Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, USA.
Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida, USA
Infect Immun. 2021 Jan 19;89(2). doi: 10.1128/IAI.00447-20.
Cholera toxin (CT) is an AB protein toxin that activates the stimulatory alpha subunit of the heterotrimeric G protein (Gsα) through ADP-ribosylation. Activation of Gsα produces a cytopathic effect by stimulating adenylate cyclase and the production of cAMP. To reach its cytosolic Gsα target, CT binds to the plasma membrane of a host cell and travels by vesicle carriers to the endoplasmic reticulum (ER). The catalytic CTA1 subunit then exploits the quality control mechanism of ER-associated degradation to move from the ER to the cytosol. ER-associated degradation is functionally linked to another quality control system, the unfolded protein response (UPR). However, the role of the UPR in cholera intoxication is unclear. We report here that CT triggers the UPR after 4 h of toxin exposure. A functional toxin was required to induce the UPR, but, surprisingly, activation of the adenylate cyclase signaling pathway was not sufficient to trigger the process. Toxin-induced activation of the UPR coincided with increased toxin accumulation in the cytosol. Chemical activation of the heterotrimeric G protein or the UPR also enhanced the onset of CTA1 delivery to the cytosol, thus producing a toxin-sensitive phenotype. These results indicate there is a cAMP-independent response to CT that activates the UPR and thereby enhances the efficiency of intoxication.
霍乱毒素（CT）是一种 AB 蛋白毒素，通过 ADP-核糖基化作用激活异三聚体 G 蛋白的刺激性α亚基（Gsα）。Gsα 的激活通过刺激腺苷酸环化酶和 cAMP 的产生产生细胞病变效应。为了到达其胞质 Gsα 靶标，CT 与宿主细胞的质膜结合，并通过囊泡载体运输到内质网（ER）。然后，催化的 CTA1 亚基利用 ER 相关降解的质量控制机制从 ER 移动到细胞质。ER 相关降解与另一个质量控制系统 unfolded protein response（UPR）在功能上相关联。然而，UPR 在霍乱中毒中的作用尚不清楚。我们在这里报告，CT 在毒素暴露 4 小时后触发 UPR。功能性毒素是诱导 UPR 的必要条件，但令人惊讶的是，激活腺苷酸环化酶信号通路不足以触发该过程。毒素诱导的 UPR 激活伴随着细胞溶质中毒素积累的增加。异三聚体 G 蛋白或 UPR 的化学激活也增强了 CTA1 向细胞质的传递起始，从而产生对毒素敏感的表型。这些结果表明，存在一种对 CT 的 cAMP 非依赖性反应，该反应激活 UPR，从而提高中毒效率。
