Phosphatidylinositol 3-kinase (PI3K) promotes cancer cell survival, migration, growth and proliferation by generating phosphatidylinositol 3,4,5-trisphosphate (PIP3) in the inner leaflet of the ...plasma membrane. PIP3 recruits pleckstrin homology domain-containing proteins to the membrane to activate oncogenic signaling cascades. Anticancer therapeutics targeting the PI3K/AKT/mTOR (mammalian target of rapamycin) pathway are in clinical development. In a mass spectrometric screen to identify PIP3-regulated proteins in breast cancer cells, levels of the Rac activator PIP3-dependent Rac exchange factor-1 (P-REX1) increased in response to PI3K inhibition, and decreased upon loss of the PI3K antagonist phosphatase and tensin homolog (PTEN). P-REX1 mRNA and protein levels were positively correlated with ER expression, and inversely correlated with PI3K pathway activation in breast tumors as assessed by gene expression and phosphoproteomic analyses. P-REX1 increased activation of Rac1, PI3K/AKT and MEK/ERK signaling in a PTEN-independent manner, and promoted cell and tumor viability. Loss of P-REX1 or inhibition of Rac suppressed PI3K/AKT and MEK/ERK, and decreased viability. P-REX1 also promoted insulin-like growth factor-1 receptor activation, suggesting that P-REX1 provides positive feedback to activators upstream of PI3K. In support of a model where PIP3-driven P-REX1 promotes both PI3K/AKT and MEK/ERK signaling, high levels of P-REX1 mRNA (but not phospho-AKT or a transcriptomic signature of PI3K activation) were predictive of sensitivity to PI3K inhibitors among breast cancer cell lines. P-REX1 expression was highest in estrogen receptor-positive breast tumors compared with many other cancer subtypes, suggesting that neutralizing the P-REX1/Rac axis may provide a novel therapeutic approach to selectively abrogate oncogenic signaling in breast cancer cells.
We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor νover ¯_{e} inverse β decay candidates observed over 1958 days ...of data collection. The installation of a flash analog-to-digital converter readout system and a special calibration campaign using different source enclosures reduce uncertainties in the absolute energy calibration to less than 0.5% for visible energies larger than 2 MeV. The uncertainty in the cosmogenic ^{9}Li and ^{8}He background is reduced from 45% to 30% in the near detectors. A detailed investigation of the spent nuclear fuel history improves its uncertainty from 100% to 30%. Analysis of the relative νover ¯_{e} rates and energy spectra among detectors yields sin^{2}2θ_{13}=0.0856±0.0029 and Δm_{32}^{2}=(2.471_{-0.070}^{+0.068})×10^{-3} eV^{2} assuming the normal hierarchy, and Δm_{32}^{2}=-(2.575_{-0.070}^{+0.068})×10^{-3} eV^{2} assuming the inverted hierarchy.
Background We examined the longitudinal associations between changes in cardiovascular biomarkers and cancer therapy-related cardiac dysfunction (CTRCD) in patients with breast cancer treated with ...cardotoxic cancer therapy. Methods and Results Repeated measures of high-sensitivity cardiac troponin T (hs-cTnT), NT-proBNP (N-terminal pro-B-type natriuretic peptide), myeloperoxidase, placental growth factor, and growth differentiation factor 15 were assessed longitudinally in a prospective cohort of 323 patients treated with anthracyclines and/or trastuzumab followed over a maximum of 3.7 years with serial echocardiograms. CTRCD was defined as a ≥10% decline in left ventricular ejection fraction to a value <50%. Associations between changes in biomarkers and left ventricular ejection fraction were evaluated in repeated-measures linear regression models. Cox regression models assessed the associations between biomarkers and CTRCD. Early increases in all biomarkers occurred with anthracycline-based regimens. hs-cTnT levels >14 ng/L at anthracycline completion were associated with a 2-fold increased CTRCD risk (hazard ratio, 2.01; 95% CI, 1.00-4.06). There was a modest association between changes in NT-proBNP and left ventricular ejection fraction in the overall cohort; this was most pronounced with sequential anthracycline and trastuzumab (1.1% left ventricular ejection fraction decline 95% CI, -1.8 to -0.4 with each NT-proBNP doubling). Increases in NT-proBNP were also associated with CTRCD (hazard ratio per doubling, 1.56; 95% CI, 1.32-1.84). Increases in myeloperoxidase were associated with CTRCD in patients who received sequential anthracycline and trastuzumab (hazard ratio per doubling, 1.28; 95% CI, 1.04-1.58). Conclusions Cardiovascular biomarkers may play an important role in CTRCD risk prediction in patients with breast cancer who receive cardiotoxic cancer therapy, particularly in those treated with sequential anthracycline and trastuzumab therapy. Clinical Trial Registration URL: https://www.clinicaltrials.gov/. Unique identifier: NCT01173341.
The first use of diazaphospholenes as chiral catalysts has been demonstrated with enantioselective imine hydroboration. A chiral diazaphospholene prepared in a simple three‐step synthesis from ...commercial materials has been shown to achieve the highest enantioselectivity for the hydroboration of alkyl imines with pinacolborane reported to date. Enantiomer ratios of up to 88:12 were obtained with low (2 mol %) catalyst loadings. Twenty examples of asymmetric reduction employing this main‐group catalysis protocol, including the synthesis of the pharmaceuticals ent‐rasagiline and fendiline, are shown.
