Signaling Flashcards
1
Q
extracellular signal molecules
A
Any secreted or cell-surface chemical signal that binds to receptors and regulates activity of the cell expressing the receptor
2
Q
receptor proteins
A
any protein that binds a SPECIFIC signal molecule (ligand) and initiates a response in the cell. Some are on the cell surface, while others are inside the cell. (Figure 15-3)
3
Q
intracellular signaling proteins
A
Protein involved in a signaling pathway inside the cell. It usually activates the next protein in the pathway or generates a small intracellular mediator.
4
Q
effector proteins
A
carry out the final response or function in a particular process
5
Q
Why do cells communicate?
A
- Regulation of metabolite function
- Growth and differentiation
- Synthesis and secretion of proteins
- Composition of intracellular and extracellular fluids
- Neuronal signaling
6
Q
How do cells communicate?
A
ligands, receptors, signaling molecules and second messengers, target proteins
7
Q
ligands
A
Any molecule that binds to a specific site on a protein or other molecule
8
Q
second messengers
A
Small intracellular signaling molecule that is formed or released for action in response to an extracellular signal and helps to relay the signal within the cell. Ex: cAMP, cGMP, IP3, Ca2+, and diacylglycerol (DAG)
9
Q
types of ligands
A
small molecules (amino acid or lipid derivatives, acetylcholine), peptides, proteins, steroids, retinoids, thyroxine* (*hydrophobic, bind intracellular receptors)
10
Q
contact-dependent signaling
A
requires cells to be in direct membrane-membrane contact
11
Q
paracrine signaling
A
depends on signals that are released into the extracellular space and act LOCALLY on neighboring cells
12
Q
synaptic signaling
A
performed by neurons that transmit signals electrically along their axons and release neurotransmitters at synapses, which are often located far away from the neuronal cell body
13
Q
endocrine signaling
A
depends on endocrine cells, which secrete hormones into the bloodstream for distribution throughout the body - diff in speed and selectivity DISTANT
14
Q
autocrine
A
act on self - ligand produced by target cell, common in tumor cells
15
Q
major classes of ligands
A
hormones, GFs, neurotransmitters (NT), pheromones, changes in metabolite concentration
16
Q
major types of cellular responses
A
- Changes in activity of pre-existing proteins (rapid response - post-translational modifications)
- Changes in amount of specific protein (slow response – changes in gene expression)
17
Q
receptor-ligand interactions
A
have effector specificity
- weak non-covalent forces (ionic, VDW, hydrophob)
- molecular complementarity
18
Q
effector specificity
A
mediates a specific cellular response
19
Q
maximal cellular response to a signaling molecule
A
may not require activation of all receptors
- occurs when only a fraction of the receptor molecules are occupied by the ligand
20
Q
IP3
A
inositol 1,4,5-triphosphate (structure 13-7)
21
Q
binding assay
A
receptors are detected and measured by their ability to bind radioactive ligands to cells or to cell fragments
22
Q
affinity labeling
A
cell-surface receptors often can be identified and followed through isolation procedures
Cells are mixed with an excess of a radiolabeled ligand for the receptor of interest…
23
Q
other important second messengers
A
Ca2+, and inositol phospholipids (phosphoinositides) - embedded in cellular membranes
24
Q
GTPase switch proteins
A
guanine nucleotide-binding proteins turned “on” when bound to GTP and “off” when bound to GDP
25
guanine nucleotide-exchange factor (GEF)
inactive to active
26
GTPase-accelerating protein (GAP)
enhances GTP hydrolysis (active to inactive)
27
Two classes of GTPase switch proteins
1. trimeric (large) G proteins - directly bind to receptors
| 2. monomeric (small) G proteins (like Ras or Ras-like) - indirectly bind
28
Activation of PKA
by 4 cAMP
29
Phosphoinositides
PI->PIP->PIP2->DAG+IP3
| can promote activation of proteins involved with actin remodeling, endocytosis, and vesicle fusion
30
Phospholipase C activation
by PIP2-> DAG and IP3
IP3-> IP3 gated Ca2+ channel gets calcium from ER
calcium attached to Protein kinase C
which attached to DAG and phosphorylates substrates...
Calcium is brought back into the cell by TRP Ca2+ channel
31
protein kinase
add phosphate
32
two types of protein kinase
1. add phosphate to the hydroxyl on tyrosine
| 2. add phosphate to hydroxyl on serine and threonine
33
phosphatases
remove phosphate
34
PDZ domains
common element in several cytosolic proteins that bind to integral plasma membrane proteins
can localize multiple proteins to a specific site in the cell
**synaptic junction
35
Src homology domains
form docking sites for other proteins (like PDZ domains)
- phosphorylated proteins bind SH2 domains
- phosphorylate SH2 containing proteins
- recruit other SH2 and SH3 domain containing proteins
36
protein clustering
```
lipid rafts (caveolae)
marked by presence of caveolin
```
37
clathrin
mediates endocytosis
| coast form the donor membrane to produce a vesicle
38
Types of receptors
1. G-protein coupled receptors
2. Cytokine receptors
3. Receptor tyrosine kinases
4. TGFb receptors
5. Hedgehog (Hh)
6. Wnt receptors
7. Notch receptors
39
What are GPCRs coupled to?
signal-transducing trimeric G proteins
40
What are the 3 subunits of signal-transducing G proteins?
