hCLE/RTRAF-HSPC117-DDX1-FAM98B: A New Cap-Binding Complex That Activates mRNA Translation

Abstract

hCLE/C14orf166/RTRAF, DDX1, and HSPC117 are components of cytoplasmic mRNA-transporting granules kinesin-associated in dendrites. They have also been found in cytoplasmic ribosome-containing RNA granules that transport specific mRNAs halted for translation until specific neuronal signals renders them accessible to the translation machinery. hCLE associates to DDX1, HSPC117, and FAM98B in HEK293T cells and all four proteins bind to cap analog-containing resins. Competition and elution experiments indicate that binding of hCLE complex to cap resins is independent of eIF4E; the cap-binding factor needed for translation. Purified hCLE free of its associated proteins binds cap with low affinity suggesting that its interacting proteins modulate its cap association. hCLE silencing reduces hCLE accumulation and that of its interacting proteins and decreases mRNA translation. hCLE-associated RNAs have been isolated and sequenced; RNAs involved in mRNA translation are specifically associated. The data suggest that RNA granules may co-transport RNAs encoding proteins involved in specific functions together with RNAs that encode proteins needed for the translation of these specific RNAs and indicate an important role for hCLE modulating mRNA translation.

General and Target-Specific DExD/H RNA Helicases in Eukaryotic Translation Initiation

“…Immunoprecipitation experiments to identify interacting partners indicated an association with the core translation factors, eIF4B, eIF3A, eIF3B, eIF3M, eIF4G1, and eIF4G2 [141]. DDX1 was also found in a complex with hCLE, HSPC117, and FAM98B, in which hCLE was reported to have cap-binding activity [142]. Suppression of hCLE reduced the incorporation of 35 S-Met into cellular proteins without impacting global mRNA levels.…”

“…Whether and how hCLE specifically and directly recognizes cap structures awaits structural resolution. In pull-down experiments, 144 mRNAs were found to interact with hCLE in HEK293 cells [142]. Whether DDX1 plays a role in selecting target mRNAs remains to be established.…”

Substrate trapping approach identifies TRIM25 ubiquitination targets involved in diverse cellular and antiviral processes

“…RTRAF, also known as hCLE or C14orf166, is an RNA binding protein involved in cellular transcription, translation, and RNA transport, and is required for influenza virus replication. [60][61][62] Notably, RTRAF is a member of a cap-binding complex that activates mRNA translation. 61 Given RTRAF's role in facilitating translation of mRNAs, it is therefore tempting to speculate that RTRAF may be required for translation of alphavirus RNA, and TRIM25-mediated ubiquitination of RTRAF may affect its ability to do so.…”

Alphavirus infection triggers selective cytoplasmic translocation of nuclear RBPs with moonlighting antiviral roles

“…The tRNA-LC component DDX1 was also reported to interact with viral RNA capping enzyme in coronaviruses (nsP14) (Xu et al, 2010), despite the lack of homology between coronavirus and alphavirus proteins. Additionally, the tRNA-LC member CIG-99 (also hCLE) has been shown to interact with the cap structure (Pazo et al, 2019).…”