Transcriptional repression of Na-K-2Cl cotransporter NKCC1 by hypoxia-inducible factor-1

Abstract

Tissue edema is commonly associated with hypoxia. Generally, such episodes of fluid accumulation are self-limiting. At present, little is known about mechanisms to compensate excessive fluid transport. Here we describe an adaptive mechanism to dampen fluid loss during hypoxia. Initial studies confirmed previous observations of attenuated electrogenic Cl- secretion after epithelial hypoxia. A screen of known ion transporters in Cl- -secreting epithelia revealed selective downregulation of Na-K-2Cl cotransporter NKCC1 mRNA, protein, and function. Subsequent studies identified transcriptional repression of NKCC1 mediated by hypoxia-inducible factor (HIF). Chromatin immunoprecipitation analysis identified a functional HIF binding site oriented on the antisense strand of genomic DNA downstream of the transcription start site corresponding to the NKCC1 5'-untranslated region. Additional in vivo studies using conditional Hif1a-null mice revealed that the loss of HIF-1alpha in Cl- -secreting epithelia results in a loss of NKCC1 repression. These studies describe a novel regulatory pathway for NKCC1 transcriptional repression by hypoxia. These results suggest that HIF-dependent repression of epithelial NKCC1 may provide a compensatory mechanism to prevent excessive fluid loss during hypoxia.

Induction of Na+/K+/2Cl− cotransporter expression mediates chronic potentiation of intestinal epithelial Cl− secretion by EGF

“…The predominant colonic SCFA, butyrate, decreases NKCC1 expression, thereby reducing epithelial secretory capacity. A recent study (24) has also demonstrated that NKCC1 is regulated by cellular O 2 supply, with decreases in its expression occurring under hypoxic conditions. Thus, our present knowledge suggests that the expression of colonic epithelial secretory responses at any given time will be determined by luminal concentrations of SCFAs, tissue oxygen supply, and levels of mucosal EGFR ligands.…”

Hydroxylase inhibition attenuates colonic epithelial secretory function and ameliorates experimental diarrhea

“…The effects of DMOG on secretory responses were relatively slow in onset and were preceded by cellular HIF1␣ accumulation, suggesting that DMOG likely mediates its effects through up-regulated HIF expression. This is not surprising, given that HIF is the primary target of DMOG-sensitive hydroxylases and has previously been shown to modulate epithelial transport protein expression under conditions of hypoxia (4,5). However, the potential involvement of other HIF-independent mechanisms cannot be ruled out.…”

Hypoxia Modulates HLA-G Gene Expression in Tumor Cells

“…This suggests that HIF-1 is involved in both induction and decrease of HLA-G gene expression, a property depending on the cell line. Notably, HIF-1 was demonstrated to repress transcriptional activity of several genes in mouse cells [33], and, for example, cad [37] and NKCCl [38] genes in human cells. However, our results did not provide evidence for the HIF-1 target.…”