Cell Communication Flashcards
(130 cards)
1
Q
Learning Objectives
A
> Define the types of signaling.
Discuss the types of signaling molecules and their receptors. (lipophili vs. hydrophilic)
Describe signaling via G protein-coupled recetors (GPCR)
- trimeric G proteins
- effector proteins and their second messengers (cAMP/cGMP)
- GPCR signaling via G1, PLC and PKC
Describe signaling via receptor tyrosine kinases
- monomeric G proteins
- insulin signaling
2
Q
Does cell signaling occur inside or outside of the cell?
A
Signal transduction occurs inside the cell.
3
Q
How do cells get the message from outside to inside of the cell?
A
Extracellular signaling molecules bind to specific receptors in target cells in initiate a chain of events referred to as signal transduction.
4
Q
What are the 2 types of major responses the external signals induce?
A
> Change in activity or function of enzymes or proteins in the cell (fast response).
> Change in amounts of proteins by change in expression of genes (slow response).
5
Q
What is a fast response in signal transduction?
A
Change in activity or function of enzymes or proteins in the cell.
6
Q
What is a slow response in signal transduction?
A
Change in amounts of proteins by change in expression of genes.
7
Q
What does leptin do?
A
Leptin is released from fat and signals hypothalamus that you are full.
8
Q
Why did leptin pills not work like they thouht they were going to?
A
Signaling sensitivity at the blood-brain-barrier.
9
Q
True of False:
Leptin is an example of endocrine signaling?
A
True
10
Q
What are types of signaling based on?
A
distance
11
Q
What is endocrine signaling?
A
long distance signaling
signal -> bloodstream -> distant target cells
12
Q
What type of signals are endocrine signaling?
A
Free diffusible signals.
13
Q
Are endocrine signals long lasting?
A
Yes - long lasting (long half-life in minutes) - takes time to go through the circulatory system to find a target cell.
14
Q
What is paracrine signaling?
A
acts locally
affects cells nearby (not as freely diffusible)
15
Q
How long do paracrine signals last?
A
short lived signal (e.g., neurotransmitters).
16
Q
What is an example of a paracrine signaling molecule?
A
neurotransmitters
17
Q
What is autocrine signaling?
A
Cells respond to signals that they themselves release or release to cells of the same type.
Cell secretes signal that feeds back and binds to a receptor on its own surface
18
Q
What is an example of a autocrine signaling molecule?
A
growth factors in cancer cells
19
Q
What is an example of direct (juxtacrine) cell signaling?
A
Ag-presenting cells to T cells.
20
Q
True or False:
Each cell interprets the combination of all the types of signaling (endocrine, paracrine, autocrine, and direct (juxtacrine) signaling) to determine what to do.
A
True
does the cell need to divide, die, differentiate, survive
21
Q
Give an example of how the same ligand can cause different responses in different cell types.
A
Acetylcholine can cause:
> heart muscle cells to relax
> skeletal muscle cells to contract
> salivary gland cells to secrete saliva
22
Q
How does signal transduction work?
A
> extracellular signal molecule binds to receptor
intracellular signaling of proteins occurs
effector proteins are activated
- metabolic enzyme -> altered metabolism
- gene regulatory protein -> altered gene expression
- cytoskeletal protein -> altered cell shape or movement
23
Q
What are the three required signaling cascade components?
A
- signals (ligands)
- receptors
- effectors
24
Q
When talking about signaling cascade components, what are the characteristics of the signals (ligands)?
A
- typically secreted by exocytosis (e.g., signal peptide)
- signals stay near or far
25
When talking about signaling cascade components, what are the characteristics of the receptors?
- bind specifically to signal molecules with high affinity (signals are produced in low levels)
26
When talking about signaling cascade components, what are the characteristics of the effectors?
- targets of receptors inside cells: alter activity of many different proteins and generate 2nd messengers (small diffusible molecules like cAMP and Ca2+).
