Host CLIC4 is essential for breast cancer metastatic competence

Chloride Intracellular Channel 4 (CLIC4) expression is elevated in the stroma of many cancers. We show that CLIC4 expression is higher in breast cancers from younger women and early stage metastatic disease, portends poor prognosis, and is linked to TGF-β expression. Two murine breast cancer models with lung metastases revealed that ablation of host Clic4 nearly eliminated lung metastases without reducing primary tumor size while Clic4 null tumor cells retained metastatic capability. Thus, CLIC4 is required for host metastatic competence. Deficiencies in circulating pro-metastatic soluble factors were detected in CLIC4 deficient hosts bearing primary tumors. Necrosis and vascular abnormalities were more abundant in primary tumors from CLIC4 deficient hosts than from CLIC4 proficient control hosts. Transcriptional profiles of lungs and primary tumors prior to the onset of metastases indicated that loss of host CLIC4 enhances an inflammatory microenvironment. Thus, CLIC4 expression in human breast cancers may serve as a prognostic biomarker, and targeting host CLIC4 could reduce metastatic competence. Transcriptional profiles of lungs and primary tumors prior to the onset of metastases. The 6DT1 mouse mammary tumor explant cell line was injected orthotopically into the fourth mammary fat pad of wildtype or CLIC4 knockout syngeneic FVB/N mice. Lung tissue was isolated from wildtype and CLIC4 knockout mice at baseline or 14 days after orthografting. Primary tumor tissue was isolated at 14 days after orthografting.

细胞内氯离子通道4（Chloride Intracellular Channel 4，CLIC4）在多种癌症的间质中表达升高。我们发现，年轻女性乳腺癌患者及早期转移性乳腺癌患者的肿瘤组织中CLIC4表达水平更高；CLIC4高表达预示不良预后，且与转化生长因子-β（Transforming Growth Factor beta，TGF-β）的表达密切相关。我们采用两种可发生肺转移的小鼠乳腺癌模型开展实验，结果显示，敲除宿主的Clic4基因可几乎完全消除肺转移，却未使原发肿瘤的体积缩小；而Clic4基因敲除的肿瘤细胞仍保留转移能力。由此可见，CLIC4是宿主获得肿瘤转移能力所必需的分子。在携带原发肿瘤的CLIC4缺陷宿主中，可检测到循环促转移可溶性因子的表达缺陷。与CLIC4功能正常的对照宿主相比，CLIC4缺陷宿主的原发肿瘤中坏死区域与血管异常更为多见。转移灶形成前的肺部及原发肿瘤转录组分析显示，宿主CLIC4缺失会增强炎症微环境的形成。综上，人类乳腺癌组织中的CLIC4表达可作为预后生物标志物，而靶向宿主CLIC4或可降低肿瘤的转移能力。转移灶形成前的肺部及原发肿瘤转录组分析。本研究将6DT1小鼠乳腺肿瘤外植体细胞系原位接种至野生型或CLIC4敲除的同基因FVB/N小鼠的第四乳腺脂肪垫中。分别在基线状态下及原位移植后14天，采集野生型与CLIC4敲除小鼠的肺组织；于原位移植后14天采集原发肿瘤组织。