17.3 Tyrosine Kinases, Signaling by MAP Kinase, and PI 3-Kinase Flashcards
largest family of cell surface receptors that are directly linked to intracellular enzymes → enzyme linked receptors
tyrosine kinases
major types of tyrosine kinases
- receptor tyrosine kinases
- nonreceptor tyrosine kinases
action of receptor tyrosine kinases results from (…) on tyrosine residues
phosphorylation of their substrates
action of nonreceptor tyrosine kinases results from (…)
stimulation of intracellular tyrosine kinases with which they are noncovalently associated
many new cancer treatment drugs are inhibitors of ()
tyrosine kinases or their downstream signaling pathways
class of tyrosine kinases that include receptors for most polypeptide growth factors
receptor tyrosine kinases
all receptor tyrosine kinases have:
- N-terminal extracellular ligand-binding domain
- 1 transmembrane alpha helix
- cytosolic C-terminal domain with protein-tyrosine kinase activity
explain how binding of ligands to receptor tyrosine kinases allows for propagation of cell signals
binding of ligands at N-terminal domain activates C-terminal domains → phosphorylation of both the receptors themselves and the intracellular target proteins that propagate the cell signal
2 main activities that occur during cell signaling of most receptor tyrosine kinases
- ligand-induced receptor dimerization
- autophosphorylation
during ligand-induced receptor dimerization of RTKs by ligands that are already dimers, receptor dimerization occurs when ()
one ligand binds to 2 different receptor molecules
during ligand-induced receptor dimerization of RTKs by ligands that exist as monomers, receptor dimerization is initiated by ()
inducing conformational changes that promote protein-protein interactions between different receptor polypeptide
dimerization of RTKs is a () interaction
homophilic
what occurs in autophosphorylation of RTKs?
receptors are phosphorylated as the dimerized polypeptides cross-phosphorylate each other
2 main roles of autophosphorylation
- increases protein kinase activity
- creates binding sites for other proteins that transmit signals downstream from the activated receptors
by phosphorylating tyrosine in the (), autophosphorylation results in an increase in protein kinase activity
catalytic domain (cytosolic tyrosine kinase domain)
by phosphorylating tyrosine located (), autophosphorylation results in the creation of creates binding sites for other proteins that transmit signals downstream from the activated receptors
outside the catalytic domain
association of () to phosphorylated tyrosine residues of receptor tyrosine kinases is mediated by protein domains that bind to specific phosphotyrosine-containing peptides
downstream signaling molecules
association of downstream signaling molecules to phosphorylated tyrosine residues of receptor tyrosine kinases is mediated by protein domains that bind to ()
specific phosphotyrosine-containing peptides
initially recognized in tyrosine kinases related to Src, the oncogenic protein of the Rous sarcoma virus; bind to specific short peptide sequences containing phosphotyrosine residues
SH2 domains
SH2 domains stand for ()
Src homology 2
SH2 domains were initially recognized in tyrosine kinases related to (1), the oncogenic protein of the ()
- Src
- Rous sarcoma virus
SH2 domains bind to specific short peptide sequences containing ()
phosphotyrosine residues
() represents the first step in the intracellular transmission of signals initiated by binding of growth factors to the cell surface
association of SH2-containing proteins with autophosphorylated receptors
association of SH2-containing proteins with activated receptor tyrosine kinases can have several effects:
- localizes SH2-containing proteins to PM
- SH2-containing proteins can associate with other proteins (can be other downstream signaling molecules)
- promotes phosphorylation of SH2-containing proteins
- stimulates enzymatic activities of SH2-containing proteins
tyrosine kinases that phosphorylate tyrosine residues of receptors with which they are noncovalently associated; they do not have intrinsic catalytic activity
nonreceptor tyrosine kinases
NRTKs contain (or are associated to) members of the ()
cytokine receptor superfamily
because NRTKs contain (or are associated to) members of the cytokine receptor family, they encompass the receptors for most (1) and for (2)
- cytokines (e.g. erythropoietin and interleukin-2)
- some polypeptide hormones (e.g. growth hormone)
give an overview of cell signaling from cytokine receptors
- ligand-induced dimerization of receptors (NOT RTKs, could be cytokine receptors, growth factor receptors, etc.)
