HuR RNA结合蛋白的功能及其与肿瘤关系的研究进展

HuR是RNA结合蛋白中胚胎致死异常视觉（ELAV）家族的一员,又称为类胚胎致死异常视觉1,在许多细胞中普遍表达.ELAV家族最初在果蝇中被发现,类胚胎致死异常视觉2、3和4主要与神经发育有关.1996年,Wei-J等利用PCR技术识别并克隆了一种HuR基因.他们首先设计了PCR引物,该引物的序列来源于临近HuD RNA识别模序Ⅲ的保守区.以HeLa细胞中的mRNA进行RT-PCR分析,结果扩增出140个核苷酸的RT产物.将此产物克隆、测序,发现其高度同源但又有别于HuD、HuC和Hel-N1序列,随命名为HuR（HuA）.HuR能够与c-fos和IL-3 mRNA的AU富含元件（ARE）结合.现将HuD RNA结合蛋白的功能及其与肿瘤关系的研究进展综述如下.     

肝细胞特异性HuR基因敲除小鼠模型的表型研究

目的 探讨肝细胞特异性敲除HuR基因对小鼠肝脏功能的影响。方法 从美国Jackson实验室引进LoxP标记的人抗原R（human antigen R,HuR）基因小鼠（HuR^fl/fl）和Alb-Cre转基因小鼠。杂交后,经数代选育配种,建立肝细胞特异性HuR基因敲除小鼠（HuR^LKO）模型。PCR技术鉴别小鼠基因型,蛋白免疫印迹和免疫荧光实验检验小鼠肝脏的HuR表达水平,同时HE染色观察肝脏结构变化。高脂喂养HuR^fl/fl/Alb-Cre和HuR^fl/fl两组小鼠,观察小鼠体重、肝重和肝体比变化,提取血清检测肝脏损伤和脂肪代谢相关指标。结果 PCR成功检测筛选子代小鼠基因型,包括HuR^fl/fl/Alb-Cre和HuR^fl/fl小鼠。蛋白免疫印迹实验和免疫荧光实验证明小鼠肝细胞特异性HuR基因敲除成功。HE染色结果提示HuR^LKO小鼠的肝细胞出现变性水肿、局部坏死。高脂喂养实验提示两组小鼠在肝重、肝体比、AST、ALT、HDL-C、血糖上的差异具有统计学意义（P＜0.05）,但在体重、TG、LDL-C的差异没有统计学意义（P＞0.05）。结论 HuR基因是维持小鼠肝细胞功能的必要基因,Cre-LoxP技术可成功构建HuR^LKO小鼠模型,且特异性高,表型明显,为研究HuR在肝脏各项疾病的发生发展中所扮演的角色,提供了一个很好的疾病模型。     

Phosphorylation of the HuR ligand APRIL by casein kinase 2 regulates CD83 expression

Fully mature DC and, to a lesser extent, activated T and B cells express CD83, a surface molecule that appears to fulfil an important role in efficient T‐cell activation. Recently, it has been shown that CD83 mRNA is transported from the nucleus to the cytoplasm by an uncommon route, involving the cellular RNA‐binding protein HuR and the nuclear export receptor CRM1. Moreover, the shuttle phosphoprotein APRIL (ANP32B) has been shown to be required for HuR‐mediated nucleocytoplasmic translocation of the CD83 mRNA by acting as an adaptor that links HuR and CRM1. Here, we are able to report that casein kinase 2 (CK2) phosphorylates APRIL on residue threonine244 (Thr²⁴⁴) and demonstrate that the CK2‐specific inhibitor 4,5,6,7‐tetrabromo‐2‐azabenzimidazole abolishes CD83 expression in activated Jurkat T cells by interfering with the nucleocytoplasmic translocation of CD83 mRNA. Depletion and knockdown studies demonstrate that the CK2 α′ subunit is necessary for this regulation, whereas the CK2 α subunit seems to be dispensable. Taken together, the data presented significantly extend our knowledge of the complex regulation of CD83 mRNA processing and provides a novel strategy to interfere with CD83 expression.     

HuR regulates the expression of stress-sensitive genes and mediates inflammatory response in human umbilical vein endothelial cells

An important aspect of vascular biology is the identification of regulators of stress-sensitive genes that play critical roles in mediating inflammatory response. Here, we show that expression of HuR in human umbilical vein endothelial cells is regulated by shear stress and statin treatment; HuR, in turn, regulates other stress-sensitive genes such as Kruppel-like factor 2 (Klf2), endothelial nitric oxide synthase (eNOS), and bone morphogenic protein 4 (BMP-4). We found that siRNA knockdown of HuR-inhibited inflammatory responses in endothelial cells, including ICAM-1 and VCAM-1 up-regulation, NFκB phosphorylation, and adhesion of monocytes. Tissue staining of the mouse aorta revealed increased HuR expression in the lesser curvature region of the arch that is exposed to disturbed flow, consistent with our in vitro data. Taken together, these results suggest that HuR plays a critical role in inducing inflammatory response of endothelial cells under mechanical and biochemical stresses.     

The induced RNA‐binding protein,HuR, targets 3′‐UTR region of IL‐6 mRNA and enhances its stabilization in periodontitis

RNA‐binding proteins (RBPs) regulate mRNA stability by binding to the 3′‐untranslated region (UTR) region of mRNA. Human antigen‐R (HuR), one of the RBPs, is involved in the progression of diseases, such as rheumatoid arthritis, diabetes mellitus and some inflammatory diseases. Interleukin (IL)‐6 is a major inflammatory cytokine regulated by HuR binding to mRNA. Periodontal disease (PD) is also an inflammatory disease caused by elevations in IL‐6 following an infection by periodontopathogenic bacteria. The involvement of HuR in the progression of PD was assessed using in‐vitro and in‐vivo experiments. Immunohistochemistry of inflamed periodontal tissue showed strong staining of HuR in the epithelium and connective tissue. HuR mRNA and protein level was increased following stimulation with Porphyromonas gingivalis (Pg), one of the periodontopathogenic bacteria, lipopolysacchride (LPS)‐derived from Pg (PgLPS) and tumour necrosis factor (TNF)‐α in OBA‐9, an immortalized human gingival epithelial cell. The luciferase activity of 3′‐UTR of IL‐6 mRNA was increased by TNF‐α, Pg and PgLPS in OBA‐9. Luciferase activity was also increased in HuR‐over‐expressing OBA‐9 following a bacterial stimulation. Down‐regulation of HuR by siRNA resulted in a decrease in mRNA expression and production of IL‐6. In contrast, the over‐expression of HuR increased IL‐6 mRNA expression and production in OBA‐9. The HuR inhibitor, quercetin, suppressed Pg‐induced HuR mRNA expression and IL‐6 production in OBA‐9. An oral inoculation with quercetin also inhibited bone resorption in ligature‐induced periodontitis model mice as a result of down‐regulation of IL‐6. These results show that HuR modulates inflammatory responses by regulating IL‐6.