Second Messenger Signaling, Insulin Signaling, Steroid Signaling Flashcards
Target cells bind to ____ via ___ embedded w/in plasma membrane or w/in cytoplasm
. Signaling molecules
. Protein receptors
Categories cell signaling receptors
. G-linked protein receptors: amplification of signals via intracellular signaling molecules (second messengers)
. Catalytic via phosphorylating Tyr residues in intracellular substances
. Intracellular receptors allow cells to respond to hydrophobic signaling molecules
G-protein linked receptors structure
. Heterotrimeric G-proteins (alpha, beta, and gamma subunits)
. Transmembrane
. 7 membrane-spanning regions
. Contain extracellular ligand-binding domains and intracellular domains that initiate signaling rxns
T/F there around close to 400 G-protein coupled receptors identified in humans
T
G protein general signaling mechanism
. After ligand binding transmembrane receptor protein confirmation changes and binds to/activates G-protein
. activated on cytoplasmic surface of plasma membrane
. Bind to GTP when activated
. Have GTPase activity that aids in eventual deactivation
. Individual subunits dissociate after GTP binding
Type of G protein activate depends on ___
Signaling molecule and type of target cell
Alpha subunit in G protein
. Interacts w/ and regulates function of intracellular enzyme localized to plasma membrane
Second messengers
. Products of enzymatic rxns
. Relay signal from ligand into cell
. Amplify original signal
. Regulate activity of Ser/Thr kinases that then phosphorylate substrates
End result of signaling cascade
. Biological response by the cell
Enzymes acted on by G proteins
. Adenylyl cyclase
. Phospholipase C
Second messenger regulated by adenylyl cyclase
cAMP
cAMP regulates ____
Protein kinase A (PKA)
Cholera
. Toxin that modifies alpha-subunit of Gs in intestinal epithelial cells
. Inhibits the alpha-polypeptide from cleaving GTP to GDP causing overproduction of cAMP in intestinal cells
. Causes continuous transport of Na and water into the lumen of the gut
. Causes diarrhea and dehydration assoc. w/ cholera
Pertussis
. Toxin disrupts normal activity of Gi inhibiting its alpha subunit
. Adenylate cyclase is not turned off when it should be
G proteins that regulate phospholipase C
Gq alpha (Same basic mechanism activates G protein and phospholipase C as in GSalpha signaling)
Catalytic receptors signal via phosphorylation of ____
Tyr residues
Receptors w/ intrinsic Tyr kinase activity
. 3 domains: ligand-binding portion w/ NH2 terminus, alpha helical domain that spans lipid bilayer, and effector region in intracellular portion of the protein
. Single transmembrane receptor chain forms dimers upon ligand binding
Mechanism of signaling in TKRs
. Catalytic receptor w/ Tyr kinase activity switches on enzyme activity of its intracellular domain when signaling molecule binds to its extracellular domain
. Binding of signaling molecule causes 2 receptor molecules to come together in membrane forming dimer
. Contact btw 2 adjacent intracellular receptor tails activates Tyr kinase function
. Each receptor tail Tyr phosphorylates the other
Adaptor proteins
. Intracellular signaling proteins that bind to phosphorylate Tyr residues
. Bind in cytoplasmic domain of receptors
. Share SH-2 and SH-3 domains
Ras
GTP-binding protein
. Molecular switch for key signaling in control of growth and differentiation
. Small G protein
. Homologous w/ alpha subunit of heterotrimeric G proteins
Percentage of tumors that have constitutively active forms of Ras causing abnormal growth
30%
T/F Ras contains SH2 domain
F. Binds to Sh-2 containing adaptor proteins that bind to Tyr phosphorylated receptors
MAP kinase cascade
Ser/Thr phosphorylation cascade activated by Ras
Final enzyme in MAP kinase cascade
Mitogen activated protein kinase (MAPK)
. Gets phosphorylated, translocated to nucleus, and phosphorylated transcription factors that induce transcription of gene
STATs
. Signal transducers and activators of transcription
. SH-2 containing latent cytoplasmic proteins that can bind to Tyr-phosphorylated residues w/in cytoplasmic domains of receptors w/ own catalytic activity
. Sometimes involved in signaling by non-receptor Tyr kinases
When bound/docked w/ phosphorylated Tyr residues, STATs are acted on by _____
Receptor Tyr kinase and become Tyr phosphorylated
What occurs w/ Tyr-phosphorylated STATs
Formed imers and then translocations to nucleus
. Bind to DNA
. Activate transcription of responsive genes
Signaling via non-receptor Tyr kinases
. Don’t possess own Tyr kinase activity but activate non-receptor Tyr kinase
. Cytoplasmic domain of receptors non-covalently assoc. w/ cytoplasmic Tyr kinase proteins
. phosphorylate Tyr residues w/in receptor tail
Best characterized non-receptor Tyr kinases
. Src family tyrosine kinases
. Janus Kinases
Insulin signal via catalytic receptors w/ ____
Intrinsic Tyr kinase activity
What happens after insulin binds to its receptor?
