Extrachromosomal telomere DNA derived from excessive strand displacements

• 成果类型: Article
• 署名作者: Lee, Junyeop; Lee, Jina; Sohn, Eric J.; Taglialatela, Angelo; O'Sullivan, Roderick J.; Ciccia, Alberto; Min, Jaewon
• 署名单位: Columbia University; Columbia University; Columbia University; Pennsylvania Commonwealth System of Higher Education (PCSHE); University of Pittsburgh; Columbia University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11164
• DOI: 10.1073/pnas.2318438121
• 发表日期: 2024-05-07
• 关键词: replication; repair; maintenance; mre11; inhibitor; overhangs; reveals; tumors; blm

摘要

Alternative lengthening of telomeres (ALT) is a telomere maintenance mechanism mediated by break - induced replication, evident in approximately 15% of human cancers. A characteristic feature of ALT cancers is the presence of C - circles, circular single - stranded telomeric DNAs composed of C - rich sequences. Despite the fact that extrachromosomal C - rich single - stranded DNAs (ssDNAs), including C - circles, are unique to ALT cells, their generation process remains undefined. Here, we introduce a method to detect single - stranded telomeric DNA, called 4SET (Strand - Specific Southern - blot for Single - stranded Extrachromosomal Telomeres) assay. Utilizing 4SET, we are able to capture C - rich single - stranded DNAs that are near 200 to 1500 nucleotides in size. Both linear C - rich ssDNAs and C - circles are abundant in the fractions of cytoplasm and nucleoplasm, which supports the idea that linear and circular C - rich ssDNAs are generated concurrently. We also found that C - rich ssDNAs originate during Okazaki fragment processing during lagging strand DNA synthesis. The generation of C - rich ssDNA requires CST - PP (CTC1/STN1/TEN1 - PRIMASE - Polymerase alpha) complex - mediated priming of the C - strand DNA synthesis and subsequent excessive strand displacement of the C - rich strand mediated by the DNA Polymerase delta and the BLM helicase. Our work proposes a model for the generation of C - rich ssDNAs and C - circles during ALT - mediated telomere elongation.