VID22counteracts G-quadruplex-induced genome instability

Abstract

Genome instability is a condition characterized by the accumulation of genetic alterations and is a hallmark of cancer cells. To uncover new genes and cellular pathways affecting endogenous DNA damage and genome integrity, we exploited a Synthetic Genetic Array (SGA)-based screen in yeast. Among the positive genes, we identified VID22, reported to be involved in DNA double-strand break repair. vid22Δ cells exhibit increased levels of endogenous DNA damage, chronic DNA damage response activation and accumulate DNA aberrations in sequences displaying high probabilities of forming G-quadruplexes (G4-DNA). If not resolved, these DNA secondary structures can block the progression of both DNA and RNA polymerases and correlate with chromosome fragile sites. Vid22 binds to and protects DNA at G4-containing regions both in vitro and in vivo. Loss of VID22 causes an increase in gross chromosomal rearrangement (GCR) events dependent on G-quadruplex forming sequences. Moreover, the absence of Vid22 causes defects in the correct maintenance of G4-DNA rich elements, such as telomeres and mtDNA, and hypersensitivity to the G4-stabilizing ligand TMPyP4. We thus propose that Vid22 is directly involved in genome integrity maintenance as a novel regulator of G4 metabolism.

Partners in crime: Tbf1 and Vid22 promote expansions of long human telomeric repeats at an interstitial chromosome position in yeast

“…In the tbf1Δi genetic background, enrichment of the Vid22 protein is quite similar (10-fold). These data demonstrate that Vid22 can bind to the repeat independently of the insulator domain of the Tbf1 protein, consistent with the results in ( 65 ).…”

“…What could be the reasons for these differences? The first possibility is that the G4-forming repeats studied in Galati et al ( 65 ) are short, as compared to our fairly long Htel. It is foreseeable, therefore, that strong protein barriers formed by multiple Tbf1/Vid22 pairs at long Htel repeats are far more detrimental for their replication and stability than their ability to form G4-DNA.…”

“…Vid22 in a complex with Tbf1 is also involved in resection at HO-induced DSBs that are repaired by nonhomologous repair pathway (NHEJ) ( 63 , 64 ). Recently, it was also demonstrated that Vid22 protein binds to and stabilizes G4-DNA forming sequences within the yeast genome ( 65 ). Note that these observations are at odds with earlier data showing that Vid22 is a plasma membrane protein required for the fructose-1,6-bisphosphatase degradation pathway ( 66 , 67 ), while Env11 is involved in lysosomal vacuole functioning ( 68 ).…”

“…Tbf1Δi protein is also clearly enriched at the repeat, owing to the fact that its DNA-binding domain lies outside of the insulator domain. Tbf1 has a physical and functional partner, Vid22, which was implicated in transcription of certain genes, binding to G4-motifs, and R-loop destabilization ( 62 , 64 , 65 ). Our ChIP analysis showed a strong presence of the Vid22 protein at the interstitial Htel repeat both in the TBF1 and the tbf1Δi genetic background (Fig.…”

“…Very recently, Galati et al ( 65 ) showed that the Vid22 protein binds to G4-containing regions in yeast genome and prevents chromosomal fragility and GCRs at those regions. In our case, however, we see that Vid22 promotes expansions of Htel that are known to form G4-DNA ( 9 ).…”