Endocrine signalling and reproductive biology 1 + 2 Flashcards
When were hormones identified?
1900s
polytene chromosomes
large chromosomes from drosophila
chromosome puffs - chromatin opening
nuclear receptor ligands
testosterone, oestradiol, cortisol, AT retinoid acid
structure of ligands
aromatic rings - lipophilic
dissolve and get to the nucleus
receptors
glucocorticoid, thyroid hormone, progesterone, oestrogen
what do nuclear receptors promote?
transactivation
what are steroid hormones based on?
CPPP nucleus - 17 carbons
cholesterol
classes of steroid hormones (carbons)
18 - oestradiol
19 - testosterone
21 - progestrone, cortisol and aldosterone
27 - secosteroid, broken ring
what groups can be added to make different hormones?
methyl, ketone, hydroxyl
what does StAR do?
steroiodenic acute regulatory protein - regulate cholesterol transfer within mitochondria
where does steroid hormone synthesis control happen?
mitochondria
acute and chronic hormone control effects
acute - increase calcium and cAMP
stAR and synthetic enzymes
catabolism of steroid hormones
can add hydrophilic groups to make it more water soluble
what does thyroid secrete?
T3 and T4
where does synthesis of throid hormone occur and what happens?
thyroid epithelia
protein suicide of thyroglobulin
catalysed by thyroperoxidase
make DIT and MIT
explain synthesis of thyroid hormone
thyroglobulin and iodide iodine and tyrosine = MIT and DIT linked to form T3 and T4 thyroglobulin colloid lysosome cleaves and release hormone
how is thyroid hormone synthesis turned on or off?
deiodinases
what receptors bind chaperones in cytoplasm?
aldosterone, oestrogen, progesterone, gluocorticoid
class 3 receptors are present where? examples?
nucleus
thyroid hormone, retinoic acid and vitamin D
3 main domains of nuclear receptors
DNA binding domain
ligand binding domain
Unique N terminal domain
LBD
binds ligand
what does the LBD form?
ligand binding pocket that restricts what may bind
what may the LBD also be required for?
dimerisation
interaction with chaperones
interaction with co-regulators
DBD - structure
8 cysteine residues
2 alpha helices perpendicular
2 zinc ions - recognition helix
C terminal extension
CTE
mediates amino acid nucleotide interactions
N terminal domain
variable
AF1 region
AF1 region
important for ligand dependent transactivation
hinge region
N terminal domain
flexible
Hormone response element
positions nuclear receptors and complexes recruited by them close to gene to be transcribed
what can sequence of HRE dictate?
whether receptor will activate or repress transcription of neighbouring promoter
4 classes of nuclear receptor based on what?
interaction with HRE
class 1 DNA binding sequence
AGAACA
all other receptors DNA binding sequence
AGGTCA
what repeat does class 1 HRE and receptors use?
inverted repeat separated by 3 nucleotides - IR3
what will activate class 1 HRE?
AR, GR, MR, PR
AR and class 1 HRE
also uses DR3 for specific control
class 2 HRE nuclear receptors
IR3 of AGGTCA
what uses class 2 HRE?
ER for specific control
what do class 3 HRE nuclear receptors use?
direct repeat AGGTCA
1 to 5 rule - number of nucleotides spacing repeat
Class 4 HRE nuclear receptors
binds as monomers
NGF1B aaaAGGTCA
2 halves of bipartite HRE
1 = more like consensus site , recognised by DBD 2 = co-operative binding of second DBD to less conserved site
3 parts of promoter
TATA box
initiator element
dowstream promoter element
how is nuclear receptor activating transcription achieved?
RNA polymerase 2 machinery of basal promoter
What is the PIC?
RNA polymerase 2, transcription factors eg TF2B
how do nuclear receptors promote formation of stable PIC?
help PIC assemble by making direct contact with components of basal transcription machinery
recruit co-activators, promote PIC assembly
what is chromatin?
repeating array of DNA-protein structures called nucleosome, DNA wrapping around histone octamers
what can change properties of nucleosome?
covalent modification of lysine, arginine, serine residues of histone N-terminals
what are the steroid receptor co-activators?
SRC1,2,3
what do SRC1,2,3 do?
bind NR and have histone deacetylase activity and promote association proteins
recruit PIC
short alpha-helical segment of SRC
NR box
LXXLL - lysine separated
interacts with hydrophobic groove on LBD when bound to agonist
shutting of the system - how is it done?
chaperone protein eg p23 promote removal of NR and RNA pol 2 from DNA
covalent modification of co-activators
eg acetylation of SRC3
SMRT/NCoR
2 nuclear receptor interaction domains with 2 amino acids
repressor activity in N terminal region
recruit histone deacetylases
uses of anti-hormones
hormone dependent tumours eg breast and prostate
bind inverse agonist
helix 12 shifts to N terminus of antagonist bound LBD
inhibit binding of co-activators and promote binding of co-repressor
Negative response element
hormone bind
HDAC activity and repression
