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OVERVIEWBiology of Estrogen &

Progesterone Receptors

Benita S. KatzenellenbogenSwanlund Professor of Physiology,

Cell and Structural BiologyUniversity of Illinois and College of Medicine

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Important Issues

• Roles of ERα and ERβ

• Distinct Functions of PR-A and PR-B

• Selective Ligands (SERMs and SPRMs)

• Coregulators

•

Interrelationships Between Estrogen andProgestin Hormone-Receptor Pathways

• Tissue Selectivity in Estrogen and

Progestin Actions

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Target Tissues in Females & Males

Also:Colon (& Intestine)

Bladder & Urogenital Tract

Lung

Korach, 2001

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Estrogen Receptor in Breast Cancer

Predicts:• Improved Disease-Free Survival

• Response to Tamoxifen/EndocrineTherapy

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New York Times, April 7, 1998, p. A1

Researchers Find the First DrugKnown to Prevent Breast Cancer

Tamoxifen Helps Women, but Has Side Effects

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Tissue Selectivity

• Antagonist - Breast, Uterus

• Agonist - Bone, Brain, Colon,

Lipid Profile, Vasomotor,Cardiovascular

- Ideal Profile for HRT -

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TRIPARTITE PHARMACOLOGYMEDIATED BY NUCLEAR HORMONE RECEPTORS

– Underlies Tissue Selectivity –

“Actions”

TRANSCRIPTION

•

“Interactions”

• natural

• synthetic

• subtypes

• isoforms• splice variants

• DNA response

elements

• Co-regulators

• Other TFs • REs

•Ligands Receptor Effectors

OTHER Actions

repressors

activators

• environmental

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B

polIIA

TBP

R

Transcription

Co-Regulators

ReceptorEREs

Estrogen

GrowthFactors

GF

Peptides andNeurotransmitters

TATAF

TAFs

R

Signaling

Second Messengersand

Protein Kinase Cascades

R

E

E

E

E

E E

Receptor Actions in Cells

(B. Katzenellenbogen et al. Recent Prog. Horm. Res.,2000)

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Human Estrogen Receptors α andβ

• Different tissue/cell distributions

• Different affinity for ligands

• Different gene activations

1 144 227255

N-

504 530

-CERβ

1 180 263302N-

552595

-CERα

AF-1 DNA Ligand / AF-2

A/B C D E F

(18) (97) (30) (59) (18)

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Small Changes

in

Ligand Structure

Major Changes

in

Biological Character

ERα , ERβDifferent Ligands

Different PharmacologyAt

Different Target Genes

Exquisite Precision in Receptor Regulation

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Estrogens Known SERMsNovel ERα /ERβ

Selective Ligands

Estradiol

Diethylstilbestrol

Tamoxifen

Raloxifene

Droloxifene, Idoxifene,

Toremifene, GW5638,EM652, Cp-336156, others

PPT (Pyrazole)ER α Agonist

R,R-THC ER α Agonist &ER β Antagonist

H O

O H

O H

H O

ON

S

O H

O

H O

N

O

N N

C H3

O H

O HH O

E t

E t

H O

O H

Ligands for Estrogen Receptors

Me

NN

HO

O

OH

N

CN

OH

HO

MPP ER α Antagonist

DPN (Nitrile)ER β Agonist

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SERM Action

(B. & J. Katzenellenbogen, Science, 295: 2380, 2002)

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Structures of Diethylstilbestrol-ERα LBDand Hydroxytamoxifen-ERα LBD

Diethylstilbestrol Hydroxytamoxifen Greene, 4/99

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PPT, an ERα Specific Ligand, PreventsOvariectomy-Induced Loss of Bone Mineral Density

0

100

200

300

400

500

600

700

800

Sham Ovx PPT (2mg/kg) 17betaestradiol

(6ug/kg)

Bo ne M i n

e ra lD

e ns it y

( mg / c m3

)

Total

Trabecular*

*

*

*

*

*

* significantly greater than ovx (p < 0.01) (Harris et al. and Katzenellenbogens,Endocrinology, 2002)

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PPT, an ERα Specific Ligand,Prevents Hot Flush in a Rat Model

0

1

2

3

4

5

6

Vehicle PPT

Tem

peratur e

Increase

(d

egrees+/ -S

EM

)

(Harris et al. and Katzenellenbogens,Endocrinology 2002)

EthinylEstradiol

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GeneGeneRegulationRegulation

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Estrogen Effects on Cell Cytoarchitecture

From Vic et al ., Cancer Res ., 1982

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Estrogen Effects in Mammary Glandand Breast Cancer

Cell Cycle Regulation --↑ Proliferation ↓Apoptosis

Cytoskeletal Organization

Signal Transduction

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Estrogen Receptor Beta

• A “dampener” of ERα activity?

