Receptors and Cancer Flashcards
Slow response
change in amounts of proteins by change in expression of genes
needs to go to nucleus first
Fast response
change in activity or function of enzymes or proteins
ex: changes in metabolism, PK, PFK2, glucagon/insulin pathway
Signaling Cascades
Signals (ligands)-secreted by exocytosis
Receptors- bind specifically to signal molecules
Effectors: targets of receptors inside cells, alter activity of different proteins and make 2nd messengers
ex: Ca and cAMP
Endocrine Signaling
long distance signaling
- signal reaches blood stream and then travels to distant target tissue/cells
- freely diffusible signals
- long lasting-takes time to go through the circulatory system
ex: hormones
Paracrine Signaling
acts locally
- affects nearby cells but not as freely diffusible
- short lived
ex: neurotransmitters (Glu)
Autocrine Signaling
cells respond to signals that they themselves release or they release cells of the same type
cell secretes signal that feeds back and binds to receptor on own surface
ex: growth factors on cancer cells
Direct/Juxtacrine signaling
- bring cell to them
ex: phagocyte engulfs bacteria/virus and delivers to B or T cell for immune function
Same ligand-different response
some ligands can create different responses in different target cells
ex: acetylcholine:
heart- causes relaxation
muscle- contraction
salivary gland- secretion of saliva
Leptin
hormone that produces satiety, or the feeling of fullness
message sent to hypothalamus to stop eating
if deficient, keep eating = obesity
G-protein coupled receptors (GPCRs)
G-alpha, beta, and gamma units
- ligand binds to receptor
- conformational change of receptor, G protein binds to receptor
- alpha subunit binds to receptor, GDP swapped for GTP which activates Galpha
- alpha breaks off from beta and gamma
- Galpha is active and binds to and activates effector molecule (membrane bound)
- Adenylyl Cyclase which catalyzes cAMP formation from ATP
- PLC which catalyzes DAG and IP3 formation
Adenylyl Cyclase and cAMP
Adenylyl cyclase generates cAMP by converting ATP to cAMP
cAMP targets PKA (has 4 subunits)
PKA then phosphorylates other proteins
Cholera epidemic
toxin gets into gut, causes G-alpha,s to remain active with GTP
this leads to a large increase in cAMP and thus an increase in PKA
PKA phosphorylates CFTR Cl channel which causes a large Cl secretion to outside the cell and doesn’t allow resorption either
this leads to an influx of water, leads to diarrhea
Desensitization of Signal
potentiate - turn up
attenuate - turn down (attenuate for what!!)
- Hormone levels drop: decreased adenylyl cyclase = decreased cAMP = decreased PKA
- Remove signaling molecule: phosphodiesterases remove cAMP and cGMP
- Receptor sequestration: via endosome, remove from membrane, can return or..
- Receptor destruction: endosome removes receptor and takes to lysosome for destruction
G protein receptor kinases (GRKs)
phosphorylates GPCR so arrestin can bind to 3rd intracellular loop
this prevents Galpha from binding and thus Galpha does not get activated and there is no downstream affects
G-alpha types
G-alpha-S: stimulatory, activates AC and then cAMP….
G-alpha-I: inhibitory, inhibits AC and thus stops pathway
G-alpha-Q: activates PLC (phospholipase C), which creates DAG and IP3 formation
Nuclear Hormones
are hydrophobic
diffuse through membrane to nucleus hormone receptor to be transcribed in the nucleus
Signaling Molecules
Lypophilic:
- steroid hormones-progesterone, testosterone
- thyroid hormone-thyroxine
- retinoids
Hydrophilic: eg. growth factors
- amino acid derived-histamine, serotonin, epinephrine
- from lipid metabolism-acetylcholine
- polypeptides-insulin, glucagon,…
Intracellular receptors
ligand-binding domain
DNA-binding domain
Transcription-binding domain
Hydrophobic ligands
cortisol estradiol testosterone vitamin D3 thyroxine retinoid acid
look for OH groups
Retinoid Acid
derived from Vit A
excess retinol (vit A) leads to abnormalities
retinal=active form
retinol=supplement
accutane for acne
2 Hit Hypothesis
2 errors to end up with cancer
inherit one “hit” or mutation and this means that you only need one more mutation to cause a disease like cancer
if you start with one, you are more likely to get cancer by accumulating another error
first error normally inherited
2nd is typically epigenetic, more dynamic
1st hit: DNA repair present to fix mutations,
P53, RB, APC, all tumor suppressors, all involved in DNA repair to check for errors (halt division until repair is doing job)
if mutation is in these, may not get repaired
2nd hit: oncogene,
Cell Growth/Division
Normal:
Cell cycle and apoptosis occurring
Tumor suppressors working
but when a mutation or error occurs: oncogene
Oncogene (growth genes)
tumor suppression avoided
uncontrolled proliferation
CANCER
Tumor Suppressors
p53, BRCA1/BRCA2, APC, Rb
Oncogenes
RAS, HER2 (an RTK), EGF receptor (an RTK)
Enzyme Coupled Receptors
Tyrosine Kinases
JAK-STAT Receptors
Ser/Thr kinases
all create docking site for other proteins
Receptor Tyrosine Kinases (RTKs)
used for response to growth factors!!!!
