Jarecki Brian W, Sheets Patrick L, Xiao Yucheng, Jackson James O, Cummins Theodore R
Department of Pharmacology and Toxicology, Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN, USA.
Channels (Austin). 2009 Jul-Aug;3(4):259-67. doi: 10.4161/chan.3.4.9341. Epub 2009 Jul 23.
Alternative splicing is known to alter pharmacological sensitivities, kinetics, channel distribution under pathological conditions, and developmental regulation of VGSCs. Mutations that alter channel properties in Na(V)1.7 have been genetically implicated in patients with bouts of extreme pain classified as inherited erythromelalgia (IEM) or paroxysmal extreme pain disorder (PEPD). Furthermore, patients with IEM or PEPD report differential age onsets. A recent study reported that alternative splicing of Na(V)1.7 exon 5 affects ramp current properties. Since IEM and PEPD mutations also alter Na(V)1.7 ramp current properties we speculated that alternative splicing might impact the functional consequences of IEM or PEPD mutations. We compared the effects alternative splicing has on the biophysical properties of Na(V)1.7 wild-type, IEM (I136V) and PEPD (I1461T) channels. Our major findings demonstrate that although the 5A splice variant of the IEM channel had no functional impact, the 5A splice variant of the PEPD channel significantly hyperpolarized the activation curve, slowed deactivation and closed-state inactivation, shifted the ramp current activation to more hyperpolarized potentials, and increased ramp current amplitude. We hypothesize a D1/S3-S4 charged residue difference between the 5N (Asn) and the 5A (Asp) variants within the coding region of exon 5 may contribute to shifts in channel activation and deactivation. Taken together, the additive effects observed on ramp currents from exon 5 splicing and the PEPD mutation (I1461T) are likely to impact the disease phenotype and may offer insight into how alternative splicing may affect specific intramolecular interactions critical for voltage-dependent gating.
已知可变剪接可改变病理条件下的药理敏感性、动力学、通道分布以及电压门控钠通道（VGSCs）的发育调控。改变Na(V)1.7通道特性的突变在被归类为遗传性红斑性肢痛症（IEM）或阵发性极端疼痛障碍（PEPD）的极端疼痛发作患者中具有遗传学关联。此外，IEM或PEPD患者报告了不同的发病年龄。最近一项研究报告称，Na(V)1.7外显子5的可变剪接会影响斜坡电流特性。由于IEM和PEPD突变也会改变Na(V)1.7斜坡电流特性，我们推测可变剪接可能会影响IEM或PEPD突变的功能后果。我们比较了可变剪接对Na(V)1.7野生型、IEM（I136V）和PEPD（I1461T）通道生物物理特性的影响。我们的主要发现表明，虽然IEM通道的5A剪接变体没有功能影响，但PEPD通道的5A剪接变体显著使激活曲线超极化，减缓失活和关闭状态失活，将斜坡电流激活转移到更超极化的电位，并增加斜坡电流幅度。我们假设外显子5编码区域内5N（Asn）和5A（Asp）变体之间的D1/S3 - S4带电残基差异可能导致通道激活和失活的变化。综上所述，在外显子5剪接和PEPD突变（I1461T）的斜坡电流上观察到的累加效应可能会影响疾病表型，并可能为可变剪接如何影响对电压依赖性门控至关重要的特定分子内相互作用提供见解。
