HORMONE DEPENDENT SYSTEMS - mechanisms Flashcards
Name three steroid receptor co-activators
AIBC (amplified in breast cancer), SRC1 (steroid receptor co-activator 1) and TIF/GRIP (transcriptional intermediary factor)
What is the difference between ppar alpha and gamma?
alpha - fatty acid uptake, beta oxidation and triglyceride metabolism
gamma - lipid storage, energy expenditure and brown fat beta oxidation
What happens to the LBD after the hormone binds?
AF2 repositions and folds against the core of the LBD to seal the binding cavity and form a hydrophobic surface that is recognised by co-activators
What does the hormone/NR bind to?
The hormone response element in the gene promoter
What are nuclear receptors?
Ligand activated transcription factors
What are the actions of co repressors
chromatin remodelling by hdac, inhibiting transcriptional machinery, inhibiting DNA binding, competing with co-activators and inhibit RNA processing
How is the receptor commonly found?
In the cytoplasm in a complex with heat shock proteins such as the dimer hsp 90. Keeps the receptor inactive but responsive to ligand binding
What are the three features of the AF1?
Ligand independent so has constitutive transcriptional activity, varies between nuclear receptors, though may rely on co-activators or co-repressors
What is the difference between AF1 and 2?
AF1 is ligand independent versus AF2 is ligand dependent
Features of the LBD?
Highly conserved, synergises with AF1 to promote transcription and forms a hydrophobic cavity to bind the ligand
What are the five genes induced by ER alpha?
PR, VEGF, IGF, Bcl2 and cyclin D
What are the 3 steps for ligand activated nuclear gene transcription?
Repression of COREPRESSORS with HISTONE DEACETYLASE ACTIVITY (HDAC), derepression to form activation complex 1 as ligand binding displaces corepressors and then TRANSACTIVATION, 2nd activator complex coactivators such as TIF and GRIP and interaction with transcriptional machinery
General difference between ER alpha and beta
Alpha in endometrium, beta in ovary, prostate and brain. Highly homologous but coded on separate chromosomes on separate genes
What is the difference between PR alpha and Beta
Beta is less transcriptionally active but has AF3
What are some non-classical steroid receptor actions
Ligands binding to promoters/TF that lack HRE in the promoter gene. 1) ER can act as a co-activator for transactivation at other promoter sites such as c-jun and c-fos 2) PR can suppress the activities of NfKB to modulate immunosuppression in pregnancy 3)PR can repress the activity of Stat 5 and AP1 TF to mediate its actions on proliferation in the mammary gland. Non genomic actions involve interaction with GF.
Which apoptotic pathway is more important in cancer development?
Intrinsic
What is a full oestrogen receptor antagonist and how does it work?
FULVESTRANT. Blocks dimerisation and translocation to the nucleus. Blocks AF1 activation and promotes degradation
How does tamoxifen work?
Partial antagonist. Promotes dimerisation and translocation to the nucleus but then blocks transcriptional machinery by blocking AF2 and the LBD. Additionally promotes co-reporessors such as NCOR and SMRT
What is mifepristone?
Partial PR antagonist. Promotes dimerisation and translocation but then blocks AF2 and coactivators
What is the point of a SARM?
To reduce prostatic hyperplasia whilst maintaining muscle strength and mass
How may one become resistant to tamoxifen?
Increased co-activators AIBC1, reduced co-repressors or p53, increased GF
What are the types of nuclear receptor?
Steroid, retinoic x, orphan monodimer and orphan heterodimers
What is progesterone involved with?
ovary - ovulation, uterus - decidualisation, breat - proliferation and lobar development, prevention of bone loss and behaviour
What is the difference between PR a ko and beta ko?
PRa KO – impaired ovulation and implantation, impaired fertility
PRb KO – reduced mammary gland ductal morphogenesis
What happens in decidualisation?
