Kinase-Linked Receptors PDF

WEEK 30 MPharm Programme Receptor Superfamilies Kinase-linked Receptors Dr Gabriel Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK Receptor Superfamilies 30 Receptor Superfamily A group of receptors with a si...

WEEK 30 MPharm Programme Receptor Superfamilies Kinase-linked Receptors Dr Gabriel Boachie-Ansah [email protected] Dale 113 ext. 2617 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK Receptor Superfamilies 30 Receptor Superfamily A group of receptors with a similar basic molecular structure and that use the same signal transduction pathway 4 Major Receptor Superfamilies Ligand-gated / Ion channel-linked receptors G-protein-coupled receptors Kinase-linked receptors Intracellular / Nuclear receptors Slide 2 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Receptor Superfamilies  Slide 3 of 28 MPharm  PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK Outline of Lecture 30 Introduction to the enzyme- or kinase-linked receptor superfamily Subclassification of enzyme-linked receptors Molecular structure, functional roles, activation mechanism and signalling pathways of the EGF receptor (EGFR) Cytokine receptors, their activation mechanism and signalling via the JAK/STAT signalling pathway The roles of EGF receptor (EGFR) & cytokine receptor signalling in health and disease Slide 4 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors Learning Outcomes WEEK 30 At the end of this lecture, you should be able to: Describe the key features/characteristics of the enzymeor kinase-linked receptor superfamily Describe the basis for the subclassification of enzymeor kinase-linked receptors Describe the molecular structure, functional roles, activation mechanism & key signalling pathways of the EGF receptor (EGFR) Describe the activation mechanism of cytokine receptors & the associated JAK/STAT signalling pathway Appreciate the roles of EGF receptor (EGFR) & cytokine receptor signalling in health and disease Slide 5 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK Enzyme-linked Receptors 30 A diverse superfamily of multi-subunit transmembrane protein complexes that either (i) contain an intrinsic enzyme activity in their intracellular domain or (ii) associate directly with an intracellular enzyme Binding of the ligand  conformational change in the receptor protein  transmitted via a transmembrane helix  activation of an intrinsic/associated enzyme  initiation of signaling cascades Mediate the actions of multiple growth factors, cytokines and hormones Play major roles in regulation of cell growth, proliferation and differentiation Slide 6 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Classification of Enzyme-linked Receptors 5 main types of enzyme-linked receptors Receptor Tyrosine Kinases (RTKs)* – e.g. EGFR, IR Contain intrinsic tyrosine kinase activity (e.g. EGFR, IR) Receptor Serine/Threonine Kinases – e.g. TGF-βR Contain intrinsic serine/threonine kinase activity Tyrosine Kinase-Associated Receptors* (Cytokine Receptors) Associate with proteins that have tyrosine kinase activity Receptor Guanylyl Cyclases – ANPR Contain intrinsic cyclase activity Receptor Tyrosine Phosphatases Slide 7 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Kinase-linked Receptors Slide 8 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Receptor Tyrosine Kinases (RTKs) A family of cell‐surface receptors that transduce signals to polypeptide & protein hormones and growth factors Contain an intrinsic tyrosine kinase domain, which becomes active upon ligand binding  initiation of signaling cascades Key regulators of critical cellular processes, e.g. proliferation & differentiation, cell survival & metabolism, cell migration & cell cycle control Mutations in receptor tyrosine kinases are implicated in a wide array of diseases, including human cancers 58 RTKs identified in human genome – classified into 20 families (Type I-XX) Focus on Type I (Epidermal Growth Factor Receptor) family Slide 9 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors Receptor Tyrosine Kinases (RTKs) WEEK 30 Structural Characteristics & Activation Mechanism Slide 10 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK Receptor Tyrosine Kinases (RTKs) 30 Activation Mechanism & Signalling Cascades Slide 11 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Epidermal Growth Factor Receptors (EGFRs) EGFRs play key roles in regulation of cell proliferation, cell differentiation, cell growth, survival & migration They mediate the actions of peptide growth factors, such as epidermal growth factor receptor (EGF) & transforming growth factor- (TGF-) EGF is synthesized & released from the kidney, submaxillary gland and other organs EGF/EGFR signalling promotes embryonic development, stem cell regeneration, regulation of ion transport, wound healing, etc Dysregulation of EGF/EGFR expression (e.g. EGFR mutation & overexpression) contributes to cancer development Slide 12 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Epidermal Growth Factor Receptors (EGFRs) Structure & Mechanism of Activation EGFRs have a typical RTK structure comprising: An extracellular ligand-binding domain A single transmembrane (TM) helix domain A juxtamembrane region An intracellular catalytic / tyrosine kinase domain (TKD), adaptor domains with tyrosine residues & a flexible C-terminal tail Binding of EGR  dimerization of EGFR monomers  conformational change  release of cis-autoinhibition  trans& autophosphorylation of tyrosine residues in the cytoplasmic domains The phosphorylated tyrosine residues then serve as a platform for recognition & recruitment of multiple adaptor/effector proteins  initiation of downstream signaling cascades Slide 13 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Epidermal Growth Factor Receptors (EGFRs) Structure & Mechanism of Activation Receptor activation