Binding of carbonic anhydrase IX to 45S rDNA genes is prevented by exportin-1 in hypoxic cells.

Emanuele Sasso,Giuseppina Minopoli,Francesca Monteleone,Bianca Crifò,Daniela Sarnataro,Mariangela Sabatella,Monica Vitale,Luca Alfredo Paolella,Nicola Zambrano,Francesca Ludovica Boffo,Corrado Garbi,Jean-Yves Winum,Margherita Santoriello

doi:10.1155/2015/674920

Abstract

Carbonic anhydrase IX (CA IX) is a surrogate marker of hypoxia, involved in survival and pH regulation in hypoxic cells. We have recently characterized its interactome, describing a set of proteins interacting with CA IX, mainly in hypoxic cells, including several members of the nucleocytoplasmic shuttling apparatuses. Accordingly, we described complex subcellular localization for this enzyme in human cells, as well as the redistribution of a carbonic anhydrase IX pool to nucleoli during hypoxia. Starting from this evidence, we analyzed the possible contribution of carbonic anhydrase IX to transcription of the 45S rDNA genes, a process occurring in nucleoli. We highlighted the binding of carbonic anhydrase IX to nucleolar chromatin, which is regulated by oxygen levels. In fact, CA IX was found on 45S rDNA gene promoters in normoxic cells and less represented on these sites, in hypoxic cells and in cells subjected to acetazolamide-induced acidosis. Both conditions were associated with increased representation of carbonic anhydrase IX/exportin-1 complexes in nucleoli. 45S rRNA transcript levels were accordingly downrepresented. Inhibition of nuclear export by leptomycin B suggests a model in which exportin-1 acts as a decoy, in hypoxic cells, preventing carbonic anhydrase IX association with 45S rDNA gene promoters.

Highlights

Reprogrammed energy metabolism was considered among the emerging hallmarks in cancer [1]
Carbonic anhydrase IX (CA IX) was found on 45S rDNA gene promoters in normoxic cells and less represented on these sites, in hypoxic cells and in cells subjected to acetazolamide-induced acidosis
carbonic anhydrases (CAs) IX was found in native complexes with the importin, TNPO1, and the exportin, XPO1; CA IX appeared to be widely distributed in the cellular compartments, including nuclei, of several human cell lines

Summary

Introduction

Reprogrammed energy metabolism was considered among the emerging hallmarks in cancer [1]. Cancer cells developing inside a hypoxic environment, and cancer cells exposed to normal oxygen levels, switch energetic metabolism towards glycolysis. Gene expression programmes mediated by HIF1α transcription factor allow cells to increase the efficiency of glycolysis via enhanced ability to uptake glucose, via stimulation of glycolytic enzymes, and via increased ability to buffer the acidic, pyruvate- and lactate-enriched intracellular environment. The carbonic anhydrases (CAs), a large family of metalloenzymes with wide subcellular distributions, are central to the adaptation of the cancer cells to the glycolytic switch. CA IX, a membrane carbonic anhydrase possessing an extracellular catalytic domain, is actively involved in the acidification of extracellular space, as a consequence of the need for buffering the intracellular compartments [2, 3]. Cancer cells may take advantage from the acidic features of their extracellular space, since it may enhance invasiveness potential [4]

Methods

Results

Conclusion