cell signaling 2 lectures

Question 1

Mechanisms by which a cell responds to an external signal—intercellular processes that result in responding cell.
1, 2, 3. Secretion of a signaling molecule (Ligand) from signaling cell 4. Ligand binds to a receptor on a different cell (Responding cell)
5. This Ligand/Receptor interaction causes a series of intracellular events leading to changes in:
Gene Expression Motility Metabolism Gene expression Contractility
Cell adhesion Development

Answer 1

Mechanisms by which a cell responds to an external signal—intercellular processes that result in responding cell.
1, 2, 3. Secretion of a signaling molecule (Ligand) from signaling cell 4. Ligand binds to a receptor on a different cell (Responding cell)
5. This Ligand/Receptor interaction causes a series of intracellular events leading to changes in:
Gene Expression Motility Metabolism Gene expression Contractility
Cell adhesion Development

Question 2

Types of Cell Signaling

4

Answer 2

Types of Cell Signaling
Signaling Molecules can act locally or a distance:
1. Endocrine:atadistance
2. Paracrine:cellsareatacloserange,juxtaposed
3. Autocrine:signalingtothesamecell
4. CellSurfacetoCellSurface:boththereceptorandtheligandareattachedtothe
cell surface

Question 3

Endocrine: The ligand is secreted by one type of cell and the ligand is transported a long distance to act on cells expressing the receptor.
e.g. Hormone secretion by an endocrine gland

Answer 3

Endocrine: The ligand is secreted by one type of cell and the ligand is transported a long distance to act on cells expressing the receptor.
e.g. Hormone secretion by an endocrine gland

Question 4

Paracrine: Secretory cells and the target cells expressing the receptor are within a close and diffusible range.

Answer 4

Paracrine: Secretory cells and the target cells expressing the receptor are within a close and diffusible range.

Question 5

Autocrine: The cell secreting the ligand also express the receptor. This can be referred to as self signaling.

Answer 5

Autocrine: The cell secreting the ligand also express the receptor. This can be referred to as self signaling.

Question 6

cell Surface to Cell Surface: One cell expresses the membrane bound receptor and the other cell expresses the membrane bound ligand.
Requires close cell to cell interaction.

Answer 6

ell Surface to Cell Surface: One cell expresses the membrane bound receptor and the other cell expresses the membrane bound ligand.
Requires close cell to cell interaction.

Question 7

Classes of Receptors

Answer 7

Classes of Receptors

1. Transmembrane Receptors: Receptorsareintegralmembraneproteins,thatis, they embedded in the plasma membrane via a transmembrane domain.
2. Intracellular Receptors: Receptors are located within the cytoplasm. They bind to ligands that either diffuse or are transported into the cytoplasm. Intracellular Receptors function as transcription factors that directly regulate transcription of target genes.

Question 8

1. TransmembraneReceptors:

Answer 8

1. TransmembraneReceptors:Receptorsareintegralmembraneproteins,thatis, they embedded in the plasma membrane via a transmembrane domain.

Question 9

2. Intracellular Receptors: Receptors are located within the cytoplasm. They bind to ligands that either diffuse or are transported into the cytoplasm. Intracellular Receptors function as transcription factors that directly regulate transcription of target genes.

Answer 9

2. Intracellular Receptors: Receptors are located within the cytoplasm. They bind to ligands that either diffuse or are transported into the cytoplasm. Intracellular Receptors function as transcription factors that directly regulate transcription of target genes.

Question 10

Transmembrane Receptors

Answer 10

ll transmembrane receptors have an extracellular domain which binds ligand, a transmembrane domain and an intracellular domain.

Question 11

Intracellular Receptors: form complexes with ligand in the cytoplasm, move to the nucleus and promote transcription

Answer 11

Intracellular Receptors: form complexes with ligand in the cytoplasm, move to the nucleus and promote transcription

Question 12

Types of Transmembrane receptors

Answer 12

notes

Question 13

G-protein Coupled Receptors:
• size of protein families?
•# different types of receptors
• __% of coded genes

Answer 13

1. G-protein Coupled Receptors:
   • One of the largest protein families • >1000 different types of receptors • >3% of coded genes

• Receptors for:
– light, odor molecules
– Histamine, dopamine, serotonin
– Protein and peptide hormones

Question 14

Structure/Function of G-protein Coupled Receptors

Seven transmembrane receptors:

Answer 14

Seven transmembrane receptors:
• N-terminus contains the ligand binding
domain.
• 7 transmembrane domains
• These receptors signal through G-proteins
• G-Proteins are “hetero-trimeric” They contain 3 different subunits: α, β, γ

Question 15

. Secondary Messengers of G-protein Coupled Receptors

Activated G proteins signal to second messengers

Answer 15

. Secondary Messengers of G-protein Coupled Receptors
Activated G proteins signal to second messengers
• cAMP ( through adenylyl cyclase) • Inositol 1,4,5-triphosphate (IP3)
• Diacytglycerol (DAG)
• Ca2+/Calmodulin
• Nitric Oxide (NO)

