Autophosphorylation of ataxia-telangiectasia mutated is regulated by protein phosphatase 2A

Ionizing radiation induces autophosphorylation of the ataxia-telangiectasia mutated (ATM) protein kinase on serine 1981; however, the precise mechanisms that regulate ATM activation are not fully understood. Here, we show that the protein phosphatase inhibitor okadaic acid (OA) induces autophosphorylation of ATM on serine 1981 in unirradiated cells at concentrations that inhibit protein phosphatase 2A-like activity in vitro. OA did not induce gamma-H2AX foci, suggesting that it induces ATM autophosphorylation by inactivation of a protein phosphatase rather than by inducing DNA double-strand breaks. In support of this, we show that ATM interacts with the scaffolding (A) subunit of protein phosphatase 2A (PP2A), that the scaffolding and catalytic (C) subunits of PP2A interact with ATM in undamaged cells and that immunoprecipitates of ATM from undamaged cells contain PP2A-like protein phosphatase activity. Moreover, we show that IR induces phosphorylation-dependent dissociation of PP2A from ATM and loss of the associated protein phosphatase activity. We propose that PP2A plays an important role in the regulation of ATM autophosphorylation and activity in vivo.     

RpoS and oxidative stress conditions regulate succinyl‐CoA: 3‐ketoacid‐coenzyme A transferase (SCOT) expression in Burkholderia pseudomallei

Burkholderia pseudomallei, a pathogenic gram‐negative bacterium, causes the severe human disease melioidosis. This organism can survive in eukaryotic host cells by escaping reactive oxygen species via the regulation of stress responsive sigma factors, including RpoS. In B. pseudomallei, RpoS has been reported to play a role in the oxidative stress response through enhanced activity of OxyR and catalase. In this study, the RpoS dependent oxidative stress responsive system was further characterized using comparative proteomic analysis. The proteomic profiles of wild‐type B. pseudomallei following exposure to H₂O₂ and between wild‐type and the rpoS mutant strains were analyzed. Using stringent criteria, 13 oxidative responsive proteins, eight of which are regulated by RpoS, were identified with high confidence. It was observed that ScoA, a subunit of the SCOT enzyme not previously shown to be involved directly in the oxidative stress response, is significantly down‐regulated after hydrogen peroxide treatment. ScoA and ScoB have been predicted to be organized in a single operon using computational methods: in this study it was confirmed by RT‐PCR that these genes are indeed co‐transcribed as a single mRNA. The present study is the first to report a role for RpoS in the down‐regulation of SCOT expression in response to oxidative stress in B. pseudomallei.     

Rescue of a cold-sensitive mutant at low temperatures by cold shock proteins from <Emphasis Type="Italic">Polaribacter irgensii</Emphasis> KOPRI 22228

Exposure to low temperatures induces the biosynthesis of specific sets of proteins, including cold shock proteins (Csps). Since many of the specific functions of pychrophilic Csps are unknown, the roles of Csps from an Arctic bacterium, Polaribacter irgensii KOPRI 22228, were examined. The genes encoding CspA and CspC of P. irgensii were cloned in this study. Sequence analysis showed that these proteins have cold shock domains containing two RNA-binding motifs, RNP1 and RNP2. Both proteins bound oligo(dT)-cellulose resins, suggesting single-stranded nucleic acid-binding activity. When the P. irgensii Csps were overexpressed in Escherichia coli, the cold-resistance of the host was increased by more than five-fold. The P. irgensii Csps also rescued a cold-sensitive E. coli csp-quadruple deletion strain, BX04, at low temperatures. These results suggest that Csps from P. irgensii play a role in survival in polar environments.     