Slide 14 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK EGFR Signalling Pathways 30 Activated EGFRs trigger TWO main downstream signalling pathways – the RAS/MAPK and PI3K/AKT signalling pathways Slide 15 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK EGFR Signalling Pathways 30 The RAS/MAPK Pathway Grb2, an adaptor Src homology 2 (SH2)-domain protein, binds directly to activated EGFRs, recruits & activates a guanine nucleotide exchange factor, GEF (SOS) GEF (SOS) activates RAS via exchange of GDP for GTP RAS-GTP then activates RAF kinase (MAPKKK)  activates MEK 1/2 (MAPKK)  activates ERK 1/2 (MAPK) MAPK (ERK 1/2) then proceeds to phosphorylate & activate a host of critical effector/target proteins in the cytoplasm MAPK (ERK 1/2) also translocates to the nucleus  phosphorylates transcription factors (CREB, ELK-1 ,c-Fos, c-Jun)  cell growth, proliferation, differentiation and survival Slide 16 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 EGFR Signalling Mechanisms The RAS/MAPK Signaling Pathway Slide 17 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 EGFR Signalling Mechanisms The RAS/MAPK Signaling Pathway Cell growth, proliferation, survival differentiation & migration Slide 18 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK EGFR Signalling Pathways 30 The PI3K/AKT signalling pathway Grb2 associates with Gab1, another adaptor protein, and recruits PI3K to the plasma membrane  phosphorylation of PIP2 on the plasma membrane to generate PIP3 Accumulation of PIP3  co-localization of Akt/Protein Kinase B & phosphoinositide-dependent protein kinase 1 (PDK1) on the plasma membrane AKT/PKB is then phosphorylated by both PDK1 and mTOR complex 2 (mTORC2) Activated AKT translocates to the cytosol  phosphorylates critical target/effector proteins  activation or suppression of cell growth, proliferation, motility, neovascularization & cell death Slide 19 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 EGFR Signalling Mechanisms The PI3K Signaling Pathway Slide 20 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 EGFR Signalling Mechanisms The PI3K Signaling Pathway Slide 21 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Tyrosine Kinase-Associated Receptors Cytokine Receptors A family of cell‐surface receptors that transduce signals to cytokines Many associate directly with intracellular non-receptor tyrosine protein kinases Cytokines are small proteins produced by immune cells – facilitate cell communication & play essential roles in cell development & differentiation, immune & inflammatory responses Cytokines use multiple signaling pathways Focus on modulation of intracellular signalling via Janus kinase and signal transducer & activator of transcription (JAK/STAT) pathway JAKs - a family of intracellular non-receptor tyrosine protein kinases – convert extracellular stimuli into a wide range of cellular processes STATs are a family of transcription factors & SH2-domain proteins Slide 22 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK The JAK/STAT Signalling Pathway 30 Binding of a cytokine to its receptor  receptor dimerization  transphosphorylation & activation of the associated JAKs Activated JAKs phosphorylate specific tyrosine residues in the cytoplasmic domains of the cytokine receptor chains, which then act as docking sites for STATs Once they have been docked, STATs are phosphorylated & activated by the receptor-associated JAKs Phosphorylated STATs then dissociate from the receptor chains and dimerize  translocate to the cell nucleus  activate gene transcription This activated transcription/translation produces proteins that mediate immune responses & inflammation  completion of the inflammation feedback loop Slide 23 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Slide 24 of 28 The JAK/STAT Signalling Pathway MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Slide 25 of 28 The JAK/STAT Signalling Pathway MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors Cytokine Receptors WEEK 30 JAK/STAT Signalling Pathways Slide 26 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 EGFR & Signalling Pathways – Pathophysiology EGFR and its signaling pathways play key roles in development of human cancers, e.g. fibro-sarcomas, glioblastomas, mammary, ovarian, colorectal and non-small cell lung cancer Oncogenic transformation may result from loss of auto-control mechanisms through mutation, overexpression of the receptor, abnormal constitutive receptor activity or  autocrine signalling Two major classes of EGFR-targeted anticancer therapies have been developed: Humanized monoclonal antibodies against the EGFR extracellular domain – block ligand (EGF) binding: e.g. cetuximab & panitumumab Tyrosine kinase inhibitors (TKIs) – ATP mimetics that bind to the receptor’s kinase pocket  exclusion of ATP  prevention of signal transduction: e.g. erlotinib, gefitinib & lapatinib Slide 27 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors WEEK 30 Cytokine Receptors & JAK/STAT Signalling Pathophysiological Role Dysregulation of cytokine receptor-stimulated JAK/STAT signaling is implicated in the development of various human cancers and immune/inflammatory disorders, e.g. rheumatoid arthritis, atopic dermatitis & psoriasis & inflammatory bowel disease Increased JAK & STAT activity and decreased activity of intrinsic negative regulators  upregulation of pro-proliferative, antiapoptotic, pro-inflammatory & immunosuppressive proteins JAK inhibitors developed to treat immune/inflammatory disorders Tofacitinib (JAK1, 2 & 3 inhibitor) – rheumatoid arthritis, psoriatic arthritis & ulcerative colitis Baricitinib (JAK1 & 2 inhibitor), Filgotinib & Upadacitinib (JAK1 inhibitors) – rheumatoid arthritis Ruxolitinib (JAK1 & 2 inhibitor) – polycythaemia, myelofibrosis Slide 28 of 28 MPharm PHA112 Receptor Superfamilies – Kinase-linked Receptors