. Insulin receptor Tyr kinase activity stimulated
. Induces Tyr phosphorylation of various insulin receptor substrates (IRS)
IRS protein types
. IRS-1, IRS-2 widely expressed
. IRS-3 found in adipose tissue, pancreatic beta cells, and possible liver
. IRS-4: thymus, brain, kidney
What can Tyr phosphorylated IRS proteins bind?
. SH-2 containing proteins including ones activated by Ras
. STATs
. Ser kinase
. PI-3 kinase
. Activation of Ras and of STAT signaling leads to regulation of transcription of specific genes
Activation of PI-3 kinase followed by activation of downstream kinases promotes _____
. Glucose transport . Protein synthesis . Glycogen synthesis . Cell proliferation . Cell survival in various cells and tissues
Molecules that signal target cells using NISS and MISS
. Sex steroid hormones . Glucocorticoids . Mineralcorticoids . Vit. A and D . Retinoids . Thyroid hormones
Nuclear-initiated steroid signaling (NISS)
. Classical steroid signaling
. Steroid hormones leave circulation and cross barrier of plasma membrane of target cell to reach receptor
. Once inside plasma membrane, steroid encounters receptor in cytosol or nucleus
. Hormone binding modifies receptor enabling it to regulate transcription of specific genes
Ligand-activated transcription factors
Intracellular steroid hormone receptors
Membrane-initiated steroid signaling (MISS)
. Steroid receptors localized to plasma membrane
. Causes rapid effects of steroid hormones that occur w/in sec. to min.
. Promotes modification of existing proteins and doe snot require synthesis of new proteins like NISS does
MISS receptor structure
. Same protein structure as intracellular steroid hormones but localized to caveolae
General mechanism of MISS
. Steroid binds
. Membrane receptor assoc. w complex of signaling proteins (G proteins, growth factors receptors, Src, and Ras)
. Protein kinases function in G protein signaling and PI=3 kinase can be activated
. Phosphorylation of target proteins causes rapid biological response by the cell
What does insulin inhibit?
. Glucose uptake
. Glycogen synthesis
. Protein synthesis
epinephrine role in metabolism
. Stimulates liver to convert glycogen to glucose using cAMP as second messenger
PKA structure
. 2 regulatory subunits bound to 2 catalytic subunits when inactive
. When cAMP binds the subunits separate and catalytic subunit phosphorylates Ser and Thr residues in proteins substrates
DAG location
Inside membrane (IP3 is free)
PKC activation
. needs DAG and Ca2+
IP3 releases what and what is it’s roel?
. Ca via binding receptors on ER
. Ca acts as second messenger
. Ca binds to calmodulin and Ca-Calmodulin activates cellular proteins
Intracellular receptor for steroid structure
. NH2-terminal genre regulatory domain . DNA binding domain . Hinge region (folded for activation, flat for inactivation) . Hormone binding site . COOH-terminal hormone binding region
