Do aposematism and Batesian mimicry require bright colours? A test,using European viper markings.

Predator avoidance of noxious prey, aposematism and defensive mimicry are normally associated with bright, contrasting patterns and colours. However, noxious prey may be unable to evolve conspicuous coloration because of other selective constraints, such as the need to be inconspicuous to their own prey or to specialist predators. Many venomous snakes, particularly most vipers, display patterns that are apparently cryptic, but nevertheless highly characteristic, and appear to be mimicked by other, non-venomous snakes. However, predator avoidance of viper patterns has never been demonstrated experimentally. Here, the analysis of 813 avian attacks on 12,636 Plasticine snake models in the field shows that models bearing the characteristic zigzag band of the adder (Vipera berus) are attacked significantly less frequently than plain models. This suggests that predator avoidance of inconspicuously but characteristically patterned noxious prey is possible. Our findings emphasize the importance of mimicry in the ecological and morphological diversification of advanced snakes.     

p38 MAP kinase-dependent regulation of endothelial cell permeability

We have previously shown that thrombin induces endothelial cell barrier dysfunction via cytoskeleton activation and contraction and have determined the important role of endothelial cell myosin light chain kinase (MLCK) in this process. In the present study we explored p38 MAP kinase as a potentially important enzyme in thrombin-mediated endothelial cell contractile response and permeability. Thrombin induces significant p38 MAP kinase activation in a time-dependent manner with maximal effect at 30 min, which correlates with increased phosphorylation of actin- and myosin-binding protein, caldesmon. Both SB-203580 and dominant negative p38 adenoviral vector significantly attenuated thrombin-induced declines in transendothelial electrical resistance. Consistent with these data SB-203580 decreased actin stress fiber formation produced by thrombin in endothelium. In addition, dominant negative p38 had no effect on thrombin-induced myosin light chain diphosphorylation. Thrombin-induced total and site-specific caldesmon phosphorylation (Ser789) as well as dissociation of caldesmon-myosin complex were attenuated by SB-203580 pretreatment. These results suggest the involvement of p38 MAP kinase activities and caldesmon phosphorylation in the MLCK-independent regulation of thrombin-induced endothelial cell permeability.     

Attenuation of chronic hypoxic pulmonary hypertension by simvastatin

The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have been shown to improve multiple normal endothelial cell functions and inhibit vascular wall cell proliferation. We hypothesized that one such agent, simvastatin, would attenuate chronic hypoxic pulmonary hypertension. Male adult Sprague-Dawley rats were exposed (14 days) to normoxia (N), normoxia plus once-a-day administered simvastatin (20 mg/kg ip) (NS), hypoxia (10% inspired O2 fraction) (H), or hypoxia plus simvastatin (HS). Mean pulmonary artery pressure, measured in anesthetized, ventilated rats with an open-chest method, was reduced from 25 +/- 2 mmHg in H to 18 +/- 1 in HS (P < 0.001) but did not reach normoxic values (12 +/- 1 mmHg). Similarly, right ventricular/left ventricular plus interventricular septal weight was reduced from 0.53 +/- 0.02 in the H group to 0.36 +/- 0.02 in the HS group (P < 0.001). The increased hematocrit in H (0.65 +/- 0.02) was prevented by simvastatin treatment (0.51 +/- 0.01, P < 0.001). Hematocrit was similar in N versus NS. Alveolar vessel muscularization and medial thickening of vessels 50-200 microM in diameter induced by hypoxia were also significantly attenuated in the HS animals. Lung endothelial nitric oxide synthase (eNOS) protein expression in the HS group was less than H (P < 0.01) but was similar in N versus NS. We conclude that simvastatin treatment potently attenuates chronic hypoxic pulmonary hypertension and polycythemia in rats and inhibits vascular remodeling. Enhancement of lung eNOS expression does not appear to be involved in mediating this effect.     

A selective inducible NOS dimerization inhibitor prevents systemic,cardiac, and pulmonary hemodynamic dysfunction in endotoxemic mice

Increased nitric oxide (NO) production by inducible NO synthase (NOS2), an obligate homodimer, is implicated in the cardiovascular sequelae of sepsis. We tested the ability of a highly selective NOS2 dimerization inhibitor (BBS-2) to prevent endotoxin-induced systemic hypotension, myocardial dysfunction, and impaired hypoxic pulmonary vasoconstriction (HPV) in mice. Mice were challenged with Escherichia coli endotoxin before treatment with BBS-2 or vehicle. Systemic blood pressure was measured before and 4 and 7 h after endotoxin challenge, and echocardiographic parameters of myocardial function were measured before and 7 h after endotoxin challenge. The pulmonary vasoconstrictor response to left mainstem bronchus occlusion, which is a measure of HPV, was studied 22 h after endotoxin challenge. BBS-2 treatment alone did not alter baseline hemodynamics. BBS-2 treatment blocked NOS2 dimerization and completely inhibited the endotoxin-induced increase of plasma nitrate and nitrite levels. Treatment with BBS-2 after endotoxin administration prevented systemic hypotension and attenuated myocardial dysfunction. BBS-2 also prevented endotoxin-induced impairment of HPV. In contrast, treatment with NG-nitro-l-arginine methyl ester, which is an inhibitor of all three NOS isoforms, prevented the systemic hypotension but further aggravated the myocardial dysfunction associated with endotoxin challenge. Treatment with BBS-2 prevented endotoxin from causing key features of cardiovascular dysfunction in endotoxemic mice. Selective inhibition of NOS2 dimerization with BBS-2, while sparing the activities of other NOS isoforms, may prove to be a useful treatment strategy in sepsis.     

