抑制性寡脱氧核苷酸的生物学效应及研究进展

DNA对于机体免疫系统具有很多复杂的作用。存在于细菌DNA中的刺激性CpG基序能够促进机体免疫细胞分泌多种细胞因子,使机体产生偏向Th1方向的免疫应答,而抑制性寡脱氧核苷酸（oligodeoxynucleotide,ODN）可以选择性阻断刺激性CpG诱导的免疫激活作用。抑制性ODN按其结构不同大致分为三类,它可能通过影响细胞对CpG-S的结合及摄取、降低CpG-S特异性受体TLR9的表达发挥抑制作用。本综述主要介绍抑制性ODN的结构特征、作用机制和它在一些疾病中发挥的作用。     

Acceleration of 5-Methylcytosine Deamination in Cyclobutane Dimers by G and Its Implications for UV-Induced C-to-T Mutation Hotspots

Sunlight-induced C→T mutation hotspots occur most frequently at methylated CpG sites in tumor suppressor genes and are thought to arise from translesion synthesis past deaminated cyclobutane pyrimidine dimers (CPDs). While it is known that methylation enhances CPD formation in sunlight, little is known about the effect of methylation and sequence context on the deamination of 5-methylcytosine (^mC) and its contribution to mutagenesis at these hotspots. Using an enzymatic method, we have determined the yields and deamination rates of C and ^mC in CPDs and find that the frequency of UVB-induced CPDs correlates with the oxidation potential of the flanking bases. We also found that the deamination of T^mC and ^mCT CPDs is about 25-fold faster when flanked by G's than by A's, C's or T's in duplex DNA and appears to involve catalysis by the O6 group of guanine. In contrast, the first deamination of either C or ^mC in AC^mCG with a flanking G was much slower (t_1/2 > 250 h) and rate limiting, while the second deamination was much faster. The observation that C^mCG dimers deaminate very slowly but at the same time correlate with C→T mutation hotspots suggests that their repair must be slow enough to allow sufficient time for deamination. There are, however, a greater number of single C→T mutations than CC→TT mutations at C^mCG sites even though the second deamination is very fast, which could reflect faster repair of doubly deaminated dimers.     

DNA疫苗佐剂研究进展

DNA疫苗在免疫应答中能诱导机体产生持久的体液免疫和细胞免疫,然而DNA疫苗刺激机体免疫应答能力往往比常规疫苗引起的免疫反应弱。最近研究表明:使用DNA疫苗佐剂如细胞因子、CpGODN、补体C3d等有助于提高DNA疫苗的免疫效价。就DNA疫苗佐剂的研究进展做一综述。     

Solution structure of DNA/RNA hybrid duplex with C8-propynyl 2′-deoxyadenosine modifications: Implication of RNase H and DNA/RNA duplex interaction

Solution structures of DNA/RNA hybrid duplexes, d(GCGCA*AA*ACGCG): r(cgcguuuugcg)d(C) (designated PP57), containing two C8-propynyl 2′-deoxyadenosines (A*) and unmodified hybrid (designated U4A4) are solved. The C8-propynyl groups on 2′-deoxyadenosine perturb the local structure of the hybrid duplex, but overall the structure is similar to that of canonical DNA/RNA hybrid duplex except that Hoogsteen hydrogen bondings between A* and U result in lower thermal stability. RNase H is known to cleave RNA only in DNA/RNA hybrid duplexes. Minor groove widths of hybrid duplexes, sugar puckerings of DNA are reported to be responsible for RNase H mediated cleavage, but structural requirements for RNase H mediated cleavage still remain elusive. Despite the presence of bulky propynyl groups of PP57 in the minor groove and greater flexibility, the PP57 is an RNase H substrate. To provide an insight on the interactions between RNase H and substrates we have modeled Bacillus halodurans RNase H-PP57 complex, our NMR structure and modeling study suggest that the residue Gly(15) and Asn(16) of the loop residues between first β sheet and second β sheet of RNase HI of Escherichia coli might participate in substrate binding.     

A study on the protective effects of CpG oligodeoxynucleotide-induced mucosal immunity against lung injury in a mouse acute respiratory distress syndrome model

This study aims to determine the feasibility of using oligodeoxynucleotides with unmethylated cytosine-guanine dinucleotide sequences (CpG ODN) as an immunity protection strategy for a mouse model of acute respiratory distress syndrome (ARDS). This is a prospective laboratory animal investigation. Twenty-week-old BALB/c mice in Animal research laboratory were randomized into groups. An ARDS model was induced in mice using lipopolysaccharides (LPSs). CpG ODN was intranasally and transrectally immunized before or after the 3rd and 7th days of establishing the ARDS model. Mice were euthanized on Day 7 after the second immunization. Then, retroorbital bleeding was carried out and the chest was rapidly opened to collect the trachea and tissues from both lungs for testing. CpG ODN significantly improved the pathologic impairment in mice lung, especially after the intranasal administration of 50 μg. This resulted in the least severe lung tissue injury. Furthermore, interleukin-6 (IL-6) and IL-8 concentrations were lower, which was second to mice treated with the rectal administration of 20 µg CpG ODN. In contrast, the nasal and rectal administration of CpG ODN in BALB/c mice before LPS immunization did not appear to exhibit any significant protective effects. The intranasal administration of CpG ODN may be a potential treatment approach to ARDS. More studies are needed to further determine the protective mechanism of CpG ODN.     

肿瘤DNA疫苗佐剂研究进展

对近年来在增加肿瘤DNA疫苗免疫原性、提高肿瘤DNA疫苗效力方面所取得的进展予以综述。简要阐述了以下几种较有效的增强肿瘤DNA疫苗效力策略的机制和进展：（1）以细胞因子表达质粒为佐剂;（2）以质粒编码的趋化因子、协同刺激分子、共刺激分子、补体为佐剂;（3）以CPGODN为佐剂;（4）其他一些佐剂。     

DNA疫苗的分子佐剂应用研究进展

DNA疫苗因在动物尤其是大型动物与人类中诱发较低的免疫反应而严重影响其推广应用。介绍提高与调节DNA疫苗诱导反应的策略：（1）以细胞因子表达质控为佐剂;（2）以质粒编码的趋化因子与共刺激分子为佐剂;（3）以CPG ODN为佐剂。