Kandpal - Signal Transduction: GPCR, Enzyme Linked Receptors and Human Cancers Flashcards
what makes up a G-protein coupled receptor (GPCR)
7 transmembrane (7TM) domains, seven pass, serpentine receptors (N-terminus is extracellular and C-terminus is intracellular)
what are the ligands for GPCR’s
hormones, neurotransmitters (proteins, peptides, amino acid derivatives, and fatty acids) photon, H+, Ca2+
what are the 3 subunits on a GPCR
alpha, beta, and gamma
how is a G-protein activated
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
what controls the activity of the alpha subunit on a G-protein and how does it work
RGS (regulator of G-protein signaling) - acts as alpha-subunit specific GTPase activator proteins (GAPs)
what is the difference between stimulatory and inhibitory G-proteins
both are GTP bound: stimulatory activates adenylate cyclase and inhibitory inhibits adenylate cyclase
what is the downstream effect of an active G-protein activating adenylate cyclase
causes an increase in cAMP
what is the downstream effect of an active G-protein activating phosphodiesterase (PED)
decrease in cAMP -> activates protein kinases
what happens when a G-protein activates phospholipase C-beta
initiates inositol phospholipid signaling
how does cAMP activate protein kinase A (PKA)
inactive PKA (regulatory subunit + inactive catalytic subunit) -> cAMP binds to regulatory subunit and dissociates 2 active catalytic subunits - ready to phosphorylate target proteins
what is the target protein for PKA
CREB- binding protein (CBP)
how does PKA induce gene transcription
activated PKA goes into nucleus and activates CREB - both bind to CRE (cAMP response elements) on promotor region and activates gene transcription
what else can PKA bind to for activation (besides activating PKA)
CFTR: cystic fibrosis transmembrane conductance regulator = Cl- channel
where is phosphatidylinositol 4,5 bisphosphate (PIP2) located
its a minor lipid in the inner half of the plasma membrane
what converts PI -> PI(4)P -> PI(4,5)P2 by adding a phosphate to carbons 4 and 5
PI kinase
what converts PI(4,5)P2 to diacylglycerol and insitol 1,4,5-triphosphate
phospholipase C-beta (*activated by GPCR -> activated G-protein)
what does diacylglycerol activate
protein kinase C (C for calcium dependent)
what does insitol 1,4,5-triphosphate (IP3) do
binds to Ca2+ channels and releases Ca2+ from ER
what does the cholera toxin target
modifies the alpha-subunit of stimulatory G-protein (ADP ribosylation of GTP-bound alpha)
how does the cholera toxin work
the ribosylated alpha-subunit remains active and GTP cannot be hydrolyzed to GDP - adenylate cyclase is active and cAMP levels rise (CFTR remains active)
what are the consequences of the cholera toxin
diarrhea and vomiting from efflux of Cl- ions and water into gut
how does the Pertusis toxin work
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)
what does the Pertusis toxin target
inhibitory G-proteins (Gi) that would normally inhibit adenylate cyclase activity
how are G-proteins and smell related and how do they work
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
when are cGMP gated Na+ channels open in rods
in the dark when cGMP levels are high
what is the activated pathway of cGMP in the rod
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
what are 3 ways rods revert back to resting levels
all negative feedback loops: RK (rhodopsin kinase), arrestin, and RGS (regulator of G-protein signaling)
how does RK (rhodopsin kinase) work
phosphorylates cytosolic tail of activated rhodopsin which then cannot activate transducin
how does arrestin work
binds to phosphorylated rhodopsin = more inhibition of rhodopsin activity
how does RGS (regulator of G-protein signaling) work
binds to activated transducin = GTP is converted to GDP = inactivation of transducin
what are enzyme linked receptors responsible for
growth, proliferation, differentiation and survival of cells
what are the characteristics of the receptor in enzyme linked receptors
transmembrane proteins that have intrinsic enzymatic activity or are associated with enzymes
what are the ligands for receptor tyrosine kinases (PTK)
secreted growth factors and hormones (EGF, PDGF, FGF, HGF, insulin, IGF-1, VEGF, NGF) or membrane bound proteins (ephrins)
what happens with receptor tyrosine kinases after a ligand binds
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
what 2 things bring cells together in receptor tyrosine kinases
a ligand and (Eph) receptors - transmembrane proteins
what does p13 kinase do
mediates cell survival and cell growth (catalyzes PI -> PI3P, PI4P -> PI3,4P2, and PI4,5 bisphosphate -> PI3,4,5P3)
what is PTEN
an IPE3 phosphatase = tumor supressor
what receptors are cytokines recognized by
receptors that bind to JAK (janus kinases) - cross phosphorylate each other on tyrosines
what do activated JAK (janus kinases) phosphorylate
STAT (signal transducers and activators of transcription) that are docked on specific phosphotyrosines on the receptor
what are 2 mutations in 2 important classes of genes in cancer
proto-oncogenes and tumor repressing genes
what is Ras
an oncogene that is activated in 30% of human cancers and can exist in 2 forms (active or inactive)
what does active Ras do
it creates a cascade of phosphorylation reactions that relay a signal to the nucleus
what are the 3 core kinases involved in the Ras cascade
MAPKKK (Raf kinase), MAPKK (Mek kinase), and MAPK (Erk kinase)
what is ErbB: Her2/neu
it is amplified in breast cancers - Her2 is an epidermal growth factor receptor 2 and maps to 17q12-q21
what is herception
antibody to Her2 (management of breast cancer) it stops intracellular signaling/transcription, proliferation and anti-apoptosis
what are cell cycle regulatory proteins
cyclin dependent kinases (cdks) specific for G1, G1/S, S, and M phases
what regulates cdk’s
cyclins D, E, A, and B (synthesized and degraded each cell cycle)
what controls the activity of cdk’s
CAK, CKI and phosphatases
what inhibits activity of cdks during cell cycle arrest
p21 which is regulated by p53
which type of Rb (retinoblastoma) has tumors in one eye and is consistent with 2 random genetic hits
the sporadic type (familial is both eyes and has single random genetic hit)
how does Rb (retinoblastoma) work
Rb is usually coupled with E2F and inhibits S-phase - tumors occur when they are not connected and E2F activates transcription
what does p53 do
senses genetic damage in cell and arrests cell “guardian of genome”
what is APC and what does it do
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
what is a wnt growth factor
it does the same thing as an APC by occupying a frizzled receptor
