MICA: The network of class I PI3K interacting proteins is dramatically rewired in a PTEN-/- mouse model of prostate cancer. What are the implications?

Cancer is a disease caused by accumulation of mutations that change the cancer cells in ways that allow them to avoid the normal restraints on their growth, survival and proliferation. Despite this simple truth understanding how mutations give cancer cells an advantage can be difficult to address yet is critical to creating strategies to kill cancer cells selectively. The major problems arise from the fact there are many changes in cancer cells that are merely reactions to the key driving events and actually make no difference to cancer progression. This project aims to understand how loss of a gene that normally resists cancer (PTEN) and is very commonly a key causal event in prostate cancer gives cancer cells an advantage. We have assembled a large amount of unpublished data using a combination of new genetic strategies to dissect signalling inside normal and cancerous mouse prostate cells. This work has revealed a totally unappreciated mechanism by which loss of PTEN can give prostate (or potentially other cell types in which PTEN is lost) new properties that help them avoid normal restraints on their growth, survival and proliferation. The mechanisms work like an in-built growth accelerator that partially bypasses the need for the driver to push on the gas pedal. We propose to do this work using a mouse model of cancer, and cultured cells derived from them, where it is possible to make single mutations and study their impacts in isolation from many other mutations and changes that have accumulated in human cancers. We will test if genetically removing the molecules that constitute the in-built accelerator mechanism slows cancer progression. Through this strategy we can build a detailed understanding of the key events causing or enabling cancer progression and hence focus efforts into creating new therapeutics into right places.

Mutations in many components of the class I PI3K signalling pathway support tumour progression and this has led to major investment in the development of PI3K inhibitors. Despite this focus and the vast body of data that has defined the proteins that CAN regulate class I PI3Ks, the network of molecules that actually DO perform this role in vivo, either in healthy tissues or in cancers, remains largely unknown.
Loss of the tumour-suppressor and PIP3-phosphatase, PTEN, leads to chronic activation of class I PI3K signalling and is a common occurrence in human cancers generally (11.8% of analysed tumours) and prostate cancer specifically (13.6%, early and over 60% late, stage).
We have unpublished proteomic data, obtained from mice expressing endogenously-tagged class I PI3K components, that for the first time reveals the proteins that interact with the class I PI3K regulatory subunits in healthy compared to PTEN-null mouse prostate (3 month, Hi-grade PIN stage). We find evidence of substantial rewiring upstream of PI3K activation in the PTEN-null tissue, including; a dramatic decrease in association of IRS1 (Insulin Receptor Substrate 1) and increases in interactions with the poorly characterised molecules AFAP1L2 (XB130) and PLEKHS1, but little change in association with cell surface receptors. We hypothesise that these events drive reduced insulin responsiveness/dependency and, through the molecular properties of AFAP1L2 and PLEKHS1, increased receptor-independent, PIP3-driven 'feed-forward' augmentation of PIP3 signalling and tumour progression. We aim to investigate the mechanisms that lead to this rewiring and its implications for prostate cancer.

The main beneficiaries will be:

1. Academics: This is dealt with more completely in the section Academic Beneficiaries.
2. The two staff employed directly on the grant.
3. Industry: including our MICA-partner AstraZeneca and the pharmaceutical sector more broadly.
4. The General public.
5. Clinicians.
6. The MRC
7. Our host organisation, the Babraham Institute

They will benefit in the following ways:

1. Academics. The following elements of our research will have a wide spread impact in the fields of cancer biology and intracellular signalling; the technology we apply to study PI3K signalling in vivo, the results of that analysis that will reveal the endogenous network of class IA PI3K regulators in vivo for the first time, the loss of IRS drive to class IA PI3Ks in the context of loss of PTEN may be a widespread phenomenon in cancer and an important event in tumour progression and the increased association of the poorly understood PI3K adaptors PLEKHS1 and AFAP1L2 in the absence of PTEN in mouse prostate may well be informative for a number of other types of cancer. The project will also create new directions for academic research; in cancer biology generally and prostate cancer specifically, these are very poorly understood and the communication of the results of this project will have a significant impact on knowledge within the public domain and will encourage other academic groups to enter these important field.
2. The named PDRA on the project will learn additional skills in cancer biology, exploitation and interrogation of mouse models of cancer and organoid culture and manipulation and transferable skills in executing and communicating a curiosity-led, but target-driven, project that will be relevant to several potential careers, including basic research, the pharmaceutical sector, scientific administration and policy making. The interactions with the MICA-partner will also give them an invaluable insight into business and life in the pharmaceutical industry. The un-named research technician will learn a wide range of important skills, particularly in simple molecular biology, management of mouse breeding and colonies and genotyping, and establishing and maintaining prostate organoid cultures.
3. Industry. We hope to identify new therapeutic targets to treat cancer and to provide a deeper understanding of the mechanisms underpinning tumour progression. Early access to the results of this work will give our MICA-partners AstraZeneca a direct competitive advantage both through their own appreciation of the cancer progression process and through the opportunity to license IP generated in the project. Many of these benefits will filter down to the broader pharmaceutical community through our communication activities, although this will be slower. This will directly impact the competitiveness of our collaborators in the commercial sector and their wider organisations and will contribute to the perception that Cambridge and the UK are centres of excellent academic/commercial collaboration that will serve to bring in more R & D investment into the region generally.
4. The general public. In the short to medium term as recipients of our public engagement activities giving them a better understanding of research and cancer biology. In the longer term as patients receiving potentially improved treatments based on our findings.
5. Clinicians. Through improved insights into the processes driving prostate tumour progress, potential new treatments or diagnostic tests.
6. The MRC. Through delivery of their strategic priorities, particularly in terms of our results improving understanding of a socio-economically important disease and our knowledge exchange and commercialisation activities as outlined in the Pathways to Impact, Communication and Academic Beneficiaries sections.
7.The Babraham Institute. Through our work delivering their plans in commercialisation, knowledge exchange and impact activities.