Transcriptional regulation of SUR1-regulated NC(Ca-ATP) channel by hypoxia inducible factor 1alpha in brain injury

Abstract

The sulfonylurea receptor 1 (SUR1)-regulated non-selective cation (NC Ca-ATP) channel is a recently identified cation channel implicated in programmed necrotic death in the central nervous system. This study examined the relationship between hypoxia, its correlate, transcription factor HIF1, and expression of SUR1 by reactive astrocytes of the gliotic capsule that forms around the gelatin sponge implanted into rat brain. We used pimonidazole hydrochloride to show that the inner zone of the gliotic capsule where the SUR1-regulated NCCa-ATP channel is localized is hypoxic, and immunohistochemistry and western immunoblotting to show that reactive astrocytes forming the gliotic capsule express elevated levels of both HIF1alpha and SUR1 proteins. Quantitative RT-PCR performed with tissue from the inner zone showed that mRNA for SUR1 is upregulated. Electrophoretic mobility shift assay (EMSA) with nuclear extract from gliotic capsule and the DNA sequence of the proximal promoter of SUR1 gene demonstrated a specific protein-DNA interaction. Chromatin immunoprecipitation assay (ChIP) was used to show specific binding between HIF1alpha protein and the SUR1 promoter DNA sequence in vivo. Knocking down HIF1alpha in vivo using antisense oligodeoxynucleotide resulted in a concurrent decrease in levels of both HIF1alpha and SUR1 proteins. We conclude that HIF1alpha is involved in transcriptional regulation of the SUR1 gene, affirming an important role for SUR1 in CNS hypoxia.