缺氧是肿瘤微环境的一个关键特征，有助于具有强大自我更新特性的乳腺癌干细胞（BCSC）的发育。然而，BCSC 诱导过程中缺氧的具体机制尚不完全清楚。在此，我们提供了证据表明，一种新型缺氧特异性circSTT3A在临床乳腺癌（BC）组织中显着上调，并且与BC患者的临床分期和不良预后密切相关。研究表明，缺氧诱导因子 1 α (HIF1α) 调节的 circSTT3A 对乳腺癌细胞中乳腺球的形成具有显着影响。从机制上讲，circSTT3A直接与热休克蛋白70（HSP70）的核苷酸结合域相互作用，从而通过其底物结合域促进磷酸甘油酸激酶1（PGK1）的募集，从而减少泛素化并增加PGK1的稳定性。 PGK1 水平升高可催化 1,3-二磷酸甘油酸 (1,3-BPG) 转化为 3-磷酸甘油酸 (3-PG)，从而导致 3-PG 积累并增加丝氨酸合成、S-腺苷甲硫氨酸 (SAM) 积累和组蛋白三甲基化H3 赖氨酸 4 (H3K4me3)。 H3K4me3 的激活通过增加干性相关因子的转录水平来促进 BCSC。特别是，我们的工作表明，circSTT3A 或 PGK1 的缺失都会显着抑制肿瘤的发生和生长，从而显着增加小鼠肿瘤对阿霉素 (DOX) 的敏感性。在小鼠体内注射 PGK1 沉默的球体和 3-PG 可以显着逆转肿瘤的发生和生长，从而增加肿瘤对 DOX 的抵抗力。总之，我们的研究揭示了缺氧通过 circSTT3A/HSP70/PGK1 介导的丝氨酸合成维持 BCSC 的功能作用，这为代谢重编程、肿瘤发生和生长提供了新的见解。我们的研究结果表明，单独靶向 circSTT3A 或联合化疗对于 BC 管理具有潜在的临床价值。版权所有 © 2023。由 Elsevier Ltd 出版。

Hypoxia is a key feature of tumor microenvironment that contributes to the development of breast cancer stem cells (BCSCs) with strong self-renewal properties. However, the specific mechanism underlying hypoxia in BCSC induction is not completely understood. Herein, we provide evidence that a novel hypoxia-specific circSTT3A is significantly upregulated in clinical breast cancer (BC) tissues, and is closely related to the clinical stage and poor prognosis of patients with BC. The study revealed that hypoxia-inducible factor 1 alpha (HIF1α)-regulated circSTT3A has a remarkable effect on mammosphere formation in breast cancer cells. Mechanistically, circSTT3A directly interacts with nucleotide-binding domain of heat shock protein 70 (HSP70), thereby facilitating the recruitment of phosphoglycerate kinase 1 (PGK1) via its substrate-binding domain, which reduces the ubiquitination and increases the stability of PGK1. The enhanced levels of PGK1 catalyze 1,3-diphosphoglycerate (1,3-BPG) into 3-phosphoglycerate (3-PG) leading to 3-PG accumulation and increased serine synthesis, S-adenosylmethionine (SAM) accumulation, and trimethylation of histone H3 lysine 4 (H3K4me3). The activation of the H3K4me3 contributes to BCSCs by increasing the transcriptional level of stemness-related factors. Especially, our work reveals that either loss of circSTT3A or PGK1 substantially suppresses tumor initiation and tumor growth, which dramatically increases the sensitivity of tumors to doxorubicin (DOX) in mice. Injection of PGK1-silenced spheroids with 3-PG can significantly reverse tumor initiation and growth in mice, thereby increasing tumor resistance to DOX. In conclusion, our study sheds light on the functional role of hypoxia in the maintenance of BCSCs via circSTT3A/HSP70/PGK1-mediated serine synthesis, which provides new insights into metabolic reprogramming, tumor initiation and growth. Our findings suggest that targeting circSTT3A alone or in combination with chemotherapy has potential clinical value for BC management.Copyright © 2023. Published by Elsevier Ltd.