IRF8 regulates acid ceramidase expression to mediate apoptosis and suppresses myelogeneous leukemia.
IRF8 regulates acid ceramidase expression to mediate apoptosis and suppresses myelogeneous leukemia.
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DOI：
10.1158/0008-5472.can-10-2493
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发表时间：
2011-04-15
期刊：
影响因子：
11.2
通讯作者：
Liu K
中科院分区：
文献类型：
--
作者：
Hu X;Yang D;Zimmerman M;Liu F;Yang J;Kannan S;Burchert A;Szulc Z;Bielawska A;Ozato K;Bhalla K;Liu K
干扰素调节因子8(IRF8)是髓系细胞分化的关键转录因子，在人髓系白血病患者的造血细胞中经常表达缺失。IRF8基因缺陷的小鼠表现出未分化的髓系细胞的不受控制的克隆性扩张，可进展到致命的原始细胞危象，从而类似于人类慢性粒细胞白血病(CML)。因此，IRF8是一种髓系白血病抑制因子。虽然对IRF8在慢性粒细胞白血病中的功能的了解最近有所改善，但其在CML中的作用的分子机制仍然很大程度上是未知的。在本研究中，我们确定酸性神经酰胺酶(A-CDase)是IRF8的通用转录靶标。我们证明了在髓系白血病细胞中，IRF8的表达受IRF8启动子DNA甲基化的调控。IRF8表达的恢复抑制了A-CDase的表达，导致C16神经酰胺积聚，增加了CML细胞对FasL诱导的凋亡的敏感性。在IRF8缺陷小鼠的髓系细胞中，A-CDase蛋白水平显著升高。此外，我们还证明了IRF8与A-CDase启动子直接结合。在功能水平上，抑制A-CDase的活性、沉默A-CDase的表达或应用外源性C16神经酰胺可使CML细胞对FasL诱导的细胞凋亡敏感，而A-CDase的过表达降低了CML细胞对FasL诱导的细胞凋亡的敏感性。因此，IRF8表达的恢复至少部分地通过Fas依赖的机制抑制了体内CML的发展。综上所述，我们的发现确定了CML细胞中IRF8下调的机制，并确定了抵抗Fas介导的细胞凋亡和疾病进展的主要途径。
IFN regulatory factor 8 (IRF8) is a key transcription factor for myeloid cell differentiation and its expression is frequently lost in hematopoietic cells of human myeloid leukemia patients. IRF8-deficient mice exhibit uncontrolled clonal expansion of undifferentiated myeloid cells that can progress to a fatal blast crisis, thereby resembling human chronic myelogeneous leukemia (CML). Therefore, IRF8 is a myeloid leukemia suppressor. While the understanding of IRF8 function in CML has recently improved, the molecular mechanisms underlying IRF8 function in CML is still largely unknown. In this study, we identified acid ceramidase (A-CDase) as a general transcription target of IRF8. We demonstrated that IRF8 expression is regulated by IRF8 promoter DNA methylation in myeloid leukemia cells. Restoration of IRF8 expression repressed A-CDase expression, resulting in C16 ceramide accumulation and increased sensitivity of CML cells to FasL-induced apoptosis. In myeloid cells derived from IRF8-deficient mice, A-CDase protein level was dramatically increased. Furthermore, we demonstrated that IRF8 directly bind to the A-CDase promoter. At the functional level, inhibition of A-CDase activity, silencing A-CDase expression or application of exogenous C16 ceramide sensitized CML cells to FasL-induced apoptosis, whereas, overexpression of A-CDase decreased CML cells sensitivity to FasL-induced apoptosis. Consequently, restoration of IRF8 expression suppressed CML development in vivo at least partially through a Fas-dependent mechanism. In summary, our findings determine the mechanism of IRF8 downregulation in CML cells and they determine a primary pathway of resistance to Fas-mediated apoptosis and disease progression.