Department of Pathology, Nanjing Medical University, Nanjing, Jiangsu, China.
Department of Breast Surgery, Institute of Breast Disease, The Second Hospital of Dalian Medical University, Dalian, Liaoning, China.
Mol Cancer. 2021 Feb 2;20(1):25. doi: 10.1186/s12943-021-01321-x.
E3 ubiquitin ligase HRD1 (HMG-CoA reductase degradation protein 1, alias synoviolin with SYVN1 as the official gene symbol) was found downregulated and acting as a tumor suppressor in breast cancer, while the exact expression profile of HRD1 in different breast cancer subtypes remains unknown. Recent studies characterized circular RNAs (circRNAs) playing an regulatory role as miRNA sponge in tumor progression, presenting a new viewpoint for the post-transcriptional regulation of cancer-related genes.
Examination of the expression of HRD1 protein and mRNA was implemented using public microarray/RNA-sequencing datasets and breast cancer tissues/cell lines. Based on public RNA-sequencing results, online databases and enrichment/clustering analyses were used to predict the specific combinations of circRNA/miRNA that potentially govern HRD1 expression. Gain-of-function and rescue experiments in vitro and in vivo were executed to evaluate the suppressive effects of circNR3C2 on breast cancer progression through HRD1-mediated proteasomal degradation of Vimentin, which was identified using immunoblotting, immunoprecipitation, and in vitro ubiquitination assays.
HRD1 is significantly underexpressed in triple-negative breast cancer (TNBC) against other subtypes and has an inverse correlation with Vimentin, inhibiting the proliferation, migration, invasion and EMT (epithelial-mesenchymal transition) process of breast cancer cells via inducing polyubiquitination-mediated proteasomal degradation of Vimentin. CircNR3C2 (hsa_circ_0071127) is also remarkably downregulated in TNBC, negatively correlated with the distant metastasis and lethality of invasive breast carcinoma. Overexpressing circNR3C2 in vitro and in vivo leads to a crucial enhancement of the tumor-suppressive effects of HRD1 through sponging miR-513a-3p.
Collectively, we elucidated a bona fide circNR3C2/miR-513a-3p/HRD1/Vimentin axis that negatively regulates the metastasis of TNBC, suggesting that circNR3C2 and HRD1 can act as potential prognostic biomarkers. Our study may facilitate the development of therapeutic agents targeting circNR3C2 and HRD1 for patients with aggressive breast cancer.
E3 泛素连接酶 HRD1（HMG-CoA 还原酶降解蛋白 1，别名与 SYVN1 作为官方基因符号的滑膜蛋白）在乳腺癌中发现下调并作为肿瘤抑制因子发挥作用，而 HRD1 在不同乳腺癌亚型中的确切表达谱尚不清楚。最近的研究描述了环状 RNA（circRNA）作为肿瘤进展中 miRNA 海绵的调节作用，为癌症相关基因的转录后调控提供了新的视角。
使用公共微阵列/RNA 测序数据集和乳腺癌组织/细胞系检查 HRD1 蛋白和 mRNA 的表达。基于公共 RNA 测序结果，使用在线数据库和富集/聚类分析预测潜在调节 HRD1 表达的 circRNA/miRNA 的特定组合。体外和体内的功能获得和挽救实验用于评估 circNR3C2 通过 HRD1 介导的波形蛋白的多泛素化降解对乳腺癌进展的抑制作用，通过免疫印迹、免疫沉淀和体外泛素化测定鉴定波形蛋白。
HRD1 在三阴性乳腺癌（TNBC）中明显表达低于其他亚型，与波形蛋白呈负相关，通过诱导波形蛋白的多泛素化降解，抑制乳腺癌细胞的增殖、迁移、侵袭和 EMT（上皮-间充质转化）过程。circNR3C2（hsa_circ_0071127）在 TNBC 中也明显下调，与浸润性乳腺癌的远处转移和致死性呈负相关。体外和体内过表达 circNR3C2 导致 HRD1 的肿瘤抑制作用显著增强，通过海绵 miR-513a-3p。
总之，我们揭示了一个真正的 circNR3C2/miR-513a-3p/HRD1/Vimentin 轴，负调节 TNBC 的转移，表明 circNR3C2 和 HRD1 可以作为潜在的预后生物标志物。我们的研究可能有助于开发针对侵袭性乳腺癌患者的靶向 circNR3C2 和 HRD1 的治疗剂。
