Phylodynamics and Dispersal of HRSV Entails Its Permanence in the General Population in between Yearly Outbreaks in Children

Background

Human respiratory syncytial virus (HRSV) is one of the major etiologic agents of respiratory tract infections among children worldwide.

Methodology/Principal Findings

Here through a comprehensive analysis of the two major HRSV groups A and B (n = 1983) which comprise of several genotypes, we present a complex pattern of population dynamics of HRSV over a time period of 50 years (1956–2006). Circulation pattern of HRSV revealed a series of expansions and fluctuations of co-circulating lineages with a predominance of HRSVA. Positively selected amino acid substitutions of the G glycoprotein occurred upon population growth of GB3 with a 60-nucleotide insertion (GB3 Insert), while other genotypes acquired substitutions upon both population growth and decrease, thus possibly reflecting a role for immune selected epitopes in linkage to the traced substitution sites that may have important relevance for vaccine design. Analysis evidenced the co-circulation and predominance of distinct HRSV genotypes in Brazil and suggested a year-round presence of the virus. In Brazil, GA2 and GA5 were the main culprits of HRSV outbreaks until recently, when the GB3 Insert became highly prevalent. Using Bayesian methods, we determined the dispersal patterns of genotypes through several inferred migratory routes.

Conclusions/Significance

Genotypes spread across continents and between neighboring areas. Crucially, genotypes also remained at any given region for extended periods, independent of seasonal outbreaks possibly maintained by re-infecting the general population.     

The ATM-BID pathway regulates quiescence and survival of haematopoietic stem cells

BID, a BH3-only BCL2 family member, functions in apoptosis as well as the DNA-damage response. Our previous data demonstrated that BID is an ATM effector acting to induce cell-cycle arrest and inhibition of apoptosis following DNA damage. Here we show that ATM-mediated BID phosphorylation plays an unexpected role in maintaining the quiescence of haematopoietic stem cells (HSCs). Loss of BID phosphorylation leads to escape from quiescence of HSCs, resulting in exhaustion of the HSC pool and a marked reduction of HSC repopulating potential in vivo. We also demonstrate that BID phosphorylation plays a role in protecting HSCs from irradiation, and that regulating both quiescence and survival of HSCs depends on BID's ability to regulate oxidative stress. Moreover, loss of BID phosphorylation, ATM knockout or exposing mice to irradiation leads to an increase in mitochondrial BID, which correlates with an increase in mitochondrial oxidative stress. These results show that the ATM-BID pathway serves as a critical checkpoint for coupling HSC homeostasis and the DNA-damage stress response to enable long-term regenerative capacity.     

Semaphorin 3A and neurotrophins: a balance between apoptosis and survival signaling in embryonic DRG neurons

Large numbers of neurons are eliminated by apoptosis during nervous system development. For instance, in the mouse dorsal root ganglion (DRG), the highest incidence of cell death occurs between embryonic days 12 and 14 (E12-E14). While the cause of cell death and its biological significance in the nervous system is not entirely understood, it is generally believed that limiting quantities of neurotrophins are responsible for neuronal death. Between E12 and E14, developing DRG neurons pass through tissues expressing high levels of axonal guidance molecules such as Semaphorin 3A (Sema3A) while navigating to their targets. Here, we demonstrate that Sema3A acts as a death-inducing molecule in neurotrophin-3 (NT-3)-, brain-derived neurotrophic factor (BDNF)- and nerve growth factor (NGF)-dependent E12 and E13 cultured DRG neurons. We show that Sema3A most probably induces cell death through activation of the c-Jun N-terminal kinase (JNK)/c-Jun signaling pathway, and that this cell death is blocked by a moderate increase in NGF concentration. Interestingly, increasing concentrations of other neurotrophic factors, such as NT-3 or BDNF, do not elicit similar effects. Our data suggest that the number of DRG neurons is determined by a fine balance between neurotrophins and Semaphorin 3A, and not only by neurotrophin levels.     

