The topoisomerase IIβ circular clamp arrests transcription and signals a 26S proteasome pathway

doi:10.1073/pnas.0736401100

The topoisomerase IIβ circular clamp arrests transcription and signals a 26S proteasome pathway

^*Department of Pharmacology, University of Medicine and Dentistry of New Jersey–Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854-5635; and ^†Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan

Edited by James C. Wang, Harvard University, Cambridge, MA, and approved February 7, 2003 (received for review October 21, 2002)

Abstract

It has been proposed that the topoisomerase II (TOP2)β–DNA covalent complex arrests transcription and triggers 26S proteasome-mediated degradation of TOP2β. It is unclear whether the initial trigger for proteasomal degradation is due to DNA damage or transcriptional arrest. In the current study we show that the TOP2 catalytic inhibitor 4,4-(2,3-butanediyl)-bis(2,6-piperazinedione) (ICRF-193), which traps TOP2 into a circular clamp rather than the TOP2–DNA covalent complex, can also arrest transcription. Arrest of transcription, which is TOP2β-dependent, is accompanied by proteasomal degradation of TOP2β. Different from TOP2 poisons and other DNA-damaging agents, ICRF-193 did not induce proteasomal degradation of the large subunit of RNA polymerase II. These results suggest that proteasomal degradation of TOP2β induced by the TOP2–DNA covalent complex or the TOP2 circular clamp is due to transcriptional arrest but not DNA damage. By contrast, degradation of the large subunit of RNA polymerase II is due to a DNA-damage signal.

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: lliu{at}umdnj.edu.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

TOP,

topoisomerase;

CPT,

camptothecin;

VM-26,

4′-demethylepipodophyllotoxin thenylidene-β-d-glucoside (teniposide);

Pol,

RNA polymerase;

ICRF-193,

4,4-(2,3-butanediyl)-bis(2,6-piperazinedione);

DRB,

5,6-dichlorobenzimidazole riboside;

h,

human;

ICE,

in vivo complex of enzyme;

Gdn⋅HCl,

guanidine hydrochloride