Endocrine 3 Receptors and Signalling PSL300 WK3 PDF

Endocrine 3 Receptors and Signalling Helen Miliotis, PhD  Receptors and Signalling Section outline How do hormones signal? What characteristics do receptors share? What are the two main types of receptors? Intracellular receptors Plasma membrane receptors How is signalling...

Endocrine 3 Receptors and Signalling Helen Miliotis, PhD  Receptors and Signalling Section outline How do hormones signal? What characteristics do receptors share? What are the two main types of receptors? Intracellular receptors Plasma membrane receptors How is signalling modulated? Textbook reading: Silverthorn 8th ed. 169-176, 179- 181 (7th ed. 170-177, 180-182 )(6th ed. 178-184, 189- 191; 5th ed. 181-188, 193-195; 4th ed. 177-184, 189-191)  How do hormones signal? Hormone binds to receptor Changes the conformation and activity of the receptor Alters the activity of intracellular signaling pathways Leads to change in synthesis of target proteins and/or modification of existing target proteins receptors hydrophobic hormones target cell hydrophilic response hormones receptor 3 What characteristics do receptors share? Large proteins Families Can be multiple receptors for one ligand or more than one ligand for a receptor Variable number in target cell (~500-100,000) Can be activated and inhibited Located in cell membrane, cytoplasm, nucleus 4  Cellular receptors are saturable Bound labelled testosterone (fmoles/mg prot) Total labelled testosterone (nM) 5  Properties of receptors High affinity Saturable Specific Reversible Estrogen in its receptor’s binding pocket 6 7 Question Hormone A binds to receptor B which causes response C. The concentration of hormone A doubles in the body causing a doubling in response C. The concentration of hormone A doubles again, but this time no change in response C. What could be happening? A) Receptor B is saturated B) This is an example of positive feedback C) This is an example of neutral feedback D) Hormone A is no longer specific to receptor B 8 Hormones and signaling Hormone binds to receptor Changes the conformation and activity of the receptor Alters the activity of intracellular signaling pathways Leads to change in synthesis of target proteins (slow) and/or modification of existing target proteins(fast). Fig 6.3  What are the two main types of receptors? 1)Intracellular receptors (bind lipid soluble hormones) Cytosolic and nuclear Directly alter gene transcription = genomic effects 2)Plasma membrane receptors G protein-coupled receptors Receptor-enzyme receptors Receptor-Channel Integrin Receptor Hormone Receptors and Mode of Action Peptide hormones – Cannot penetrate target cell – Bind to surface receptors and activate intracellular processes through second messengers Steroid hormones – Penetrate plasma membrane and bind to internal receptors (usually in nucleus) – Influence expression of genes of target cell – Take several hours to days to show effect due to lag for protein synthesis  Intracellular receptors Lipophilic messenger Extracellular fluid Diffusion 1a Nucleus Target cell 1b DNA 5 Nuclear Proteins Cytoplasmic receptor 4 receptor Ribosome 3 mRNA 2 Hormone- mRNA Hormone receptor response complex Nuclear envelope element (HRE) Nuclear pore Hormone response elements = specific DNA sequences e.g. estrogen response element in DNA Sometimes receptors recruit co-repressors to inhibit transcription Only genes with the response elements will be activated/repressed 12  Membrane Receptors 13 Fig 6.3c 16  G Protein–Coupled Receptors (GPCR) Membrane-spanning proteins Cytoplasmic tail linked to G protein, a three-part transducer molecule G protein-coupled adenylyl cyclase-cAMP system is the signal transduction system for many protein hormones G protein-coupled receptors use some lipid second messengers: e.g., diacylglycerol (DAG) and inositol trisphosphate (IP3) When G proteins are activated, they – Open ion channels in the membrane – Alter enzyme activity on the cytoplasmic side of the membrane © 2016 Pearson Education, Inc. Gs activates adenylyl cyclase Extracellular fluid Messenger Adenylate 1 cyclase Receptor 2 a a b g 3 GDP GTP G protein GDP GTP cAMP 4 Activates ATP Protein kinase A 5 Protein Protein- P + + ATP ADP 6 Cytosol Response in cell Figure 6.8a G protein-coupled signal transduction Slide 1 GPCR-Adenylyl Cyclase Signal Transduction and Amplification Signal molecule binds to G protein– One signal coupled receptor (GPCR), which