Hormones • • • • • Biochemical classification Mechanism of action Hierarchy Feedback loops Signal transduction Polypeptides Insulin glucagon somatotropin Steroids Estrogen testosterone cortisol FSH LH vasopressin Oxytocin thyrotropin ACTH Aldosterone corticosterone Progesterone Amino acid derivatives Epinephrine norepinephrine dopamine Thyroxine, T3 and T4 Melatonin Serotonin Rule: All hormones interact with target cells by first binding to specific receptors located either on the plasma membrane or as a cytosolic protein Rule: The receptor for hormones must be linked to a component that is able to respond to the binding of hormone with its receptor Rule: Substances that fool the responder into thinking a hormone has bound are call agonists Rule: Substances that prevent the binding of the natural hormone and do not elicit a response from the receptor are called antagonists 1 2 Nitric oxide 3 5 4 T-cell Activation Glucagon 1 3 2 G G protein Cyclic AMP G G Cyclic GMP PK-A PK-G 4 IP3 Insulin 5 G Ca2+ Diacylgycerol Calmodulin PK-C Tyrosine Protein kinase substrates Protein Ser/Thr kinases Protein substrates End result is phosphorylation of one or more proteins Multifunctional kinases Protein substrates Protein substrates Other phospholipases Hypothalamus Releasing hormones Anterior pituitary Nervous Posterior pituitary Thyrotropin Somatotropin FSH Vasopressin Prolactin LH Oxytocin ACTH Adrenal Thyroid Cortex Pancreas Ovary T3 Testis Cortisol Insulin, Estradiol Testosterone aldosterone glucagon, somatostatin Muscles liver Tissues Liver, muscles Adrenal Medulla Epinephrine Reproductive Mammary organs glands Feedback Loops Rule: Hormones elicit their own shut off mechanism Hypothalamus Anterior Pituitary Corticotropin releasing factor + Adrenal Cortex -Corticotropin + Cortisol Rule: All peptide hormones are synthesized as inactive “pre-pro” precursors Rule: A signal peptide must be cleaved off to activate the mature form of the hormone Signal Transduction Definition: The series events and components that take part in transmitting a hormonal signal to a the interior of the cell Membrane or cytosolic Receptor Signal Initiator Signal mediator Target molecule Action Cyclic AMP System Receptor G-protein Stimulate (Gs) and inhibit (Gi) Adenylate cyclase c-AMP Protein kinases G-Proteins A family of membrane proteins that exist in an inactive (GDP) and an active (GTP) state So-named because they bind GTP, displacing GDP Work with many receptors Both Stimulate and inhibit hormone signals GTP is a time-bomb slowly ticking When GTP is hydrolyzed to GDP, stimulation is stopped GTP GDP AC Resting ATP GTP Active AC cAMP GDP Inactive AC PO4 Resting GDP AC hormone Inhibitor Ri RS GTP GDP GTP AC GDP 4 ATP AT 4 cAMP Adenylate cyclase Signaling System P Protein kinase Inactive protein ADP Active protein Cell response N Ligand Cross phosphorylation C Tyrosine Kinase Receptors Extracellular Growth hormone Extracellular domain of Growth Hormone Receptor =O 3PO- -OPO3= Tyrosines Intracellular Binding to receptor forces dimerization of receptor subunits for cross phosphorylation Cell membrane (lipid bilayer) Growth Hormone Receptor Cell Signaling via RTK and Ras Kinases Challenge to Students • Many of the proteins that you just saw are coded by genes referred to as “oncogenes”, meaning they are capable of transforming a normal cell into a cancer cell. Src, Ras, ErbB, affect cell growth and differentiation. • The viral forms of these genes lack regulation, and the mammalian form (proto-oncogenes) are subject to mutation. • If you want to learn what causes a normal cell to become a cancer cell (malignant transformation), this is a good place to start. What is Behind the Biochemistry of Cancer? 1. An alteration of genes/proteins involved in: a. Cell proliferation b. Apoptosis (programmed cell death) c. Differentiation 2. Acquisition of a phenotype that allows cells to: a. Proliferate without limits b. Evade apoptosis c. Generate its own mitogenic signals Late Stage d. Ignore growth inhibitory signals e. Acquire vasculature (angiogenesis) – solid tumors f. Invade and colonize (metastasize) other tissue Genes Mutated 1. ras protein (25% of cancers) 2. p53 tumor suppressor (50% of cancers) a. controls DNA repair b. controls apoptosis 3. Tyrosine kinase receptor (HER2/neu) a. controls ras (overexpression) We Know 1. Biochemical pathways from ras to p53 2. Role of p53 in apoptosis and DNA repair We Don’t Know 1. Molecular circuitry for enhancing secretion of angiogenic factors from cancer cells 2. The regulation of elements controlling the migration and extravastion capabilities of cancer cells Take Home • • • • • • Most hormones never penetrate cells All hormones have receptors Internal responses are initiated by the receptor Receptors work with G proteins G proteins stimulate protein kinases Protein kinases comprise a cell signaling cascade • G proteins turn off when GTP is hydrolyzed to GDP, canceling the hormone action Take Home (Part 2) • • • • • • • Some receptors are protein tyrosine kinases Kinase activity is initiated by dimerization Kinase autophosphorylate receptors Phosphotyrosines bind to SH-2 domains Activation starts a kinase cascade Phosphorylated proteins enter nucleus DNA transcription turns on specific genes Final Exam Monday, May 10 10:30 a.m. – 12:30 p.m.