RTK, RSTK, intracellular receptors + rhythms Flashcards
what are the 2 types of tyrosine kinase receptors (RTK)?
- typically, RTKs function as ________
- receptors with intrinsic kinase activity –> receptors themselves have catalytic activity
- receptors that recruit a kinase when bound to a ligand
- function as dimers/in pairs –> signal initiation requires 2 receptors binding to ligand (but some work as monomers as well: ie VEGF receptor)
what is the most studied RTK with intrinsic tyrosine kinase activity?
- _______-______ structure –> 4 subunits
- MW = ___ kDA
- each dimer is processed from a ________ precursor protein/gene –> formation of _____ bonds + proteolytic ____________
- btw ____ and ________ receptors per cell –> highest in which 2 types of cells?
- homology with which receptor?
- insulin receptor!
- hetero-tetrameric structure –> 2 a and 2 b chains held together by S-S bonds
- MW = 400 kDa
- a single precursor –> disulfide bonds + proteolytic cleavage
- btw 100 and 200 000 receptors per cell (highest in adipocytes and hepatocytes)
- with insulin-like growth factor-1 receptor (IGF-1)
what are the 3 main steps of insulin receptor? after binding of ligand
(binding of ligand)
1. autophosphorylation of intracellular/cytoplasmic domain of receptor
2. docking and phosphorylation of IRS-1 or IRS-2 (2nd messengers: insulin receptor substrate)
3. activation of 2 major signal pathways (MAPK and PIP3)
what is the first protein that RTK phosphorylates?
IRS-1 or IRS-2
MAPK pathway –> also called what pathway?
- 7 steps
- insulin receptor binds insulin and undergoes autophosphorylation on its carboxyl-terminal Tyr residues
- insulin receptor phosphorylates IRS-1 on its Tyr residue
- SH2 domain of Grb2 (adaptor protein) binds to phosphorylated Tyr residue of IRS-1 –> Grb2 recruits sos, sos recruits Ras, causing GDP release and GTP binding to Ras
- activated Ras binds and activates Raf-1
- Raf-1 phosphorylates MEK on 2 Ser residues, activating it. MEK phosphorylates ERK on Thr and Tyr residues, activating it
- ERK moves into nucleus and phosphorylates nucleus transcription factors such as Elk1, activating them
- phosphorylated Elk1 joins SRF to stimulate the transcription and translation of a set of genes needed for cell division
- what type of protein are grb2, sos and ras?
- ras is similar to which protein. why?
- ERK1/2 –> typically activated separately or together
- ERK1/2 phosphorylating TFs like (4) is well defined mechanism of regulation of what?
- ERK __ can bind to ____ and inhibit other ____ from binding = ______ modulation
- adaptor proteins! (connecting proteins)
- to G protein bc has to replace GDP by GTP
- together!
- like Elk, SRF, Ets, c-Fos –> well defined mechanism of regulation of gene expression
- ERK 2 can bind to DNA and inhibit other TFs from binding = direct modulation
- where is ERK 1/2 phosphorylated? by who?
- ERK 1/2 can modulate proteins located where?
- phosphorylated in cytoplasm by MEK
- can modulate both nucleus and cytoplasmic proteins! by phosphorylating them!
- what does MAPK stands for?
- MAPK pathway includes a large complex _______ of proteins
- what is the uppermost level of kinase activity? vs 2nd level vs 1st level?
- give examples of each level for mitogen. –> leads to what? (6)
- mitogen activated protein kinase
- complex family of proteins
- MAPKKK –> MAPKK –> MAPK
- Raf1/A/B –> MEK 1/2 –> ERK 1/2
(MLK –> MKK4/7 –> JNK1/2/3) (pathway for stress that’s analogous to ERK1/2 pathway) - leads to proliferation, differentiation, apoptosis, gene expression, cell motility, change in metabolism
RTK signaling through PIP3
- 4 steps
- insulin receptor binds insulin and undergoes autophosphorylation on its carboxyl-terminal Tyr residues
- insulin receptor phosphorylates IRS-1 on its Tyr residue
- phosphorylated IRS-1 or IRS-2 activates PI3K by bindint to its SH2 domain. PI3K converts PIP2 to PIP3 (by adding a PO4 group)
- PKB bound to PIP3 is phosphorylated by PKD1. activated PKB phosphorylates GSK3 on a ser residue, inactivating it
*stop here, will continue rest when we talk about glucose metabolism
which enzyme converts phosphatidylinositol(4,5) bisphosphate to phosphatidylinositol (3,4,5) trisphosphate?
