Department of Cell Biology, The Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
EMBO J. 2011 Apr 6;30(7):1324-34. doi: 10.1038/emboj.2011.38. Epub 2011 Feb 22.
Expression of vascular endothelial growth factor-A (VEGFA) by tumour-associated macrophages is critical for tumour progression and metastasis. Hypoxia, a common feature of the neoplastic microenvironment, induces VEGFA expression by increased transcription, translation, and mRNA stabilization. Here, we report a new mechanism of VEGFA regulation by hypoxia that involves reversal of microRNA (miRNA)-mediated silencing of VEGFA expression. We show that the CA-rich element (CARE) in the human VEGFA 3'-UTR is targeted by at least four miRNAs. Among these miRNAs, miR-297 and -299 are endogenously expressed in monocytic cells and negatively regulate VEGFA expression. Unexpectedly, hypoxia completely reverses miRNA-mediated repression of VEGFA expression. We show that heterogeneous nuclear ribonucleoprotein L (hnRNP L), which also binds the VEGFA 3'-UTR CARE, prevents miRNA silencing activity. Hypoxia induces translocation of nuclear hnRNP L to the cytoplasm, which markedly increases hnRNP L binding to VEGFA mRNA thereby inhibiting miRNA activity. In summary, we describe a novel regulatory mechanism in which the interplay between miRNAs and RNA-binding proteins influences expression of a critical hypoxia-inducible angiogenic protein. These studies may contribute to provide miRNA-based anticancer therapeutic tools.
肿瘤相关巨噬细胞中血管内皮生长因子 A（VEGFA）的表达对于肿瘤的进展和转移至关重要。缺氧是肿瘤微环境的一个常见特征，通过增加转录、翻译和 mRNA 稳定化来诱导 VEGFA 的表达。在这里，我们报告了一种新的缺氧调节 VEGFA 的机制，该机制涉及 miRNA 介导的 VEGFA 表达沉默的逆转。我们表明，人 VEGFA 3'-UTR 中的 CA 丰富元件（CARE）是至少四种 miRNA 的靶标。在这些 miRNA 中，miR-297 和 miR-299 在单核细胞中内源性表达，并负调控 VEGFA 的表达。出乎意料的是，缺氧完全逆转了 miRNA 对 VEGFA 表达的抑制作用。我们表明，异质核核糖核蛋白 L（hnRNP L）也与 VEGFA 3'-UTR CARE 结合，可防止 miRNA 沉默活性。缺氧诱导核 hnRNP L 向细胞质易位，从而显著增加 hnRNP L 与 VEGFA mRNA 的结合，从而抑制 miRNA 的活性。总之，我们描述了一种新的调节机制，其中 miRNA 和 RNA 结合蛋白之间的相互作用影响关键的缺氧诱导血管生成蛋白的表达。这些研究可能有助于提供 miRNA 为基础的抗癌治疗工具。
