Abstract G protein-coupled receptors (GPCRs) mediate the actions of a wide variety of hormones and neurotransmitters to control functions in all mammalian cells. As such, GPCRs are major targets of therapeutics. Individual GPCRs directly couple to distinct complements of heterotrimeric G protein and subunits that drive downstream signaling pathways to shape the cellular responses that determine GPCR efficacy. Both G and G subunits interact directly with effectors to produce cellular responses. Our laboratory has focused largely on G subunit signaling and Phospholipase C (PLC) signaling on projects ranging from analysis of basic biochemical reaction mechanisms to identification of roles in disease. In this proposal we seek to combine all of the funded laboratory directions into one proposal. Project 1. We were recently the first to demonstrate that phosphatidylinositol 4-phosphate is a substrate for PLC activity in cells. This initial study was performed in cardiac cells. This project is concerned with generalizing this reaction to multiple cell types with the evidence suggesting that PI4P is a major substrate for receptor stimulated PLC signaling. This has the potential to alter the paradigm for receptor-dependent regulation of phosphoinositide hydrolysis. Project 2. This project is to define roles for PLC signaling in the development of heart failure. We have shown the PLC deletion prevents development of hypertrophy in vitro and in mice. Here we are focused on identifying the mechanistic roles for PLC signaling in cardiac cells that regulate heart failure. Project 3. We have pioneered the identification of small molecules that modulate G protein subunit signaling downstream of GPCRs and have shown that these molecules have potential therapeutic utility. Here we will further explore the mechanism of action of these compounds, follow up from results of using these compounds to identify new G protein pathways in cell migration and identify novel chemical scaffolds for therapeutic development.