- what converts it back?
- PI3-K adds PO4
- PTEN removes PO4
what are the best known receptors in the class of recruited tyrosine kinase activity receptors? (4)
- also include ______/_______ receptors
- growth hormone, prolactin, interferon and leptin
- cytokine/haemopoietic receptors (over 20 members)
- Growth hormone has ___ bindings sites
1. GH binds to what?
2. what happens? –> initiates what?
3. what?
2 binding sites!
1. GH binds to receptor 1
2. binding of GH to receptor 1 recruits receptor 2 –> forming a dimeric complex –> dimerization of the cytoplasmic regions initiates signal transduction
3. GH-dimeric receptor complex recruits and activates JAK-2 (janus kinase = tyrosine kinase –> similar to IRS = first signal mediator)
RECEPTORS WITH RECRUITED TYROSINE KINASE ACTIVITY
- receptor recruits JAK –> what happens? (2 ish)
- then, 3 branches can be activated
- JAKs cross-phosphorylate each other on tyrosines (ie autophosphorylates) + phosphorylates receptors on tyrosines
1. activation of transcription regulatory proteins STAT (4 isoforms)
2. activation of MAPK pathway (as insulin signaling, but here JAK2 plays role of IRS1)
3. activation of PIP3 pathway
- what does STAT stand for?
- STATs act as what? where do they go?
- explain JAK-STAT pathway
- signal transducer and activator of transcription
- act as transcription factor –> they dock onto the the phosphorylated cytoplasmic domain of receptors
1. JAKs cross-phosphorylate each other on tyrosines (ie autophosphorylates)
2. JAKs phosphorylates receptors on tyrosines
3. STATs dock onto specific phosphotyrosines on receptor through SH2 domains –> JAKs phorphorylates them
4. STATS dissociate from receptor and dimerize via their SH2 domain
5. STATs migrate to nucleus, bind to DNA and other gene regulatory proteins –> regulate gene expression
what are the similarities and differences between IRS-1 and JAK?
- both can activate MAPK and PIP3 pathways
- IRS-1 is from intrinsic tyrosine activity receptors
- JAK is from recruited tyrosine activity receptors + can activate STAT pathway
what is the main signal modulator for serine-threonine kinase receptors (RSTK)?
- 3 categories
- what doe they serve as?
- smad proteins are mediators of TGF-b signaling (best known receptor in RSTK class of receptors)
1. regulatory smad
2. copartner smad
3. inhibitory smad - smads serve as transcription factors –> regulate gene expression
explain 6 steps of TGF-b1 receptor (transforming growth factor beta 1 receptor)
- TGF-b1 binds to TGF-bRII
- TGF-bRI is recruited –> dimerizes (NOTE that RII and RI are 2 different receptors (unlike GH receptors) and coded by 2 different genes = heterodimers)
- phosphorylation of dimer
- phosphorylation of smad3 and smad2 (both regulatory smads)
*smad7 (inhibitory smad) can inhibit phosphorylation of smad 3 and 2 - phosphorylated smad 2 and smad 3 recruit smad 4 (copartner smad)
- complex enters nucleus and act as transcription factor to regulate gene expression
- which 2 types of hormones bind to a family of intracellular receptors?
- where are intracellular receptors located in? (2)
- intracellular receptors function as what?
- typically, response is slow/fast? why?
- steroid and thyroid hormones –> both lipid soluble hormones (+ some smaller like vit B and D)
- cytoplasm or nucleus
- function as hormone regulated transcription factors
- typically, response is slow since transcription and translation of proteins are necessary (vs all kinase pathways can change enzymatic function in cytoplasm = response is quicker)
