Lyso-phospholipids exert a major injurious effect on lung cell membranes during Acute Respiratory Distress Syndrome (ARDS), but the mechanisms leading to their in vivo generation are still unknown. Intratracheal administration of LPS to guinea pigs induced the secretion of type II secretory phospholipase A2 (sPLA2-II) accompanied by a marked increase in fatty acid and lyso-phosphatidylcholine (lyso-PC) levels in the bronchoalveolar lavage fluid (BALF). Administration of LY311727, a specific sPLA2-II inhibitor, reduced by 60% the mass of free fatty acid and lyso-PC content in BALF. Gas chromatography/mass spectrometry analysis revealed that palmitic acid and palmitoyl-2-lyso-PC were the predominant lipid derivatives released in BALF. A similar pattern was observed after the intratracheal administration of recombinant guinea pig (r-GP) sPLA2-II and was accompanied by a 50-60% loss of surfactant phospholipid content, suggesting that surfactant is a major lung target of sPLA2-II. In confirmation, r-GP sPLA2-II was able to hydrolyze surfactant phospholipids in vitro. This hydrolysis was inhibited by surfactant protein A (SP-A) through a direct and selective protein-protein interaction between SP-A and sPLA2-II. Hence, our study reports an in vivo direct causal relationship between sPLA2-II and early surfactant degradation and a new process of regulation for sPLA2-II activity. Anti-sPLA2-II strategy may represent a novel therapeutic approach in lung injury, such as ARDS. (

Several Gi‐linked neurotransmitter receptors, including dopamine D2 receptors, act synergistically with Ca2+‐mobilizing stimuli to potentiate release of arachidonic acid (AA) from membrane phospholipids. In brain, AA and its metabolites are thought to act as intracellular second messengers, suggesting that receptor‐dependent potentiation of AA release may participate in neuronal transmembrane signaling. To study the molecular mechanisms underlying this modulatory response, we have now used Chinese hamster ovary cells transfected with rat D2‐receptor cDNA, CHO(D2). Two antisense oligodeoxynucleotides corresponding to distinct cDNA sequences of cytosolic, AA‐specific phospholipase A2 (cPLA2) were synthesized and added to cultures of CHO(D2) cells. Incubation with antisense oligodeoxynucleotides inhibited D2 receptor‐dependent release of AA but had no effect on D2‐receptor binding or D2 inhibition of cyclic AMP accumulation. In addition, pharmacological experiments showed that D2 receptor‐dependent AA release was prevented by nonselective phospholipase inhibitors (such as mepacrine) but not by inhibitors of membrane‐bound, non‐AA‐specific PLA2 (such as p‐bromophenacyl bromide). cPLA2 is expressed in brain tissue. The results, showing that cPLA2 participates in receptor‐dependent potentiation of AA release in CHO(D2) cells, suggest that this phospholipase may serve a similar signaling function in brain.

Background: Regulation of integrin activation has important implications for tumor cell invasion and metastasis. Results: EGF activates ERK/p90RSK and Rho/Rho kinase signaling in A431 and DiFi colon cancer cells, leading to phosphorylation of filamin A (FLNa) and inactivation of the ␣5␤1 integrin receptor. Conclusion: EGF promotes ␣5␤1 inactivation through the p90RSK-dependent phosphorylation of FLNa. Significance: We have identified a novel EGF-dependent mechanism controlling the ␣5␤1 integrin activation state.

SummaryPAI1 stimulates assembly of the fibronectin matrix in osteosarcoma cells through crosstalk between the αvβ5 and α5β1 integrins

We have shown previously that guinea pig alveolar macrophages (AM) synthesize a secretory phospholipase A2 (PLA2) during in vitro incubation. Here, we report the molecular cloning of this enzyme and show that it has structural features closely related to all known mammalian type-II PLA2. The mRNA and PLA2 activity were undetectable in freshly collected AM, but their levels increased dramatically to reach maximal values after 16 h of culture. Thereafter, the PLA2 activity remained constant with a parallel secretion in the medium, in contrast to mRNA level which returned to near basal values after 32 h. Incubation of AM for 16 h with the inflammatory secretagogue peptide f-Met-Leu-Phe (fMLP) markedly reduced the PLA2 activity and mRNA levels. This inhibition was prevented by preexposure of AM to pertussis toxin, an inhibitor of G-protein. In contrast, when AM were first cultured for 16 h and then incubated with fMLP, no significant change was observed in their PLA2 activity. In conditions where the type-II PLA2 was completely abrogated by fMLP, the latter did not alter the lipopolysaccharide-induced accumulation of tumor necrosis factor alpha mRNA or the release of arachidonic acid induced by the subsequent addition of the calcium ionophore A23187. These studies show that the inflammatory peptide fMLP down-regulates the expression of the type-II PLA2 by AM through a process mediated by G-protein. A possible negative control of the type-II PLA2 expression during AM activation is suggested.