Functional Activation of Heat Shock Factor and Hypoxia-Inducible Factor in the Kidney

Abstract

Abstract. Renal ischemia is the result of a complex series of events, including decreases in oxygen supply (hypoxia) and the availability of cellular energy (ATP depletion). In this study, the functional activation of two stress-responsive transcription factors, i.e., heat shock factor-1 (HSF-1) and hypoxia-inducible factor-1 (HIF-1), in the kidney was assessed. When rats were subjected to 45 min of renal ischemia, electrophoretic mobility shift assays of kidney nuclear extracts revealed rapid activation of both HIF-1 and HSF. Western blot analyses further demonstrated that this activation resulted in increased expression of the HSF and HIF-1 target genes heat shock protein-72 and heme oxygenase-1, respectively. Whether hypoxia or ATP depletion alone could produce similar activation patterns in vitro was then investigated. Renal epithelial LLC-PK 1 cells were subjected to either ATP depletion (0.1 M antimycin A and glucose deprivation) or hypoxia (1% O 2 ). After ATP depletion, HSF was rapidly activated (within 30 min), whereas HIF-1 was unaffected. In contrast, hypoxia led to the activation of HIF-1 but not HSF. Hypoxic activation of HIF-1 was observed within 30 min and persisted for 4 h, whereas no HSF activation was detected even with prolonged periods of hypoxia. HIF-1 was transcriptionally active in LLC-PK 1 cells, as demonstrated by luciferase reporter gene assays using the vascular endothelial growth factor promoter or a synthetic promoter construct containing three hypoxia-inducible elements. Interestingly, intracellular ATP levels were not affected by hypoxia but were significantly reduced by ATP depletion. These findings suggest that HIF-1 is activated specifically by decreased O 2 concentrations and not by reduced ATP levels alone. In contrast, HSF is activated primarily by metabolic stresses associated with ATP depletion and not by isolated O 2 deprivation. In vivo, the two transcription factors are simultaneously activated during renal ischemia, which might account for observed differences between in vivo and in vitro epithelial cell injury and repair. Selective modulation of either pathway might therefore be of potential interest for modification of the response of the kidney to ischemia, as well as the processes involved in recovery from ischemia.

Nitric Oxide InhibitorNω-Nitro-l-arginine Methyl Ester Potentiates Induction of Heme Oxygenase-1 in Kidney Ischemia/Reperfusion Model: A Novel Mechanism for Regulation of the Oxygenase

“…Therefore, rendering the second possibility less likely. This is in line with the report that activation of hypoxia-inducible factor 1 (HIF-1) in ischemic kidney persists only for 4 h (Eickelberg et al, 2002). In the first case scenario, NO derivatives could: 1) directly cause dissolution of the transcript, 2) activate cellular factors that accelerate HO-1 mRNA degradation, or 3) inactivate factors that stabilize the transcript.…”

The effect of surgically induced ischaemia on gene expression in a colorectal cancer xenograft model

“…It may be that in vivo tissue ischaemia following vascular occlusion involves distinct responses to hypoxia and cellular energy depletion. A 45 min of rat renal ischaemia induced by vascular clamping was associated with increased HIF-1 and heat shock factor-1 (HSF-1) levels, whereas in vitro ATP depletion increased HSF-1 levels in isolation and hypoxia led to increased HIF-1 expression alone (Eickelberg et al, 2002).…”

Induction of HSF1 expression is associated with sporadic colorectal cancer

“…HSF1 stands for heat shock transcription factor 1 and is a transcription factor with a molecular weight of 82KD. HSF1 could be induced by heat, chemicals and hypoxia [17][18][19] and usually exists as a monomer in the cytoplasm. After heat stimulation, it became a trimer and could be translocated into nucleus [20] .…”

“…The prolonged exposure of these "stress" substances could lead to activation of heat shock stress pathway, thus leading to carcinogenesis through enhancing function of oncogenic proteins occurring in cells. The heat shock stress pathway could be further activated by hypoxia occurring in the tumor which was found to increase HSF1 expression as well [18,19] . Vegetables, nonsteroidal anti-inflammatory drugs (NSAIDs), hormone replacement therapy, and physical activity [31] could reverse the activation of heat shock stress pathway and therefore suppress carcinogenesis.…”