National Brain Research Centre, Manesar, Haryana, 122 050, India.
J Mol Med (Berl). 2011 Feb;89(2):123-36. doi: 10.1007/s00109-010-0683-5. Epub 2010 Sep 24.
We observed elevated levels of pro-inflammatory cytokine IL-1β in glioblastoma multiforme tumor samples. Since hypoxia-inducible factor-1α (HIF-1α) plays a crucial role in linking inflammatory and oncogenic pathways, we investigated the effect of IL-1β on HIF-1α expression in glioma cells under normoxia. IL-1β-mediated elevation of HIF-1α transcriptional activity was dependent on Ras-induced NF-κB activation, as IL-1β failed to induce NF-κB and HIF-1α activity in cells transfected with dominant negative RasN17. Increased Ras expression was accompanied by increased phosphorylation of Ras effectors AKT, ERK, JNK, and p38MAPK. While inhibition of these effectors individually failed to block the IL-1β-mediated increase in HIF-1α induction, co-inhibition of both AKT and ERK resulted in a significant decrease in IL-1β-induced HIF-1α activation. Interestingly, IL-1β elevated Wnt-1 expression in a Ras-dependent manner, and small interfering RNA (siRNA)-mediated knockdown of Wnt-1 decreased HIF-1α activity. Although Wnt-1-mediated HIF-1α was independent of the canonical Wnt/β-catenin signaling pathway, it regulated HIF-1α through NF-κB. siRNA-mediated HIF-1α knockdown attenuated elevated IL-1β mRNA levels induced upon IL-1β treatment. This was accompanied by increased interaction of HIF-1α with HIF responsive element on the IL-1β promoter upon IL-1β treatment, under normoxia. Our studies highlights for first time that (1) Ras is a key mediator of IL-1β-induced NF-κB and HIF-1α activation, under normoxia; (2) Wnt-1 regulates IL-1β-mediated HIF-1α induction via NF-κB; (3) Ras and Wnt-1 are intermediaries in the canonical IL-1β-NF-κB signaling pathway downstream of MyD88; and (4) IL-1β-induced HIF-1α drives a HIF-1α-IL-1β autocrine loop to maintain persistently elevated IL-1β level.
我们观察到多形性胶质母细胞瘤肿瘤样本中促炎细胞因子 IL-1β水平升高。由于缺氧诱导因子-1α(HIF-1α)在连接炎症和致癌途径方面起着至关重要的作用,我们研究了 IL-1β在常氧条件下对胶质瘤细胞中 HIF-1α表达的影响。IL-1β介导的 HIF-1α转录活性的升高依赖于 Ras 诱导的 NF-κB 激活,因为在转染显性失活 RasN17 的细胞中,IL-1β未能诱导 NF-κB 和 HIF-1α活性。Ras 表达增加伴随着 Ras 效应物 AKT、ERK、JNK 和 p38MAPK 的磷酸化增加。虽然这些效应物的单独抑制未能阻断 IL-1β介导的 HIF-1α诱导增加,但 AKT 和 ERK 的共同抑制导致 IL-1β 诱导的 HIF-1α 激活显著减少。有趣的是,IL-1β以 Ras 依赖性方式上调 Wnt-1 表达,并且 Wnt-1 的小干扰 RNA(siRNA)介导的敲低降低了 HIF-1α 活性。虽然 Wnt-1 介导的 HIF-1α不依赖于经典的 Wnt/β-catenin 信号通路,但它通过 NF-κB 调节 HIF-1α。HIF-1α 的 siRNA 介导的敲低减弱了 IL-1β 处理后诱导的升高的 IL-1β mRNA 水平。这伴随着在常氧条件下,IL-1β 处理后 HIF-1α与 IL-1β 启动子上的 HIF 反应元件的相互作用增加。我们的研究首次强调:(1)Ras 是 IL-1β 诱导的 NF-κB 和 HIF-1α 激活的关键介质;(2)Wnt-1 通过 NF-κB 调节 IL-1β 介导的 HIF-1α 诱导;(3)Ras 和 Wnt-1 是 MyD88 下游经典 IL-1β-NF-κB 信号通路的中间介质;(4)IL-1β 诱导的 HIF-1α 驱动 HIF-1α-IL-1β 自分泌环以维持持续升高的 IL-1β 水平。
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