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Exposure to microbe-associated molecular patterns (MAMPs) causes dendritic cells (DCs) to undergo a remarkable activation process characterized by changes in key biochemical mechanisms. These enhance antigen processing and presentation, as well as strengthen DC capacity to stimulate naïve T cell proliferation. Here, we show that in response to the MAMPS lipopolysaccharide and polyriboinosinic:polyribocytidylic acid (Poly I:C), RNA polymerase III (Pol lII)-dependent transcription and consequently tRNA gene expression are strongly induced in DCs. This is in part caused by the phosphorylation and nuclear export of MAF1 homolog negative regulator of Poll III (MAF1), via a synergistic casein kinase 2 (CK2)- and mammalian target of rapamycin-dependent signaling cascade downstream of Toll-like receptors (TLRs). De novo tRNA expression is necessary to augment protein synthesis and compensate for tRNA degradation driven by TLR-dependent DC exposure to type-I IFN. Although protein synthesis is not strongly inhibited in absence of RNA Pol III activity, it compromises the translation of key DC mRNAs, like those coding for costimulatory molecules and proinflammatory cytokines, which instead can be stored in stress granules, as shown for CD86 mRNA. TLR-dependent CK2 stimulation and subsequent RNA Pol III activation are therefore key for the acquisition by DCs of their unique T cell immunestimulatory functions. [ABSTRACT FROM AUTHOR]

CD98 heavy chain (CD98hc) forms heteromeric amino acid (AA) transporters by interacting with different light chains. Cancer cells overexpress CD98hc-transporters in order to meet their increased nutritional and antioxidant demands, since they provide branched-chain AA (BCAA) and aromatic AA (AAA) availability while protecting cells from oxidative stress. Here we show that BCAA and AAA shortage phenocopies the inhibition of mTORC1 signalling, protein synthesis and cell proliferation caused by CD98hc ablation. Furthermore, our data indicate that CD98hc sustains glucose uptake and glycolysis, and, as a consequence, the pentose phosphate pathway (PPP). Thus, loss of CD98hc triggers a dramatic reduction in the nucleotide pool, which leads to replicative stress in these cells, as evidenced by the enhanced DNA Damage Response (DDR), S-phase delay and diminished rate of mitosis, all recovered by nucleoside supplementation. In addition, proper BCAA and AAA availability sustains the expression of the enzyme ribonucleotide reductase. In this regard, BCAA and AAA shortage results in decreased content of deoxynucleotides that triggers replicative stress, also recovered by nucleoside supplementation. On the basis of our findings, we conclude that CD98hc plays a central role in AA and glucose cellular nutrition, redox homeostasis and nucleotide availability, all key for cell proliferation. [ABSTRACT FROM AUTHOR]

Arginyltransferase ATE1 mediates posttranslational arginylation and plays key roles in multiple physiological processes. ATE1 utilizes arginyl (Arg)-tRNAArg as the donor of Arg, putting this reaction into a direct competition with the protein synthesis machinery. Here, we address the question of ATE1- Arg-tRNAArg specificity as a potential mechanism enabling this competition in vivo. Using in vitro arginylation assays and Ate1 knockout models, we find that, in addition to full-length tRNA, ATE1 is also able to utilize short tRNAArg fragments that bear structural resemblance to tRNA-derived fragments (tRF), a recently discovered class of small regulatory non-coding RNAs with global emerging biological role. Ate1 knockout cells show a decrease in tRFArg generation and a significant increase in the ratio of tRNAArg:tRFArg compared with wild type, suggesting a functional link between tRFArg and arginylation. We propose that generation of physiologically important tRFs can serve as a switch between translation and protein arginylation. • ATE1-mediated arginylation is highly specific toward arginyl-tRNAArg • ATE1 selectively binds to tRNA and can utilize all mouse tRNAArg species • tRNAArg-derived fragments can mediate arginylation • ATE1 deletion alters the ratio of tRNAArg to tRFArg in cells Avcilar-Kucukgoze et al. dissect the tRNA-dependent mechanisms of regulation of arginylation and suggest a role for tRNA-derived fragments, a type of small non-coding RNAs, in arginylation. [ABSTRACT FROM AUTHOR]

In all branches of life, stalled translation intermediates are recognized and processed by ribosome-associated quality control (RQC) pathways. RQC begins with the splitting of stalled ribosomes, leaving an unfinished polypeptide still attached to the large subunit. Ancient and conserved NEMF family RQC proteins target these incomplete proteins for degradation by the addition of C-terminal "tails." How such tailing can occur without the regular suite of translational components is, however, unclear. Using single-particle cryo-electron microscopy (EM) of native complexes, we show that C-terminal tailing in Bacillus subtilis is mediated by NEMF protein RqcH in concert with RqcP, an Hsp15 family protein. Our structures reveal how these factors mediate tRNA movement across the ribosomal 50S subunit to synthesize polypeptides in the absence of mRNA or the small subunit. • Molecular architecture of RqcH on a peptidyl-tRNA 50S complex revealed • The NFACT-N domain of RqcH distorts and monitors the anticodon of tRNAAla • Discovery of the involvement of RqcP/YabO in ribosome-associated quality control (RQC) • Model for how RqcH and RqcP/YabO mediate tRNA movement during polyalanine tailing Crowe-McAuliffe et al. present cryo-EM structures of native ribosome-associated quality control complexes from Bacillus subtilis , revealing how RqcH cooperates with RqcP/YabO to mediate protein synthesis on the large 50S subunit in the absence of the translocase EF-G, mRNA, and the small 30S subunit. [ABSTRACT FROM AUTHOR]

eIF3, a multi-subunit complex with numerous functions in canonical translation initiation, is known to interact with 40S and 60S ribosomal proteins and translation elongation factors, but a direct involvement in translation elongation has never been demonstrated. We found that eIF3 deficiency reduced early ribosomal elongation speed between codons 25 and 75 on a set of ∼2,700 mRNAs encoding proteins associated with mitochondrial and membrane functions, resulting in defective synthesis of their encoded proteins. To promote elongation, eIF3 interacts with 80S ribosomes translating the first ∼60 codons and serves to recruit protein quality-control factors, functions required for normal mitochondrial physiology. Accordingly, eIF3e+/− mice accumulate defective mitochondria in skeletal muscle and show a progressive decline in muscle strength. Hence, eIF3 interacts with 80S ribosomes to enhance, at the level of early elongation, the synthesis of proteins with membrane-associated functions, an activity that is critical for mitochondrial physiology and muscle health. • eIF3—via eIF3e—promotes mRNA selective early translation elongation • eIF3e-dependent mRNAs encode membrane, secretory, and organelle targeted proteins • eIF3 travels with 80S ribosomes until nascent chains emerge for subcellular targeting • In vivo , eIF3e promotes mitochondrial function and skeletal muscle health Lin et al. discovered that, in addition to its function in canonical translation initiation, multi-subunit eIF3 migrates with post-initiation 80S ribosomes to promote early translation elongation of mRNAs encoding organellar, secretory, and membrane-targeted proteins. Loss of eIF3's elongation and subcellular targeting activity leads to mitochondrial and skeletal muscle dysfunction. [ABSTRACT FROM AUTHOR]