IFN-gamma-producing gamma delta T cells help control murine West Nile virus infection

West Nile (WN) virus causes fatal meningoencephalitis in laboratory mice, thereby partially mimicking human disease. Using this model, we have demonstrated that mice deficient in gammadelta T cells are more susceptible to WN virus infection. TCRdelta(-/-) mice have elevated viral loads and greater dissemination of the pathogen to the CNS. In wild-type mice, gammadelta T cells expanded significantly during WN virus infection, produced IFN-gamma in ex vivo assays, and enhanced perforin expression by splenic T cells. Adoptive transfer of gammadelta T cells to TCRdelta(-/-) mice reduced the susceptibility of these mice to WN virus, and this effect was primarily due to IFN-gamma-producing gammadelta T cells. These data demonstrate a distinct role for gammadelta T cells in the control of and prevention of mortality from murine WN virus infection.     

Specific interaction of protein tyrosine phosphatase-MEG2 with phosphatidylserine

Protein tyrosine phosphatase (PTP)-MEG2 is an intracellular tyrosine phosphatase that contains a Sec14 homology domain. We have purified the full-length and truncated forms of the enzyme from recombinant adenovirus-infected human 293 cells. By using lipid-membrane overlay and liposome binding assays, we demonstrated that PTP-MEG2 specifically binds phosphatidylserine among over 20 lipid compounds tested. The binding is mediated by its N-terminal Sec14 domain. In intact cells, the Sec14 domain is responsible for localization of PTP-MEG2 to the perinuclear region, and uploading of PS into the cell membrane causes translocation of PTP-MEG2 to the plasma membrane. Phosphatidylserine is a relatively abundant cell membrane phospholipid non-symmetrically distributed in the outer layer and inner layer of cell membranes. It has recently been defined as an important ligand for clearance of apoptotic cells. By specifically binding phosphatidylserine, PTP-MEG2 may play an important role in regulating signaling processes associated with phagocytosis of apoptotic cells.     

Phosphorylation-regulated cleavage of the tumor suppressor PTEN by caspase-3: implications for the control of protein stability and PTEN-protein interactions

PTEN phosphatase is one of the most commonly targeted tumor suppressors in human cancers and a key regulator of cell growth and apoptosis. We have found that PTEN is cleaved by caspase-3 at several target sites, located in unstructured regions within the C terminus of the molecule. Cleavage of PTEN was increased upon TNFalpha-cell treatment and was negatively regulated by phosphorylation of the C-terminal tail of PTEN by the protein kinase CK2. The proteolytic PTEN fragments displayed reduced protein stability, and their capability to interact with the PTEN interacting scaffolding protein S-SCAM/MAGI-2 was lost. Interestingly, S-SCAM/MAGI-2 was also cleaved by caspase-3. Our findings suggest the existence of a regulatory mechanism of protein stability and PTEN-protein interactions during apoptosis, executed by caspase-3 in a PTEN phosphorylation-regulated manner.     

Adenine release is fast in MutY-catalyzed hydrolysis of G:A and 8-Oxo-G:A DNA mismatches

MutY, a DNA repair enzyme, is unusual in that it binds exceedingly tightly to its products after the chemical steps of catalysis. Until now it was not known whether the product being released in the rate-limiting step was DNA, adenine, or both. MutY hydrolyzes adenine from 8-oxo-G:A (OG:A) base pair mismatches as the first step in the base excision repair pathway, as well as from G:A mismatches. The products are adenine and DNA containing an apurinic (AP) site. Tight product binding may have a physiological role in preventing further damage at the OG:AP site. We developed a rate assay using [8-14C]adenine in OG:A or G:A mismatches that distinguishes between adenine hydrolysis and adenine release. [8-14C]Adenine was released quickly from the MutY.AP-DNA.[8-14C]adenine complex, with a rate constant greater than 5 min-1. This was much faster than the rate-limiting step, at 0.006-0.015 min-1. Gel retardation experiments showed that AP-DNA release was very slow, consistent with it being the rate-limiting step. Thus, the kinetic mechanism involves fast adenine release after hydrolysis followed by rate-limiting AP-DNA release. Adenine appears to be buried deep in the protein.DNA interface, but there is enough flexibility or open space for it to dissociate from the MutY.APDNA.adenine complex. These results have implications for the catalytic mechanism of MutY.