Dataset Information

Alpha-actinin2 cytoskeletal protein is required for the functional membrane localization of a Ca2+-activated K+ channel (SK2 channel).

ABSTRACT: The importance of proper ion channel trafficking is underpinned by a number of channel-linked genetic diseases whose defect is associated with failure to reach the cell surface. Conceptually, it is reasonable to suggest that the function of ion channels depends critically on the precise subcellular localization and the number of channel proteins on the cell surface membrane, which is determined jointly by the secretory and endocytic pathways. Yet the precise mechanisms of the entire ion channel trafficking pathway remain unknown. Here, we directly demonstrate that proper membrane localization of a small-conductance Ca(2+)-activated K(+) channel (SK2 or K(Ca)2.2) is dependent on its interacting protein, alpha-actinin2, a major F-actin crosslinking protein. SK2 channel localization on the cell-surface membrane is dynamically regulated, and one of the critical steps includes the process of cytoskeletal anchoring of SK2 channel by its interacting protein, alpha-actinin2, as well as endocytic recycling via early endosome back to the cell membrane. Consequently, alteration of these components of SK2 channel recycling results in profound changes in channel surface expression. The importance of our findings may transcend the area of K(+) channels, given that similar cytoskeletal interaction and anchoring may be critical for the membrane localization of other ion channels in neurons and other excitable cells.

SUBMITTER: Lu L

PROVIDER: S-EPMC2775294 | biostudies-literature | 2009 Oct

REPOSITORIES: biostudies-literature

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Alpha-actinin2 cytoskeletal protein is required for the functional membrane localization of a Ca2+-activated K+ channel (SK2 channel).

Lu Ling L Timofeyev Valeriy V Li Ning N Rafizadeh Sassan S Singapuri Anil A Harris Todd R TR Chiamvimonvat Nipavan N

Proceedings of the National Academy of Sciences of the United States of America 20091008 43

The importance of proper ion channel trafficking is underpinned by a number of channel-linked genetic diseases whose defect is associated with failure to reach the cell surface. Conceptually, it is reasonable to suggest that the function of ion channels depends critically on the precise subcellular localization and the number of channel proteins on the cell surface membrane, which is determined jointly by the secretory and endocytic pathways. Yet the precise mechanisms of the entire ion channel ...[more]

PMID: 19815520

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Project description:Junctophilins (JPs), a protein family of the junctional membrane complex, maintain the close conjunction between cell surface and intracellular membranes in striate muscle cells mediating the crosstalk between extracellular Ca2+ entry and intracellular Ca2+ release. The small-conductance Ca2+ -activated K+ channels are activated by the intracellular calcium and play an essential role in the cardiac action potential profile. Molecular mechanisms of regulation of the SK channels are still uncertain. Here, we sought to determine whether there is a functional interaction of junctophilin type 2 (JP2) with the SK channels and whether JP2 gene silencing might modulate the function of SK channels in cardiac myocytes. Association of JP2 with SK2 channel in mouse heart tissue as well as HEK293 cells was studied using in vivo and in vitro approaches. siRNA knockdown of JP2 gene was assessed by real-time PCR. The expression of proteins was analysed by Western blotting. Ca2+ -activated K+ current (IK,Ca ) in infected adult mouse cardiac myocytes was recorded using whole-cell voltage-clamp technique. The intracellular Ca2+ transient was measured using an IonOptix photometry system. We showed for the first time that JP2 associates with the SK2 channel in native cardiac tissue. JP2, via the membrane occupation and recognition nexus (MORN motifs) in its N-terminus, directly interacted with SK2 channels. A colocalization of the SK2 channel with its interaction protein of JP2 was found in the cardiac myocytes. Moreover, we demonstrated that JP2 is necessary for the proper cell surface expression of the SK2 channel in HEK293. Functional experiments indicated that knockdown of JP2 caused a significant decrease in the density of IK,Ca and reduced the amplitude of the Ca2+ transient in infected cardiomyocytes. The present data provide evidence that the functional interaction between JP2 and SK2 channels is present in the native mouse heart tissue. Junctophilin 2, as junctional membrane complex (JMC) protein, is an important regulator of the cardiac SK channels.

Dataset Information

Alpha-actinin2 cytoskeletal protein is required for the functional membrane localization of a Ca2+-activated K+ channel (SK2 channel).

Publications

Alpha-actinin2 cytoskeletal protein is required for the functional membrane localization of a Ca2+-activated K+ channel (SK2 channel).

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