1 nuclear translocation and SRE-dependent gene expression. Mutating these sites into inactive residues or using a synthetic penetrating peptide (TAT-DEF-Elk-1), which specifically interferes with the DEF docking domain of Elk-1, prevents Elk-1 nuclear translocation without interfering with ERK nor MSK1 (mitogenand stress-activated protein kinase 1), a CREB kinase downstream from ERK-activation. This results in a differential regulation of glutamate-induced IEG regulation when compared with classical inhibitors of the ERK pathway. Using the TAT-DEF-Elk-1 peptide or the dominant-negative version of Elk-1, we show that Elk-1 phosphorylation controls dendritic elongation, SRF and Actin expression levels as well as cytoskeleton dynamics.

Alterations of Molecular and Behavioral Responses to Cocaine by Selective Inhibition of Elk-1 Phosphorylation

“…In contrast, PC12 cells overexpressing a constitutively nuclear mutant of Elk-1 show a facilitation of neuronal differentiation (Vanhoutte et al, 2001;Salinas et al, 2004). More recently, using the TDE peptide or a dominant-negative version of Elk-1 in primary striatal cultured cells, we found an inhibition of spontaneous dendritic outgrowth as well as cytoskeleton dynamics (Lavaur et al, 2007). As described previously (Shen et al, 2008), we found a global increase of spine density in NAcc shell MSNs after a chronic treatment with cocaine.…”

“…8). In cultured striatal neurons, the TDE is a selective inhibitor of ERK-dependent Elk-1 phosphorylation induced by glutamate in vitro (Lavaur et al, 2007). One important constraint of our in vivo study was to determine whether ERK-dependent phosphorylation of Elk-1 and MSK-1 occurred in the same striatal population in response to cocaine.…”

“…5G). Because our previous studies in vitro indicated that chronic blockade of Elk-1 activation inhibits SRF and Actin protein levels during spontaneous differentiation of striatal neurons (Lavaur et al, 2007), we analyzed expression levels of these genes during acute cocaine administration. We did not detect any variation of srf and actin mRNA levels 45 min after acute cocaine, and the pretreatment with TDE did not affect the basal levels of mRNA encoding for both proteins (Fig.…”

“…cells (Lavaur et al, 2007). We thus asked whether Elk-1 phosphorylation could affect morphological remodeling induced by chronic cocaine treatments.…”

“…We thus developed a strategy aimed at interfering with Elk-1 phosphorylation downstream from ERKs without blocking ERK activity toward other substrates. We designed a cell-penetrating peptide, named TDE peptide (TDE), which interferes with the DEF docking domain of Elk-1 toward ERKs (Lavaur et al, 2007), and analyzed molecular, morphological, and behavioral responses to cocaine in mice.…”