27
In cell signaling, what can ligands be?
```
- Can be:
> proteins
> small peptides
> amino acid derivatives
> hydrophobic molecules (steroid hormones like estrogen)
```
- even gases (NO)
28
What are the main categories of ligands?
> Small lipophilic molecules: steroid hormones.
> Water soluble molecules - hydrophilic - e.g., growth factors.
*steroid hormones and growth factors*
29
What are the properties of growth factors?
Water soluble molecules - hydrophilic.
30
What are the properties of steroid hormones?
Small lipophilic molecules.
31
Where are the receptors found for lypophilic ligands?
> found in the cytoplasm and nucleus
| > family of DNA-binding transcription factors
32
Where are the receptors found for hydrophilic ligands?
> found on the surface of plasma membranes
| > includes transmembrane proteins such as G protein-coupled receptors and receptor tyrosine kinases
33
Give some examples of lypophilic ligands.
> Steroid hormones:
- progesterone
- estradiol
- testosterone
- cortisol
- aldosterone
- vitamin D
> Thyroid hormone:
- thyroxine
> Retinoids:
- retinol
- retinoic acid
34
Give some examples of hydrophilic ligands.
> Amino acid derived:
- histamine
- serotonin
- melatonin
- dopamine
- norepinephrine
- epinephrine
> From lipid metabolism:
- acetylcholine
> Polypeptides:
- insulin
- glucagon
- cytokines
- thyroid-stimulating hormone
35
What are the two general types of receptors?
- intracellular receptors
| - cell surface receptors
36
What are the characteristics of intracellular receptors?
- steroid receptor can have receptor in cytosol (e.g., estrogen)
- alters gene expression in nucleus
37
What are the characteristics of cell surface receptors?
- external domain binds ligand
- transmembrane domain anchors receptor
- cytoplasmic domain initiates signal by change in conformation
38
True of False:
Receptors have a high affinity and bind to ligands with great specificity (concentration of ligand in bloodstream is low).
True
39
What does the cytoplasmic domain of cell surface receptors initiate?
Initiates signal by change in conformation.
40
What does the transmembrane domain of cell surface receptors do?
Anchors receptor.
41
What does the external domain of cell surface receptors do?
Binds ligand.
42
True or False:
Most signaling molecules are lipophilic and require intracellular receptors.
False - most signaling molecules are HYDROPHILIC and require CELL-SURFACE RECEPTORS.
43
True of False:
Small hydrophilic signaling molecules can diffuse across the cytoplasmic membrane and bind to intracellular receptors.
False - SMALL HYDROPHOBIC signaling molecules can diffuse across the cytoplasmic membrane and bind to INTRACELLULAR RECEPTORS.
44
List some hydrophobic ligands and signals.
- cortisol
- estradiol
- testosterone
- vitamin D3
- thyroxine
- retinoic acid
45
For transcription of a target gene by the signaling via hormone ligands, what must be present at the DNA level?
coactivator proteins
46
What are the three main types of cell signaling receptors in the plasma membrane?
- ion channel-coupled receptors
- G-Protein-Coupled Receptors
- Enzyme-Coupled Receptors
**not covering ion channel-coupled receptors**
47
In what type of tissue are gated ion channels commonly found?
nervous tissue
48
How many pass transmembrane proteins are used by GPCRs?
7
49
In which receptor class are tyrosine kinases (RTKs) in?
enzyme-coupled receptor class
50
What are the characteristics of transmembrane receptors?
- Receptor mediated signaling.
- Most ligands or hormones are hydrophilic or large and can't get into a cell.
- They need some way to transduce a binding event on the cell surface to send signal inside the cell.
- One major class of surface receptors that mediate these signals are G-protein couple receptors (also called 7 transmembrane receptors).
- There are > 1,000 GPCRs
- Affect olfaction, sight, and taste.
**Over 60% of all drugs target GPCRs**
51
What are the three parts of a GPCR?
