Term
| Why do polypeptide growth factors require tyrosine kinases? |
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Definition
| They are polar, hydrophillic molecules that can't pass the plasma membrane on their own! |
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Term
| What are the common structural features of receptor tyrosine kinases (RTKs)? |
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Definition
1) N-terminal extracellular ligand-binding domain
2) Single transmembrane domain
3) Cytosolic c-terminal domain with protein tyrosine kinase activity |
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Term
| What is the role of autophosphorylation in Receptor Tyrosine Kinase activation? |
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Definition
Ligands bind to extracellular domains, inducing dimerization of the receptor through autophosphorylation and cross phosphorylation, which serves to
1) increase receptor kinase activity
2) Create binding sites for specific proteins |
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Term
| What is the importance of the SH2 domain? SH3? |
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Definition
1) Localizes proteins to plasma membrane, promoting their phosphorylation and associations with other proteins.
Phosphotyrosine residues on autophosphorylated RTKs bind SH2 containing proteins.
2) SH3 domains bind proline-rich sequences to further P-P interactions. |
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Term
| Why/How is phospholipase C-y phosphorylation important for IP3 activation? |
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Definition
PLC-y contains a SH2 domain which interacts with activated receptor tyrosine kinases.
Phosphorylated PLC-y can then cleave PIP2 and produce IP3 and DAG. |
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Term
| Other than the DAG and IP3 pathways, what else is PIP2 cleavage important for? |
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Definition
| AKT (Ser/Thr kinase) signaling is critical for cell survival |
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Term
| How is Ras-GDP activated to induce the MAPK pathway? |
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Definition
Short Answer
Growth factor binds and activates TK, which recruits Sos-bound Grb2. Sos makes GTP-Ras (exchanging GDP), which activates MAPKKK to MAPKK to MAPK
Explanation
1) Growth factor stimulation of tyrosine kinase receptors leading to autophosphorylation
2) Grb2 binds activated receptor (Grb2 is bound to a GEF called "Sos")
3) Sos is localized to plasma membrane where it interacts with Ras-GDP to make Ras-GTP, which can then activate MAPKKK, activating MAPKK, activates MAPK.
4) MAPK phopshorylates cytoplasmic and nuclear proteins. |
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Term
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Definition
GAPs promote the GDP-bound, innactive form of Ras
Interestingly, receptor tyrosine kinases can activate Ras by activating GEFs like Sos or by deactivating GAPs. |
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Term
1) How do cytokine receptors influence the immune response through receptor-binding, despite lacking intrinsic enzyme activity?
2) How are they similar to Serpentine receptors? |
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Definition
1) They act through non-receptor Tyrosine Kinase pathways such as Src and Jak/STAT.
2) Serpentine receptors also act through these pathways |
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Term
| How does the Jak/STAT pathway work in response to cytokine receptor activation via interferon and TNF? |
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Definition
SAT proteins are usually cytoplasmic and inactive.
1) Cytokine receptor stimulation leads to STAT protein binding via Sh2 domains to phosphotyrosine.
2) STAT phosphorylation via JAK non-receptor protein tyrosine kinases (dual kinase domains) associated with cytokine receptors.
3) Phosphotyrosine-STAT proteins dimerize and translocate to the nucleus where they stimulate transcription.
4) In nucleus, STAT proteins activate immediate early genes (not requiring p-synthesis) and delayed-response genes (require p-synthesis) |
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Term
| Why might mutations in protein tyrosine phosphatases receptors be of clinical significance? |
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Definition
They deactivate receptor tyrosine kinases and lead to their endocytosis! Mutations could cause abnormal gene expression via the Jak/STAT pathway.
Dephosphorylate phosphotryrosine residues in membrane-bound and soluble forms
** can sometimes be stimulatory such as in CD45-expressing B and T lymphocytes ** |
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Term
| A patient presents with symptoms indicating Achondroplasia, but you are unsure if it might be hypochondroplasia. How would you determine which disorder it was? |
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Definition
PCR and different locations of FGFR3! These diseases are caused by premature activation of FGFR receptors
Achondroplasia is caused by a single AA mutation in the transmembrane domain of FGFR3.
Hypochondroplasia is caused by a substitution in the split tyrosine kinase domain of FGFR3 (should appear milder, with transient bow-legs and short stature. |
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Term
| How do FGFs act in limb formation? |
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Definition
| They generally bind to receptor tyrosine kinases and signal through MAPK and PLCg, STOPING the proliferation of cells at the epiphyseal growth plate of long bones and facial cartilage. |
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Term
A patient presents with protruding eyes, limb defects and premature fusion of cranial sutures leading to craniosynostosis.
1) What phenotypic features would you use to determine if the patient had Pfiefer syndrome or Crouzon syndrome?
