Title: Steroid Hormone/Nuclear Receptors Don DeFranco, Ph.D., dod1@pitt.edu
1Steroid Hormone/Nuclear ReceptorsDon DeFranco,
Ph.D., dod1_at_pitt.edu
- Steroid Hormone Structure
- Nuclear Receptors
- Description
- Structure
- Signal Transduction
- DNA-Binding Properties
- Regulation of Gene Expression
- Diseases
- Drug Targets
2Steroid Hormone/Nuclear ReceptorsClinical
Relevance
- Endocrine Disorders (Hormone Insensitivity
Syndromes Cancer) - Regulators of Various Metabolic Processes
- Therapeutic Use to Reduce Inflammatory Diseases
3GLUCOCORTICOIDS
- Reduce inflammation and immune responses
- In clinical practice since 1948
- 10,000,000,000./year market size in US
4Glucocorticoids Side Effects
5Steroid Hormones Derived from Cholesterol
Lipid Soluble Able to cross plasma membrane by
passive diffusion
6- SUMMARY OF INITIAL STEPS IN STEROID HORMONE
SIGNAL TRANSDUCTION - Stimulation of hormone production by releasing
hormones or factors that are synthesized and
secreted from neuroendocrine cells (e.g.
Adrenocorticotrophic hormone ACTH from
specialized cells in the anterior pituitary
stimulates glucocorticoid production from
specialized adrenal cortical cells). - Transport of hormone to its target cell via
plasma transport proteins in the bloodstream. - Dissociation from the plasma transporter proteins
and diffusion of the free hormone across the
plasma cell membrane. - Hormone encounters receptor either in the
cytoplasm or the nucleus.
7Hypothalamic-Pituitary-Adrenal (HPA) Axis
Regulation of Cortisol Synthesis and Secretion
8Nuclear Localization of Steroid Receptors
Unliganded GR
Liganded GR
Unliganded/ Liganded ER
NOTE Steroid Receptors Shuttle Between the
Nucleus Cytoplasm
9Domain Organization of Steroid Receptors
10Steroid Hormone Receptors Limited Forms
Hormone Receptor (s) Androgens AR Min
eralocorticoids MR Estrogens ERa ER
b Progesterone PRA PRB Glucocort
icoids GR GRb
11TWO RECEPTORS FOR ESTROGEN ER? ER?
Note Both types of ER can form homodimers (e.g.
ER?/ER?) or heterodimers (i.e. ER?/ER?)
12Estrogen Receptor Distribution Within the Body
13Differential Actions of ERa and ERb
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15Ligands for Some Nuclear Receptors
Vitamin D
16Ligands for Various Orphan Receptors
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18- Active ingredient of Gugulipid
- Gum resin of Commiphor mukl
- In use since 600 BC
- Antagonist of FXR
- (Farnesoid or Bile Acid Receptor)
- Lowers cholesterol and triglyceride
- levels
19- Active ingredient in St. Johns Wart
- Extract of Hypericum perforatum
- In use over 2000 years
- Ligand for PXR
- (Pregnane X or Xenobiotic Receptor)
- Induction of CYP3A4
20NR Classification
- Nuclear receptors can be classified by
- Their DNA binding specificity
- Their hormone binding specificity
- Their dimerization properties
21DNA Binding Configurations of NRs
HETERODIMER
MONOMER
HOMODIMER
- Steroid hormone receptors bind primarily as
homodimers - Retinoid X Receptor (RXR 9-cis RA) is a common
dimerization partner for various nuclear
receptors including thyroid hormone receptor,
retinoic acid receptor (all-trans RA), vitamin D
receptor and others
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24Glucocorticoid Response Unit of the PEPCK Gene
GR
GR
HNF3
HNF4
COUP
1
CEBP/ß
TBP
-27
-90
-325
-380
-410
-445
Accessory DNA-binding Factors Required!! (Can
impart tissue-specificity)
NOTE Phosphoenolpyruvate carboxykinase (PEPCK)
gene is glucocorticoid regulated in liver only
25Estrogen Regulated Promoters Association of other
Transcription Factors
All EREs on chromosomes 21 22
From Myles Brown laboratory (Dana Farber Cancer
Institute), 2005, 2006
Genome wide analysis
26Basic Mechanisms of Transcriptional
Activation/Repression by the Glucocorticoid
Receptor
27Glucocorticoid Side Effects Molecular Mechanisms
28CHROMATIN Higher Order DNA Compaction Within the
Nucleus
Histone Core 2 copies each of H2A, H2B, H3, H4
(all basic proteins-rich in Arg, Lys residues)
29Histone Acetylation/Deacetylation
30Other transcription factors
NOTE Rubinstein-Taybi Syndrome caused by
mutations in CBP.
NOTE Overexpression of some coactivators (e.g.
Amplified in Breast Cancer-1 AIB-1) associated
with hormone-independent breast cancer
(From Glass and Rosenfeld)
31Other transcription factors
NOTE HDAC inhibitors in clinical trials for
cancer treatment
(From Glass and Rosenfeld)
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33Nuclear Receptors as Drug Targets
- Reproductive or Endocrine Disorders
- Hormone-dependent Cancers (ER-breast cancer, AR-
prostate cancer) - Metabolic Diseases (PPAR-? for Type 2 Diabetes
and Metabolic Syndrome)
NOTE Ligands for nuclear receptors are small
ligands that are cell permeable
CELL OR TISSUE-SPECIFIC LIGANDS POSSIBLE?
34Thiazolidinediones (TZD) PPAR-? Ligands
Activation of PPAR-? in fat cells increases fatty
acid and triglyceride uptake and storage as well
as impacts adipokine gene expression (e.g.
downregulates the insulin resistance factor
resistin while upregulating the insulin
sensitizing factor adiponectin)
Endogenous PPAR-? ligand
35Steroid Hormone Action
Steroid Hormone Action
Selective Estrogen Receptor Modulators (SERMs)
36Estrogen Receptor Ligand-binding Domain
Ligand-induced Conformational Change
Helix 12 Contacts Coactivator proteins!
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38MECHANISM OF SERM ACTION
SERM as Agonist Recruitment of Coactivators! (e.g.
Tamoxifen in uterus)
SERM as Antagonist Recruitment of Corepressors!
(e.g. Tamoxifen in breast)
39- Summary or Nuclear Receptor Action SPECIFICITY
DETERMINANTS - Hormone binding
- DNA binding
- Cooperation with DNA-bound accessory factors
(tissue-specificity) - Recruitment of coactivator and/or corepressor
complexes (i.e. histone modifications-alterations
in chromatin structure) - Ligand-induced conformational changes