The analysis of rare cancer pedigrees has proven to be one of the most informative approaches to understanding human cancer. These studies have defined numerous genes, including P53 in Li- Fraumeni syndrome, RB in hereditary retinoblastoma and BLM in Bloom’s syndrome. These cancer predisposition syndromes have provided critical insight into the molecular biology and genetics of cancer initiation and maintenance. Rothmund-Thomson Syndrome (RTS, OMIM 268400) is a familial cancer predisposition syndrome associated with elevated rates of osteosarcoma (OS), haematological neoplasms and skeletal dysplasia. RTS is one of three familial OS syndromes, together with Li-Fraumeni and hereditary retinoblastoma. RTS is caused by inherited homozygous in RECQL4.
RECQL4 protein is a RecQ helicase, related to BLM and WRN helicases, that are also involved in cancer predisposition. BLM and WRN are considered to act as caretakers of the genome to ensure genome fidelity through promotion of DNA repair. However it is unclear if RECQL4 also regulates DNA repair or whether it is main role is in DNA replication. Our team has used animal models and recombinant protein expression to analyse the function of RECQL4 in both DNA replication and DNA repair.
We hypothesise that RECQL4 has two separable functions: the first is essential and key to DNA replication and requires the N-terminal Sld2 homology regions; the second is a DNA repair function reliant on its ATP-dependent helicase activity. We have used an allelic series of Recql4 mouse mutants to understand the in vivo effects of different Recql4 mutations on homeostasis and cancer predisposition. In parallel, we will present detailed in vitro biochemical characterisation of the RECQL4 mutant proteins to define the key functional properties of mutant Recql4. These studies will enable us to categorise mutations in RECQL4 observed in cancer, and predict their responses to DNA damaging agents, allowing personalisation of chemotherapy based on the mutation type.
We will present results on the purification and biochemical characterisation of wildtype full length RecQL4 and the ATPase dead K525A mutant for is ability to hydrolyse ATP and bind and unwind DNA.