HUWE1 interacts with PCNA to alleviate replication stress

Defects in DNA replication, DNA damage response, and DNA repair compromise genomic stability and promote cancer development. In particular, unrepaired DNA lesions can arrest the progression of the DNA replication machinery during S‐phase, causing replication stress, mutations, and DNA breaks. HUWE1 is a HECT‐type ubiquitin ligase that targets proteins involved in cell fate, survival, and differentiation. Here, we report that HUWE1 is essential for genomic stability, by promoting replication of damaged DNA. We show that HUWE1‐knockout cells are unable to mitigate replication stress, resulting in replication defects and DNA breakage. Importantly, we find that this novel role of HUWE1 requires its interaction with the replication factor PCNA, a master regulator of replication fork restart, at stalled replication forks. Finally, we provide evidence that HUWE1 mono‐ubiquitinates H2AX to promote signaling at stalled forks. Altogether, our work identifies HUWE1 as a novel regulator of the replication stress response.     

The Synthesis and Activity of cis-and trans-2-(Aminomethyl) cyclopropanecarboxylic Acid as Conformationally Restricted Analogues of GABA

Abstract: The synthesis of cis -2-(aminomethyl) cyclopropanecarboxylic acid, a new analogue of GABA in a folded conformation, is described, as is also an improved preparation of trans -2-(aminomethyl) cyclopropanecarboxylic acid. When adminstered microelectrophoretically the trans isomer was more potent than GABA as a bicuculline-sensitive depressant of the firing of cat spinal neurons in vivo , whereas the cis-isomer was less potent than GABA and its effects appeared not to be sensitive to bicuculline methochloride. Trans -2-(aminomethyl) cyclopropanecarboxylic acid was a weak inhibitor of the sodium-dependent uptake of GABA by mini slices of rat cerebral cortex and a substrate for the GABA: 2-oxoglutarate aminotransferase activity in extracts of rat brain mitochondria. The cis isomer did not influence GABA uptake or aminotransferase activity and neither isomer reduced glutamate decar-boxylase activity in rat brain homogenates. Both cyclopropane isomers inhibited the sodium-independent binding of GABA to synaptic membranes from rat brain and their relative potencies together with those found for the stereochemically related unsaturated derivatives, cis -and trans -4-aminocrotonic acid, were broadly consistent with the activity observed for these compounds in vivo on cat spinal neurons. These studies reinforce the evidence that extended rather than folded conformations of GABA are active at most GABA recognition sites within the mammalian central nervous system.     

Both temperature fluctuations and East Asian monsoons have driven plant diversification in the karst ecosystems from southern China

Karst ecosystems in southern China are species‐rich and have high levels of endemism, yet little is known regarding the evolutionary processes responsible for the origin and diversification of karst biodiversity. The genus Primulina (Gesneriaceae) comprises ca. 170 species endemic to southern China with high levels of ecological (edaphic) specialization, providing an exceptional model to study the plant diversification in karsts. We used molecular data from nine chloroplast and 11 nuclear regions and macroevolutionary analyses to assess the origin and cause of species diversification due to palaeoenvironmental changes and edaphic specialization in Primulina. We found that speciation was positively associated with changes in past temperatures and East Asian monsoons through the evolutionary history of Primulina. Climatic change around the mid‐Miocene triggered an early burst followed by a slowdown of diversification rate towards the present with the climate cooling. We detected different speciation rates among edaphic types, and transitions among soil types were infrequently and did not impact the overall speciation rate. Our findings suggest that both global temperature changes and East Asian monsoons have played crucial roles in floristic diversification within the karst ecosystems in southern China, such that speciation was higher when climate was warmer and wetter. This is the first study to directly demonstrate that past monsoon activity is positively correlated with speciation rate in East Asia. This case study could motivate further investigations to assess the impacts of past environmental changes on the origin and diversification of biodiversity in global karst ecosystems, most of which are under threat.     

Trapped in a vicious loop: Toll-like receptors sustain the spontaneous cytokine production by rheumatoid synovium

Synovial tissue of patients with rheumatoid arthritis (RA) spontaneously produces several cytokines, of which a fundamental role in joint inflammation and destruction has been established. However, the factors sustaining this phenomenon remain poorly understood. In a recent report, blockade of Toll-like receptor 2 (TLR2) was found to inhibit the spontaneous release of inflammatory cytokines by intact RA synovial explant cultures. Adding to the recent evidence implicating other TLRs (in particular, TLR4), this observation highlights the potential of TLRs as therapeutic targets to suppress the local production of multiple cytokines and to control the chronic inflammatory loop in RA.     

