beta-catenin Ser45 in development and disease

Mutations in the beta-catenin signalling pathway are found in many types of cancer. It is widely assumed that all these mutations activate this pathway. We are interested in the development of Wilms' tumours, kidney cancers found in young children that are the result of normal kidney development before birth going wrong. A subset of these tumours has mutations in beta-catenin. Interestingly, whereas there are four different mutations possible, almost all patients have exactly the same mutation, suggesting this mutation is specifically important for this type of cancer. In the work leading up to this proposal we have made mouse models that carry different mutant copies of beta-catenin, including the mutation found in Wilms' tumours. We found that this mutation resulted in kidney abnormalities that would fit with a role in Wilms' tumours but, surprisingly, this mutation did not seem to activate the protein. Unfortunately, these models were made in a way that differs from the way the gene is mutated in patients, and it is therefore not possible to conclude this mutation will have the same effect in tumours.

In this project we will therefore first make the mutation in exactly the same way as found in human tumours. We will repeat the analyses we have done before on the other model to see if the surprising findings we did are confirmed. We will study the effect of this mutation in mice, with an emphasis on the kidney and neuron / brain.

It is assumed that oncogenic mutations found in beta-catenin result in activation of the pathway. We have a strong interest in the early steps in the development of Wilms' tumours, in particular the subset that is caused by loss of WT1 and activation of beta-catenin. Interestingly, almost all cases of Wilms' tumour with mutant beta-catenin carry a mutation affecting the Ser45 residue. To study the reason for this selection we have previously generated several mouse models that express different beta-catenin mutations from the Rosa26 locus. We found that the Ser45 mutant does not have an increased signalling capacity, despite being stabilized at the protein level as expected. Still, the Ser45 mutation has a biological effect on Wt1-deficient kidney mesenchyme cells which were driven a step closer towards Wilms' tumours. This finding suggests a complete new dimension to the role of beta-catenin mutations in cancer. However, the fact that our models express their mutant beta-catenin from Rosa26 means we cannot directly translate these finding to patients. In this project we will therefore generate a Cre-inducible Ser45 mutation in the endogenous mouse beta-catenin gene. We will test its capability to increase target gene transcription in ES cells as we did for the Rosa26 models. In vivo we will activate the expression of the mutant allele through a Cre deleter strain and analyse the phenotype in development and/or postnatal. To study the role of this mutation in Wilms' tumour development we will cross the mice with our kidney mesenchyme-specific Wt1 knockout. We will use genome-wide expression analysis to identify molecular changes that could explain the selection for this mutation in WT1-mutant Wilms' tumours. The mice will be followed for Wilms' tumour development and other phenotypes. Finally, we will specifically analyse any phenotypes in the neuronal system caused by the Ser45 mutation.

The proposed project will have a potential impact on the following stake holders.

The academic community working on cancer genetics in general, and Wilms' tumour genetics in particular. The information gained in this project will increase our understanding of cancer genetics, Darwinian selection in tumourigenesis and the roles of specific cancer-related mutations in the origin of tumours.

The health sector. Better understanding of the earlier steps in cancer development will ultimately lead to improvement in cancer treatment options.

Cancer patients. Better understanding of the origins of cancer and identification of the processes that, when disturbed, lead to cancer development will allow the design of more efficient and more specific therapies. This will result in better treatments with fewer side-effects, leading to a significant increase in quality of life.

General public. As the public pays for MRC-funded research through their taxes there is an obvious right of information on what is done with the money.

The pharmaceutical industry. There is an important lack in sufficiently good animal models for cancer. The use of models that are available for design and testing of therapies have in many cases been found not to be predictive for the efficacy of a therapy in patients. As a result too many new drug candidates are failing to make it to the clinic. Models as proposed here that mimic the genetic events in cancer in patients as closely as possible will undoubtedly lead to better and more predictive models for these purposes.

The staff on the project. Biomedical sciences increasingly require a multitude of techniques and approaches to answer a scientific question. The experimental models used become more sophisticated as technical possibilities improve. For both named staff this project will allow the extension of their expertise. For Dr. Ozdemir this project will help to further establish her reputation in the Wilms' tumour and mouse model field. She will be able to increase her expertise in the generation of genetically modified mouse models using the latest technologies, and introduce her to next-generation sequencing approaches. Mrs Sheraz has so far been running the mouse colony of the Hohenstein lab and been involved in developing and optimizing in vitro culture methods for mesenchymal kidney progenitor cells. This project will allow her to become experienced in all steps in the generation and analysis of transgenic mouse models.