Differential expression of APE1 and APE2 in germinal centers promotes error-prone repair and A:T mutations during somatic hypermutation

Somatic hypermutation (SHM) of antibody variable region genes is initiated in germinal center B cells during an immune response by activation-induced cytidine deaminase (AID), which converts cytosines to uracils. During accurate repair in nonmutating cells, uracil is excised by uracil DNA glycosylase (UNG), leaving abasic sites that are incised by AP endonuclease (APE) to create single-strand breaks, and the correct nucleotide is reinserted by DNA polymerase β. During SHM, for unknown reasons, repair is error prone. There are two APE homologs in mammals and, surprisingly, APE1, in contrast to its high expression in both resting and in vitro-activated splenic B cells, is expressed at very low levels in mouse germinal center B cells where SHM occurs, and APE1 haploinsufficiency has very little effect on SHM. In contrast, the less efficient homolog, APE2, is highly expressed and contributes not only to the frequency of mutations, but also to the generation of mutations at A:T base pair (bp), insertions, and deletions. In the absence of both UNG and APE2, mutations at A:T bp are dramatically reduced. Single-strand breaks generated by APE2 could provide entry points for exonuclease recruited by the mismatch repair proteins Msh2–Msh6, and the known association of APE2 with proliferating cell nuclear antigen could recruit translesion polymerases to create mutations at AID-induced lesions and also at A:T bp. Our data provide new insight into error-prone repair of AID-induced lesions, which we propose is facilitated by down-regulation of APE1 and up-regulation of APE2 expression in germinal center B cells.During humoral immune responses, the recombined antibody variable [V(D)J] region genes undergo somatic hypermutation (SHM), which, after selection, greatly increases the affinity of antibodies for the activating antigen. This process occurs in germinal centers (GCs) in the spleen, lymph nodes, and Peyer’s patches (PPs) and entirely depends on activation-induced cytidine deaminase (AID) (1, 2). AID initiates SHM by deamination of cytidine nucleotides in the variable region of antibody genes, converting the cytosine (dC) to uracil (dU) (1, 3, 4). Some AID-induced dUs are excised by the ubiquitous enzyme uracil DNA glycosylase (UNG), resulting in abasic (AP) sites that can be recognized by apurinic/apyrimidinic endonuclease (APE) (4, 5). APE cleaves the DNA backbone at AP sites to form a single-strand break (SSB) with a 3′ OH that can be extended by DNA polymerase (Pol) to replace the excised nucleotide (6). In most cells, DNA Pol β performs this extension with high fidelity, reinserting dC across from the template dG. In contrast, GC B cells undergoing SHM are rapidly proliferating, and some of the dUs are replicated over before they can be excised and are read as dT by replicative polymerases, resulting in dC to dT transition mutations. Unrepaired AP sites encountering replication lead to the nontemplated addition of any base opposite the site, causing transition and transversion mutations. However, it is not clear why dUs and AP sites escape accurate repair by the highly efficient enzymes UNG and APE1 and lead instead to mutations.Instead of removal by UNG, some U:G mismatches created by AID activity are recognized by the mismatch repair proteins Msh2–Msh6, which recruit exonuclease 1 to initiate excision of one strand surrounding the mismatch (7–9). The excised region (estimated at ∼200 nt; ref. 10) is subsequently filled in by DNA Pols, including error-prone translesion Pols, which spreads mutations beyond the initiating AID-induced lesion. The combined, but noncompeting interaction of the UNG and MMR pathways in generating mutations at A:T base pairs (bp) has been described (10–12). This mismatch repair-dependent process has been termed phase II of SHM (3). Pol η and Msh2–Msh6 have been shown to be essential for nearly all mutations at A:T bp (13–15). During repair of the excision patch, additional C:G bp can be mutated by translesion Pols, but mutations at C:G bp due to AID activity can also be repaired back to the original sequence during this step (16).Mammals express two known homologs of AP endonuclease (APE), APE1 and APE2. APE1 is the major APE; it is ubiquitously expressed and essential for early embryonic development in mice and for viability of human cell lines (17–19). APE1 has strong endonuclease activity and weaker 3′-5′ exonuclease (proofreading) and 3′-phosphodiesterase (end-cleaning) activities (20, 21). Recombinant purified human APE2 has much weaker AP endonuclease activity than APE1, but its 3′-5′ exonuclease activity is strong compared with APE1, although it is not processive (20). However, APE2 has been shown to interact with proliferating cell nuclear antigen (PCNA) (22), which can recruit error-prone translesion polymerases (23, 24), and PCNA also increases the processivity of APE2 exonuclease in vitro (25). Both APE1 and APE2 are expressed in splenic B cells activated in culture (26). APE2 is nonessential, but APE2-deficient mice show a slight growth defect, a twofold reduction of peripheral B and T cells (27), and impaired proliferation of B-cell progenitors in the bone marrow (28).In this study we examine SHM in GC B cells isolated from the PPs of unimmunized apex1^+/−, apex2^Y/−, and apex1^+/−apex2^Y/− mice relative to WT mice. [Because the APE2 gene is located on the X chromosome, we used APE2-deficient male mice (apex2^Y/−) in all experiments.] We demonstrate that not only is APE2 important for SHM frequency, as reported (29), but APE2 also contributes to the generation of A:T mutations. The proportion of mutations at A:T bp is reduced in apex2^Y/− mice to the same extent as it is in ung^−/− mice, consistent with APE2 acting as an endonuclease that incises AP sites generated by UNG. Surprisingly, in the absence of both UNG and APE2, mutations at A:T bp are greatly reduced. In addition, we find that expression of APE1 is dramatically reduced in GC B cells, and APE1 haploinsufficiency has very little effect on SHM. We propose a model in which APE2 promotes SHM through inefficient and error-prone repair, whereas APE1, which is known to interact with XRCC1 and Pol β to promote error-free SSB repair (30, 31), is suppressed in GC B cells.     

