The Organellular Chloride Channel Protein CLIC4/mtCLIC Translocates to the Nucleus in Response to Cellular Stress and Accelerates Apoptosis

Kwang S Suh,Michihiro Mutoh,Kunio Nagashima,Ester Fernandez-Salas,Lindsay E Edwards,Daniel D Hayes,John M Crutchley,Keith G Marin,Rebecca A Dumont,Joshua M Levy,Christina Cheng,Susan Garfield,Stuart H Yuspa

doi:10.1074/jbc.m311632200

Abstract

CLIC4/mtCLIC, a chloride intracellular channel protein, localizes to the mitochondria and cytoplasm of keratinocytes and participates in the apoptotic response to stress. We now show that multiple stress inducers cause the translocation of cytoplasmic CLIC4 to the nucleus. Immunogold electron microscopy and confocal analyses indicate that nuclear CLIC4 is detected prior to the apoptotic phenotype. CLIC4 associates with the Ran, NTF2, and Importin-alpha nuclear import complexes in immunoprecipitates of lysates from cells treated with apoptotic/stress-inducing agents. Deletion or mutation of the nuclear localization signal in the C terminus of CLIC4 eliminates nuclear translocation, whereas N terminus deletion enhances nuclear localization. Targeting CLIC4 to the nucleus via adenoviral transduction accelerates apoptosis when compared with cytoplasmic CLIC4, and only nuclear-targeted CLIC4 causes apoptosis in Apaf null mouse fibroblasts or in Bcl-2-overexpressing keratinocytes. These results indicate that CLIC4 nuclear translocation is an integral part of the cellular response to stress and may contribute to the initiation of nuclear alterations that are associated with apoptosis.

Highlights

CLIC4/mtCLIC, a chloride intracellular channel protein, localizes to the mitochondria and cytoplasm of keratinocytes and participates in the apoptotic response to stress
These results indicate that CLIC4 nuclear translocation is an integral part of the cellular response to stress and may contribute to the initiation of nuclear alterations that are associated with apoptosis
To determine if CLIC4 intracellular localization was altered in stressed cells, agents that are DNA-damaging, metabolic inhibitors or cytotoxic were tested on primary mouse keratinocytes

Summary

Introduction

CLIC4/mtCLIC, a chloride intracellular channel protein, localizes to the mitochondria and cytoplasm of keratinocytes and participates in the apoptotic response to stress. Targeting CLIC4 to the nucleus via adenoviral transduction accelerates apoptosis when compared with cytoplasmic CLIC4, and only nuclear-targeted CLIC4 causes apoptosis in Apaf null mouse fibroblasts or in Bcl-2-overexpressing keratinocytes These results indicate that CLIC4 nuclear translocation is an integral part of the cellular response to stress and may contribute to the initiation of nuclear alterations that are associated with apoptosis. This paper is available on line at http://www.jbc.org mtCLIC/CLIC4 Nuclear Translocation Initiates Apoptosis studies have indicated that nuclear translocation of CLIC4 was detected in cells responding to various stress and apoptotic signals. This dynamic trafficking occurs early after stress signals and is mediated by the nuclear localization signal (NLS) and the nuclear import machineries. These results suggest that CLIC4 participates in the stressinduced apoptotic response in several cellular compartments

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Conclusion