The use of chiral diazaphospholenes as catalysts for asymmetric synthesis is reported. A conveniently synthesized diazaphospholene catalyzes the asymmetric reduction of imines, with pinacolborane, to secondary amines with low catalyst loadings at ambient temperature (see example).
The 26S proteasome mediates degradation of ubiquitin-conjugated proteins. Although ubiquitin is recycled from proteasome substrates, the molecular basis of deubiquitination at the proteasome and its ...relation to substrate degradation remain unknown. The Rpn11 subunit of the proteasome lid subcomplex contains a highly conserved Jab1/MPN domain-associated metalloisopeptidase (JAMM) $motif-EX_nHXHX_{10}D$. Mutation of the predicted active-site histidines to alanine (rpn11AXA) was lethal and stabilized ubiquitin pathway substrates in yeast. $Rpn11^{AXA}$ mutant proteasomes assembled normally but failed to either deubiquitinate or degrade ubiquitinated Sic1 in vitro. Our findings reveal an unexpected coupling between substrate deubiquitination and degradation and suggest a unifying rationale for the presence of the lid in eukaryotic proteasomes.
We demonstrate pyridine hydroboration catalyzed by a diazaphospholene hydride precatalyst. Pyridines bearing electron-withdrawing groups in the 3-position are hydroborated efficiently. This system ...features low catalyst loadings, fast reaction times at ambient temperature, and tolerance of other reducible functionality. Off-cycle products of pyridine hydrophosphination were also obtained in one case from a stoichiometric reaction and structurally characterized.
A high precision calibration of the nonlinearity in the energy response of the Daya Bay Reactor Neutrino Experiment’s antineutrino detectors is presented in detail. The energy nonlinearity originates ...from the particle-dependent light yield of the scintillator and charge-dependent electronics response. The nonlinearity model is constrained by γ calibration points from deployed and naturally occurring radioactive sources, the β spectrum from 12B decays, and a direct measurement of the electronics nonlinearity with a new flash analog-to-digital converter readout system. Less than 0.5% uncertainty in the energy nonlinearity calibration is achieved for positrons of kinetic energies greater than 1 MeV.
Context. Low- and intermediate-mass stars lose most of their stellar mass at the end of their lives on the asymptotic giant branch (AGB). Determining gas and dust mass-loss rates (MLRs) is important ...in quantifying the contribution of evolved stars to the enrichment of the interstellar medium. Aims. This study attempts to spectrally resolve CO thermal line emission in a small sample of AGB stars in the Large Magellanic Cloud (LMC). Methods. The Atacama Large Millimeter Array was used to observe two OH/IR stars and four carbon stars in the LMC in the CO J = 2−1 line. Results. We present the first measurement of expansion velocities in extragalactic carbon stars. All four C stars are detected and wind expansion velocities and stellar velocities are directly measured. Mass-loss rates are derived from modelling the spectral energy distribution and Spitzer/IRS spectrum with the DUSTY code. The derived gas-to-dust ratios allow the predicted velocities to agree with the observed gas-to-dust ratios. The expansion velocities and MLRs are compared to a Galactic sample of well-studied relatively low MLRs stars supplemented with extreme C stars with properties that are more similar to the LMC targets. Gas MLRs derived from a simple formula are significantly smaller than those derived from dust modelling, indicating an order of magnitude underestimate of the estimated CO abundance, time-variable mass loss, or that the CO intensities in LMC stars are lower than predicted by the formula derived for Galactic objects. This could be related to a stronger interstellar radiation field in the LMC. Conclusions. Although the LMC sample is small and the comparison to Galactic stars is non-trivial because of uncertainties in their distances (hence luminosities), it appears that for C stars the wind expansion velocities in the LMC are lower than in the solar neighbourhood, while the MLRs appear to be similar. This is in agreement with dynamical dust-driven wind models.
Symbiotic microbes help a myriad of insects acquire nutrients. Recent work suggests that insects also frequently associate with actinobacterial symbionts that produce molecules to help defend against ...parasites and predators. Here we explore a potential association between Actinobacteria and two species of fungus-farming ambrosia beetles,
Xyleborinus saxesenii
and
Xyleborus affinis
. We isolated and identified actinobacterial and fungal symbionts from laboratory reared nests, and characterized small molecules produced by the putative actinobacterial symbionts. One 16S rRNA phylotype of
Streptomyces
(XylebKG-1) was abundantly and consistently isolated from the galleries and adults of
X. saxesenii
and
X. affinis
nests. In addition to
Raffaelea sulphurea
, the symbiont that
X. saxesenii
cultivates, we also repeatedly isolated a strain of
Nectria
sp. that is an antagonist of this mutualism. Inhibition bioassays between
Streptomyces griseus
XylebKG-1 and the fungal symbionts from
X. saxesenii
revealed strong inhibitory activity of the actinobacterium toward the fungal antagonist
Nectria
sp. but not the fungal mutualist
R. sulphurea.
Bioassay guided HPLC fractionation of
S. griseus
XylebKG-1 culture extracts, followed by NMR and mass spectrometry, identified cycloheximide as the compound responsible for the observed growth inhibition. A biosynthetic gene cluster putatively encoding cycloheximide was also identified in
S. griseus
XylebKG-1. The consistent isolation of a single 16S phylotype of
Streptomyces
from two species of ambrosia beetles, and our finding that a representative isolate of this phylotype produces cycloheximide, which inhibits a parasite of the system but not the cultivated fungus, suggests that these actinobacteria may play defensive roles within these systems.
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