Control of hypertension with medication: a comparative analysis of national surveys in 20 countries

Objective

To examine hypertension management across countries and over time using consistent and comparable methods.

Methods

A systematic search identified nationally representative health examination surveys from 20 countries containing data from 1980 to 2011 on blood pressure measurements, the diagnosis and treatment of hypertension and its control with antihypertensive drugs. For each country, the prevalence of hypertension (i.e. systolic blood pressure ≥ 140 mmHg or antihypertensive use) and the proportion of hypertensive individuals whose condition was diagnosed, treated or controlled with medications (i.e. systolic pressure < 140 mmHg) were estimated.

Findings

The age-standardized prevalence of hypertension varied between countries: for individuals aged 35 to 49 years, it ranged from around 12% in Bangladesh, Egypt and Thailand to around 30% in Armenia, Lesotho and Ukraine; for those aged 35 to 84 years, it ranged from 20% in Bangladesh to more than 40% in Germany, the Russian Federation and Turkey. The age-standardized percentage of hypertensive individuals whose condition was diagnosed, treated or controlled was highest in the United States of America: for those aged 35 to 49 years, it was 84%, 77% and 56%, respectively. Percentages were especially low in Albania, Armenia, the Islamic Republic of Iran and Turkey. Although recent trends in prevalence differed in England, Japan and the United States, treatment coverage and hypertension control improved over time, particularly in England.

Conclusion

Globally the proportion of hypertensive individuals whose condition is treated or controlled with medication remains low. Greater efforts are needed to improve hypertension control, which would reduce the burden of noncommunicable diseases.     

B-cell growth factor receptor expression and B-cell growth factor response of leukemic B cell precursors and B lineage lymphoid progenitor cells

