Loss of circadian clock gene expression is associated with tumor progression in breast cancer

Several studies suggest a link between circadian rhythm disturbances and tumorigenesis. However, the association between circadian clock genes and prognosis in breast cancer has not been systematically studied. Therefore, we examined the expression of 17 clock components in tumors from 766 node-negative breast cancer patients that were untreated in both neoadjuvant and adjuvant settings. In addition, their association with metastasis-free survival (MFS) and correlation to clinicopathological parameters were investigated. Aiming to estimate functionality of the clockwork, we studied clock gene expression relationships by correlation analysis. Higher expression of several clock genes (e.g., CLOCK, PER1, PER2, PER3, CRY2, NPAS2 and RORC) was found to be associated with longer MFS in univariate Cox regression analyses (HR<1 and FDR-adjusted P < 0.05). Stratification according to molecular subtype revealed prognostic relevance for PER1, PER3, CRY2 and NFIL3 in the ER+/HER2- subgroup, CLOCK and NPAS2 in the ER-/HER2- subtype, and ARNTL2 in HER2+ breast cancer. In the multivariate Cox model, only PER3 (HR = 0.66; P = 0.016) and RORC (HR = 0.42; P = 0.003) were found to be associated with survival outcome independent of established clinicopathological parameters. Pairwise correlations between functionally-related clock genes (e.g., PER2-PER3 and CRY2-PER3) were stronger in ER+, HER2- and low-grade carcinomas; whereas, weaker correlation coefficients were observed in ER- and HER2+ tumors, high-grade tumors and tumors that progressed to metastatic disease. In conclusion, loss of clock genes is associated with worse prognosis in breast cancer. Coordinated co-expression of clock genes, indicative of a functional circadian clock, is maintained in ER+, HER2-, low grade and non-metastasizing tumors but is compromised in more aggressive carcinomas.

多项研究表明，昼夜节律（circadian rhythm）紊乱与肿瘤发生（tumorigenesis）存在关联。然而，目前尚未有研究系统探讨生物钟基因与乳腺癌预后之间的关联。因此，我们对766例未接受新辅助及辅助治疗的淋巴结阴性乳腺癌患者的肿瘤组织中17种生物钟组件的表达水平进行了检测。此外，我们还分析了这些基因的表达与无转移生存期（metastasis-free survival, MFS）的相关性，以及其与临床病理参数的关联。为评估生物钟系统的功能状态，我们通过相关性分析研究了生物钟基因的表达关联。单因素Cox回归分析显示，多种生物钟基因（如CLOCK、PER1、PER2、PER3、CRY2、NPAS2及RORC）的高表达与更长的无转移生存期相关（风险比（Hazard Ratio, HR）<1，错误发现率（False Discovery Rate, FDR）校正后的P值<0.05）。按分子亚型进行分层分析后发现，PER1、PER3、CRY2及NFIL3在ER+/HER2-（雌激素受体阳性/人表皮生长因子受体2阴性）亚组中具有预后价值；CLOCK与NPAS2在ER-/HER2-（雌激素受体阴性/人表皮生长因子受体2阴性）亚组中具有预后价值；而ARNTL2在HER2+（人表皮生长因子受体2阳性）乳腺癌中具有预后价值。在多因素Cox模型中，仅PER3（HR=0.66；P=0.016）与RORC（HR=0.42；P=0.003）在校正已确立的临床病理参数后，仍与生存结局存在独立关联。功能相关的生物钟基因间的两两相关性（如PER2-PER3与CRY2-PER3）在ER+、HER2-及低级别癌组织中更强；而在ER-、HER2+肿瘤、高级别肿瘤以及发生转移的肿瘤中，相关系数则较弱。综上，生物钟基因的表达缺失与乳腺癌不良预后相关。生物钟的协同共表达（提示功能性昼夜节律钟的存在）在ER+、HER2-、低级别及非转移性肿瘤中得以维持，但在更具侵袭性的癌组织中遭到破坏。