molecule activates the G protein. Adenylyl cyclase G protein turns on adenylyl cyclase, an amplifier enzyme. GPCR ATP G protein Adenylyl cyclase converts ATP to cyclic AMP. cAMP cAMP activates protein kinase A. Protein kinase A Protein kinase A phosphorylates other proteins, leading ultimately to a cellular response. Phosphorylated protein Cell response Second messengers such as cAMP amplify target cell responses © 2016 Pearson Education, Inc. Gq activates phospholipase C 18 Gai inactivates adenylyl cyclase G protein-coupled receptors Hormone Outside cell Inside cell 3 main types of G proteins: Target Activity Gs Adenylyl cyclase stimulatory Gq Phospholipase C stimulatory Gi Adenylyl cyclase inhibitory 20 Example: Fight or flight responses mediated by G-protein coupled receptors 21  Fight or flight responses Liver: glucose release Fat: fatty acid release epinephrine Heart: muscle contraction OH Skeletal muscle blood vessels: less vasoconstriction Intestine, skin, norepinephrine kidney: vasoconstriction 22 Figure 6.14 Target response depends on the target receptor Epinephrine can bind to different isoforms of the adrenergic receptor. a-Receptor Response b2-Receptor Response a-Receptor b2-Receptor Intestinal blood vessel Skeletal muscle blood vessel Epinephrine + a-Receptor Epinephrine + b2-Receptor Vessel constricts. Vessel dilates. © 2016 Pearson Education, Inc. Epinephrine, norepinephrine: diverse physio-logical effects via different receptors, effectors Adrenergic b1 b2 a2 a1 Receptor G proteins Gs + Gs _ Gi Gq + + Adenylyl Cyclase Phospholipase C cAMP Inositol Diacyl- triphosphate glycerol Protein kinase A Ca2+ Protein kinase C Protein Target cell response phosphorylation 24  Take away points: 1) GPCR sit in an inactive state with multiple G-protein subunits. 2) The alpha subunit has multiple isoforms: Gas, Gai, Gaq responsible for signaling. 3) Gas  adenylyl cyclase  cAMP  PKA  cell response 4) Gai  (-)adenylyl cyclase  cAMP.. 5) Gaq  PLC  (a) DAG  PKC (b) IP3  Ca2+  Cellular response 25  How is signalling modulated? Hormone degraded Receptor down-regulation or up-regulation Receptor desensitization Breakdown of second messengers Modification of any component in the pathway Biological effect provides feedback to reduce hormone secretion 26 Off Switch: Membrane receptors 2 Zn fingers on either side of hormone binding domain  Key points of lecture Receptors – two types (intracellular and membrane bound – how they work). Intracellular primarily work through gene transcription and translation (and some cell signaling) Membrane bound can alter membrane potential, work through cell signaling, influence transcription, translation, metabolism etc. Epinephrine can cause diverse physiological effects through different receptors 2 8 Endocrine Part 2 Hormones Helen Miliotis, PhD  Hormones Lecture outline What are the three main types of hormones? How are hormones synthesized? How is hormone release controlled? How do the stimuli trigger hormone release? How do hormones interact? Textbook reading:Silverthorn 8th ed. 199-214 (7th ed. 201- 216 )(6th ed. 211-224) (5th ed. 221-232)  Classification of Hormones Hormone types Hydrophilic hormones – Water soluble, can dissolve in plasma – Not lipid soluble (lipophobic), cannot cross plasma membranes – Examples: peptide hormones, protein hormones and catecholamines Hydrophobic hormones – Not water soluble, do not dissolve in plasma – Lipid soluble (lipophilic), readily cross plasma membrane – Examples: steroid and thyroid hormones  Classification of Hormones Hydrophilic hormone Hydrophobic hormone Membrane solubility:not lipid Membrane solubility: lipid soluble soluble Synthesis: On demand Synthesis: In advance, stored Release: Diffusion Release: Exocytosis Transport in Blood: Bound to Transport in Blood: Dissolved carrier proteins What are the three main types of hormones? Peptide/Protein (3 or more amino acids) Steroid (derived from cholesterol) Amine (derived from single amino acids) 5  Hormone Chemistry Steroid Monoamine Peptides Chemistry Derived from Made from amino acids Made from chains of amino cholesterol acids Examples Sex steroids Catecholamines Insulin (estrogen), cortisol (epinephrine), thyroxine Transport Hydrophobic, so bind Hydrophilic, so mix easily Hydrophilic, so mix easily with to transport proteins in with blood plasma blood plasma the blood  Peptide/Protein Hormones Linked amino acids Most hormones Made in advance e.g. glucagon Synthesized like