Question 16

Types of Gα proteins: ****

Answer 16

Types of Gα proteins:
G-Protein α Subunit
Gαs Gαi Gαq
Gα(12/13)
2nd Messenger
cAMP cAMP
IP3 and DAG
GDP-GTP exchange
Activity
Stimulates Adenylyl Cyclase Inhibits Adenylyl Cyclase
Stimulates Phospholipase Cβ Stimulates cytoskeletal
proteins
Muise-Helmericks, Cell Signaling

Question 17

Molecular Mechanism of G-protein Coupled Receptor Signal Transduction

Answer 17

1. In the resting state G alpha subunit is bound to GDP.
2. Upon ligand binding the G-protein undergoes a conformational change that results in the release of GDP and the binding of GTP. GDP to GTP exchange causes the α subunit to dissociate from the β and γ subunits
3. GTP bound Gα can then bind to target enzymes such as adenylyl cyclase which is then activated to catalyze the reaction of ATP→cAMP.
4. When GTP is hydrolyzed to GDP, Gα dissociates from the target protein and is available to re-associate with the G proteins to reform the resting G-protein coupled receptor

Question 18

Different Gα protein subunits signal to different effectors (see table above)

Answer 18

Different Gα protein subunits signal to different effectors (see table above)

Question 19

Role of Second Messengers in G-protein Coupled Receptor Signaling 1. cAMP-produced by activation of
adenylyl cyclase
Adenylyl cyclase converts ATP to cAMP
cAMP levels are controlled by cAMP phosphodiesterases which cleave the cyclic nucleotide to AMP

Answer 19

Role of Second Messengers in G-protein Coupled Receptor Signaling 1. cAMP-produced by activation of
adenylyl cyclase
Adenylyl cyclase converts ATP to cAMP
cAMP levels are controlled by cAMP phosphodiesterases which cleave the cyclic nucleotide to AMP
cAMP is an activator of protein kinase A (PKA), a serine threonine protein kinase that phosphorylates a large number of metabolic enzymes.
PKA is composed of four subunits; two regulatory subunits and two catalytic subunits.
Four molecules of cAMP are required to activate PKA.
Upon cAMP binding to the regulatory subunits of PKA, the catalytic subunits dissociate.
The catalytic subunits are then free to phosphorylate and regulate PKA target proteins.

Question 20

P3 and DAG
G-protein coupled receptors that activate Gαq stimulate phospholipase C (PLCβ) to phosphorylate lipids called phosphtidylinositols to form DAG and IP3
PIP2 (phosphatidylinositol 4,5-bisphosphate) →DAG, IP3 (inositol 1,4,5-trisphosphate)
Both IP3 and DAG are required to activate protein kinase C (PKC)
IP3 binds calcium channels in the endoplasmic reticulum to trigger Ca2+ release

Answer 20

P3 and DAG
G-protein coupled receptors that activate Gαq stimulate phospholipase C (PLCβ) to phosphorylate lipids called phosphtidylinositols to form DAG and IP3
PIP2 (phosphatidylinositol 4,5-bisphosphate) →DAG, IP3 (inositol 1,4,5-trisphosphate)
Both IP3 and DAG are required to activate protein kinase C (PKC)
IP3 binds calcium channels in the endoplasmic reticulum to trigger Ca2+ release
DAG binds to PKC directly

Question 21

PKC is a monomer that contains regulatory and catalytic domains.
The regulatory domains bind to Ca2+ and DAG.
This figure shows that inactive PKC undergoes a conformational change upon binding to Ca2+ and DAG, and that active PKC translocates to the plasma membrane.
The catalytic domain of activated PKC phosphorylates target proteins.

Answer 21

PKC is a monomer that contains regulatory and catalytic domains.
The regulatory domains bind to Ca2+ and DAG.
This figure shows that inactive PKC undergoes a conformational change upon binding to Ca2+ and DAG, and that active PKC translocates to the plasma membrane.
The catalytic domain of activated PKC phosphorylates target proteins.

Question 22

This figure shows PKC in green in untreated cells and those treated with PMA, an activator of PKC. Notice the membrane localization of PKC

Answer 22

This figure shows PKC in green in untreated cells and those treated with PMA, an activator of PKC. Notice the membrane localization of PKC

Question 23

This Table shows that Ca2+ flux through IP3 also affects other proteins.

