Receptor-mediated control of the HPG axis.

Question 1

Name the 3 types of cell surface receptors.

Answer 1

• Receptor tyrosine kinase.
• G coupled protein receptors.
• JAK/STAT.

Question 2

Name an example of an intracellular receptor..

Answer 2

Nuclear receptors.

Question 3

Are extracellular ligands hydrophilic or hydrophobic?

Answer 3

Hydrophilic.

Question 4

Are intracellular ligands hydrophilic or hydrophobic?

Answer 4

Hydrophobic.

Question 5

Outline the structure of GPCRs.

Answer 5

• Large region to promote binding of FSH/LH.
• Intracellular binding pockets, where G protein domain can be found.
• Important for mediating signal activation. G protein heterodimers are attached to this region.

Question 6

What are the ligands for g-protein coupled receptors?

Answer 6

• Small molecules, e.g. aas, nucleotides, catecholamines: dopamine and adrenaline. Peptides: GnRH, THR.
• Proteins, e.g. TSH, LH, FSH, Interleukins, chemokines.

Question 7

Why are GPCR such good targets?

Answer 7

> 800 in humans. 40% of marketed drugs, including 25/100 top selling drugs. Largest class of receptors.

Question 8

Which G protein heterodimer confers signalling pathway?

Answer 8

The alpha subunit.

Question 9

What are g-proteins like in the resting state?

Answer 9

They are inactive = GDP bound.

Question 10

Outline the Gs pathway.

Answer 10

Increased adenylate cyclase, increased cAMP, increased pKa.

Question 11

Outline the Gi pathway.

Answer 11

Opposite of Gs.

Question 12

Outline the Ga12/13 pathway.

Answer 12

Increases RhoGEF.

Increases RhoA.

Question 13

Outline the Gq pathway.

Answer 13

Increases levels of phospholipase C, increases IP3 and DAG, and then PKC and increases calcium influx.

Question 14

What regulated GPCR signalling?

Answer 14

• Signal transduction isn’t linear, it can get cross talked between pathways.
• Life cycle of GPRC presents different stages through which receptor function is regulated.
• Most GPCR can also activate non-GCR dependant signalling through beta arrestins.
• Trafficking of GPCR to intracellular regions is highly organised and coordinated. Receptors are targetted for degradation or recycled to the plasma membrane.
  GPCR - can dimerise/oligomerise (homo or hetero)

Question 15

Describe the LHR.

Answer 15

• Coupled to G protein dependant and independant pathways.
• Dysregulation leads to infertility.
• Receptor shown to homodimerise in vitro.
• Physiologically relevant.

Question 16

Outline an experiment showing the physiological significance of LHR.

Answer 16

• 2 different mutant LHRs generated
• 1 that could bind LH but was truncated
• 1 that couldn’t bind LH.
• Rescued by transactivation.
• Transactivation is functionally relevant mechanism of activation and signalling for LHR in male mice.
• LHR induced in thecae and granulosa.

Question 17

Outline how nuclear receptors work.

Answer 17

• Family of ligand-activated transcription factors
• Humans ~48 members of NR family
• 4 classes of receptors- SHR=Class 1-Classical NR
• Diverse functions- metabolism, development, reproduction
• Hydrophobic, cell permeable ligands …. steroid hormones- Oestrogens, Androgens, Progestogens
• Intracellular receptors-SHR cytosolic!
• Act as transcription factors, directly modulating gene transcription events.

Question 18

Describe the N-terminal domain of the nuclear receptor.

Answer 18

Regulatory. AF-1 (ligand-independent activation.) Highly variable.

Question 19

Describe the DNA binding domain of the nuclear receptor.

Answer 19

Conserved, 2 Zn fingers, binding to response elements.

Question 20

Describe the hinge region of the nuclear receptor.

Answer 20

Flexibility for dimerisation on ligand binding and DNA binding.

Question 21

Describe the ligand binding domain of the nuclear receptor.

Answer 21

Binds ligands, coactivators/corepressors. Contains AF-2 domain. Ligand dependant activation.
Followed by the C-terminal domain.

Question 22

Outline steroid hormone receptor activation.

Answer 22

• SHR are cytosolic, inactive-complexed with heat shock proteins
• Ligand binding- conformational change release of HSP, homodimerisation of receptors
• Translocation to nucleus

Question 23

Outline Nuclear receptor activation.

Answer 23

• Recruitment of co-activators (usually ligand induced)- histone acetyltransferase activity- weaken association of DNA-histone transcriptional activity enhanced
• Recruitment of co-repressor (usually via antagonist)- histone deacetylase (HDAC) activity – strengthen DNA-histone association  transcriptional activity reduced.
  Binds DNA- palindromic sequence e.g., AR- 5’-AGAACA-3’
• Modulates gene transcription  cellular response.

Question 24

What is the biology of androgen receptors?

Answer 24

• Mediates function of androgens e.g. testosterone, DHT.
• Found in numerous cellular location in the male and female reproductive tract, bones, hypothalamus.
• Important during development (male sex differentiation.)

Question 25

Outline AIS.

Answer 25

• Partial or complete loss of responsiveness to circulating androgens
• Mainly from androgen receptor mutations, >300 identified
• XY genotype, presenting with ranging phenotypes dependent on position of mutation- partial or full loss of AR function.
• X-linked, recessive, therefore female carriers but generally no presenting features.
• Approx. 1 in 20,400 births
• Normal circulating testosterone levels, increased oestrogens.

Question 26

What is the clinical presentation of CAIS?

Answer 26

Presentation as female, failure of testes descent and external genitalia presenting as female at birth. Hypotrophic vagina. Almost always assigned female and testes retained until puberty completed.

Question 27

What is the clinical presentation of PAIS?

Answer 27

Complex with ranging presentation from male….micropenis to ambiguous external genitalia, with or without cryptorchidism. Complex to assign gender and extent of virilisation at puberty.

Question 28

What is the scale used to measure AIS?

Answer 28

Quigley Scale. 1-7 (7=highest grading)