RASSF1A–LATS1 signalling stabilizes replication forks by restricting CDK2-mediated phosphorylation of BRCA2

Genomic instability is a key hallmark of cancer leading to tumour heterogeneity and therapeutic resistance. ​BRCA2 has a fundamental role in error-free DNA repair but also sustains genome integrity by promoting ​RAD51 nucleofilament formation at stalled replication forks. ​CDK2 phosphorylates ​BRCA2 (pS3291-​BRCA2) to limit stabilizing contacts with polymerized ​RAD51; however, how replication stress modulates ​CDK2 activity and whether loss of pS3291-​BRCA2 regulation results in genomic instability of tumours are not known. Here we demonstrate that the Hippo pathway kinase ​LATS1 interacts with ​CDK2 in response to genotoxic stress to constrain pS3291-​BRCA2 and support ​RAD51 nucleofilaments, thereby maintaining genomic fidelity during replication stalling. We also show that ​LATS1 forms part of an ​ATR-mediated response to replication stress that requires the tumour suppressor ​RASSF1A. Importantly, perturbation of the ​ATR–​RASSF1A–​LATS1 signalling axis leads to genomic defects associated with loss of ​BRCA2 function and contributes to genomic instability and ‘BRCA-ness’ in lung cancers

The identification and analysis of molecular biomarkers in the p53 tumour suppressor pathway that affect cancer progression in humans

The tumour suppressor p53 is at the centre of the signalling pathway that controls cellular processes crucial in tumourogenesis, cancer progression and tumour clearance. Alterations in the p53 pathway that lead to cancer progression can be good candidates for molecular biomarkers that would assist in the identification of patients with different prognoses, but also serve as good predictors of appropriate targeted therapies. Patient cohorts and cancer cell panels are utilised to seek associations with the attenuation of the p53 pathway and cancer progression. Firstly, the alternatively spliced transcript of the p53 inhibitor HDMX, which is frequently found in tumours with poor prognosis, is studied. The high ratio of the alternatively spliced HDMX-S transcript over the full-length HDMX-FL transcript (HDMX-S/FL) is demonstrated to associate with p53 pathway attenuation in cancer cells and breast carcinomas, and with faster metastatic progression of osteosarcoma and breast cancer patients. Secondly, inherited polymorphism in the HDMX gene is investigated and demonstrated as a unique and highly reproducible eQTL, which identifies patients with different prognoses for metastatic disease in breast cancer and melanoma cohorts. Lastly, a screening approach to identify novel inherited polymorphisms in the p53 pathway genes that associate with metastatic progression of melanoma is developed and implemented, and subsequently in silico and in vitro functional analyses are performed to investigate a mechanism behind the FOXO3 SNP, identified as the strongest candidate, whereby the experimental evidence demonstrate that the causal SNP in the FOXO3 haplotype is controlled by the GATA3 transcription factor. Together, the work presented in this thesis provides strong support for the role of the p53 pathway in the metastatic progression of cancer, and suggests that molecular biomarkers that can detect changes in the activity of p53 pathway genes could offer a robust set of biomarkers for cancer progression applicable to different types of cancer.</p

Interaction between p53 mutation and a somatic HDMX biomarker better defines metastatic potential in breast cancer

Abstract TP53 gene mutation is associated with poor prognosis in breast cancer, but additional biomarkers that can further refine the impact of the p53 pathway are needed to achieve clinical utility. In this study, we evaluated a role for the HDMX-S/FL ratio as one such biomarker, based on its association with other suppressor mutations that confer worse prognosis in sarcomas, another type of cancer that is surveilled by p53. We found that HDMX-S/FL ratio interacted with p53 mutational status to significantly improve prognostic capability in patients with breast cancer. This biomarker pair offered prognostic utility that was comparable with a microarray-based prognostic assay. Unexpectedly, the utility tracked independently of DNA-damaging treatments and instead with different tumor metastasis potential. Finally, we obtained evidence that this biomarker pair might identify patients who could benefit from anti-HDM2 strategies to impede metastatic progression. Taken together, our work offers a p53 pathway marker, which both refines our understanding of the impact of p53 activity on prognosis and harbors potential utility as a clinical tool. Cancer Res; 75(4); 698–708. ©2015 AACR.</jats:p

The importance of p53 pathway genetics in inherited and somatic cancer genomes

Decades of research have shown that mutations in the p53 stress response pathway affect the incidence of diverse cancers more than mutations in other pathways. However, most evidence is limited to somatic mutations and rare inherited mutations. Using newly abundant genomic data, we demonstrate that commonly inherited genetic variants in the p53 pathway also affect the incidence of a broad range of cancers more than variants in other pathways. The cancer-associated single nucleotide polymorphisms (SNPs) of the p53 pathway have strikingly similar genetic characteristics to well-studied p53 pathway cancer-causing somatic mutations. Our results enable insights into p53-mediated tumour suppression in humans and into p53 pathway-based cancer surveillance and treatment strategies