272, 1395-1401).Here, we examine whether cholesterol-enriched compartments in the plasma membrane are responsible for such differential regulation. Pretreatment of BAEC with a cholesterol-binding antibiotic, filipin, did not inhibit shear-dependent activation of JNK. In contrast, filipin and other membrane-permeable cholesterol-binding agents (digitonin and nystatin), but not the lipid-binding agent xylazine, inhibited shear-dependent activation of ERK. The effect of cholesterol-binding drugs did not appear to be due to membrane permeabilization, since treatment of BAEC with a detergent, Triton X-100 which also permeabilizes membranes, did not inhibit shear-dependent activation of ERK. Furthermore, shear-dependent activation of ERK, but not JNK, was inhibited by cyclodextrin, a membrane-impermeable cholesterol-binding agent, which removes cell-surface cholesterol. Moreover, the effects of cyclodextrin were prevented by adding cholesterol during the incubation. These results indicate that cholesterol or cholesterol-sensitive compartments in the plasma membrane play a selective and essential role in activation of ERK, but not JNK, by shear stress. Although exposure to shear stress (1 h) increased the number of caveolae by 3-fold, treatment with filipin had no effect in either control or shear-exposed cells suggesting that caveolae density per se is not a crucial determinant in shear-dependent ERK activation. In summary, the current study suggests that cholesterol-sensitive microdomains in the plasma membrane, such as caveolae-like domains, play a critical role in differential activation of ERK and JNK by shear stress.Vascular endothelial cells recognize shear stress by unknown mechanosensing system(s) that respond both acutely and chronically to flow by producing autocrine and paracrine factors (1). Through these endothelial responses, shear stress controls vascular tone, vessel wall remodeling, binding of blood cells to endothelium, and hemostasis (1). Shear stress selectively and differentially regulates expression of many genes that are important in the pathophysiology of vessel wall function (2-10). Furthermore, a conserved cis-acting shear stress response element has been identified in many shear-sensitive genes including platelet-derived growth factor-B, intercellular adhesion molecule-1, tissue plasminogen activator, and transforming growth factor ␤-1, suggesting its broad implication in shear-dependent regulation of gene expressions (6,8). Shear stress also transiently activates nuclear factor-B, immediate early response genes, and transcription factors that are likely to be involved in the regulation of shear-dependent gene expression (8,11).How does shear stress selectively and differentially regulate such a diverse range of nuclear responses? At least some of these responses appeared to be mediated through regulation of MAP 1 kinases (12-16). Members of the MAP kinase family, ERK, JNK (also known as stress-activated protein kinase), and p38 kinase, have been proposed as important signaling components li...

An auxiliary factor of mammalian multi-aminoacyltRNA synthetases, p43, is thought to be a precursor of endothelial monocyte-activating polypeptide II (EMAP II) that triggers proinflammation in leukocytes and macrophages. In the present work, however, we have shown that p43 itself is specifically secreted from intact mammalian cells, while EMAP II is released only when the cells are disrupted. Secretion of p43 was also observed when its expression was increased. These results suggest that p43 itself should be a real cytokine secreted by an active mechanism. To determine the cytokine activity and active domain of p43, we investigated tumor necrosis factor (TNF) and interleukin-8 (IL-8) production from human monocytic THP-1 cells treated with various p43 deletion mutants. The full length of p43 showed higher cytokine activity than EMAP II, further supporting p43 as the active cytokine. p43 was also shown to activate MAPKs and NFB, and to induce cytokines and chemokines such as TNF, IL-8, MCP-1, MIP-1␣, MIP-1␤, MIP-2␣, IL-1␤, and RANTES. Interestingly, the high level of p43 was observed in the foam cells of atherosclerotic lesions. Therefore, p43 could be a novel mediator of atherosclerosis development as well as other inflammation-related diseases.

