Chemical Control of Intracellular Signaling Cascades in Time and Space

Protein-protein interactions, and their localization in cellular space determine the activation status of signaling cascades in physiology and disease. A striking example for these processes is the translocation of protein and lipid kinases to the plasma membrane when cells are stimulated via growth factor-, immune- or G protein-coupled receptors. It has been established recently that cytosolic or membrane localization of signaling molecules is crucial, but in many cases a more specific integration in signalosomes and membrane micro-domains determines function. Current available molecular tools to dissect spatial signaling include a Rapamycin-inducible FKBP12/FRB dimerization system. As the FRB domain is derived from target of rapamycin (TOR), rapamycin-derivatives used here interfere with a central hub in cellular signaling, making it unsuitable to study processes involved in growth, immunity and metabolic control.

Here we present a novel protein dimerization and translocation system based on protein tags that have no endogenous signaling counterparts. The chemical dimerizers have been optimized for fast reactivity and excellent intra-cellular availability. The resulting system integrating chemical development and matched molecular biology offers multiple opportunities to study protein-protein interactions in vitro or in a cellular environment. In the latter context, protein homo and hetero-dimerization and/or translocation to various cellular organelles can be achieved. Sub-membrane domain signaling of lipid modifying enzymes like phosphoinositide kinases (PIK) and phosphatases (PIP) is currently explored. As an example, we recently managed translocation of regulatory subunit of PI3K to the plasma membrane inducing hereby activation of PI3K/PKB/mTOR pathway.

Although mainly outlined here for lipid modifying enzymes, these novel chemical probes should be useful for the exploration of any intra-and extracellular signaling pathways.