Research article

Differential regulation of NAB corepressor genes in Schwann cells

Rajini Srinivasan¹ , Sung-Wook Jang² , Rebecca M Ward¹ , Shrikesh Sachdev³ , Toshihiko Ezashi⁴ and John Svaren¹

¹Department of Comparative Biosciences, University of Wisconsin-Madison, Madison, WI, USA

²Program in Cellular and Molecular Biology, University of Wisconsin-Madison, Madison, WI, USA

³Department of Biochemistry, University of Missouri-Columbia, Columbia, MO, USA

⁴Department of Animal Sciences, University of Missouri-Columbia, Columbia, MO, USA

author email corresponding author email

BMC Molecular Biology 2007, 8:117doi:10.1186/1471-2199-8-117

Published:	20 December 2007

Abstract

Background

Myelination of peripheral nerves by Schwann cells requires not only the Egr2/Krox-20 transactivator, but also the NGFI-A/Egr-binding (NAB) corepressors, which modulate activity of Egr2. Previous work has shown that axon-dependent expression of Egr2 is mediated by neuregulin stimulation, and NAB corepressors are co-regulated with Egr2 expression in peripheral nerve development. NAB corepressors have also been implicated in macrophage development, cardiac hypertrophy, prostate carcinogenesis, and feedback regulation involved in hindbrain development.

Results

To test the mechanism of NAB regulation in Schwann cells, transfection assays revealed that both Nab1 and Nab2 promoters are activated by Egr2 expression. Furthermore, direct binding of Egr2 at these promoters was demonstrated in vivo by chromatin immunoprecipitation analysis of myelinating sciatic nerve, and binding of Egr2 to the Nab2 promoter was stimulated by neuregulin in primary Schwann cells. Although Egr2 expression activates the Nab2 promoter more highly than Nab1, we surprisingly found that only Nab1 – but not Nab2 – expression levels were reduced in sciatic nerve from Egr2 null mice. Analysis of the Nab2 promoter showed that it is also activated by ETS proteins (Ets2 and Etv1/ER81) and is bound by Ets2 in vivo.

Conclusion

Overall, these results indicate that induction of Nab2 expression in Schwann cells involves not only Egr2, but also ETS proteins that are activated by neuregulin stimulation. Although Nab1 and Nab2 play partially redundant roles, regulation of Nab2 expression by ETS factors explains several observations regarding regulation of NAB genes. Finally, these data suggest that NAB proteins are not only feedback inhibitors of Egr2, but rather that co-induction of Egr2 and NAB genes is involved in forming an Egr2/NAB complex that is crucial for regulation of gene expression.