Sarcoma Center, Departments of Medical Oncology, Pathology and Neuropathology, Trauma and Orthopedic Surgery, Visceral and Transplant Surgery, West German Cancer Center, University Duisburg-Essen, University Hospital Essen, Germany.
Cancer Res. 2013 Jun 15;73(12):3661-70. doi: 10.1158/0008-5472.CAN-12-3839. Epub 2013 Apr 10.
Gastrointestinal stromal tumors (GIST) are characterized by activating mutations of KIT or platelet-derived growth factor receptor α(PDGFRA), which can be therapeutically targeted by tyrosine kinase inhibitors (TKI) such as imatinib. Despite long-lasting responses, most patients eventually progress after TKI therapy. The calcium-dependent chloride channel DOG1 (ANO1/TMEM16A), which is strongly and specifically expressed in GIST, is used as a diagnostic marker to differentiate GIST from other sarcomas. Here, we report that loss of DOG1 expression occurs together with loss of KIT expression in a subset of GIST resistant to KIT inhibitors, and we illustrate the functional role of DOG1 in tumor growth, KIT expression, and imatinib response. Although DOG1 is a crucial regulator of chloride balance in GIST cells, we found that RNAi-mediated silencing or pharmacologic inhibition of DOG1 did not alter cell growth or KIT signaling in vitro. In contrast, DOG1 silencing delayed the growth of GIST xenografts in vivo. Expression profiling of explanted tumors after DOG1 blockade revealed a strong upregulation in the expression of insulin-like growth factor-binding protein 5 (IGFBP5), a potent antiangiogenic factor implicated in tumor suppression. Similar results were obtained after selection of imatinib-resistant DOG1- and KIT-negative cells derived from parental DOG1 and KIT-positive GIST cells, where a 5,000-fold increase in IGFBP5 mRNA transcripts were documented. In summary, our findings establish the oncogenic activity of DOG1 in GIST involving modulation of IGF/IGF receptor signaling in the tumor microenvironment through the antiangiogenic factor IGFBP5.
胃肠道间质瘤（GIST）的特征是存在 KIT 或血小板衍生生长因子受体α（PDGFRA）的激活突变，这些突变可通过酪氨酸激酶抑制剂（TKI）如伊马替尼进行治疗性靶向。尽管有持久的反应，但大多数患者在 TKI 治疗后最终会进展。钙依赖性氯离子通道 DOG1（ANO1/TMEM16A）在 GIST 中强烈且特异性表达，可用作诊断标志物，将 GIST 与其他肉瘤区分开来。在这里，我们报告在对 KIT 抑制剂耐药的 GIST 亚群中，DOG1 表达的丧失与 KIT 表达的丧失同时发生，并说明了 DOG1 在肿瘤生长、KIT 表达和伊马替尼反应中的功能作用。尽管 DOG1 是 GIST 细胞中氯离子平衡的关键调节剂，但我们发现 RNAi 介导的 DOG1 沉默或药理学抑制在体外并没有改变细胞生长或 KIT 信号。相比之下，DOG1 沉默延迟了 GIST 异种移植物在体内的生长。DOG1 阻断后对移植瘤的表达谱分析显示，胰岛素样生长因子结合蛋白 5（IGFBP5）的表达强烈上调，IGFBP5 是一种强效的抗血管生成因子，与肿瘤抑制有关。在从 DOG1 和 KIT 阳性 GIST 细胞衍生的 DOG1 和 KIT 阴性、对伊马替尼耐药的细胞中选择后，也得到了类似的结果，其中 IGFBP5 mRNA 转录物增加了 5000 倍。总之，我们的研究结果确立了 DOG1 在 GIST 中的致癌活性，涉及通过抗血管生成因子 IGFBP5 调节肿瘤微环境中的 IGF/IGF 受体信号。
