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Nonclassic functions of human topoisomerase I: genome-wide and pharmacologic analyses

Ze-Hong Miao1, Audrey Player, Uma Shankavaram

  • 1Laboratories of Molecular Pharmacology, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, Maryland, USA.

Cancer Research
|September 19, 2007
PubMed

Insights

Topoisomerase I (Top1) is crucial for genomic stability and gene transcription. New cell models reveal Top1

Area of Science:

  • Molecular Biology
  • Genetics
  • Cancer Research

Background:

  • Studying nuclear topoisomerase I (Top1) functions is challenging due to the lethality of TOP1 knockout in metazoans.
  • Previous research has not fully elucidated the non-canonical roles of Top1 beyond its DNA nicking-closing activity.

Purpose of the Study:

  • To investigate the biological functions of human Top1 using novel cell models.
  • To understand Top1's role in genomic stability, gene transcription, and cellular response to anticancer agents.

Main Methods:

  • Generation of stable Top1 small interfering RNA (siRNA) cell lines (HCT116-siTop1 and MCF-7-siTop1) from human carcinomas.
  • Analysis of Top1 deficiency effects on genomic instability, replication, nucleolar structure, and gene expression.
  • Genome-wide transcription profiling and pharmacologic profiling of siTop1 cells.

Main Results:

  • Top1 deficiency led to genomic instability, chromosomal aberrations, and replication defects.
  • Top1 reduction altered nucleolar structure and increased nuclear volume.
  • Down-regulation of Top1 significantly impacted asparagine synthetase (ASNS) expression and conferred L-asparaginase hypersensitivity.

Conclusions:

  • Top1 plays critical non-canonical roles in maintaining genomic stability, regulating gene-specific transcription (e.g., ASNS), and influencing cellular responses to DNA-damaging agents.
  • The generated Top1-deficient cell lines provide valuable tools for further functional analysis of Top1.
  • Top1's functions extend beyond DNA topology regulation to encompass broader cellular processes relevant to cancer therapy.

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