- cross-phosphorylation of associated NRTKs
- phosphorylation of dimerized receptors by activated NRTKs
- phosphorlyation of receptors leads to formation of binding sites for SH2-containing downstream signaling molecules
combination of cytokine receptors and nonreceptor tyrosine kinases function analogously to ()
receptor tyrosine kinases
kinases associated with cytokine receptors include members of the () → consists of 4 related nonreceptor TKs
Janus kinase (or JAK) family
primary targets of JAKs are the () → transcription factors with SH2 domains
STAT proteins (signal transducers and activators or transcription)
STAT transcription factors serve as direct links between ()
cytokine receptors on the cell surface and regulation of gene expression in the nucleus
give an overview of the JAK/STAT pathway
- STAT proteins are unactive in cytosol until cytokine receptors are activated
- activation of STAT proteins leads to binding of their SH2 domains to phosphotyrosine sites on cytokine receptors
- once associated to the cytokine receptors, STAT proteins are then phosphorylated by JAK
- phosphorlyated STAT proteins then dimerize and translocate to the nucleus to stimulate transcription of target gene
additional NRTKs belong to the Src family → consists of ()
Src and 8 closely related proteins
members of the () play key roles in signaling downstream of cytokine receptors, RTKs, antigen receptors on B and T lymphocytes, and receptors involved in cell-cell and cell-matrix interactions; they can also work in coordination with integrins
Src family
() also serve as receptors on which NRTKs (Src in particular) act; they serve as receptors that activate intracellular pathways, thereby controlling cell movements and other aspects of cell behavior
integrins
similar to cytokine receptors, integrins have short cytoplasmic tails that ()
lack enzymatic activity
() is an early response to integrin interaction with EC matrix
tyrosine phosphorylation
one mode of signaling downstream integrins involves the activation of a NRTK called ()
FAK (focal adhesion kinase)
FAK is localized to (1) and rapidly becomes tyrosine-phosphorlyated following the (2)
- focal adhesions
- binding of integrins to EC matrix components
activation of FAK involves () induced by clustering (i.e. dimerization) of integrins bound to EC matrix
autophosphorylation
similarities of receptor and nonreceptor tyrosine kinases
- both work to cross-phosphorylate tyrosine residues on receptor polypeptides
- both activate downstream signaling molecules that contain SH2 domains
differences of receptor and nonreceptor protein kinases
- nonreceptor kinases function in association with cytokine receptors (receptors without intrinsic enzymatic activity)
- receptor tyrosine kinases have catalytic domains that allow them to have intrinsic catalytic activity
cascade of protein kinases and is one of the major pathways of signal transduction activated downstream of both RTKs and NRTKs
MAP kinase pathway
family of serine/threonine kinases that are activated in response to a variety of growth factors and other signaling molecules
MAP kinases (mitogen-activated kinases)
MAP kinases were initially found to belong to the () family
ERK (extracellular signal-regulated kinase)
central role of ERK signaling emerged from studies of ()
Ras proteins (oncogenic proteins of viruses that cause sarcomas in rats)
proteins upstream of the MAP kinase pathway
Ras proteins
inital step in MAP kinase signaling from growth factor receptors is ()
activation of the GTP-binding protein Ras
Ras proteins are analogous to (), however it functions as a monomer
alpha subunits of G proteins
mutations of Ras genes in human cancers have the effect of () → mutated Ras proteins remain in active GTP-bound form and drive unregulated proliferation even wiithout growth factor stimulation
inhibiting GTP hydrolysis by the Ras proteins
mutations of ras genes in human cancers have the effect of inhibiting GTP hydrolysis by the Ras proteins → ()
mutated Ras proteins remain in active GTP-bound form and drive unregulated proliferation even wiithout growth factor stimulation
overview of Ras protein regulation
- GEFs (guanine nucleotide exchange factors) stimulate the activation of Ras proteins by exchanging GTP for bound-GDP
- Ras activity is terminated by GTP hydrolysis, stimulated by GTPase-activating proteins (GAPs)
how can Ras activation be mediated by RTKs
autophosphorylation of RTKs leads to the binding of Ras GEFs through their SH2 domains → localizes GEFs to PM where they can interact with Ras proteins