in the cytoplasmic tail
- ligand binds
- causes conformational change in receptor and inducing dimerization of 2 monomer receptors
- Autophosphorylation occurs to act as scaffold
- phosphotyrosine binds to SH2 domain of Grb2
- SH3 domain of Grb2 binds to SOS
- SOS binds to Ras (monomeric G protein-small GTPase)
- Ras binds to Raf (MAP kinase, kinase, kinase), cascade affect
- Raf to Mek to Erk (progress down pathway by phosphorylation) = gene transcription thru this pathway
(Ras first discovered human oncogene)
Growth Factors
named after the tissue they were discovered in
EGF - epidermal PDGF - platelet derived FGF - fibroblast IGF-1 - insulin-like NGF - nerve
Insulin Signaling
RAS dependent:
- uses Grb2
- slower because makes alterations in gene transcription
e. g. increased transcription of glucokinase = glycog synth
RAS independent:
- uses PI3-kinase
- faster because changes enzyme/protein activity
e. g. increased GLUT 4 movement = increase glycog synth
JAK-STAT Receptors
receptors bind cytokines, receptors dimerize, bind JAKs
JAKs phosphorylate each other (autophosphorylate)
receptor binds and phosphorylates STATs
STATs (transcription factor) dissociate from receptor, dimerize, translocate to the nucleus
Serine-Threonine receptors & Smad
R-Smad: receptor specific Smad and forms complex with Co-Smad (common Smad)
Activation of Cell Cycle
Myc activation from MAP Kinase (Erk)
Active G1CDK
(CDK-cyclin dependent kinase)
Rb is inactivated via phosphorylation and allows E2F to be activated
active E2F will activate G1S/-CDK and S-CDK and all 3 of these will positively feedback to create more E2F
once there is enough E2F, DNA synthesis (S-phase) can begin
Cell Cycle
M-mitotic phase, cell division
interphase-long growth period and includes:
-Gap 1 (G1) phase
RNA and protein synthesis needed for DNA replication
-DNA synthesis (S) phase
-Gap 2 (G2) phase
DNA stability is checked
-G0, when conditions not appropriate, cells arrest here, as we age, stuck in G0
Restriction and Checkpoints
Restriction point (R)- occurs if growth factors are limiting
G1 checkpoint
-correct any DNA damage (chemical modifications)
G2 checkpoint
-verify completeness
Metaphase checkpoint
-ensure chromosomes are attached to mitotic spindle
Retinoblastoma
Rb protein is major regulator or cell cycle/apoptosis
Rb:
active = hypophosphorylated
inactive = hyperphosphorylated
S-phase requires E2F transcription factors Cyclin E and Cyclin A (both activate CDK2, keep Rb inactive/E2F active)
Cyclin dependent kinases (CDKs)
binding of cyclin to CDKs partially activate them
-full activation requires CDK-activating kinase (CAK)
p27: CDK inhibitor (CDKI)
- binds to cyclin-CDK complex to inactive kinase activity
- using p27 is a slow step because it needs to be transcribed
Cyclin-CDK activity
G1/S transition phase: Cyclin E-CDK2
S phase: Cyclin A-CKD2
M-phase: Cyclin A-CKD1
Wee1
Inhibits CDK by phosphorylating “roof” site
Cdc25 (phosphatase)
dephosphorylates “roof” site to increase CDK activity
p27 vs. kinase-phosphatase pathways
p27 is a CDKI (inhibitor) and attaches to the active CDK to inactive its kinase activity
Wee1 is kinase that phosphorylates the CDK to inactivate it
Cdc25 is a phosphatase that dephosphorylates the phosphate to make CDK active again
APC/C
targets S-cyclins and M-cyclins
inactive APC/C is activated by binding to Cdc20
cyclins destroyed, inactivates most CDKs,
CDK’s dephosphorylated
p53 (tumor suppressor)
guardian of the genome, transcription factor
p53 promotes apoptosis
p53 promotes cell cycle arrest/DNA repair
Apoptosis
is an intracellular proteolytic cascade
intrinsic and extrinsic pathway
Intrinsic: mitochondrial dependent
-BAX/BCL are both key regulators
Extrinsic: mitochondrial independent
Intrinsic Pathway, Apoptosis
cytochrome-c is released from the mitochondria and binds to Apaf1 (procaspase-activating adaptor protein)
Apaf1 forms an apoptosome which then activates caspase-9 (initiator caspase)
Caspase-9 activates caspase-3 (executioner caspase)
BAX: activates/promotes apoptosis
BCL2: inhibits apoptosis by inhibiting BAX
Extrinsic Pathway, apoptosis
Fas binds to Fas death receptor
FADD activates Procaspase 8, activates caspase 3 for apoptosis
TNF-alpha binds to receptor, TRADD activates procaspase 8, activates caspase 3 for apoptosis
BRCA (tumor suppressor)
responds to DNA damage
stops replication if damage is noted
Chronic Myelogenous Leukemia (CML)
BCR-ABL fusion protein
v-erb
mutated RTK, constant proliferation
Src
similar to Ras
when activated, results in ligand independent signal transduction
mutation occurs during viral replication!!
see correlation box