secreted proteins Stored in vesicles Release by exocytosis upon a signal Water soluble (dissolved in plasma) Short half life in plasma Bind to membrane receptors (next lecture) 7  Peptide/Protein Hormones: synthesis, packaging and release Signal seq + hormone (1+ copies) + cleaved peptide fragments 8 Post-translational processing produces biologically active peptide  Single preprohormone can contain: Several copies of the same hormone One than one type of hormone Active peptides released depends on specific 9 proteolytic processing enzymes Peptide/Protein Hormone (Processing) Formation of disulfide bonds Insulin Fox K M et al. Molecular Endocrinology 2001;15:378-389  Review Question Insulin is degraded in the body extremely quickly and is difficult to measure because of this. How else could we indirectly measure insulin release? A) Measure preproinsulin protein B) Measure C-peptide levels C) Measure fatty acid levels D) Measure beta cell mass  Steroid Hormones Synthesized only from cholesterol Made on demand Not stored in vesicles Released from cell by simple diffusion Water insoluble (bound to carriers in blood) Long half life Diffuse into target cells or taken up by endocytosis of steroid hormone carrier proteins Cytoplasm or nucleus receptors (but can also act on plasma membrane receptors) 12 Type of hormone made depends on the which enzymes are present in the cell 13  Amine Hormones Synthesized only from tryptophan or tyrosine Tryptophan derivative: Melatonin (behaves like peptides or steroids) Tyrosine derivatives: Catecholamines (behave like peptides) Thyroid hormones (behave like steroids) 14  Melatonin Darkness hormone Secreted at night (Sleep) Made in pineal gland (also gi tract, leukocytes, other brain regions) Diverse effects: Transmits information (light-dark cycles to govern the biological clock) Immune modulation Anti-oxidant ***Do Not Tyrosine-derivatives Memorize structures***  Synthesis of catecholamines Synthesized in adrenal medulla (mainly in cytosol) Stored in vesicles prior to release Released via exocytosis Lipophobic, water soluble Bind to membrane receptors (adrenaline) Figure from: http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/adrenal/medhormones.html Control of hormone release: Endocrine cells directly sense stimuli, then secrete the hormone Stimuli Endocrine cell Hormone release Metabolite H H Hormone H H Neurohormone H H Neurotransmitter H H example Glucose pancreatic b cell Insulin 18 How do the stimuli trigger hormone release? Act through intracellular pathways to: change the membrane potential increase free cytosolic Ca2+ change enzymatic activity increase the transport of hormone substrates into the cell alter transcription of genes coding for hormones or for enzymes needed for hormone synthesis promote survival and in some cases growth of the endocrine cell 19  Example: glucose stimulation of insulin release http://ciitn.missouri.edu/cgi-bin/pub_view_project_ind.cgi?g_num=11&c_id=2007009  Review question Sulfonylurea blocks KATP channels, what effect would this have? a) Keeps voltage-gated Ca2+ channels closed b) Enhances insulin secretion c) Causes the cell to hyperpolarize d) Directly reduces the levels of ATP in the cell 21 Hormones released from the hypothalamus and anterior pituitary regulate the release of several hormones Just review – will go into detail in other lectures Anterior pituitary Hypothalamic releasing and inhibiting hormones Anterior pituitary hormones insulin-like thyroid cortisol estrogens, growth factors hormones testosterone, etc  Hormone Interactions  Most cells sensitive to more than one hormone and exhibit interactive effects  Synergistic effects  Multiple hormones act together for greater effect  Synergism between FSH and testosterone on sperm production  Permissive effects  One hormone enhances the target organ’s response to a second later hormone  Estrogen prepares uterus for action of progesterone  Antagonistic effects  One hormone opposes the action of another  Insulin lowers blood glucose and glucagon raises it 17-25 Figure 7.12 Synergism © 2016 Pearson Education, Inc. Key Points to take away: -Protein hormones – where they act – Preprohormone concept and how this can results in changes on multiple systems -Steroid hormones – where they act – enzyme deficiency can cause no production of some hormones and excess amounts of others -Tyrosine hormones – produce thyroxine and epinephrine -Think about about insulin release – we will