Ras activates the (), which in turn activates MEK (MAP kinase/ERK kinase) and ERK
Raf protein kinase
Raf protein kinase activates ()
MEK (MAP kinase/ERK kinase) and ERK
a dual-specificity kinase that activates ERKs by phosphorylation of both threonine and tyrosine residues separated by 1 amino acid
MEK (MAP kinase/ERK kinase)
some activated ERK goes to the nucleus, where it regulates ()
transcription factors by phosphorylation
a primary response to growth factor stimulation is the rapid transcriptional induction of ()
immediate early genes
induction of IE genes is mediated by a regulatory sequence called the ()
serum response element (SRE)
SRE is recognized by a complex of transcription factors, including the (1) and (2)
- serum response factor (SRF)
- Elk-1
what is the direct link between the ERK family of MAP kinases and IE gene induction
ERK phosphorylates and activates Elk-1
induction of IE genes leads to altered expression of a battery of other downstream genes called ()
secondary response genes
() directly link ERK signaling to cell proliferation stimulation induced by growth factors
alterations in gene expression
a second major pathway of intracellular signaling (downstream of tyrosine kinases and stimulated by some G proteins) is based on the use of a second messenger derived from a membrane lipid called ()
phosphatidylinositol 4,5-biphosphate (PIP2)
PIP2 is an (1) PM component; can be phosphorylated on the 3 position of inositol by the enzyme (2)
- inner leaflet
- phosphatidylinositol (PI) 3-kinase
tyrosine kinase-activated form of PI 3-kinase has SH2 domains; thus they can be recruited and activated by association with ()
receptor tyrosine kinases
phosphorylation of PIP2 yields the second messenger () → critical for signaling cell proliferation and survival
phosphatidylinositol 3,4,5-triphosphate (PIP3)
key target of PIP3 is (), a serine/threonine kinase
Akt
overview of PI 3-kinase/Akt pathway
- PIP3 binds to the pleckstrin homology (PH) domain of Akt → leads to recruitment of Akt to inner face of PM
- at PM, Akt is phosphorylated and activated by 2 other protein kinases (PDK1 and mTORC2) that also contain PH domains and bind PIP3
- once activated, Akt phosphorylates a number of target proteins that are direct regulators of cell survival, transcription factors, and other protein kinases
in the PI 3-kinase/Akt pathway, binding of PIP3 to () domain of Akt leads to recruitment of Akt to inner leaflet of PM
pleckstrin homology (PH)
in the PI 3-kinase/Akt pathway, 2 protein kinases (1) and (2) phosphorylate and activate Akt; they also contain PH domains and bind PIP3
- PDK1
- mTORC2
critical transcription factors targeted by Akt include members of the () → genes that prevent cell proliferation or signal cell death
FOXO family
give an overview of how the PI 3-kinase/Akt pathway can regulate gene transcription
- phosphorylation of FOXO by Akt (activated by PI 3-kinase/Akt pathway) creates a binding site for cytosolic chaperones → escorts inactive FOXO in the cytoplasm and prevents it from entering the nucleus
- without growth factor signaling and Akt activity, FOXO translocates to nucleus and stimulates transcription of genes that inhibit cell proliferation or induce cell death
the central pathway that regulates cell growth; couples control of protein synthesis to availability of growth factors, nutrients, and energy
mTOR pathway
the mTOR pathway regulates () in response to Akt signaling and availability of energy and amino acids
protein synthesis and autophagy
mTOR protein kinase exists in 2 distinct complexes is cells:
- mTORC2 complex
- mTORC1
mTOR protein kinase complex that phosphorylates and activated Akt
mTORC2 complex
mTOR protein kinase complex that is activated downstream of Akt and functions to regulate protein synthesis → regulates cell size
mTORC1
overview of mTOR pathway
- Akt inhibits TSC, leading to activation of the GTP-binding protein Rheb and mTORC1 in response to growth factor stimulation
- AMPK activates TSC, leading to inhibition of Rheb and mTORC1 if cell energy stores are depleted
- mTORC1 is also inhibited by amino acid starvation
- when activated, mTORC1 stimulates translation by phosphorlyating S6 kinase and eIF4E binding protein-1 (4E-BP1)
- inhibition of tranlation factor eIF4E is relieved
- mTORC1 also inhibits autophagy
mammalian MAP kinases include (1), (2), and (3) kinases
- ERK
- JNK
- p38
() organize complexes of signaling molecules
scaffold proteins
