A Chemical Genetic Approach to Understand Inositol Polyphosphate Signalling

Abstract

Inositol polyphosphates (InsPs) are highly energetic small molecules that are thought to play an important role in cellular signaling. Genetic studies have implicated highly phosphorylated InsPs such as 5-diphosphoinositol pentakisphosphate (5PP-InsP5) in insulin signaling in mammalian cells and stress-signaling response pathways in yeast. Despite these reports, the exact mechanism of action of InsPs in the context of signaling remains elusive do to a dearth of suitable pharmacological tools that selectively target InsP kinase activity.

In this study, a chemical genetic technique largely applied to protein kinases was developed for small molecule inositol polyphosphate kinases (Arg82p, Ipk1p, and Kcs1p). These kinases were genetically engineered (via a gatekeeper mutation) to bind orthogonal inhibitors, and Arg82p L117A (gatekeeper-engineered kinase) as well as Kcs1p L762A (gatekeeper-engineered kinase) were specifically and temporally inhibited through in vitro and in vivo assays.

Using tritiated inositol labeling experiments, InsP metabolic profiles of the gatekeeper-engineered strains were characterized in the presence of inhibitors. Additionally, the engineered strains were used in conjunction with metabolomic and transcriptomic studies to begin to elucidate the role of these small molecules in signal transduction pathways.

Overall, this study demonstrated that the gatekeeper-engineering method used to craft selectively inhibitable protein and lipid kinases can also be applied to small molecule InsP kinases. Additionally, the InsP profiles, metabolic, and transcriptomic profiles of inhibited InsP gatekeeper-engineered kinase strains varied drastically from their respective deletion and kinase dead strains, thus demonstrating the importance of using pharmacological tools to analyze signaling pathways. Moving forward, the InsP gatekeeper-engineered kinase strains will surely provide the InsP field with a vital tool for studying the signaling role of these intriguing small molecules.