Hormone Biosynthesis Flashcards
Rate limiting steps in:
Steroidogenesis?
Prostaglandin production?
Melatonin synthesis?
FSH/LH/TSH synthesis?
Estrogen synthesis?
Steroid biosynthesis – StAR enzyme transport of cholesterol form the outer to the inner mitochondrial membrane
Prostaglandin formation – release of free arachidonic acid
Melatonin synthesis – increase in cAMP leading to N-acetyltransferase activity
FSH/LH/TSH synthesis – availability of β subunits
Estrogen synthesis – aromatase activity
Responsible for cholesterol transport across mitochondrial membrane
STAR
Congenital lipoid adrenal hyperplasia (mutation, location, inheritance, functional change)
Loss of function mutation in STAR, chromosome 8, AR, limited intracellular transport of cholesterol 000? intracellular lipid accumulation 00> cellular destruction
Locations of steroid synthesis
Mitochondrial membrane, cytoplasm, endoplasmic reticulum
Locations of steroid receptor
Nucleus, cytoplasm
Mechanism of steroid hormone transport across cell membrane
Simple diffusion
Characteristics of steroid hormones
Small, non-polar, lipophilic
G-protein receptors
cAMP, calcium messenger, protein kinase/MAP kinase
cAMP second messenger hormones
Which G subunit?
FSH, LH, HCG, ACTH, TSH, CRH
Gs-alpha
Calcium second messenger hormones
Which G subunit?
GnRH, TRH, GHRH, kisspeptin, oxytocin, vasopressin, AGII
Gq-alpha
Protein kinase/MAP kinase hormone
Oxytocin (here also, through PKC)
cAMP receptor function
o Hormone binds cell membrane receptor
o Adenylate cyclase activated
o Gα-GTP subunit binds catalytic unit forming active enzyme converting ATP to cAMP
o Forms cAMP-receptor protein complex which activates protein kinase A (PKA)
o Inactive form: tetramer, 2 regulatory subunits and 2 catalytic subunits
o Bound: Catalytic units released, regulatory units form dimer
o Catalytic units phosphorylate serine and threonine residues of cellular proteins (enzymes and mitochondrial, microsomal, and chromatin proteins) (energy-producing)
o Physiologic effect
o Enzyme activity terminated by hydrolysis of GTP to GDP returning the enzyme to its inactive state
Calcium messenger receptor function
o Phospholipase C (PLC) catalyzes hydrolysis of polyphosphatidylinositols (IPI2) into two intracellular messengers: IP3 (inositol triphosphate) and DAG (diacylglycerol)
o IP3 binds with a receptor in the smooth ER and mitochondria and opens the Ca2+ channel
o DAG activates protein kinase C
o Calmodulin binding Ca2+ causes a conformational change
o Modifies calcium transport, enzyme activity, calcium regulation of cyclic nucleotide and glycogen metabolism and secretion and cell motility
Single transmembrane domain receptor types
Tyrosine kinase, cytokine, serine/threonine kinase
Tyrosine kinase receptor hormones
Insulin, IGF, EGF, PDGF, FGF
Cytokine receptor hormones
GH, PRL, hPL, leptin
Serine/threonine kinase ligands?
& what do ligands act by?
Activin, inhibin
- Activin acts via Type I and Type II serine/threonine specific receptor kinases
- Inhibin acts by blocking the Type II serine/threonine specific receptor kinase
Tyrosine kinase receptor function
o 3 domains: extracellular domain for ligand binding, single transmembrane domain, cytoplasmic domain
o Receptor has 2 alpha and 2 beta subunits (each w/ 3 domains as above) linked by disulfide bridge
o Ligand specificity determined by unique AA sequence that determines 3D conformation
o Ligand binding –> conformational change of cytoplasmic domain –> autophosphorylation
Cytokine receptor second messenger
JAK-STAT
Serine/threonine kinase receptor second messenger
SMAD4 –> FOXH1
A/B Regulatory Domain
Amino acid terminal
Most variable in superfamily (i.e. only 18% homology between ERα and ERβ)
In ER-α contains TAF1 which can stimulate transcription in absence of hormone binding
C DNA Binding Domain
Most homologous
Hormone binding induces conformational change in the 3 helices allowing binding to HRE (hormone responsive elements) of target genes
Contains 2 zinc fingers: determine specificity for binding to enhancer site in gene promoter
D HInge REgion
Contains nuclear localization signal
E Hormone Binding Domain
Harbors TAF2 which requires hormone binding for full activity
Functions:
o Pocket for hormone binding
o Sites for cofactor binding
o Responsible for dimerization
o Harbors TAF-2
o Binding site for HSP (when no hormone bound)
F Carboxy Terminal
no notes
TAF1 location/function
(A/B, regulatory domain) can stimulate transcription in the absence of hormone when fused to DNA
TAF2 location/function
(E, hormone binding domain) must have hormone binding for full activity
TAF3 location/function
(B-upstream segment [BUS]) autonomously activates transcription OR synergizes w/ other TAFs
TAFs on ER’s
ERα has TAF1 and TAF2
ERβ only has TAF2
TAFs on PR’s
PRα has TAF1 and TAF2
PRβ has TAF1, TAF2, and TAF3
Steroid hormones with nuclear receptors
Estrogen, thyroid (alpha-chrom 17, beta-chrom3), retinol, vit D
maybe progesterone & androgens?
Steroid hormones with cytoplasmic receptors
(still called nuclear receptors because the action is done there)
Mineralocorticoids, glucocorticoids
ER receptor expression during menstrual cycle
Peak late proliferative (self induced by E2), declines in early secretory (increased P4), increased in mid- and late-secretory (decreased P4)
ER alpha dominant tissues
Uterus/cervix/vagina, ovarian STROMA, breast, bone, hypothalamus, pituitary, kidney / adrenal (E2 and EE most sensitive)
ER beta dominant tissues
Granulosa cells, brain, colon, bladder, prostate
ER alpha and beta tissues
ovary, breast (alpha in dev and fxn, beta as natural suppressor of alpha activity)
2 SERMS and MOA
Raloxifene, tamoxifen; competitive inhibitor of estrogen binding to ER
Tamoxifen SEs
VTE, vaginal bleeding, endometrial hyperplasia/cancer, hot flashes, cataracts
Raloxifene SEs
Hot flashes, vaginal dryness, VTE (less than tamoxifen), decreases LDL, increase HDL, no change in TG
Raloxifene location of estrogenic and antiestrogenic effect
Estrogenic effect on bone
Antiestrogenic effects on breast and uterus
Tamoxifen location of estrogenic and antiestrogenic effect
Estrogenic: liver (decrease AT3, total chol, LDL, increase binding globulins, stimulates P4-R synthesis), bone, vaginal mucosa, endometrium
Antiestrogenic: cystostatic at breast, cytotoxic with breast ca
PR-alpha action and TAFs
Negative action (inhibits activity of PR-B) TAF1 on reg domain, TAF2 on hormone binding domain
PR-beta action and TAFs
Positive reg of progesterone response genes
TAF1 on reg domain, TAF2 on hormone binding domain, TAF3 in B-upstream segment (BUS) at 5’ terminal
PR receptor expression
Induced by E2, inhibited by P4
Peak late-proliferative phase, nearly undetectable by midpoint of secretory phase