Mechanism of action of steroids Transport: By being bound to plasma proteins Sex hormone-binding globulin (SHBG) binds and transports testosterone and estradiol Corticosteroid Binding Globulin (CBG) binds and transports cortisol Specificity Steroids act in only specific tissues and have specific functions due to the presence of an intracellular receptor specific for the hormone.
Steroid Hormone Receptor DNA binding domain DNA binding domain: Zinc fingers bind to DNA hormone binding domain
Coactivators- 1.histone acetyltransferase activity 2.affect RNA Polymerase II
Patients whose breast tumors are ER+ respond to hormone ablative therapy 1)Anti estrogens (such as taxmoxifen) 2) Aromatase inhibitors (letrozole) (aromatase – enzyme responsible for estradiol synthesis)
Peptides 1.proteins (10-40,000 mw) 2.membrane receptors 3.act within minutes 4.activate enzymes Steroids 1.derived from cholesterol (~300 mw) 2.cytoplasmic and nuclear receptors 3.act within hours 4.affect transcription !!!!