Wang Yi-Tian, Tang Fan, Hu Xin, Zheng Chuan-Xi, Gong Tao-Jun, Zhou Yong, Luo Yi, Min Li
Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, China.
IUBMB Life. 2020 Oct;72(10):2146-2153. doi: 10.1002/iub.2349. Epub 2020 Jul 30.
Osteosarcoma (OS) is a malignant bone neoplasm, mostly occurring in pediatric patients. OS is characterized by a highly aggressive and metastatically active tumor. Chemotherapy followed by surgical excision is the treatment of choice but is often associated with both chemoresistance and relapse. Hence, it is important to develop further understanding of OS pathogenesis and identify potential therapeutic targets. Both the signal transducer and activator of transcription 3 (STAT3) and mammalian target of rapamycin (mTOR) have been implicated in OS pathogenesis. Crosstalk between mTOR and STAT3 signaling has been shown to regulate hypoxia-induced angiogenesis in other diseases. In this study, we determined using OS cell lines if there is a crosstalk between these two pathways and how that impacts sensitivity to treatment with Rapamycin. OS cell lines exhibited differential sensitivity to mTOR inhibitor Rapamycin. Evaluation of phosphorylated STAT3 showed that in Rapamycin-sensitive 143B cells, the inhibitor decreased phosphorylation of STAT3 at Y705, but not at S727 whereas, in Rapamycin-resistant U2OS cells, the inhibitor decreased S727 phosphorylation but not Y705. However, knockdown of STAT3 in U2OS cells made them sensitive to Rapamycin. Immunofluorescence (IF) analysis showed that mTOR is constitutively activated in the 143B cells but is suppressed in the U2OS cells, indicating that this might be their reason for being resistant to Rapamycin. Both cell lines were sensitive to treatment with the STAT3 inhibitor Napabucasin (NP). Treatment with NP inhibited STAT3 activation at Y705 and additionally inhibited mTOR activation, indicating crosstalk between STAT3 and mTOR signaling pathways. Rapamycin could effectively prevent lung metastasis in an orthotropic OS mice model using 143B cells. However, Rapamycin could not inhibit lung metastasis in mice injected with U2OS cells. The STAT3 inhibitor NP attenuated lung metastasis with the U2OS cells. Our results thus established yet undefined crosstalk of STAT3 and mTOR signaling pathways in OS and highlight the possibility of using mTOR inhibitors for treatment in patients with OS.
骨肉瘤（OS）是一种恶性骨肿瘤，主要发生于儿科患者。OS的特征是具有高度侵袭性和转移活性的肿瘤。化疗后进行手术切除是首选治疗方法，但常伴有化疗耐药和复发。因此，进一步了解OS发病机制并确定潜在治疗靶点非常重要。信号转导和转录激活因子3（STAT3）和雷帕霉素哺乳动物靶蛋白（mTOR）均与OS发病机制有关。mTOR和STAT3信号之间的串扰已被证明在其他疾病中调节缺氧诱导的血管生成。在本研究中，我们使用OS细胞系确定这两条途径之间是否存在串扰以及这如何影响对雷帕霉素治疗的敏感性。OS细胞系对mTOR抑制剂雷帕霉素表现出不同的敏感性。磷酸化STAT3的评估表明，在对雷帕霉素敏感的143B细胞中，该抑制剂降低了Y705处STAT3的磷酸化，但未降低S727处的磷酸化；而在对雷帕霉素耐药的U2OS细胞中，该抑制剂降低了S727的磷酸化，但未降低Y705的磷酸化。然而，在U2OS细胞中敲低STAT3使其对雷帕霉素敏感。免疫荧光（IF）分析表明，mTOR在143B细胞中持续激活，但在U2OS细胞中受到抑制，这表明这可能是它们对雷帕霉素耐药的原因。两种细胞系对STAT3抑制剂萘布卡生（NP）治疗均敏感。NP治疗抑制了Y705处的STAT3激活，并额外抑制了mTOR激活，表明STAT3和mTOR信号通路之间存在串扰。雷帕霉素可有效预防使用143B细胞的原位OS小鼠模型中的肺转移。然而，雷帕霉素不能抑制注射U2OS细胞的小鼠中的肺转移。STAT3抑制剂NP减轻了U2OS细胞的肺转移。因此，我们的结果确立了OS中STAT3和mTOR信号通路尚未明确的串扰，并突出了使用mTOR抑制剂治疗OS患者的可能性。