- extracellular domain - binds to ligand
> transmembrane domain - anchors receptor
> cytoplasmic domain - associates with G-proteins
52
What are heterotrimeric G-proteins?
Are guanine nucleotide-binding proteins that consist of three subunits designated alpha, beta, and gamma.
53
What do GPCRs regulate?
Regulate target enzymes.
54
Do GPCRs have intrinsic catalytic activity?
No - no intrinsic catalytic activity.
55
What is the mechanism of GPCR activity?
GPCR -> Trimeric G Protein -> Effector Enzyme -> 2nd Messenger -> Targets of 2nd Messenger -> Biological Response.
56
After the ligand binds to the GPCR, what does it have to do to trigger cell signaling?
GPCR has to turn on an enzyme to create a 2nd messenger for cell signaling.
57
Is the active alpha subunit bound by GTP an active kinase?
No - G-proteins do not transfer phosphates. They are not kinases. GTP just changes the conformation.
58
In the regulation of G-proteins, is the GAP protein (guanine activating protein) essential to hydrolyze GTP bound by the active form.
No - it has GTPase activity and facilitates the 3rd phosphate falling off quicker, but it naturally wants to fall of anyways.
59
In the regulation of G-proteins, does GEF (guanine nucleotide exchange factor) phophorylate GDP to GTP?
No - GEF signals we need more GTP - helps facilitate the exchange of a phosphate...NOT a kinase. It just changes the conformation to release the GDP.
60
What are the steps of G-protein relaying signals?
1. Ligand binds to receptor.
2. Conformational change occurs in receptor.
3. Receptor binds to G protein.
4. Receptor then acts as a GEF (guanine exchange factor).
5. Confirmation of G-alpha protein is changed such that it kicks out GDP and GTP binds to it.
6. G-alpha now becomes active and can bind to effector molecule and activate effector molecule.
7. Effector molecule in this case is adenylyl cyclase which catalyzes formation of cAMP.
> eventually hydrolysis of GTP bound to G-alpha occurs and changes to GDP (occurs after a certain amount of time).
> G-alpha returns to inactive step to be recycled through process again.
61
What common subunit is upstream of cAMP production?
Gs-alpha
62
What does adenylyl cyclase do?
Adenylyl cyclase generates cAMP which then goes on to interact with it's target proteins to cause a biological response.
63
What are the targets of cAMP?
- cAMP activates cAMP-dependent protein kinase (PKA) - 4 subunits.
- Inactive PKA: 2 catalytic subunits and 2 regulatory subunits.
- Binding of 2 cAMP molecules to regulatory subunits of tetramer results in release of active C subunits.
- Active PKA can now phophorylate other proteins.
64
What does cAMP activate?
cAMP-dependent protein kinase (PKA) - 4 subunits.
65
What are the properties of the 4 subunits of inactive PKA?
> Inactive PKA:
- 2 catalytic subunits
- 2 regulatory subunits
66
What results in the release of active C subunits?
Binding of 2 cAMP molecules to regulatory subunits of tetramer.
67
What can active PKA now go do?
phosphorylate other proteins
68
How can PKA regulate proteins?
By the addition of phosphate groups: addition of 2 negative charges can change conformation of protein.
69
PKA can regulate proteins by addition of phosphate groups: addition of 2 negative charges can change conformation of protein. What are the 4 possibilities that can happen?
1) Phosphate group can form part of structure that other proteins recognize.
2) Activation or inactivation of enzymatic target proteins.
3) Alteration of intracellular localization of target proteins.
4) Alterations in abundance of target proteins.
70
List the signal amplification in the cAMP pathway.
```
> GPCR
> Trimeric Gs-protein
> Adenylyl cyclase
> cAMP
> PKA
> Enzyme
> Substrate/product
> Amplification
```
71
What disease can result when G-protein relaying signals goes wrong?
```
Cholera - causes you to pump a lot of water into your gut.
