SET8 is degraded via PCNA-coupled CRL4(CDT2) ubiquitylation in S phase and after UV irradiation

The eukaryotic cell cycle is regulated by multiple ubiquitin-mediated events, such as the timely destruction of cyclins and replication licensing factors. The histone H4 methyltransferase SET8 (Pr-Set7) is required for chromosome compaction in mitosis and for maintenance of genome integrity. In this study, we show that SET8 is targeted for degradation during S phase by the CRL4(CDT2) ubiquitin ligase in a proliferating cell nuclear antigen (PCNA)-dependent manner. SET8 degradation requires a conserved degron responsible for its interaction with PCNA and recruitment to chromatin where ubiquitylation occurs. Efficient degradation of SET8 at the onset of S phase is required for the regulation of chromatin compaction status and cell cycle progression. Moreover, the turnover of SET8 is accelerated after ultraviolet irradiation dependent on the CRL4(CDT2) ubiquitin ligase and PCNA. Removal of SET8 supports the modulation of chromatin structure after DNA damage. These results demonstrate a novel regulatory mechanism, linking for the first time the ubiquitin-proteasome system with rapid degradation of a histone methyltransferase to control cell proliferation.     

Two cases of human thelaziasis and brief review of Korean cases

The present study was performed to describe 2 cases of human thelaziasis (HT) which occurred in Gyeongsangnam- do and to briefly review the previously reported Korean cases. A 58-year old woman, residing in Hadong-gun, Gyeongsangnam-do, came to Gyeongsang National University Hospital (GNUH) complaining of foreign body sensation and itching of the right eye in March 2000. Total 6 adult nematodes of Thelazia callipaeda (2 males and 4 females) were detected in her right eye. A 80-year old man, residing in Jinju-si, Gyeongsangnam-do, came to GNUH complaining of foreign body sensation, itching, and pain of the right eye in December 2007. A total of 5 worms (4 females and 1 degenerated) were removed from his right eye. We analyzed characteristics of the total 39 Korean HT cases reported to date, including the present 2 cases. Most of the cases (71.8%) occurred in Seoul and Gyeonggi-do before 2000, and 21 cases (53.8%) were males and 18 (46.2%) were females. The prevalence was higher in younger ages below 30 years (48.7%) than 31-60 years (41.0%) and over 61 years (10.3%). The seasonal prevalence showed a higher incidence in autumn (43.6%) than in other seasons. Most of the cases (94.9%) were conjunctival sac infections and only 2 (5.1%) were intraocular cases. The present 2 HT cases are the first reported cases in Gyeongsangnam-do. Some characteristics of Korean HT cases were analyzed.     

MyD88 plays an essential role in inducing B cells capable of differentiating into antibody-secreting cells after vaccination

We investigated the roles of MyD88, an innate adaptor signaling molecule, in inducing protective humoral immunity after vaccination with influenza virus-like particles (VLPs). MyD88 knockout C57BL/6 mice (MyD88(-/-) mice) vaccinated with influenza VLPs showed significant defects in inducing IgG2a/c isotype antibodies and in generating splenic recall memory B cell responses and antibody-secreting plasma cells in the bone marrow. The protective efficacy of influenza VLP vaccination was lower in MyD88(-/-) mice than in the wild-type mice. Our findings indicate that MyD88-mediated innate signaling pathways are important for effectively inducing primary and boost immune responses, T helper type 1 isotype-switched antibodies, and gamma interferon (IFN-γ)-secreting T cell responses. In particular, the results in this study demonstrated for the first time that MyD88-mediated immune activation is likely an essential pathway for effective generation of long-lived antibody-secreting plasma cells and highly protective immunity after vaccination with influenza VLPs. This study provides insight into mechanisms by which recombinant viral vaccines induce protective immunity via the MyD88-mediated innate immune signaling pathway.     

