Academy of Integrative Medicine, Shanghai University of Traditional Chinese Medicine, Shanghai, China; Laboratory of Gene Regulation and Signal Transduction, Department of Pharmacology, School of Medicine, University of California San Diego, San Diego, CA, USA.
Laboratory of Gene Regulation and Signal Transduction, Department of Pharmacology, School of Medicine, University of California San Diego, San Diego, CA, USA.
J Hepatol. 2023 Aug;79(2):362-377. doi: 10.1016/j.jhep.2023.03.016. Epub 2023 Mar 28.
BACKGROUND & AIMS: Hepatocellular carcinoma (HCC), a leading cause of cancer-related death, is associated with viral hepatitis, non-alcoholic steatohepatitis (NASH), and alcohol-related steatohepatitis, all of which trigger endoplasmic reticulum (ER) stress, hepatocyte death, inflammation, and compensatory proliferation. Using ER stress-prone MUP-uPA mice, we established that ER stress and hypernutrition cooperate to cause NASH and HCC, but the contribution of individual stress effectors, such as activating transcription factor 4 (ATF4), to HCC and their underlying mechanisms of action remained unknown.
Hepatocyte-specific ATF4-deficient MUP-uPA mice (MUP-uPA/Atf4) and control MUP-uPA/Atf4 mice were fed a high-fat diet to induce NASH-related HCC, and Atf4 and Atf4 mice were injected with diethylnitrosamine to model carcinogen-induced HCC. Histological, biochemical, and RNA-sequencing analyses were performed to identify and define the role of ATF4-induced solute carrier family 7a member 11 (SLC7A11) expression in hepatocarcinogenesis. Reconstitution of SLC7A11 in ATF4-deficient primary hepatocytes and mouse livers was used to study its effects on ferroptosis and HCC development.
Hepatocyte ATF4 ablation inhibited hepatic steatosis, but increased susceptibility to ferroptosis, resulting in accelerated HCC development. Although ATF4 activates numerous genes, ferroptosis susceptibility and hepatocarcinogenesis were reversed by ectopic expression of a single ATF4 target, Slc7a11, coding for a subunit of the cystine/glutamate antiporter xCT, which is needed for glutathione synthesis. A ferroptosis inhibitor also reduced liver damage and inflammation. ATF4 and SLC7A11 amounts were positively correlated in human HCC and livers of patients with NASH.
Despite ATF4 being upregulated in established HCC, it serves an important protective function in normal hepatocytes. By maintaining glutathione production, ATF4 inhibits ferroptosis-dependent inflammatory cell death, which is known to promote compensatory proliferation and hepatocarcinogenesis. Ferroptosis inhibitors or ATF4 activators may also blunt HCC onset.
Liver cancer or hepatocellular carcinoma (HCC) is associated with multiple aetiologies. Most HCC aetiologies cause hepatocyte stress and death, as well as subsequent inflammation, and compensatory proliferation, thereby accelerating HCCdevelopment. The contribution of individual stress effectors to HCC and their underlying mechanisms of action were heretofore unknown. This study shows that the stress-responsive transcription factor ATF4 blunts liver damage and cancer development by suppressing iron-dependent cell death (ferroptosis). Although ATF4 ablation prevents hepatic steatosis, it also increases susceptibility to ferroptosis, due to decreased expression of the cystine/glutamate antiporter SLC7A11, whose expression in human HCC and NASH correlates with ATF4. These findings reinforce the notion that benign steatosis may be protective and does not increase cancer risk unless accompanied by stress-induced liver damage. These results have important implications for prevention of liver damage and cancer.
肝细胞癌（HCC）是癌症相关死亡的主要原因之一，与病毒性肝炎、非酒精性脂肪性肝炎（NASH）和酒精性脂肪性肝炎有关，所有这些都会引发内质网（ER）应激、肝细胞死亡、炎症和代偿性增殖。我们使用易发生 ER 应激的 MUP-uPA 小鼠建立了模型，证实 ER 应激和营养过剩共同导致 NASH 和 HCC，但 ER 应激的单个效应因子（如激活转录因子 4（ATF4））对 HCC 的贡献及其潜在作用机制仍不清楚。
我们构建了肝细胞特异性 ATF4 缺失的 MUP-uPA 小鼠（MUP-uPA/Atf4）和对照 MUP-uPA/Atf4 小鼠，用高脂肪饮食诱导 NASH 相关 HCC，并用二乙基亚硝胺（DEN）注射构建致癌剂诱导的 HCC 模型。我们进行了组织学、生化和 RNA 测序分析，以鉴定和定义 ATF4 诱导溶质载体家族 7 成员 11（SLC7A11）表达在肝癌发生中的作用。我们还在 ATF4 缺陷型原代肝细胞和小鼠肝脏中重建 SLC7A11，以研究其对铁死亡和 HCC 发展的影响。
肝细胞 ATF4 缺失抑制肝脂肪变性，但增加铁死亡易感性，从而加速 HCC 发展。尽管 ATF4 激活了许多基因，但通过异位表达单个 ATF4 靶标 Slc7a11（编码胱氨酸/谷氨酸反向转运体 xCT 的亚基）可以逆转铁死亡易感性和 HCC 发生，xCT 是合成谷胱甘肽所必需的。铁死亡抑制剂也减少了肝损伤和炎症。在人类 HCC 和 NASH 患者的肝脏中，ATF4 和 SLC7A11 的含量呈正相关。
尽管 ATF4 在已建立的 HCC 中上调，但它在正常肝细胞中发挥着重要的保护作用。通过维持谷胱甘肽的产生，ATF4 抑制铁依赖性细胞死亡（铁死亡），已知铁死亡会促进代偿性增殖和 HCC 发生。铁死亡抑制剂或 ATF4 激活剂也可能抑制 HCC 的发生。
肝癌或肝细胞癌（HCC）与多种病因有关。大多数 HCC 的病因会导致肝细胞应激和死亡，以及随后的炎症和代偿性增殖，从而加速 HCC 的发展。单个应激效应因子对 HCC 的贡献及其潜在作用机制此前尚不清楚。本研究表明，应激反应转录因子 ATF4 通过抑制铁依赖性细胞死亡（铁死亡）来减轻肝损伤和癌症的发展。尽管 ATF4 缺失可预防肝脂肪变性，但由于胱氨酸/谷氨酸反向转运体 SLC7A11 的表达减少，也会增加铁死亡的易感性，而 SLC7A11 的表达与人类 HCC 和 NASH 中的 ATF4 相关。这些发现进一步证实了良性脂肪变性可能具有保护作用，除非伴有应激引起的肝损伤，否则不会增加癌症风险。这些结果对预防肝损伤和癌症具有重要意义。
