Department of Microbiology and Immunology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
Tropical Medicine College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
Kaohsiung J Med Sci. 2024 Jul;40(7):631-641. doi: 10.1002/kjm2.12853. Epub 2024 Jun 3.
Autophagy is a self-recycling machinery to maintain cellular homeostasis by degrading harmful materials in the cell. Autophagy-related gene 5 (Atg5) is required for autophagosome maturation. However, the role of Atg5 in tumorigenesis under autophagy deficient conditions remains unclear. This study focused on the autophagy-independent role of Atg5 and the underlying mechanism in tumorigenesis. We demonstrated that knockout of autophagy-related genes including Atg5, Atg7, Atg9, and p62 in mouse embryonic fibroblast (MEF) cells consistently decreased cell proliferation and motility, implying that autophagy is required to maintain diverse cellular functions. An Atg7 knockout MEF (Atg7 MEF) cell line representing deprivation of autophagy function was used to clarify the role of Atg5 transgene in tumorigenesis. We found that Atg5-overexpressed Atg7MEF (clone A) showed increased cell proliferation, colony formation, and migration under autophagy deficient conditions. Accordingly, rescuing the autophagy deficiency of clone A by overexpression of Atg7 gene shifts the role of Atg5 from pro-tumor to anti-tumor status, indicating the dual role of Atg5 in tumorigenesis. Notably, the xenograft mouse model showed that clone A of Atg5-overexpressed Atg7 MEF cells induced temporal tumor formation, but could not prolong further tumor growth. Finally, biomechanical analysis disclosed increased Wnt5a secretion and p-JNK expression along with decreased β-catenin expression. In summary, Atg5 functions as a tumor suppressor to protect the cell under normal conditions. In contrast, Atg5 shifts to a pro-tumor status under autophagy deprivation conditions.
自噬是一种自我循环的机制，通过降解细胞内的有害物质来维持细胞内的平衡。自噬相关基因 5（Atg5）是自噬体成熟所必需的。然而，在自噬缺乏的情况下，Atg5 在肿瘤发生中的作用尚不清楚。本研究集中研究了 Atg5 在自噬独立条件下的作用及其在肿瘤发生中的潜在机制。我们证明，包括 Atg5、Atg7、Atg9 和 p62 在内的自噬相关基因在小鼠胚胎成纤维细胞（MEF）中的敲除一致降低了细胞增殖和迁移能力，这表明自噬是维持多种细胞功能所必需的。我们使用缺乏自噬功能的 Atg7 敲除 MEF（Atg7 MEF）细胞系来阐明 Atg5 转基因在肿瘤发生中的作用。我们发现，在自噬缺乏的情况下，Atg5 过表达的 Atg7 MEF（克隆 A）表现出细胞增殖、集落形成和迁移的增加。相应地，通过过表达 Atg7 基因来恢复克隆 A 的自噬缺陷，将 Atg5 的作用从促肿瘤转变为抗肿瘤状态，表明 Atg5 在肿瘤发生中具有双重作用。值得注意的是，异种移植小鼠模型表明，Atg5 过表达的 Atg7 MEF 细胞的克隆 A 诱导了暂时的肿瘤形成，但不能进一步延长肿瘤生长。最后，生物力学分析揭示了 Wnt5a 分泌增加和 p-JNK 表达增加，同时β-catenin 表达减少。总之，Atg5 在正常条件下作为肿瘤抑制因子发挥作用。相比之下，在自噬缺乏的情况下，Atg5 转变为促肿瘤状态。
