Shandong Provincial Key Laboratory of Radiation Oncology, Cancer Research Center, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong Province, 250117, China.
Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, 02215, USA.
Theranostics. 2020 Apr 6;10(11):4983-4996. doi: 10.7150/thno.43046. eCollection 2020.
Esophageal squamous cell carcinoma (ESCC) accounts for about 90% of all incident esophageal cancers, with a 5-year survival rate of < 20%. Autophagy is of particular importance in cancers; however, the detailed regulatory mechanisms of oncogenic autophagy in ESCC have not been fully elucidated. In the present study, we address how splicing control of is involved in mTOR-regulated oncogenic autophagy. Alternative splicing events controlled by DAZAP1 in ESCC cells were identified via RNAseq. Differential phosphorylation of short or long TSC2 splicing variants by AKT and their impacts on mTOR signaling were also examined. We found that starvation-induced miR-10b could enhance autophagy via silencing DAZAP1, a key regulator of pre-mRNA alternative splicing. Intriguingly, we observed a large number of significantly changed alternative splicing events, especially exon skipping, upon RNAi of DAZAP1. was verified as one of the crucial target genes of DAZAP1. Silencing of DAZAP1 led to the exclusion of exon 26 (from Leu947 to Arg988), producing a short TSC2 isoform. The short TSC2 isoform cannot be phosphorylated at Ser981 by AKT, which resulted in continuous activation of TSC2 in ESCC. The active TSC2 inhibited mTOR via RHEB, leading to continually stimulated oncogenic autophagy of ESCC cells. Our data revealed an important physiological function of tumor suppressor DAZAP1 in autophagy regulation and highlighted the potential of controlling mRNA alternative splicing as an effective therapeutic application for cancers.
食管鳞状细胞癌（ESCC）约占所有食管癌病例的 90%，其 5 年生存率<20%。自噬在癌症中具有特别重要的意义；然而，ESCC 中致癌自噬的详细调节机制尚未完全阐明。在本研究中，我们研究了 DAZAP1 如何参与 mTOR 调控的致癌自噬中的剪接调控。通过 RNAseq 鉴定了 ESCC 细胞中 DAZAP1 控制的 可变剪接事件。还研究了 AKT 对短或长 TSC2 剪接变体的差异磷酸化及其对 mTOR 信号的影响。我们发现饥饿诱导的 miR-10b 可以通过沉默 pre-mRNA 可变剪接的关键调节因子 DAZAP1 来增强自噬。有趣的是，我们观察到大量显著改变的可变剪接事件，特别是外显子跳跃，当 DAZAP1 的 RNAi 时。 被验证为 DAZAP1 的关键靶基因之一。沉默 DAZAP1 导致 外显子 26（从 Leu947 到 Arg988）缺失，产生短的 TSC2 异构体。短的 TSC2 异构体不能被 AKT 在 Ser981 处磷酸化，这导致 ESCC 中 TSC2 的持续激活。活性 TSC2 通过 RHEB 抑制 mTOR，导致 ESCC 细胞持续刺激致癌自噬。我们的数据揭示了肿瘤抑制因子 DAZAP1 在自噬调节中的重要生理功能，并强调了控制 mRNA 可变剪接作为癌症有效治疗应用的潜力。
