Cell signaling pathways, apoptosis, angiogensis, stem cells, metabolism, senesence Flashcards
Which of the following are split kinases?
PDGFR STAT3 RON CSF-1R VEGFR INSR FGFR KIT/SCFR MET FLK2/FLT3 ERRB2 EGFR TIE1/2 TRK
- PDGFR, CSF-1R (receptor for M-CSF), KIT/SCFR, FLK2/FLT3, VEGFR, FGFR, TIE1/2
- Split kinases have 2 cytoplasmic kinase domains; important autophosphorylation sites are present on a kinase insert within the catalytic domain
Which TKR are homodimers?
TGF-B VEGFR Notch ERRB2 TIE1/2 TRK Integrins PDGFR SCF EGFR
EGFR can form homo- or heterodimers
VEGFR
SCF
Which TKR are heterodimers?
TGF-B Notch ERRB2 EGFR TIE1/2 TRK Integrins PDGFR SCF ERBB2
TGF-B receptors
Integrins
Notch
EGFR
Cytokine receptors lack TK activity, so they noncovalently associate with what receptors?
JAK receptors (cytoplasmic tyrosine kinases)
• Ligand binds –> cytokine receptor dimerization –> JAK transphosphorylates/activates itself –> also phosphorylates/activates the C-terminal tails of their cytokine receptors, creating a docking site for SH2-containing proteins such as STATs
• Type I cytokine receptors of the IL-6 family –> JAK2 –> STAT3
o STAT3 activating mutations in some tumors
How is or what activates and deactivates RAS in its pathway?
• A balance of activity btw GEFs and GAPs determines the activity of normal RAS proteins
Describe the states in which RAS is turned on vs. off.
- GTPase-activating proteins (GAPs) convert GTP to GDP to deactivate RAS
- RAS is activated by guanine nucleotide exchange factors (GEFs), which release RAS-bound GDP to allow for GTP binding
Once RAS proteins are made, they require what process to occur in order to associate with intracellular membranes?
posttranscriptional modification (prenylation)
How does RAS prenylation occur?
Addition of a covalently-linked lipid chain (either farnesyl or geranylgeranyl group) by farnesyl transferase or geranylgeranyl transferase
o H-RAS and N-RAS are additionally modified by the addition of 2 long chain fatty acids to facilitate membrane localization
What treatment would be most effective for a RAF mutation?
MEK 1/2 because is downstream RAF (not RAS)
MEK/ERK inhibition
What are the basic steps of the PI3K pathway?
PI3K –> converts PIP2 to PIP3 –> AKT–>
AKT phosphorylates a million proteins on their serine/threonine residues
Based on the list below determine which of the downstream proteins is inhibited by AKT:
Mdm2 GSK-3B mTOR HIF-1a FOXO4 Tsc2 NF-KB Bad
INHIBITED by AKT
GSK-3B: anti-proliferative protein; phosphorylates B-catenin, cyclin D1, and Myc
FOXO4: anti-proliferative protein; induces expression of p27Kip1, a CDK inhibitor
Tsc2: anti-growth protein; normally forms a complex that inactivates mTOR
Bad: pro-apoptotic protein; belongs to Bcl-2 family
Based on the list below determine which of the downstream proteins is activated by AKT:
Mdm2 GSK-3B mTOR HIF-1a FOXO4 Tsc2 NF-KB Bad
o ACTIVATED by AKT Mdm2: anti-apoptotic protein; triggers destruction of p53 HIF-1a: stimulates angiogenesis mTOR: protein synthesis NF-KB
What is the main function of PTEN as part of the PI3K pathway?
Antagonizes PI3K signaling by acting as a lipid phosphatase for PIP3 (converting it back to PIP2)
What would happen if PTEN was downregulated?
Downregulation of PTEN –> increased PIP3 –> hyperactive PKB/AKT signaling
What pathway is the target of stem cells?
NOTCH
Notch plays a critical role in stem cell self-renewal
Describe the process of the Notch pathway?
NOTCH matures in Golgi and is cleaved into 2 fragments forms heterodimer on cell surface
binds DELTA-LIKE or JAGGED ligands
ligand binding triggers 2 sequential proteolytic cleavages:
(1) ADAM family MMPs release extracellular domain
(2) Presenilin-protease (y-secretase) complex releases cytoplasmic domain (NIC)
NIC enters nucleus to activate transcription of HES and HEY
Based on the targets of c-MYC listed below, what are the functions of each of these in regards to the development of cancer? (Hint: They are the hallmarks of cancer)
- IL-1B
- Cyclin D1, CDK4, CDC25, GADD45, E2F1, E2F2, E2F3
- TERT
- VEGF
- EZRIN
- MAD2 and BUBR1
- LDHA and GLUT-1
- ICAM-1
- IL-1B : tumor promoting inflammation
- Cyclin D1, CDK4, CDC25, GADD45, E2F1, E2F2, E2F3: self-sufficient growth signals, resistance to growth inhibition
• Inhibits p21CIP1, p27KIP1 - TERT: limitless replication
- VEGF: angiogenesis
- EZRIN: upregulation of metastasis
- MAD2 and BUBR1: genomic instability
- LDHA and GLUT-1: deregulated metabolism
- ICAM-1: avoidance of immune destruction
What is the activated (“on”) canonical WNT signaling pathway?