Answer 23

Ca Regulated Proteins
Functions
Ca activated Cl channels
secretion
Ca activated K+ channels
Membrane potentials
Protein Kinase C
Phosphorylates and activates other proteins
Adenylyl cyclase
Produces cAMP
Nitric oxide synthetase (NOS1, 2, 3)
Produces Nitric oxide

Question 24

Calcium and Cell Injury:
Increased Calcium inside the cell can cause the activation of enzymes that result in cell damage.
It has to be tightly controlled

Answer 24

Calcium and Cell Injury:
Increased Calcium inside the cell can cause the activation of enzymes that result in cell damage.
It has to be tightly controlled

Question 25

Ca2+/Calmodulin
Ca2+ overload can lead to cell death via increased apoptosis and decreased mitochondrial integrity.
Free Ca2+ must therefore be tightly regulated.
The major Ca2+ regulator is a chaperone called Calmodulin
Calmodulin- Ca2+ chaperone (a protein that shuttles proteins or molecules to where they are needed in the cell)
Each Calmodulin can bind 4 molecules of Ca2+ (Figure) Most Ca2+ is bound to Calmodulin.
Calmodulin brings Ca2+ to Calcium responsive proteins

Answer 25

Ca2+/Calmodulin
Ca2+ overload can lead to cell death via increased apoptosis and decreased mitochondrial integrity.
Free Ca2+ must therefore be tightly regulated.
The major Ca2+ regulator is a chaperone called Calmodulin
Calmodulin- Ca2+ chaperone (a protein that shuttles proteins or molecules to where they are needed in the cell)
Each Calmodulin can bind 4 molecules of Ca2+ (Figure) Most Ca2+ is bound to Calmodulin.
Calmodulin brings Ca2+ to Calcium responsive proteins

Question 26

Calcium in Muscle Contraction: example of Ca2+/calmodulin complexes:
• Ca2+ /Calmodulin complexes bind MLCK
• This allows for a conformational change to activate the kinase
• Activated MLCK then can phosphorylate downstream targets such as myosin light
chain →Contraction

Answer 26

Calcium in Muscle Contraction: example of Ca2+/calmodulin complexes:
• Ca2+ /Calmodulin complexes bind MLCK
• This allows for a conformational change to activate the kinase
• Activated MLCK then can phosphorylate downstream targets such as myosin light
chain →Contraction

Question 27

Nitric Oxide

Answer 27

NO is an oxygen containing free radical that in small concentrations is essential for cellular function.
Diffuses rapidly through membranes (no channels needed)
First shown to be secreted by macrophage to kill microorganisms and tumor cells
NO can activate Guanylate Cyclase: produces cGMP from GTP
This can activate PKG (a serine threonine protein kinase)
Breakdown of cGMP is inhibited by Viagra, a cGMP phosphodiesterase inhibitor
NO is required for:
• smooth muscle relaxation
• vasodilation, increased blood flow
• angiogenesis
cGMP can effect cAMP turnover, Ca flux, and PKG

Question 28

Summary of G-protein Coupled Receptors:
• 7-transmembrane spanning domains
• Intracellular domain coupled to G-proteins
• Signal to second messengers: cAMP, IP3, DAG, NO
• Two major kinases are activated: PKA, PKC
• Ca2+ levels are tightly controlled and chaperoned in the cell by Calmodulin

Answer 28

Summary of G-protein Coupled Receptors:
• 7-transmembrane spanning domains
• Intracellular domain coupled to G-proteins
• Signal to second messengers: cAMP, IP3, DAG, NO
• Two major kinases are activated: PKA, PKC
• Ca2+ levels are tightly controlled and chaperoned in the cell by Calmodulin

Question 29

Target for the majority of best-selling drugs (___%-__% of all prescription pharmaceuticals on the market).

examples

Answer 29

G-proteins

Target for the majority of best-selling drugs (40%-50% of all prescription pharmaceuticals on the market).
Examples:
– Zyprexa (bipolar disorder & schizophrenia, Eli Lilly)
– Clarinex (antihistamine against seasonal & year-round allergies,
– Schering-Plough)
– Zantac (treat and prevent ulcers in the stomach and intestines; histamine
receptor antagonists, GlaxoSmithKline)
– Zelnorm (severe, chronic, irritable bowel syndrome (IBS); increases the
action of serotonin in the intestines, Novartis)

Question 30

Kinase and Kinase Associated Receptors
• These receptors are generally single-pass transmembrane proteins.
• A ligand binds to a domain on the extracellular surface and promotes dimerization
• Dimerization is required for the phosphorylation of the receptor
• Phosphorylation either causes activation of either an intrinsic kinase (part of the
receptor) or an associated kinase.
• Phosphorylation of the receptor generates binding sites in the intracellular domain
to which signal transduction proteins dock and initiate cell signaling pathways.

Answer 30

Kinase and Kinase Associated Receptors
• These receptors are generally single-pass transmembrane proteins.
• A ligand binds to a domain on the extracellular surface and promotes dimerization
• Dimerization is required for the phosphorylation of the receptor
• Phosphorylation either causes activation of either an intrinsic kinase (part of the
receptor) or an associated kinase.
• Phosphorylation of the receptor generates binding sites in the intracellular domain
to which signal transduction proteins dock and initiate cell signaling pathways.

