Here we propose to identify and characterize a new class of signaling molecules critical for a core mechanism of cellular communication, i.e., signaling via trimeric G proteins. Trimeric G proteins play a pivotal role in a signal transduction mechanism that is conserved from yeast to humans and that constitutes the target for >25% of marketed drugs. Despite major advances in the last decades, the understanding of this signaling mechanism remains incomplete- the network of regulators that control trimeric G proteins has expanded beyond what the traditional view of this signaling pathway proposes. This has made evident that the regulation of trimeric G proteins is more complex than previously appreciated and that novel therapeutic targets may arise from the discovery of alternative mechanisms of G protein regulation. Our goal is to further the understanding of the G protein regulatory network by identifying a new family of activators, dissecting the molecular basis of their coupling to G proteins and characterizing the basic molecular mechanisms by which the prototype member of this family promotes cancer progression towards metastasis. Based on previous observations by us and others we hypothesize that a new family of non-receptor G protein activators is defined by the presence of a guanine nucleotide exchange factor (GEF) motif and that these activators assemble alternative G protein signaling circuits involved in disease. These new activators are not necessarily membrane proteins and may work in lieu of or in parallel to the canonical activators, i.e., G protein-coupled receptors (GPCRs), thereby representing a detour from the classical view of this signaling pathway. The experiments in SA#1 are designed to identify and characterize novel non-receptor G protein activators with a GEF motif by using bioinformatics, high-throughput peptide array screening and functional assays in yeast. We have validated this overall approach by identifying and partially characterizing the physiological function for some of the predicted candidates. In SA#2 we propose experiments to understand the structural basis for how this new family of non-receptor GEFs bind and activate G proteins. Taken together, these studies will determine the basic molecular principles that define a whole new family of G protein regulators and will also generate the tools required for future mechanistic studies on them. Experiments proposed in SA#3 tests the general hypothesis that these non-receptor GEFs assemble alternative signaling circuits in disease for the particular case of GIV, the prototype member of this new family of GEFs. Our work to date suggests a model in which GIV-dependent activation of G proteins is required to assemble a signaling pathway linking stimulation of integrins by extracellular matrix proteins to the acquisition of pro-metastatic features by tumor cells. In summary, we hope to unravel a new general mechanism of G protein regulation with broad implications in disease by combining discovery-based and targeted mechanistic studies.

Public Health Relevance

The vast majority of diseases that severely afflict the public health (including cancer, cardiovascular diseases, diabetes, inflammation, Parkinson's) are consequence of derangements in the molecular mechanisms by which our cells respond to external stimuli. Here we propose studies to identify a new class of signaling molecules and investigate the mechanisms by which they influence human disease. This work will have broad biomedical implications by providing insight to understand, manipulate and target a new class of molecular interfaces that control aberrant signal transduction in disease.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular and Integrative Signal Transduction Study Section (MIST)
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Flicker, Paula F
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Boston University
Schools of Medicine
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Garcia-Marcos, Mikel; VanHook, Annalisa M (2016) Science Signaling Podcast for 12 April 2016: G proteins in auriculo-condylar syndrome. Sci Signal 9:pc9
Marivin, Arthur; Leyme, Anthony; Parag-Sharma, Kshitij et al. (2016) Dominant-negative Gα subunits are a mechanism of dysregulated heterotrimeric G protein signaling in human disease. Sci Signal 9:ra37
Leyme, Anthony; Marivin, Arthur; Garcia-Marcos, Mikel (2016) GIV/Girdin (Gα-interacting, Vesicle-associated Protein/Girdin) Creates a Positive Feedback Loop That Potentiates Outside-in Integrin Signaling in Cancer Cells. J Biol Chem 291:8269-82
Gupta, Vijay; Bhandari, Deepali; Leyme, Anthony et al. (2016) GIV/Girdin activates Gαi and inhibits Gαs via the same motif. Proc Natl Acad Sci U S A 113:E5721-30
Coleman, Brantley D; Marivin, Arthur; Parag-Sharma, Kshitij et al. (2016) Evolutionary Conservation of a GPCR-Independent Mechanism of Trimeric G Protein Activation. Mol Biol Evol 33:820-37
Garcia-Marcos, Mikel; Ghosh, Pradipta; Farquhar, Marilyn G (2015) GIV/Girdin transmits signals from multiple receptors by triggering trimeric G protein activation. J Biol Chem 290:6697-704
Aznar, Nicolas; Midde, Krishna K; Dunkel, Ying et al. (2015) Daple is a novel non-receptor GEF required for trimeric G protein activation in Wnt signaling. Elife 4:e07091
Leyme, Anthony; Marivin, Arthur; Perez-Gutierrez, Lorena et al. (2015) Integrins activate trimeric G proteins via the nonreceptor protein GIV/Girdin. J Cell Biol 210:1165-84
Bhandari, Deepali; Lopez-Sanchez, Inmaculada; To, Andrew et al. (2015) Cyclin-dependent kinase 5 activates guanine nucleotide exchange factor GIV/Girdin to orchestrate migration-proliferation dichotomy. Proc Natl Acad Sci U S A 112:E4874-83