Voltage opens unopposed gap junction hemichannels formed by a connexin 32 mutant associated with X-linked Charcot-Marie-Tooth disease
Voltage opens unopposed gap junction hemichannels formed by a connexin 32 mutant associated with X-linked Charcot-Marie-Tooth disease
复制标题
DOI：
10.1073/pnas.261713499
复制
发表时间：
2002-03-19
影响因子：
11.1
通讯作者：
Bargiello, TA
中科院分区：
文献类型：
--
作者：
Abrams, CK;Bennett, MVL;Bargiello, TA
X连锁型腓骨肌萎缩症（CMTX）是一种遗传性周围神经病变，其发生于编码差距连接蛋白连接蛋白32（Cx 32）的基因突变的患者中，所述间隙连接蛋白连接蛋白32由雪旺细胞表达。我们最近发现，Cx 32含有CMTX相关的突变，Ser-85-Cys（S85 C），在配对的非洲爪蟾卵母细胞中形成功能性细胞-细胞通道。在这里，我们描述了这种突变的连接蛋白也显示了增加开放的半通道在非连接表面膜。开放的半通道可能通过离子梯度和小代谢物的损失以及Ca 2+内流的增加来损伤细胞，并且提供了一种机制，通过该机制和Cx 32的其他突变形式可能损伤表达它们的细胞。开放半通道的证据包括：（i）表达Cx 32（S35 C）突变体的卵母细胞在内部正电位下显示出显著增加的电导，显著大于表达野生型Cx 32（Cx 32 WT）的卵母细胞;和（ii）诱导的电流类似于先前对几种其它连接蛋白半通道描述的电流，当细胞内pH降低或细胞外Ca ~（2+）浓度增加时，随着阳性水平的增加和可逆性还原，显示缓慢发展的增加。尽管观察到电流增加，但表达Cx 32（S35 C）的卵母细胞在表面和总匀浆中的蛋白质水平低于表达Cx 32 WT的卵母细胞;因此，在本文研究的条件下，由Cx 32（S85 C）突变体形成的表面膜中的半通道比由Cx 32 WT形成的半通道具有更高的开放概率。这种功能性半通道的增加可能会损害雪旺细胞，并最终导致携带这种突变的患者的外周神经功能丧失。
The X-linked form of Charcot-Marie-Tooth disease (CMTX) is an inherited peripheral neuropathy that arises in patients with mutations in the gene encoding the gap junction protein connexin 32 (Cx32), which is expressed by Schwann cells. We recently showed that Cx32 containing the CMTX-associated mutation, Ser-85-Cys (S85C), forms functional cell-cell channels in paired Xenopus oocytes. Here, we describe that this mutant connexin also shows increased opening of hemichannels in nonjunctional surface membrane. Open hemichannels may damage the cells through loss of ionic gradients and small metabolites and increased influx of Ca2+, and provide a mechanism by which this and other mutant forms of Cx32 may damage cells in which they are expressed. Evidence for open hemichannels includes: (i) oocytes expressing the Cx32(S35C) mutant show greatly increased conductance at inside positive potentials, significantly larger than in oocytes expressing wild-type Cx32 (Cx32WT); and (ii) the induced currents are similar to those previously described for several other connexin hemichannels, and exhibit slowly developing increases with increasing levels of positivity and reversible reduction when intracellular pH is decreased or extracellular Ca2+ concentration is increased. Although increased currents are seen, oocytes expressing Cx32(S35C) have lower levels of the protein in the surface and in total homogenates than do oocytes expressing Cx32WT; thus, under the conditions examined here, hemichannels in the surface membrane formed of the Cx32(S85C) mutant have a higher open probability than hemichannels formed of Cx32WT. This increase in functional hemichannels may damage Schwann cells and ultimately lead to loss of function in peripheral nerves of patients harboring this mutation.