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—SMYD2, SETD3, and NO66—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. SMYD2 and SETD3 mRNA levels correlated with protein expression assessed by immunohistochemistry. SMYD2 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 SMYD2, SETD3, and NO66 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）是泌尿系统常见恶性肿瘤中致死性最高的一类。随着影像学检查的广泛普及，肾脏小肿物的检出率显著升高，因此精准区分良恶性肾细胞肿瘤的需求愈发迫切，这对制定合理的治疗策略至关重要。组蛋白甲基化已被证实参与肾肿瘤发生发展过程，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挖掘。
本研究的核心目标为筛选可用于肾细胞肿瘤诊断与预后评估的差异表达组蛋白甲基转移酶（histone methyltransferases, HMTs）与组蛋白去甲基化酶（histone demethylases, HDMs），重点区分嗜酸性细胞瘤（良性肾肿瘤）与肾细胞癌（renal cell carcinoma, RCC），尤其是其嫌色细胞亚型（chromophobe subtype, chRCC）。
本研究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，并在大型独立验证队列中得到了证实。相较于正常肾组织（normal renal tissues, RNTs），肾细胞肿瘤中上述基因的表达水平显著升高；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亦更高。免疫组织化学检测结果显示，SMYD2与SETD3的mRNA表达水平与其蛋白表达水平呈显著正相关。
SMYD2的转录水平可有效区分肾细胞肿瘤与正常肾组织，灵敏度达82.1%、特异性达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%、特异性为73.3%（AUC=0.784）。低表达SMYD2、SETD3与NO66的患者，其疾病特异性生存期与无病生存期均显著缩短，这一关联在非器官局限性肿瘤患者中尤为显著。
综上，筛选出的组蛋白甲基转移酶与去甲基化酶的表达水平，有望成为辅助肾细胞肿瘤诊断及评估肿瘤侵袭性的新型生物标志物。