Posttranslational Arginylation Enzyme Arginyltransferase1 Shows Genetic Interactions With Specific Cellular Pathways in vivo

Arginylation Regulates Cytoskeleton Organization and Cell Division and Affects Mitochondria in Fission Yeast

Protein arginylation mediated by arginyltransferase Ate1 is a posttranslational modification of emerging importance implicated in the regulation of mammalian embryogenesis, the cardiovascular system, tissue morphogenesis, cell migration, neurodegeneration, cancer, and aging. Ate1 deletion results in embryonic lethality in mice but does not affect yeast viability, making yeast an ideal system to study the molecular pathways regulated by arginylation. Here, we conducted a global analysis of cytoskeleton-related arginylation-dependent phenotypes in Schizosaccharomyces pombe, a fission yeast species that shares many fundamental features of higher eukaryotic cells. Our studies revealed roles of Ate1 in cell division, cell polarization, organelle transport, and interphase cytoskeleton organization and dynamics. We also found a role of Ate1 in mitochondria morphology and maintenance. Furthermore, targeted mass spectrometry analysis of the total Sc. pombe arginylome identified a number of arginylated proteins, including those that play direct roles in these processes; lack of their arginylation may be responsible for ate1-knockout phenotypes. Our work outlines global biological processes potentially regulated by arginylation and paves the way to unraveling the functions of protein arginylation that are conserved at multiple levels of evolution and potentially constitute the primary role of this modification in vivo.

Liquiritin Attenuates Angiotensin II-Induced Cardiomyocyte Hypertrophy via ATE1/TAK1-JNK1/2 Pathway

Objective

To investigate the protective effect and mechanism of liquiritin (LIQ) on cardiomyocyte hypertrophy induced by angiotensin II (Ang II).

Methods

H9c2 cells were pretreated with LIQ before and after Ang II treatment. CCK8 assay was performed to evaluate cell viability. The cell surface area was measured by phalloidin staining. The mRNA expression of atrial and B-type natriuretic peptides (ANP and BNP, respectively) and β-myosin heavy chain (β-MHC) was determined by quantitative reverse transcription-polymerase chain reaction (RT-qPCR); the protein levels of arginyltransferase 1 (ATE1), transforming growth factor beta-activated kinase 1 (TAK1), phos-TAK1, c-Jun N-terminal kinases1/2 (JNK1/2), and phos-JNK1/2 were determined by Western blotting. After constructing the ATE1 overexpression cell models with the pcDNA3.1/ATE1, the abovementioned indicators were tested using the introduced methods.

Results

LIQ at a concentration of ≤30 μM was not cytotoxic to H9c2 cells before exposure to Ang II. The protective effect of LIQ was best observed at 30 μM after Ang II treatment. Phalloidin staining and RT-qPCR results indicated that the deposition of Ang II increased the cell surface area and levels of ANP, BNP, and β-MHC. On the other hand, Western blotting results showed that Ang II increased the ATE1 protein levels and TAK1 and JNK1/2 phosphorylation, which were significantly alleviated after LIQ treatment. LIQ also directly inhibited the ATE1 overexpression in H9c2 cells transfected with pcDNA3.1/ATE1 and further inhibited TAK1 and JNK1/2 phosphorylation.

Conclusion

LIQ can attenuate Ang II-induced cardiomyocyte hypertrophy by regulating the ATE1/TAK1-JNK1/2 pathway.

Ablation of arginyl-tRNA-protein transferase in oligodendrocytes impairs central nervous system myelination

Addition of arginine (Arg) from tRNA can cause major alterations of structure and function of protein substrates. This post-translational modification, termed protein arginylation, is mediated by the enzyme arginyl-tRNA-protein transferase 1 (Ate1). Arginylation plays essential roles in a variety of cellular processes, including cell migration, apoptosis, and cytoskeletal organization. Ate1 is associated with neuronal functions such as neurogenesis and neurite growth. However, the role of Ate1 in glial development, including oligodendrocyte (OL) differentiation and myelination processes in the central nervous system, is poorly understood. The present study revealed a peak in Ate1 protein expression during myelination process in primary cultured OLs. Post-transcriptional downregulation of Ate1 reduced the number of OL processes, and branching complexity, in vitro. We conditionally ablated Ate1 from OLs in mice using 2',3'-cyclic nucleotide 3'-phosphodiesterase-Cre promoter ("Ate1-KO" mice), to assess the role of Ate1 in OL function and axonal myelination in vivo. Immunostaining for OL differentiation markers revealed a notable reduction of mature OLs in corpus callosum of 14-day-old Ate1-KO, but no changes in spinal cord, in comparison with wild-type controls. Local proliferation of OL precursor cells was elevated in corpus callosum of 21-day-old Ate1-KO, but was unchanged in spinal cord. Five-month-old Ate1-KO displayed reductions of mature OL number and myelin thickness, with alterations of motor behaviors. Our findings, taken together, demonstrate that Ate1 helps maintain proper OL differentiation and myelination in corpus callosum in vivo, and that protein arginylation plays an essential role in developmental myelination.

Regulation of Mitochondrial Respiratory Chain Complex Levels, Organization, and Function by Arginyltransferase 1

Arginyltransferase 1 (ATE1) is an evolutionary-conserved eukaryotic protein that localizes to the cytosol and nucleus. It is the only known enzyme in metazoans and fungi that catalyzes posttranslational arginylation. Lack of arginylation has been linked to an array of human disorders, including cancer, by altering the response to stress and the regulation of metabolism and apoptosis. Although mitochondria play relevant roles in these processes in health and disease, a causal relationship between ATE1 activity and mitochondrial biology has yet to be established. Here, we report a phylogenetic analysis that traces the roots of ATE1 to alpha-proteobacteria, the mitochondrion microbial ancestor. We then demonstrate that a small fraction of ATE1 localizes within mitochondria. Furthermore, the absence of ATE1 influences the levels, organization, and function of respiratory chain complexes in mouse cells. Specifically, ATE1-KO mouse embryonic fibroblasts have increased levels of respiratory supercomplexes I+III₂+IV_n. However, they have decreased mitochondrial respiration owing to severely lowered complex II levels, which leads to accumulation of succinate and downstream metabolic effects. Taken together, our findings establish a novel pathway for mitochondrial function regulation that might explain ATE1-dependent effects in various disease conditions, including cancer and aging, in which metabolic shifts are part of the pathogenic or deleterious underlying mechanism.