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Receptors Functions and Signal Transduction- L4- L5
Faisal I. Mohammed, MD, PhD University of Jordan 1
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Tyrosine Kinase Receptors:
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Receptors superfamilies: Ionotropic receptors (ligand-gated channels)
Metabotropic receptors (G protein-coupled receptors) Tyrosine Kinase Almost all neurotransmitters discovered so far have more than one kind of receptor -- called receptor subtypes. University of Jordan 4
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Epinephrine Can Act Through Two 2nd Messenger Systems
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Lipid-soluble Hormones
1 Lipid-soluble hormone diffuses into cell Blood capillary Activated receptor-hormone complex alters gene expression Nucleus Receptor mRNA Newly formed mRNA directs synthesis of specific proteins on ribosomes DNA Cytosol Target cell New proteins alter cell's activity Transport protein Free hormone Ribosome New 2 3 4 1 Lipid-soluble hormone diffuses into cell Blood capillary Activated receptor-hormone complex alters gene expression Nucleus Receptor mRNA Newly formed mRNA directs synthesis of specific proteins on ribosomes DNA Cytosol Target cell Transport protein Free hormone Ribosome 2 3 1 Lipid-soluble hormone diffuses into cell Blood capillary Activated receptor-hormone complex alters gene expression Nucleus Receptor mRNA DNA Cytosol Target cell Transport protein Free hormone 2 1 Lipid-soluble hormone diffuses into cell Blood capillary Target cell Transport protein Free hormone Lipid-soluble Hormones
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Hormones That Bind to Nuclear Receptor Proteins
Lipophilic steroid and thyroid hormones are attached to plasma carrier proteins. Hormones dissociate from carrier proteins to pass through lipid component of the target plasma membrane. Receptors for the lipophilic hormones are known as nuclear hormone receptors.
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Nuclear Hormone Receptors
Steroid receptors are located in cytoplasm and in the nucleus. Function within cell to activate genetic transcription. Messenger RNA directs synthesis of specific enzyme proteins that change metabolism. Each nuclear hormone receptor has 2 regions: A ligand (hormone)-binding domain. DNA-binding domain. Receptor must be activated by binding to hormone before binding to specific region of DNA called HRE (hormone responsive element). Located adjacent to gene that will be transcribed. University of Jordan
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Mechanisms of Steroid Hormone Action
Cytoplasmic receptor binds to steroid hormone. Translocates to nucleus. DNA-binding domain binds to specific HRE of the DNA. Dimerization occurs. Process of 2 receptor units coming together at the 2 half-sites. Stimulates transcription of particular genes. University of Jordan
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Water-soluble Hormones
Receptor cAMP serves as a second messenger to activate protein kinases G protein Protein kinases cAMP Activated protein Protein— Second messenger Activated adenylate cyclase converts ATP to cAMP Activated protein phosphorylate cellular proteins Millions of phosphorylated proteins cause reactions that produce physiological responses Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell P ADP Protein ATP 1 2 4 3 5 Water-soluble hormone Receptor cAMP serves as a second messenger to activate protein kinases G protein Protein kinases cAMP Activated protein Protein— Second messenger Phosphodiesterase inactivates cAMP Activated adenylate cyclase converts ATP to cAMP Activated protein phosphorylate cellular proteins Millions of phosphorylated proteins cause reactions that produce physiological responses Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell P ADP Protein ATP 1 2 6 4 3 5 Water-soluble hormone Receptor cAMP serves as a second messenger to activate protein kinases G protein Protein kinases cAMP Activated protein Second messenger Activated adenylate cyclase converts ATP to cAMP Activated protein phosphorylate cellular proteins Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell ATP 1 2 4 3 Protein— P ADP Protein Water-soluble hormone Receptor cAMP serves as a second messenger to activate protein kinases G protein Protein kinases cAMP Second messenger Activated adenylate cyclase converts ATP to cAMP Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell ATP 1 2 3 Activated protein Water-soluble hormone Receptor G protein Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell 1 Water-soluble hormone Receptor G protein cAMP Second messenger Activated adenylate cyclase converts ATP to cAMP Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell ATP 1 2 Water-soluble Hormones University of Jordan
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Hypophysiotropic Hormones
Predominant hypothalamic localization Hormone Structure Actions on Anterior Pituitary Thyrotropin-releasing hormone (TRH) Paraventricular Arcuate Anterior periventricular Peptide consisting of 3 amino acids Single chain of 10 amino acids Single chain of 41 Single chain of 44 Single chain of 14 Dopamine Stimulates secretion of TSH by thyrotropes; stimulates expression of genes for and ß subunits of TSH thyrotropes; stimulates synthesis of PRL by lactotropes Stimulates secretion of FSH and LH by gonadotropes Stimulates secretion of ACTH by corticotropes; stimulates expression of gene for POMC in corticotropes Stimulates secretion of GH by somatotropes; stimulates expression of gene for GH in somatotropes Inhibits secretion of GH by somatotropes Inhibits biosynthesis and secretion of PRL by lactotropes Gonadotropin-releasing hormone (GnRH) Corticotropin-releasing hormone (CRH) Growth hormone-releasing hormone (GHRH) Growth hormone-inhibiting hormone (somatostatin) Prolactin-inhibiting hormone (PIH)
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Mechanism of Thyroid Hormone Action
T4 passes into cytoplasm and is converted to T3. Receptor proteins located in nucleus. T3 binds to ligand-binding domain. Other half-site is vitamin A derivative (9-cis-retinoic) acid. DNA-binding domain can then bind to the half-site of the HRE. Two partners can bind to the DNA to activate HRE. Stimulate transcription of genes.
