Scardocci A, Guidi F, D'Alo' F, Gumiero D, Fabiani E, Diruscio A, Martini M, Larocca L M, Zollino M, Hohaus S, Leone G, Voso M T
Istituti di Ematologia, di, Universita' Cattolica Sacro Cuore, L.go A. Gemelli 1, 00168 Roma, Italy.
Br J Cancer. 2006 Oct 23;95(8):1108-13. doi: 10.1038/sj.bjc.6603392.
BRCA1 plays a pivotal role in the repair of DNA damage, especially following chemotherapy and ionising radiation. We were interested in the regulation of BRCA1 expression in acute myeloid leukaemia (AML), in particular in therapy-related forms (t-AML). Using real-time PCR and Western blot, we found that BRCA1 mRNA was expressed at barely detectable levels by normal peripheral blood granulocytes, monocytes and lymphocytes, whereas control BM-mononuclear cells and selected CD34+ progenitor cells displayed significantly higher BRCA1 expression (P=0.0003). Acute myeloid leukaemia samples showed heterogeneous BRCA1 mRNA levels, which were lower than those of normal bone marrows (P=0.0001). We found a high frequency of hypermethylation of the BRCA1 promoter region in AML (51/133 samples, 38%), in particular in patients with karyotypic aberrations (P=0.026), and in t-AML, as compared to de novo AML (76 vs 31%, P=0.0002). Examining eight primary tumour samples from hypermethylated t-AML patients, BRCA1 was hypermethylated in three of four breast cancer samples, whereas it was unmethylated in the other four tumours. BRCA1 hypermethylation correlated to reduced BRCA1 mRNA (P=0.0004), and to increased DNA methyltransferase DNMT3A (P=0.003) expression. Our data show that reduced BRCA1 expression owing to promoter hypermethylation is frequent in t-AML and that this could contribute to secondary leukaemogenesis.
BRCA1在DNA损伤修复中起关键作用，尤其是在化疗和电离辐射后。我们对急性髓系白血病（AML）中BRCA1表达的调控感兴趣，特别是在治疗相关型（t-AML）中。通过实时PCR和蛋白质印迹法，我们发现正常外周血粒细胞、单核细胞和淋巴细胞中BRCA1 mRNA的表达水平几乎检测不到，而对照骨髓单个核细胞和选定的CD34+祖细胞显示出明显更高的BRCA1表达（P = 0.0003）。急性髓系白血病样本显示BRCA1 mRNA水平存在异质性，低于正常骨髓样本（P = 0.0001）。我们发现AML中BRCA1启动子区域的高甲基化频率较高（51/133个样本，38%），尤其是核型异常的患者（P = 0.026），与初发AML相比，t-AML中的高甲基化频率更高（76%对31%，P = 0.0002）。检测来自高甲基化t-AML患者的8个原发性肿瘤样本，4个乳腺癌样本中有3个BRCA1发生高甲基化，而其他4个肿瘤中未甲基化。BRCA1高甲基化与BRCA1 mRNA减少相关（P = 0.0004），与DNA甲基转移酶DNMT3A表达增加相关（P = 0.003）。我们的数据表明，由于启动子高甲基化导致的BRCA1表达降低在t-AML中很常见，这可能促成继发性白血病的发生。
