Kandpal - Signal Transduction: GPCR, Enzyme Linked Receptors and Human Cancers

Question 1

what makes up a G-protein coupled receptor (GPCR)

Answer 1

7 transmembrane (7TM) domains, seven pass, serpentine receptors (N-terminus is extracellular and C-terminus is intracellular)

Question 2

what are the ligands for GPCR’s

Answer 2

hormones, neurotransmitters (proteins, peptides, amino acid derivatives, and fatty acids) photon, H+, Ca2+

Question 3

what are the 3 subunits on a GPCR

Answer 3

alpha, beta, and gamma

Question 4

how is a G-protein activated

Answer 4

receptor protein is activated with signal molecule -> attracts GDP on alpha-subunit inactive GPCR -> phosphates GDP = GTP and alpha subunit dissociates from beta/gamma active complex

Question 5

what controls the activity of the alpha subunit on a G-protein and how does it work

Answer 5

RGS (regulator of G-protein signaling) - acts as alpha-subunit specific GTPase activator proteins (GAPs)

Question 6

what is the difference between stimulatory and inhibitory G-proteins

Answer 6

both are GTP bound: stimulatory activates adenylate cyclase and inhibitory inhibits adenylate cyclase

Question 7

what is the downstream effect of an active G-protein activating adenylate cyclase

Answer 7

causes an increase in cAMP

Question 8

what is the downstream effect of an active G-protein activating phosphodiesterase (PED)

Answer 8

decrease in cAMP -> activates protein kinases

Question 9

what happens when a G-protein activates phospholipase C-beta

Answer 9

initiates inositol phospholipid signaling

Question 10

how does cAMP activate protein kinase A (PKA)

Answer 10

inactive PKA (regulatory subunit + inactive catalytic subunit) -> cAMP binds to regulatory subunit and dissociates 2 active catalytic subunits - ready to phosphorylate target proteins

Question 11

what is the target protein for PKA

Answer 11

CREB- binding protein (CBP)

Question 12

how does PKA induce gene transcription

Answer 12

activated PKA goes into nucleus and activates CREB - both bind to CRE (cAMP response elements) on promotor region and activates gene transcription

Question 13

what else can PKA bind to for activation (besides activating PKA)

Answer 13

CFTR: cystic fibrosis transmembrane conductance regulator = Cl- channel

Question 14

where is phosphatidylinositol 4,5 bisphosphate (PIP2) located

Answer 14

its a minor lipid in the inner half of the plasma membrane

Question 15

what converts PI -> PI(4)P -> PI(4,5)P2 by adding a phosphate to carbons 4 and 5

Answer 15

PI kinase

Question 16

what converts PI(4,5)P2 to diacylglycerol and insitol 1,4,5-triphosphate

Answer 16

phospholipase C-beta (*activated by GPCR -> activated G-protein)

Question 17

what does diacylglycerol activate

Answer 17

protein kinase C (C for calcium dependent)

Question 18

what does insitol 1,4,5-triphosphate (IP3) do

Answer 18

binds to Ca2+ channels and releases Ca2+ from ER

Question 19

what does the cholera toxin target

Answer 19

modifies the alpha-subunit of stimulatory G-protein (ADP ribosylation of GTP-bound alpha)

Question 20

how does the cholera toxin work

Answer 20

the ribosylated alpha-subunit remains active and GTP cannot be hydrolyzed to GDP - adenylate cyclase is active and cAMP levels rise (CFTR remains active)

Question 21

what are the consequences of the cholera toxin

Answer 21

diarrhea and vomiting from efflux of Cl- ions and water into gut

Question 22

how does the Pertusis toxin work

Answer 22

modifies the GDP-bound inactive alpha-subunit and it cannot be activated to GTP - no inhibition of adenylate cyclase and cAMP remain elevated (CFTR is activated)

Question 23

what does the Pertusis toxin target

Answer 23

inhibitory G-proteins (Gi) that would normally inhibit adenylate cyclase activity

Question 24

how are G-proteins and smell related and how do they work

Answer 24

olfactory receptors have G-proteins: activated G-protein -> stimulates adenylate cyclase -> elevated levels of cAMP open gated ion channels to increase Na+ and induce action potential

Question 25

when are cGMP gated Na+ channels open in rods

Answer 25

in the dark when cGMP levels are high

Question 26

what is the activated pathway of cGMP in the rod

Answer 26

light activates rhodopsin -> 11-cis converts to all-trans -> activates transducin (Gt) -> activates cGMP phosphodiesterase (PDE) and cGMP levels fall -> closure of Na+ channels and inhibition of synaptic signaling

