SteroidIntracellular Receptor Pharmacology

1
Steroid/Intracellular Receptor Pharmacology

• Therapeutic uses of agonist/antagonists
• Replacement therapy
• adrenal steroids for Addisons disease
• estrogen and progesterone for menopause
• thyroid (hypothyroid disorders)
• Pharmacologic (non-physiological) uses
• glucocorticoids as anti-inflammatory agents
• estrogen/progesterone for contraception
• androgens for increased muscle mass (abused by
  athletes)
• mifepristone (RU486) for pregnancy termination
• Cancer chemotherapy
• tamoxifen, anastrozole for breast cancer
• flutamide/bicalutamide, leuprolide for prostate
  cancer

2
AF2
AF1
a b
LXR oxysterols FXR farnesoids PXR zenobiotics CAR
phenobarbital
Vitamin D, thyroid hormone, Retinoic Acid
Receptors Adopted Orphan Receptors
Classical Steroid Hormone Receptors these are a
small subset of the 48 Nuclear/Intracellular
Receptor Family members found in the human genome.
3
There are two genes coding for estrogen receptors
in the human genome ERa and ERb
18
97
60
homology
(there appears to be no AF-1 function in human
ERb)
They bind the same DNA sequences, dimerize with
themselves and each other. Are they just
redundant or do they have specific physiological
roles?
4
Expression patterns of ERs

• ERb
• ovary
• prostate, testis
• spleen, thymus
• lung
• hypothalamus, other brain regions

• ERa
• breast
• uterus
• cervix
• vagina
• brain regions

Knockout phenotype female sterility, no
mammary gland development, obesity, male
sterility, epididymal dysfunction, testicular
degeneration
Knockout phenotype male--fertile,
female--reduced fertility, ovarian
dysfunction, vascular problems/develop hypertensio
n as they age
5
Structure of the DNA binding domain
6
(No Transcript)
7
antagonists or partial agonists
agonists
The classic view of estrogen action E binds to
ER (displaces a complex of chaperone proteins),
ER forms dimers and interacts with the ERE to
activate genes by recruitment of co-activators.
8
How does estrogen act in classical mode to induce
gene expression from genes that have EREs in
their promoter?
9
However, a number of observations do not fit this
model

• some genes induced by E do not have a
  recognizable ERE
• tamoxifen can inhibit E induction of genes in
  breast but can be stimulatory of E responsive
  genes in uterus
• some of the effects of E are too fast to be
  transcriptional (e.g. rapid activation of the MAP
  kinase pathway in lt5 min.)
• pharmacological actions of agonists and
  antagonists do not make sense in the classical
  model

10
new observation ER does not need to bind to an
ERE in order to induce gene expression.
Induction can occur when ER binds indirectly to
other transcription factors such AP1 and then
recruits coactivators.
classic pathway
(fos/jun)
indirect gene activation pathway
11
The regulation of ERE versus AP1-activated
promoters depends on the receptor subtype, the
ligand, and the cell type
ERa ERb
Promoter E TAM E TAM
ERE
AP1
12
A Structural basis for the differences in ER
activity when agonist or antagonist ligands are
bound
the C-terminal trans- activation helix (H12) is
in green
AF2
13
(No Transcript)
14
Steroid Receptors also signal through non nuclear
mechanisms to activate MAP kinase
15
Summary and prospects for the future

• 1. estrogen receptor ligands can act through
  multiple mechanisms
• (1) classical ligand dependent induction thru an
  ERE
• (2) indirect ligand dependent induction by
  interaction with AP1 or perhaps other DNA bound
  transcription factors.
• (3) ligand-dependent interactions with Src
  kinase in the cytoplasm and the activation of
  Map kinase signaling
• 2. ligands can have agonist or antagonist
  properties depending on whether the receptor is
  ERa or ERb and the tissue complement of
  co-regulators
• 3. the complexity of biological responses can be
  utilized
• pharmacologically by the design of SERMs
  (selective estrogen receptor modulators --other
  nuclear receptors such as AR, GR may also be
  approached this way.

16
genistein a phytoestrogen that is a selective
estrogen receptor modulator (SERM) every
morning with breakfast!
17
Results from the 2002 Womens Health Initiative
Study on Hormone Replacement Therapy in
Postmenopausal Women
18
WHI subject profile

• note
• many subjects had been E deficient for 10 yrs
• high percentage were overweight.
• Conjugated equine estrogen (a mixture of
  estrogens from pregnant horse urine) and
  medroxyprogesterone were given orally--the liver
  sees highest conc.

19
Corticosteroid Receptors
AF2
AF1
a b
LXR oxysterols FXR farnesoids PXR zenobiotics CAR
phenobarbital
cortisol binds to both GR and MR aldosterone
specific for MR (mineralcorticoid receptor)
Vitamin D, thyroid hormone, Retinoic Acid
Receptors Adopted Orphan Receptors
20
Therapeutic use of adrenal steroids

• 1) Replacement therapy
• Addisons disease administer a glucocorticoid
  (e.g. cortisol)
• and a mineralocorticoid (e.g. fludrocortisone)
• Congenital adrenal hyperplasia
• 21 b-hydroxylase deficiency is the most common
  cause
• 2) Diagnosis of Cushings syndrome
• 3) Cancer chemotherapy (especially
  lymphoma/leukemia)
• 4) Anti-inflammatory agents

21
The HPA axis regulates the immune system, the
musculoskeletal system and many tissues involved
in overall metabolism like liver and fat.
22
Physiological effects of glucocorticoids
Metabolic gluconeogenesis (liver) release of
amino acids (muscle) release of fatty
acids-lipolysis (fat) plasma glucose insulin
secretion (pancreas-in response to
glucose) glucose uptake (muscle) bone
resorption fibroblast proliferation collagen
synthesis changes in mood and excitability alter
ed leukocyte functions (anti-inflammatory)
23
Glucocorticoid anti-inflammatory mechanisms

• leukocyte traffic control
• leukocyte function
• inhibition of the prostaglandin/leukotriene
  pathway

24
GC
REC
GC
GC blocks NF-kB function and may also induce
inhibitors of the NF-kB pathway like IkB
25
(No Transcript)
26
Glucocorticoids block neutrophil migration out of
blood vessels by inhibiting response to
chemotactic molecules and by preventing passage
of neutrophils through endothelial gap junctions
27
Glucocorticoids inhibit macrophage-Tcell
interactions by blocking interleukin induction
and preventing macrophage activation
28
Glucocorticoids inhibit tissue destruction by
macrophage by blocking both macrophage activation
and subsequent release of proteases like
collagenase, elastase, and plasminogen activator
29
Toxic effects of chronic glucocorticoids
gluconeogenesis (liver)--hyperglycemia release
of amino acids-catabolism (muscle)--muscle
weakness release of fatty acids-lipolysis
(fat)--together with increase in insulin,
leads to inappropriate fat deposition,
obesity insulin secretion (pancreas-in response
to glucose) hyperinsulinemia bone
resorption--leading to osteoporosis,
fractures fibroblast proliferation--thin skin,
bruising, poor wound healing collagen
synthesis growth retardation (in
children) changes in mood and excitability--eupho
ria, restlessness altered leukocyte functions
(anti-inflammatory)--may mask underlying
symptoms suppression of the HPA axis acute
withdrawl can lead to death
30
Other members of the nuclear receptor family
AF2
AF1
a b
LXR oxysterols FXR farnesoids PXR zenobiotics CAR
phenobarbital

• LXR and FXR regulate cholesterol
• and bile acid homeostasis

PXR regulates drug metabolic (cyp)genes