Yang Chuan He, Pfeffer Susan R, Sims Michelle, Yue Junming, Wang Yinan, Linga Vijay G, Paulus Elena, Davidoff Andrew M, Pfeffer Lawrence M
From the Departments of Pathology and Laboratory Medicine, the Center for Cancer Research, University of Tennessee Health Science Center, Memphis, Tennessee 38163 and.
Surgery, and.
J Biol Chem. 2015 Mar 6;290(10):6037-46. doi: 10.1074/jbc.M114.632125. Epub 2015 Jan 14.
The microRNA miR-21 is overexpressed in most human cancers and accumulating evidence indicates that it functions as an oncogene. Since miRNAs suppress the expression of their target genes, we hypothesized that some miR-21 targets may act as tumor suppressors, and thus their expression would be anticipated to be reduced by the high miR-21 levels observed in various human cancers. By microarray analysis and quantitative PCR we identified and validated FBXO11 (a member of the F-box subfamily lacking a distinct unifying domain) as a miR-21 target gene. FBXO11 is a component of the SKP1-CUL1-F-box ubiquitin ligase complex that targets proteins for ubiquitination and proteosomal degradation. By loss of function and gain of function studies, we show that FBXO11 acts as a tumor suppressor, promotes apoptosis and mediates the degradation of the oncogenic protein BCL6. The critical role that FBXO11 plays in miR-21-mediated tumorigenesis was demonstrated by a rescue experiment, in which silencing FBXO11 in miR-21KD cancer cells restored their high tumorigenicity. Expression of miR-21 and FBXO11 are inversely correlated in tumor tissue, and their expression correlates with patient survival and tumor grade. High FBXO11 expression correlates with better patient survival and lower tumor grade consistent with its tumor suppressor activity. In contrast high miR-21 expression, which correlates with poor patient survival and higher tumor grade, is consistent with its oncogenic activity. Our results identify FBXO11 as a novel miR-21 target gene, and demonstrate that the oncogenic miRNA miR-21 decreases the expression of FBXO11, which normally acts as a tumor suppressor, and thereby promotes tumorigenesis.
微小RNA miR-21在大多数人类癌症中过表达，越来越多的证据表明它起着癌基因的作用。由于微小RNA会抑制其靶基因的表达，我们推测一些miR-21的靶标可能作为肿瘤抑制因子发挥作用，因此预计它们的表达会因在各种人类癌症中观察到的高miR-21水平而降低。通过微阵列分析和定量PCR，我们鉴定并验证了FBXO11（F-box亚家族的一个成员，缺乏独特的统一结构域）作为miR-21的靶基因。FBXO11是SKP1-CUL1-F-box泛素连接酶复合物的一个组成部分，该复合物将蛋白质靶向泛素化和蛋白酶体降解。通过功能丧失和功能获得研究，我们表明FBXO11作为肿瘤抑制因子发挥作用，促进细胞凋亡并介导致癌蛋白BCL6的降解。一项挽救实验证明了FBXO11在miR-21介导的肿瘤发生中的关键作用，在该实验中，在miR-21KD癌细胞中沉默FBXO11恢复了它们的高致瘤性。miR-21和FBXO11的表达在肿瘤组织中呈负相关，并且它们的表达与患者生存率和肿瘤分级相关。高FBXO11表达与更好的患者生存率和更低的肿瘤分级相关，这与其肿瘤抑制活性一致。相比之下，高miR-21表达与较差的患者生存率和较高的肿瘤分级相关，这与其致癌活性一致。我们的结果鉴定FBXO11为一个新的miR-21靶基因，并证明致癌性微小RNA miR-21降低了通常作为肿瘤抑制因子的FBXO11的表达，从而促进肿瘤发生。
