Implication of IRF4 Aberrant Gene Expression in the Acute Leukemias of Childhood

The most frequent targets of genetic alterations in human leukemias are transcription factor genes with essential functions in normal blood cell development. The Interferon Regulatory Factor 4 (IRF4) gene encodes a transcription factor important for key developmental stages of hematopoiesis, with known oncogenic implications in multiple myeloma, adult leukemias and lymphomas. Very few studies have reported an association of IRF4 with childhood malignancy, whereas high transcript levels have been observed in the more mature immunophenotype of ALL. Our aim was to investigate the expression levels of IRF4 in the diagnostic samples of pediatric leukemias and compare them to those of healthy controls, in order to determine aberrant gene expression and whether it extends to leukemic subtypes other than the relatively mature ALL subpopulation. Quantitative real-time RT-PCR methodology was used to investigate IRF4 expression in 58 children with acute leukemias, 4 leukemic cell lines and 20 healthy children. We show that aberrant IRF4 gene expression is implicated in a variety of leukemic subtypes; higher transcript levels appear in the more immature B-common ALL subtype and in T-cell than in B-cell leukemias, with the highest expression levels appearing in the AML group. Interestingly, we show that childhood leukemia, irrespective of subtype or cell maturation stage, is characterised by a minimum of approximately twice the amount of IRF4 gene expression encountered in healthy children. A statistically significant correlation also appeared to exist between high IRF4 expression and relapse. Our results show that ectopic expression of IRF4 follows the reverse expression pattern of what is encountered in normal B-cell development and that there might be a dose-dependency of childhood leukemia for aberrantly expressed IRF4, a characteristic that could be explored therapeutically. It is also suggested that high IRF4 expression might be used as an additional prognostic marker of relapse at diagnosis.

人类白血病中最常见的遗传变异靶点，是在正常血细胞发育中发挥核心功能的转录因子基因。干扰素调节因子4（Interferon Regulatory Factor 4, IRF4）基因编码一种对造血过程关键发育阶段具有重要作用的转录因子，目前已知其在多发性骨髓瘤、成人白血病及淋巴瘤中存在致癌作用。目前鲜有研究报道IRF4与儿童恶性肿瘤的关联，但此前已在急性淋巴细胞白血病（Acute Lymphoblastic Leukemia, ALL）的成熟免疫表型中观察到高转录本水平。

本研究旨在检测儿童白血病诊断样本中IRF4的表达水平，并与健康对照样本进行比对，以明确其基因异常表达情况，以及该异常是否不仅局限于相对成熟的ALL亚群，还可拓展至其他白血病亚型。本研究采用实时定量逆转录聚合酶链反应（quantitative real-time RT-PCR）方法，对58例急性白血病患儿、4株白血病细胞系及20例健康儿童的样本进行IRF4表达检测。

研究结果显示，IRF4基因异常表达与多种白血病亚型相关；相较于B细胞白血病，未成熟程度更高的普通B型ALL亚群及T细胞型白血病中IRF4转录本水平更高，而急性髓系白血病（Acute Myeloid Leukemia, AML）组的表达水平最高。值得注意的是，本研究证实，无论亚型或细胞成熟阶段如何，儿童白血病的IRF4基因表达量至少为健康儿童的两倍左右。此外，高IRF4表达与疾病复发之间存在统计学意义上的显著相关性。

本研究结果表明，IRF4的异位表达模式与正常B细胞发育中的表达模式完全相反，且儿童白血病的发生可能与IRF4异常表达的剂量依赖性相关，这一特性可为治疗干预提供潜在方向。同时，研究提示IRF4高表达可作为诊断时预测疾病复发的额外预后标志物。