The inhibitory receptor IRp60 (CD300a) is expressed and functional on human mast cells

Mast cell-mediated responses are likely to be regulated by the cross talk between activatory and inhibitory signals. We have screened human cord blood mast cells for recently characterized inhibitory receptors expressed on NK cells. We found that IRp60, an Ig superfamily member, is expressed on human mast cells. On NK cells, IRp60 cross-linking leads to the inhibition of cytotoxic activity vs target cells in vitro. IRp60 is constitutively expressed on mast cells but is down-regulated in vitro by the eosinophil proteins major basic protein and eosinophil-derived neurotoxin. An immune complex-mediated cross-linking of IRp60 led to inhibition of IgE-induced degranulation and stem cell factor-mediated survival via a mechanism involving tyrosine phosphorylation, phosphatase recruitment, and termination of cellular calcium influx. To evaluate the role of IRp60 in regulation of allergic responses in vivo, a murine model of allergic peritonitis was used in which the murine homolog of IRp60, LMIR1, was neutralized in BALB/c mice by mAbs. This neutralization led to a significantly augmented release of inflammatory mediators and eosinophilic infiltration. These data demonstrate a novel pathway for the regulation of human mast cell function and allergic responses, indicating IRp60 as a candidate target for future treatment of allergic and mast cell-associated diseases.     

S-glutathiolation of Ras mediates redox-sensitive signaling by angiotensin II in vascular smooth muscle cells

Angiotensin II (AII) increases production of reactive oxygen species from NAD(P)H oxidase, a response that contributes to vascular hypertrophy. Here we show in cultured vascular smooth muscle cells that S-glutathiolation of the redox-sensitive Cys(118) on the small GTPase, Ras, plays a critical role in AII-induced hypertrophic signaling. AII simultaneously increased the Ras activity and the S-glutathiolation of Ras (GSS-Ras) detected by biotin-labeled GSH or mass spectrometry. Both the increase in activity and GSS-Ras was labile under reducing conditions, suggesting the essential nature of this thiol modification to Ras activation. Overexpression of catalase, a dominant-negative p47(phox), or glutaredoxin-1 decreased GSS-Ras, Ras activation, p38, and Akt phosphorylation and the induction of protein synthesis by AII. Furthermore, expression of a Cys(118) mutant Ras decreased AII-mediated p38 and Akt phosphorylation as well as protein synthesis. These results show that H(2)O(2) from NAD(P)H oxidase forms GSS-Ras on Cys(118) and increases its activity leading to p38 and Akt phosphorylation, which contributes to the induction of protein synthesis. This study suggests that GSS-Ras is a redox-sensitive signaling switch that participates in the cellular response to AII.     

FliZ induces a kinetic switch in flagellar gene expression

FliZ is an activator of class 2 flagellar gene expression in Salmonella enterica. To understand its role in flagellar assembly, we investigated how FliZ affects gene expression dynamics. We demonstrate that FliZ participates in a positive-feedback loop that induces a kinetic switch in class 2 gene expression.     

Carbon:chlorophyll <Emphasis Type="Italic">a</Emphasis> ratio,assimilation numbers and turnover times of Lake Kinneret phytoplankton

Carbon to chlorophyll a (C:Chl) ratios, assimilation numbers (A.N.) and turnover times of natural populations of individual species and taxonomic groups were extracted from a long-term database of phytoplankton wet-weight biomass, chlorophyll a concentrations, and primary production in Lake Kinneret, Israel. From a database spanning more than a decade, we selected data for samples dominated by a single species or taxonomic group. The overall average of C:Chl was highest for cyanophytes and lowest for diatoms, while chlorophytes and dinoflagellates showed intermediate values. When converting chlorophyll a to algal cellular carbon this variability should be taken into account. The variability in C:Chl within each phylum and species (when data were available) was high and the variability at any particular sampling date tended to be greater than the temporal variability. The average chlorophyll a-normalized rate of photosynthetic activity of cyanophytes was higher and that of the dinoflagellates lower than that of other phyla. Turnover time of phytoplankton, calculated using primary productivity data at the depth of maximal photosynthetic rate, was longest in dinoflagellates and shortest in cyanophytes, with diatoms and chlorophytes showing intermediate values. The more extreme C:Chl and turnover times of dinoflagellates and cyanobacteria in comparison with chlorophytes and diatoms should be taken into consideration when employed in ecological modeling.     

On the mechanisms of the reaction of dodecatungstophosphate with alkyl radicals in aqueous solutions

The reduced lacunary polyoxotungstate, [PW₁₁O₃₉]⁸⁻, reacts with the ^.CH₂CH(OH)CH₃ and ^.CH₂C(CH₃)₂OH radicals via a mechanism involving β-hydroxide elimination to yield propene and 2-methyl propene respectively, and [PW₁₁O₃₉]⁷⁻. [PW₁₁O₃₉]⁸⁻ is also oxidized by methyl radicals in a reaction which yields methane as the major product. It is proposed that the reactions proceed via the formation of short lived transients with W-C σ bonds.     

Ligand-binding specificities of laminin-binding integrins: a comprehensive survey of laminin-integrin interactions using recombinant alpha3beta1, alpha6beta1, alpha7beta1 and alpha6beta4 integrins.

The interactions of cells with basement membranes are primarily mediated via the engagement of laminins by a group of integrin family proteins, including integrins alpha3beta1, alpha6beta1, alpha7beta1 and alpha6beta4. To explore the ligand-binding specificities of these laminin-binding integrins, we produced these integrins, including two alpha7beta1 splice variants (alpha7X1beta1 and alpha7X2beta1), as soluble recombinant proteins and determined their binding specificities and affinities toward a panel of purified laminin isoforms containing distinct alpha chains. Among the five laminin-binding integrins investigated, alpha3beta1 and alpha6beta4 exhibited a clear specificity for laminin-332 (alpha3beta3gamma2) and laminin-511 (alpha5beta1gamma1)/521 (alpha5beta2gamma1), while integrin alpha6beta1 showed a broad specificity, binding to all laminin isoforms with a preference for laminin-111 (alpha1beta1gamma1), laminin-332 and laminin-511/521. The two alpha7beta1 variants were distinct from alpha3beta1, alpha6beta1 and alpha6beta4 in that they did not bind to laminin-332. alpha7X1beta1 bound to all laminins, except laminin-332, with a preference for laminin-211 (alpha2beta1gamma1)/221 (alpha2beta2gamma1) and laminin-511/521, while alpha7X2beta1 bound preferentially to laminin-111 and laminin-211/221. Laminin-511/521 was the most preferred ligand for all the laminin-binding integrins, except for alpha7X2beta1, whereas laminin-411 was the poorest ligand, capable of binding to alpha6beta1 and alpha7X1beta1 with only modest binding affinities. These comprehensive analyses of the interactions between laminin-binding integrins and a panel of laminins clearly demonstrate that the isoforms of both integrins and laminins differ in their binding specificities and affinities, and provide a molecular basis for better understanding of the adhesive interactions of cells with basement membranes of defined laminin compositions.