Question 31

ypes of Kinase and Kinase-associated Receptors
Receptor Tyrosine Kinases: Growth Factors such as Epidermal Growth Factor (EGF) Fibroblast Growth Factor (FGF), Nerve Growth Factor (NGF), Insulin and Insulin-like Growth Factor 1 (IGF-1)
JAK-STAT Receptors: Growth Hormone (GH), Prolactin and Cytokines such as the Interleukin family
Receptor Serine-Threonine Kinases: Transforming Growth Factor superfamily such as TGF-β and BMP (Bone Morphogenetic Protein)
Muise-Helmericks, Cell Signaling

Answer 31

ypes of Kinase and Kinase-associated Receptors
Receptor Tyrosine Kinases: Growth Factors such as Epidermal Growth Factor (EGF) Fibroblast Growth Factor (FGF), Nerve Growth Factor (NGF), Insulin and Insulin-like Growth Factor 1 (IGF-1)
JAK-STAT Receptors: Growth Hormone (GH), Prolactin and Cytokines such as the Interleukin family
Receptor Serine-Threonine Kinases: Transforming Growth Factor superfamily such as TGF-β and BMP (Bone Morphogenetic Protein)
Muise-Helmericks, Cell Signaling

Question 32

Structure and function of the EGF Receptor: Also called Erb-B
Ligand Binding Domain: Region where the growth factor (EGF) binds to promote dimerization.
In the resting (inactive) state,
EGF receptors exist as monomers.
Ligand binding causes dimerization.
Transmembrane Domain: An α-helical domain formed by hydrophobic amino acids that span the plasma membrane
Kinase Domain: Dimerization generates an active site that catalyzes cross-phosphorylation on tyrosine residues.
Signal Transducer (Effector): phospho tyrosine residues provide “docking” sites for effector proteins that contain domains that can bind to tyrosines (SH2 domains).

Answer 32

Structure and function of the EGF Receptor: Also called Erb-B
Ligand Binding Domain: Region where the growth factor (EGF) binds to promote dimerization.
In the resting (inactive) state,
EGF receptors exist as monomers.
Ligand binding causes dimerization.
Transmembrane Domain: An α-helical domain formed by hydrophobic amino acids that span the plasma membrane
Kinase Domain: Dimerization generates an active site that catalyzes cross-phosphorylation on tyrosine residues.
Signal Transducer (Effector): phospho tyrosine residues provide “docking” sites for effector proteins that contain domains that can bind to tyrosines (SH2 domains).
c. Molecular Mechanisms of EGF Receptor Signal Transduction:

Question 33

effector proteins

Answer 33

notes

Question 34

Ligand Binding Domain: Region where the growth factor (EGF) binds to promote dimerization.

Answer 34

Ligand Binding Domain: Region where the growth factor (EGF) binds to promote dimerization.

Question 35

Transmembrane Domain: An α-helical domain formed by hydrophobic amino acids that span the plasma membrane

Answer 35

Transmembrane Domain: An α-helical domain formed by hydrophobic amino acids that span the plasma membrane
Kinase Domain: Dimerization generates an active site that catalyzes cross-phosphorylation on tyrosine residues.
Signal Transducer (Effector): phospho tyrosine residues provide “docking” sites for effector proteins that contain domains that can bind to tyrosines (SH2 domains).

Question 36

Kinase Domain: Dimerization generates an active site that catalyzes cross-phosphorylation on tyrosine residues.

Answer 36

Kinase Domain: Dimerization generates an active site that catalyzes cross-phosphorylation on tyrosine residues.
Signal Transducer (Effector): phospho tyrosine residues provide “docking” sites for effector proteins that contain domains that can bind to tyrosines (SH2 domains).

Question 37

Signal Transducer (Effector): phospho tyrosine residues provide “docking” sites for effector proteins that contain domains that can bind to tyrosines (SH2 domains).

Answer 37

Signal Transducer (Effector): phospho tyrosine residues provide “docking” sites for effector proteins that contain domains that can bind to tyrosines (SH2 domains).

Question 38

Molecular Mechanisms of EGF Receptor Signal Transduction: 1. Growth factor binding, dimerization and cross phosphorylation.

Answer 38

Molecular Mechanisms of EGF Receptor Signal Transduction:
1. Growth factor binding, dimerization and cross phosphorylation.
2. Docking of effector proteins that promote a signaling cascade:
Grb2 is a signal transducer protein that contains an SH2 domain for binding to Tyr-P residues in the EGF receptor.
SH2 domains bind to phosphorylated tyrosine residues

Docking of Grb2 recruits a guanine nucleotide exchange protein (GEF) that activates Ras by exchange of GDP for GTP.
Ras-GTP binds to and activates Raf, a serine protein kinase in MAP kinase pathway.
MAP Kinase (MAPK) is activated by phosphorylation. MAPK-Pi phosphorylates many effector proteins in the cytosol and the nucleus to regulate cell signaling, gene expression, cell growth and development, and cell survival.

