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G Protein Coupled Receptors (GPCRs) perceive many extracellular signals and transduce them to heterotrimeric G proteins, which further transduce these signals intracellular to appropriate downstream effectors and thereby play an important role in various signaling pathways. G proteins are specialized proteins with the ability to bind the nucleotides guanosine triphosphate (GTP) and guanosine diphosphate (GDP). In unstimulated cells, the state of G alpha is defined by its interaction with GDP, G beta-gamma, and a GPCR. Upon receptor stimulation by a ligand, G alpha dissociates from the receptor and G beta-gamma, and GTP is exchanged for the bound GDP, which leads to G alpha activation. G alpha then goes on to activate other molecules in the cell. These effects include activating the MAPK and PI3K pathways, as well as inhibition of the Na+/H+ exchanger in the plasma membrane, and the lowering of intracellular Ca2+ levels.
Most human GPCRs can be grouped into five main families named; Glutamate, Rhodopsin, Adhesion, Frizzled/Taste2, and Secretin, forming the GRAFS classification system.
A series of studies showed that aberrant GPCR Signaling including those for GPCR-PCa, PSGR2, CaSR, GPR30, and GPR39 are associated with tumorigenesis or metastasis, thus interfering with these receptors and their downstream targets might provide an opportunity for the development of new strategies for cancer diagnosis, prevention and treatment. At present, modulators of GPCRs form a key area for the pharmaceutical industry, representing approximately 27% of all FDA-approved drugs.
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