Endocrine 2 - Cell Signaling Flashcards
What are the two types of cell receptors?
- Surface receptors
2. Intracellular receptors
What three things determine cellular response to ligand binding?
- Receptor type
- 2nd messenger signals
- Cellular state
Is downregulation important (turning off receptor signaling)?
Yeah
How do intracellular receptors work?
- Inactive intracellular receptors are bound to inhibitory proteins.
- Hormone binds to receptor binding side (separate from where the inhibitory protein is).
- Conformational change –> inhibitory protein leaves, exposes the DNA binding site.
- Receptor binds DNA, regulates transcription.
What are the three types of surface receptors?
- Ion-channel linked
- G-protein linked
- Enzyme-linked
How do heterotrimeric G-protein receptors work?
- Receptor (separate from G-protein) binds ligand –> conformational change of the receptor opens a binding site for G-protein.
- G-protein (beta+gamma+alpha subunits) is bound to GDP (inactive) and binds to the new site on the receptor.
- G-protein conformational change –> GTP displaces GDP.
- alpha G-protein subunit + GTP dissociates from everything and goes to bind adenylyl cyclase.
- The alpha-GP-adenylyl cyclase thing converts ATP–>cAMP + PPi
- GTP hydrolysis –> alpha re-associates with beta gamma and it starts over.
How does cholera toxin work?
It crosses the plasma membrane in enterocytes and its enzymatic activity binds an ADP ribose to G-alpha S, blocking its GTPase activity –> always on –> Cl- channel is always open –> Cl- flows into GI lumen, water follows –> diarrhea.
What enzyme makes cAMP? What enzyme degrades it?
adenylyl cyclase makes it from ATP.
cAMP phosphodiesterase turns cAMP into 5’-AMP
How does cAMP work?
It binds to the regulatory subunits on protein kinase A (two regulatory subunits each with two cAMP sites per protein kinase A) –> regulatory subunit dissociation from the catalytic subunits –> catalytic subunits are active.
How do protein kinases that go into the nucleus work?
They phosphorylate a cyclic AMP response element binding factor (CREB), a transcription factor –> binds to promoters on DNA
What are the three mechanisms of signal inactivation?
- cAMP phosphodiesterase cleavage of cAMP –> 5’-AMP
- Protein kinase A can come back and phosphorylate the receptor –> desensitization.
- Protein kinase A phosphorylates another kinase –> other kinase multi-phosphorylates the receptor –> receptor binds to B-arrestin –> signal shut down
Is calcium concentration much higher outside the cell than inside the cell?
Yeah
Which second messenger molecule is responsible for opening intracellular calcium stores?
IP3
How does IP3 work?
Phosphatidyl inositol bisphosphate (a plasma membrane lipid) is cleaved by phospholipase C-beta –> DAG (still in plasma membrane) + IP3 (from the head group).
DAG activates protein kinase C
IP3 binds to receptors in the ER and mitochondria –> opens channels –> Ca2+ release from intracellular stores
Ca2+ can bind _______, which regulates the activity of ~50 enzymes.
calmodulin
What does calmodulin do in T cells? What is the clinical significance of this?
Once activated by Ca2+, calmodulin binds to calcineurin (a phosphatase), which goes and dephosphorylates a transcription factor called NfatC –> activation of T cells.
Clinical significance: immunosuppresive therapies deactivate calmodulin –> no T cell activation
RAS is a type of monomeric ___ protein that act as molecular switches.
monomeric G protein
When is RAS active? What does it activate?
When its bound to GTP it then binds MAP kinases –> transcription regulation
How do integral tyrosine kinase receptors work?
- Ligand binds
- Dimerization activates
- Autophosphorylation of the receptor
- Downstream signaling molecules bind to the receptor dimer
- Molecules get phosphorylated
- Signal propagates
The insulin receptor is a ________ ________ receptor that activates which second messenger molecule?
tyrosine kinase receptor that activates PI-3 kinase
How do JAK/STAT receptors work?
- Ligand binds, activates JAK tyrosine kinase
- JAK phosphorylates STAT on a tyrosine residue (signal tranducers and activators of transcription)
- STATs dimerize causing exposure of a nuclear translocation signal
- STAT dimer goes to the nucleus, binds DNA, regulates transcription
What did Eero Mantyranta have?
Autosomal dominant erythrocytosis. Messed up C-terminal region of EPO receptor –> receptor could not recruit a tyrosine phosphatase to turn off –> increased RBC synthesis.
cAMP levels can be increased in cells by all of the following except:
a) stimulation of adenylyl cyclase activity
b) binding of epinephrine to its plasma membrane receptor
c) inhibition of phosphodiesterase activity
d) binding of insulin to its plasma membrane receptor
e) activation of G proteins
d) binding of insulin to its plasma membrane receptor
- its a tyrosine kinase and activates a PI-3 kinase, not cAMP (G-protein receptors do that)
IP3:
a) is a membrane-bound activator of protein kinase C
b) activates adenylyl cyclase thereby increasing cAMP levels
c) is a water soluble inducer of Ca2+ release from the ER
d) is an intracellular Ca2+ binding protein
e) directly activates protein kinase G
c) is a water soluble inducer of Ca2+ release from the ER
You have discovered a “new” hormone that is a protein with a molecular size of 180 AAs. Which statement is most likely to be correct about this hypothetical hormone?
a) It will probably have its action by entering the cell and binding a nuclear receptor
b) It will probably be degraded by sulfanation in the liver followed by excretion in the urine
c) It can be effectively administered orally
d) It will be stored in the cell in membrane-bound secretory vesicles
d) it will be stored in the cell in membrane bound secretory vesicles
