Tissue-specific alternative splicing separates the catalytic and cell signaling functions of human leucyl-tRNA synthetase

Max Baymiller,Benjamin Nordick,Connor M Forsyth,Susan A Martinis

doi:10.1016/j.jbc.2022.101757

Max Baymiller, Benjamin Nordick + Show 2 more

Open Access

https://doi.org/10.1016/j.jbc.2022.101757

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Abstract

The aminoacyl-tRNA synthetases are an ancient and ubiquitous component of all life. Many eukaryotic synthetases balance their essential function, preparing aminoacyl-tRNA for use in mRNA translation, with diverse roles in cell signaling. Herein, we use long-read sequencing to discover a leukocyte-specific exon skipping event in human leucyl-tRNA synthetase (LARS). We show that this highly expressed splice variant, LSV3, is regulated by serine-arginine-rich splicing factor 1 (SRSF1) in a cell-type-specific manner. LSV3 has a 71 amino acid deletion in the catalytic domain and lacks any tRNA leucylation activity in vitro. However, we demonstrate that this LARS splice variant retains its role as a leucine sensor and signal transducer for the proliferation-promoting mTOR kinase. This is despite the exon deletion in LSV3 including a portion of the previously mapped Vps34-binding domain used for one of two distinct pathways from LARS to mTOR. In conclusion, alternative splicing of LARS has separated the ancient catalytic activity of this housekeeping enzyme from its more recent evolutionary role in cell signaling, providing an opportunity for functional specificity in human immune cells.

Highlights

Aminoacyl-tRNA synthetases (AARS) are ancient, ubiquitous, and essential enzymes which attach amino acids to their cognate tRNAs [1]
Previous reports showed that immunological tissues contain a large number of AARS splice variants [20]
As would be expected from the primary sequence, we found that LSV3 did not aminoacylate crude tRNA with leucine (Fig. 2D) under conditions in which recombinant full-length human LARS was active

Summary

Introduction

Aminoacyl-tRNA synthetases (AARS) are ancient, ubiquitous, and essential enzymes which attach amino acids to their cognate tRNAs [1]. LSV3, which skips exon 20, dominated the alternative splicing landscape of LARS in leukocytes, representing over 20% of reads in the PacBio dataset (Fig. 1B). Despite removal of a portion of the catalytic domain for aminoacylation, LSV3 retains key features in the primary sequence that are important for mTOR signaling, including the conserved leucine binding site and RagD binding peptide [21] (Fig. 3A).

Results

Conclusion