Repair mechanisms of topoisomerase II DNA lesions

Introduction

Topoisomerase II (TOP2) chemotherapeutics such as etoposide have been widely used in the clinic to treat leukemias, lymphomas, lung, testicular, and ovarian cancers. Etoposide was first approved for clinical usage in 1983. By intercalating into DNA, etoposide stalls the TOP2 catalytic cycle, generating toxic DNA lesions known as TOP2-DNA-protein crosslinks (TOP2-DPCs).

Research Background

After 40 years of intense research, the mechanisms employed by cells that counteract these lesions are starting to emerge. These include:

• Enzymes that reverse the crosslink
• Degradation of the protein adduct
• Removal of the lesion by DNA incisions

Moreover, the protein ZATT was recently described as an essential regulatory enzyme that SUMOylates TOP2 and thereby stimulates TOP2-DPC resolution.

Key Questions

Important and long-standing questions in the field relate to our understanding of how the different modes of repair are activated, coordinated between one another, and preferentially used by cells. Based on genetic data, ZATT appears to be the primary responder to TOP2-DPCs, but how ZATT coordinates the different modes of repair via TOP2-SUMOylation is currently unclear.

Proposed Approach

To address these questions and study TOP2-DPC repair, we propose to use a novel approach based on Xenopus egg extracts, which can recapitulate DNA repair mechanisms in a soluble environment.

Preliminary Data

As part of our preliminary data, we show that these extracts can recapitulate TOP2-DPC repair via ZATT SUMOylation, providing a unique opportunity to delineate the molecular mechanisms underlying this reaction.

Objectives

By combining this system with complementary and innovative approaches, we seek to obtain a clear molecular understanding of the different mechanisms counteracting TOP2 lesions and unravel the molecular triggers that activate the different routes of repair.

Impact

By doing this, we will provide new opportunities and targets to improve cancer treatment.