SDF1α/CXCR4 Signaling, via ERKs and the Transcription Factor Egr1, Induces Expression of a 67-kDa Form of Glutamic Acid Decarboxylase in Embryonic Hippocampal Neurons

Abstract

Stromal cell-derived factor ␣ (SDF1␣) and its cognate receptor CXCR4 play an important role in neuronal development in the hippocampus, but the genes directly regulated by SDF1␣/ CXCR4 signaling are unknown. To study the role of CXCR4 targeted genes in neuronal development, we used neuronal cultures established from embryonic day 18 rats. Hippocampal neurons express CXCR4 receptor proteins and are stimulated by SDF1␣ resulting in activation of extracellular signal-regulated kinase (ERK)1/2 and the transcription factor cAMPresponse element-binding protein. SDF1␣ rapidly induces the expression of the early growth response gene Egr1, a transcription factor involved in activity-dependent neuronal responses, in a concentration-dependent manner. Gel-shift analysis showed that SDF1␣ enhances DNA binding activity to the Egr1-containing promoter for GAD67. Chromatin immunoprecipitation analysis using an Egr1 antibody indicated that SDF1␣ stimulation increases binding of Egr1 to a GAD67 promoter DNA sequence. SDF1␣ stimulation increases the expression of GAD67 at both the mRNA and protein levels, and increases the amount and neurite localization of ␥-aminobutyric acid (GABA) in neurons already expressing GABA. SDF1␣-induced Egr1/GAD67 expression is mediated by the G protein-coupled CXCR4 receptor and activation of the ERK pathway. Reduction of Egr1 gene expression using small interfering RNA technology lowers the level of GAD67 transcripts and inhibits SDF1␣-induced GABA production. Inhibition of CXCR4 activation in the developing mouse brain in utero greatly reduced Egr1 and GAD67 mRNA levels and GAD67 protein levels, suggesting a pivotal role for CXCR4 signaling in the development of GABAergic neurons in vivo. Our data suggest that SDF1␣/CXCR4/G protein/ERK signaling induces the expression of the GAD67 system via Egr1 activation, a mechanism that may promote the maturation of GABAergic neurons during development.

Maternal Care and DNA Methylation of a Glutamic Acid Decarboxylase 1 Promoter in Rat Hippocampus

“…The effect of 5-HT on GAD1 expression in hippocampal neuronal cultures was mimicked by NGFI-A overexpression. This finding is consistent with that of a report showing that SDF1␣-induced increases in GAD1 expression in cultured hippocampal neurons are mediated by an increased association of NGFI-A to the GAD1 promoter (Luo et al, 2008). These findings replicate previous results showing that maternally induced increases in NGFI-A expression are associated with an increase in NGFI-A association with NGFI-A-sensitive promoters, and stable epigenetic alterations (Weaver et al, 2004b(Weaver et al, , 2007.…”

Upregulation of Chemokine CXCL12 in the Dorsal Root Ganglia and Spinal Cord Contributes to the Development and Maintenance of Neuropathic Pain Following Spared Nerve Injury in Rats

“…Previous studies have shown that the binding of CXCL12 to CXCR4 activates multiple intracellular signaling pathways, including the ERK pathway [32], so we assessed ERK activation in the spinal cord following SNI. The level of p-ERK increased on day 1, peaked on days 3 and 7, and lasted for 3 weeks after SNI (Fig.…”

“…In a primary astrocyte culture model, Han et al showed that CXCL12 stimulation triggers the activation of NF-jB and ERK, and that both of these contribute to the secretion of TNF-a [9]. In cultured hippocampal neurons, CXCL12-induced GAD67 (a key enzyme in GABA synthesis) expression is mediated by the G-protein-coupled CXCR4 and activation of the ERK pathway [32]. These results imply that ERK might be an important signal in CXCR4-mediated neuromodulation, and our present results provide evidence that spinal ERK activation contributes to CXCL12/CXCR4-mediated neuropathic pain.…”

Structure-based design of inhibitors of CXCR4.

“…This is an important distinction to make, as there are multiple signaling pathways that could potentially influence CXCR4-mediated chemotaxis. Cell migration due to CXCR4 activation is the result of activation of multiple signaling pathways [133][134][135], including the ERK1/2, JNK, MAPK, and GSK 3a/~ phosphorylation systems, [129] activation of phospholipase C to enhance calcium mobilization [130], activation of the phosphoinositide-3-kinase pathway to activate AKT [130], and activation of PKa or CREB [131,132]. Thus anti-chemotaxis activity of ECl VS 14…”

“…Activation of the G~y subunit also results in signaling by the Phospholipase C pathway to enhance calcium mobilization as well as signaling by the Phosphoinositide-3-kinase pathway to activate AKT. CXCR4 binding of CXCL 12 also serves to augment intracellular cAMP levels [130] and activate cAMP-dependant signaling pathways, such as PKa or CREB [131,132]. The combined activation of these factors results in cell migration [133][134][135].…”