Suppression of PKR promotes network excitability and enhanced cognition by interferon-γ-mediated disinhibition

The double-stranded RNA-activated protein kinase (PKR) was originally identified as a sensor of virus infection, but its function in the brain remains unknown. Here, we report that the lack of PKR enhances learning and memory in several behavioral tasks while increasing network excitability. In addition, loss of PKR increases the late phase of long-lasting synaptic potentiation (L-LTP) in hippocampal slices. These effects are caused by an interferon-γ (IFN-γ)-mediated selective reduction in GABAergic synaptic action. Together, our results reveal that PKR finely tunes the network activity that must be maintained while storing a given episode during learning. Because PKR activity is altered in several neurological disorders, this kinase presents a promising new target for the treatment of cognitive dysfunction. As a first step in this direction, we show that a selective PKR inhibitor replicates the Pkr(-/-) phenotype in WT mice, enhancing long-term memory storage and L-LTP.     

Differential degradation of bicyclics with aromatic and alicyclic rings by Rhodococcus sp. strain DK17

The metabolically versatile Rhodococcus sp. strain DK17 is able to grow on tetralin and indan but cannot use their respective desaturated counterparts, 1,2-dihydronaphthalene and indene, as sole carbon and energy sources. Metabolite analyses by gas chromatography-mass spectrometry and nuclear magnetic resonance spectrometry clearly show that (i) the meta-cleavage dioxygenase mutant strain DK180 accumulates 5,6,7,8-tetrahydro-1,2-naphthalene diol, 1,2-indene diol, and 3,4-dihydro-naphthalene-1,2-diol from tetralin, indene, and 1,2-dihydronaphthalene, respectively, and (ii) when expressed in Escherichia coli, the DK17 o-xylene dioxygenase transforms tetralin, indene, and 1,2-dihydronaphthalene into tetralin cis-dihydrodiol, indan-1,2-diol, and cis-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene, respectively. Tetralin, which is activated by aromatic hydroxylation, is degraded successfully via the ring cleavage pathway to support growth of DK17. Indene and 1,2-dihydronaphthalene do not serve as growth substrates because DK17 hydroxylates them on the alicyclic ring and further metabolism results in a dead-end metabolite. This study reveals that aromatic hydroxylation is a prerequisite for proper degradation of bicyclics with aromatic and alicyclic rings by DK17 and confirms the unique ability of the DK17 o-xylene dioxygenase to perform distinct regioselective hydroxylations.     

Plasmid typing and resistance profiling of Escherichia fergusonii and other Enterobacteriaceae isolates from South Korean farm animals

In this study, we focused on determining the distribution and prevalence of major plasmid replicons in β-lactam-resistant Escherichia fergusonii and Enterobacteriaceae of animal and human origin. A high degree of plasmid variability and multiple plasmid replicons were observed among the isolates. The IncF and IncI1 replicons were the most prevalent in E. fergusonii and Salmonella enterica serovar Indiana isolated from swine and poultry in South Korea, respectively. The presence of broad-host-range plasmid replicons such as IncN, IncA/C, IncHI1, and IncHI2 that are associated with important virulence genes and toxins as well as antimicrobial resistance determinants indicates that E. fergusonii has the potential to become an important pig pathogen and possible emerging opportunistic zoonotic pathogen.     

A stress-responsive caleosin-like protein, AtCLO4, acts as a negative regulator of ABA responses in Arabidopsis

Caleosins or related sequences have been found in a wide range of higher plants. In Arabidopsis, seed-specific caleosins are viewed as oil-body (OB)-associated proteins that possess Ca(2+)-dependent peroxygenase activity and are involved in processes of lipid degradation. Recent experimental evidence suggests that one of the Arabidopsis non-seed caleosins, AtCLO3, is involved in controlling stomatal aperture during the drought response; the roles of the other caleosin-like proteins in Arabidopsis remain largely uncharacterized. We have demonstrated that a novel stress-responsive and OB-associated Ca(2+)-binding caleosin-like protein, AtCLO4, is expressed in non-seed tissues of Arabidopsis, including guard cells, and down-regulated following exposure to exogenous ABA and salt stress. At the seed germination stage, a loss-of-function mutant (atclo4) was hypersensitive to ABA, salt and mannitol stresses, whereas AtCLO4-overexpressing (Ox) lines were more hyposensitive to those stresses than the wild type. In adult stage, atclo4 mutant and AtCLO4-Ox plants showed enhanced and decreased drought tolerance, respectively. Following exposure to exogenous ABA, the expression of key ABA-dependent regulatory genes, such as ABF3 and ABF4, was up-regulated in the atclo4 mutant, while it was down-regulated in AtCLO4-Ox lines. Based on these results, we propose that the OB-associated Ca(2+)-binding AtCLO4 protein acts as a negative regulator of ABA responses in Arabidopsis.     

