Endocrine Principles II 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 Receptor Signal Response H H H H Ninth day of creation discovery of the receptor Target tissue Hormone H H H H H Response Feedback 2 Hormone signaling H Start hormone binds to receptor on target tissue Type depends on hormone class Protein hormones Hydrophilic do not pass through membranes Cell surface receptors Steroids Hydrophobic pass through membranes Receptors usually in the cytoplasm sometimes nucleus 3 Four paths to a target response H Autocrine same cell Response sig al n H H n sig l a sign al H Paracrine nearby H Paracrine autocrine hard to tell Endocrine response distant 4 Steroid signaling Nuclear receptors Modification of transcription Broad effects 5 All steroids regulate transcription Receptors are similar Part of nuclear receptor gene family o o 50 in gene family encode proteins Only 9 interact with hormones Effects Transcriptional Activation Levels of specific proteins Transcriptional Inhibition Levels of specific proteins Very broad effects Can involve 100 genes Result Cell growth division Organism level developmental changes 6 Nuclear hormone receptor Type I cytoplasmic Steroid binding protein forms homodimer Conformational change nuclear localization Hormone Response Element Steroid Transcriptional regulation Unique sequence for each receptor 15 bp nuclear localization signal Ligand binding Dimerizatio n hsp90 DNA Binding 7 Nuclear hormone receptor Type II Steroid Type II receptor resides in the nucleus Heterodimer Hormone Response Element Transcriptional regulation 8 Steroids can activate transcription Coactivator 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 corepresso r Euchromatin Histone deacetylase HDAC Pol II corepresso r HDAC Po l II Heterochromati n 10 Other mechanisms of steroid action 1 2 1 2 Cell surface receptor Cytoplasmic modulation Minor mechanisms Faster than transcriptional regulation More important you know the transcriptional regulation mechanisms signal Response signal Response ALL steroids regulate transcription 11 Steroid metabolism influences specificity Response Target tissue inactivates Steroid Prohormone Response NO RECEPTOR NO RESPONSE Active hormone 12 Protein hormone signaling Cell surface receptors Modifies cytoplasmic signaling Many effects 13 Protein hormones bind cell surface receptors H Protein hormones do not enter cells Signal is intracellular Many receptors few signaling mechanisms Link binding to action through effector Effector transmits function Types broad Bifunctional One protein binds both hormone receptor serves as effector Monofunctional Binds hormone but must recruit effector protein membrane intracellular signa l extracellular Effector Response 14 G protein coupled receptors GPCR 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 15 3 classes of G protein transduce endocrine signals G s Gi Gq Different subunits Also G s G i G q q 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 16 G s G i work through PKA via adenylyl cyclase H Hstim cAMP dependent protein kinases PKA AC AC s Hinhib i ATP cAMP H ATP PKAii PKA PKAii P Enzymes ADP PKA regulates 1 Metabolic pathways CREB 2 Transcription factors 3 Exocytosis ATP P Pol II ADP CRE 17 G q activates PKC releases Ca2 through PLC qH Inositol 1 4 5 triphosphate IP3 diacylglycerol DAG Protein Kinase C PKC Phosphatidylinositol 4 5 phosphate ATP q PLC DAG ATP PKC PKC Ca Phospholipase C Ca2 Ca2 Ca binding protein Ca2 Intracellular calcium stores IP3 sensitive calcium release channel ATP ADP Ca 2 P Ca2 2 P Enzymes 18 Key effect of Ca release exocytosis qH H q Ca2 PLC H 19 Gq controls internal calcium release Calcium critical 2nd messenger Intracellular Ca held in internal stores 2 3 mM Ca2 o Most ER Mitochondria Response Concentrations Cytoplasm 100 nM Internal stores 100 M Release through Ca release channel cytoplasmic Ca to 1 M Calcium signals in the cytoplasm response Ca2 Ca2 100 M Ca2 in stores 100 nM Ca2 in cytoplasm 20 Summary of G protein second messenger systems H PKC PKA act on many enzymes H Direct modification Indirectly by controlling transcription Ca2 influences many enzymes by similar mechanisms PKA Ca2 stimulate secretion Many protein hormones that control secretion of other protein hormones do so through Gq and Gs coupled receptors H 21 Complex effects Mostly on gene expression Enzyme linked receptors 1 Receptor tyrosine kinases RTK 2 Tyrosine kinase associated receptors 3 Cytokine serine threonine kinases TGF H Hormone Receptor Kinase activation Autophosphorylation Substrate phosphorylation 2 1 Tyr H H P JAK TK P P TK H JAK P I Tyr P 3 Tyr Ser II Tyr P P Ser P 22 The basics of endocrine signaling are simple Protein hormones G proteins Enzyme linked receptors Steroids Nuclear receptor transcription factors Complexity in signaling 23 Sources of complexity Many receptors 359 G protein coupled receptors 850 olfactory receptors 18 G subunits 4 7 subunits 7 PLC 6 adenylyl cyclases 6 forms of PKA 10 PKCs 50 Nuclear hormone steroid receptors 100 enzyme linked receptors Cross talk all tissues have multiple receptors signaling proteins We won t worry about this We will worry about Timing differences Signaling events Persistence of the signal 24 Timing of a signal is critical is understanding its source Millisecond ion channels Sec min exocytosis protein phosphorylation Min hours secondary responses to signaling Nuclear receptors G protein coupled Enzyme linked receptors hours min hours Protein degradation Translational control Hours Transcription Days Response to transcription days sec min sec 10 5 10 4 10 3 10 2 0 1 1 10 100 Time in hours Cell division Development 25 Endocrine intracellular signal termination H signa l Signals that are not reinforced will