The unfolded protein response is shaped by the NMD pathway

Endoplasmic reticulum (ER) stress induces the unfolded protein response (UPR), an essential adaptive intracellular pathway that relieves the stress. Although the UPR is an evolutionarily conserved and beneficial pathway, its chronic activation contributes to the pathogenesis of a wide variety of human disorders. The fidelity of UPR activation must thus be tightly regulated to prevent inappropriate signaling. The nonsense-mediated RNA decay (NMD) pathway has long been known to function in RNA quality control, rapidly degrading aberrant mRNAs, and has been suggested to regulate subsets of normal mRNAs. Here, we report that the NMD pathway regulates the UPR. NMD increases the threshold for triggering the UPR in vitro and in vivo, thereby preventing UPR activation in response to normally innocuous levels of ER stress. NMD also promotes the timely termination of the UPR. We demonstrate that NMD directly targets the mRNAs encoding several UPR components, including the highly conserved UPR sensor, IRE1α, whose NMD-dependent degradation partly underpins this process. Our work not only sheds light on UPR regulation, but demonstrates the physiological relevance of NMD''s ability to regulate normal mRNAs.     

Discovery of benzothiazole-based adenosine A2B receptor antagonists with improved A2A selectivity

The highly potent but modestly selective N-(2-amino-4-methoxy-benzothiazol-7-yl)-N-ethyl-acetamide derivative 2 was selected as the starting point for the design of novel selective A_2B antagonists, due to its excellent potency, and good drug-like properties. A series of compounds containing nonaromatic amides or ureas of five- or six-membered rings, and also bearing an m-trifluoromethyl-phenyl group (shown to impart superior potency) was prepared and evaluated for their selectivity against the A_2A and A₁ receptors. This work resulted in the identification of compound 30, with excellent potency and high selectivity against both A_2A and A₁ receptors.     

Ecology and evolution of mammalian biodiversity

Mammals have incredible biological diversity, showing extreme flexibility in eco-morphology, physiology, life history and behaviour across their evolutionary history. Undoubtedly, mammals play an important role in ecosystems by providing essential services such as regulating insect populations, seed dispersal and pollination and act as indicators of general ecosystem health. However, the macroecological and macroevolutionary processes underpinning past and present biodiversity patterns are only beginning to be explored on a global scale. It is also particularly important, in the face of the global extinction crisis, to understand these processes in order to be able to use this knowledge to prevent future biodiversity loss and loss of ecosystem services. Unfortunately, efforts to understand mammalian biodiversity have been hampered by a lack of data. New data compilations on current species' distributions, ecologies and evolutionary histories now allow an integrated approach to understand this biodiversity. We review and synthesize these new studies, exploring the past and present ecology and evolution of mammalian biodiversity, and use these findings to speculate about the mammals of our future.     

MGMT is a molecular determinant for potency of the DNA-EGFR-combi-molecule ZRS1

To enhance the potency of current EGFR inhibitors, we developed a novel strategy that seeks to confer them an additional DNA damaging function, leading to the design of drugs termed combi-molecules. ZRS1 is a novel combi-molecule that contains an EGFR tyrosine kinase targeting quinazoline arm and a methyltriazene-based DNA damaging one. We examined its effect on human tumor cell lines with varied levels of EGFR and O6-methylguanine DNA methyltransferase (MGMT). ZRS1 was more potent than the clinical methylating agent temozolomide in all cell lines, regardless of their MGMT status. However, its potency was in the same range as or less than that of Iressa, an EGFR inhibitor, against MGMT-proficient cells. In the MGMT-deficient or in MGMT-proficient cells exposed to the MGMT inhibitor O6-benzylguanine, its potency was superior to that of Iressa and temozolomide or a temozolomide+Iressa combination. Cell signaling analysis in A549 (MGMT(+)) and A427 (MGMT(-)) showed that ZRS1 strongly inhibited EGFR phosphorylation and related signaling pathways. In addition, the p53 pathway was activated by DNA damage in both cell lines, but apoptosis was significantly more pronounced in A427 cells. Using MGMT shRNA to block endogenous MGMT protein expression in A549 resulted in significant sensitization to ZRS1. Furthermore, transfection of MGMT into A427 greatly decreased the potency of ZRS1. These results conclusively show that MGMT is a critical molecular determinant for the full-blown potency of the dual EGFR-DNA targeting combi-molecule.     

