Signaling #10 Flashcards
What is the main focus of today’s lecture?
Introduction to receptor tyrosine kinase (RTK) signaling
The lecture covers signaling modules, dimerization, and the activation of RTKs.
What is GPCR desensitization?
The process by which G-protein coupled receptors (GPCRs) become less responsive to stimulation over time.
What are the five well-known classes of enzyme-linked cell surface receptors?
- Receptor guanylyl cyclases
- Receptor tyrosine kinases (RTKs)
- Tyrosine-kinase associated receptors
- Receptor tyrosine phosphatases
- Receptor serine/threonine kinases
What role does phosphorylation of tyrosine residues play in cellular signaling?
It is the major mechanism for receptor signal transduction, mediating processes like cell growth and differentiation.
True or False: Tyrosine phosphorylation is more common than serine/threonine phosphorylation.
False
What activates receptor tyrosine kinases (RTKs)?
Ligand/agonist binding leading to dimerization and activation of the catalytic domain.
What is the significance of dimerization for RTK activation?
Dimerization is critical for the activation of RTKs, allowing the intracellular kinase domains to be in proper orientation for transphosphorylation.
What are Src homology (SH) domains?
Protein domains that mediate protein-protein interactions in cellular signaling cascades.
Fill in the blank: The first cancer-causing retrovirus to be isolated is the _______.
Rous sarcoma virus
What is the role of SH1, SH2, and SH3 domains in proteins?
- SH1: Catalytic domain with kinase activity
- SH2: Binds phospho-tyrosine peptides
- SH3: Interacts with proline-rich peptides
What occurs upon ligand binding to RTKs?
Dimerization and activation of the receptor, leading to transphosphorylation of tyrosines.
What is the function of receptor tyrosine phosphatases?
They remove phosphate groups from tyrosine residues of specific intracellular signaling molecules.
What is the significance of tyrosine kinases (TKs) in cellular processes?
They mediate cell growth, differentiation, host defense, and metabolic regulation.
What is the unique feature of the insulin receptor kinase (IRK) compared to other RTKs?
It is activated through conformational changes without requiring dimerization.
True or False: All receptor tyrosine kinases exist as monomers in the resting cell membrane.
False
What is the primary mechanism by which activated tyrosine kinases exert their effects?
Phosphorylation of target proteins’ tyrosine residues.
What is a threshold model in relation to receptor tyrosine kinase signaling?
A proposed model that explains signaling specificity and cell fate determination based on receptor activation.
How do tyrosine kinases differ from serine/threonine kinases?
Tyrosine kinases specifically phosphorylate tyrosine residues, while serine/threonine kinases phosphorylate serine and threonine residues.
What happens to RTKs upon ligand binding?
They dimerize and become activated, leading to downstream signaling events.
What are the various versions of the TrkB receptor?
Full length TrkB with SH1 catalytic domains, truncated versions TrkB.T1 and TrkB.T2
Truncated versions have a ligand binding domain and transmembrane domain but no catalytic domain.
What happens when TrkB receptors become activated?
They modify calcium channels in the membrane, leading to the release of radioactive 45Ca++
This is used to assess TrkB receptor activation/response.
What is the purpose of the experiment discussed in the text?
To determine whether dimerization of full length TrkB receptors is required for activation and release of 45Ca++.
What occurs when full length TrkB receptors are expressed and exposed to BDNF?
They dimerize, become activated, and result in calcium efflux, releasing radioactive Ca++.
What is the outcome when a truncated form of the TrkB receptor (T1) is expressed in Xenopus oocytes?
They can bind BDNF but do not elicit a cellular response due to lack of a catalytic domain.
What effect does co-expression of TrkB with truncated T1 receptors have?
Proportional reductions in calcium efflux from the cells when exposed to BDNF.
What is the dominant effect of truncated TrkB receptors on cell signaling?
They have a dominant inhibitory effect, reducing the probability of homodimer assembly of full length TrkB.
What is the role of tyrosine phosphorylation in RTK signaling?
Increases kinase activity and creates high-affinity binding sites for intracellular signaling proteins.
Which proteins are involved in the signaling cascade initiated by RTK activation?
Phospholipase Cγ, SRC tyrosine kinases, and adaptor proteins such as Grb-2.
What is the function of Grb-2 in RTK signaling?
It recruits SOS and activates Ras.
What is the significance of Ras in cellular signaling?
Ras is a small monomeric G-protein that switches between active and inactive states, regulated by GEFs and GAPs.
True or False: Mutant Ras proteins can dissociate GTP.
False
Mutant Ras proteins are unable to dissociate GTP, remaining in the ON state.
What is the role of GEFs and GAPs in Ras signaling?
GEFs activate Ras by facilitating GTP exchange, while GAPs accelerate the hydrolysis of GTP to GDP.
What happens to G-proteins when GDP is exchanged for GTP?
The G-protein is activated and can stimulate various signaling responses.
What distinguishes monomeric G-proteins like Ras from trimeric G-proteins?
Monomeric G-proteins consist of a single subunit, while trimeric G-proteins have three subunits (e.g., Gs, Gi, Gq).
What is the role of SOS in the RTK MAPK pathway?
SOS is a GEF that regulates Ras activity.
What are the domains of Grb-2?
SH2 and SH3 domains.
Fill in the blank: The SH2 domain of Grb-2 binds to specific ______ on activated RTKs.
phosphotyrosines
How does Grb-2 link activated RTKs to downstream signaling proteins?
By acting as an adaptor protein that couples them to Ras.