The purpose of this study was to analyze the expression of B cell growth factor (BCGF) receptors and to elucidate the biologic effects of biochemically purified natural BCGF at the B cell precursor stage of human B lineage lymphoid differentiation. The specific binding of radioiodinated high-mol-wt BCGF (125I-HMW-BCGF) and low-molecular-wt BCGF (125I-LMW-BCGF) to fresh marrow blasts from B cell precursor acute lymphoblastic leukemia (ALL) patients was initially investigated. The estimated number of radioiodinated BCGF molecules bound per blast ranged from undetectable to 24.3 X 10(3) for HMW-BCGF, and from 11.5 X 10(3) to 457.8 X 10(3) for LMW-BCGF. In 3H-TdR incorporation assays, 75% of cases showed a significant response to LMW-BCGF with a median stimulation index of 9.3. By comparison, only 33% of cases showed a significant response to HMW-BCGF with a median stimulation index of 2.4. Subsequently, B cell precursor colony assays were performed to assess and compare the biologic effects of BCGF on leukemic B lineage lymphoid progenitor cells. Among 28 cases studied, 57% responded to both HMW-BCGF and LMW-BCGF, 21% responded only to LMW-BCGF, and the remaining cases showed no proliferative response to either growth factor. The response patterns of virtually pure populations of FACS- sorted leukemic B cell precursors were essentially identical to the proliferative responses of unsorted leukemic B-cell precursors. Synergistic effects between HMW-BCGF and LMW-BCGF were observed in 80% of the cases that responded to both. The numbers of cell-bound radioiodinated BCGF molecules, the stimulation indices, as well as the number of B cell precursor colonies in BCGF-stimulated cultures showed a marked interpatient variation. Patients with structural chromosomal abnormalities (SCAs) involving 12p11-13 or patients with a Philadelphia chromosome showed a greater HMW-BCGF response at the level of leukemic progenitor cells than did other patients (P = .02). The LMW-BCGF response was significantly greater for patients with SCA than for patients without SCA (P = .04). The response of leukemic progenitor cells to HMW-BCGF or LMW-BCGF did not correlate with sex, age, disease status, FAB morphology, WBC at diagnosis, or immunophenotype. To our knowledge, this study represents the first detailed analyses of BCGF receptor expression and BCGF effects in B cell precursor ALL. The data presented provide direct evidence for the expression of functional receptors for both HMW-BCGF and LMW-BCGF in B cell precursor ALL.     

Epidemiology of tuberculosis and HIV coinfections in Singapore, 2000–2014

Cross‐matching of records between Singapore's tuberculosis and HIV registries showed that 3.3% of individuals with tuberculosis (TB) were coinfected with HIV (2000?2014), the TB incidence among individuals with HIV infection was 1.65 per 100 person‐years, and 53% of coinfections were diagnosed within 1 month of each other. The findings supported joint prevention programmes for early diagnosis and treatment.     

AMP-18,一种新发现的胃黏膜保护因子

AMP-18是一种新发现的由胃腺体上皮细胞合成的小分子蛋白质,独特表达于胃黏膜,机体其他部位少见,胃癌组织中表达缺失．AMP-18 由185个氨基酸组成,除去N端信号肽(20个氨基酸)后大小约18 ku,第54-150个氨基酸组成高度保守的结构域(BRICHOS区域)承担主要的生理功能．AMP-18由胃腺体上皮细胞以胞吐的方式分泌到胃黏液中,他的合成和分泌与个体生长发育有关,并受福斯高林、吲哚美辛、地塞米松等药物的影响．目前发现 AMP-18的生理功能主要有促进胃黏膜上皮细胞的有丝分裂,促进细胞的迁徙,促胃肠黏膜损伤的修复,保持胃肠黏膜的完整等．     

A prognostic system applicable to patients with resectable liver metastasis from colorectal carcinoma staged by positron emission tomography with [18F]fluoro-2-deoxy-D-glucose: role of primary tumor variables

BACKGROUND: The purpose of this study was to develop a prognostic system applicable to patients with hepatic metastasis from colorectal cancer in whom extrahepatic disease was excluded by preoperative PET with [(18)F]fluoro-2-deoxy-D-glucose (FDG-PET). Data from two institutions were analyzed separately and together to improve general applicability of results. STUDY DESIGN: Data were analyzed for 285 consecutive patients undergoing liver resection for colorectal metastases from 1995 to 2005 at 2 institutions routinely using preoperative FDG-PET with. Fifteen clinicopathologic variables of the primary and secondary tumors were examined to identify factors predictive of survival. RESULTS: Outcomes were correlated with poorly differentiated tumor grade in both data sets. Because patients with poorly differentiated tumors comprised a small proportion (16%) of the population, patients with well-differentiated or moderately differentiated tumors were analyzed independently. In this subgroup, positive lymph node status in the primary colorectal tumor resection specimen was the only characteristic that predicted survival of patients in both institutions. Consequently, patients were sorted into three prognostic categories: poor tumor differentiation; well-differentiated or moderately differentiated tumors and node positive; and well-differentiated or moderately differentiated tumors and node negative. These groups had significantly different overall survival on Kaplan-Meier analysis (p=0.0014). CONCLUSIONS: In patients with colorectal liver metastases staged with FDG-PET with overall survival can be predicted directly from data in the pathology report of the colorectal primary tumor. This study also indicates the need for new molecular tumor markers of prognosis to complement clinicopathologic markers if the goal of prediction of outcomes in individual patients is to be reached.     

