The CLIC1 Chloride Channel Is Regulated by the Cystic Fibrosis Transmembrane Conductance Regulator when Expressed in Xenopus Oocytes
CLIC proteins comprise a family of chloride channels whose physiological roles are uncertain. To gain further insight into possible means of CLIC1 channel activity regulation, this protein was expressed in Xenopus oocytes alone or in combination with the cystic fibrosis transmembrane conductance regulator (CFTR). Whole-cell currents were determined using two-electrode voltage-clamp methods. Expression of CLIC1 alone did not increase whole-cell conductance either at rest or in response to increased intracellular cyclic adenosine monophosphate (cAMP). However, expression of CLIC1 with CFTR led to increased cAMP-activated whole-cell currents compared to expression from the same amount of CFTR mRNA alone. IAA-94 is a drug known to inhibit CLIC family channels but not CFTR. In oocytes expressing both CLIC1 and CFTR, a fraction of the cAMP-activated whole-cell current was sensitive to IAA-94, whereas in oocytes expressing CFTR alone, the cAMP-stimulated current was resistant to the drug. Cell fractionation studies revealed that the presence of CFTR conferred cAMP-stimulated redistribution of a fraction of CLIC1 from a soluble to a membrane-associated form. We conclude that when expressed in Xenopus oocytes CFTR confers cAMP regulation to CLIC1 activity in the plasma membrane and that at least part of this regulation is due to recruitment of CLIC1 from the cytoplasm to the membrane.
KeywordsChloride channel CLIC Cystic fibrosis transmembrane conductance regulator cAMP-activated chloride channel Cystic fibrosis NCC27 CLIC1
I thank Dr. Colin Nichols and members of his laboratory, including Qun Sha and Decha Enkvetchakul in the Department of Cell Biology and Physiology at Washington University School of Medicine for helpful discussions and technical advice. I thank Brian Plummer, Diana Johnson, and Ryan Emnet for technical assistance. The work was supported by a VA Merit Award and by NIH grants RO1 DK060551 and AR44838.
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