Berberine Induces hERG Channel Deficiency through Trafficking Inhibition
Aims: The human ether-a-go-go-related gene (hERG) encodes the α subunit of the IKr, which plays an essential role in repolarization of action potentials. hERG channels are targeted by various pro-arrhythmic drugs. Berberine (BBR) was previously found to acutely inhibit hERG currents and prolong acti...
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| Format: | Article |
| Language: | English |
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Cell Physiol Biochem Press GmbH & Co KG
2014-08-01
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| Series: | Cellular Physiology and Biochemistry |
| Subjects: | |
| Online Access: | http://www.karger.com/Article/FullText/363034 |
| _version_ | 1818508705469038592 |
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| author | Kaiping Zhang Duo Zhi Ting Huang Yan Gong Meng Yan Chen Liu Ting Wei Zengxiang Dong Baoxin Li Baofeng Yang |
| author_facet | Kaiping Zhang Duo Zhi Ting Huang Yan Gong Meng Yan Chen Liu Ting Wei Zengxiang Dong Baoxin Li Baofeng Yang |
| author_sort | Kaiping Zhang |
| collection | DOAJ |
| description | Aims: The human ether-a-go-go-related gene (hERG) encodes the α subunit of the IKr, which plays an essential role in repolarization of action potentials. hERG channels are targeted by various pro-arrhythmic drugs. Berberine (BBR) was previously found to acutely inhibit hERG currents and prolong action potential duration. The present study aimed to determine long-term effects of BBR on the expression of 135kDa/155kDa hERG and the mechanism. Methods and Results: hERG expression was assessed by western blot. Mature hERG (155 kDa) was reduced, whereas ER-located hERG (135 kDa) was increased by BBR. This indicated that hERG was restricted to the ER and that BBR disrupted channel trafficking. To determine the mechanism of trafficking inhibition, we performed western blot and immunoprecipitation to test folding of hERG by assessing interaction between hERG and Hsp90/Hsp70. Both the expression of Hsp90 and its interaction with hERG were strongly decreased by BBR. These data suggest that BBR reduces channel folding to induce trafficking inhibition. Western blot and confocal imaging were used to further detect whether the unfolded protein response (UPR) was activated. Active ATF6, a marker of the UPR, was activated by BBR. Calnexin and calreticulin, chaperones that are activated by ATF6 to assist channel folding, were also elevated and increasingly colocalized with hERG. These data also demonstrate that the UPR was activated. Immunoprecipitation and western blot assays were performed after BBR treatment to examine ubiquitination and degradation, common endpoints of the UPR. We found that the ER-restricted hERG was ubiquitinized and degraded in the lysosomes and proteasomes. Conclusion: Our study demonstrates that BBR induces hERG channel deficiency by inhibiting channel trafficking after incubation for 24h. Trafficking inhibition activated the UPR, and the ER-restricted hERG was ubiquitinized and degraded in lysosomes and proteasomes. |
| first_indexed | 2024-12-10T22:35:40Z |
| format | Article |
| id | doaj.art-dbff2aa9e80b4c49beb7de2767d3f6df |
| institution | Directory Open Access Journal |
| issn | 1015-8987 1421-9778 |
| language | English |
| last_indexed | 2024-12-10T22:35:40Z |
| publishDate | 2014-08-01 |
| publisher | Cell Physiol Biochem Press GmbH & Co KG |
| record_format | Article |
| series | Cellular Physiology and Biochemistry |
| spelling | doaj.art-dbff2aa9e80b4c49beb7de2767d3f6df2022-12-22T01:30:55ZengCell Physiol Biochem Press GmbH & Co KGCellular Physiology and Biochemistry1015-89871421-97782014-08-0134369170210.1159/000363034363034Berberine Induces hERG Channel Deficiency through Trafficking InhibitionKaiping ZhangDuo ZhiTing HuangYan GongMeng YanChen LiuTing WeiZengxiang DongBaoxin LiBaofeng YangAims: The human ether-a-go-go-related gene (hERG) encodes the α subunit of the IKr, which plays an essential role in repolarization of action potentials. hERG channels are targeted by various pro-arrhythmic drugs. Berberine (BBR) was previously found to acutely inhibit hERG currents and prolong action potential duration. The present study aimed to determine long-term effects of BBR on the expression of 135kDa/155kDa hERG and the mechanism. Methods and Results: hERG expression was assessed by western blot. Mature hERG (155 kDa) was reduced, whereas ER-located hERG (135 kDa) was increased by BBR. This indicated that hERG was restricted to the ER and that BBR disrupted channel trafficking. To determine the mechanism of trafficking inhibition, we performed western blot and immunoprecipitation to test folding of hERG by assessing interaction between hERG and Hsp90/Hsp70. Both the expression of Hsp90 and its interaction with hERG were strongly decreased by BBR. These data suggest that BBR reduces channel folding to induce trafficking inhibition. Western blot and confocal imaging were used to further detect whether the unfolded protein response (UPR) was activated. Active ATF6, a marker of the UPR, was activated by BBR. Calnexin and calreticulin, chaperones that are activated by ATF6 to assist channel folding, were also elevated and increasingly colocalized with hERG. These data also demonstrate that the UPR was activated. Immunoprecipitation and western blot assays were performed after BBR treatment to examine ubiquitination and degradation, common endpoints of the UPR. We found that the ER-restricted hERG was ubiquitinized and degraded in the lysosomes and proteasomes. Conclusion: Our study demonstrates that BBR induces hERG channel deficiency by inhibiting channel trafficking after incubation for 24h. Trafficking inhibition activated the UPR, and the ER-restricted hERG was ubiquitinized and degraded in lysosomes and proteasomes.http://www.karger.com/Article/FullText/363034BerberinehERGArrhythmiaLong QT SyndromeEndoplasmic reticulum stress responseUnfolded protein response |
| spellingShingle | Kaiping Zhang Duo Zhi Ting Huang Yan Gong Meng Yan Chen Liu Ting Wei Zengxiang Dong Baoxin Li Baofeng Yang Berberine Induces hERG Channel Deficiency through Trafficking Inhibition Cellular Physiology and Biochemistry Berberine hERG Arrhythmia Long QT Syndrome Endoplasmic reticulum stress response Unfolded protein response |
| title | Berberine Induces hERG Channel Deficiency through Trafficking Inhibition |
| title_full | Berberine Induces hERG Channel Deficiency through Trafficking Inhibition |
| title_fullStr | Berberine Induces hERG Channel Deficiency through Trafficking Inhibition |
| title_full_unstemmed | Berberine Induces hERG Channel Deficiency through Trafficking Inhibition |
| title_short | Berberine Induces hERG Channel Deficiency through Trafficking Inhibition |
| title_sort | berberine induces herg channel deficiency through trafficking inhibition |
| topic | Berberine hERG Arrhythmia Long QT Syndrome Endoplasmic reticulum stress response Unfolded protein response |
| url | http://www.karger.com/Article/FullText/363034 |
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