2) What molecular tests could you run? |
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Definition
1) Crouzon patients have normal hands while Pfeiffer individuals have broad thumbs and big toe.
2) Mutations in extracellular domain of FGFR1 cause PFeiffer, while FGFR-2 cause Crouzon. |
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Term
| A fetus dies at birth due to reduced thoracic capacity ad compression of the brainstem. At the autopsy, to determine if the patient had thanatophoric dysplasia (a lethal form of dwarfism), you would test for mutations in what gene and where in that gene? |
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Definition
Either the extracellular portion OR the Tyrosine kinase domain of FGFR3.
Note- the transmembrane domain mutations are associated with achondroplasia, which is not lethal. |
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Term
| Which mutations in FGFR3 are lethal and which can lead to a life with dwarfism? |
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Definition
Extracellular and Tyrosine Kinase domains often cause thanatophoric dysplasia, which is lethal
Transmembrane mutations often cause achondroplasia, which includes disproportionate shortening of long bones. |
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Term
| What are the two mechanisms by which EGFs normally act? |
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Definition
They are synthesized as transmembrane precursors and interact with ErbB receptors ("HERs" in humans)
1) Cleaved to release soluble hormone
2) Function as membrane-acnchored hormone in juxtacrine signalling |
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Term
| EGFRs have a number of ligands produced by multiple genes. Provide some examples. |
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Definition
Fast Answer: EGF (EGF gene), NDG, GGF and ARIA (Neuregulin gene)
Explanation
1) EGF encoded by a single gene
2) EGF-like ligands (Neu differentiation factor "NDF", glial growth factor "GGF", acetycholine receptor inducing activity "ARIA) encoded by neuregulin gene (NRG) |
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Term
| Why is ErbB-3 receptor an example where ligand binding is not sufficient to activate a receptor? |
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Definition
| ErbB-3 must "heterodimerize" with other ErbB proteins to be sensitive to EGF and to achieve normal development, because homodimers are inactive. |
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Term
| Provide 4 methods that determine EGF response specificity. |
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Definition
Fast Answer- 1 receptor and many ligands, 1 ligand and many receptors, homo and heterodimeric receptor forms, diversity of recruited signals
1. Single receptor binds multiple hormones with different effects
2. Single ligand binds multiple receptors
3. EGFR dimerisation can take place between identical molecules or with related Erb receptors (homo and heterodimers)
4. Diversity of recruited signals in response to receptor phosphorylation |
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Term
| Over-expression of certain EGFRs such as Her2 have been implicated in cancer progression. What are 4 possible therapeutic interventions? |
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Definition
Short- 1) Growth factor-receptor interaction
2) Intrinsic tyrosine kinase activity
3) Immunotoxin
4) Antisense
1. Growth-factor reception- use antibodies to bind to extracellular domain to
a) block growth factor-receptor interaction
b) induce immune responses that cause cell lysis
c) modulate downstream signal transduction
-drugs include Herceptin and Panitumamab
2) Interfere with intrinsic kinase activity to block receptor activation
a) ATP analogues that compete and block RTK activation (Erolotinib hydrochloride named "Tarceva")
b) "Gleevac" binds to non-receptor tyrosine kinase abl AND TRK- potent inhibitor of abnormal tyrosine kinase generated in Chronic myeloid leukemia.
3) Immunotoxins- contain bacterial toxins such as diptheria, which fuse with growth factors, biniding to RTK. They are internalized and inhibit protein synthesis in cytosol leading to cell death.
4) Antisense strategies- targeted to regions of receptor or growth factor. |
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Term
| What is DAB389EGF and how is it used to treat cancer? |
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Definition
Fusion protein between EGF and diphtheria toxin used to treat breast and small lung cancers.
Example of "Immunotoxin" therapy. |
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Term
| Why might you treat a patient with Gleevac? |
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Definition
inhibits abnormal tyrosine kinase generated in Chronic myeloid leukemia.
Binds non-receptor tyrosine kinase "abl" as well as other tRK such as PDGFR and cKit
An Example of treating cancer by interfering with intrinsic kinase activity. |
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Term
| Why would you treat with drugs like Erlotinib hydrochloride (also called "Tarceva") and Iressa |
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Definition
They are ATP analogues used to treat breast, ovarian and colon cancer that express EGFR and its ligand TGFa.
Compete with ATP binding site to block RTK activation. |
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Term
| What are Herceptin, Cetuximab and Panitumumab used for? |
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Definition
Anticancer drugs that interfere with growth factor reception (antibodies) by:
a) block growth factor-receptor interactions
b) induce immune responses that cause cell lysis and death
c) modulate downstream signal transduction cascades. |
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