Defective trafficking of cone photoreceptor CNG channels induces the unfolded protein response and ER-stress-associated cell death.
Defective trafficking of cone photoreceptor CNG channels induces the unfolded protein response and ER-stress-associated cell death.
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DOI：
10.1042/bj20111004
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发表时间：
2012-01-15
期刊：
影响因子：
--
通讯作者：
Varnum MD
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文献类型：
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作者：
Duricka DL;Brown RL;Varnum MD
干扰光感受器环核苷酸门控(CNG)通道功能的突变与几种人类视网膜疾病有关，但导致光感受器功能障碍和退化的分子和细胞机制尚不清楚。许多功能缺失突变导致CNG通道亚基在细胞内积聚。已知内质网(ER)中蛋白质的积累会导致内质网应激并触发未折叠蛋白反应(UPR)，UPR是一种进化保守的细胞程序，通过增加蛋白质处理能力或导致细胞凋亡而导致适应。我们假设，锥体光感受器CNG通道的缺陷运输可以诱导UPR介导的细胞死亡。为了验证这一想法，携带R563H和Q655X突变的CNGA3亚基在带有CNGB3亚基的光感受器来源的661W细胞中表达。与野生型相比，R563H和Q655X亚基的降解速率发生改变和/或保留在内质网中。内质网滞留与内质网应激的UPR相关标记物的表达增加和细胞存活率下降有关。化学和药理伴侣(TUDCA、4PBA和cGMP类似物CPT-cGMP)不同程度地减少缺陷亚基的降解和/或促进缺陷亚基的质膜定位。亚基成熟度的提高与ER应激标志物表达的减少和表达定位缺陷通道的细胞活力的提高是一致的。这些结果表明，内质网应激可由定位缺陷的CNG通道的表达引起，并可能是光感受器退化的一个促成因素。
Mutations that perturb the function of photoreceptor cyclic nucleotide-gated (CNG) channels are associated with several human retinal disorders, but the molecular and cellular mechanisms leading to photoreceptor dysfunction and degeneration remain unclear. Many loss-of-function mutations result in intracellular accumulation of CNG channel subunits. Accumulation of proteins in the endoplasmic reticulum (ER) is known to cause ER stress and trigger the unfolded protein response (UPR), an evolutionarily conserved cellular program that results in either adaptation via increased protein processing capacity or apoptotic cell death. We hypothesize that defective trafficking of cone photoreceptor CNG channels can induce UPR-mediated cell death. To test this idea, CNGA3 subunits bearing the R563H and Q655X mutations were expressed in photoreceptor-derived 661W cells with CNGB3 subunits. Compared to wild type, R563H and Q655X subunits displayed altered degradation rates and/or were retained in the ER. ER retention was associated with increased expression of UPR-related markers of ER stress and with decreased cell viability. Chemical and pharmacological chaperones (TUDCA, 4PBA, and the cGMP analog CPT-cGMP) differentially reduced degradation and/or promoted plasma-membrane localization of defective subunits. Improved subunit maturation was concordant with reduced expression of ER stress markers and improved viability of cells expressing localization-defective channels. These results indicate that ER stress can arise from expression of localization defective CNG channels, and may represent a contributing factor for photoreceptor degeneration.