EGF Receptors are a family of receptor tyrosine kinases called the ErbB family. Each family member can form heterodimers.
Heterodimer formation increases specificity and complexity of the signaling cascades.
So in addition to EGF, these receptors can also bind other ligands such as neuregulins and affect numerous different cell types.

Question 39

d. Structure and function of the Insulin Receptor
Insulin receptor exists as a heterotetramer composed of 2 alpha and 2 beta subunits.
A disulfide linkage between the α subunits hold the 2 halves of the receptor together.
This is different than all other tyrosine kinase receptors.
Upon insulin binding there is a conformational change that “opens” the kinase domains in the β subunit and allows for cross phosphorylation.
α Subunit: Contains the hormone binding domain

Answer 39

d. Structure and function of the Insulin Receptor
Insulin receptor exists as a heterotetramer composed of 2 alpha and 2 beta subunits.
A disulfide linkage between the α subunits hold the 2 halves of the receptor together.
This is different than all other tyrosine kinase receptors.
Upon insulin binding there is a conformational change that “opens” the kinase domains in the β subunit and allows for cross phosphorylation.
α Subunit: Contains the hormone binding domain
β Subunit: Contains an α-helical domain that spans the membrane and a tyrosine kinase domain that catalyzes cross-phosphorylation of the receptor on multiple tyrosine residues
Proteins with SH2 domains such as IRS bind to phosphotyrosine sites in the receptor
Insulin Receptor Substrate (IRS): Phosphorylated by the receptor on multiple tyrosine residues.

Question 40

α Subunit: Contains the hormone binding domain

Answer 40

α Subunit: Contains the hormone binding domain

Question 41

β Subunit: Contains an α-helical domain that spans the membrane and a tyrosine kinase domain that catalyzes cross-phosphorylation of the receptor on multiple tyrosine residues

Answer 41

β Subunit: Contains an α-helical domain that spans the membrane and a tyrosine kinase domain that catalyzes cross-phosphorylation of the receptor on multiple tyrosine residues

Question 42

Insulin Receptor Substrate (IRS): Phosphorylated by the receptor on multiple tyrosine residues.

Answer 42

Insulin Receptor Substrate (IRS): Phosphorylated by the receptor on multiple tyrosine residues.

Question 43

Phosphorylation of IRS1 allows for the docking and activation of effector molecules:
• Grb2
• PLCγ (which promotes IP3 and DAG formation)—Remember back to G-protein
coupled receptors. The gamma isoform associates with IRS1
• PI3 Kinase (phosphoinositol 3-kinase):

Answer 43

Phosphorylation of IRS1 allows for the docking and activation of effector molecules:
• Grb2
• PLCγ (which promotes IP3 and DAG formation)—Remember back to G-protein
coupled receptors. The gamma isoform associates with IRS1
• PI3 Kinase (phosphoinositol 3-kinase):

Question 44

PI-3 Kinase converts the membrane lipid PIP2 (phosphatidylinositol 4,5-bisphosphate) to PIP3 (phosphatidylinositol 3, 4, 5 trisphosphate).
PIP3 functions as a membrane docking site for proteins with pleckstrin homology (PH) domains such as Protein Kinase B (PKB/Akt) and Phosphoinositide-dependent Kinase (PDK1).
PKB (Akt) is a serine-threonine kinase is activated by phosphorylation. Activated PKB regulates GLUT4 translocation and signaling pathways involved in cell growth, proliferation, cell survival and protein synthesis.

Answer 44

PI-3 Kinase converts the membrane lipid PIP2 (phosphatidylinositol 4,5-bisphosphate) to PIP3 (phosphatidylinositol 3, 4, 5 trisphosphate).
PIP3 functions as a membrane docking site for proteins with pleckstrin homology (PH) domains such as Protein Kinase B (PKB/Akt) and Phosphoinositide-dependent Kinase (PDK1).
PKB (Akt) is a serine-threonine kinase is activated by phosphorylation. Activated PKB regulates GLUT4 translocation and signaling pathways involved in cell growth, proliferation, cell survival and protein synthesis.

Question 45

Activation of PKB (Akt) results in:
• phosphorylation and activation of transcription factors that are involved in cell
growth and proliferation.
• phosphorylation of BAD (a pro-apoptotic protein)—Akt activation is a major cell
survival factor.
• mTOR—sensor of nutrient levels (important for control of autophagy) and
controller of protein synthesis.

Answer 45

Activation of PKB (Akt) results in:
• phosphorylation and activation of transcription factors that are involved in cell
growth and proliferation.
• phosphorylation of BAD (a pro-apoptotic protein)—Akt activation is a major cell
survival factor.
• mTOR—sensor of nutrient levels (important for control of autophagy) and
controller of protein synthesis.

