Sequential Activation of Hypoxia-Inducible Factor 1 and Specificity Protein 1 is Required for Hypoxia-Induced Transcriptional Stimulation of Abcc8

Abstract

Cerebral ischemia causes increased transcription of sulfonylurea receptor 1 (SUR1), which forms SUR1-regulated NC(Ca-ATP) channels linked to cerebral edema. We tested the hypothesis that hypoxia is an initial signal that stimulates transcription of Abcc8, the gene encoding SUR1, via activation of hypoxia-inducible factor 1 (HIF1). In the brain microvascular endothelial cells, hypoxia increased SUR1 abundance and expression of functional SUR1-regulated NC(Ca-ATP) channels. Luciferase reporter activity driven by the Abcc8 promoter was increased by hypoxia and by coexpression of HIF1α. Surprisingly, a series of luciferase reporter assays studying the Abcc8 promoter revealed that binding sites for specificity protein 1 (Sp1), but not for HIF, were required for stimulation of Abcc8 transcription by HIF1α. Luciferase reporter assays studying Sp1 promoters of three species, and chromatin immunoprecipitation analysis in rats after cerebral ischemia, indicated that HIF binds to HIF-binding sites on the Sp1 promoter to stimulate transcription of the Sp1 gene. We conclude that sequential activation of two transcription factors, HIF and Sp1, is required to stimulate transcription of Abcc8 following cerebral ischemia. Sequential gene activation in cerebral ischemia provides a plausible molecular explanation for the prolonged treatment window observed for inhibition of the end-target gene product, SUR1, by glibenclamide.

On Potential Interactions between Non-selective Cation Channel TRPM4 and Sulfonylurea Receptor SUR1

“…We provide compelling evidence that in a recombinant system, TRPM4 channels are not modulated by SUR1; although we cannot discard the possibility that interaction may occur in a different cellular environment, our data do not support the hypothesis that the cationic currents measured in astrocytes and endothelial cells from rodent models for neurovascular trauma are due to TRPM4 channels under direct modulation by SUR1 subunits (9). At the foundation of this hypothesis lies the observation that these currents are apparently inhibited by sulfonylureas (11,12,45,54). It is unclear whether the effect of these drugs was tested once desensitization of TRPM4-like currents was complete and a steady-state had been reached, as done in our study (Figs.…”

“…Accordingly, expression of SUR1 is up-regulated in reactive astrocytes, neurons, and capillaries of rodent models for ischemia, traumatic brain injury, and spinal cord injury (11,12,(43)(44)(45). The effects of trauma appear to be reduced by administration of glibenclamide (46,47); clinical trials to test the potential of this antidiabetic drug as a treatment for brain edema are under way (48), but the subject remains controversial (49,50).…”

Pituitary Adenylate Cyclase-activating Polypeptide Type 1 Receptor (PAC1) Gene Is Suppressed by Transglutaminase 2 Activation

“…Regarding the effect on viability of neuronal cells, treatment with either OGD or TM reduced their survival rate, which was significantly ameliorated by the pretreatment with salubrinal or cystamine (data not shown) in agreement with previous reports (14,15,17,24,30,31). The present finding that CHOP, GRP78, and cleaved caspase-3 were attenuated by the pretreatment with cystamine supports the previous report that the downstream activity of TG2 activates the calpain/caspase pathway (32).…”

“…Although other reports demonstrated the augmentation of TG2 expression in the hippocampus after reperfusion in a gerbil model of global cerebral ischemia (17,30,31), we found OGD-induced ER stress increased expression of TG2 not only in cytosol but also in nuclei of neuronal cells. Then OGD-induced nuclear TG2 expression and TG2 activity were markedly attenuated by salubrinal in agreement with previous findings (23).…”

Glyburide Advantage in Malignant Edema and Stroke (GAMES-RP) Trial: Rationale and Design

“…Like the KATP channel in pancreatic beta cells, the SUR1-TRPM4 channel is regulated by SUR1 and is blocked by sulfonylureas such as glyburide. In preclinical models of malignant infarction, glyburide prevents the development of edema and reduces secondary damage with treatment delays of up to 10 h following stroke [12].…”