Continuous versus interrupted sutures for repair of episiotomy or second-degree perineal tears: a randomised controlled trial

Objective  To evaluate the repair techniques of continuous and interrupted methods for episiotomy or perineal tears.
Design  A randomised controlled trial.
Setting  The Hospital Universitario Principe de Asturias, a state hospital belonging to the community of Madrid.
Sample  Four hundred forty-five women who had undergone vaginal deliveries with episiotomies or second-grade tearing of the perineum between September 2005 and July 2007.
Methods  One group was repaired with continuous, nonlocking sutures involving the vagina, perineum, and subcutaneous tissues. The other group had continuous, locking sutures of the vagina, interrupted sutures in the perineal muscles, and interrupted transcutaneous sutures. The threads used for stitching were identical in both groups.
Main outcome measures  The participants were questioned regarding the sensation of pain and the use of painkillers on the second and the tenth days, and 3 months postpartum.
Results  When comparing the group with continuous suture to the group with interrupted sutures, the differences included less repair time (1 minute; P = 0.017) and less suture material used (relative risk [RR], 3.2, 95% CI: 2.6–4.0). The comparison of pain on the second and tenth days, and 3 months postpartum were not statistically different between the two techniques (RR, 1.08, 95% CI: 0.74–1.57; RR, 0.96, 95% CI: 0.59–1.55; and RR, 0.68, 95% CI: 0.19–2.46, respectively).
Conclusions  Although we did not demonstrate that one technique was better than the other in the incidence of pain in the short or long term, we showed that episiotomy and perineal tear repairs with continuous suturing were quicker and used less suture material without an increase in complication than interrupted suturing.     

北京市社区妇女人乳头瘤病毒感染率及其对HPV和疫苗认知情况的调查分析

[目的]评估北京市社区妇女人乳头瘤病毒（HPV）的感染率;调查社区人群对HPV的认知情况以及对HPV疫苗接种的态度。[方法]采用横断面调查方法,对北京市展览路社区15￣54岁女性进行HPV认知和流行病学问卷调查,并留取了宫颈脱落细胞或会阴部标本进行HPV DNA检测。[结果]1013名女性接受了问卷调查,832例HPV DNA检测结果纳入了统计学分析。HPV总检出率为15.38%,高、低危型HPV感染率分别为13.34%和3.25%,同时感染高、低危型HPV的检出率为1.20%。1013名调查对象中有30.7%听说过HPV,其中51.78%知道HPV感染与宫颈癌有关;HPV的知晓率与年龄和教育程度有关（P〈0.05）;经过简单宣教后,75.91%愿意接种HPV疫苗。[结论]北京市社区妇女HPV现患率较高,对HPV的知晓率也较高。开展公众健康教育,提高人群的认识水平是疫苗计划获得成功的关键因素。     

Immunity to hepatitis B, poliomyelitis and measles in fully vaccinated Aboriginal and Torres Strait Island children

Objective: To determine the immunity to hepatitis B, poliomyelitis and measles in fully vaccinated Aboriginal and Torres Strait Island children in north Queensland.
Methodology: A cross-sectional survey of immunity in a sample of children; 101 fully vaccinated Aboriginal and Torres Strait Island children, with a median age of 24.5 months, from 10 communities in North Queensland participated in this study. The main outcome measures were the prevalence of adequate antibody levels against hepatitis B, poliomyelitis and measles.
Results: Only 54% (95% Cl 44–63%) of the children had adequate immunity (10 m iu/mL) to hepatitis B, and one child had been infected despite vaccination. Although all the children (95% Cl 96–100%) had adequate immunity (i.e. neutralizing antibodies at a dilution of 1:8) to poliovirus 2, only 93% (95% Cl 86–96%) and 60% (95% Cl 50–69%) had adequate immunity to polioviruses 1 and 3, respectively. Nearly all (96%; 95% Cl 90–98%) of the children had adequate immunity (i.e. detectable IgG antibody) to measles.
Conclusions: Although a relatively low proportion of the children had adequate antibody levels against hepatitis B the clinical significance of this observation is uncertain. Further studies are needed to determine whether fully vaccinated Torres Strait Island children have been adequately protected and whether they require a booster dose of hepatitis B vaccine. A substantial proportion of fully vaccinated Aboriginal and Torres Strait Island children are inadequately protected against poliomyelitis, and therefore any such child with acute flaccid paralysis should be investigated fully for poliomyelitis. Vaccinated Aboriginal and Torres Strait Island children are well protected against measles, as are other Australian children.