STC1 promotes temozolomide resistance of glioblastoma through STAT3-mediated regulation of MGMT.

Resistance to temozolomide (TMZ) is one of the major challenges for glioblastoma (GBM) therapy while the underlying mechanisms demand further exploration. Tumor-repopulating cells (TRCs) have been proven to be involved in chemotherapy resistentce. We first enriched GBM TRCs by culturing DBTRG cells in 3D soft fibrin gels and performed RNA-seq. By anlyzing the differentially expressed genes (DEGs) between TRCs and 2D conventionally cultured DBTRG cells, we identified the glycoprotein gene Stanniocalcin-1 (STC1), which is highly expressed in TRCs. Our analyses using patient data from CGGA disclosed that high STC1 expression was associated with poor prognosis, high glioma grade and TMZ therapy resistance. Both our in vitro and in vivo expreriments showed that overexpression of STC1 promoted while knockdown of STC1 inhibited GBM cell proliferation and TMZ resistance. Our mechanistic study revealed that STC1 elevated the phosphoralation of STAT3 to increase MGMT expression, which inhibited the TMZ-induced DNA damage and apoptosis. Our study provides rationale for targeting STC1 to overcome TMZ resistance. We cultured DBTRG cells with rigid dish or soft gel, cells were harvested cells separately for RNA-seq analysis after being cultured for 5 days.

替莫唑胺（temozolomide, TMZ）耐药是胶质母细胞瘤（glioblastoma, GBM）治疗面临的主要挑战之一，其潜在作用机制仍有待进一步探索。
肿瘤复殖细胞（tumor-repopulating cells, TRCs）已被证实与化疗耐药相关。本研究首先通过在三维（3D）软纤维蛋白凝胶中培养DBTRG细胞以富集胶质母细胞瘤TRCs，并开展RNA测序（RNA-seq）。
通过分析TRCs与常规二维（2D）培养的DBTRG细胞之间的差异表达基因（differentially expressed genes, DEGs），我们鉴定出在TRCs中高表达的糖蛋白基因司坦钙蛋白-1（Stanniocalcin-1, STC1）。
利用中国胶质瘤基因组图谱（Chinese Glioma Genome Atlas, CGGA）的患者数据进行分析后发现，STC1高表达与不良预后、高级别胶质瘤以及TMZ化疗耐药显著相关。
体外与体内实验均证实，过表达STC1可促进胶质母细胞瘤细胞增殖与TMZ耐药，而敲低STC1则会抑制上述过程。
机制研究表明，STC1通过增强信号转导与转录激活因子3（signal transducer and activator of transcription 3, STAT3）的磷酸化水平，提升O6-甲基鸟嘌呤-DNA甲基转移酶（O6-methylguanine-DNA methyltransferase, MGMT）的表达，进而抑制TMZ诱导的DNA损伤与细胞凋亡。
本研究为靶向STC1以克服TMZ耐药提供了理论依据。
本研究中，我们分别在刚性培养皿与软凝胶中培养DBTRG细胞，于培养5天后分别收集细胞进行RNA测序分析。