Bianchi L, Wible B, Arcangeli A, Taglialatela M, Morra F, Castaldo P, Crociani O, Rosati B, Faravelli L, Olivotto M, Wanke E
Dipartimento di Fisiologia e Biochimica Generali, Università delgi Studi di Milano, Milan, Italy.
Cancer Res. 1998 Feb 15;58(4):815-22.
The human ether-a-go-go-related gene (herg) encodes a K+ current (IHERG) that plays a fundamental role in heart excitability by regulating the action potential repolarization (IKr); mutations of this gene are responsible for the chromosome 7-linked long QT syndrome (LQT2). In this report, we show that in a variety (n = 17) of tumor cell lines of different species (human and murine) and distinct histogenesis (neuroblastoma, rhabdomyosarcoma, adenocarcinoma, lung microcytoma, pituitary tumors, insulinoma beta-cells, and monoblastic leukemia), a novel K+ inward-rectifier current (IIR), which is biophysically and pharmacologically similar to IHERG, can be recorded with the patch-clamp technique. Northern blot experiments with a human herg cDNA probe revealed that both in human and murine clones the very high expression of herg transcripts can be quantified in at least three clearly identifiable bands, suggesting an alternative splicing of HERG mRNA. Moreover, we cloned a cDNA encoding for IIR from the SH-SY5Y human neuroblastoma. The sequence of this cDNA result was practically identical to that already reported for herg, indicating a high conservation of this gene in tumors. Consistently, the expression of this clone in Xenopus oocytes showed that the encoded K+ channel had substantially all of the biophysical and pharmacological properties of the native IIR described for tumor cells. In addition, in the tumor clones studied, IIR governs the resting potential, whereas it could not be detected either by the patch clamp or the Northern blot techniques in cells obtained from primary cell cultures of parental tissues (sensory neurons and myotubes), whose resting potential is controlled by the classical K+ anomalous rectifier current. This current substitution had a profound impact on the resting potential, which was markedly depolarized in tumors as compared with normal cells. These results suggest that IIR is normally only expressed during the early stages of cell differentiation frozen by neoplastic transformation, playing an important pathophysiological role in the regulatory mechanisms of neoplastic cell survival. In fact, because of its biophysical features, IIR, besides keeping the resting potential within the depolarized values required for unlimited tumor growth, could also appear suitable to afford a selective advantage in an ischemic environment.
人类醚 - 去极化相关基因（herg）编码一种钾离子电流（IHERG），该电流通过调节动作电位复极化（IKr）在心脏兴奋性中起重要作用；该基因的突变是导致7号染色体连锁的长QT综合征（LQT2）的原因。在本报告中，我们表明，在多种（n = 17）不同物种（人类和小鼠）且组织发生各异（神经母细胞瘤、横纹肌肉瘤、腺癌、肺微细胞瘤、垂体瘤、胰岛素瘤β细胞和单核细胞白血病）的肿瘤细胞系中，可通过膜片钳技术记录到一种新型钾离子内向整流电流（IIR），其在生物物理学和药理学上与IHERG相似。用人herg cDNA探针进行的Northern印迹实验表明，在人类和小鼠克隆中，herg转录本的高表达均可在至少三条清晰可辨的条带中定量，提示HERG mRNA存在可变剪接。此外，我们从人SH - SY5Y神经母细胞瘤中克隆了编码IIR的cDNA。该cDNA序列与已报道的herg序列几乎完全相同，表明该基因在肿瘤中具有高度保守性。一致地，该克隆在非洲爪蟾卵母细胞中的表达表明，所编码的钾离子通道基本上具有已描述的肿瘤细胞天然IIR的所有生物物理学和药理学特性。此外，在所研究的肿瘤克隆中，IIR调节静息电位，而在亲本组织（感觉神经元和肌管）的原代细胞培养获得的细胞中，无论是通过膜片钳技术还是Northern印迹技术均未检测到IIR，这些细胞的静息电位由经典的钾离子异常整流电流控制。这种电流替代对静息电位产生了深远影响，与正常细胞相比，肿瘤细胞的静息电位明显去极化。这些结果表明，IIR通常仅在肿瘤转化所冻结的细胞分化早期阶段表达，在肿瘤细胞存活的调节机制中发挥重要的病理生理作用。实际上，由于其生物物理学特性，IIR除了将静息电位维持在肿瘤无限生长所需的去极化值范围内外，在缺血环境中似乎也适合提供选择性优势。
