Camptothecin releases P-TEFb from the inactive 7SK snRNP complex

Stefano Amente, Barbara Gargano, Giuliana Napolitano, Luigi Lania, Barbara Majello

Research output: Contribution to journalArticlepeer-review

Abstract

An immediate effect of DNA Topoisomerase I inhibitors camptothecin (CPT) and its derivates is the inhibition of transcription. These fast-acting drugs are believed to inhibit transcription by blocking topoisomerase-mediated relief of DNA supercoiling that occurs during transcription elongation. The CPT effects are commonly considered to be due to a collision between the drug-trapped enzyme on the DNA template and the elongating RNAPII. Here we present evidences that CPT treatment induces an early affect on the positive elongation factor b (P-TEFb). The P-TEFb activity is tightly and dynamically regulated, and a reservoir of P-TEFb is kept in an inactive state in the multisubunit 7SK snRNP. We found that, shortly after treatment, CPT disrupts the large inactive P-TEFB complex, and such effect is reversible and independent from DNA replication. Thus, CPT modulates P-TEFb equilibrium in a manner similar to Flavopiridol (FP), a pan-Cdk inhibitor proposed as chemotherapeutic agents against cancers. We determined that while FP inhibits Cdk9 leading to hypo-phosphorylation of RNA polymerase II, CPT-mediated release of free P-TEFb correlates with a concomitant hyper-phosphorylation of RNAPII, which in turn alters the levels and distribution of the RNAPII along transcribed genes. The findings that CPT affects P-TEFb activity provide a direct evidence of the mechanism of this drug to inhibit transcription.

Original languageEnglish
Pages (from-to)1249-1255
Number of pages7
JournalCell Cycle
Volume8
Issue number8
Publication statusPublished - Apr 15 2009

Keywords

  • Camptothecin
  • P-TEFb
  • RNA polymerase II
  • Transcription

ASJC Scopus subject areas

  • Cell Biology
  • Developmental Biology
  • Molecular Biology

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