Takata Laboratory
Institute for Basic Science - Center for Genomic Integrity
Introduction
We aim to understand ways to repair DNA double strand breaks (DSBs) and DNA interstrand crosslinks (ICLs). DSBs and ICLs, which are induced by multiple cancer therapies, are a particularly deleterious form of DNA damage that can result in cell death if not repaired.
Additionally, the repair process itself can result in deletions, insertions and translocations, hallmarks of genomic instability that are often found in cancer. A better understanding of how cells die as a result of DSBs and ICLs or survive with increased genomic instability will lead to improved procedures for cancer treatment and prevention.
We investigate the mechanisms of how human cells process DSBs or ICLs. This will yield a better understanding of how these processes maintain genome integrity, and how tumor cells gain resistance to cancer therapies.
Our long-term goal is to find a way to prevent cancers. One of our research topics is therefore to elucidate the mechanism of how DNA mutations accumulate during cancer development.
Keywords: DNA polymerase theta (POLQ); DNA helicase HELQ; Radiation therapy, Chemotherapy, DNA double strand breaks; DNA crosslinks; CRISPR/Cas9; Next-Generation Sequencing (NGS); Cancer mutation signatures
The POLQ/ HELQ/ POLN family in DNA damage tolerance
We characterize POLQ and HELQ and their associating factors to understand ways to repair DSBs and ICLs.
In Drosophila, mutations in the mus308 locus cause hypersensitivity to ICL reagents. Its human homologs are DNA helicase HELQ, DNA polymerase θ and ν ( POLQ and POLN).
HELQ is important for tolerating ICLs, while POLQ is involved in one of the DNA double strand break (DSB) repair pathways, and POLN does not influence cellular sensitivity to ICLs or DSBs.
DNA polymerase θ (POLQ)-mediated end joining (TMEJ)
is a distinct pathway for mediating DSB repair
There are three major pathways for repair of DSBs: (i) nonhomologous end joining (NHEJ), (ii) homologous recombination (HR) and (iii) DNA polymerase θ (POLQ)-mediated end joining (TMEJ). TMEJ mediates the joining of two resected 3′ ends harboring DNA sequence microhomology (MH). TMEJ is an important alternative to the major DSB repair pathways, HR and NHEJ. The requirement of POLQ for the viability of BRCA-mutated cancer cells underscores the importance of TMEJ. The choice of DSB repair pathway influences the fidelity of DSB repair, which eventually influences the rate of tumorigenesis.
HELQ operates DNA repair and signaling in response to ICL
HELQ is a 3′–5′ DNA helicase. HELQ operates in an arm of DNA repair and signaling in response to ICLs. HELQ is associated with the RAD51 paralogs RAD51B/C/D and XRCC2 (BCDX2 complex) and with the DNA checkpoint proteins ATR/ATRIP. After treatment with ICL-forming agents, phosphorylation of the ATR substrate CHK1 is reduced in HELQ knockout cells, and the checkpoint dependent accumulation of G2/M cells is attenuated.