- WNT binds to Frizzled/LRP5/6 complex
- cytoplasmic recruitment of Dishevelled
- inactivation of glycogen synthase kinase 3 (GSK3)
- β-catenin stabilized
- translocation to nucleus
- β-catenin acts alongside LEF/TFC to enhance transcription of c-myc, cyclin D1, and MMP-7
What is the in-activated (“off”) canonical WNT signaling pathway?
- WNT is absent
- β-catenin is phosphorylated by a destruction complex (APC, GSK3, AXIN)
- targeted for ubiquitin-dependent proteasomal degradation
- TCF acts with coreceptors such as HDACs and Groucho/transducing-like enhancer of split (TLE) to repress gene transcription
The key mediator of canonical WNT signaling is what?
B-catenin
What are the known target genes of B-catenin?
c-myc, cyclin D1, and MMP-7
Which TSG is part of the WNT pathway and has is encoded by the gene responsible for the onset of familial adenomatous polyposis that predisposes patients to colorectal cancer?
APC (part of the destruction complex)
What is the progression of normal epithelium to a carcinoma in a patient that develops colon cancer?
Normal epithelium (loss of APC)--> hyperplastic epithelium (DNA hypomethylation)--> Early adenoma (activation of K-ras)--> intermediate adenoma (loss of 18q TSG)--> late adenoma (loss of p53)--> carcinoma--> invasion and mets
Describe the “off” HH pathway.
- In the absence of HH, patched silences smoothened (the key signal transducer of pathway)
- If smoothened is silenced, there is prevention of disassembly of the Cos2, FU, SU[FU], Gli complex which is bound to microtubules
- Gli cannot be transfered to the nucleus
Describe the “on” HH pathway.
- Binding of HH to patched prevents the inhibition of smoothened
- Activation of smoothened causes dissassembly of the complex, releasing Gli and allowing nuclear translocation of activated Gli transcription factors and HH target gene expression
What are the target genes of HH signaling?
WNT, BMP, Patched
Which pathway can be a tumor suppressor initially and a tumor promoter in at the end?
TGF-B
o Loss of Rb = cells lose responsiveness to cytostatic effects of TGF-B
o Pushes TGF-B to favor cell proliferation
Which members of the TGF-B family of extracellular ligands perform the following:
(1) inhibit stem cell expansion by suppression of Wnt signaling, (2) induce CSC differentiation, (3) increase sensitivity to chemotherapy in vivo – potential therapeutic approach for CSC drug target
BMPs
Answer the following questions regarding TGF-B:
- What are the 2 major branches of TGF-B superfamily?
- Describe the TGF-B receptor pathway.
- Which receptor signals to Smads?
- Under basal conditions Smad receptors are doing what activity?
- TGF-B/activin/nodal branch
BMP branch – diverse and often complementary effects - TGF-β is synthesized as an inactive precursor and proteolytically processed into a mature ligand –>
must dimerize to becomes active –> binds to type I and II cell surface receptors that contain an intracellular serine-threonine kinase –> heterotrimeric complex –>
phosphorylation and activation of type I receptor by type II - Type I receptor phosphorylates R-SMADs R-SMADs interact with SMAD4 nuclear accumulation and associated with cofactors regulation of target genes
o Smad receptors are in constant motion and shuttle between the nucleus and cytoplasm (predominantly cytoplasmic).
TGF-B phosphorylates which Smads?
Smads 2 and 3
What are the 3 classes of SMADS?
- Receptor-regulated or R-SMADs (SMADS 1, 2, 3, 5, and 8)
- Common mediator or Co-SMAD4
- Inhibitory SMADS 6 and 7
- The SMADS within the TGF-B pathway can be inhibited by what?
- What inhibits TGF-B?
- Inhibitory SMADs: counteract R-SMADs
Ski and Sno inhibit SMAD 3 and 4
SMURF 1/2: E3 ubiquitin ligases that target R-SMAD for degradation - MYC: normally TGF-B overrides Myc (they have opposing functions), but when Myc oncogenes are present, cells become unresponsive to TGF-B signaling