LSECtin interacts with filovirus glycoproteins and the spike protein of SARS coronavirus

Cellular attachment factors like the C-type lectins DC-SIGN and DC-SIGNR (collectively referred to as DC-SIGN/R) can augment viral infection and might promote viral dissemination in and between hosts. The lectin LSECtin is encoded in the same chromosomal locus as DC-SIGN/R and is coexpressed with DC-SIGNR on sinusoidal endothelial cells in liver and lymphnodes. Here, we show that LSECtin enhances infection driven by filovirus glycoproteins (GP) and the S protein of SARS coronavirus, but does not interact with human immunodeficiency virus type-1 and hepatitis C virus envelope proteins. Ligand binding to LSECtin was inhibited by EGTA but not by mannan, suggesting that LSECtin unlike DC-SIGN/R does not recognize high-mannose glycans on viral GPs. Finally, we demonstrate that LSECtin is N-linked glycosylated and that glycosylation is required for cell surface expression. In summary, we identified LSECtin as an attachment factor that in conjunction with DC-SIGNR might concentrate viral pathogens in liver and lymph nodes.     

DC-SIGN,DC-SIGNR and LSECtin: C-Type Lectins for Infection

The C-type lectins DC-SIGN, DC-SIGNR and LSECtin are encoded by the lectin gene cluster on chromosome 19p13.3 and perform cell-adhesion and pathogen recognition functions on dendritic cells, liver cells and lymph node sinusoidal endothelial cells. DC-SIGN and DC-SIGNR share similar overall gene and protein molecule structures, and they exhibit high affinity for high-mannose carbohydrates. LSECtin, a Ca²⁺-dependent C-type lectin, interacts with mannose, NAcGlc and fucose. These lectins allow pathogen recognition (e.g., viruses, bacteria and allergens) and cell adhesion for dendritic and endothelial cells in different tissues, which may enhance the infection and facilitate the spread of those pathogens. A better understanding of these lectins may yield information about how pathogens are captured by particular cells and how they spread in different tissues. These studies would provide more detail about the physiopathological mechanisms of viral and bacterial infections and may also lead to new strategies to treat or prevent infections.     

DC-SIGNR基因多态性与丙型肝炎病毒载量的相关性研究

目的了鹪丙型肝炎患者DC-SIGN／DC-SIGNR基因颈区重复序列的遗传多态性分布，探讨DC-SIGNR基因多态性与丙型肝炎病毒（HCV）载量的关系。方法采用PCR结合DNA测序对300例丙型肝炎患者DC—SIGNR重复序列多态性进行基因分型和测序分析；同时检测了患者的HCV病毒载量。结果该研究发现携带7等位基因（中等的）的患者、其HCV病毒载量水平低于携带9等位基因（较长的）的患者（P〈0.05），此外7／7基因型的患者组其HCV病毒载量水平低于9／7基因型的患者组，两组的差异有统计学意义（P〈0．05）、提示HCV病毒更易与携带较长DC—SINGR等位基因的患者结合。结论DC-SIGNR遗传多态性可能与HCV病毒在个体内的复制有关。     

The protease allergen Der p 1 cleaves cell surface DC-SIGN and DC-SIGNR: experimental analysis of in silico substrate identification and implications in allergic responses

Background The cysteine protease Der p 1 from the house dust mite Dermatophagoides pteronyssinus is one of the most potent allergens known. An attractive mechanism for a component of Der p 1 allergenicity lies in its ability to cleave key regulatory molecules from leucocyte surfaces, subverting cellular function and driving abnormal immunoglobulin E (IgE) responses. Objective Although CD23, CD25 and CD40 have already been identified as major Der p 1 targets, other significant substrates may also exist. Methods To investigate this, knowledge of the proteolytic properties of Der p 1 was used to perform in silico digestion of human dendritic cell surface proteins, using the prediction of protease specificity (PoPS) bioinformatics tool, in conjunction with cellular in vitro analysis and cleavage site determination. Results Targets identified included DC‐SIGN and DC‐SIGNR, two C‐type lectins implicated mostly in pathogen trafficking. Treatment of positively expressing cells with Der p 1 led to loss of detectable surface DC‐SIGN and DC‐SIGNR. Digestion of purified soluble recombinant DC‐SIGN and DC‐SIGNR, followed by N‐terminal sequencing and MALDI mass spectrometry, indicated in each case one major cleavage site and several minor sites, the former correlating well with Der p 1 enzymology and the folded state of the substrate proteins. Loss of DC‐SIGN from the cell surface led to reduced binding of intracellular adhesion molecule‐3, an endogenous DC‐SIGN ligand expressed on naïve T cells which is thought to be involved in T‐helper type 1 cytokine signalling. Conclusion These data provide evidence of lectin involvement in the initiation of the allergic response and the value of using genome‐wide in silico digestion tools.     

