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Abstract
BackgroundG protein-coupled receptors (GPCRs) usually regulate cellular processes via activation of intracellular signaling pathways. However, we have previously shown that in several cell lines, GqPCRs induce immediate inactivation of the AKT pathway, which leads to JNK-dependent apoptosis. This apoptosis-inducing AKT inactivation is essential for physiological functions of several GqPCRs, including those for PGF2α and GnRH.MethodsHere we used kinase activity assays of PI3K and followed phosphorylation state of proteins using specific antibodies. In addition, we used coimmunoprecipitation and proximity ligation assays to follow protein–protein interactions. Apoptosis was detected by TUNEL assay and PARP1 cleavage.ResultsWe identified the mechanism that allows the unique stimulated inactivation of AKT and show that the main regulator of this process is the phosphatase PP2A, operating with the non-canonical regulatory subunit IGBP1. In resting cells, an IGBP1-PP2Ac dimer binds to PI3K, dephosphorylates the inhibitory pSer608-p85 of PI3K and thus maintains its high basal activity. Upon GqPCR activation, the PP2Ac-IGBP1 dimer detaches from PI3K and thus allows the inhibitory dephosphorylation. At this stage, the free PP2Ac together with IGBP1 and PP2Aa binds to AKT, causing its dephosphorylation and inactivation.ConclusionOur results show a stimulated shift of PP2Ac from PI3K to AKT termed “PP2A switch” that represses the PI3K/AKT pathway, providing a unique mechanism of GPCR-stimulated dephosphorylation.9Vm-TQNungMKvUWU45aeyUVideo
Highlights
G protein-coupled receptors (GPCRs) usually regulate cellular processes via activation of intracellular signaling pathways
immunoglobulin-α-binding protein 1 (IGBP1) regulates the Protein phosphatase 2A (PP2A) switch‐dependent Tetradecanoylphorbol acetate (TPA)‐induced apoptosis We show here that the PP2A switch can induce the inactivation of AKT, and this is regulated by IGBP1, which is important both for the release of PP2Ac from Phosphoinositol-3 kinase (PI3K) and for its binding to AKT
Upon GqPCR stimulation, the PP2A detaches from PI3K and interacts with AKT to form a complex, composed of AKT, PP2Ac, IGBP1, and PP2Aa
Summary
G protein-coupled receptors (GPCRs) usually regulate cellular processes via activation of intracellular signaling pathways. We have previously shown that in several cell lines, GqPCRs induce immediate inac‐ tivation of the AKT pathway, which leads to JNK-dependent apoptosis. This apoptosis-inducing AKT inactivation is essential for physiological functions of several GqPCRs, including those for PGF2α and GnRH. PP2A is a Ser/Thr protein phosphatase that plays a role in the regulation of many cellular processes [9, 10]. Under most circumstances it acts as a heterotrimer composed of a scaffold (A subunit, PP2Aa), a catalytic (C subunit, PP2Ac) and a regulatory subunit ((B subunit) [11, 12]). The ability of PP2Aa to interact with this dimer and affect its activity is still controversial ([15, 19] vs [20, 21]), and needs further clarification
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