Département d'Immunologie-Hématologie, Institut Cochin, Paris, France.
Mol Cancer Res. 2013 Jul;11(7):724-35. doi: 10.1158/1541-7786.MCR-12-0607. Epub 2013 Apr 19.
The death domain containing TNF receptor 6 (CD95/Fas) is a direct target for the NF-κB transcription factor and is repressed in solid tumors such as colon carcinomas. Previously, we reported that the Fas death receptor, while overexpressed in low-risk myelodysplastic syndromes (MDS), becomes undetectable on CD34(+) progenitors when the disease progresses to secondary acute myeloid leukemia (AML). This study determined the interplay between NF-κB and Fas during MDS progression. We first observed that Fas was induced by TNF-α in the HL60 cell line. In these cells, p65 (RELA) was associated with the FAS promoter, and inhibition of the NF-κB pathway by an IKKα inhibitor (BAY11-7082) or lentiviral expression of a nondegradable mutant of IκBα (IκSR) blocked Fas expression. In contrast, TNF-α failed to induce Fas expression in the colon carcinoma cell line SW480, due to hypermethylation of the FAS promoter. Azacitidine rescued p65 binding on FAS promoter in vitro, and subsequently Fas expression in SW480 cells. Furthermore, inhibition of the NF-κB pathway decreased the expression of Fas in MDS CD45(lo)CD34(+) bone marrow cells. However, despite the nuclear expression of p65, Fas was often low on CD45(lo)CD34(+) AML cells. TNF-α failed to stimulate its expression, while azacitidine efficiently rescued p65 binding and Fas reexpression. Overall, these data suggest that DNA methylation at NF-κB sites is responsible for FAS gene silencing.
死亡结构域包含 TNF 受体 6（CD95/Fas）是 NF-κB 转录因子的直接靶标，在结肠癌等实体瘤中受到抑制。先前，我们报道 Fas 死亡受体在低危骨髓增生异常综合征（MDS）中过度表达，但当疾病进展为继发性急性髓系白血病（AML）时，在 CD34+祖细胞上无法检测到。本研究确定了 NF-κB 和 Fas 之间在 MDS 进展过程中的相互作用。我们首先观察到 TNF-α 在 HL60 细胞系中诱导 Fas。在这些细胞中，p65（RELA）与 FAS 启动子结合，NF-κB 途径的抑制（通过 IKKα 抑制剂（BAY11-7082）或非降解型 IκBα 突变体（IκSR）的慢病毒表达）阻断 Fas 表达。相比之下，TNF-α 未能诱导结肠癌细胞系 SW480 中 Fas 的表达，这是由于 FAS 启动子的高度甲基化。阿扎胞苷在体外挽救了 FAS 启动子上的 p65 结合，随后在 SW480 细胞中表达 Fas。此外，NF-κB 途径的抑制降低了 MDS CD45（lo）CD34+骨髓细胞中 Fas 的表达。然而，尽管存在 p65 的核表达，CD45（lo）CD34+AML 细胞上 Fas 通常较低。TNF-α 未能刺激其表达，而阿扎胞苷有效地挽救了 p65 结合和 Fas 重新表达。总的来说，这些数据表明 NF-κB 位点的 DNA 甲基化是 FAS 基因沉默的原因。
