Steroids - What Are They and How Do They Work?

Question 1

Glucocorticoids signal through which receptor?

Answer 1

Glucocorticoid receptor (GR)

Question 2

Glucocorticoids are dervived from what?

Answer 2

Cholesterol

Question 3

What naturally secretes glucocorticoids in the body?

Answer 3

Zona fasciculata of adrenal glands

Question 4

How is the release of glucocorticoid in the body regulated?

Answer 4

Hypothalmic-pituitary-adrenal axis

Question 5

The availability of endogenous glucocorticoids in the body is regulated by what?

Answer 5

11β-hydroxysteroid dehydrogenase (11β-HSD) enzymes

(especially 11β-HSD2)

Question 6

What are the key differences between synthetic and natural glucocorticoids?

Answer 6

Synthetic glucocorticoids are:

1. More potent
2. Not susceptible to metabolic clearance by 11β-HSD2
3. Do not bind to corticosteroid binding globulin

Question 7

What are the three key actions of glucocorticoids?

Answer 7

1. Anti-inflammatory
2. Anti-proliferative (aids in cancer treatment)
3. Anti-angiogenic (aids in cancer treatment)

Question 8

Where does the GR reside by default?

Answer 8

Cell cytoplasm

Question 9

Before binding to steroids, the GR is bound to what?

Answer 9

Chaperone proteins

(especially Heat Shock Protein 90 (HSP90))

Question 10

What are chaperone proteins?

Answer 10

Proteins which assist in conformational changes of other proteins after synthesis

They aid with unfolding and assembly/disassembly of macromolecuar structures

Question 11

How do glucocorticoids enter a cell?

Answer 11

Diffusion

(they are lipophilic)

Question 12

Describe the process which results in binding of the glucocorticoid to the GR

Answer 12

Glucocorticoid diffuses into cell cytoplasm

Phosphorylation and ligand binding of glucocorticoid to GR causes dissociation from accessory proteins (HSP90)

Question 13

What are the three main reasons for the vast diveristy in GR signalling?

Answer 13

1. Multiple isoforms of GR
2. Multiple actions from different glucocorticoid response elements (GREs)
3. Post-translational modifications of GR

Question 14

GR is the product of which gene?

Answer 14

NR3C1

Question 15

GR is a modular protein as it has many different domains. What are these 4 domains?

Answer 15

1. N terminal transactivation domain
2. Central DNA binding domain (DBD)
3. C-terminal ligand-binding domain (LBD)
4. Flexible “hinge region” separating the DBD and LBD

Question 16

Why does the N terminal tranactivation domain have strong transcriptional activation functionality?

Answer 16

Presence of Activation Factor 1 (AF1)

Question 17

What is the basic role of AF1?

Answer 17

1. Recruit coregulators
2. Recruit transcription machinery

Question 18

AF1 is active independent of ligand (glucocorticoid) binding

True or false

Answer 18

True

(studies have shown AF1 can cause certain responses even with the complete absence of the LBD)

Question 19

In order for Activation Factor 2 (AF2) to activate, what is required?

Answer 19

Ligand (glucocorticoid) binding

Question 20

After a glucocortoid binds to the GR in the cell cytoplasm what happens?

Answer 20

Translocation to the nucleus

Question 21

For what reason does glucocorticoid (ligand) binding to the GR induce translocation to the nucleus?

Answer 21

The DBD, hinge region and LBD possess nuclear localisation signals

This allows translocation to the nucleus via importin dependent mechanisms

Question 22

How does the GR-Glucocorticoid complex “know” which DNA sequence to bind?

Answer 22

Two zinc “fingers” localised to the DBD can bind specific sequences on target genes

These specific sequences are glucocorticoid response elements (GREs)

Question 23

Which isoforms of the GR receptors have been associated with glucocorticoid insensitivity?

