Class IA PI3K signalosome
Class IA PI3K is a heterodimer of a catalytic and a regulatory subunit, with three catalytic (p110α, β, δ) and five regulatory (p85α, p50α, p55α, p85β, p55γ) isoforms known to exist.
Many tissues express the complete set of Class IA isoforms, all of which catalyse the formation of PI(3,4,5)P3. Despite this apparent redundancy, there is accumulating evidence that individual Class IA isoforms predominate in specific (patho)physiological contexts. We are hence interested in addressing how this complexity within the pathway has evolved to allow its adaptation to fit different contexts of cell signalling.
Our specific aim is to rigorously define the individual roles of the three Class IA PI3Ks in a single, therapeutically-relevant, signalling network, in the context of a defined pattern of interactions between, and concentrations of, Class IA PI3K components. We also aim to understand the molecular mechanisms that explain the differential usage of Class IA PI3Ks thus defined.
Towards this goal, we have generated a set of knock-in mice that express endogenous Class IA catalytic (p110α, β, δ) and regulatory (p85α/p50α/p55α and p85β) subunits, individually tagged with a biotinylation consensus sequence (‘AviTag’). This protein tagging approach allows for efficient isolation of the different Class IA isoforms at endogenous levels as well as cell localisation and tracking studies.
Application of these tools in defined cell contexts can offer an array of information including relative and absolute subunit concentrations, patterns of binding to adaptors, catalytic subunit-specific interactions with any given adaptor and the differences in interactions with both membranes and regulatory proteins conferred by their constituent domains.