MutSβ regulates G4-associated telomeric R-loops to maintain telomere integrity in ALT cancer cells
Despoina Sakellariou,
Sara Thornby Bak,
Esin Isik,
Sonia I. Barroso,
Antonio Porro,
Andrés Aguilera,
Jiri Bartek,
Pavel Janscak,
Javier Peña-Diaz
Affiliations
Despoina Sakellariou
Center for Healthy Aging, Department of Neuroscience and Pharmacology, University of Copenhagen, 2200 Copenhagen, Denmark; Danish Cancer Society Research Center, 2100 Copenhagen, Denmark
Sara Thornby Bak
Center for Healthy Aging, Department of Neuroscience and Pharmacology, University of Copenhagen, 2200 Copenhagen, Denmark
Esin Isik
Institute of Molecular Cancer Research, University of Zurich, 8057 Zürich, Switzerland
Sonia I. Barroso
Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, University of Seville-CSIC-UPO, Seville, Spain
Antonio Porro
Institute of Molecular Cancer Research, University of Zurich, 8057 Zürich, Switzerland
Andrés Aguilera
Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, University of Seville-CSIC-UPO, Seville, Spain
Jiri Bartek
Danish Cancer Society Research Center, 2100 Copenhagen, Denmark; Division of Genome Biology, Department of Medical Biochemistry and Biophysics, Science for Life Laboratory, Karolinska Institute, 17177 Stockholm, Sweden; Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 14300 Prague, Czech Republic
Pavel Janscak
Institute of Molecular Cancer Research, University of Zurich, 8057 Zürich, Switzerland; Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 14300 Prague, Czech Republic; Corresponding author
Javier Peña-Diaz
Center for Healthy Aging, Department of Neuroscience and Pharmacology, University of Copenhagen, 2200 Copenhagen, Denmark; Corresponding author
Summary: Up to 15% of human cancers maintain their telomeres through a telomerase-independent mechanism, termed “alternative lengthening of telomeres” (ALT) that relies on homologous recombination between telomeric sequences. Emerging evidence suggests that the recombinogenic nature of ALT telomeres results from the formation of RNA:DNA hybrids (R-loops) between telomeric DNA and the long-noncoding telomeric repeat-containing RNA (TERRA). Here, we show that the mismatch repair protein MutSβ, a heterodimer of MSH2 and MSH3 subunits, is enriched at telomeres in ALT cancer cells, where it prevents the accumulation of telomeric G-quadruplex (G4) structures and R-loops. Cells depleted of MSH3 display increased incidence of R-loop-dependent telomere fragility and accumulation of telomeric C-circles. We also demonstrate that purified MutSβ recognizes and destabilizes G4 structures in vitro. These data suggest that MutSβ destabilizes G4 structures in ALT telomeres to regulate TERRA R-loops, which is a prerequisite for maintenance of telomere integrity during ALT.