Answer 23

1. GRγ
2. GR-A
3. GR-P

Question 24

Once translocated to the nucleus what 3 options does the GR-glucocorticoid complex?

Answer 24

1. Complex binds directly to simple or negative GREs (with or without homodimerising previously)
2. Complex binds to DNA via tethering to other transcription factors
3. Complex binds by direct binding and interacting with other transcription factors

Question 25

What is the outcome of the GR-Glucocorticoid complex binding to a negative GRE?

Answer 25

Transrepression

Question 26

What is the outcome of the GR-Glucocorticoid complex tethering to a DNA-bound transcription factor?

Answer 26

Transrepression

(transcription factor activity is inhibited)

Question 27

What is a key transcription factor which may be inhibited by glucocorticoids?

Answer 27

NF-kappa b

Question 28

What is the outcome of the GR-Glucocorticoid complex binding directly to DNA with other transcription factors?

Answer 28

Transcription or transrepression may occur

(dependent on GRE bound to and activity of transcription factors)

Question 29

What is TTP and what does it do?

Answer 29

TTP (tristetraproline)is a protein which binds to mRNA of proinflammatory genes and causes destabilisation

Question 30

One way a GR-glucocorticoid complex can reduce inflammation is by inducing expression of what?

Answer 30

TTP (tristetraproline)

Question 31

The GR-glucocorticoid complex can also modulate gene expression of arrestins 1 and 2. What is the fucntion of these proteins?

Answer 31

Regulate signal transduction at G-protein coupled receptor

Question 32

Glucocorticoids can exert some effects via a non-genomic manner, through which pathway is this possible?

Answer 32

MAP kinase

Question 33

By exerting effects through non-genomic mechanisms, what does this mean for novel glucocorticoid therapies?

Answer 33

They may be able to work in minutes versus hours

Question 34

As well as activating GR receptors, which other class of receptors can glucocorticoids activate?

Answer 34

Mineralocorticoid receptors (MR)

Question 35

What is the impact of endogenous steroids on the kidneys?

Answer 35

1. Increase renal blood flow
2. Increase glomerular filtration rate

Question 36

For what reason do endogenous glucocorticoids not act excessively on MR receptors in mineralocorticoid sensitive tissues such as the kidneys?

Answer 36

11β-hydroxysteroid dehydrogenase 2 (11β-HSD2) can break them down

Question 37

What may be a negative side effect in the kidneys to excessive synthetic glucocorticoid use?

Answer 37

Binding to aldosterone (MR) receptors in the kidneys

This will increase Na+ retention and elevating blood pressure independent to the RAAS

Question 38

Why is it not just synthetic steroids which may be able to elevate blood pressure by acting on aldosterone receptors in the kidneys?

Answer 38

In the distal convoluted tubule, 11β-HSD2 concentrations are low

Endogenous glucocorticoids can evade breakdown and induce their effect as an aldosterone antagonist

Question 39

In which conditions if the raise of blood pressure caused by endogenous glucocorticoids particularly impactful?

Answer 39

1. Metabolic syndrome
2. Chronic stress

Glucocorticoid levels are raised above normal

Question 40

For what reason is it proposed that glucocorticoids cause thin skin?

Answer 40

They act on mineralocorticoid receptors in the epidermis as well as glucocorticoid receptors

Question 41

Epidermal atrophy in steroid use is hypothesised to be due to what?

Answer 41

Binding of glucocorticoids to mineralocorticoid receptors

Question 42

How may epidermal atrophy as a result of glucocorticoid application be prevented?

Answer 42

Co-administration of spironolactone

(an aldosterone antagonist which will block MRs)

Question 43

In which part of the brain are glucocorticoid receptors found which may contribute to alcohol addiction?

Answer 43

Amygdala

Question 44

Based on the fact that glucocorticoid receptor binding in the amygdala can contribute to alcohol addiction, what has been proposed as a future therapy for such addiction?

Answer 44

Glucocorticoid antagonists