Department of Oncology, Shengjing Hospital of China Medical University, Shenyang, 110004, China.
Department of Urology, Shengjing Hospital of China Medical University, Shenyang, 110004, China.
Cell Oncol (Dordr). 2022 Dec;45(6):1203-1215. doi: 10.1007/s13402-022-00710-8. Epub 2022 Sep 22.
Bladder carcinoma (BLCA) is the most common urinary tract malignancy and exhibits a poor response to chemotherapy. Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase involved in a wide variety of regulatory cellular processes, including apoptosis and the DNA-damage response (DDR). LB100, a small molecule inhibitor of PP2A, has been shown to act as a chemo-sensitizer in multiple types of cancer. However, the anti-tumor effect and mode of action of LB100 in BLCA have yet to be identified.
In vitro and in vivo experiments were performed to assess the anti-tumor effect of LB100 alone or in combination with gemcitabine. Mass spectrometry (MS)-based phosphoproteomics analysis was used to identify the downstream substrates of PP2A and to explore the mechanism underlying LB100-induced DNA damage and apoptosis. In addition, we established a chemo-resistant BLCA cell line (RT-112-R) by prolonged drug exposure and determined the effect of LB100 in enhancing genotoxicity in BLCA cell lines and xenograft mouse models.
We found that LB100 is sufficient to induce an anti-tumor response in BLCA cells by inducing DNA damage and apoptosis both in vitro and in vivo. Furthermore, we found that PP2A potentially dephosphorylates p-p21-ser130 to stabilize p21. Inhibition of PP2A by LB100 increased the level of p-p21-ser130, subsequently leading to a reduction in p21 level in a dose-dependent manner. In addition, we found that treatment of LB100 abrogated the G1/S cell cycle checkpoint, resulting in increased phosphorylation of γH2AX in BLCA cells. Moreover, LB100 enhanced genotoxicity in chemo-resistant BLCA cells by inducing DNA damage and apoptosis in vitro and in vivo.
Our findings indicate that PP2A may serve as a potential therapeutic target in BLCA through regulating p21 stability.
膀胱癌（BLCA）是最常见的泌尿道恶性肿瘤，对化疗反应不佳。蛋白磷酸酶 2A（PP2A）是一种丝氨酸/苏氨酸磷酸酶，参与多种调节细胞过程，包括细胞凋亡和 DNA 损伤反应（DDR）。小分子抑制剂 LB100 已被证明在多种类型的癌症中作为化疗增敏剂发挥作用。然而，LB100 在 BLCA 中的抗肿瘤作用和作用机制尚未确定。
进行了体外和体内实验，以评估 LB100 单独或与吉西他滨联合使用的抗肿瘤作用。基于质谱（MS）的磷酸化蛋白质组学分析用于鉴定 PP2A 的下游底物，并探讨 LB100 诱导的 DNA 损伤和细胞凋亡的机制。此外，我们通过长期药物暴露建立了一种化疗耐药 BLCA 细胞系（RT-112-R），并确定了 LB100 在增强 BLCA 细胞系和异种移植小鼠模型中的遗传毒性的作用。
我们发现 LB100 足以通过在体外和体内诱导 DNA 损伤和细胞凋亡来诱导 BLCA 细胞的抗肿瘤反应。此外，我们发现 PP2A 可能使 p-p21-ser130 去磷酸化，从而稳定 p21。LB100 通过抑制 PP2A 增加 p-p21-ser130 的水平，随后以剂量依赖性方式降低 p21 水平。此外，我们发现 LB100 消除了 G1/S 细胞周期检查点，导致 BLCA 细胞中 γH2AX 的磷酸化增加。此外，LB100 通过在体外和体内诱导 DNA 损伤和细胞凋亡来增强化疗耐药 BLCA 细胞的遗传毒性。
我们的研究结果表明，通过调节 p21 稳定性，PP2A 可能成为 BLCA 的潜在治疗靶点。
