bims-hypusi 2024-02-04 papers

Issue of 2024–02–04
two papers selected by
Sebastian J. Hofer, University of Graz

Int J Biol Macromol. 2024 Jan;pii: S0141-8130(23)04641-X. [Epub ahead of print]254(Pt 1): 127743

eIF5A promotes +1 programmed ribosomal frameshifting in Euplotes octocarinatus.

Yu Xiao, Jia Li, Ruanlin Wang, Yajiao Fan, Xiaxia Han, Yuejun Fu, Paula Alepuz, Wei Wang, Aihua Liang.

Programmed ribosomal frameshifting (PRF) exists in all branches of life that regulate gene expression at the translational level. The single-celled eukaryote Euplotes exhibit high frequency of PRF. However, the molecular mechanism of modulating Euplotes PRF remains largely unknown. Here, we identified two novel eIF5A genes, eIF5A1 and eIF5A2, in Euplotes octocarinatus and found that the Eo-eIF5A2 gene requires a -1 PRF to produce complete protein product. Although both Eo-eIF5As showed significant structural similarity with yeast eIF5A, neither of them could functionally replace yeast eIF5A. Eo-eIF5A knockdown inhibited +1 PRF of the η-tubulin gene. Using an in vitro reconstituted translation system, we found that hypusinated Eo-eIF5A (Eo-eIF5AH) can promote +1 PRF at the canonical AAA_UAA frameshifting site of Euplotes. The results showed eIF5A is a novel trans-regulator of PRF in Euplotes and has an evolutionary conserved role in regulating +1 PRF in eukaryotes.

Keywords: Euplotes octocarinatus; Programmed ribosomal frameshifting; eIF5A

DOI: https://doi.org/10.1016/j.ijbiomac.2023.127743

J Biol Chem. 2024 Jan 30. pii: S0021-9258(24)00079-6. [Epub ahead of print] 105703

eIF5 stimulates the CUG initiation of RAN translation of poly-GA dipeptide repeat protein (DPR) in C9orf72 FTLD/ALS.

Shiho Gotoh, Kohji Mori, Yuzo Fujino, Yuya Kawabe, Tomoko Yamashita, Tsubasa Omi, Kenichi Nagata, Shinji Tagami, Yoshitaka Nagai, Manabu Ikeda.

Tandem GGGGCC repeat expansion in C9orf72 is a genetic cause of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). Transcribed repeats are translated into dipeptide repeat proteins (DPR) via repeat-associated non-AUG (RAN) translation. However, the regulatory mechanism of RAN translation remains unclear. Here, we reveal a GTPase-activating protein, eukaryotic initiation factor 5 (eIF5), which allosterically facilitates the conversion of eIF2-bound GTP into GDP upon start codon recognition, as a novel modifier of C9orf72 RAN translation. Compared to global translation, eIF5, but not its inactive mutants, preferentially stimulates poly-GA RAN translation. RAN translation is increased during integrated stress response (ISR), but the stimulatory effect of eIF5 on poly-GA RAN translation was additive to the increase of RAN translation during ISR, with no further increase in phosphorylated eIF2α. Moreover, an alteration of the CUG near cognate codon to CCG or AUG in the poly-GA reading frame abolished the stimulatory effects, indicating that eIF5 primarily acts through the CUG-dependent initiation. Lastly, in a Drosophila model of C9orf72 FTLD/ALS that expresses GGGGCC repeats in the eye, knockdown of endogenous eIF5 by two independent RNAi strains significantly reduced poly-GA expressions, confirming in vivo effect of eIF5 on poly-GA RAN translation. Together, eIF5 stimulates the CUG initiation of poly-GA RAN translation in cellular and Drosophila disease models of C9orf72 FTLD/ALS.

DOI: https://doi.org/10.1016/j.jbc.2024.105703