p38 is essential for the assembly and stability of macromolecular tRNA synthetase complex: Implications for its physiological significance

Abstract

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.

AIMP2/p38, the scaffold for the multi-tRNA synthetase complex, responds to genotoxic stresses via p53

“…2D), suggesting that the components of the multi-ARS complex respond differentially to incoming stimuli. Despite the importance of AIMP2 for the integrity of the multi-ARS complex (11,14), the assembly of the whole complex does not seem to be significantly affected by the UV-dependent dissociation of AIMP2. Perhaps the majority of the complex remains intact because the amount of AIMP2 dissociated from the multi-ARS complex upon UV irradiation appears to be minor (Fig.…”

“…Polyclonal rabbit antibodies against p53 (FL-393) and MDM2 (C-18) were purchased from Santa Cruz Biotechnology, adriamycin, trichostatin A (TSA), and nutlin-3 from Sigma, and ALLN, CHX, staurosporin, JNK inhibitor II, CK2 inhibitor, U0126, SB202190, and EGF from Calbiochem. The anti-AIMP2 antibody was described above (11).…”

“…S1]. Thymocytes could not be obtained from AIMP2 Ϫ/Ϫ mice because of their neonatal lethality (11,12). Conversely, overexpression of AIMP2 enhanced UV-induced cell death (Fig.…”

“…AIMP3 is a tumor suppressor required for chromosome integrity (9,10). Although AIMP2 is critical for the assembly of the multi-ARS complex (11), it also suppresses cell proliferation via down-regulation of c-Myc (12). In addition, AIMP2 was shown to be involved in Parkinson's disease, inducing neural cell death (13).…”

The N Terminus of Pro-endothelial Monocyte-activating Polypeptide II (EMAP II) Regulates Its Binding with the C Terminus, Arginyl-tRNA Synthetase, and Neurofilament Light Protein

“…Intracellularly, pro-EMAP II directly interacts with other components of the MSC, such as p38, arginyl-tRNA synthetase (RARS), and glutaminyl-tRNA synthetase (QARS) (21)(22)(23)(24). Such an interaction plays an important role in the assembly and function of the MSC.…”