Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
J Biol Chem. 2011 Jul 15;286(28):25377-86. doi: 10.1074/jbc.M111.222760. Epub 2011 May 18.
Epidermal growth factor receptor (EGFR) is involved in development and progression of many human cancers. We have previously demonstrated that the ubiquitin-specific peptidase Usp18 (Ubp43) is a potent regulator of EGFR protein expression. Here we report that the 3'-untranslated region (3'-UTR) of the EGFR message modulates RNA translation following cell treatment with Usp18 siRNA, suggesting microRNA as a possible mediator. Given earlier evidence of EGFR regulation by the microRNA miR-7, we assessed whether miR-7 mediates Usp18 siRNA effects. We found that Usp18 depletion elevates miR-7 levels in several cancer cell lines because of a transcriptional activation and/or mRNA stabilization of miR-7 host genes and that miR-7 acts downstream of Usp18 to regulate EGFR mRNA translation via the 3'-UTR. Also, depletion of Usp18 led to a decrease in protein levels of other known oncogenic targets of miR-7, reduced cell proliferation and soft agar colony formation, and increased apoptosis. Notably, all of these phenotypes were reversed by a specific inhibitor of miR-7. Thus, our findings support a model in which Usp18 inhibition promotes up-regulation of miR-7, which in turn inhibits EGFR expression and the tumorigenic activity of cancer cells.
表皮生长因子受体（EGFR）参与许多人类癌症的发展和进展。我们之前已经证明，泛素特异性肽酶 Usp18（Ubp43）是 EGFR 蛋白表达的有效调节剂。在这里，我们报告 EGFR 消息的 3'-非翻译区（3'-UTR）在细胞用 Usp18 siRNA 处理后调节 RNA 翻译，表明 microRNA 可能是一种可能的介导物。鉴于先前有证据表明 EGFR 受 microRNA miR-7 调节，我们评估了 miR-7 是否介导 Usp18 siRNA 的作用。我们发现，由于 miR-7 宿主基因的转录激活和/或 mRNA 稳定，Usp18 耗尽会在几种癌细胞系中升高 miR-7 水平，并且 miR-7 作为 Usp18 的下游因子通过 3'-UTR 调节 EGFR mRNA 翻译。此外，Usp18 的耗竭导致其他已知的 miR-7 致癌靶蛋白的蛋白质水平降低，细胞增殖和软琼脂集落形成减少，凋亡增加。值得注意的是，所有这些表型都被 miR-7 的特异性抑制剂逆转。因此，我们的发现支持这样一种模型，即 Usp18 抑制促进 miR-7 的上调，反过来又抑制 EGFR 表达和癌细胞的致瘤活性。
