The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor whose physiological function is poorly understood. The AhR is highly expressed in barrier organs such as the skin, intestine and lung. The lungs are continuously exposed to environmental pollutants such as cigarette smoke (CS) that can induce cell death mechanisms such as apoptosis, autophagy and endoplasmic reticulum (ER) stress. CS also contains toxicants that are AhR ligands. We have previously shown that the AhR protects against apoptosis, but whether the AhR also protects against autophagy or ER stress is not known. Using cigarette smoke extract (CSE) as our in vitro surrogate of environmental tobacco exposure, we first assessed the conversion of LC3I to LC3II, a classic feature of both autophagic and ER stress-mediated cell death pathways. LC3II was elevated in CSE-exposed lung structural cells (mouse lung fibroblasts [MLFs], MLE12 and A549 cells) when AhR was absent. However, this heightened LC3II expression could not be explained by increased expression of key autophagy genes (Gabarapl1, Becn1, Map1lc3b), upregulation of upstream autophagic machinery (Atg5-12, Atg3) or by impaired autophagic flux, suggesting that LC3II may be autophagy-independent. This was further supported by the absence of autophagosomes in Ahr^-/- lung cells. However, Ahr^-/- lung cells had widespread ER-dilation, elevated expression of the ER stress markers CHOP and GADD34 and an accumulation of ubiquitinated proteins. These findings collectively illustrate a novel role for the AhR in attenuating ER stress by a mechanism that may be autophagy-independent.

中文翻译：

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芳烃受体降低LC3II表达并控制内质网应激

芳基烃受体（AhR）是一种配体激活的转录因子，其生理功能尚不清楚。AhR在皮肤，肠和肺等屏障器官中高度表达。肺部持续暴露于环境污染物中，例如香烟烟雾（CS），可诱导细胞死亡机制，例如凋亡，自噬和内质网（ER）应激。CS还包含作为AhR配体的有毒物质。先前我们已经表明，AhR可以防止凋亡，但是尚不清楚AhR是否也可以防止自噬或内质网应激。使用香烟烟雾提取物（CSE）作为环境烟草暴露的体外替代方法，我们首先评估了LC3I向LC3II的转化，这是自噬和内质网应激介导的细胞死亡途径的经典特征。缺少AhR时，CSE暴露的肺结构细胞（小鼠肺成纤维细胞[MLF]，MLE12和A549细胞）中的LC3II升高。然而，不能通过关键自噬基因（Gabarapl1，Becn1，Map1lc3b）的表达增加，上游自噬机制（Atg5-12，Atg3）的上调或自噬通量受损来解释这种升高的LC3II表达，这表明LC3II可能是自噬的。独立。Ahr中不存在自噬体进一步支持了这一点 提示LC3II可能是自噬独立的。Ahr中不存在自噬体进一步支持了这一点 提示LC3II可能是自噬独立的。Ahr中不存在自噬体进一步支持了这一点^-/-肺细胞。然而，Ahr ^-/-肺细胞具有广泛的ER扩张，ER应激标记CHOP和GADD34的表达升高以及泛素化蛋白的积累。这些发现共同说明了AhR通过一种可能与自噬无关的机制减轻ER应激的新作用。