Expression of histone methyltransferases as novel biomarkers for renal cell tumor diagnosis and prognostication

Renal cell tumors (RCTs) are the most lethal of the common urological cancers. The widespread use of imaging entailed an increased detection of small renal masses, emphasizing the need for accurate distinction between benign and malignant RCTs, which is critical for adequate therapeutic management. Histone methylation has been implicated in renal tumorigenesis, but its potential clinical value as RCT biomarker remains mostly unexplored. Hence, the main goal of this study was to identify differentially expressed histone methyltransferases (HMTs) and histone demethylases (HDMs) that might prove useful for RCT diagnosis and prognostication, emphasizing the discrimination between oncocytoma (a benign tumor) and renal cell carcinoma (RCC), especially the chromophobe subtype (chRCC). We found that the expression levels of 3 genes—<i>SMYD2, SETD3</i>, and <i>NO66</i>—was significantly altered in a set of RCTs, which was further validated in a large independent cohort. Higher expression levels were found in RCTs compared to normal renal tissues (RNTs) and in chRCCs comparatively to oncocytomas. <i>SMYD2</i> and <i>SETD3</i> mRNA levels correlated with protein expression assessed by immunohistochemistry. <i>SMYD2</i> transcript levels discriminated RCTs from RNT, with 82.1% sensitivity and 100% specificity [area under curve (AUC) = 0.959], and distinguished chRCCs from oncocytomas, with 71.0% sensitivity and 73.3% specificity (AUC = 0.784). Low expression levels of <i>SMYD2, SETD3</i>, and <i>NO66</i> were significantly associated with shorter disease-specific and disease-free survival, especially in patients with non-organ confined tumors. We conclude that expression of selected HMTs and HDMs might constitute novel biomarkers to assist in RCT diagnosis and assessment of tumor aggressiveness.

肾细胞肿瘤（Renal cell tumors, RCTs）是临床常见泌尿系统恶性肿瘤中致死性最强的亚型。影像学检查的广泛应用使得小肾肿物的检出率显著提升，这也凸显了准确区分良性与恶性肾细胞肿瘤的迫切需求——而该区分对于制定合理的治疗方案至关重要。组蛋白甲基化（histone methylation）已被证实参与肾肿瘤发生过程，但其作为肾细胞肿瘤生物标志物的潜在临床价值仍未得到充分探索。因此，本研究的核心目标是筛选出差异表达的组蛋白甲基转移酶（histone methyltransferases, HMTs）与组蛋白去甲基化酶（histone demethylases, HDMs），以期将其用于肾细胞肿瘤的诊断与预后评估，重点关注嗜酸性细胞瘤（oncocytoma，良性肿瘤）与肾细胞癌（renal cell carcinoma, RCC），尤其是嫌色细胞亚型（chromophobe subtype, chRCC）之间的鉴别诊断。我们在一组肾细胞肿瘤样本中发现，SMYD2、SETD3与NO66这3个基因的表达水平存在显著异常，该结果随后在大型独立队列中得到了验证。与正常肾组织（normal renal tissues, RNTs）相比，肾细胞肿瘤样本中的上述基因表达水平更高；而相较于嗜酸性细胞瘤，嫌色细胞肾细胞癌中的基因表达水平同样更高。SMYD2与SETD3的mRNA表达水平与免疫组化（immunohistochemistry）检测得到的蛋白表达水平呈显著相关。SMYD2的转录本表达水平可有效区分肾细胞肿瘤与正常肾组织，灵敏度达82.1%，特异度达100%[曲线下面积（area under curve, AUC）=0.959]；同时可区分嫌色细胞肾细胞癌与嗜酸性细胞瘤，灵敏度为71.0%，特异度为73.3%（AUC=0.784）。SMYD2、SETD3与NO66的低表达水平与更短的疾病特异性生存期（disease-specific survival）及无病生存期（disease-free survival）显著相关，在非器官局限性肿瘤（non-organ confined tumors）患者中这一关联尤为显著。本研究最终表明，筛选出的组蛋白甲基转移酶与去甲基化酶的表达水平有望成为新型生物标志物，用于辅助肾细胞肿瘤的诊断以及肿瘤侵袭性（tumor aggressiveness）的评估。