Bleomycin-induced pulmonary injury in mice deficient in SPARC

SPARC (secreted protein, acidic and rich in cysteine) is a component of the matrix that appears to regulate tissue remodeling. There is evidence that it accumulates in the lung in the setting of pulmonary injury and fibrosis, but direct evidence of its involvement is only now emerging. We therefore investigated the development of pulmonary fibrosis induced by bleomycin administered either intratracheally or intraperitoneally in mice deficient in SPARC. Bleomycin (0.15 U/mouse) given intratracheally induced significantly more pulmonary fibrosis in mice deficient in SPARC compared with that in wild-type control mice, with the mutant mice demonstrating greater neutrophil accumulation in the lung. However, in wild-type and SPARC-deficient mice given intraperitoneal bleomycin (0.8 U/injection x 5 injections over 14 days), the pattern and severity of pulmonary fibrosis, as well as the levels of leukocyte recruitment, were similar in both strains of mice. These findings suggest that the involvement of SPARC in pulmonary injury is likely to be complex, dependent on several factors including the type, duration, and intensity of the insult. Furthermore, increased neutrophil accumulation in the peritoneal cavity was also observed in SPARC-null mice after acute chemical peritonitis. Together, these data suggest a possible role for SPARC in the recruitment of neutrophils to sites of acute inflammation.     

Prior reproduction and weather affect berry crops in central Ontario, Canada

Populations of many perennial plants intermittently produce large seed crops—a phenomenon referred to as mast seeding or masting. Masting may be a response to spatially correlated environmental conditions (the Moran effect), an adaptive reproductive strategy reflecting economies of scale, or a consequence of the internal resource budgets of individual plants. Fruit production by endozoochorous plants representing eight genera varied synchronously over much of central Ontario, Canada, 1998–2009. We tested for effects of weather and prior reproduction on fruit production by comparing AIC_c values among regression models fit to time series of fruit production scores and partitioning contributions by different predictors to multiple R ² into independent and joint contributions. Fruit production by mountain ash (Sorbus spp.), juneberry (Amelanchier spp.), dogwoods (Cornus spp.), nannyberry (Viburnum lentago), and possibly cherries (Prunus spp.) was inversely related to production in the previous year. These effects were independent of weather conditions, suggesting that intrinsic factors such as internal resource budgets or an adaptive strategy of variable reproductive output influenced fruit production. To our knowledge, this is the first evidence of masting in members of the genera Cornus, Viburnum, and Amelanchier, and in members of Prunus and Sorbus in North America. All species produced fewer fruits when weather conditions were dry, so the Moran effect could have synchronized fruit production both within and among species. Patterns and causes of variation in berry crops have implications for ecosystem dynamics, particularly in boreal and subArctic environments where berry crops are important wildlife foods.     

Mechanism of the binding of Z-L-tryptophan and Z-L-phenylalanine to thermolysin and stromelysin-1 in aqueous solutions

The chemical shift of the carboxylate carbon of Z-tryptophan is increased from 179.85 to 182.82 ppm and 182.87 ppm on binding to thermolysin and stromelysin-1 respectively. The chemical shift of Z-phenylalanine is also increased from 179.5 ppm to 182.9 ppm on binding to thermolysin. From pH studies we conclude that the pK_a of the inhibitor carboxylate group is lowered by at least 1.5 pK_a units when it binds to either enzyme. The signal at ~ 183 ppm is no longer observed when the active site zinc atom of thermolysin or stromelysin-1 is replaced by cobalt. We estimate that the distance of the carboxylate carbon of Z-[1-¹³C]-L-tryptophan is ≤ 3.71 Å from the active site cobalt atom of thermolysin. We conclude that the side chain of Z-[1-¹³C]-L-tryptophan is not bound in the S₂′ subsite of thermolysin. As the chemical shifts of the carboxylate carbons of the bound inhibitors are all ~ 183 ppm we conclude that they are all bound in a similar way most probably with the inhibitor carboxylate group directly coordinated to the active site zinc atom. Our spectrophotometric results confirm that the active site zinc atom is tetrahedrally coordinated when the inhibitors Z-tryptophan or Z-phenylalanine are bound to thermolysin.     

Discovery and Targeted LC-MS/MS of Purified Polerovirus Reveals Differences in the Virus-Host Interactome Associated with Altered Aphid Transmission

Circulative transmission of viruses in the Luteoviridae, such as cereal yellow dwarf virus (CYDV), requires a series of precisely orchestrated interactions between virus, plant, and aphid proteins. Natural selection has favored these viruses to be retained in the phloem to facilitate acquisition and transmission by aphids. We show that treatment of infected oat tissue homogenate with sodium sulfite reduces transmission of the purified virus by aphids. Transmission electron microscopy data indicated no gross change in virion morphology due to treatments. However, treated virions were not acquired by aphids through the hindgut epithelial cells and were not transmitted when injected directly into the hemocoel. Analysis of virus preparations using nanoflow liquid chromatography coupled to tandem mass spectrometry revealed a number of host plant proteins co-purifying with viruses, some of which were lost following sodium sulfite treatment. Using targeted mass spectrometry, we show data suggesting that several of the virus-associated host plant proteins accumulated to higher levels in aphids that were fed on CYDV-infected plants compared to healthy plants. We propose two hypotheses to explain these observations, and these are not mutually exclusive: (a) that sodium sulfite treatment disrupts critical virion-host protein interactions required for aphid transmission, or (b) that host infection with CYDV modulates phloem protein expression in a way that is favorable for virus uptake by aphids. Importantly, the genes coding for the plant proteins associated with virus may be examined as targets in breeding cereal crops for new modes of virus resistance that disrupt phloem-virus or aphid-virus interactions.     

Disabled-2 (Dab2) inhibits Wnt/β-catenin signalling by binding LRP6 and promoting its internalization through clathrin

Canonical Wnt signalling requires caveolin-dependent internalization of low-density lipoprotein receptor-related protein 6 (LRP6). Here we report that the tumour suppressor and endocytic adaptor disabled-2 (Dab2), previously described as an inhibitor of Wnt/β-catenin signalling, selectively recruits LRP6 to the clathrin-dependent endocytic route, thereby sequestering it from caveolin-mediated endocytosis. Wnt stimulation induces the casein kinase 2 (CK2)-dependent phosphorylation of LRP6 at S1579, promoting its binding to Dab2 and internalization with clathrin. LRP6 receptor mutant (S1579A), deficient in CK2-mediated phosphorylation and Dab2 binding, fails to associate with clathrin, and thus escapes the inhibitory effects of Dab2 on Wnt/β-catenin signalling. Our data suggest that the S1579 site of LRP6 is a negative regulatory point during LRP6-mediated dorsoventral patterning in zebrafish and in allograft mouse tumour models. We conclude that the tumour suppressor functions of Dab2 involve modulation of canonical Wnt signalling by regulating the endocytic fate of the LRP6 receptor.