G-Protein-Coupled Receptors 2 (2023-24) PDF

WEEK 27 MPharm Programme Receptor Superfamilies G-Protein-Coupled Receptors 2 Dr Gabriel Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK The cAMP Signalling Pathway 27 Gs-GTP stimulates the activation of Adenylyl C...

WEEK 27 MPharm Programme Receptor Superfamilies G-Protein-Coupled Receptors 2 Dr Gabriel Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK The cAMP Signalling Pathway 27 Gs-GTP stimulates the activation of Adenylyl Cyclase (AC), a membrane-bound enzyme Adenylyl Cyclase (AC) converts ATP to cAMP The increased cAMP level leads to activation of protein kinase A (PKA) Activated PKA mediates phosphorylation of multiple downstream effector targets  cellular response cAMP can also modulate the activity of several Guanine Exchange Factors (GEFs) and ion channels On the contrary, Gi/o-GTP inhibits the activity of AC and lowers cellular cAMP level & PKA activation  cellular response Slide 33 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Slide 34 of 60 cAMP Signalling Pathway MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 cAMP Signalling Pathway Cellular Response Slide 35 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Synthesis and Degradation of cAMP Slide 36 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Slide 37 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Slide 38 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Slide 39 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Slide 40 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Signal Amplification in cAMP Signalling Pathway Slide 41 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 The 2+ IP3/Ca Signalling Pathway Gq/11-GTP activates Phospholipase C- (PLC) in cell membrane Phospholipase C- (PLC) catalyzes the conversion of phosphatidylinositol 4,5-bisphosphate (PIP2) to inositol triphosphate (IP3) & diacylglycerol (DAG) IP3 acts on the endoplasmic reticulum (ER) & trigger the release of Ca2+ into the cytoplasm Ca2+ modulates the activity of Ca2+-dependent effector proteins (e.g. calmodulin, transcription factors)  cellular response DAG, in concert with the increased Ca2+ level, activates protein kinase C (PKC) in the cell membrane PKC induces phosphorylation of multiple target downstream effector proteins  cellular response Slide 42 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 2+ IP3/Ca Signalling Pathway IP3R Slide 43 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs IP3/Ca2+ Signalling Pathway WEEK 27 Phosphatidylinositol-biphosphate (PIP2) is a membrane phospholipid Cleaved by G-GTP activated phospholipase C- (PLC) to generate 2nd messengers: Inositol triphosphate (IP3) Diacylglycerol (DAG) IP3 diffuses through the cytosol and releases Ca2+ from the ER DAG stays in the membrane & activates protein kinase C Slide 44 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Slide 45 of 60 2+ IP3/Ca MPharm Signalling Pathway PHA112 Receptor Superfamilies - GPCRs WEEK 27 Slide 46 of 60 IP3/Ca2+ Signalling Pathway MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 IP3/Ca2+ Signalling Pathway & SM Contraction Ach (M3-R) Epi (1-R) Slide 47 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 IP3/Ca2+ Signalling Pathway & Smooth Muscle Contraction Slide 48 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Diversity of GPCR Signalling Mechanisms Signalling via the G Dimer The G & G subunits are tightly bound/associated to form an obligate functional heterodimer There are 5 G and 12 G subunits in the human genome  a large number of potential combinations of G dimers Lipid modification of the G subunit  attachment & localisation of the G dimer to the membrane GPCR activation  dissociation of G-GTP  free G dimer The free G dimer plays key roles in GPCR signalling by regulating a host of downstream effectors – voltage-gated Ca++ channels, inwardly-rectifying K channels, GPCR kinases, phosphoinositide 3 kinases, adenylyl cyclase, phospholipase C- Slide 49 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Signalling via the G Dimer Ach-induced Lowering of Heart Rate Slide 50 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 GPCR Desensitization and Intracellular Trafficking Temporal and spatial signalling of activated GPCRs is controlled by desensitisation & internalisation Involves the sequential action of 2 major intracellular actors: G protein-coupled receptor kinases (GRKs) -arrestins (cytoplasmic adaptor proteins) First, GRK docks onto activated GPCR  phosphorylation of serine & threonine residues in the receptor  inhibition of G-protein activation (homologous desensitisation) PKA, PKC & other S/T kinases are also able to phosphorylate inactive GPCRs, leading to heterologous desensitisation Slide 51 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 GPCR Desensitization and Intracellular Trafficking Next, -arrestins bind to phosphorylated GPCR & sterically hinder GPCR-G protein coupling interactions  inhibition of further activation of G protein-mediated signalling -arrestins then couple the phosphorylated GPCRs to clathrin-coated pits to facilitate receptor internalisation The internalised GPCRs are trafficked to endosomes, with one of three possible fates: They may be dephosphorylated by phosphatases & recycled back to the cell surface for future signalling (recycling) They may be sorted to lysosomes for degradation They may activate β-arrestin-dependent and G-proteinindependent GPCR signalling cascades Slide 52 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Desensitization & Trafficking of GPCRs Slide 53 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Examples of GPCRs that Mediate the Actions of Key Chemical Messengers Slide 54 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Role of GPCRs in Adrenergic Actions Norepinephrine Epinephrine 1, 2, 3 1 Slide 55 of 60 MPharm PHA112 2 Receptor Superfamilies - GPCRs WEEK 27 Role of GPCRs in Acetylcholine Actions Acetylcholine, Carbachol Slide 56 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Role of GPCRs in mediating Autonomic Nervous System Control of Heart Function Slide 57 of 60 MPharm PHA112 Receptor Superfamilies - GPCRs WEEK 27 Role of GPCRs in Histamine Actions Histamine H1 Slide 58 of 60 MPharm H2 PHA112 H3, H4 Receptor Superfamilies - GPCRs WEEK 27 Role of GPCRs in Dopamine Actions Dopamine D1, D5 Slide 59 of 60 MPharm D2, D3, D4 PHA112 Receptor Superfamilies - GPCRs WEEK 27 Role of GPCRs in Serotonin (5-HT) Actions Serotonin (5-HT) 5-HT4, 5-HT6, 5-HT7 5-HT2A, 5-HT2B, 5-HT2C Slide 60 of 60 MPharm PHA112 5-HT1 Receptor Superfamilies - GPCRs