Dubois Ludwig, Magagnin Michaël G, Cleven Arjen H G, Weppler Sherry A, Grenacher Beat, Landuyt Willy, Lieuwes Natasja, Lambin Philippe, Gorr Thomas A, Koritzinsky Marianne, Wouters Bradly G
Department of Radiation Oncology (Maastro Laboratory), GROW-School for Oncology and Developmental Biology, Maastricht University, Maastricht, the Netherlands.
Int J Radiat Oncol Biol Phys. 2009 Mar 15;73(4):1219-27. doi: 10.1016/j.ijrobp.2008.12.003.
Eukaryotic initiation factor 4E (eIF4E) is an essential rate-limiting factor for cap-dependent translation in eukaryotic cells. Elevated eIF4E activity is common in many human tumors and is associated with disease progression. The growth-promoting effects of eIF4E are in turn negatively regulated by 4E-BP1. However, although 4E-BP1 harbors anti-growth activity, its expression is paradoxically elevated in some tumors. The aim of this study was to investigate the functional role of 4E-BP1 in the context of solid tumors.
In vitro and in vivo growth properties, hypoxia tolerance, and response to radiation were assessed for HeLa and U87 cells, after stable expression of shRNA specific for 4E-BP1.
We found that loss of 4E-BP1 expression did not significantly alter in vitro growth but did accelerate the growth of U87 tumor xenografts, consistent with the growth-promoting function of deregulated eIF4E. However, cells lacking 4E-BP1 were significantly more sensitive to hypoxia-induced cell death in vitro. Furthermore, 4E-BP1 knockdown cells produced tumors more sensitive to radiation because of a reduction in the viable fraction of radioresistant hypoxic cells. Decreased hypoxia tolerance in the 4E-BP1 knockdown tumors was evident by increased cleaved caspase-3 levels and was associated with a reduction in adenosine triphosphate (ATP).
Our results suggest that although tumors often demonstrate increases in cap-dependent translation, regulation of this activity is required to facilitate energy conservation, hypoxia tolerance, and tumor radioresistance. Furthermore, we suggest that targeting translational control may be an effective way to target hypoxic cells and radioresistance in metabolically hyperactive tumors.
真核生物起始因子4E（eIF4E）是真核细胞中帽依赖性翻译的关键限速因子。eIF4E活性升高在许多人类肿瘤中很常见，且与疾病进展相关。eIF4E的促生长作用反过来受到4E-BP1的负调控。然而，尽管4E-BP1具有抗生长活性，但其表达在某些肿瘤中却反常地升高。本研究旨在探讨4E-BP1在实体瘤中的功能作用。
在稳定表达针对4E-BP1的短发夹RNA（shRNA）后，评估HeLa和U87细胞的体外和体内生长特性、缺氧耐受性及对辐射的反应。
我们发现，4E-BP1表达缺失并未显著改变体外生长，但确实加速了U87肿瘤异种移植瘤的生长，这与eIF4E失调的促生长功能一致。然而，缺乏4E-BP1的细胞在体外对缺氧诱导的细胞死亡更为敏感。此外，由于抗辐射缺氧细胞的存活分数降低，4E-BP1基因敲低的细胞产生的肿瘤对辐射更敏感。4E-BP1基因敲低的肿瘤中缺氧耐受性降低表现为裂解的半胱天冬酶-3水平升高，且与三磷酸腺苷（ATP）减少有关。
我们的结果表明，尽管肿瘤通常表现出帽依赖性翻译增加，但调节这种活性对于促进能量保存、缺氧耐受性和肿瘤抗辐射性是必需的。此外，我们认为靶向翻译控制可能是靶向代谢活跃肿瘤中的缺氧细胞和抗辐射性的有效方法。
