Department of Endocrinology and Metabolism, Medical Center for Comprehensive Weight Control, Guangdong Provincial Key Laboratory of Diabetology, Guangzhou Key Laboratory of Mechanistic and Translational Obesity Research, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China.
Department of Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, USA.
Cell Death Dis. 2023 Aug 18;14(8):531. doi: 10.1038/s41419-023-06046-x.
Unfolded protein response (UPR) maintains the endoplasmic reticulum (ER) homeostasis, survival, and physiological function of mammalian cells. However, how cells adapt to ER stress under physiological or disease settings remains largely unclear. Here by a genome-wide CRISPR screen, we identified that RBBP8, an endonuclease involved in DNA damage repair, is required for ATF4 activation under ER stress in vitro. RNA-seq analysis suggested that RBBP8 deletion led to impaired cell cycle progression, retarded proliferation, attenuated ATF4 activation, and reduced global protein synthesis under ER stress. Mouse tissue analysis revealed that RBBP8 was highly expressed in the liver, and its expression is responsive to ER stress by tunicamycin intraperitoneal injection. Hepatocytes with RBBP8 inhibition by adenovirus-mediated shRNA were resistant to tunicamycin (Tm)-induced liver damage, cell death, and ER stress response. To study the pathological role of RBBP8 in regulating ATF4 activity, we illustrated that both RBBP8 and ATF4 were highly expressed in liver cancer tissues compared with healthy controls and highly expressed in Ki67-positive proliferating cells within the tumors. Interestingly, overexpression of RBBP8 in vitro promoted ATF4 activation under ER stress, and RBBP8 expression showed a positive correlation with ATF4 expression in liver cancer tissues by co-immunostaining. Our findings provide new insights into the mechanism of how cells adapt to ER stress through the crosstalk between the nucleus and ER and how tumor cells survive under chemotherapy or other anticancer treatments, which suggests potential therapeutic strategies against liver disease by targeting DNA damage repair, UPR or protein synthesis.
未折叠蛋白反应 (UPR) 维持着内质网 (ER) 的内稳态、哺乳动物细胞的存活和生理功能。然而，细胞在生理或疾病状态下如何适应 ER 应激仍然很大程度上不清楚。在这里，通过全基因组 CRISPR 筛选，我们发现参与 DNA 损伤修复的内切酶 RBBP8 在体外 ER 应激下 ATF4 的激活是必需的。RNA-seq 分析表明，RBBP8 缺失导致细胞周期进程受损、增殖减缓、ATF4 激活减弱和 ER 应激下整体蛋白质合成减少。小鼠组织分析表明，RBBP8 在肝脏中高度表达，其表达对 tunicamycin 腹腔注射的 ER 应激有反应。用腺病毒介导的 shRNA 抑制 RBBP8 的肝细胞对 tunicamycin (Tm) 诱导的肝损伤、细胞死亡和 ER 应激反应具有抗性。为了研究 RBBP8 在调节 ATF4 活性中的病理作用，我们表明 RBBP8 和 ATF4 在肝癌组织中均高度表达，与健康对照相比，在肿瘤内的 Ki67 阳性增殖细胞中高度表达。有趣的是，体外过表达 RBBP8 可在 ER 应激下促进 ATF4 的激活，并且 RBBP8 的表达与肝癌组织中 ATF4 的表达通过共免疫染色呈正相关。我们的发现为细胞如何通过核与 ER 之间的串扰来适应 ER 应激以及肿瘤细胞如何在化疗或其他抗癌治疗下存活提供了新的见解，这表明通过靶向 DNA 损伤修复、UPR 或蛋白质合成来治疗肝脏疾病的潜在治疗策略。
