PI 3-kinases (PI3Ks) generate intracellular lipid second messengers that regulate many cellular processes including cell survival, proliferation, migration and differentiation. The PI3K signalling pathway has been implicated in diseases such as cancer, inflammation and diabetes, and PI3Ks are therefore considered as attractive new therapeutic targets in the pharmaceutical and biotech industry. Mammals have 8 isoforms of PI3K, and therapeutic interference with PI3K signalling may have to be targeted at individual (or groups of) PI3K isoforms, in order to overcome systemic toxicity. This research proposal aims to gain insight in the role of PI3K isoforms in cell transformation by selected oncogenes, and the associated signalling mechanisms. We also aim to uncover mechanisms by which cells can resist inactivation of one or more isoforms of PI3K, in order to gain insight into PI3K isoform-selective signalling pathways, but also as a prelude to understand possible therapeutic resistance to PI3K inhibitors. This study will make use of a series of unique PI3K gene-targeted mice, made in the Host Laboratory, and which are seen as the ‘gold standard’ in the field. For the signalling studies, we will make used of a new phosphoproteomic technique, called Targeted In-depth QUAntification of Signalling (TIQUAS; unpublished; patents pending), recently developed by the Host Laboratory. The overall aim is to identify isoform-specific protein kinase/phospho-peptide signatures that could also be used as biomarkers.