Question 46

Structure and function of the JAK-STAT Receptors
These receptors have no intrinsic tyrosine kinase activity.
They associate with tyrosine kinases known as Janus Kinases (JAK). Upon ligand binding, receptors will dimerize and bind JAKs.
JAKs will phosphorylate eachother and the receptor
Allows for activation of STAT transcription factors.
Each monomer has several domains:
• Ligand binding domain: Specific binding to cytokines and other ligands
• Transmembrane domain: α-Helical domain that spans the plasma membrane
• JAK binding domain: Binding site for JAK; phosphorylation of the receptor by JAK
creates phosphotyrosine sites to which STATs (Signal Transducer and Activator of Transcription) bind

Answer 46

Structure and function of the JAK-STAT Receptors
These receptors have no intrinsic tyrosine kinase activity.
They associate with tyrosine kinases known as Janus Kinases (JAK). Upon ligand binding, receptors will dimerize and bind JAKs.
JAKs will phosphorylate eachother and the receptor
Allows for activation of STAT transcription factors.
Each monomer has several domains:
• Ligand binding domain: Specific binding to cytokines and other ligands
• Transmembrane domain: α-Helical domain that spans the plasma membrane
• JAK binding domain: Binding site for JAK; phosphorylation of the receptor by JAK
creates phosphotyrosine sites to which STATs (Signal Transducer and Activator of Transcription) bind

Question 47

each monomer has several domains:

Answer 47

• Ligand binding domain: Specific binding to cytokines and other ligands
• Transmembrane domain: α-Helical domain that spans the plasma membrane
• JAK binding domain: Binding site for JAK; phosphorylation of the receptor by JAK
creates phosphotyrosine sites to which STATs (Signal Transducer and Activator of Transcription) bind

Question 48

Molecular Mechanisms for JAK/STAT signaling:

Answer 48

1. Binding of ligand promotes dimerization of the receptor and cross-phosphorylation of JAK.
2. Activated JAK generates phosphotyrosine binding sites in the JAK-STAT receptor.
3. STATs bind to the phosphotyrosine sites in the receptor via SH2 domains.
4. STATs “docked” to the receptor are phosphorylated by JAK and dissociate.
5. Phosphorylated STATs dimerize and translocate to the nucleus to activate transcription of target genes.

Question 49

Structure and function of the Receptor Serine-Threonine Kinases
These receptors generally are composed of Type I and Type II receptors, each of which has a serine-threonine kinase domain.
• Ligand binding domain: Specific binding site for TGFβ and other ligands
• Transmembrane domain: α-helical region that spans the plasma membrane
• Serine-Threonine Kinase domain-has an intrinsic serine-threonine kinase

1. Binding of ligand to the Type II receptor causes recruitment of Type I receptor and formation of a stable receptor complex.
2. Type II receptor catalyzes serine phosphorylation of Type I receptor. The type II receptor does not signal to SMADs, only the Type 1 receptor does—obligate heterodimer.
3. Phosphorylation of Type I receptor activates its intrinsic serine-threonine kinase.
4. R-Smads are phosphorylated on serines by the activated Type I receptor.
5. Phosphorylated R-Smads dissociate from the Type I receptor and forms a complex with a Co- Smad (Smad4). R-Smads/Co-Smad complex translocates to the nucleus and binds to cis-acting elements in hundreds of target genes, thereby regulating transcription.

Answer 49

Structure and function of the Receptor Serine-Threonine Kinases
These receptors generally are composed of Type I and Type II receptors, each of which has a serine-threonine kinase domain.
• Ligand binding domain: Specific binding site for TGFβ and other ligands
• Transmembrane domain: α-helical region that spans the plasma membrane
• Serine-Threonine Kinase domain-has an intrinsic serine-threonine kinase

Question 50

Downstream effects of TGFβ and Bone morphogenic proteins:
Transforming growth factor-β (TGF-β) is a multifunctional cytokine involved in regulation of the following:
a. differentiation and development
b. stimulation of extracellular matrix synthesis and deposition
c. inflammation and allergy
d. Generally anti-proliferative and inhibits cell growth
e. Epithelial to mesenchymal transitions (EMT) and metastatic cancer

Answer 50

Downstream effects of TGFβ and Bone morphogenic proteins:
Transforming growth factor-β (TGF-β) is a multifunctional cytokine involved in regulation of the following:
a. differentiation and development
b. stimulation of extracellular matrix synthesis and deposition
c. inflammation and allergy
d. Generally anti-proliferative and inhibits cell growth
e. Epithelial to mesenchymal transitions (EMT) and metastatic cancer

