Modulation of the Proteostasis Machinery to  Overcome Stress Caused by Diminished Levels of  t6A‐Modified tRNAs in Drosophila

Abstract

Transfer RNAs (tRNAs) harbor a subset of post-transcriptional modifications required for structural stability or decoding function. N6-threonylcarbamoyladenosine (t6A) is a universally conserved modification found at position 37 in tRNA that pair A-starting codons (ANN) and is required for proper translation initiation and to prevent frame shift during elongation. In its absence, the synthesis of aberrant proteins is likely, evidenced by the formation of protein aggregates. In this work, our aim was to study the relationship between t6A-modified tRNAs and protein synthesis homeostasis machinery using Drosophila melanogaster. We used the Gal4/UAS system to knockdown genes required for t6A synthesis in a tissue and time specific manner and in vivo reporters of unfolded protein response (UPR) activation. Our results suggest that t6A-modified tRNAs, synthetized by the threonyl-carbamoyl transferase complex (TCTC), are required for organismal growth and imaginal cell survival, and is most likely to support proper protein synthesis.

Elongator Subunit 3 (Elp3) Is Required for Zebrafish Trunk Development

“…We observed an upregulation of targets related to the unfolded protein response (UPR) which is consistent with previous data [25], suggesting that the synthesis of misfolded and unfolded proteins is occurring in this condition. This outcome has also been observed when other tRNA modifications are absent or their levels are diminished [25,41,42], supporting the idea that Elongator complex original function is tRNA modification. Previous work in humans and zebrafish had shown that the loss of elp3 leads to a shortening of motoneuron axons [7].…”

“…How translation is regulated in different contexts is of great interest and as tRNAs are central players in decoding genetic information, all forms of regulation over them may have a deep impact in gene expression. Post-transcriptional modification of tRNAs is highly dynamic and adaptable to different situations [49] and has been shown to have deep impact in protein synthesis [38,39,41,50,51]. Understanding the underlying mechanisms that regulate this process, might allow us to manipulate cell behaviors, cell fate or cell death and can have strong impact in cancer treatment [52][53][54] and even be important for establishment of long-term memory [55].…”

Defects in t6A tRNA modification due to GON7 and YRDC mutations lead to Galloway-Mowat syndrome

“…It is likely that the requirement for t 6 A-modified tRNAs levels is dependent of the cell-type and/or cell cycle as has been previously shown in D . melanogaster where highly proliferative cells of the wing imaginal discs are more affected by the absence of t 6 A modification than fully differentiated photoreceptors 35 . Neuronal progenitors that have high mitotic activity probably have higher demands for protein translation, making them more vulnerable to any perturbation in the tight regulation of tRNA modifications.…”

Impact of tRNA Modifications and tRNA-Modifying Enzymes on Proteostasis and Human Disease

“…This indicates a link between deficient translation in the absence of CDKAL1 and increased risk of type 2 diabetes [35,90]. In drosophila, lack of N6-threonylcarbamoyadenosine (t 6 A) at position 37 of tRNAs leads to the accumulation of aberrant proteins in the lumen of the ER and activation of the UPR [101]. Recently, a t 6 A biosynthesis defect in humans due to a mutation in KAE1, a component of the KEOPS complex that catalyzes the second biosynthetic step of t 6 A, was reported [34].…”