Hypoxia-inducible Factor-1 (HIF-1)-independent Hypoxia Response of the Small Heat Shock Protein hsp-16.1 Gene Regulated by Chromatin-remodeling Factors in the Nematode Caenorhabditis elegans

Jihyun Lee,Junho Lee

doi:10.1074/jbc.m112.401554

Abstract

Oxygen deprivation is accompanied by the coordinated expression of numerous hypoxia-responsive genes, many of which are controlled by hypoxia-inducible factor-1 (HIF-1). However, the cellular response to hypoxia is not likely to be mediated by HIF-1 alone, and little is known about HIF-1-independent hypoxia responses. To better establish the molecular mechanisms of HIF-1-independent hypoxia responses, we sought to characterize the molecular basis of the hypoxia response of the hsp-16.1 gene in the nematode Caenorhabditis elegans; this gene has been shown to be induced by hypoxia independently of hif-1. Using affinity purification followed by LC-MS/MS, we identified HMG-1.2 as a protein that binds to a specific promoter region under hypoxic conditions. By systematic prediction followed by validation of these interactions through RNAi, we identified the chromatin modifiers isw-1 and hda-1, histone H4, and NURF-1 chromatin-remodeling factors as new components of the hif-1-independent hypoxia response. These data suggest that the modulation of nucleosome positioning at the hsp-16.1 promoter may be important for the hypoxia response. In addition, we found that calcineurin acts independently of hif-1 to modulate the cellular response to hypoxia and that calcium ions are necessary for the induction of hsp-16.1 under hypoxic conditions.

Highlights

To characterize an unknown molecular basis of the hif-1-independent hypoxia response, we used the nematode hsp-16.1 gene as a model
We found that calcineurin acts independently of hif-1 to modulate the cellular response to hypoxia and that calcium ions are necessary for the induction of hsp-16.1 under hypoxic conditions
Identification of HMG-1.2 as a Hypoxia-induced Promoterbinding Protein—Previously, we showed that the sequence CAC(A/T)CT is required for the hypoxia-inducible factor-1 (HIF-1)-independent hypoxia response of hsp-16 genes; we demonstrated that regulatory proteins bind to block I-containing sequences in vitro [18]

Summary

Background

To characterize an unknown molecular basis of the hif-1-independent hypoxia response, we used the nematode hsp-16.1 gene as a model. To better establish the molecular mechanisms of HIF-1-independent hypoxia responses, we sought to characterize the molecular basis of the hypoxia response of the hsp-16.1 gene in the nematode Caenorhabditis elegans; this gene has been shown to be induced by hypoxia independently of hif-1. By systematic prediction followed by validation of these interactions through RNAi, we identified the chromatin modifiers isw-1 and hda-1, histone H4, and NURF-1 chromatin-remodeling factors as new components of the hif-1-independent hypoxia response These data suggest that the modulation of nucleosome positioning at the hsp-16.1 promoter may be important for the hypoxia response. To establish the HIF-1-independent hypoxia response pathway, we dissected the molecular mechanism that mediates the hypoxia-inducible transcription of the C. elegans hsp-16.1 gene. Our results indicate that chromatin-remodeling complex proteins are involved in the modulation of hsp-16.1 expression under hypoxic conditions. We report the existence of an alternative, HIF-1-independent mechanism by which cells adapt to hypoxic conditions

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION