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Strong cooperativity between subunits in voltage-gated proton channels.

ABSTRACT: Voltage-activated proton (Hv) channels are essential components in the innate immune response. Hv channels are dimeric proteins with one proton permeation pathway per subunit. It is unknown how Hv channels are activated by voltage and whether there is any cooperation between subunits during voltage activation. Using cysteine accessibility measurements and voltage-clamp fluorometry, we show data consistent with the possibility that the fourth transmembrane segment S4 functions as the voltage sensor in Ciona intestinalis Hv channels. Unexpectedly, in a dimeric Hv channel, the S4 in both subunits must move to activate the two proton permeation pathways. In contrast, if Hv subunits are prevented from dimerizing, the movement of a single S4 is sufficient to activate the proton permeation pathway in a subunit. These results indicate strong cooperativity between subunits in dimeric Hv channels.

SUBMITTER: Gonzalez C

PROVIDER: S-EPMC2935852 | biostudies-literature | 2010 Jan

REPOSITORIES: biostudies-literature

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Strong cooperativity between subunits in voltage-gated proton channels.

Gonzalez Carlos C Koch Hans P HP Drum Ben M BM Larsson H Peter HP

Nature structural & molecular biology 20091220 1

Voltage-activated proton (Hv) channels are essential components in the innate immune response. Hv channels are dimeric proteins with one proton permeation pathway per subunit. It is unknown how Hv channels are activated by voltage and whether there is any cooperation between subunits during voltage activation. Using cysteine accessibility measurements and voltage-clamp fluorometry, we show data consistent with the possibility that the fourth transmembrane segment S4 functions as the voltage sens ...[more]

PMID: 20023639

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Project description:Expression of the voltage gated proton channel (Hv1) as identified by immunocytochemistry has been reported previously in breast cancer tissue. Increased expression of HV1 was correlated with poor prognosis and decreased overall and disease-free survival but the mechanism of its involvement in the disease is unknown. Here we present electrophysiological recordings of HV1 channel activity, confirming its presence and function in the plasma membrane of a breast cancer cell line, MDA-MB-231. With western blotting we identify significant levels of HV1 expression in 3 out of 8 "triple negative" breast cancer cell lines (estrogen, progesterone, and HER2 receptor expression negative). We examine the function of HV1 in breast cancer using MDA-MB-231 cells as a model by suppressing the expression of HV1 using shRNA (knock-down; KD) and by eliminating HV1 using CRISPR/Cas9 gene editing (knock-out; KO). Surprisingly, these two approaches produced incongruous effects. Knock-down of HV1 using shRNA resulted in slower cell migration in a scratch assay and a significant reduction in H2O2 release. In contrast, HV1 Knock-out cells did not show reduced migration or H2O2 release. HV1 KO but not KD cells showed an increased glycolytic rate accompanied by an increase in p-AKT (phospho-AKT, Ser473) activity. The expression of CD171/LCAM-1, an adhesion molecule and prognostic indicator for breast cancer, was reduced in HV1 KO cells. When we compared MDA-MB-231 xenograft growth rates in immunocompromised mice, tumors from HV1 KO cells grew less than WT in mass, with lower staining for the Ki-67 marker for cell proliferation rate. Therefore, deletion of HV1 expression in MDA-MB-231 cells limits tumor growth rate. The limited growth thus appears to be independent of oxidant production by NADPH oxidase molecules and to be mediated by cell adhesion molecules. Although HV1 KO and KD affect certain cellular mechanisms differently, both implicate HV1-mediated pathways for control of tumor growth in the MDA-MB-231 cell line.

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Strong cooperativity between subunits in voltage-gated proton channels.

Publications

Strong cooperativity between subunits in voltage-gated proton channels.

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