ORCA/LRWD1 Regulates Homologous Recombination at ALT-Telomeres by Modulating Heterochromatin Organization
Rosaline Y.C. Hsu,
Yo-Chuen Lin,
Christophe Redon,
Qinyu Sun,
Deepak K. Singh,
Yating Wang,
Vasudha Aggarwal,
Jaba Mitra,
Abhijith Matur,
Branden Moriarity,
Taekjip Ha,
Mirit I. Aladjem,
Kannanganattu V. Prasanth,
Supriya G. Prasanth
Affiliations
Rosaline Y.C. Hsu
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601S Goodwin Avenue, Urbana, IL 61801, USA
Yo-Chuen Lin
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601S Goodwin Avenue, Urbana, IL 61801, USA
Christophe Redon
Developmental Therapeutics Branch, Center for Cancer Research, NCI, NIH, Bethesda MD 20892, USA
Qinyu Sun
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601S Goodwin Avenue, Urbana, IL 61801, USA
Deepak K. Singh
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601S Goodwin Avenue, Urbana, IL 61801, USA
Yating Wang
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601S Goodwin Avenue, Urbana, IL 61801, USA
Vasudha Aggarwal
Biophysics and Biophysical Chemistry, Johns Hopkins University, Baltimore, MD 21205, USA
Jaba Mitra
Materials Engineering Department, UIUC, Urbana, IL 61801, USA
Abhijith Matur
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601S Goodwin Avenue, Urbana, IL 61801, USA
Branden Moriarity
Department of Pediatrics, University of Minnesota, MN 55455 USA
Taekjip Ha
Biophysics and Biophysical Chemistry, Johns Hopkins University, Baltimore, MD 21205, USA; Howard Hughes Medical Institute, Johns Hopkins University, Baltimore, MD 21205, USA
Mirit I. Aladjem
Developmental Therapeutics Branch, Center for Cancer Research, NCI, NIH, Bethesda MD 20892, USA
Kannanganattu V. Prasanth
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601S Goodwin Avenue, Urbana, IL 61801, USA; Cancer Center at Illinois, UIUC, Urbana, IL 61801, USA
Supriya G. Prasanth
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601S Goodwin Avenue, Urbana, IL 61801, USA; Cancer Center at Illinois, UIUC, Urbana, IL 61801, USA; Corresponding author
Summary: Telomeres are maintained by telomerase or in a subset of cancer cells by a homologous recombination (HR)-based mechanism, Alternative Lengthening of Telomeres (ALT). The mechanisms regulating telomere-homeostasis in ALT cells remain unclear. We report that a replication initiator protein, Origin Recognition Complex-Associated (ORCA/LRWD1), by localizing at the ALT-telomeres, modulates HR activity. ORCA's localization to the ALT-telomeres is facilitated by its interaction to SUMOylated shelterin components. The loss of ORCA in ALT-positive cells elevates the levels of two mediators of HR, RPA and RAD51, and consistent with this, we observe increased ALT-associated promyelocytic leukemia body formation and telomere sister chromatid exchange. ORCA binds to RPA and modulates the association of RPA to telomeres. Finally, the loss of ORCA causes global chromatin decondensation, including at the telomeres. Our results demonstrate that ORCA acts as an inhibitor of HR by modulating RPA binding to ssDNA and inducing chromatin compaction.