Positive relationships among aboveground biomass,tree species diversity,and urban greening management in tropical coastal city of Haikou

Within urban green spaces, tree species diversity is believed to correlate with aboveground biomass, though there is some disagreement within the literature on the strength and directionality of the relationship. Therefore, we assessed the relationship between the biodiversity of woody species and the aboveground biomass of woody plant species in the tropical, coastal city of Haikou in southern China. To accomplish this, we obtained comprehensive tree and site data through field sampling of 190 urban functional units (UFUs, or work units) corresponding to six types of land uses governmental‐institutional, industrial‐commercial, park‐recreational, residential, transport infrastructure, and undeveloped area. Based on our field data, we investigated the relationship between tree species diversity and aboveground biomass using multiple regression, which revealed significant relationships across all five types of land uses. Aboveground biomass in green spaces was also correlated with anthropogenic factors, especially time since urban development, or site age, annual maintenance frequency by human caretakers, and human population density. Among these factors, maintenance is the strongest predictor of aboveground biomass in urban green space. Therefore, this study highlights the critical role of maintenance of urban green space in promoting both aboveground biomass and woody biodiversity in urban ecosystems and, consequently, on urban ecosystem services. Our findings contribute to a deeper understanding of the ecosystem services provided by communities of woody plant species in urban areas.     

Inferring the biogeographic origins of inter‐continental disjunct endemics using a Bayes‐DIVA approach

The arcto‐Tertiary relictual flora is comprised of many genera that occur non‐contiguously in the temperate zones of eastern Asia, Europe, eastern North America, and western North America. Within each distributional area, species are typically endemic and may thus be widely separated from closely related species within the other areas. It is widely accepted that this common pattern of distribution resulted from of the fragmentation of a once more‐continuous arcto‐Tertiary forest. The historical biogeographic events leading to the present‐day disjunction have often been investigated using a phylogenetic approach. Limitations to these previous studies have included phylogenetic uncertainty and uncertainty in ancestral range reconstructions. However, the recently described Bayes‐DIVA method handles both types of uncertainty. Thus, we used Bayes‐DIVA analysis to reconstruct the stem lineage distributions for 185 endemic lineages from 23 disjunct genera representing 17 vascular plant families. In particular, we asked whether endemic lineages within each of the four distributional areas more often evolved from (1) widespread ancestors, (2) ancestors dispersed from other areas, or (3) endemic ancestors. We also considered which of these three biogeographic mechanisms may best explain the origins of arcto‐Tertiary disjunct endemics in the neotropics. Our results show that eastern Asian endemics more often evolved from endemic ancestors compared to endemics in Europe and eastern and western North America. Present‐day endemic lineages in the latter areas more often arose from widespread ancestors. Our results also provide anecdotal evidence for the importance of dispersal in the biogeographic origins of arcto‐Tertiary species endemic in the neotropics.     

Regulation of T cell priming by lymphoid stroma

The priming of immune T cells by their interaction with dendritic cells (DCs) in lymph nodes (LN), one of the early events in productive adaptive immune responses, occurs on a scaffold of lymphoid stromal cells, which have largely been seen as support cells or sources of chemokines and homeostatic growth factors. Here we show that murine fibroblastic reticular cells (FRCs), isolated from LN of B6 mice, play a more direct role in the immune response by sensing and modulating T cell activation through their upregulation of inducible nitric oxide synthase (iNOS) in response to early T cell IFNγ production. Stromal iNOS, which only functions in very close proximity, attenuates responses to inflammatory DC immunization but not to other priming regimens and preferentially affects Th1 cells rather than Th2. The resultant nitric oxide production does not affect T cell-DC coupling or initial calcium signaling, but restricts homotypic T cell clustering, cell cycle progression, and proliferation. Stromal feedback inhibition thus provides basal attenuation of T cell responses, particularly those characterized by strong local inflammatory cues.     

Mouse models to unravel the role of inhaled pollutants on allergic sensitization and airway inflammation

Background

Nicotinic acetylcholine receptors (nAChR) have been identified on a variety of cells of the immune system and are generally considered to trigger anti-inflammatory events. In the present study, we determine the nAChR inventory of rat alveolar macrophages (AM), and investigate the cellular events evoked by stimulation with nicotine.

Methods

Rat AM were isolated freshly by bronchoalveolar lavage. The expression of nAChR subunits was analyzed by RT-PCR, immunohistochemistry, and Western blotting. To evaluate function of nAChR subunits, electrophysiological recordings and measurements of intracellular calcium concentration ([Ca²⁺]_i) were conducted.

Results

Positive RT-PCR results were obtained for nAChR subunits α3, α5, α9, α10, β1, and β2, with most stable expression being noted for subunits α9, α10, β1, and β2. Notably, mRNA coding for subunit α7 which is proposed to convey the nicotinic anti-inflammatory response of macrophages from other sources than the lung was not detected. RT-PCR data were supported by immunohistochemistry on AM isolated by lavage, as well as in lung tissue sections and by Western blotting. Neither whole-cell patch clamp recordings nor measurements of [Ca²⁺]_i revealed changes in membrane current in response to ACh and in [Ca²⁺]_i in response to nicotine, respectively. However, nicotine (100 μM), given 2 min prior to ATP, significantly reduced the ATP-induced rise in [Ca²⁺]_i by 30%. This effect was blocked by α-bungarotoxin and did not depend on the presence of extracellular calcium.

Conclusions

Rat AM are equipped with modulatory nAChR with properties distinct from ionotropic nAChR mediating synaptic transmission in the nervous system. Their stimulation with nicotine dampens ATP-induced Ca²⁺-release from intracellular stores. Thus, the present study identifies the first acute receptor-mediated nicotinic effect on AM with anti-inflammatory potential.