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.

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.

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The clinical and preclinical use of high-field intensity (HF, 3 T and above) magnetic resonance imaging (MRI) scanners have significantly increased in the past few years. However, potential health risks are implied in the MRI and especially HF MRI environment due to high-static magnetic fields, fast gradient magnetic fields, and strong radiofrequency electromagnetic fields. In this study, the genotoxic potential of 3 T clinical MRI scans in cultured human lymphocytes in vitro was investigated by analyzing chromosome aberrations (CA), micronuclei (MN), and single-cell gel electrophoresis. Human lymphocytes were exposed to electromagnetic fields generated during MRI scanning (clinical routine brain examination protocols: three-channel head coil) for 22, 45, 67, and 89 min. We observed a significant increase in the frequency of single-strand DNA breaks following exposure to a 3 T MRI. In addition, the frequency of both CAs and MN in exposed cells increased in a time-dependent manner. The frequencies of MN in lymphocytes exposed to complex electromagnetic fields for 0, 22, 45, 67, and 89 min were 9.67, 11.67, 14.67, 18.00, and 20.33 per 1000 cells, respectively. Similarly, the frequencies of CAs in lymphocytes exposed for 0, 45, 67, and 89 min were 1.33, 2.33, 3.67, and 4.67 per 200 cells, respectively. These results suggest that exposure to 3 T MRI induces genotoxic effects in human lymphocytes.