Convergence of the PR classical nuclear receptor pathway and g protein coupled PR
What is the key TSG in type 1 endometrial cancer vs t2?
Type 1 - PTEN, 2 - p53. Oncogene ras
What do caspases do?
exist as procaspases and lead to proteolysis of key structural elements and activates DNAses
What binds to the extrinsic pathway.
TNFR family of which the ligands are TNF and Fas (Fas expressed by cytotoxic t lymphocytes. The intracellular DD of TNFR recruits FADD (adaptor molecule) for caspase 8 cleavage and activation of the caspase cascade. Binding of Fas induced trimeristion of CD 95 forming the DISC. FLIP stops procaspase 8> capsize. Apoptosis occuring is a balance between FADD and FLIP
What initiates the intrinsic pathway? What happens in it?
Loss of mitochondrial membrane potential and the main initiator apoptotic protein is cytochrome c. Cytochrome c binds to APAF 1 card (caspase activation and recruitment domain). APAF-1 undergoes an ATP dependent conformational change allowing it to bind to procaspase 9 in the CARD domain and activate apoptosis. Balance between pro-apoptotic Bid, Bad, Bax and antiapoptotic Bcl and BCLx
Controlling one area of the cell cycle, what is an initiator of apoptosis?
ATR-ATM detect double stranded DNA breaks that activated P53 that initiates apoptosis
What can be used to treat endometrial carcinoma?
Progestins to reverse hyperplasia and induce decidualisation and endometrial thinning
What are glycoprotein hormone receptors? Which hormones and how is specificity achieve?
G-protein linked including LH, FSH and TSH. Through the leucine rich repeats in the ectodomain
What happens when a ligand binds to the glycoprotein receptor?
Recruitment of alpha, beta and gamma subunits. Alpha subunit releases GDP for GTP, then there is dissociation of the alpha and beta/gamma subunits. Then regulate respective effector proteins. The serpentine transmembrane domain transmits the signal the g protein receptor.
The ectodomain acts as an inverse agonist
Discuss the TSHR. Where is it found? What does it act as and do? What do germline, both activating and inactivation mutations cause? other factors
It is a glycoprotein g protein linked receptor that is found in the thyroid, thymus, brain, pituitary and lymphocytes. Acting as a dimer, it stimulates thyroid cell proliferation and differentiation through transport of sodium-iodide transporter, thyroperoxidase and thyroglobulin.
Germline activating mutations lead to autosomal dominant non autoimmune hyperthyroidism whereas inactivating lead to TSH resistance (congenital hypothyroidism).
TSHR stimulating antibodies - graves, blocking is hashimotos hypothyroidism. Can by activated promiscuously by bhCG in pregnancy for gestational hyperthyroidism
What do glycoprotein hormones consist of?
They are heterodimeric and consist of a common alpha subunit and varying beta
What can thyroid hormones do?
Heterodimerise with the retinoic x receptor
Describe the DBD?
2 zinc fingers each with 4 conserved cysteine residues, The nuclear receptors can bind as homodimers, heterodimers or monomers. The DNA helix makes base specific contacts in the major groove.
Describe the LBD
Highly conserved amongst receptors. WEDGE SHAPED HYDROPHOBIC CAVITY which contains the ligand binding site and is recognized by co-activators. Synergises with AF1 to promote transcriptional activation. It displaces co-repressors and activators. Allows heterodimerization
What do steroid hormones mainly bind as?
Homodimers
Where are steroid receptors found
In the nucleus or the cytoplasm
What is the androgen receptor like?
Androgen receptor: a single isoform that is responsive to testosterone and 5DHT
What are three classic non-classical activities of the steroid receptors?
Ligands binding to promoters/TF that lack HRE in the promoter gene. 1) ER can act as a co-activator for transactivation at other promoter sites such as c-jun and c-fos 2) PR can suppress the activities of NfKB to modulate immunosuppression in pregnancy 3)PR can repress the activity of Stat 5 and AP1 TF to mediate its actions on proliferation in the mammary gland. Non genomic actions involve interaction with GF
What can steroid receptors do, non genomically?