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Cyclic Monophasphate (cAMP) Second Messenger Mechanism
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Cell Membrane Phospholipid Second Messenger System
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Tyrosine Kinase University of Jordan
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Tyrosine Kinase Insulin receptor consists of 2 units that dimerize when they bind with insulin. Insulin binds to ligand–binding site on plasma membrane, activating enzymatic site in the cytoplasm. Autophosphorylation occurs, increasing tyrosine kinase activity. Activates signaling molecules. Stimulate glycogen, fat and protein synthesis. Stimulate insertion of GLUT-4 carrier proteins. University of Jordan
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Tyrosine Kinase (continued)
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The Insulin Receptor & Mechanisms of Insulin Action
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Protein Hormones – Mechanisms of Action
Adenylyl Cyclase Mechanism Phospholipid Mechanism Guanylate Cyclase Mechanism Tyrosine Kinase Mechanism ACTH LH FSH TSH GHRH Somatostatin ADH (V2 receptor) HCG MSH CRH Calcitonin PTH Glucagon GnRH TRH Angiotensin II ADH (V1 receptor) Oxytocin ANP Insulin IGF-1 GH Prolactin University of Jordan
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Steroid & Thyroid Hormones - Mechanism of Action
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Determinants of Free Hormone Receptor Binding
Carrier-bound hormone Endocrine cell Free Hormone Hormone receptor Hormone degradation Biological effects University of Jordan
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Correlation of Plasma Half-Life & Metabolic Clearance of Hormones with Degree of Protein Binding
(ml/minute) Thyroid Thyroxine Triiodothyronine Steroids Cortisol Testosterone Aldosterone Proteins Thyrotropin Insulin Antidiuretic hormone 99.97 99.7 94 89 15 little 6 days 1 day 100 min 85 min 25 min 50 min 8 min 0.7 18 140 860 1100 50 800 600 MCR = (mg/minute removed) / (mg/ml of plasma) = ml cleared/minute University of Jordan
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Circulating Transport Proteins
Principle Hormone Transported Transport Protein Specific Corticosteroid binding globulin (CBG, transcortin) Thyroxine binding globulin (TBG) Sex hormone-binding globulin (SHBG) Nonspecific Albumin Transthyretin (prealbumin) Cortisol, aldosterone Thyroxine, triiodothyronine Testosterone, estrogen Most steroids, thyroxine, triiodothyronine Thyroxine, some steroids University of Jordan
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Feedback Mechanisms Negative Feedback Positive Feedback Endocrine cell
+ + Endocrine cell Target cell Endocrine cell Target cell _ + Biological effects Biological effects University of Jordan
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Steroid & Thyroid Hormones - Receptors
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Actions of Thyroid Hormones
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Insulin Action on Cells:
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Signaling molecule (hormones) Signal transduction
Receptor of target cell Signal transduction Intracellular molecule (second messengers) biological effect University of Jordan
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Third messengers: Third messengers are the molecules which transmit message from outside to inside of nucleous or from inside to outside of nucleous, also called DNA binding protein. University of Jordan
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Signal molecules Proteins and peptides: Hormones, cytokines
Effect by membrane receptors Amino acid derivatives: Catecholamines Extracellular molecules Fatty acid derivatives: Prostaglandins Effect by intracellular receptors Signal molecules Steroid hormones, Thyroxine, VD3 Intracellular molecules cAMP, cGMP, IP3, DG, Ca2+ University of Jordan
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