In vitro and in vivo evaluation of doxorubicin conjugates with the divalent peptide E-[c(RGDfK)2] that targets integrin alphavbeta3

Integrins, especially integrin alpha vbeta3, are attractive receptors for vascular targeting strategies. Recently, a divalent RGD peptidomimetic, E-[c(RGDfK)2], has been described that demonstrates increased uptake in human ovarian carcinoma OVCAR-3 xenograft tumors. Inspired by these results, we set out to develop doxorubicin conjugates with E-[c(RGDfK)2] by binding two different maleimide derivatives of doxorubicin to E-[c(RGDfK)2] that was thiolated with iminothiolane. In this way, two water-soluble derivatives were obtained, E-[c(RGDfK)2]-DOXO-1 and E-[c(RGDfK)2]-DOXO-2. In E-[c(RGDfK)2]-DOXO-1, doxorubicin was bound to the peptide through a stable amide bond, and in E-[c(RGDfK)2]-DOXO-2, a MMP-2/MMP-9 cleavable octapeptide was introduced between doxorubicin and the peptide. The rationale for a MMP-2/MMP-9-cleavable linker was that MMP-2 and MMP-9 bind to integrin alpha vbeta3 and both are overexpressed in tumor vasculature. In addition, analogous control doxorubicin-containing peptides bearing c(RADfK) that does not bind to integrin alpha vbeta3 were synthesized, i.e., c(RADfK)-DOXO-1 and c(RADfK)-DOXO-2. Whereas E-[c(RGDfK) 2]-DOXO-2 was cleaved effectively by MMP-2 and in OVCAR-3 tumor homogenates releasing a doxorubicin-tetrapeptide or doxorubicin as the final cleavage product, no release of doxorubicin was observed for E-[c(RGDfK)2]-DOXO-1. Proliferation of HUVEC in the presence of MMP-2-cleavable doxorubicin-containing peptides exhibited 6- to 10-fold increased inhibition compared to the amide-linked doxorubicin-containing peptides. In addition, inhibition of HUVEC sprouting during a 24 h exposure was approximately 3-fold stronger for E-[c(RGDfK) 2]-DOXO-2 and 20-fold stronger for the reference peptide conjugate c(RADfK)-DOXO-2 than for doxorubicin alone. In vivo studies in an OVCAR-3 xenograft model demonstrated no or only moderate antitumor efficacy for either E-[c(RGDfK)2], E-[c(RGDfK)2]-DOXO-1, E-[c(RGDfK)2]-DOXO-2, or c(RADfK)-DOXO-2, even at doses of 3 x 24 mg/kg doxorubicin equivalents, compared to an improved antitumor effect for doxorubicin at 2 x 8 mg/kg.     

Identification of novel glycogen synthase kinase-3beta substrate-interacting residues suggests a common mechanism for substrate recognition

Substrate recognition and specificity are essential for the reliability and fidelity of protein kinase function. GSK-3 has a unique substrate specificity that requires prior phosphorylation of its substrates. However, how the enzyme selects its phosphorylated substrates is unknown. Here, we combined in silico modeling with mutagenesis and biological studies to identify GSK-3-substrate interaction sites located within its binding cleft. Protein-protein docking of GSK-3beta and the phosphorylated cAMP responsive element binding protein (pCREB) (using the available experimentally determined structures), identified Phe67, Gln89, and Asn95 of GSK-3beta as putative binding sites interacting with the CREB phosphorylation motif. Mutations of these residues to alanine impaired GSK-3beta phosphorylation of several substrates, without abrogating its autocatalytic activity. Subsequently, expression of the GSK-3beta mutants in cells resulted in decreased phosphorylation of substrates CREB, IRS-1, and beta-catenin, and prevented their suppression of glycogen synthase activity as compared with cells expressing the wild-type GSK-3beta. Our studies provide important additional understanding of how GSK-3beta recognizes its substrates: In addition to prior phosphorylation typically required in GSK-3 substrates, substrate recognition involves interactions with GSK-3beta residues: Phe67, Gln89, and Asn95, which confer a common basis for substrate binding and selectivity, yet allow for substrate diversity.     

