Endocrine Signalling 2

Question 1

What is the hormone response element

Answer 1

The region of DNA the hormone binds to (promoter usually)

Question 2

What can the sequence of the HRE determine

Answer 2

Whether the receptor will activate or repress transcription of the neighbouring promoter

Question 3

What are the classes of hormone response elements and their sequences

Answer 3

Class I - AGAACA repeats
All others - AGGTCA repeats

Question 4

What receptors activate class 1 HRE

Answer 4

Androgen receptor
Glucocorticod receptor
Mineralcorticod receptor
Progesterone receptor

Question 5

What are class two HREs specific for

Answer 5

Oestrogen receptor

Question 6

What are class III HREs specific for

Answer 6

Use AGGTCA but different receptors bind depending on the number of spaces (random bases) between two AGGTCA sequences

Provides specificity

Question 7

What are class IV HREs specific for

Answer 7

Bind as monomers to nerve growth factor 1B and REv-erb (orphan receptor)

Question 8

How do these DNA binding domains bind to HRE sites

Answer 8

Split into two halves -
One will have a high affinity for its HRE
One will not match up with HRE so low affinity.

When the high-affinity one binds, the poor affinity site changes shape (due to hinge etc) and this makes it complementary to the other HRE.
Causes a double bind

Question 9

Why are there two HRE sites per binding

Answer 9

Because most nuclear receptors pair up and bind as dimers

Question 10

What role do cofactors have regarding AF1 and AF2

Answer 10

Form a bridge between them

Question 11

What do basal transcription factors bind to

Answer 11

The basal transcription factors bind to a set of core elements in a promoter (TATA box, Initiator element (Inr) and downstream promoter element (DPE)

Question 12

How do nuclear receptors work in transcribing

Answer 12

The binding of nuclear receptors to an HRE (enhancer) stimulates the assembly of a stable basal factor/RNA pol II transcription PIC at the promoter.

Via chromatin

Question 13

How do nuclear receptors form a stable PIC (2 processes)

Answer 13

Help PIC assembly by making direct contact with components of the basal transcription machinery

Recruits coactivators that promote PIC assembly through direct contact with components.

Question 14

How does the action on chromatin by DNA receptors work to initiate transcription

Answer 14

Covalent modification of lysine, arginine and serine residues occurs and the histone N-terminal tails can change properties which opens up the chromatin by acting on the histones (co-factors directly)

Question 15

How do these co-factors governed by the DNA receptors open the chromatin

Answer 15

Enzymatic activity to post-translatory modification of the histone which opens up the DNA
This can be reversible by the receptors bringing in repressive co-factors to tightly bind the DNA again

Question 16

How is the shutting off of DNA binding and transcription done

Answer 16

Chaperone protein (P23 and hsp90) can promote the removal of nuclear receptors and RNA pol II from DNA potentially to be ready again to receive a signal.

If need them again quickly - keep nuclear receptors in the nucleus
If don’t need them again quickly - remove them from the nucleus

Question 17

What is the difference between gene repression and shutting off the gene by nuclear receptors

Answer 17

Gene repression binds to the gene to prevent ANY activity from happening
Gene shut off stops transcription but allows other binding to take place if needed

Question 18

What hormones are good at gene repression

Answer 18

Steroid hormones stay bound to the DNA -

With ligand-activation
Without ligand - repression (as allows nothing else to bind)

Question 19

How does nuclear receptor gene repression occur

Answer 19

No ligand is bound to the nuclear receptor which changes its shape.
It recruits corepressors which inhibits the binding of the PIC and RNA polymerase via methylation usually

Question 20

How do anti-hormones act and what is their role

Answer 20

Anti-hormones, important for pharmaceutical agents.
It works by entering the cell as hydrophobic, it then binds to the nuclear receptor which causes a different shape change which causes it to recruit co-repressors.

Question 21

What is the negative response element and how does it work

Answer 21

In the absence of hormone to these elements, it activates transcription and in the presence of the hormone in these elements, it represses transcription.

It does this through the DNA repeats - changes from serious when bound to in parallel.

Question 22

What is repression and cross-talk between pathways and how does it work

Answer 22

Method of nuclear receptors working without binding to hormone response elements.

Fos and Jun (regulate the expression of a myriad of genes in a variety of tissues and cell types) are phosphorylated by JNK and inhibited by nuclear receptors such as thyroid and glucocorticoid receptors.

Glucocorticoid receptors can inhibit NF-kappaB (an important inflammatory mediator)

Thyroid hormone receptors bind to cAMP which is important for gene transcription.

