Genome Instability and Transcription Elongation Impairment in Human Cells Depleted of THO/TREX

TLDR

In yeast, the THO/TREX complex links transcription to genome integrity, but its role in mammalian cells remains unclear, indicating possible species‑specific differences in mRNP biogenesis factors. Depleting human THO impairs transcription elongation and mRNA export, elevates DNA‑break–associated instability, triggers hyper‑recombination and γH2AX/53BP1 foci, alters replication dynamics, and causes R‑loop‑dependent genome instability that can be mitigated by RNaseH and is linked to increased class‑switching in CH12 cells, demonstrating that mammalian THO prevents R‑loop formation and preserves genome integrity.

Abstract

THO/TREX connects transcription with genome integrity in yeast, but a role of mammalian THO in these processes is uncertain, which suggests a differential implication of mRNP biogenesis factors in genome integrity in yeast and humans. We show that human THO depletion impairs transcription elongation and mRNA export and increases instability associated with DNA breaks, leading to hyper-recombination and γH2AX and 53BP1 foci accumulation. This is accompanied by replication alteration as determined by DNA combing. Genome instability is R-loop-dependent, as deduced from the ability of the AID enzyme to increase DNA damage and of RNaseH to reduce it, or from the enhancement of R-loop-dependent class-switching caused by THOC1-depletion in CH12 murine cells. Therefore, mammalian THO prevents R-loop formation and has a role in genome dynamics and function consistent with an evolutionary conservation of the functional connection between these mRNP biogenesis factors and genome integrity that had not been anticipated.