PGY452 552 Endocrine physiology 2 Endocrine signaling A B C D E Specificity Steroid signaling Protein hormone signaling Complexity in signaling Signal termination Ninth day of creation Input Input Endocrine tissue Hormone H H H Receptor Signal Response H H Ninth day of creation discovery of the receptor Target tissue Hormone H H H H H H Response Feedback 2 Hormone signaling Start hormone binds to receptor on target cell Type depends on hormone class Protein hormones Hydrophilic do not pass through membranes Cell surface receptors Always true H Target cell Steroids Hydrophobic pass through membranes Receptors usually in the cytoplasm or nucleus 3 Steroid signaling Nuclear receptors Transcription factors Modification of transcription Broad effects 4 All steroids regulate transcription Transcription factors Receptors are similar Part of nuclear receptor gene family o 50 in gene family o 9 interact with hormones Effects Transcriptional Activation Transcriptional Inhibition Levels of specific proteins Levels of specific proteins Very broad effects Can involve 100 genes Result Cell growth division Organism level developmental changes 5 Nuclear receptors have common structural domains 427 to 980 amino acidsN4 5 domains A B binds other proteins AF 1 C DNA binding dimerization D hinge domain nuclear localization E F Ligand binding Activation Repression A B C D E F C A B E F D C estrogen receptor bound to DNA 6 Nuclear hormone receptor Type I cytoplasmic Steroid binding protein forms homodimer Conformational change nuclear localization Inactive receptor chaperone Transcriptional regulation Hormone Response Element Steroid Unique sequence for each receptor 15 bp Hormones that interact with type I receptors Cortisol Aldosterone Androgens Estrogens Progesterone 7 Nuclear hormone receptor Type II Hormones that interact with type II receptors Thyroid hormone Calcitriol vitamin D Steroid Type II receptor resides in the nucleus Heterodimer with retinoid X receptor Coactivator Corepressor RXR Hormone Response Element Transcriptional regulation 8 Steroids can activate transcription Co activator proteins Histone acetyl transferase HAT Heterochromatin transcriptionally silent Histones DNA Euchromatin transcriptionally active HRE HAT Pol II General transcription factors RNA polymerase 2 9 Steroids can repress transcription Histone deacetylase corepressor HDAC Pol II Po l corepressor Euchromatin II HDAC Heterochromati n 10 Nuclear receptors can work with other transcription factors PROBLEM Many steroids regulate many more genes than can be explained by this simple mechanism Transcriptional regulation Tethering Composite co or acti rep va res tor so r HRE half site Other binding site Other DNA binding transcription factors 11 Non genomic actions of steroids PROBLEM Some actions of steroids are too fast to be explained by transcriptional regulation 1 sig n 2 3 Response al Response 1 2 signal signal Response 3 Cell surface receptor Cytoplasmic modulation Nuclear receptor bound to cytoplasmic protein no translocation Minor mechanisms 12 Steroid metabolism influences specificity Inactive steroid Response Target tissue inactivates Steroid Prohormone Response NO RECEPTOR NO RESPONSE Active hormone 13 Notes SLIDE 5 A transcription factor is a protein that participates in the regulation of the rate of transcription by interacting with a protein s in the RNA polymerase transcriptional complex SLIDE 6 This is just an orientation I don t care if you know this stuff SLIDE 7 A hormone response element HRE is a short sequence of DNA within the promoter of a gene that is able to bind a specific hormone receptor complex and therefore regulate transcription The sequence is most commonly a pair of inverted repeats separated by three nucleotides which also indicates that the receptor binds as a dimer A chaperone protein prevents certain proteins in the cell inactive nuclear hormone receptors or unassembled glycoprotein hormones for example from losing their structure and being marked for disposal SLIDE 9 This symbol denotes that the protein is acetylated at a specific lysine SLIDE 16 Monofuctional and bifunctional receptor definitions are on the slide SLIDE 17 Heterotrimeric refers to a protein with three non identical subunits 14 What I want you to know 1 ALL STEROIDS REGULATE TRANSCRIPTION 2 The difference between type 1 and type 2 receptors 3 The type 1 receptor activation pathway 4 The role of HAT and HDAC in chromatin modification how that influences transcription 5 HRE binding is not necessary 6 Non genomic actions of steroids explain responses too fast for transcription 7 How steroid metabolism influences response 15 Protein hormone signaling Cell surface receptors Modifies cytoplasmic signaling Many effects 16 Protein hormones bind cell surface receptors Bifunctional H signal H signa l Protein hormones do not enter cells Signal is intracellular Many receptors few signaling mechanisms Link binding to action through effector that transmits function Types Monofunctional Binds hormone but must recruit effector G protein coupled Bifunctional One protein binds both hormone serves as effector enzyme linked Monofunctional Monofunctional Response 17 G protein coupled receptors By far the most common Monofunctional G protein effectors G proteins have 3 subunits heterotrimeric Activation Hormone binds G protein binds activated receptor GDP GTP dissociates binds effector protein Response H H GDP GTP Effector protein Many different subunit subtypes of each most commonly bind effectors The subunits come as a pair can bind different effectors Response 18 3 classes of G protein transduce endocrine signals G s G i G q Different subunits Also Gs Gi Gq q s i AC Effectors G s and G i stimulate or inhibit adenylyl cyclase AC G q stimulates phospholipase C PLC q One receptor can interact 1 G protein 19 G s G i work through PKA via adenylyl cyclase Hstim Hinhib AC AC s i ATP cAMP dependent protein kinases PKA ATP P cAMP PKAii PKA Enzymes ADP PKAii ATP Transcriptional regulation CREB BP P CREB ADP Pol II CRE 20 Gq controls internal calcium release Calcium critical 2nd messenger Intracellular Ca held in internal stores 2 3 mM Ca2 o Most ER Mitochondria Concentrations ECF 2 3 mM Cytoplasm 100 nM Internal stores 100 M Response Release through Ca release channel cytoplasmic Ca to 1 M Calcium signals in the cytoplasm Ca2 Ca2 100 M Ca2 in stores 100 nM Ca2 in cytoplasm 21 G q activates PKC releases Ca2 through PLC qH Inositol 1 4 5