begin of exam 3 stuff. signaling pathways for gene activity Flashcards
most famous oncogene? what are two mechanisms that cause it to stay on
Ras. if it is always on (always GTP loaded) then it can’t hydrolyze GTP or it can’t attach to a GAP to turn off
long term signaling changes what for proteins?
it changes transcription
what are the four types of signaling transduction?
protein kinase cascades: 1 = TGF beta, 2= cytokine receptor, 3= receptor tyrosine kinase, 4 = G protein-coupled receptors
cytokine signaling: what should you think
jak signaling (just another kinase); these are critical to transcription factor activation
TGF beta is?
simplest pathway, typically inhibitory, represses cell proliferation; receptor binds ligand and the first target is the transcription factor.
how many steps between TGF beta and nucleus
receptor; transcription factor; DNA. 3
transcritption factors usually reside __ in a __ form
cytoplasm; inactive
what does transcrition factor do?
undergo a targeting trafficing event then go to the nucleus to do their job
what are some ways you can activate a transcription factor (TF)
can disrupt ); can proteolytically cleave and allow the TF to go to the nucleus(NF kappaB)
what does TGF beta stand for?
transforming growth factor
receptor mediated endocytosis can regulate things by?
many receptors will be endocytosed and destroyed after they start the cascade. if you have a problem here, thats bad
in general how does the TGF beta signal work?
what signal is secreted from cell, they are bound do be inactive. to be active you have to proteolytically process in extracellular matrix. [you can either destroy the propeptide or you can bring in another one to compete for interaction]
what holds the TGF ligand together
disulfide
what do rII and rIII do
3 has an extraplasmic part. its a shuttle. it collects things and keeps them until RII can come over and pick it up. that one has a protein kinase that is always on. it allows us to activate RI
what does RI do when its turned on?
it doesn’t bond with a ligand, so it has to be turned on by RII but it is a serine threonine kinase. it phosphorylates Smads
where are TF in relation to TGF beta?
smads (TF) are directly downstream
how many smads are there
multiple
R-smad = receptor directly changed by TGF
I-smad = inhibitory nuclear transcription factor
Co-smad =
does RIII have to play a role?
nope. it may not be required since this is a multipart receptor complex
what keeps smad 3 in an autoinhibited form
protein protein interaction between smad3 and MH parts
what happens when smad is changed by the RI complex
conformational change exposes an NLS
what is an NLS
nuclear localization signal (usually basic charged amino acids. sometimes two stretches) it tells you where a protein should go
what is the receptor for NLS
importin
so to get into the nucleus smad hooks up with __ __ and __
co-smad 4, beta importin, NLS
what process would inactivate TGF beta signaling
phosphorylation activates, so phosphatase will deactivate.
SnoN and Ski are inhibitors of the transcription factor complex
what does ski stand for
sloan kettering institute. this guy was identified as a tumor inhibitor. its a supressor of the transcription factor complex by bringing in a histone deacetylase that leads to gene inactivation
disruption of TGF beta results in?
cell transformation
example: pancreatic cancer has a deletion of co-smad4 so they can NOT inhibit gene transcription
what is loss of TGF beta RI or RII associated with?
retinoblastoma, colon cancer, liver cancer
TGF beta controls
cell proliferation and cell differentiation.
if you lose the peptide hormone for miostatin, what happens
you get a buff bull
when you see cytokine signaling, what should you think?
promotes cell growth and differentiation; activation of gene expression
what is the cytokine signal
small polypeptide.
examples of cytokines
prolactin, interferon alpha, and erytropoietin
what does erythropoetin (epo) do
signal that you should make more red blood cells; PREVENTS cell death
does the intracellular domain of the cytokine receptor have a kinase
NO. it is attached, however, to JAK (he IS a kinase). he is activated by phosphorylation (usually on tyr residues)
how do you dock additional proteins on phosphorylation sites?
SH2 loves to bind phospho-tyr to a protein
what is STAT
SH2 domain plus a dna binding domain. it dimerizes and goes to the nucleus and goes to work
what is STAT 5 involved in
interacts with BCL-xL for programmed cell death (see apoptosis lecture) to INHIBIT programmed cell death
how do you turn off JAK/STAT signalling
SHP1 dephosphorylates JAK. this is short term
SOCS destroy JAK by proteosome and polyubiquitization
SOCS protein has two parts. what are they
the SH2 domain and SOCS box
what is the famous cancer signalling pathway
receptor tyrosine kinase (RTK)- Ras-MAPK cascade
how is RTK different from the other two signals
the kinase recruits a G protein to the cell surface and activates it (Ras in this case) which does another cascade through MAPK
what do you HAVE TO KNOW
ras is typically mutated in most oncogenes (disruption of Gly12) this leads to a protein that is always GTP loaded that blocks the binding of a GAP and lock the ras in the active GTP-bound state
what is her 2
human epidermal growth factor receptor 2
what are the ligands for the RTK? what does that do to the receptor
peptide or protein hormones like NGF; dimerizes
there is a battery of ___ and ___ for RTK
multiple ligands, multiple receptors, mix and match for different combos
when you phosphorylate the receptor on the cytosol side, what gets recruited?
something with an SH2 domain. GRB2
how do you turn on Ras with RTK?
GRB2 is the docks and is a recruiter of Ras and SOS. SOS is a GEF that is attracted to GRB2’s SH3 site
what does ras do? what does that do?
activates Raf, it is autophosphorylated and a cascade of kinases are activated. Raf does MEK who does ERK who does
what does the map kinase do
when phosphorylated it can go into the nucleus and phosphorylates other things to allow for a MULTIMERIC regulation to control early response genes. examples are C-Fos and C-Jun