• Some overlap with ERα but also some

different gene activations

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Gene Expression Profiling by DNA MicroarraysDifferentiates Estrogen and SERM Activities

• Estrogen Stimulates Many Genes

• Tamoxifen also Stimulates Some of these Genes

• Raloxifene Stimulates a Few of these Genes

• Different Ligands Stimulate Somewhat Different Gene Sets

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Comparative Patterns of Gene Stimulation byEstradiol and SERMs (MCF-7 Cells) [n = 33]

E2 and TOT (n = 12)

C E2 ICI Ral TOT

E2, Ral and TOT (n = 4)

C E2 ICI Ral TOT

E2 Only (n = 17)

C E2 ICI Ral TOT

A B

C

Re s

p o n s e

Re s

p o ns e

Re s p o ns e

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SERM Antagonism of Estradiol Stimulation(MCF-7 Cells) [n = 35]

All 3 Antagonists (n = 12) ICI and Ral (n = 12) ICI only (n = 4)

A B C

R

e s p o ns e

R

e s p o ns e

R

e s p o ns e

C E2 E2+

ICI

E2+

RAL

E2+

TOT

C E2 E2+

ICI

E2+

RAL

E2+

TOT

C E2 E2+

ICI

E2+

RAL

E2+

TOT

Ral and TOT (n = 4) Ral only (n = 3)

D E

Re s p o ns e

Re s p o ns e

C E2 E2+

ICI

E2+

RAL

E2+

TOT

C E2 E2+

ICI

E2+

RAL

E2+

TOT

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ProgesteroneProgesteroneReceptor Receptor

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Ligands for Progesterone Receptor

O

H3CO

O

H3CO

O

O

H

O

H3CO

O

OHCH3

NCH3H3C

O

OH

NCH3H3C

Et

Et

Et

OAc

CH3

OH

Progestins Antiprogestins

R5020

(Promegestone)

ORG2058

Progesterone[natural]

RU486 (Mifepristone)

ZK98299(Onapristone)

MedroxyprogesteroneAcetate (MPA)

[HRT]

O

OH

HH

Norethindrone[oral contraceptives]

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Human Progesterone Receptor:

A and B Forms

hPR-B

hPR-A

AF-3 AF-1 AF-2DBD HBD

AF-1 AF-2DBD HBD

• From single gene by alternate transcriptioninitiation (different promoters)

• Different activities

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Human Progesterone Receptor

Isoforms A and B

•

Differential transcriptional activitiesCell type- and promoter-specific

Often PR-B > PR-A

• PR-A repressor of PR-B and ER signaling

• Present at unequal levels in breast tumors; some tissues

PR-A predominance as early event in carcinogenesis

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Interrelationships Between Estrogen andProgestin Receptor Signaling Pathways

ER

PR

Uterus Breast

+

–

PR Opposes ER Stimulation

PR Enhances ER Stimulation

Other Tissues?

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Women’s Health Initiative (WHI) Clinical Trial

Ended at 5.2 years, May 2002[JAMA 288:321-333, 2002]

16,608 Healthy postmenopausal US women

Estrogen (CEE 0.625 mg/d)

+ Progestin (MPA 2.5 mg/d)

together daily

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Would outcome be different if:

…estrogen only?

…different formulations, dosages?

…different estrogen(s)?

…different progestin?

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Biology of Estrogens and Progestins

are Determined By:

• Ligand structure

• ER subtype (α or β ) and PR isoform (A or B)

• Gene promoter responsive unit

• Character and balance of coactivators and

corepressors

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Take-Home Messages

1. Estrogens and progestins act through ER and PR.

2. Ligands can be:

Agonists-------SERMs/SPRMs-------Antagonists

(mixed agonists/antagonists)

3. Different ligands induce different receptor

conformations that determine all further interactions.

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4. ER and PR work with partner proteins that modulatetheir activity. Coregulator levels vary in different

tissues.Ligand Receptor Coregulator Tissue Responses

5. Many interrelationships between ER and PR pathways:

• Progestins modulate estrogen action but also actindependently.

• Progestin effects on estrogen actions vary in

different tissues -Mid-luteal when progesterone levels high --

– Breast: enhances mitotic activity – Uterus: suppresses mitotic activity

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Questions that Remain

• What estrogen/SERM (± progestin/SPRM

combination) will give the best benefit/risk

for HRT in the diverse tissues in which

these hormones act ?

• Respective roles of ERα and ERβ in

mediating the desired vs. undesired effectsof estrogen, and modulation of these

activities by progestins

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