Sun Datong, Yang Shenghui, Zhang Xufeng, Li Sai, Wang Lin, Chen Junmin, Qiu Chun, Xu Ke
Department of Oncology, Hainan Provincial People's Hospital, Haikou, Hainan 571101, P.R. China.
Department of Stomatology, First Affiliated Hospital of Hainan Medical University, Haikou, Hainan 570102, P.R. China.
Oncol Lett. 2021 Apr;21(4):328. doi: 10.3892/ol.2021.12580. Epub 2021 Feb 25.
Glioblastoma multiforme (GBM) is the most common type of malignant brain tumor. GBM is currently treated with temozolomide (TMZ), although patients often exhibit resistance to this agent. Although several mechanisms underlying the resistance of GBM to TMZ have been identified, the combination of these mechanisms is not sufficient to fully account for this phenomenon. Our previous study demonstrated that knocking down the Forkhead box protein O3a (FoxO3a) gene, a member of the FoxO subfamily of transcription factors, resulted in glioma cell sensitization to TMZ, accompanied by reduced levels of nuclear β-catenin. The aim of the present study was to specify how FoxO3a and β-catenin are implicated in glioma cell TMZ resistance. Using the U87 and U251 parental cell lines (also designated as sensitive cell lines) and corresponding resistant cell lines (U87-TR and U251-TR, generated by repeated TMZ treatments), coupled with a combined knockdown/overexpression strategy, it was revealed that FoxO3a or β-catenin overexpression in TMZ-treated U87 and U251 cells markedly increased cellular proliferation; co-expression of both FoxO3a and β-catenin resulted in the highest increase. Knockdown of either FoxO3a or β-catenin in U87-TR and U251-TR cells led to a significant decrease in cell viability, which was rescued by the re-expression of FoxO3a in FoxO3a-knockdown cells. Subsequent experiments demonstrated that, in U87-TR and U251-TR cells, FoxO3a knockdown significantly reduced the protein levels of matrix metallopeptidase (MMP)9, while overexpression of FoxO3a in U87 and U251 cells enhanced the nuclear accumulation of β-catenin, concomitantly with an increase in MMP9 levels. Furthermore, MMP9 knockdown markedly reduced the levels of nuclear β-catenin. Collectively, the findings of the present study suggest that FoxO3a may regulate the nuclear accumulation of β-catenin by modulating MMP9 expression, thereby rendering glioblastoma cells resistant to TMZ, and may provide unique molecular insights into the mechanisms underlying the development of TMZ resistance in GBM.
多形性胶质母细胞瘤（GBM）是最常见的恶性脑肿瘤类型。目前，GBM采用替莫唑胺（TMZ）进行治疗，尽管患者常常对这种药物表现出耐药性。虽然已经确定了GBM对TMZ耐药的几种潜在机制，但这些机制的组合并不足以完全解释这一现象。我们之前的研究表明，敲低叉头框蛋白O3a（FoxO3a）基因（转录因子FoxO亚家族的成员）会导致胶质瘤细胞对TMZ敏感，同时核β-连环蛋白水平降低。本研究的目的是明确FoxO3a和β-连环蛋白如何与胶质瘤细胞对TMZ的耐药性相关。使用U87和U251亲本细胞系（也称为敏感细胞系）以及相应的耐药细胞系（通过反复使用TMZ处理产生的U87-TR和U251-TR），结合联合敲低/过表达策略，结果显示在经TMZ处理的U87和U251细胞中，FoxO3a或β-连环蛋白的过表达显著增加细胞增殖；FoxO3a和β-连环蛋白的共表达导致细胞增殖增加最多。在U87-TR和U251-TR细胞中敲低FoxO3a或β-连环蛋白会导致细胞活力显著降低，而在敲低FoxO3a的细胞中重新表达FoxO3a可挽救这种降低。随后的实验表明，在U87-TR和U251-TR细胞中，敲低FoxO3a显著降低基质金属蛋白酶（MMP）9的蛋白水平，而在U87和U251细胞中过表达FoxO3a会增强β-连环蛋白的核积累，同时MMP9水平增加。此外，敲低MMP9显著降低核β-连环蛋白的水平。总的来说，本研究结果表明，FoxO3a可能通过调节MMP9的表达来调节β-连环蛋白的核积累，从而使胶质母细胞瘤细胞对TMZ产生耐药性，并且可能为GBM中TMZ耐药性发展的潜在机制提供独特的分子见解。
