Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada (J.L., J.M., S.M.L., H.T.K.) and Department of Neurodevelopmental Medicine, Cortica Healthcare, San Rafael, California (E.J.M.).
Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada (J.L., J.M., S.M.L., H.T.K.) and Department of Neurodevelopmental Medicine, Cortica Healthcare, San Rafael, California (E.J.M.)
Mol Pharmacol. 2020 Sep;98(3):192-202. doi: 10.1124/mol.120.119644. Epub 2020 Jun 24.
Neuronal voltage-gated potassium channels (Kv) are critical regulators of electrical activity in the central nervous system. Mutations in the KCNQ (Kv7) ion channel family are linked to epilepsy and neurodevelopmental disorders. These channels underlie the neuronal "M-current" and cluster in the axon initial segment to regulate the firing of action potentials. There is general consensus that KCNQ channel assembly and heteromerization are controlled by C-terminal helices. We identified a pediatric patient with neurodevelopmental disability, including autism traits, inattention and hyperactivity, and ataxia, who carries a de novo frameshift mutation in KCNQ3 (KCNQ3-FS534), leading to truncation of ∼300 amino acids in the C terminus. We investigated possible molecular mechanisms of channel dysfunction, including haplo-insufficiency or a dominant-negative effect caused by the assembly of truncated KCNQ3 and functional KCNQ2 subunits. We also used a recently recognized property of the KCNQ2-specific activator ICA-069673 to identify assembly of heteromeric channels. ICA-069673 exhibits a functional signature that depends on the subunit composition of KCNQ2/3 channels, allowing us to determine whether truncated KCNQ3 subunits can assemble with KCNQ2. Our findings demonstrate that although the KCNQ3-FS534 mutant does not generate functional channels on its own, large C-terminal truncations of KCNQ3 (including the KCNQ3-FS534 mutation) assemble efficiently with KCNQ2 but fail to promote or stabilize KCNQ2/KCNQ3 heteromeric channel expression. Therefore, the frequent assumption that pathologies linked to KCNQ3 truncations arise from haplo-insufficiency should be reconsidered in some cases. Subtype-specific channel activators like ICA-069673 are a reliable tool to identify heteromeric assembly of KCNQ2 and KCNQ3. SIGNIFICANCE STATEMENT: Mutations that truncate the C terminus of neuronal Kv7/KCNQ channels are linked to a spectrum of seizure disorders. One role of the multifunctional KCNQ C terminus is to mediate subtype-specific assembly of heteromeric KCNQ channels. This study describes the use of a subtype-specific Kv7 activator to assess assembly of heteromeric KCNQ2/KCNQ3 (Kv7.2/Kv7.3) channels and demonstrates that large disease-linked and experimentally generated C-terminal truncated KCNQ3 mutants retain the ability to assemble with KCNQ2.
神经元电压门控钾通道（Kv）是中枢神经系统电活动的关键调节因子。KCNQ（Kv7）离子通道家族的突变与癫痫和神经发育障碍有关。这些通道构成了神经元“M 电流”，并聚集在轴突起始段，以调节动作电位的发射。人们普遍认为，KCNQ 通道的组装和异源二聚体形成受 C 端螺旋控制。我们鉴定了一名患有神经发育障碍的儿科患者，包括自闭症特征、注意力不集中和多动以及共济失调，该患者携带 KCNQ3（KCNQ3-FS534）的从头移码突变，导致 C 端截断约 300 个氨基酸。我们研究了通道功能障碍的可能分子机制，包括杂合功能不全或由截断的 KCNQ3 和功能性 KCNQ2 亚基组装引起的显性负效应。我们还使用最近发现的 KCNQ2 特异性激活剂 ICA-069673 的特性来鉴定异源二聚体通道的组装。ICA-069673 表现出一种依赖于 KCNQ2/3 通道亚基组成的功能特征，使我们能够确定截断的 KCNQ3 亚基是否可以与 KCNQ2 组装。我们的研究结果表明，尽管 KCNQ3-FS534 突变本身不能产生功能性通道，但 KCNQ3 的大 C 端截断（包括 KCNQ3-FS534 突变）与 KCNQ2 有效组装，但不能促进或稳定 KCNQ2/KCNQ3 异源二聚体通道的表达。因此，在某些情况下，应重新考虑与 KCNQ3 截断相关的病理学源于杂合功能不全的常见假设。像 ICA-069673 这样的亚型特异性通道激活剂是识别 KCNQ2 和 KCNQ3 异源二聚体组装的可靠工具。
截断神经元 Kv7/KCNQ 通道 C 端的突变与一系列癫痫发作障碍有关。多功能 KCNQ C 端的一个作用是介导异源二聚体 KCNQ 通道的亚型特异性组装。本研究描述了使用亚型特异性 Kv7 激活剂来评估异源二聚体 KCNQ2/KCNQ3（Kv7.2/Kv7.3）通道的组装，并表明与疾病相关的大的和实验产生的 C 端截断 KCNQ3 突变保留了与 KCNQ2 组装的能力。