Extended haplotype analysis of cystic fibrosis mutations and its implications for the selective advantage hypothesis

The major cystic fibrosis (CF) mutation, F508, is associated with one haplotype (B) determined by the two polymorphic markers, XV2C and KM19. This haplotype is rare (15%) among non-F chromosomes. Its frequency among non-F508 CF chromosomes is 50% with variation between populations. One hypothesis for the high frequency of CF haplotype B chromosomes suggests that there was a selective advantage for CF mutations on this specific background as a result of epistatic selection at other closely linked loci. Since the XV2C and KM19 markers are located 200kb 5 to the CF gene and span only 60 kb, an extended haplotype analysis was needed to test this hypothesis. Haplotypes were determined for 183 CF and 120 non-CF Israeli chromosomes at the XV2C and KM19 loci and at three intragenic polymorphic sites (GATT in intron 6A, TUB18 in intron 19, and 24M in exon 24). Among the studied chromosomes the frequency of non-F508 CF chromosomes associated with haplotype B was 70% (88% among Ashkenazi CF chromosomes). Nine mutations (F508, W1282X, G542X, N1303K, 3849+10 kb CT, Q359K/T360K, S549I, S549R, and 1717-1GA) were identified among the studied chromosomes. These mutations accounted for 96% of CF chromosomes of Ashkenazi origin. Haplotype B was associated with seven of these (F508, W1282X, G542X, N1303K, Q359K/ T360K, S549R, and 1717-1GA). The extended haplotype analysis revealed that in five of the seven mutations associated with the haplotype B, 97% of the chromosomes shared the same intragenic haplotype, 212. The variation found in 3% of the chromosomes was only in the GATT repeat. Two mutations, W1282X and 1717-1GA, were associated with a completely different intragenic haplotype, 121. The results of this study indicate that grouping of CF chromosome by haplotype analysis spanning a small extragenic region might not be sufficient. In addition, the results of the extended haplotype analysis indicate that all the studied CF chromosomes that carry the same mutation derived from the same origin. Furthermore, the results indicate that the majority of the CF mutations are associated with the same extended haplotype, supporting the selective advantage hypothesis.     

Rat lactate dehydrogenase A and B subunit concentrations are not regulated by mRNA abundance in liver and heart

RNA was isolated from rat liver and heart tissues at various times up to 12 weeks after birth, and probed on slot blots with lactate dehydrogenase A and B cDNA probes. Although the relative abundances of LDH A in liver and LDH B in heart increased substantially in the 12 weeks after birth, mRNAs for both isoenzymes remained remarkably stable in both tissues over the same period. The implications of these observations for the regulation of constitutive gene expression are discussed.     

DDM1 binds Arabidopsis methyl-CpG binding domain proteins and affects their subnuclear localization

Methyl-CpG binding domain (MBD) proteins in Arabidopsis thaliana bind in vitro methylated CpG sites. Here, we aimed to characterize the binding properties of AtMBDs to chromatin in Arabidopsis nuclei. By expressing in wild-type cells AtMBDs fused to green fluorescent protein (GFP), we showed that AtMBD7 was evenly distributed at all chromocenters, whereas AtMBD5 and 6 showed preference for two perinucleolar chromocenters adjacent to nucleolar organizing regions. AtMBD2, previously shown to be incapable of binding in vitro-methylated CpG, was dispersed within the nucleus, excluding chromocenters and the nucleolus. Recruitment of AtMBD5, 6, and 7 to chromocenters was disrupted in ddm1 and met1 mutant cells, where a significant reduction in cytosine methylation occurs. In these mutant cells, however, AtMBD2 accumulated at chromocenters. No effect on localization was observed in the chromomethylase3 mutant showing reduced CpNpG methylation or in kyp-2 displaying a reduction in Lys 9 histone H3 methylation. Transient expression of DDM1 fused to GFP showed that DDM1 shares common sites with AtMBD proteins. Glutathione S-transferase pull-down assays demonstrated that AtMBDs bind DDM1; the MBD motif was sufficient for this interaction. Our results suggest that the subnuclear localization of AtMBD is not solely dependent on CpG methylation; DDM1 may facilitate localization of AtMBDs at specific nuclear domains.