Question 23

How is endocrine signalling important in myeloid progenitor cells

Answer 23

A retinoic acid receptor is required for myeloid cell differentiation.

If no ligand is present, the retinoic acid receptor is repressed - increasing myeloid progenitor cell proliferation increases.

When retinoic acid is bound to its nuclear receptor, the myeloid progenitor cell proliferation stops and differentiation of these cells occur

Question 24

What happens to the endocrine signalling pathway of retinoic acid in acute promyelocytic leukaemia

Answer 24

Chromosomal translocation mutation causes a new hybrid gene (part retinoic acid receptor and part PML gene) - still works as a transcription factor but proliferation continues causing leukaemia

Question 25

How is acute promyelocytic leukaemia treated by endocrine signalling

Answer 25

Add enough ligand for retinoic acid can switch the nuclear receptor back to its normal function of reducing transcription and repressing differentiation

However if RER PLZF mutation - doesn’t respond to the ligand.

Question 26

How does the androgen receptor work

Answer 26

Ligand (testosterone) binds to the androgen receptor

Question 27

What disease does the androgen receptor cause if mutated

Answer 27

Kennedy’s disease through - polyglutamine repeats (trinucleotide repeats).

Question 28

How does Kennedy’s disease present

Answer 28

Slow and progressive motor neuron neuropathy initially in the proximal muscles of the hip and shoulder.
Death uncommon
Some reduction of male repro system - hypogonadism this shows the AR still works but due to repeat it has gained function as shown via neuropathy
Only males are severely affected.

Question 29

What causes androgen insensitivity syndrome

Answer 29

AR mutant severely impairing amount structure or function - 300 different mutations mostly in the ligand-binding domain.

Only males are affected but born female in appearance but no uterus fallopian tubes or ovaries - testes in Abdo

Question 30

Why are nuclear receptors so important in pharmacology

WIDER READING - Overington 2006

Answer 30

Make up 13% of FDA approved drug targets

Question 31

What are selective nuclear receptor modulators (SNuRMs)

WIDER READING - Jordan 2003

Answer 31

Nuclear receptor drugs that have been modulated to act cell-specifically

Question 32

Give an example of SNuRMs and its uses

Wider reading - Maximov - 2013

Answer 32

Tamoxifen - Osteoporosis prevention, breast cancer, infertility

Question 33

How does tamoxifen work

WIDER READING - Huang 2012

Answer 33

Competitive partial agonist of the ER which different tissues have different degrees of sensitivty to it based on intrinsic activty (ability of a drug-receptor to produce maximal response).

Tamoxifen is a middle IA SERM.

Question 34

What tissues are stimulated by tamoxifen

WIDER READING - Musa 2007

Answer 34

Bone, liver, and CV

Question 35

What tissues are repressed by tamoxifen

WIDER READING - Musa 2007

Answer 35

Breast and uterus

Question 36

How can tamoxifen have different effects in different tissues

WIDER READING - Feng 2014

Answer 36

Through different combinations of coactivators and corepressors on ER target genes and regulates coactivator activity through post-translational modifications (e.g. phosphorylation etc)

Question 37

What are inverse agonists

WIDER READING - Busch 2004

Answer 37

Reduce the basal activity of gene transcription that is present in some nuclear receptors

Question 38

What did post-translational modifications of the androgen receptor do to the prostate cancer patients

WIDER READING - McCall 2008

Answer 38

Upregulation of PI3K/Akt pathway which causes phosphorylation of androgen receptor which results in prostate cancer which is resistant to hormone treatment shown through clinical test subjects

Question 39

What is the underlying pathophysiological process of kennedys disease

WIDER READING - McCall 2008

Answer 39

AR phosphorylation which reduces ligand binding

Question 40

What does the glucocorticoid receptor undergo post-translational modifications for in physiological states

WIDER READING - Wang et al 2007

Answer 40

Phosphorylation at basal levels in absence of ligand and opposite in activate states.

Question 41

What does post-translational modifications do to the PPARgamma receptor

WIDER READING - Corrales 2018

Answer 41

Phosphorylation regulates the balance between differentiation and growth in adipose tissue which is linked to obesity and insulin resistance

Question 42

How do glucocortoid drugs do when they bind to the cystolic glucocorticoid receptor

WIDER READING - Auphan 1995

Answer 42

Inhibits KappaB activation in mice and cultured cells which prevents pro-inflammatory processes occurring.