The Polycomb group （PcG） genes repress gene expression mainly through chromatin modifications and regulation of chromatin structure. At present, at/east four protein complexes of PcG proteins are identified, including Polycomb repressive complex 1 （PRC1）, Polycomb repressive complex 2 （PRC2）, PHO-repressive complex （PhoRC） and Polycomb repressive deubiquitinase （PR-DUB）. In this review, the recent discoveries of the composition of the above complexes, as well as their roles in regulating histone modifications and gene silencing are discussed. We mainly focus on the composition of PRC1 and PRC2 complex and recruitment of PcG to target genes and mechanisms of PRC1 and PRC2-mediated gene silencing. Although much progress has been made in understanding gene silencing mediated by PcG proteins, we also discuss several important questions that still remained unanswered, such as the inheritance of histone modifications during cell division.
目的应用CS-SELEX(cell surface-system evolution of ligands by exponential enrichment)技术筛选与丙型肝炎病毒(hepatitis C virus,HCV)非结构蛋白4B(non protein 4B,NS4B)特异性结合的ssDNA适配子,建立检测HCV NS4B的酶联寡聚核苷酸吸附试验(enzyme-linked oligonucleotide assay,ELONA)方法。方法构建pDisplay-NS4B质粒,并转染至HepG2细胞中,在G418存在情况下连续筛选1个月,得到单克隆细胞群,经过Western blot以及流式细胞术验证,获得稳定表达NS4B的HepG2细胞。设计并合成随机序列ssDNA文库,以稳定表达NS4B的细胞为正向筛选靶细胞,以HepG2细胞为反筛细胞进行CS-SELEX技术筛选。每轮筛选获得的具有结合NS4B能力的ssDNA适配子,通过PCR扩增得到富集,随后通过不对称PCR获得下一轮筛选的ssDNA文库。经过16轮筛选,将亲和力最高的筛选产物克隆并测序,用ELONA方法检测适配子的亲和力。结果成功构建表面展示表达重组质粒pDisplay-NS4B。分别将该质粒转入HepG2细胞,通过G418筛选获得稳定表达HCV-NS4B的细胞系NS4B-HepG2。对CS-SELEX筛选的各轮适配子库进行亲和力测定,其中第14轮库适配子与NS4B的亲合力最高。分别对第14轮库中的单个适配子进行亲和力测定,以适配子ZN1和ZN5与NS4B的亲合力最高。ZN1和ZN5不仅能结合展示在细胞表面的NS4B蛋白,还能结合丙型肝炎病毒感染细胞(HCV cell culture,HCVcc)中的HCV-NS4B蛋白。结论适配子ZN1和ZN5对NS4B有高亲和力,这对研究HCV-NS4B致癌机制、HCV诊断以及治疗方面有潜在的应用价值。
Ficolin-2 is a lectin complement pathway activator present in normal human plasma and usually associated with infectious diseases, but little is known about the role of ficolin-2 in human immunodeficiency virus(HIV) infection. Here, we describe our novel findings that serum ficolin-2concentrations of 103 HIV-1 patients were much higher compared to those of 57 healthy donors. In vitro analysis showed that HIV-1 infection could enhance ficolin-2 expression. We further demonstrated that recombinant ficolin-2 protein could bind with HIV-1 envelope glycoprotein gp120, and subsequently induce complement dependent cytotoxicity. Moreover, ficolin-2 could block the entry of HIV-1 into target cells(TZM-b1 and MT-2 cells) and infection in a ficolin-2 dosedependent manner. To our knowledge, this is the first report about the protective role of ficolin-2against HIV-1 infection and our study suggests that ficolin-2 is an important human innate immune molecule against HIV.
Human ficolin-2 is an important lectin complement pathway activator that is secreted from liver cells and has been implicated as an anti-infection innate immune molecule. However, the role of ficolin-2 protein and its dynamic changes over the course of and in the prognosis of chronic hepatitis B(CHB) and hepatocellular carcinoma(HCC) remain unclear. In this study, we analyzed ficolin-2 protein expression in a cohort of individuals with CHB infection, HCC and cirrhosis. A sandwich enzyme-linked immunosorbent assay(ELISA) method was used to measure serum ficolin-2 concentrations. Ficolin-2 expression in liver tissues was detected by immunohistochemical staining. Serum ficolin-2 concentrations in CHB patients were significantly higher than in healthy controls and HBV carriers. After 48 weeks of routine amelioration liver function treatment, serum ficolin-2 concentrations decreased and were positively correlated with favorable alanine aminotransferase(ALT), HBV DNA and HBe Ag-seroconversion outcomes. Interestingly, we observed much lower expression of serum and intrahepatic ficolin-2 in HCC and cirrhosis compared with healthy controls. Our findings suggest that serum and intrahepatic ficolin-2 levels may be considered one of the indicators for the response of chronic HBV infection, HCC and cirrhosis.
Ficolins are serum complement lectins,with a structure similar to mannose-binding lectin （MBL） and lung surfactant protein （SP）-A and SP-D.Ficolins activate the lectin complement system and play important roles in host innate immunity.Ficolins are members of the collectin family of proteins,which act as pattern recognition receptors （PRRs）.They are soluble oligomeric defense proteins with lectin-like activity,and are able to recognize pathogen-associated molecular patterns （PAMPs）,which are carbohydrate molecules on the surface of pathogens,and of apoptotic,necrotic,and malignant cells.Upon binding to their specific PAMPs,ficolins may trigger activation of the immune system either （1） by initiating activation of complement via the lectin pathway,（2） by a primitive type of opsonophagocytosis,or （3） by stimulating secretion of the inflammatory cytokines interferon （IFN）-γ,interleukin （IL）-17,IL-6,and tumor necrosis factor （TNF）-α,and production of nitric oxide （NO）by macrophages,thus limiting the infection and concurrently orchestrating the subsequent adaptive immune response.Recently,a number of reports have shown that dysfunction or abnormal expression of ficolins may play crucial roles in viral and bacterial diseases and in inflammation.This review summarizes the reports on the roles of ficolins in the infectious diseases,and provides insight into ficolins as novel innate immune therapeutic options to treat these diseases.
