L06- Mechanisms of action of peptide hormones Flashcards
Describe how peptide hormones produce intracellular signals?
Peptide = polar
Cannot penetrate plasma membrane
» bind to extracellular domain of specific cell-surface receptor protein
» Cause receptor conformational change at intracellular domain
» produce intracellular signal
List some examples of peptide hormones?
- Calcitonin • Glucagon
- Endorphins • Adrenocorticotropic hormone
- Antidiuretic hormone• Oxytoxin
Describe the mechanism of GPCR for cAMP production.
α-subunit attach to plasma membrane through lipid anchor
α-subunit binds GDP
1) Hormone-receptor complex cause conformational change in transmembrane domain of GPCR
2) cause GDP dissociation and GTP attachment to activate α-subunit on G-protein
3) βγ-subunits dissociate
4) α- subunit associates with adenyl cyclase (AC)
Describe the mechanism of tyrosine kinase receptors?
1) Ligand binding cause dimerization/ oligomerization
2) Mutual self-phosphorylation of tyrosine residues on cytosolic domain
3) Activate protein kinases at intracellular domain»_space; phosphorylate adaptor proteins»_space; in turn phosprylate effector proteins for intracellular signalling
List 3 examples of effector proteins for making secondary messengers?
Adenylyl cyclase (AC)
Guanylyl cyclase
Phospholipase C (PLC)
Reaction catalyzed by Adenylyl cyclase?
turns ATP into adenosine 3’,5’-cyclic monophosphate (cAMP) + PPi
Reaction catalyzed by Guanylyl cyclase?
turns GTP into guanosine 3’,5’-cyclic monophosphate (cGMP) + PPi
Reaction catalyzed by PLC?
cleaves phosphatidylinositol 4,5-bisphosphate (= phospholipid) to produce:
- Inositol 1,4,5-trisphosphate (InsP3/IP3)
- diacylglycerol (DAG)
Compare the functions of IP3 and DAG as intracellular signals?
Inositol 1,4,5-trisphosphate (InsP3) = releases Ca2+ from endoplasmic reticulum
Diacylglycerol (DAG) = activates protein kinase C
Define the 2 routes to form IP3 and DAG?
1) Activate GPCR/7-transmembrane receptors
» Activate G-protein»_space; α-subunit (GTP-bound) (and sometimes βγ-subunits) activate PLC
» Produce IP3 and DAG
2) Activate kinase/ single transmembrane region receptors
» receptor activation and cross phosphorylation
» activate PLC
» produce IP3 and DAG
Describe how G proteins of GPCR can intrinsically self-limit their activity? On-Off control
- Intrinsic GTPase activity of α-subunit hydrolyzes GTP to GDP»_space; cause adenylyl cyclase to dissociate from GDP/α-subunit»_space; inactivation
- βγ subunits stabilize the association of GDP with Gα
> > ready for another cycle of activity
Explain how the hormone/ receptor complex itself can self-limit/regulate its activity?
1) Hormone binding changes receptor conformation
» act as guanine nucleotide exchange factor (GEF)
» increase exchange of GDP for GTP on Gα
» ACTIVATE
2) GTPase accelerating protein (GAP, aka regulator of G-protein signaling (RGS)) promote the intrinsic GTPase activity of Gα»_space; faster hydrolysis of GTP into GDP
» INACTIVATE
WHat enzyme degrades cAMP?
𝑝ℎ𝑜𝑠𝑝ℎ𝑜𝑑𝑖𝑒𝑠𝑡𝑒𝑟𝑎𝑠𝑒
turns cAMP into adenosine 5’
monophosphate (AMP)
Describe the pattern of activity of phosphodiesterase?
On and off rhythmically to decrease or increase cAMP level within cell»_space; oscillation
List all the intrinsic modulations of G protein and adenylyl cyclase activity?
- Intrinsic enzyme activity of a-subunit to turn GTP into GDP
- Stabilization of GDP to a-subunit by βγ-subunits
- Receptor conformational change to act as guanine nucleotide exchange factor (GEF)
- GTP-ase accelerating protein (GAP)
List all the extrinsic inhibition on G protein and adenylyl cyclase activity?
- Activate Phosphodiesterase to degrade cAMP
- PGE1, adenosine activate Gai»_space; inhibition on adenylyl cyclase
Describe the mechanism of PGE1/ adenosine on adenylyl cyclase?
PGE1/ adenosine = inhibitory ligands
Complex with inhibitory G protein - Gαi
> > α-subunit of Gαi bind to adenylyl cyclase
> > Inactivation
List the different levels of intervention to regulate production of peptide hormone?
intervene at different points:
- at gene transcription level
- Translation at RER (preprohormone, prohormone)
- Processing at Golgi complex
- Packaging of mature hormones into secretory vesicle
- Transport of secretory vesicle
- Exocytosis
Explain how GnRH causes release of FSH and LH in anterior pituitary? detail intracellular signalling
GnRH binds to GnRH receptor (= GPCR) on gonadotropic cell membrane
phospholipase C activation: turn PIP2/ phospholipids into:
i) DAG (activate PKC)
ii) IP3»_space; increase intracellular Ca»_space; induce exocytosis of FSH and LH
Describe the intrinsic negative feedback control of hormone receptors when triggered by high cytosolic cAMP.
High cytosolic cAMP activates cAMP-dependent protein kinase (cAPK)*****
> > activate protein kinase A
> > nonspecifically phosphorylates receptors
> > decrease affinity of hormones to receptors/ desensitization
Which type of hormone receptor is down-regulated by GRK-arrestin pathway?
downregulates β adrenergic receptors
Mechanism of GRK-arrestin pathway?
1) βγ subunits recruit GRK to hormone-bound receptor
2) GRK phosphorylate specific a.a. on receptor for β-arrestin to bind
3) β-arrestin bind to receptor = promote receptor endocytosis by membrane invagination
4) clathrin-coated vesicles migrate into cytosol and fully internalized
5) receptor inside vesicle either degraded or recycled later
What is the function of down-regulation of hormone receptors?
Prevent cells from overstimulation by a particular extracellular hormone
by reducing the abundance of the receptor
Which ion level determines the secretion of peptide hormones by exocytosis?
Calcium ion
Name the 2 molecules for desensitization of intracellular cAMP mechanisms.
βARK- G-protein coupled receptor kinase - triggered by increased βγ subunits
cAPK - cAMP-dependent protein kinase - triggered by increased cAMP levels
> > both phosphorylate surface receptors for desensitization when intracellular cAMP is high
