Second Messenger Signaling, Insulin Signaling, Steroid Signaling

Question 1

Target cells bind to ____ via ___ embedded w/in plasma membrane or w/in cytoplasm

Answer 1

. Signaling molecules

. Protein receptors

Question 2

Categories cell signaling receptors

Answer 2

. 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

Question 3

G-protein linked receptors structure

Answer 3

. 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

Question 4

T/F there around close to 400 G-protein coupled receptors identified in humans

Answer 4

T

Question 5

G protein general signaling mechanism

Answer 5

. 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

Question 6

Type of G protein activate depends on ___

Answer 6

Signaling molecule and type of target cell

Question 7

Alpha subunit in G protein

Answer 7

. Interacts w/ and regulates function of intracellular enzyme localized to plasma membrane

Question 8

Second messengers

Answer 8

. Products of enzymatic rxns
. Relay signal from ligand into cell
. Amplify original signal
. Regulate activity of Ser/Thr kinases that then phosphorylate substrates

Question 9

End result of signaling cascade

Answer 9

. Biological response by the cell

Question 10

Enzymes acted on by G proteins

Answer 10

. Adenylyl cyclase

. Phospholipase C

Question 11

Second messenger regulated by adenylyl cyclase

Answer 11

cAMP

Question 12

cAMP regulates ____

Answer 12

Protein kinase A (PKA)

Question 13

Cholera

Answer 13

. 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

Question 14

Pertussis

Answer 14

. Toxin disrupts normal activity of Gi inhibiting its alpha subunit
. Adenylate cyclase is not turned off when it should be

Question 15

G proteins that regulate phospholipase C

Answer 15

Gq alpha (Same basic mechanism activates G protein and phospholipase C as in GSalpha signaling)

Question 16

Catalytic receptors signal via phosphorylation of ____

Answer 16

Tyr residues

Question 17

Receptors w/ intrinsic Tyr kinase activity

Answer 17

. 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

Question 18

Mechanism of signaling in TKRs

Answer 18

. 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

Question 19

Adaptor proteins

Answer 19

. Intracellular signaling proteins that bind to phosphorylate Tyr residues
. Bind in cytoplasmic domain of receptors
. Share SH-2 and SH-3 domains

Question 20

Ras

Answer 20

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

Question 21

Percentage of tumors that have constitutively active forms of Ras causing abnormal growth

Answer 21

30%

Question 22

T/F Ras contains SH2 domain

Answer 22

F. Binds to Sh-2 containing adaptor proteins that bind to Tyr phosphorylated receptors

Question 23

MAP kinase cascade

Answer 23

Ser/Thr phosphorylation cascade activated by Ras

Question 24

Final enzyme in MAP kinase cascade

Answer 24

Mitogen activated protein kinase (MAPK)
. Gets phosphorylated, translocated to nucleus, and phosphorylated transcription factors that induce transcription of gene

Question 25

STATs

Answer 25

. 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

Question 26

When bound/docked w/ phosphorylated Tyr residues, STATs are acted on by _____

Answer 26

Receptor Tyr kinase and become Tyr phosphorylated

Question 27

What occurs w/ Tyr-phosphorylated STATs

Answer 27

Formed imers and then translocations to nucleus . Bind to DNA . Activate transcription of responsive genes

Question 28

Signaling via non-receptor Tyr kinases

Answer 28

. 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

Question 29

Best characterized non-receptor Tyr kinases

Answer 29

. Src family tyrosine kinases | . Janus Kinases

Question 30

Insulin signal via catalytic receptors w/ ____

Answer 30

Intrinsic Tyr kinase activity

Question 31

What happens after insulin binds to its receptor?

Answer 31

. Insulin receptor Tyr kinase activity stimulated | . Induces Tyr phosphorylation of various insulin receptor substrates (IRS)

Question 32

IRS protein types

Answer 32

. IRS-1, IRS-2 widely expressed . IRS-3 found in adipose tissue, pancreatic beta cells, and possible liver . IRS-4: thymus, brain, kidney

Question 33

What can Tyr phosphorylated IRS proteins bind?

Answer 33

. 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

Question 34

Activation of PI-3 kinase followed by activation of downstream kinases promotes _____

Answer 34

``` . Glucose transport . Protein synthesis . Glycogen synthesis . Cell proliferation . Cell survival in various cells and tissues ```

Question 35

Molecules that signal target cells using NISS and MISS

Answer 35

``` . Sex steroid hormones . Glucocorticoids . Mineralcorticoids . Vit. A and D . Retinoids . Thyroid hormones ```

Question 36

Nuclear-initiated steroid signaling (NISS)

Answer 36

. 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

Question 37

Ligand-activated transcription factors

Answer 37

Intracellular steroid hormone receptors

Question 38

Membrane-initiated steroid signaling (MISS)

Answer 38

. 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

Question 39

MISS receptor structure

Answer 39

. Same protein structure as intracellular steroid hormones but localized to caveolae

Question 40

General mechanism of MISS

Answer 40

. 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

Question 41

What does insulin inhibit?

Answer 41

. Glucose uptake . Glycogen synthesis . Protein synthesis

Question 42

epinephrine role in metabolism

Answer 42

. Stimulates liver to convert glycogen to glucose using cAMP as second messenger

Question 43

PKA structure

Answer 43

. 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

Question 44

DAG location

Answer 44

Inside membrane (IP3 is free)

Question 45

PKC activation

Answer 45

. needs DAG and Ca2+

Question 46

IP3 releases what and what is it’s roel?

Answer 46

. Ca via binding receptors on ER . Ca acts as second messenger . Ca binds to calmodulin and Ca-Calmodulin activates cellular proteins

Question 47

Intracellular receptor for steroid structure

Answer 47

``` . NH2-terminal genre regulatory domain . DNA binding domain . Hinge region (folded for activation, flat for inactivation) . Hormone binding site . COOH-terminal hormone binding region ```