Department of Ophthalmology and Visual Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Department of Pathology and Laboratory Medicine, The Center for Cancer Research, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee, USA.
J Cell Mol Med. 2022 Jul;26(14):3873-3890. doi: 10.1111/jcmm.17421. Epub 2022 Jun 6.
Despite advances in molecular characterization, glioblastoma (GBM) remains the most common and lethal brain tumour with high mortality rates in both paediatric and adult patients. The signal transducer and activator of transcription 3 (STAT3) is an important oncogenic driver of GBM. Although STAT3 reportedly plays a role in autophagy of some cells, its role in cancer cell autophagy remains unclear. In this study, we found Serine-727 and Tyrosine-705 phosphorylation of STAT3 was constitutive in GBM cell lines. Tyrosine phosphorylation of STAT3 in GBM cells suppresses autophagy, whereas knockout (KO) of STAT3 increases ULK1 gene expression, increases TSC2-AMPKα-ULK1 signalling, and increases lysosomal Cathepsin D processing, leading to the stimulation of autophagy. Rescue of STAT3-KO cells by the enforced expression of wild-type (WT) STAT3 reverses these pathways and inhibits autophagy. Conversely, expression of Y705F- and S727A-STAT3 phosphorylation deficient mutants in STAT3-KO cells did not suppress autophagy. Inhibition of ULK1 activity (by treatment with MRT68921) or its expression (by siRNA knockdown) in STAT3-KO cells inhibits autophagy and sensitizes cells to apoptosis. Taken together, our findings suggest that serine and tyrosine phosphorylation of STAT3 play critical roles in STAT3-dependent autophagy in GBM, and thus are potential targets to treat GBM.
尽管在分子特征方面取得了进展，但胶质母细胞瘤（GBM）仍然是最常见和最致命的脑肿瘤，无论在儿童还是成人患者中，死亡率都很高。信号转导子和转录激活子 3（STAT3）是 GBM 的一个重要致癌驱动因子。尽管有报道称 STAT3 在一些细胞的自噬中发挥作用，但它在癌细胞自噬中的作用尚不清楚。在这项研究中，我们发现 STAT3 的丝氨酸 727 和酪氨酸 705 磷酸化在 GBM 细胞系中是组成性的。GBM 细胞中 STAT3 的酪氨酸磷酸化抑制自噬，而 STAT3 的敲除（KO）则增加 ULK1 基因表达，增加 TSC2-AMPKα-ULK1 信号通路，并增加溶酶体组织蛋白酶 D 的加工，从而刺激自噬。通过强制表达野生型（WT）STAT3 来拯救 STAT3-KO 细胞，可逆转这些途径并抑制自噬。相反，在 STAT3-KO 细胞中表达 Y705F-和 S727A-STAT3 磷酸化缺陷突变体并不能抑制自噬。在 STAT3-KO 细胞中抑制 ULK1 活性（通过 MRT68921 处理）或其表达（通过 siRNA 敲低）会抑制自噬并使细胞对细胞凋亡敏感。总之，我们的研究结果表明，STAT3 的丝氨酸和酪氨酸磷酸化在 GBM 中 STAT3 依赖性自噬中发挥关键作用，因此是治疗 GBM 的潜在靶点。
