Cellular Signaling and Secondary Messengers (Sayner)

Question 1

G protein coupled receptors (GPCRs)

Answer 1

seven membrane spanning domains

• bind signaling molecule/ligand on EXTRACELLULAR domain
  
  • activates G protein binding domain in the cytosol/recruits heterotrimeric G protein on intracellular domain

Question 2

First messengers

Answer 2

act as a ligand on multiple cell types to coordinate a whole body response

• extracelluar signals; often small molecules
• glucagon, dopamine, histamine, epinephrine, serotonin
• odorants
• tase molecules
  
  • photons (active rhodopsin)

Question 3

Activation of heterotrimeric G-proteins

Answer 3

1. ligand binding: occurs in extracellular space; recruitment of inactive heterotrimeric G-protein
2. GPCR acts as a guanine exchange factor; alpha subunit is activated by exchange of GDP for GTP → when Galpha is bound to GTP, it releases betagamma subunits and dissociates from the GPCR → alpha and betagamma can independently activate target proteins

Question 4

target product: ion channels

Answer 4

target protein will change plasma membrane ion permeability

Question 5

target product: enzyme

Answer 5

signal amplification: generation of secondary messenger

• adenylyl cyclase → generates cAMP
• phospholipase C → generates DAG, IP3, calcium

Question 6

GalphaS

Answer 6

activation of adenylyl cyclase generation of cAMP

• cAMP targets:
  
  • protein kinase A
  • cyclic nucleotide gated ion channels
  • exchange protein activated by cAMP

Question 7

Inactivation of cAMP signal

Answer 7

phosphodiesterase → turns off by hydrolyzing to 5’AMP

Question 8

cAMP controls what cellular functions?

Answer 8

cell growth and differentiation

movement and migration

learning and memory

hormone secretion

metabolism

gene transcription

Question 9

GalphaI

Answer 9

inhibits adenylyl cyclase

Question 10

Protein kinase A

Answer 10

cAMP activates

PKA is a serine/threonine kinase

• phosphorylates proteins to alter their activity

Question 11

cAMP response element (CRE)

Answer 11

cAMP regulatory sequence found on genes

Question 12

cAMP response element binding protein (CREB)

Answer 12

PKA diffuses into nucleus to phosphorylate CREB → phospho-CREB binds to CRE on specific genes and recruits CREB-binding protein → gene transcription activated

Question 13

increased cAMP effects

Answer 13

altered transcription of genes with a CRE/long term changes

Question 14

Gqalpha

Answer 14

Activates phospholipase C → cleaves PIP2 in the plasma membrane → IP2 and DAG are produced

IP3 binds receptor (calcium channel) on ER → promotes release of calcium

Calmodulin → binds calcium → activates CaM kinase → activates myosin light chain kinase (MLCK) in smooth muscle cells to induce contraction

Question 15

Inactivation of heterotrimeric G-proteins

Answer 15

alpha subunit has slow GTPase activity

regulator of G-protein signaling (RGS) or effector protein acts as GAPs → subunits reassociate

Question 16

TGFbeta

Answer 16

receptor serine/threonine kinase

Question 17

TGFbeta proteins regulate:

Answer 17

cellular proliferation and ECM deposition

Question 18

TGFbeta receptor

Answer 18

1. TGFbeta binds to type II receptor
2. Type II receptor recruits type I heterodimer
3. Ligand binds
4. Type II receptor phosphorylates type I receptor → fully active receptor
5. Type I receptor binds and phosphorylates Smad⅔
6. Smad⅔ is released from receptor
7. Smad ⅔ binds Smad 4
8. Smad 4 translocates to the nucleus to regulate gene transcription

Question 19

Receptor Tyrosine Kinase mutation

Answer 19

stuck on → uncontrollable proliferation → cancer

Question 20

receptor tyrosine kinase

Answer 20

1. ligand binding triggers receptor dimerization and activation of tyrosine kinase activity
2. trans-autophosphorylation occurs
3. downstream signaling molecules with an SH2 domain bind to phosphotyrosine residues on the receptor, acting as docking sites

Question 21

RTK activation of Ras and MAP kinase

Answer 21

1. activated RTK undergoes auto-phosphorylation
2. The SH2 domains on Grb2 bind to the phosphorylated RTK
3. The binding of Grb2 recruis the Ras-GEF, Sos
4. Sos activates Ras (a monomeric G protein requiring GTP for activity)
5. Ras activates Raf
6. Raf phosphorylates and activates MEK
7. MEK phosphorylates MAPK (Erk)
8. Erk can:
   
   1. phosphorylate target proteins in the cytosol
   2. be translocated to the nucleus to phosphorylate gene regulatory. proteins/alter gene expression
      
      1. survival, differentiation, proliferation

Question 22

Tyrosine-kinase associated receptors

Answer 22

receptors themselves have NO ENZYMATIC ACTIVITY

1. ligand binding results in receptor dimerization and tyrosine kinase activity
2. phosphorylation of kinase and receptor
3. receptor phosphorylation recruits STAT proteins via SH2 domains
4. Phosphorylation of STAT by JAKs releases it from receptor for translocation to the nucleus to activate gene transcription