Question 27

what are 3 ways rods revert back to resting levels

Answer 27

all negative feedback loops: RK (rhodopsin kinase), arrestin, and RGS (regulator of G-protein signaling)

Question 28

how does RK (rhodopsin kinase) work

Answer 28

phosphorylates cytosolic tail of activated rhodopsin which then cannot activate transducin

Question 29

how does arrestin work

Answer 29

binds to phosphorylated rhodopsin = more inhibition of rhodopsin activity

Question 30

how does RGS (regulator of G-protein signaling) work

Answer 30

binds to activated transducin = GTP is converted to GDP = inactivation of transducin

Question 31

what are enzyme linked receptors responsible for

Answer 31

growth, proliferation, differentiation and survival of cells

Question 32

what are the characteristics of the receptor in enzyme linked receptors

Answer 32

transmembrane proteins that have intrinsic enzymatic activity or are associated with enzymes

Question 33

what are the ligands for receptor tyrosine kinases (PTK)

Answer 33

secreted growth factors and hormones (EGF, PDGF, FGF, HGF, insulin, IGF-1, VEGF, NGF) or membrane bound proteins (ephrins)

Question 34

what happens with receptor tyrosine kinases after a ligand binds

Answer 34

dimerization of receptor, activation of tyrosine kinase domain, phosphorylation of tyrosines on receptor and other signaling proteins or autophosphoylation - increase kinase activity and docking sites for proteins

Question 35

what 2 things bring cells together in receptor tyrosine kinases

Answer 35

a ligand and (Eph) receptors - transmembrane proteins

Question 36

what does p13 kinase do

Answer 36

mediates cell survival and cell growth (catalyzes PI -> PI3P, PI4P -> PI3,4P2, and PI4,5 bisphosphate -> PI3,4,5P3)

Question 37

what is PTEN

Answer 37

an IPE3 phosphatase = tumor supressor

Question 38

what receptors are cytokines recognized by

Answer 38

receptors that bind to JAK (janus kinases) - cross phosphorylate each other on tyrosines

Question 39

what do activated JAK (janus kinases) phosphorylate

Answer 39

STAT (signal transducers and activators of transcription) that are docked on specific phosphotyrosines on the receptor

Question 40

what are 2 mutations in 2 important classes of genes in cancer

Answer 40

proto-oncogenes and tumor repressing genes

Question 41

what is Ras

Answer 41

an oncogene that is activated in 30% of human cancers and can exist in 2 forms (active or inactive)

Question 42

what does active Ras do

Answer 42

it creates a cascade of phosphorylation reactions that relay a signal to the nucleus

Question 43

what are the 3 core kinases involved in the Ras cascade

Answer 43

MAPKKK (Raf kinase), MAPKK (Mek kinase), and MAPK (Erk kinase)

Question 44

what is ErbB: Her2/neu

Answer 44

it is amplified in breast cancers - Her2 is an epidermal growth factor receptor 2 and maps to 17q12-q21

Question 45

what is herception

Answer 45

antibody to Her2 (management of breast cancer) it stops intracellular signaling/transcription, proliferation and anti-apoptosis

Question 46

what are cell cycle regulatory proteins

Answer 46

cyclin dependent kinases (cdks) specific for G1, G1/S, S, and M phases

Question 47

what regulates cdk's

Answer 47

cyclins D, E, A, and B (synthesized and degraded each cell cycle)

Question 48

what controls the activity of cdk's

Answer 48

CAK, CKI and phosphatases

Question 49

what inhibits activity of cdks during cell cycle arrest

Answer 49

p21 which is regulated by p53

Question 50

which type of Rb (retinoblastoma) has tumors in one eye and is consistent with 2 random genetic hits

Answer 50

the sporadic type (familial is both eyes and has single random genetic hit)

Question 51

how does Rb (retinoblastoma) work

Answer 51

Rb is usually coupled with E2F and inhibits S-phase - tumors occur when they are not connected and E2F activates transcription

Question 52

what does p53 do

Answer 52

senses genetic damage in cell and arrests cell "guardian of genome"

Question 53

what is APC and what does it do

Answer 53

APC is mutated in tumor cells and prevents beta-catenin from binding to complex which prevents phosphorylation and degradation of catenin = promotes proliferation and transcription of tumor cells in colon cancer

Question 54

what is a wnt growth factor

Answer 54

it does the same thing as an APC by occupying a frizzled receptor