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Alterations in genes encoding for proteins that control fucosylation are known to play causative roles in several developmental disorders, such as Dowling-Degos disease 2 and congenital disorder of glycosylation type IIc (CDGIIc). Recent studies have provided evidence that changes in fucosylation can contribute to the development and progression of several different types of cancers. It is therefore important to gain a detailed understanding of how fucosylation is altered in disease states so that interventions may be developed for therapeutic purposes. In this report, we find that fucosylation occurs on many intracellular proteins. This is an interesting finding, as the fucosylation machinery is restricted to the secretory pathway and is thought to predominately affect cell-membrane-bound and secreted proteins. We find that Ribosomal protein S3 (RPS3) is fucosylated in normal tissues and in cancer cells, and that the extent of its fucosylation appears to respond to stress, including MAPK inhibitors, suggesting a new role in posttranslational protein function. Our data identify a new ribosome-independent species of fucosylated RPS3 that interacts with proteins involved in posttranscriptional regulation of RNA, such as Heterogeneous nuclear ribonucleoprotein U (HNRNPU), as well as with a predominance of non-coding RNAs. These data highlight a novel role for RPS3, which, given previously reported oncogenic roles for RPS3, might represent functions that are perturbed in pathologies such as cancer. Together, our findings suggest a previously unrecognized role for fucosylation in directly influencing intracellular protein functions.

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At the center of translation are the ancient and essential aminoacyl‐tRNA synthetases (AARS). These proteins set the genetic code by attaching amino acids to their cognate tRNAs with very high accuracy. Over a lengthy evolutionary time, AARS have developed functions beyond aminoacylation through the addition of new domains and repurposing of existing structural motifs. Non‐canonical functions of AARS are especially widespread in eukaryotes and range from cell signaling to transcription and translation regulation. For example, human cytoplasmic leucyl‐tRNA synthetase (LeuRS) has been adapted as an intracellular leucine sensor for the mammalian target of the rapamycin complex 1 (mTORC1) master regulatory pathway (Han, 2012). Ten alternatively‐spliced variants of cytoplasmic LeuRS were identified in humans using RNA Seq (Lo, 2014). It is possible that each of these splice variants contributes to novel and idiosyncratic functions. We have found that one of these variants, LeuRS AS04, is overexpressed in both Jurkat T cells and peripheral blood mononuclear cells (PBMC), suggesting a potential immune‐cell specific role. Despite the absence of key catalytic residues, LeuRS AS04 is a potent and specific activator of mTORC1. In particular, downstream phosphorylation of mTORC1 target ribosomal protein S6 kinase beta‐1 (p70S6K1) was significantly enhanced in cells overexpressing AS04 compared to those overexpressing full‐length LeuRS. We hypothesize that this alternately spliced LeuRS variant might have evolved to enhance and regulate the non‐canonical function of LeuRS‐dependent mTORC1 signaling.Support or Funding InformationW.M. Keck Foundation Biomedical Research GrantThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.