Department of Pathology, Vall d'Hebron University Hospital, Faculty of Biosciences, and Department of Biochemistry and Molecular Biology, Universitat Autónoma de Barcelona, Barcelona, Spain.
Oncol Rep. 2012 Jan;27(1):225-31. doi: 10.3892/or.2011.1462. Epub 2011 Sep 14.
Translational control is a crucial component of cancer development and progression. Eukaryotic initiation factor (eIF) 4E mediates eIF4F association with the mRNA 5' cap structure to stimulate cap-dependent translation initiation. The eIF4E-binding protein, 4E-BP1, regulates cap-dependent translation through its phosphorylation at multiple sites. It has been described that some human carcinomas present a high level of p-4E-BP1, not always associated with high levels of p-mTOR. These previous observations suggest that other kinases could be involved in 4E-BP1 phosporylation. Investigation in new kinases that could be implicated in 4E-BP1 phosphorylation and mechanisms that affect 4E-BP1 stability is important to understand the role of eIF4E in cell transformation. In this study, we examined 48 kinases that could be involved in 4E-BP1 phosphorylation and stability. The screening study was based on analysis of 4E-BP1 status after inhibition of these kinases in a breast carcinoma cell line. Several kinases affecting 4E-BP1 stability (LRRK2, RAF-1, p38γ, GSK3β, AMPKα, PRKACA and PRKACB) and 4E-BP1 phosphorylation (CDK1, PDK1, SRC, PRKCB1, PAK2, p38β, PRKCA and CaMKKB) were identified. These findings provide evidence that 4E-BP1 can be regulated and stabilized by multiple kinases implicated in several cell signaling pathways. We focus on the finding that LRRK2 down-regulation was associated with a clearly decreased 4E-BP1 protein (and not with mRNA down-regulation). Importantly, knockdown of LRRK2 associated with high proliferative rate in normal cells and treatment with rapamycin and/or proteosome inhibition suppressed 4E-BP1 protein degradation. These results offer new insights into the regulation of total and phosphorylated 4E-BP1.
翻译控制是癌症发生和发展的关键组成部分。真核起始因子（eIF）4E 介导 eIF4F 与 mRNA 5'帽结构的结合，以刺激帽依赖性翻译起始。eIF4E 结合蛋白 4E-BP1 通过其在多个位点的磷酸化来调节帽依赖性翻译。已经描述了一些人类癌瘤表现出高水平的 p-4E-BP1，并不总是与高水平的 p-mTOR 相关。这些先前的观察结果表明，其他激酶可能参与 4E-BP1 的磷酸化。研究可能参与 4E-BP1 磷酸化的新激酶以及影响 4E-BP1 稳定性的机制对于理解 eIF4E 在细胞转化中的作用很重要。在这项研究中，我们检查了 48 种可能参与 4E-BP1 磷酸化和稳定性的激酶。该筛选研究基于在乳腺癌细胞系中抑制这些激酶后 4E-BP1 状态的分析。鉴定了几种影响 4E-BP1 稳定性的激酶（LRRK2、RAF-1、p38γ、GSK3β、AMPKα、PRKACA 和 PRKACB）和 4E-BP1 磷酸化的激酶（CDK1、PDK1、SRC、PRKCB1、PAK2、p38β、PRKCA 和 CaMKKB）。这些发现提供了证据，表明 4E-BP1 可以被多种涉及几种细胞信号通路的激酶调节和稳定。我们专注于发现 LRRK2 的下调与 4E-BP1 蛋白的明显减少（而不是与 mRNA 下调）相关。重要的是，LRRK2 的敲低与正常细胞中的高增殖率相关，并且用雷帕霉素和/或蛋白酶体抑制处理抑制了 4E-BP1 蛋白的降解。这些结果为调节总和磷酸化 4E-BP1 提供了新的见解。