Gap junctions mediate STAT5-independent β-casein expression in CID-9 mammary epithelial cells

Crosstalk between gap junction intracellular communication (GJIC), STAT5 and OCT-1 in gap junction (GJ)-dependent β-casein expression was investigated. CID-9 mammary cells plated with prolactin on non-adherent substratum (poly-HEMA) expressed β-casein independent of STAT5 only in the presence of the GJIC inducer, cAMP. Nuclear STAT5 levels were not detectable. By contrast, cells on EHS-drip expressed β-casein in a STAT5-dependent manner and nuclear STAT5 levels were up-regulated. A 75 kDa OCT-1 isoform was detected in conditions that induced β-casein expression regardless of substratum. Interestingly, 40 and 28 kDa OCT-1 isoforms were induced in cells on polyHEMA with cAMP. Electrophoretic mobility shift assays (EMSA) for OCT-1 revealed two band shifts in cells on polyHEMA with cAMP and on EHS-drip, which were repressed by the GJIC inhibitor, 18α-GA. These studies demonstrated that mammary cells on polyHEMA expressed β-casein in response to prolactin in a pathway that involves GJIC and OCT-1 and is independent of STAT5 nuclear translocation.     

Biophysical profiling of tumor cell lines

Despite significant differences in genetic profiles, cancer cells share common phenotypic properties, including membrane-associated changes that facilitate invasion and metastasis. The Corning Epic optical biosensor was used to monitor dynamic mass rearrangements within and proximal to the cell membrane in tumor cell lines derived from cancers of the colon, bone, cervix, lung and breast. Data was collected in real time and required no exogenously added signaling moiety (signal-free technology). Cell lines displayed unique profiles over the time-courses: the time-courses all displayed initial signal increases to maximal values, but the rate of increase to those maxima and the value of those maxima were distinct for each cell line. The rate of decline following the maxima also differed among cell lines. There were correlations between the signal maxima and the observed metastatic behavior of the cells in xenograft experiments; for most cell types the cells that were more highly metastatic in mice had lower time-course maxima values, however the reverse was seen in breast cancer cells. The unique profiles of these cell lines and the correlation of at least one profile characteristic with metastatic behavior demonstrate the potential utility of biophysical tumor cell profiling in the study of cancer biology.     

Functional coupling of adenine nucleotide translocase and mitochondrial creatine kinase is enhanced after exercise training in lung transplant skeletal muscle

Mechanisms responsible for limitation of exercise capacity in lung transplant recipients (LR) and benefits gained by exercise training were studied. Mitochondrial respiration parameters, energy transfer, and cell structure were assessed in vastus lateralis biopsies using the permeabilized fiber technique with histochemical and morphometric measurements. Twelve male controls (C) and 12 LR performed exercise training over 12 wk. Before exercise training, there were strong correlations between exercise capacity (maximal O(2) consumption and endurance time at 70% maximal power output) and cellular events, as assessed by percentage of type I fibers and apparent K(m) for exogenous ADP. Anticalcineurins were not involved in LR exercise limitation, since there were no differences in maximal mitochondrial rate of respiration before exercise training and no abnormalities in respiratory chain complexes compared with C. Training resulted in a significant increase in physiological parameters both at the cellular (apparent K(m) for exogenous ADP and stimulating effect of creatine) and integrated (maximal O(2) consumption, power output at ventilatory threshold, maximal power output, and endurance time at 70% maximal power output) levels in LR and C. After the training period, improvements in maximal O(2) consumption and in maximal mitochondrial rate of respiration were noted, as well as changes in endurance time and percentage of type I fibers. Because there were no changes in diameters and fiber types, baseline alteration of apparent K(m) for exogenous ADP and its improvement after training might be related to changes within the intracellular energetic units. After the training period, intracellular energetic units exhibited a higher control of mitochondrial respiration by creatine linked to a more efficient functional coupling adenine nucleotide translocase-mitochondrial creatine kinase, resulting in better exercise performances in C and LR.     

An EMG fractal indicator having different sensitivities to changes in force and muscle fatigue during voluntary static muscle contractions.

During a sustained contraction, electromyographic signals (EMGs) undergo a spectral compression. This fatigue behaviour induces a shift of the mean and the median frequencies to lower frequencies. On the other hand, several studies conclude that the mean/median frequency can increase, decrease or remain constant with an increasing force level. Such inconsistency is embarrassing since the fatigue state may be influenced by the force level. In this paper, we propose a frequency indicator which is sensitive to the force level independently of the fatigue state evaluated at 70% of the maximal voluntary contraction. Ten healthy volunteers participated in the study and both surface EMGs (from the short head of the biceps brachii) and force signals were measured. This study compared force and fatigue effects on the EMGs during short (3-s) isometric contractions at different strength intensities and during a sustained isometric contraction until exhaustion. The EMGs partly show 1/falpha spectral behaviours since their power spectral densities may experimentally fit with two linear segments in a log-log representation. The measured "right" slope produces variations of force as 20 times the variations of fatigue. 1/falpha Behaviour may be related to stochastic fractals. This fractal indicator is a new frequency indicator that is thus complementary to other known classical frequency indicators when studying force during unknown fatigue states.