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

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1 Scopus citations


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.

Original languageEnglish (US)
Article number101038
Issue number5
StatePublished - May 22 2020

Bibliographical note

Funding Information:
We thank members of the Prasanth laboratory for discussions and suggestions. We thank Drs. A. Chakraborty, T. deLange, R. Flynn, R. Greenberg, C. Mizzen, C. Prives, Z. Shen, B. Stillman, L. Zou, and V. Mohan for providing reagents and suggestions. We thank Dr. D. Rivier and Ms. Adusumilli for critical reading of the manuscript. We thank Dr. Lorinc Pongor for advice on statistical analysis of sequencing data. This work was supported by NSF -CMMB-IGERT fellowship to R.Y.C.H.; The Intramural Program of the National Cancer Institute , Center for Cancer Research ( 1ZIABC010419 to M.I.A.), National Institutes of Health ( R21AG065748 ), National Science Foundation EAGER ( MCB 1723008 ) and Cancer Center at Illinois Seed Grant and Prairie Dragon Paddlers awards to K.V.P., and NSF ( 1243372 and 1818286 ) and NIH ( GM099669 and GM125196 ) awards to S.G.P. T.H. is an investigator with Howard Hughes Medical Institute. The authors declare no competing financial interests.


  • Biological Sciences
  • Chromosome Organization
  • Molecular Biology
  • Molecular Structure

PubMed: MeSH publication types

  • Journal Article

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