STEROID RECEPTORS AND GROWTH FACTORS CROSS TALK.
EGF signaling can either occur through Ras/MAPK or through PI3/AKT. It is mitogenic in breast or uterus and its signaling is enhanced by oestradiol or progesterone. Membrane associated ERalpha can activate EGF family of receptors.
ER acts synergistically with IGF1 and insulin to promote tumour cell division in utero. Serines in ERalpha can be phosphorylated by activated MAPK which makes it hypersensitive to oestradiol
What evidence is there that oestrogen and egf cross talk?
EVIDENCE: UTERINE AND BREAST TISSUE PROLIFERATIVE RESPONSE TO EGF IS BLOCKED BY OESTROGEN SIGNALLING BLOCKADE, and the inverse that response to oestradiol is blocked by blocking egf signalling.
Er alpha directly communicates with p85 subunit of PI3K
What factors can oestrogen amplify>
Mapkinase signalling through EGF and PI3 kinase signalling through IGF1
What makes oestrogen receptors hypersensitive to E2? What is this similar to?
Serines in ERalpha can be phosphorylated by activated MAPK which makes it hypersensitive to oestradiol. What happens in progesterone
What is one mechanisms by which oestrogen receptor cross talk occurs?
Er alpha directly communicates with p85 subunit of PI3K
What is c-Src essential for?
The non genomic proliferative effects or ER, AR and PR
What are the 2 main co-repressors?
NCoR: nuclear receptor corepressor
SMRT: silencing mediator for retinoid and thyroid receptor
Overall how do steroid receptors work?
- lipophilic steroid hormone passes across cell membrane
- steroid hormone is bound by receptor
- ligand-activated receptor localises in the nucleus
- ligand-activated receptor binds to SRE
- ligand-activated receptor initiates DNA transcription
What is the role of ER alpha vs Beta?
ER alpha and beta are highly homologous but are coded on separate genes, can form heterodimers and have different AF1 binding domains. Alpha more in endometrium and beta more in ovary, prostate and brain. Very similar DBD but only 56% in LBD
What genes does ER alpha induce?
Genes induced by ER alpha. PR, VEGF, IGF, Bcl2 and cyclin D
AF2 role?
AF2 activity requires ligand binding which enduces a conformational change that activates the LBD. AF2 repositions and folds against the core of the LBD to seal the binding cavity and form a hydrophobic surface that is recognised by co-activators
How do direct oestrogen antagonists vs agonists work?
OESTROGEN DIRECT ANTAGONISTS -bind to the LBD and prevent h12 from adopting the agonist confirmation, h12 is positioned over the site where co-activators would normally contact the LBD
INDIRECT – lack a side chain that displaces H12
Describe the progesterone receptor?
2 isoforms (alpha and beta) with similar binding affinities. They are derived from the same gene with alternate promoters. Beta generally less transcriptionally active but has AF3 and a proleine rich sequence. PR is required for side branching In Puberty and Alveologenesis in Pregnancy.
What happens in PR KO models?
PRa KO – impaired ovulation and implantation, impaired fertility
PRb KO – reduced mammary gland ductal morphogenesis
How can progesterone derivatives be used in cancer?
PROGESTINS CAN BE USED TO TREAT ENDOMETRIAL HYPERPLASIA BY INDUCING DECIDUALISATION AND ENDOMETRIAL THINNING.
How does egf contribute to steroid receptors?
Ras/MAPK or through PI3/AKT. It is mitogenic in breast or uterus and its signaling is enhanced by oestradiol or progesterone. Membrane associated ERalpha can activate EGF family of receptors
What is EGF?
It is a receptor tyrosine kinase. It is mitogenic in breast or uterus and its signaling is enhanced by oestradiol or progesterone. Membrane associated ERalpha can activate EGF family of receptors.