Slide 1Ninth day of creation?Hormone signalingSteroid signalingAll steroids regulate transcriptionNuclear receptors have common structural domainsNuclear hormone receptor Type I: cytoplasmicNuclear hormone receptor Type IISteroids can activate transcriptionSteroids can repress transcriptionNuclear receptors can work with other transcription factorsNon-genomic actions of steroidsSteroid metabolism influences specificityNotesWhat I want you to knowProtein hormone signalingProtein hormones bind cell surface receptorsG protein coupled receptors3 classes of G-protein transduce endocrine signalsGαs & Gαi work through PKA via adenylyl cyclaseGq controls internal calcium releaseGαq activates PKC & releases Ca2+ through PLCβGαq releases Ca2+ through PLCβCa²⁺, PKC, and PKA all stimulate exocytosisSummary of G protein second messenger systemsEnzyme linked receptorsThe basics of endocrine signaling are simpleSources of complexityTiming of a signal is critical is understanding its sourceEndocrine intracellular signal terminationSignal termination of G-protein coupled receptor signalsPhosphoprotein phosphatases reverse kinase effectsCalcium activity limited by “reuptake”Quantitative description of hormone actionFactors that determine efficacyGraphic representation of efficacyNotes (cont.)Notes (cont.)Review questionsPGY452/552: Endocrine physiology2. Endocrine signalingA. SpecificityB. Steroid signalingC. Protein hormone signalingD. Complexity in signalingE. Signal terminationNinth day of creation?InputEndocrine tissueHormoneNinth day of creation – discovery of the receptorTarget tissueReceptorSignal○ResponseFeedback2HHHHHHHHHHHInputInputResponseHormone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Steroids○Hydrophobic: pass through membranes○Receptors usually in the cytoplasm or nucleus3HTarget cellTarget cellSteroid signalingNuclear receptorsTranscription factorsModification of transcriptionBroad effects4All steroids regulate transcriptionVery broad effects○Can involve >>100 genes○Result●Cell growth & division●Organism-level developmental changesVery broad effects○Can involve >>100 genes○Result●Cell growth & division●Organism-level developmental changes5•Transcription factors•Receptors are similar•Part of “nuclear receptor” gene familyo50 in gene familyo9 interact with hormones•Transcription factors•Receptors are similar•Part of “nuclear receptor” gene familyo50 in gene familyo9 interact with hormonesTranscriptionalActivationTranscriptionalActivationTranscriptionalInhibitionTranscriptionalInhibitionEffects:Effects: Levels of specific proteins Levels of specific proteins Levels of specific proteins Levels of specific proteinsNuclear receptors have common structural domains427 to 980 amino acids4-5 domainsA/B → binds other proteins (AF-1)C → DNA binding & dimerizationD (hinge domain)→ nuclear localization E/F → ○Ligand binding○Activation○Repression6A/B C D EN- -CFCA/BDE/Festrogen receptor bound to DNANuclear hormone receptor Type I: cytoplasmic7Steroidforms homodimerforms homodimerConformational change & nuclear localizationInactive receptor + chaperoneSteroid binding proteinHormoneResponse Element± ± Transcriptional regulationUnique sequence for each receptor15 bpHormones that interact with type I receptors•Cortisol•Aldosterone•Androgens•Estrogens•ProgesteroneNuclear hormone receptor Type IISteroidHormoneResponse Element± ± Transcriptional regulation•Type II receptor resides in the nucleus•Heterodimer with retinoid X receptor8Hormones that interact with type II receptors•Thyroid hormone•Calcitriol (vitamin D)CorepressorCoactivatorRXRSteroids can activate transcription9Heterochromatin transcriptionally silentHeterochromatin transcriptionally silentHistonesDNAHREEuchromatin transcriptionally activeEuchromatin transcriptionally activeCo-activator proteinsHistone acetyl transferaseGeneral transcription factors + RNA polymerase 2HAT−−−−−−−−−−−−HATPol IIco-repressorSteroids can repress transcription10−−−−−−−−−−−−EuchromatinEuchromatinHistone deacetylase−−Pol IIHeterochromatinHeterochromatinPol IIHDACco-repressorHDACTranscriptional regulationNuclear receptors can work with other transcription factors11± ± co-activator or repressor± ± PROBLEM: Many steroids regulate many more genes than can be explained by this simple mechanismPROBLEM: Many steroids regulate many more genes than can be explained by this simple mechanismOther DNA-binding transcription factorsTetheringHRE half siteCompositeOther binding siteNon-genomic actions of steroids1221ResponsesignalResponsesignal3ResponsesignalPROBLEM: Some actions of steroids are too fast to be explained by transcriptional regulationPROBLEM: Some actions of steroids are too fast to be explained by transcriptional regulation1. Cell surface receptor2. Cytoplasmic modulation3. Nuclear receptor bound to cytoplasmic protein  no translocationMinor mechanisms (?)Steroid metabolism influences specificity13ResponseTarget tissue inactivatesTarget tissue inactivatesNO RECEPTOR → NO RESPONSESteroid=ProhormoneActive hormoneResponseInactive steroidNotes•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