7th Oct - Nuclear Receptors

Question 1

What are nuclear receptor response elements?

Answer 1

Distinct sequences for each receptor type to bind to

Question 2

What are the three classes of nuclear receptor?

Answer 2

Class 1
Class 2
Class 3

Question 3

Give some examples of class 1 nuclear receptors

Answer 3

Thyroid hormone receptors
Retinoic acid receptors
Vitamin D receptors
Peroxisome-proliferated activated receptors

Question 4

Give an example of a class 2 nuclear receptor

Answer 4

Retinoid X receptor

Question 5

Give an example of a class 3 nuclear receptor

Answer 5

Glucocorticoid receptor
Androgen receptor
Progesterone receptor
Oestrogen receptor

Question 6

What are the typical domains of a nuclear receptor?

Answer 6

A/b Domain 
C (DBD) domain
D  (Hinge region) domain
E (LBD) domain
F domain

Question 7

Describe an A/B domain of a nuclear receptor

Answer 7

Usually contains an AF-1 domain

Can be modulated by phosphorylation

Question 8

Describe a C domain of a nuclear receptor

Answer 8

Most conserved domain
Contains 9 cysteines
2 zinc fingers and a c-terminal extension

Question 9

Describe a D domain of a nuclear receptor

Answer 9

Not well conserved
Hinge between LBD and DBD allowing rotation of DBD
D domain often has NLS

Question 10

Describe an E domain of a nuclear receptor

Answer 10

Ligand binding
Mediates dimerisation
Interaction with heat shock proteins
Ligand dependent transcriotional activity
2 well conserved regions
AF2 responsible for ligand dependent transcriptional activation
Mainly hydrophobic ligand binding pocket

Question 11

What are hormone response elements?

Answer 11

Specific DNA sequences in target genes, often close to the core promoter, to which nuclear receptors can bind

Question 12

Do steroid receptors bind DNA as monomers?

Answer 12

No as homodimers

Question 13

Are hormone response elements highly specific?

Answer 13

No, some hormone response elements can bind different heterodimers with high affinity

Question 14

What are the two binding domains on a co-activator?

Answer 14

Receptor interacting domain

Histone acetyltransferase domain

Question 15

What are the key binding domains within a co-repressor?

Answer 15

Indirect histone deaceteylase recruitment domain
Direct histone deacetylase recruitment domain
Receptor interactin domain

Question 16

Give an example of a nuclear co-repressor

Answer 16

SMRT (silencing mediator for the retinoic and thyroid hormone receptors)

Question 17

Outline the ligand dependent activation of a standard nuclear receptor

Answer 17

Unbound - receptor binds co-repressor recruiting HDACs

Bound - receptor binds co-activator with HAT activity

Question 18

Give an example of an endogenous lipophillic ligand for a nuclear receptor

Answer 18

Steroid hormones
Thyroid hormones
Vitamin A derivatives (retinoid)
Vitamin D

Question 19

Outline the signalling mechanism used by Oestrogen, Progesterone, Androgen and Glucocorticoid receptors

Answer 19

1. Lipophillic ligand permeates the plasma membrane and binds to the receptor
2. Receptor undergoes ligand-dependent release from cytoplasmic sequestration (usually sequestered by HSP90)
3. The liganded receptor dimerizes and translocates to the nucleus
4. The receptor binds DNA and recruits co-activators to enhance transcription of target genes

Question 20

Outline the signalling mechanism used by the thyroid, retinoic acid, ppa and vitamin D receptors

Answer 20

1. Receptor dimer (usually heterdimer with RXR) is stably bound to DNA in an inactive state
2. Lipophillic ligand permeates the PM and nucleus or ligand precursor is converted to ligand intracellularly
3. Ligand binds to the receptor allowing recruitments of co-activators and transcription of specific target genes

Question 21

What is the most probable mechanism for a lot of orphan nuclear receptors?

Answer 21

1. Receptor monomer is stably bound to the DNA in an inactive state
2. The ligand permeates the plasma membrane and enters the nucleus OR post-translational receptor modification occurs
3. The receptor recruits co-activators and transcription of specific target genes

Question 22

What is a retinoid?

Answer 22

A vitamin A derivative, which acts as a lipophillic lignad

Question 23

What would be the therapeutic benefit of targeting retinoids?

Answer 23

Stimulate them to inhibit cell proliferation in cancer

Treat dermatoses

Question 24

Give an example of a retinoid and the receptor it binds to

Answer 24

13-cis retinoic acid –> RAR
All-trans retinoic acid –> RAR
9-cis retinoic acid –> RXR

Question 25

What would be the therapetic benefit of using PPARalpha agonists?

Answer 25

Treat dyslipedimias by lowering trigylcerides and VLDL and increasing HDL

Question 26

What is dyslipidemia?

Answer 26

an abnormal amount of lipids (e.g.,triglycerides, cholesterol and/or fat phospholipids) in the blood

Question 27

How would PPAR gamma agonists be of use therapeutically?

Answer 27

To treat Type II diabetes as it restores insulin sensitivity

Question 28

How can nuclear receptor activity be measured?

Answer 28

Reporter assay
RT PCR
western blot

Question 29

How was the endogeous ligand for PPARalpha discovered by Chakravathy 2009?

Answer 29

Used two genetically modified mice: 1 FAS+/+, PPARalpha -/- and 1 FAS -/-, PPAR alpha -/-

Added flag tagged PPAR Alpha to both and immunopurified them:

• -In FAS +/+ mice there was a peak in Mass Spec that wasn’t present in FAS-/- = GPC
• -Compared GPC regulators with known targets of PPARalpha