DNA topoisomerases are required during DNA replication and transcription, where they constantly remove the DNA supercoiling generated, whenever the two DNA strands are separated to read the genetic information. The enzymes act by introducing transient single- and double strand breaks in the DNA backbone in a process resulting in covalently attachment of the enzymes to the broken DNA ends and formation of the so-called topoisomerase-DNA cleavage complexes. Dysfunction or lack of the enzymes has severe consequences for the cell and result in genomic instability, development of cancer and eventually cell death. Besides their physiological functions the enzymes are important as cellular targets in cancer chemotherapy in that drugs targeting the enzymes stabilize the transient cleavage complexes, causing fragmentation of the DNA upon collision of RNA- and DNA polymerases with the stabilized complexes. The cellular response to treatment with anticancer drugs is activation of different repair processes, whereby the cell tries to repair the damage, which will otherwise kill the cancer cell. The efficiency of anticancer drugs targeting topoisomerases can therefore be increased by identification and subsequent inhibition of factors involved in this repair.
DNA topoisomerases genetically interact with enzymes belonging to the RecQ helicase family. Mutations in the genes encoding two of the human RecQ helicases, WRN and BLM, lead to genomic instability resulting in premature aging (Werners syndrome) and development of cancer (Blooms syndrome), respectively, but the exact mechanism underlying this is so far not known.
Our research focuses on topoisomerases and RecQ helicases to understand the interplay between them, their cellular functions as well as why dysfunction or absence of the enzymes lead to genomic instability, cancer and premature aging. At the same time we are interested in the identification of repair factors, which are activated, when anticancer drugs targeting topoisomerases are used in the treatment of cancer.
Specific aims of ongoing projects:
Besides general molecular biological techniques including epitope tagging and knock out of endogenous genes we use Chromatin Immunoprecipitation (ChIP), FACS analyses, checkpoint studies, Real time PCR, 2D gel electrophoresis to separate replication intermediates, fluorescent foci studies, and Pulsed Field Gel Electrophoresis (PFGE) to separate intact chromosomal DNA.