> first global epidemic
> 1st outbreak was in India
> Cholera is a water born disease
> Can kill in 12-48 hours
> Dr. John Snow
```
72
How does Vibria cholerae cause Cholera?
> Cholera toxin modifies G protein by keeping the G-alpha in the GTP active form indefinitely.
> Leads to 100 fold increase in cAMP.
> PKA phosphorylates the CFTR Cl channel.
> Leads to secretion of water.
73
What is the desensitization of signal?
Ability to turn off or reject the signal - Important: cell cycle - cancer.
74
What does potentiate mean?
turn up
75
What does attenuate mean?
turn down
76
How does desensitization of signal occur when hormone levels drop?
Decreased adenylyl cyclase activity -> decreased cAMP -> decreased PKA activity.
77
How does removing the signal molecule cause desensitization of signal?
Remove the signaling molecule: phosphodiesterases will remove cAMP/cGMP.
**Can thus turn off the 2nd messenger that the mutated alpha subunit continuously is activating adenylyl cyclase.
78
How does receptor sequestration cause desensitization of signal?
Receptor sequestration: endosome.
**receptor can be destructed or taken out of the membrane in an endosome**
79
How does receptor destruction cause desensitization of signal?
Receptor destruction: endosomes + lysosomes (proteases).
80
How can GRKs (G protein receptor kinases) cause desensitization of signals?
> GRKs phosphorylate the receptor such that another protein called arrestin will bind to the 3rd intracellular loop and prevents G-alpha from interacting with the third loop.
> Result is that Galpha-GDP does not get converted to Galpha-GTP.
81
Will desensitization of signals by GRKs turn off Galpha-GDP from converting Galpha-GTP no matter how many ligands flood the system?
Yes - regardless of ligands flooding the system, GRK will turn off Galpha-GDP to converting to Galpha-GTP, thus desensitization occurs.
82
What does Gi/o G-proteins do to adenylyl cyclase?
inhibits AC
**remember, AC activates PKA**
83
What does Gq alpha G -proteins do to PLC?
activates PLC (phospholipase C) instead of AC
84
What 2nd messenger directly activates PKC?
DAG
85
What 2nd messenger in-directly activates PKC?
IP3 by the release of calcium from the SR/ER.
86
What membrane protein does phospholipase C (PLC) cleave?
PIP2
87
What does the cleavage of PIP2 by PLC produce?
IP3 and DAG (2nd messengers)
88
Is IP3 (inositol 1,4,5-triphophate) a diffusible 2nd messenger or a membrane bound 2nd messenger?
diffusible 2nd messenger
89
Is DAG (1,2-diacylglycerol) a diffusible 2nd messenger or a membrane bound 2nd messenger?
membrane bound 2nd messenger
90
Does PKC have slight kinase activity?
Yes, has to have proper localization.
91
What does IP3 trigger the release of?
Release of Ca2+ from endoplasmic reticulum (calcium storage in ER).
92
How does IP3 trigger the release of calcium?
By binding to an IP3-gated Ca2+ channel + triggers opening.
> Ca 2+ released into cytosol so you get increased calcium concentration.
> Ca2+ is a second messenger too.
> IP3 is done.
93
What does DAG do now that the cytosolic calcium concentrations are high after IP3 triggered its release from the ER?
> Both Ca2+ and DAG bind to another protein kinase called protein kinase C (PKC).
> Conformational change occurs in PKC and it is activated.
> PKC phosphorylates a variety of membrane and cytoplasmic substrates.
94
Know the difference between subunit Q, subunit I, and subunit S and their roles in signaling.
Know this well for the exam. Also, know that if PKC is not active, what is happening upstream that could be causing this.
95
What do enzyme-coupled receptors do?
Create docking sites for other proteins.
96
List the 3 enzyme-coupled receptors.