Question 51

Summary of Transmembrane Receptors so far:
1. G-protein Coupled Receptors
2. Kinase or Kinase Associated Receptors:
• Receptor Tyrosine Kinases: EGF-dimerization,crossphosphorylation, RAS/MAPK activation Insulin-conformational change, IRS1 binding, PI3K/PKB activation
• JAK-STAT Receptors-growth hormone, prolactin, no intrinsic kinase (associates with JAK) activates STAT transcription factor
• Receptor Serine-Threonine Kinases-obligate heterodimer, type II receptor phosphorylates type I receptor, phosphorylation of SMAD transcription factors
Muise-Helmericks, Cell Signaling

Answer 51

Summary of Transmembrane Receptors so far:
1. G-protein Coupled Receptors
2. Kinase or Kinase Associated Receptors:
• Receptor Tyrosine Kinases: EGF-dimerization,crossphosphorylation, RAS/MAPK activation Insulin-conformational change, IRS1 binding, PI3K/PKB activation
• JAK-STAT Receptors-growth hormone, prolactin, no intrinsic kinase (associates with JAK) activates STAT transcription factor
• Receptor Serine-Threonine Kinases-obligate heterodimer, type II receptor phosphorylates type I receptor, phosphorylation of SMAD transcription factors
Muise-Helmericks, Cell Signaling

Question 52

Ion Channel Receptors
a. Structure and function of ion channel receptors:
Ion channels are integral membrane proteins that control the flow of ions (Ca2+, Na/K, Cl) across the cell membrane.
Classified by “gating”—what opens or closes the channel.
• Voltage gated-open/ close depending on current
• Ligand gated-open/close depending on ligand binding
Signaling consists of conformational changes when ligands bind. These receptors are generally responsive to neurotransmitters.
All ion channels are composed of multiple subunits that span the plasma membrane.

Answer 52

Ion Channel Receptors
a. Structure and function of ion channel receptors:
Ion channels are integral membrane proteins that control the flow of ions (Ca2+, Na/K, Cl) across the cell membrane.

Question 53

• Ligand gated-open/close depending on ligand binding

Answer 53

• Ligand gated-open/close depending on ligand binding

Question 54

Ion Channel Receptors
There are ____ major families depending on their structure:
*****

Answer 54

There are three major families depending on their structure:
Cys-loop-pentamer
Glutamate receptor-tetramer
P2X family- trimer

Question 55

Molecular mechanisms of ion channels
1. Nicotinic acetylcholine receptor is a Na+/K+ channel consisting of five subunits.
Binding of ligand causes ion flux. Na+/K+ flux causes a change in action potential and causes muscle contraction.
2. GABAA receptor is a Cl- channel structurally similar to the nicotinic receptor. Ligand binding results in Cl- flux and reductions in neurotransmission by inhibiting action potentials.
. Serotonin 5-HT3 receptors, are ligand-gated ion channels of the Cys-loop family. The receptor consists of 4-transmembrane domains that form an intrinsic cation-selective channel. This receptor controls Ca2+ flux

Answer 55

Molecular mechanisms of ion channels
1. Nicotinic acetylcholine receptor is a Na+/K+ channel consisting of five subunits.
Binding of ligand causes ion flux. Na+/K+ flux causes a change in action potential and causes muscle contraction.
2. GABAA receptor is a Cl- channel structurally similar to the nicotinic receptor. Ligand binding results in Cl- flux and reductions in neurotransmission by inhibiting action potentials.
. Serotonin 5-HT3 receptors, are ligand-gated ion channels of the Cys-loop family. The receptor consists of 4-transmembrane domains that form an intrinsic cation-selective channel. This receptor controls Ca2+ flux

Question 56

Intracellular Receptors: Nuclear Hormone Receptors
Nuclear Hormone Receptors are actually transcription factors
Domains:
1. Ligand binding domain (hormone is the ligand)
2. DNA binding domain
3. Transcriptional Activation domain

Steroid hormones are lipophilic and
diffuse across the lipid membrane and bind their nuclear hormone receptors. This activates the receptor. Activated receptors function as transcription factors that directly regulate gene expression.
This figure shows that in the absence of hormone the receptors for estrogen and progesterone are located in the cytoplasm.
Addition of ligand results in the transposition of receptor into the nucleus.

Answer 56

Intracellular Receptors: Nuclear Hormone Receptors
Nuclear Hormone Receptors are actually transcription factors
Domains:
1. Ligand binding domain (hormone is the ligand)
2. DNA binding domain
3. Transcriptional Activation domain

Question 57

Domains:

1. Ligand binding domain (hormone is the ligand)
2. DNA binding domain
3. Transcriptional Activation domain

Answer 57

Domains:

1. Ligand binding domain (hormone is the ligand)
2. DNA binding domain
3. Transcriptional Activation domain

Question 58

This Table contains some examples of steroid hormone receptors.

Answer 58

Hormone
Origin
Activity

 Estradiol Ovary, Placenta Female sex characteristics

Progesterone
Ovary, Placenta
Prepare uterine wall for pregnancy

 T estosterone T estis Male sex characteristics

Thyoxine
Thyroid
Increase metabolic activity

 Cortisol Adrenal Metabolism, suppress inflammation

Question 59

Cell Signaling in Cancer

Many signaling pathways are dysregulated during cancer development.

