The endotoxic shock syndrome is characterized by systemic inflammation, multiple organ damage, circulatory collapse and death. Systemic release of tumor necrosis factor (TNF)-α and other cytokines purportedly mediates this process. However, the primary tissue target remains unidentified. The present studies provide evidence that endotoxic shock results from disseminated endothelial apoptosis. Injection of lipopolysaccharide (LPS), and its putative effector TNF-α, into C57BL/6 mice induced apoptosis in endothelium of intestine, lung, fat and thymus after 6 h, preceding nonendothelial tissue damage. LPS or TNF-α injection was followed within 1 h by tissue generation of the pro-apoptotic lipid ceramide. TNF-binding protein, which protects against LPS-induced death, blocked LPS-induced ceramide generation and endothelial apoptosis, suggesting systemic TNF is required for both responses. Acid sphingomyelinase knockout mice displayed a normal increase in serum TNF-α in response to LPS, yet were protected against endothelial apoptosis and animal death, defining a role for ceramide in mediating the endotoxic response. Furthermore, intravenous injection of basic fibroblast growth factor, which acts as an intravascular survival factor for endothelial cells, blocked LPS-induced ceramide elevation, endothelial apoptosis and animal death, but did not affect LPS-induced elevation of serum TNF-α. These investigations demonstrate that LPS induces a disseminated form of endothelial apoptosis, mediated sequentially by TNF and ceramide generation, and suggest that this cascade is mandatory for evolution of the endotoxic syndrome.

A proline-directed serine/threonine ceramide-activated protein (CAP) kinase mediates transmembrane signaling through the sphingomyelin pathway. CAP kinase reportedly initiates proinflammatory TNF alpha action by phosphorylating and activating Raf-1. The present studies delineate kinase suppressor of Ras (KSR), identified genetically in Caenorhabditis elegans and Drosophila, as CAP kinase. Mouse KSR, like CAP kinase, renatures and autophosphorylates as a 100-kDa membrane-bound polypeptide. KSR overexpression constitutively activates Raf-1. TNF alpha or ceramide analogs markedly enhance KSR autophosphorylation and its ability to complex with, phosphorylate, and activate Raf-1. In vitro, low nanomolar concentrations of natural ceramide stimulate KSR to autophosphorylate, and transactivate Raf-1. Other lipid second messengers were ineffective. Moreover, Thr269 the Raf-1 site phosphorylated by CAP kinase, is also recognized by KSR. Thus, by previously established criteria, KSR appears to be CAP kinase.

A high-resolution structure of a ligand-bound, soluble form of human monoglyceride lipase (MGL) is presented. The structure highlights a novel conformation of the regulatory lid-domain present in the lipase family as well as the binding mode of a pharmaceutically relevant reversible inhibitor. Analysis of the structure lacking the inhibitor indicates that the closed conformation can accommodate the native substrate 2-arachidonoyl glycerol. A model is proposed in which MGL undergoes conformational and electrostatic changes during the catalytic cycle ultimately resulting in its dissociation from the membrane upon completion of the cycle. In addition, the study outlines a successful approach to transform membrane associated proteins, which tend to aggregate upon purification, into a monomeric and soluble form.