Cellular processing determinants for the activation of damage signals in response to topoisomerase I-linked DNA breakage

Ting-Hsiang Huang, Hsiang-Chin Chen, Shang-Min Chou, Yu-Chen Yang, Jia-Rong Fan, Tsai-Kun Li

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


Recent studies have suggested an involvement of processing pathways for the initiation of cellular responses induced by topoisomerase-targeting drugs. Here, we showed that cellular exposure to camptothecin (CPT) induced formation of topoisomerase I cleavable complex (TOP1cc), degradation of TOP1 and activation of DNA damage responses (DDR). Transcription and proteasome-dependent proteolysis, but not replication, were involved in CPT-induced TOP1 degradation, while none of above three processing activities affected TOP1cc formation. Replication-and transcription-initiated processing (RIP and TIP) of TOP1cc were identified as two independent pathways, which contribute distinctly to various CPT-activated DDR. Specifically, in cycling cells, RIP-processed TOP1cc triggered the CPT-induced RPA phosphorylation. At higher CPT dosages, the TIP pathway is required for other DDR activation, including ATM, p53 and Chk1/2 phosphorylation. The TIP pathway was further demonstrated to be S-phase independent by using three nonreplicating cell models. Furthermore, the effect of proteasome inhibitors mimicked that of transcription inhibition on the CPT-induced activation of DDR, suggesting the involvement of proteasome in the TIP pathway. Interestingly, the TIP pathway was important for TOP1cc-activated, but not ionization radiation-activated ATM, p53 and Chk2 phosphorylation. We have also found that pharmacological interferences of TIP and RIP pathways distinctively modulated the CPT-induced cell killing with treatments at low and high dosages, respectively. Together, our results support that both RIP and TIP pathways of TOP1cc are required for the activation of CPT-induced DDR and cytotoxicity. © 2010 IBCB, SIBS, CAS. All rights reserved.
Original languageEnglish
Pages (from-to)1060-1075
Number of pages16
JournalCell Research
Issue number9
Publication statusPublished - 2010
Externally publishedYes


  • cleavable complex
  • DNA damage responses
  • downregulation
  • processing
  • protein-linked DNA break
  • ATM protein
  • camptothecin
  • cell cycle protein
  • checkpoint kinase 2
  • DNA binding protein
  • DNA topoisomerase
  • protein p53
  • protein serine threonine kinase
  • replication factor A
  • RPA2 protein, human
  • tumor suppressor protein
  • article
  • DNA repair
  • DNA replication
  • DNA strand breakage
  • genetic transcription
  • genetics
  • human
  • metabolism
  • phosphorylation
  • signal transduction
  • tumor cell line
  • Camptothecin
  • Cell Cycle Proteins
  • Cell Line, Tumor
  • DNA Breaks
  • DNA Repair
  • DNA Replication
  • DNA Topoisomerases, Type I
  • DNA-Binding Proteins
  • Humans
  • Phosphorylation
  • Protein-Serine-Threonine Kinases
  • Replication Protein A
  • Signal Transduction
  • Transcription, Genetic
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins


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