Answer 59

Cell Signaling in Cancer
Many signaling pathways are dysregulated during cancer development.

1. Ras→ MAPK → Cell Proliferation
   Breast, colon, prostate, etc. A high percentage of cancers with mutations within this pathway are always activated, leading to uncontrolled cellular proliferation. 95% of pancreatic cancers have constitutive activation of Ras.
2. PI3 Kinase Activation → Cell Survival (phosphorylates and inhibits BAD)
   Components of this pathway are dysregulated in most types of human cancers. PTEN, a signaling protein which negatively regulates PI3 Kinase, is mutated in most prostate cancers.

Activated EGF Receptor can increase cell proliferation and secretion of angiogenic factors (growth factors that affect surrounding vasculature)

This can lead to increased blood vessel supply and increased growth and tumor metastasis:

o many of the components in these pathways have become targets for development of
chemotherapies: This is just an example, you do not need to memorize.

Question 60

1. Ras→ MAPK → Cell Proliferation
   Breast, colon, prostate, etc. A high percentage of cancers with mutations within this pathway are always activated, leading to uncontrolled cellular proliferation. 95% of pancreatic cancers have constitutive activation of Ras.

Answer 60

1. Ras→ MAPK → Cell Proliferation
   Breast, colon, prostate, etc. A high percentage of cancers with mutations within this pathway are always activated, leading to uncontrolled cellular proliferation. 95% of pancreatic cancers have constitutive activation of Ras.
2. PI3 Kinase Activation → Cell Survival (phosphorylates and inhibits BAD)
   Components of this pathway are dysregulated in most types of human cancers. PTEN, a signaling protein which negatively regulates PI3 Kinase, is mutated in most prostate cancers.

Question 61

2. PI3 Kinase Activation → Cell Survival (phosphorylates and inhibits BAD)
   Components of this pathway are dysregulated in most types of human cancers. PTEN, a signaling protein which negatively regulates PI3 Kinase, is mutated in most prostate cancers.

Answer 61

2. PI3 Kinase Activation → Cell Survival (phosphorylates and inhibits BAD)
   Components of this pathway are dysregulated in most types of human cancers. PTEN, a signaling protein which negatively regulates PI3 Kinase, is mutated in most prostate cancers.

Question 62

1. Specify the main classes of plasma membrane receptors

Answer 62

note

Question 63

2. Describe the molecular structure-function of the following types of receptors:
   a) G-protein Coupled Receptors (GPCR)
   b) Receptor Tyrosine Kinases
   c) JAK-STAT Receptors
   c) Receptor Serine-Threonine Kinases

Answer 63

2. Describe the molecular structure-function of the following types of receptors:
   a) G-protein Coupled Receptors (GPCR) b) Receptor Tyrosine Kinases
   c) JAK-STAT Receptors
   c) Receptor Serine-Threonine Kinases
3. Specify 4 types of Gα subunits, their molecular targets, and the 2nd messengers that are generated following ligand binding to a GPCR
4. Describe how PKA and PKC are activated by their respective 2nd messengers
5. Explain how binding of a ligand to a receptor tyrosine kinase activates MAP Kinase
6. Describe PKB and its central role in insulin receptor signal transduction
7. Describe JAK-STAT receptors and their signaling
8. Describe the role of Smads in signal transduction via the TGF-β receptor

Question 64

3. Specify 4 types of Gα subunits, their molecular targets, and the 2nd messengers that are generated following ligand binding to a GPCR

Answer 64

3. Specify 4 types of Gα subunits, their molecular targets, and the 2nd messengers that are generated following ligand binding to a GPCR

Question 65

4. Describe how PKA and PKC are activated by their respective 2nd messengers

Answer 65

!!

Question 66

5. Explain how binding of a ligand to a receptor tyrosine kinase activates MAP Kinase

Answer 66

5. Explain how binding of a ligand to a receptor tyrosine kinase activates MAP Kinase
6. Describe PKB and its central role in insulin receptor signal transduction
7. Describe JAK-STAT receptors and their signaling
8. Describe the role of Smads in signal transduction via the TGF-β receptor

Question 67

6. Describe PKB and its central role in insulin receptor signal transduction

Answer 67

!

Question 68

7. Describe JAK-STAT receptors and their signaling

Answer 68

!

Question 69

8. Describe the role of Smads in signal transduction via the TGF-β receptor

Answer 69

!

Question 70

all transmembrane receptors have what number of domains?

Answer 70

3: All transmembrane receptors have an extracellular domain which binds ligand, a transmembrane domain and an intracellular domain

(extracellular, transmembrane, intracellular)

Question 71

PKA is composed of ___ subunits:

Answer 71

PKA is composed of four subunits; two regulatory subunits and two catalytic subunits.