- Tyrosine kinases
- JAK-STAT Receptors
- Serine/threonine kinases
97
Where is the enzymatic domain of receptor tyrosine kinases?
cytoplasmic tail of the integral membrane protein
98
In receptor tyrosine kinases (RTKs), how many times does the transmembrane domain pass?
single pass
99
What does the ligand that binds to receptor tyrosine kinases (RTKs) cause?
Ligand binding to this receptor causes a conformational change.
100
What does the conformational change caused by the ligand binding to an RTK induce?
dimerization of two receptor monomers
101
When does autophosphorylation occur?
After dinerization of two receptor monomers is triggered by the ligand binding to the RTK receptor causing a conformational change.
102
What are RTKs important for?
Receptor tyrosine kinases are used for response to growth factors: mediate growth factor signals.
103
What are growth factors?
Proteins released by cells to promote growth of other cells.
104
List common growth factors?
```
> EGF - epidermal growth factor (53 aa's long)
> PDGF - platelet derived growth factor
> FGF - fibroblast growth factor
> IGF-1 - insulin-like growth factor 1
> NGF - nerve growth factor
```
105
Are growth factors hydrophilic or lipophilic?
hydrophilic
106
What does autophosphorylation cause?
The receptor to act as a scaffold to recruit other proteins to the plasma membrane.
107
What is the outside event of RTKs?
binding to receptor
108
True or False:
Receptor does not bind to G protein but receptor binds to proteins with domains called the SH2 domains (src homology) - SH2 domain binds to phosphotyrosine.
True
109
What was the first oncogene discovered?
Src
110
What is the SH2 protein in mammals?
Grb2 (adaptor protein)
111
List the receptor tyrosine kinase activity?
> RTK binds to SH2 domain of Grb2.
> SH3 of Grb2 binds to prolines in SOS.
> Sevenless = controls photoreceptor development, receptor tyrosine kinase.
> ligand = BOSS (bride of son of sevenless)
> Downstream effectors found were Grb2 and SOS.
112
How many SH2 domains does Grb2 have?
2
113
Is SOS a GEF?
Yes
114
What does SOS bind to?
Both Grb2 and Ras.
115
What does Ras paly a crucial role in?
Cell division and a frequent mutation in cancer.
116
What does Ras bind to?
Raf
117
What does SH3 of Grb2 bind to?
prolines in SOS which then binds to Ras (small monomeric G protein - small GTPase)
118
Do both Mek and Erk get hyper-phosphorylated?
Yes
119
Does Erk go into the nucleus?
Yes
120
True or False:
Protein kinase cascades propagate the signal downstream of Ras by phosphorylation.
True
121
What are the two Ras signaling pathways via RTK?
Ras-dependent
| Ras-independent
122
Is RAS-dependent signaling slow or fast?
Slow
123
Is RAS-independent signaling slow or fast?
Fast
124
What does RAS-dependent signaling cause?
Alterations in gene transcription.
| *e.g., increased transcription of glucokinase.
125
What does RAS-independent signaling cause?
Alterations in protein and enzyme activity.
| *e.g., increased GLUT4 movement to plasma membrane; activation of glycogen synthase.
126
List the summary of RTKs?
> growth factor binds to receptor.
> receptor becomes active tyrosine kinase.
> autophosphorylates.
> binds to Grb2-SOS-Ras-Raf
> gene transcription through MAP kinase pathway.
> many signaling molecules are proto-oncogenes that can mutate into oncogenes and cause cancer.
127
Is JAK-STAT receptors a more direct route for impacting transcription?
Yes
128
What are the 4 steps in JAK-STAT receptors signaling?
1) receptors bind cytokines, dimerize, and bind JAKs
2) JAKs phosphorylate each other and the receptor
3) receptor binds and phosphorylates STATs
4) STATs dissociate from receptor, dimerize, translocate to nucleus
129
Do enzyme-coupled receptors have enzymatic activity?
Yes
130
What is a R-Smad?
R-Smad = receptor specific Smad and forms complex with Co-Smad: common Smad.
*serine-threonine receptor and Smad*
