a School of Pharmaceutical Sciences, National and Local United Engineering Lab of Druggability and New Drugs Evaluation, Guangdong Provincial Key Laboratory of New Drug Design and Evaluation , Sun Yat-Sen University , Guangzhou , Guangdong , China.
b Department of Pathology and Laboratory Medicine , Indiana University School of Medicine , Indianapolis , IN , USA.
Autophagy. 2019 Feb;15(2):295-311. doi: 10.1080/15548627.2018.1517073. Epub 2018 Sep 20.
Human Atg4 homologs are cysteine proteases, which play key roles in the macroautophagy/autophagy process by cleaving Atg8 homologs for conjugation to lipid membranes and for deconjugation of Atg8 homologs from membranes. Expression of ATG4B is significantly increased in colorectal cancer cells compared to normal cells, suggesting that ATG4B may be important for cancer biology. Inhibition of ATG4B may reduce the autophagy activity, thereby sensitizing cancer cells to therapeutic agents. Thus, developing specific and potent ATG4B inhibitors for research as well as for potential therapeutic uses is highly needed. In this study, we integrated screening and assays to discover a potent ATG4B inhibitor, named S130, from a noncommercial library. This chemical binds to ATG4B with strong affinity and specifically suppresses the activity of ATG4B but not other proteases. S130 did not cause the impairment of autophagosome fusion, nor did it result in the dysfunction of lysosomes. Instead, S130 might attenuate the delipidation of LC3-II on the autolysosomes to suppress the recycling of LC3-I, which normally occurs after LC3-II cleavage by ATG4B. Intriguingly, S130 induced cell death, which was accompanied with autophagy stress and could be further exacerbated by nutrient deprivation. Such cytotoxicity could be partially reversed by enhancing ATG4B activity. Finally, we found that S130 was distributed in tumor tissues in vivo and was also effective in arresting the growth of colorectal cancer cells. Thus, this study indicates that ATG4B is a potential anticancer target and S130 might be a novel small-molecule candidate for future cancer therapy.
人类 Atg4 同源物是半胱氨酸蛋白酶，通过切割 Atg8 同源物用于与脂质膜缀合和从膜上解缀合 Atg8 同源物，在巨自噬/自噬过程中发挥关键作用。与正常细胞相比，结直肠癌细胞中 ATG4B 的表达显著增加，这表明 ATG4B 可能对癌症生物学很重要。抑制 ATG4B 可能会降低自噬活性，从而使癌细胞对治疗剂敏感。因此，开发用于研究以及潜在治疗用途的特异性和有效的 ATG4B 抑制剂是非常需要的。在这项研究中，我们整合了筛选和测定，从非商业文库中发现了一种有效的 ATG4B 抑制剂，命名为 S130。这种化学物质与 ATG4B 具有很强的亲和力，并特异性抑制 ATG4B 的活性，但不抑制其他蛋白酶。S130 不会导致自噬体融合受损，也不会导致溶酶体功能障碍。相反，S130 可能会减弱自溶酶体上 LC3-II 的去脂化，从而抑制 LC3-I 的循环利用，这通常发生在 ATG4B 切割 LC3-II 之后。有趣的是，S130 诱导细胞死亡，伴随着自噬应激，并且在营养剥夺时可以进一步加剧。这种细胞毒性可以通过增强 ATG4B 的活性部分逆转。最后，我们发现 S130 在体内肿瘤组织中分布，并能有效抑制结直肠癌细胞的生长。因此，这项研究表明 ATG4B 是一个潜在的抗癌靶点，S130 可能是未来癌症治疗的一种新型小分子候选药物。
