EIF3 interacts with histone H4 messenger RNA to regulate its translation

Hassan Hayek,Lauriane Gross,Aurélie Janvier,Laure Schaeffer,Franck Martin,Gilbert Eriani,Christine Allmang

doi:10.1016/j.jbc.2021.100578

Abstract

In eukaryotes, various alternative translation initiation mechanisms have been unveiled for the translation of specific mRNAs. Some do not conform to the conventional scanning-initiation model. Translation initiation of histone H4 mRNA combines both canonical (cap-dependent) and viral initiation strategies (no-scanning, internal recruitment of initiation factors). Specific H4 mRNA structures tether the translation machinery directly onto the initiation codon and allow massive production of histone H4 during the S phase of the cell cycle. The human eukaryotic translation initiation factor 3 (eIF3), composed of 13 subunits (a-m), was shown to selectively recruit and control the expression of several cellular mRNAs. Whether eIF3 mediates H4 mRNA translation remains to be elucidated. Here, we report that eIF3 binds to a stem-loop structure (eIF3-BS) located in the coding region of H4 mRNA. Combining cross-linking and ribonucleoprotein immunoprecipitation experiments in vivo and in vitro, we also found that eIF3 binds to H1, H2A, H2B, and H3 histone mRNAs. We identified direct contacts between eIF3c, d, e, g subunits, and histone mRNAs but observed distinct interaction patterns to each histone mRNA. Our results show that eIF3 depletion in vivo reduces histone mRNA binding and modulates histone neosynthesis, suggesting that synthesis of histones is sensitive to the levels of eIF3. Thus, we provide evidence that eIF3 acts as a regulator of histone translation.

Highlights

Present address for Hassan Hayek: Department of Thoracic Medicine and Surgery, Center for Inflammation, Translational and Clinical Lung Research, Temple University, Philadelphia, PA 19140, USA
It was previously established that human translation initiation factor eukaryotic translation initiation factor 3 (eIF3) can target mRNAs in a transcriptspecific manner and can function as an activator or repressor of translation [19,20,21]
Purified eIF3 complex directly interacted with H4 FL with an estimated Kd of 4 μM. eIF3 moderately interacted with H4 241 to 375 and with H4 1 to 137 (TWJ) and shifted 39% and 28% of the RNAs respectively at high concentrations of eIF3 (Fig. 1C)

Summary

Results

It was previously established that human translation initiation factor eIF3 can target mRNAs in a transcriptspecific manner and can function as an activator or repressor of translation [19,20,21]. Depletion of eIF3e to 12% strongly reduced the level of eIF3d to 39%, as previously published [39], as well as weakly eIF3i to 73% but had no significant impact on the integrity of the rest of the complex (Table S1) It reduced histone mRNA and c-JUN binding by 68% on average, revealing the importance of eIF3e for mRNA binding. No effect was observed in samples treated with control siRNAs (Fig. 8) Under these conditions, the depletion of different individual eIF3 subunits seems to have modest and not always significant effects on histone translation (Fig. S3C) when compared with their impact on histone mRNA binding (Fig. 7). EIF3c knockdown reduced the expression levels of histones H2B/H3 and H4, recapitulating SLBP or eIF4E depletion effects (Fig. S3C)

H2A H2B

Discussion

C Acid-soluble fraction kDa 250 130 100 70

Experimental procedures