Small heat shock protein Hsp17.8 functions as an AKR2A cofactor in the targeting of chloroplast outer membrane proteins in Arabidopsis

Plastid proteins that are encoded by the nuclear genome and synthesized in the cytosol undergo posttranslational targeting to plastids. Ankyrin repeat protein 2A (AKR2A) and AKR2B were recently shown to be involved in the targeting of proteins to the plastid outer envelope. However, it remains unknown whether other factors are involved in this process. In this study, we investigated a factor involved in AKR2A-mediated protein targeting to chloroplasts in Arabidopsis (Arabidopsis thaliana). Hsp17.8, a member of the class I (CI) cytosolic small heat shock proteins (sHsps), was identified in interactions with AKR2A. The interaction between Hsp17.8 and AKR2A was further confirmed by coimmunoprecipitation experiments. The carboxyl-terminal ankyrin repeat domain of AKR2A was responsible for AKR2A binding to Hsp17.8. Other CI cytosolic sHsps also interact with AKR2A to varying degrees. Additionally, Hsp17.8 binds to chloroplasts in vitro and enhances AKR2A binding to chloroplasts. HSP17.8 was expressed under normal growth conditions, and its expression increased after heat shock. Hsp17.8 exists as a dimer under normal physiological conditions, and it is converted to high oligomeric complexes, ranging from 240 kD to greater than 480 kD, after heat shock. High levels of Hsp17.8 together with AKR2A resulted in increased plastid targeting of Outer Envelope Protein7 (OEP7), a plastid outer envelope protein expressed as a green fluorescent protein fusion protein. In contrast, artificial microRNA suppression of HSP17.8 and closely related CI cytosolic sHSPs in protoplasts resulted in a reduction of OEP7:green fluorescent protein targeting to plastids. Based on these data, we propose that Hsp17.8 functions as an AKR2A cofactor in targeting membrane proteins to plastid outer membranes under normal physiological conditions.     

An ankyrin repeat protein is involved in anthocyanin biosynthesis in Arabidopsis

The ankyrin domain is one of the most common protein motifs in eukaryotic proteins. Repeated ankyrin domains are ubiquitous and their mediation of protein-protein interactions is involved in a number of physiological and developmental responses such as the cell cycle, signal transduction and cell differentiation. A novel putative phytochrome-interacting ankyrin repeat protein 2 (PIA2) containing three repeated ankyrin domains was identified in Arabidopsis. An in vitro pull-down and phosphorylation assay revealed that PIA2 is phosphorylated and interacts directly with oat phytochrome A. The N-terminal domain of PIA2 was specifically phosphorylated, whereas interactions between the domains of PIA2 and phytochrome A had no Pr/Pfr preference. PIA2 was ubiquitously expressed in most tissues and was localized in both the nucleus and the cytoplasm independent of treatment with light of specific wavelengths. Anthocyanin accumulation in seedlings grown under far-red light, a typical phenotype of wild-type plants, was reduced in a loss-of-function mutant of PIA2 (pia2), whereas anthocyanin accumulation was increased in an overexpressing plant (PIA2-OX). The gene expression of UDP-flavonoid-3'-glucosyl-transferase (UF3GT), a major enzyme in the anthocyanin biosynthesis processes, was decreased in pia2 knockout plants suggesting that decreased anthocyanin was because of the decreased expression of UF3GT. Our results suggest that PIA2 plays a role in the anthocyanin biosynthesis during seedling development as a novel phytochrome-interacting protein.