Hormone Action Brian Feldman, MD, PhD Department of Pediatrics/ Endocrinology

Hormones that act at the membrane also have the potential to have nuclear (genomic) actions but usually not by translocating the receptor to the nucleus. NRs vs. Membrane Receptors

Outline Major steroid hormones and their source General properties of NHRs Specificity of hormone activity Therapeutic uses of hormones Diseases caused by hormonal abnormalities

Major Types of Steroid Hormones

Molecular Structure of Hormones

General Properties of NRs

This is not your mother’s Endo lecture BUT hormones have tissue and context specific effects Some genes are regulated by a hormone in one cell type but not another Other genes are regulated by a hormone only during specific times (i.e. cell division, differentiation, etc) We need to understand these details to understand physiology, pathophysiology and pharmacology

Major Active Hormones and Receptors

Specificity of hormone activity

Hormones have complex systemic and tissue specific effects Cushing’s syndrome: increased fat (central), decreased bone and muscle; metabolic syndrome Metabolic syndrome: Insulin resistance/ diabetes, HTN, dyslipidemia Larsen: Williams Textbook of Endocrinology

How is Diversity and Specificity Achieved? (We don’t really know but part of) the explanation: Intracellular regulation of hormone Allosteric effects on receptor caused by hormone and other factors binding to receptor DNA (availability and sequence) Co-factor interactions (availability and complex) RESULT: receptor/ligand complex form highly context specific structures

Role of Intracellular Enzymes to Regulate Ligand Availability Or Hormone Activation TestosteroneDHT 5alpha reductase Cortisol Cortisone 11BHSD

3 Ways to Decorate A Nuclear Receptor at the Response Element Simple: Homodimer Complex: Heterodimer Tethering: Intermediate Protein

GR Nuclear envelope Target gene GR Response element NHR Co-regulator Steroid Hormones Regulate transcription Via a Variety of Mechanisms Simple

GR Nuclear envelope Target gene GR Response element Steroid Hormones Regulate transcription Via a Variety of Mechanisms Complex

GR Nuclear envelope Target gene GR Response element NHR Co-regulator Steroid Hormones Regulate transcription Via a Variety of Mechanisms Tethering

Allostery

Agonist BoundAntagonist Bound Receptor Conformation with Agonist or Antagonist Note different positions of Helix 12 if an agonist or antagonist is bound in the LBD pocket.

Antagonists alter receptor structure

Availability of DNA is Regulated

DNA sequence regulates Receptor complex formation AGGTCAxxxAGGTCA AGGTCAxxxxAGGTCA AGGTCAxxxxxAGGTCA

The DNA Sequence Regulates Receptor Structure Meijsing et al, Science, 2009

Small Structural Differences Produce Specificity of Receptor Activity Meijsing et al, Science, 2009

Therapeutics

With Complexity Comes Opportunity Physiologic replacement Design of potent agonists Design of potent antagonists Design of selective hormone receptor modifiers

Pharmacological Use of Hormones Use of hormones at physiological levels for replacement –Glucocorticoids, thyroid, estrogens, androgens, vitamin D Use of hormones at pharmacological levels as drugs –Glucocorticoids, PPAR ligands, ATRA Use of hormone antagonists as drugs –Spironolactone (anti-MR), anti-androgens Use of selective receptor modifiers – (SERMs) to treat breast cancer –tamoxifen, raloxifene

Agonist therapy: Differentiation Therapy for Acute Promyelocytic Leukemia (APL) with Retinoids (ATRA) APL is caused by a gene rearrangment of RAR (ch.15) and PML (ch.17) to give the PML-RAR fusion gene that acts as an oncoprotein and blocks normal RAR action. PML gene function is unclear. RAR action is essential to differentiate PMLs. Rx with ATRA overcomes the block and differentiates the malignant clone.

Use of Hormone Receptor Antagonists as Drugs Mineralocorticoid blocker- spironolactone Androgen blocker - flutamide, bicalutamide Estrogen blocker - fluvestrant Glucocorticoid blocker - RU486 Progesterone blocker - RU486

What is the basis of antagonist or SERM activity? How can a hormone/drug bind to the receptor but fail to act? How can a hormone/drug have different actions in different organs although binding to the same receptor?

Molecular basis for SERMs

SERM Activity in Different Organs Tamoxifen Antagonist Agonist Raloxifene Antagonist Neutral Agonist Breast Uterus Bone

Diseases caused by hormonal abnormalities

Patient also has decreased bone, muscle; diabetes Sperling: Pediatric Endocrinology What is your Dx?

5 alpha reductase deficiency 2% of live births in isolated village of Dominican Republic Pseudohermaphrodites: first females, then males Deficient in 5  -reductase Lack dihydrotestosterone (DHT) Adult males: scant beard, no acne, small prostate, small testes

Karyotype: 46 XY Hints: Patient did not shave

Androgen Insensitivity Syndrome Absent pubic and axillary hair Normal female external anatomy Male internal anatomy (undescended testis) Results from mutations in AR

Hereditary 1,25 Dihydroxyvitamin D Resistant Rickets AR disease Early onset rickets, hypo Ca, elevated 1,25(OH)2D3, often alopecia Results from mutation in VDR

Clinical Importance of Steroid Receptor Mutations Vitamin D receptor –hereditary vitamin D resistant rickets Androgen receptor –testicular feminization –androgen independent prostate cancer Estrogen receptor –ER negative breast cancer Thyroid receptor –Thyroid hormone resistance