Matouk Imad J, Mezan Shaul, Mizrahi Aya, Ohana Patricia, Abu-Lail Rasha, Fellig Yakov, Degroot Nathan, Galun Eithan, Hochberg Abraham
The Department of Biological Chemistry, Alexander Silberman Institute of life Science, The Hebrew University of Jerusalem, Israel.
Biochim Biophys Acta. 2010 Apr;1803(4):443-51. doi: 10.1016/j.bbamcr.2010.01.010. Epub 2010 Feb 1.
Expression of the imprinted H19 gene is remarkably elevated in a large number of human cancers. Recently, we reported that H19 RNA is up-regulated in hypoxic stress and furthermore, it possesses oncogenic properties. However, the underlying mechanism(s) of these phenomena remain(s) unknown. Here we demonstrate a tight correlation between H19 RNA elevation by hypoxia and the status of the p53 tumor suppressor. Wild type p53 (p53(wt)) prevents the induction of H19 upon hypoxia, and upon its reconstitution in p53(null) cells. The last case is accompanied by a decrease in cell viability. The p53 effect is nuclear and seems independent of its tetramerization. Furthermore, using knockdown and over-expression approaches we identified HIF1-alpha as a critical factor that is responsible for H19 induction upon hypoxia. Knocking down HIF1-alpha abolishes H19 RNA induction, while its over-expression significantly enhances the H19 elevation in p53(null) hypoxic cells. In p53(wt) hypoxic cells simultaneous suppression of p53 and over-expression of HIF1-alpha are needed to induce H19 significantly, while each treatment separately resulting in a mild induction, indicating that the molecular mechanism of p53 suppression effect on H19 may at least in part involve interfering with HIF1-alpha activity. In vivo a significant increase in H19 expression occurred in tumors derived from p53(null) cells but not in p53(wt) cells. Taken together, our results indicate that a functional link exists between p53, HIF1-alpha and H19 that determines H19 elevation in hypoxic cancer cells. We suggest that this linkage plays a role in tumor development.
印记基因H19在大量人类癌症中表达显著升高。最近，我们报道H19 RNA在缺氧应激中上调，此外，它具有致癌特性。然而，这些现象的潜在机制仍然未知。在这里，我们证明了缺氧导致的H19 RNA升高与p53肿瘤抑制因子的状态之间存在紧密关联。野生型p53（p53(wt)）可防止缺氧时H19的诱导，以及在p53缺失细胞中重新构建时的诱导。后一种情况伴随着细胞活力的降低。p53的作用是在细胞核内，且似乎与其四聚化无关。此外，通过基因敲低和过表达方法，我们确定缺氧诱导H19的关键因子是HIF1-α。敲低HIF1-α可消除H19 RNA的诱导，而过表达则显著增强p53缺失缺氧细胞中H19的升高。在p53(wt)缺氧细胞中，同时抑制p53和过表达HIF1-α才能显著诱导H19，而单独每种处理仅导致轻度诱导，这表明p53对H19抑制作用的分子机制可能至少部分涉及干扰HIF1-α的活性。在体内，源自p53缺失细胞的肿瘤中H19表达显著增加，而源自p53(wt)细胞的肿瘤中则没有。综上所述，我们的结果表明p53、HIF1-α和H19之间存在功能联系，这决定了缺氧癌细胞中H19的升高。我们认为这种联系在肿瘤发展中起作用。