talk more about this. -Review Ant pituitary hormones – we will talk more about this. Endocrine Principles Helen Miliotis, PhD [email protected]  Endocrine Principles Lecture outline Homeostasis Negative and Positive Feedback Mechanisms Cell-Cell Communication Short and Long Reflexes Features and Location of Hormones Identifying Hormones Textbook reading: 8th ed: 13-18, 165-167, 181-190, 195-196 7th ed. 13-18, 166-168, 182-191, 197-198 (6th ed. 14-19, 175- 177, 192-200, 207-21); (5th ed. 179-181, 196-205, 216-220);  What is homeostasis? = The process of maintaining a constant internal environment despite changing conditions “the constancy of the internal environment” “homeostasis”, regulation of the internal environment Claude Bernard, 1880’s Walter B. Cannon, 1929 How does the internal environment stay stable? Deviation from set point Homeostasis: The tendency towards a relatively constant internal environment  Homeostasis isn’t equilibrium! Dynamic steady state Figs 1.5 & 1.7 Feedback control setpoint Oscillation around a setpoint Fig 1.11  Negative feedback for homeostasis Positive feedback for change Negative Feedback Positive Feedback Initial Initial Stimulus Stimulus Response Response Outside Feedback factor Stimulus Stimulus Stabilizing Reinforcing  Negative feedback e.g. Regulation of cortisol - Negative secretion feedback action of cortisol - suppresses CRH release and ACTH release Positive feedback e.g. oxytocin and the control of uterine contractions Note: This is NOT homeostatic  Review question Imagine a hormone that is released in response to low blood pressure and acts to reduce blood pressure. What is this an example of? a) Positive feedback b) Negative feedback c) Feed forward control d) Neutral feedback  Maintaining homeostasis and other body functions requires intercellular communication Local control Autocrine Gap junctions Contact-dependent Small ions Membrane protein Molecules and molecules binds to move through move through membrane protein interstitial fluid; gap junctions short distance connecting cells Fig 6.1 Long-distance communication Neuroendocrine Fig 6.1  Simple and Complex Reflexes – Simple are mediated either by the nervous or the endocrine system – Complex reflexes are mediated by both systems and go through several integrating systems Compare neural and endocrine reflexes © 2016 Pearson Education, Inc. Figure 1.9 A comparison of local control and reflex control © 2016 Pearson Education, Inc. Homeostatic reflex pathways SENSOR can be Specialized cells or structures that convert various stimuli into electrical signals Modified Figs 6.16 & 6.17 Reflex pathway patterns – Nervous system Fig 6.19 Simple endocrine reflex Receptor Endocrine cell Hormone Target cell (effector) Modified Fig 6.19 Why do you need different control systems?  What are hormones & the endocrine system? Epithelium Connective tissue proliferation Exocrine: Exocrine Endocrine Endocrine: Exo = outside Endo = inside krinein = to secrete krinein = to secrete Into a duct* Into the bloodstream^ * Substances secreted to environment ^ Hormones secreted into the external to self bloodstream  Take ONE minute and map as many hormones to their respective organs as you can! Hypothalamus Pineal gland Pituitary gland Primary Thyroid gland Endocrine Heart Organs Parathyroid gland (main function is Liver to release hormone) Secondary Pancreas Adrenal glands Endocrine Organs Kidneys (release hormones & do something else) Stomach & small intestine Placenta Adipose Tissue Testes (male) Skin  What are some features of hormones? can be made in different places in the body chemicals made by cells in specific endocrine glands or other tissues transported in the blood to distant targets bind to specific receptors may act on multiple tissues alter activity of target cells action must be terminated maintain homeostasis or precipitate change in many physiological processes  How were hormones identified? Remove gland & observe results Replace gland…. Replace extract from gland…. Give excess gland (or extract)…… Purify extract & test in biological assay Based on an 1849 experiment by the German physiologist AA Berthold  Key points Homeostasis is a core concept in physiology that requires cell-cell communication Cell-cell communication often involves the nervous system or the endocrine system The endocrine system communicates via messengers known as hormones Hormones produced in endocrine glands have various effects on target cells