DC-SIGNR基因绞链区重复序列多态性检测方法的建立与应用

目的建立树突状细胞表面的蛋白质DC-SIGNR基因绞链区重复序列多态性的检测方法，了解宿主因素在抗艾滋病病毒1型（HIV-1）所起的作用。方法设计特定引物，用PCR方法对DC-SIGNR基因绞链区重复序列进行扩增，用凝胶电泳法对其产物进行分析。结果根据DC-SIGNR绞链区重复序列的数量，DC-SIGNR绞链区重复序列具有高度基因多态性，而DC-SIGN则罕见基因多态性。结论所建立的检测DC-SIGNR绞链区重复序列的方法简单，易于掌握。由于DC-SIGNR重复序列数量的改变可能会影响其正常功能，从而影响宿主与HIV-1的结合能力，因此该法为研究宿主因素在抗HIV-1感染中所起作用的一种好方法。     

Impact of polymorphisms in the DC-SIGNR neck domain on the interaction with pathogens

The lectins DC-SIGN and DC-SIGNR augment infection by human immunodeficiency virus (HIV), Ebolavirus (EBOV) and other pathogens. The neck domain of these proteins drives multimerization, which is believed to be required for efficient recognition of multivalent ligands. The neck domain of DC-SIGN consists of seven sequence repeats with rare variations. In contrast, the DC-SIGNR neck domain is polymorphic and, in addition to the wild type (wt) allele with seven repeat units, allelic forms with five and six sequence repeats are frequently found. A potential association of the DC-SIGNR genotype and risk of HIV-1 infection is currently under debate. Therefore, we investigated if DC-SIGNR alleles with five and six repeat units exhibit defects in pathogen capture. Here, we show that wt DC-SIGNR and patient derived alleles with five and six repeats bind viral glycoproteins, augment viral infection and tetramerize with comparable efficiency. Moreover, coexpression of wt DC-SIGNR and alleles with five repeats did not decrease the interaction with pathogens compared to expression of each allele alone, suggesting that potential formation of hetero-oligomers does not appreciably reduce pathogen binding, at least under conditions of high expression. Thus, our results do not provide evidence for diminished pathogen capture by DC-SIGNR alleles with five and six repeat units. Albeit, we cannot exclude that subtle, but in vivo relevant differences remained undetected, our analysis suggests that indirect mechanisms could account for the association of polymorphisms in the DC-SIGNR neck region with reduced risk of HIV-1 infection.     

DC-SIGN和DC-SIGNR外显子4在中国结核患者中的遗传多态性

目的探讨DC-SIGN和DC-SIGNR外显子4在中国结核患者中是否存在遗传易感性。方法采用PCR结合DNA测序对227例结核患者和520例健康人群的DC-SIGN和DC-SIGNR外显子4重复序列多态性进行基因分型和测序分析。结果 DC-SIGN外显子4基因型与等位基因频率在结核患者和健康人群间差异无统计学意义（P〉0.05）;DC-SIGNR外显子4等位基因的频率差异也无计学意义（P〉0.05）;但6/6基因型分布频率在结核患者和健康人群间的差异有统计学意义（P〈0.05）。结论 DC-SIGN外显子4遗传多态性与结核感染易感性无明显相关;6/6基因型DC-SIGNR外显子4在结核患者中的分布频率较高,可能与结核感染的易感性相关,值得进一步研究。     

暗娼人群DC-SIGN及DC-SIGNR基因多态性初步研究

目的分析中国暗娼人群中DC-SIGN及DC-SIGNR基因多态性的分布,比较不同研究人群等位基因频率分布。方法PCR检测234例HIV阴性暗娼DC-SIGN及DC-SIGNR基因多态性。结果DC-SIGN基因型在234例中发现4例突变杂合子。DC-SIGNR等位基因频率以7次重复最为常见(65.2%),其次为5次重复(18.4%)和9次重复(11.9%),其基因频率分布与国外报道差异有统计学意义。结论DC-SIGN基因具有多态性,而DC-SIGNR基因多态性分布同国外报道比较存在差异。     

HIV-1暴露未感染人群DC-SIGN和DC-SIGNR基因多态性

目的研究HIV-1高暴露未感染人群(ESN)、正常对照人群和HIV-1携带者DC-SIGN和DC-SIGNR基因型和基因频率分布,探讨这两个基因多态性与HIV-1不易感性的关系。方法应用PCR技术扩增两个基因颈区重复序列,以琼脂糖凝胶电泳区分两个基因不同重复序列的电泳图差异,以卡方检验分析基因型和基因频率分布差异。结果DC-SIGN在三组人群中以7/7型为主,三组人群共检出9个非7/7基因型,但DC-SIGN各基因型分布差异无统计学意义(P=0.648);DC-SIGNR具有高度多态性,7/5、5/5和6/7基因型的频率从ESN人群、健康对照人群和HIV-1携带者逐渐降低,同时5和6等位基因的频率也呈现均匀下降,但各基因型分布差异无统计学意义(P=0.782)。结论我国汉族人群DC-SIGN基因多态性变异很低,其对于今后HIV-1人群不易感性的研究意义不大;DC-SIGNR基因多态性对于HIV-1不易感性的意义尚需要大样本的验证或细胞生物学实验数据的支持。     

The tandem-repeat polymorphism of the DC-SIGNR gene does not affect the susceptibility to HIV infection and the progression to AIDS

DC-SIGNR is a C-type lectin that functions as a transreceptor for HIV-1. The exon 4 of the DC-SIGNR gene comprises a variable number of 69-bp tandem repeats, encoding for parts of the extracellular protein domain. Here, we analyzed the relevance of this gene polymorphism for the interindividual transmission of HIV-1 and the progression to AIDS. A cross-sectional comparison between HIV-1-infected patients (n = 391) and healthy volunteers (n = 134) did not reveal significant differences with regard to the DC-SIGNR allele distribution. Moreover, DC-SIGNR allele frequencies were similar in slowly progressing HIV patients (n = 31) and patients who rapidly progressed to AIDS (n = 46). Additionally, in a cohort of 149 newly HIV-infected patients, no relationship was found between HIV set point viremia and DC-SIGNR genotypes. Thus, the DC-SIGNR tandem-repeat polymorphism in exon 4 does not have a significant impact on the host's susceptibility to HIV and the clinical progression to AIDS.