Ohioensins F and G: protein tyrosine phosphatase 1B inhibitory benzonaphthoxanthenones from the Antarctic moss Polytrichastrum alpinum

Ohioensins F and G (1 and 2), two new benzonaphthoxanthenones, have been isolated from the MeOH extract of Antarctic moss Polytrichastrum alpinum by various chromatographic methods. The structures of these compounds were determined mainly by analysis of NMR spectroscopic data. The known compounds ohioensins A and C (3 and 4) were also obtained. Compounds 1-4 showed potent inhibitory activity against therapeutically targeted protein tyrosine phosphatase 1B (PTP1B). Kinetic analysis of PTP1B inhibition by ohioensin F (1) suggested that benzonaphthoxanthenones inhibited PTP1B activity in a non-competitive manner.     

Meta-Analysis of Combined Therapy with Angiotensin Receptor Antagonists versus ACE Inhibitors Alone in Patients with Heart Failure

Background

There is insufficient evidence whether the benefit of adding angiotensin II receptor blockers (ARBs) to angiotensin-converting enzyme (ACE) inhibitors outweighs the increased risk of adverse effects in patients with heart failure.

Methodology/Principal Findings

Two independent reviewers searched and abstracted randomized controlled trials of ARBs and ACE inhibitors compared to ACE inhibitor therapy alone in patients with heart failure reporting mortality and hospitalizations having a follow-up of at least 6 months identified by a systematic literature search. Eight trials including a total of 18,061 patients fulfilled our inclusion criteria. There was no difference between patients treated with combination therapy and ACE inhibitor therapy alone for overall mortality, hospitalization for any reason, fatal or nonfatal MI. Combination therapy was, however, associated with fewer hospital admissions for heart failure (RR 0.81, 95%CI 0.72–0.91), although there was significant heterogeneity across trials (p-value for heterogeneity = 0.04; I² = 57% [95%CI 0–83%]). Patients treated with combination therapy had a higher risk of worsening renal function and symptomatic hypotension, and their trial medications were more often permanently discontinued. Lack of individual patient data precluded the analysis of time-to-event data and identification of subgroups which potentially benefit more from combination therapy such as younger patients with preserved renal function and thus at lower risk to experience worsening renal function or hyperkalemia.

Conclusions/Significance

Combination therapy with ARBs and ACE inhibitors reduces admissions for heart failure in patients with congestive heart failure when compared to ACE inhibitor therapy alone, but does not reduce overall mortality or all-cause hospitalization and is associated with more adverse events. Thus, based on current evidence, combination therapy with ARBs and ACE inhibitors may be reserved for patients who remain symptomatic on therapy with ACE inhibitors under strict monitoring for any signs of worsening renal function and/or symptomatic hypotension.     

Regulation of helper T cell responses to staphylococcal superantigens

Staphylococcal superantigens (sAgs) including toxic shock syndrome toxin-1 (TSST-1) and related enterotoxins are exoproteins with unique immunobiological properties. They bind to major histocompatibility complex (MHC) class II molecules of antigen-presenting cells outside the peptide groove, and induce massive proliferation of T cells bearing specific V beta determinants. This tri-molecular interaction leads to uncontrolled release of various proinflammatory cytokines especially interferon-gamma (IFN-gamma) and tumor necrosis factor-a (TNF-alpha), the key cytokines causing sAg-mediated shock. The effector T cells involved in this hyper-immune response are predominantly of the T helper-1 (Th1) phenotype. There is also some evidence that polarization to a Th2 response with the production of classical anti-inflammatory cytokines (such as interleukins IL-4 and IL-6) also occurs. Moreover, the emergence of a novel regulatory T cell (Tr1) subset, producing mainly IL-10 but little or no IL-2 and IL-4, has recently been described following repeated sAg stimulation. In this review, the current knowledge regarding the regulation of T helper cell subsets in response to staphylococcal sAgs is critically evaluated, and the role of various cytokines which directly influence T cell differentiation and polarization is summarized. Particular emphasis is directed towards pro-inflammatory as well as anti-inflammatory and regulatory effector functions during toxic shock. Based on this review, we propose that a delayed production of IL-10 by Tr1 cells may be the most prominent driving force in the down-regulation of the Th1 hyper-immune response, and the critical determinant for the eventual recovery of the host.