Insulin-Regulated Expression of Egr-1 and Krox20: Dependence on ERK1/2 and Interaction with p38 and PI3-Kinase Pathways

Abstract

In addition to its ability to rapidly alter metabolism, insulin is also able to regulate the expression of numerous genes via activation of the PI3-kinase (PI3-K), MAPK kinase (MEK)-ERK, or p38 pathways. Using differential screening of H4IIE cells, we have identified two members of the Egr zinc-finger transcription factor family of early response genes, Egr-1 and Krox20, whose transcription is induced by insulin treatment. Egr-1 may be involved in insulin's regulation of hepatic gene expression. Krox20 regulation and expression have been primarily studied in neural cells and tissues, but little has been previously reported on the presence of Krox20 in cells of hepatic origin or its regulation by insulin. In the present studies, insulin treatment rapidly increased transcription of both Egr-1 and Krox20. In cells pretreated with a PI3-K inhibitor, there was no reduction in the effect of insulin on Egr-1 and Krox20, but an increase in Egr-1 transcription. The rapid induction of ERK1/2 phosphorylation was completely blocked by pretreatment with a MEK1 inhibitor and was associated with a nearly complete inhibition of insulin-stimulated induction of both Egr-1and Krox20, indicating this pathway is necessary for insulin's effect on these genes. Finally, inhibition of the p38 pathway, followed by insulin addition, caused an additive induction of both Egr-1and Krox20. In conclusion, these genes are induced by insulin via coordinated regulation of the MEK-ERK and p38 pathways and, in the case of Egr-1, the PI3-K pathway.

Upregulation of rat Ccnd1 gene by exendin-4 in pancreatic beta cell line INS-1: interaction of early growth response-1 with cis-regulatory element

“…In our experiments, the rapid and transient induction of EGR1 protein in response to exendin-4 ( Fig. 8a) was consistent with previous studies [9,34]. In addition, the time course of EGR1 protein induction was consistent with that of EGR1 binding to the radiolabelled oligo 5′ probe (Fig.…”

“…Expression of Egr1 is rapidly induced by mitogens, insulin and glucose in different cells, including beta cells [19,20,34,35]. In our experiments, the rapid and transient induction of EGR1 protein in response to exendin-4 ( Fig.…”

Egr-1 binds the GnRH promoter to mediate the increase in gene expression by insulin

“…Consistent with its role as an immediate early gene, Egr-1 mRNA levels rise and peak early after stimulation with insulin then decline quickly, with a corresponding pattern of protein expression (Figure 1). This time course of insulin induced increase in Egr-1 mRNA levels has been observed in many tissues (Barroso and Santisteban, 1999;Tan et al, 2003;Silverman and Collins, 1999;Leung-Theung-Long et al, 2005;Garnett et al, 2005) as has its dependence on the MAP kinase pathway (Leung-Theung-Long et al, 2005;Garnett et al, 2005;Keeton et al, 2003). The GnRH mRNA level peak after one hour of insulin treatment corresponds with the time of maximal Egr-1 protein levels, suggesting that higher protein levels, rather than protein activation, promote binding of Egr-1 to the GnRH promoter.…”

“…We previously demonstrated that insulin exerts its effect on GnRH promoter activity via a MAP kinase pathway (Kim et al, 2005); in other cell systems, insulin mediated induction of Egr-1 is dependent upon activation of the Ras/Raf/MAP kinase pathway (Keeton et al, 2003). In order to investigate whether the effect of insulin on Egr-1 is mediated by the MAP kinase pathway in the GN11 cells, cells were pre-treated with PD98059--a specific inhibitor of MEK, the upstream regulator of MAP kinase-then treated with insulin.…”

“…The induction of Egr-1 gene expression by insulin is primarily mediated by the MAP kinase pathway. PI3 and p38 kinase pathways have a modulating effect on Egr-1 transcription, but are not essential pathways for signal transduction (Keeton et al, 2003). The zinc finger DNA binding domain of Egr-1 binds GC rich regions of its target gene to increase or decrease transcription.…”