Kang Kwonyoon, Ryoo Hyung Don, Park Jung-Eun, Yoon Jee-Hyun, Kang Min-Ji
Department of Biomedical Sciences, University of Ulsan College of Medicine, Seoul, Republic of Korea.
Department of Cell Biology, New York University School of Medicine, New York, New York, United States of America.
PLoS One. 2015 May 15;10(5):e0126795. doi: 10.1371/journal.pone.0126795. eCollection 2015.
Eukaryotic cells have evolved signaling pathways that help to restore cellular homeostasis in response to various physiological or pathological conditions. ATF4 is a transcription factor whose mRNA translation is stimulated in response to stress-activated eIF2alpha kinases. Established conditions that activate eIF2alpha phosphorylation and ATF4 translation include excessive stress in the endoplasmic reticulum (ER) and amino acid deprivation. ATF4 is activated through a unique translational activation mechanism that involves multiple upstream open reading frames (uORFs) in the 5'-untranslated region (UTR), which is conserved from yeast to mammals. Taking advantage of this, we developed a translational activation reporter of ATF4 in Drosophila, in which the dsRed reporter coding sequence was placed downstream of the Drosophila ATF4 5' UTR. This reporter remained inactive in most tissues under normal conditions, but showed dsRed expression when starved, or when challenged with conditions that imposed ER stress. In normally developing flies, a small number of cell types showed reporter expression even without exogenous stress, which included the salivary gland, gut, the male reproductive organ, and the photoreceptor cells, suggestive of inherent stress during the normal development of these cell types. These results establish a new tool to study ATF4-mediated stress response in Drosophila development and disease.
真核细胞已经进化出信号通路，以帮助在各种生理或病理条件下恢复细胞内稳态。ATF4是一种转录因子，其mRNA翻译在应激激活的eIF2α激酶作用下被刺激。激活eIF2α磷酸化和ATF4翻译的既定条件包括内质网（ER）中的过度应激和氨基酸剥夺。ATF4通过一种独特的翻译激活机制被激活，该机制涉及5'-非翻译区（UTR）中的多个上游开放阅读框（uORF），从酵母到哺乳动物都是保守的。利用这一点，我们在果蝇中开发了一种ATF4的翻译激活报告基因，其中dsRed报告基因编码序列位于果蝇ATF4 5'UTR的下游。该报告基因在正常条件下在大多数组织中保持无活性，但在饥饿或受到内质网应激条件刺激时显示dsRed表达。在正常发育的果蝇中，即使没有外源应激，少数细胞类型也显示报告基因表达，其中包括唾液腺、肠道、雄性生殖器官和光感受器细胞，这表明这些细胞类型在正常发育过程中存在内在应激。这些结果建立了一种新工具，用于研究果蝇发育和疾病中ATF4介导的应激反应。