Glutamine has been known to be an apoptosis suppressor, since it blocks apoptosis induced by heat shock, irradiation, and c-Myc overexpression. Here, we demonstrated that HeLa cells were susceptible to Fas-mediated apoptosis under the condition of glutamine deprivation. Fas ligation activated apoptosis signalregulating kinase 1 (ASK1) and c-Jun N-terminal kinase (JNK; also known as stress-activated protein kinase (SAPK)) in Gln-deprived cells but not in normal cells, suggesting that Gln might be involved in the activity control of ASK1 and JNK/SAPK. As one of the possible mechanisms for the suppressive effect of Gln on ASK1, we investigated the molecular interaction between human glutaminyl-tRNA synthetase (QRS) and ASK1 and found the Gln-dependent association of the two molecules. While their association was enhanced by the elevation of Gln concentration, they were dissociated by Fas ligation within 5 min. The association involved the catalytic domains of the two enzymes. The ASK1 activity was inhibited by the interaction with QRS as determined by in vitro kinase and transcription assays. Finally, we have shown that QRS inhibited the cell death induced by ASK1, and this antiapoptotic function of QRS was weakened by the deprivation of Gln. Thus, the antiapoptotic interaction of QRS with ASK1 is controlled positively by the cellular concentration of Gln and negatively by Fas ligation. The results of this work provide one possible explanation for the working mechanism of the antiapoptotic activity of Gln and suggest a novel function of mammalian ARSs.

The redox potential of the plasma cysteine/cystine couple (E h CySS) is oxidized in association with risk factors for cardiovascular disease (CVD), including age, smoking, type 2 diabetes, obesity, and alcohol abuse. Previous in vitro findings support a cause-effect relationship for extracellular E h CySS in cell signaling pathways associated with CVD, including those controlling monocyte adhesion to endothelial cells. In this study, we provide evidence that mitochondria are a major source of reactive oxygen species (ROS) in the signaling response to a more oxidized extracellular E h CySS. This increase in ROS was blocked by overexpression of mitochondrial thioredoxin-2 (Trx2) in endothelial cells from Trx2-transgenic mice, suggesting that mitochondrial thiol antioxidant status plays a key role in this redox signaling mechanism. Mass spectrometry-based redox proteomics showed that several classes of plasma membrane and cytoskeletal proteins involved in inflammation responded to this redox switch, including vascular cell adhesion molecule, integrins, actin, and several Ras family GTPases. Together, the data show that the proinflammatory effects of oxidized plasma E h CySS are due to a mitochondrial signaling pathway that is mediated through redox control of downstream effector proteins.

Mammalian tRNA synthetases form a macromolecular complex with three nonenzyme factors: p43, p38, and p18. Here we introduced a mutation within the mouse p38 gene to understand its functional significance for the formation of the multi-tRNA synthetase complex. The complex was completely disintegrated by the deficiency of p38. In addition, the protein levels and catalytic activities of the component enzymes and cofactors were severely decreased. A partial truncation of the p38 polypeptide separated the associated components into different subdomains. The mutant mice showed lethality within 2 days of birth. Thus, this work provides the first evidence, to our knowledge, that p38 is essential for the structural integrity of the multi-tRNA synthetase complex and mouse viability.aminoacyl-tRNA synthetase ͉ macromolecular protein complex ͉ gene trap ͉ protein-protein interaction A minoacyl-tRNA synthetases (ARSs) are essential enzymes catalyzing the ligation of their cognate amino acids and tRNAs. Eight different enzymes of higher eukaryotes form a macromolecular complex with three nonsynthetase factors: p43, p38, and p18 (1-3). Although this complex was first reported more than two decades ago, the functional reason for their molecular assembly and the structural organization of the components still remain unknown.Recently, much information has been obtained about the associations and interactions of the component proteins. The assembly of the complex is mediated by heat-shock protein 90 (4) and involves protein-protein interactions via the unique noncatalytic peptides attached to each of the component enzymes (5-7) and their catalytic core domains (8). It was expected that the three associating factors would also contribute to the complex formation. Among the three auxiliary factors, the interaction and function of p43 have been best elucidated. The p43 protein is located in the middle of the complex (9) and is associated with arginyl-tRNA synthetase via its N-terminal region (10). Its C-terminal domain contains an OB-fold, which is responsible for the interaction with tRNA (11, 12) and facilitates the catalytic activity of the bound enzyme (10). Interestingly, p43 is also secreted to work as a proinflammatory cytokine (13,14). The functions of the two other factors are less understood. p38 interacts with many components of the complex (2, 15). To understand the in vivo functional significance of p38 in the formation of the multi-ARS complex, we mutated the p38 structural gene in the mouse and investigated its effects on the cellular stability of the multi-ARS complex and the component proteins. Deletion analyses of p38 were also conducted to map the organization of the component proteins within the complex.