alpha beta gamma
41
Galpha subunit
GTPase switch protein that alternative between active and inactive (GDP)
42
effector proteins of GPCR
membrane bound ion channels or enzymes that catalyze formation of 2nd messengers (camp, dag, ip3)
43
Major classes of trimeric G-proteins
s, i, olf, q, o, t
44
Transduction of signal by GPCR from extracellylar hormones to associated effector proteins
1. Binding of hormone induces a conformational change in receptor
2. Activated receptor binds to Gα subunit
3. Binding induces conformational change in Gα; bound GDP dissociates and is replaced by GTP; Gα dissociates from Gβγ
4. Hormone dissociates from receptor; Gα binds to effector, activating it
5. Hydrolysis of GTP to GDP causes Gα to dissociate from effector and reassociate with Gβγ
45
How to measure the GPCR-mediated dissociation of trimeric G proteins?
fluorescence energy transfer
demonstrates the dissociation of Ga and Gby within a few seconds of ligand addition providing further evidence for the model of G protein cycling
(use this follow formation and dissociation of other protein-protein complexes in living cells)
46
all epinephrine receptors
GPCRs
47
stimulatory G protein (Gs)
activates adenylyl cyclase (makes cAMP)
48
functional expression assay
can identify a cDNA encoding a cell-surface receptor
49
inhibitory G protein (Gi)
inhibits adenylyl cyclase
50
What structure of GPCR is important for interactions between a receptor and its coupled G protein?
C3 loop between zlpha helices 5 and 6
51
x-ray crystallographic analysis
pinpointed the regions in Gsalpha-GTP that interact with adenylyl cyclase
52
cAMP-dependent protein kinase
protein kinase A
53
virtually all effects of cAMP are mediated through...
protein kinase A
54
structure of inactive PKA
tetramer with two regulatory (R) subunits and two catalytic (C) subunits
- each R subunit has two distinct cAMP-bidning sites
- binding of cAMP releases Cs and activating kinase activity
55
residues that PKA phosphorylates
serine or threonine
56
first cAMP mediated cellular response -
release of glucose from glycogen
57
glycogen synthase
UDP-glucose to glycogen
58
degradation of glycogen
catalyzed by glycogen phosphorylase
| glucose 1 phosphate
59
how does epinephrine enhance conversion of glycogen to G1P
inhibiting glycogen synthesis, stimulating glycogen degradation
- stimulates an increase in cAMP and PKA activation
60
PKA inhibition of glycogen synthesis
phosphorylates glycogen synthase
61
PKA stimulation of gygogen degradation
indirectly phosphorylating glycogen phosphorylase kinase (GPK) which phophorylates and activates glycogen phophorylase
62
removes phophate residues from inactive glycogen synthase and active glycogen phosphorylase kinase and glycogen phosphorylase
phophoprotein phosphatase
63
PKA regulated of phosphoprotein phosphatase
low camp levels, inactive PKA does not phosphorylate an inhibitor
synthesis of glycogen*
64
amplification of signal through GPCR pathway
epinephrine to many adenylyl cyclases to many cAMP to half as many protein kinase A to many more activated enzymes to many more products
65
B-arrestin
cytosolic protein that binds to receptors extensively phosphorylated by BARK (cannot activate Gs)
-also binds to clathrin/AP2-->endocytosise
66
What does B-arrestin bind to for endocytosis?
clathrin and AP2
67
what does B-arrestin bind to for activation of MAP kinase cascade?
cSRC, leading to phosphorylation of key transcription factors
68
What does b-arrestin bind to activate c-Jun kinase cascade?
AJK-1, MKKY,JNK-1
69
A kinase associated proteins (AKAPs)
localize PKA isoforms to specific subcelllular regions, therby restricting cAMP-dependent responses to these locations
70
mAKAP in heart muscle
anchors PKA and cAMP phosphodiesterase (PDE)
| negative feedback loop provides close local control of the cAMP level
71
PDE
phosphodiesterase attaches to mAKAP near PKA to create a negative feedback loop for cAMP level control
72
Ion channel regulation by GPCRs
direct mechanism: muscarinic acetylcholine
| indirect: Gt-coupled receptors
73
cardiac muscarinic acetylcholine receptors activate
a G protein that opens a K+ channel
74
Gt-coupled receptors are activated
by light
75
rhodopsin
a GPCR that is activated by light and localized to the thousand or so flattened membrane disks that make up the outer segment of rod cells
76
the trimeric G protein coupled to rhodopsin
transducin (Gt) - found only in rod cells
77
absorption of light by rhodopsin leads to
closing of ion channels
| less neurotransmitter release
78
structural change in rhodopsin
11-cis to all trans - activates Gt
79
activation of rhodopsin induces
closing of cGMP-Gated Cation channels
80
cGMP
the key transducing molecule linking activated opsin to the closing of cation channels in rod-cell plasma membrane
81
light absorption induces (enzyme)
cGMP phosphodiesterase which hydrolyzes cGMP to 5'GMP
82
rod cells adapt to
varying levels of ambient light
83
cleavage of PIP2
by PLC to generate DAG and IP3 (IP3/DAG pathway)
84
inositol 1,4, 5-triphosphate triggers release
of calcium ions from the endoplasmic reticulum which then activated protein kinaseC with DAG
85
DAG activates
PKC which regulates many other proteins
86
signal-induced relaxation of vascular smooth muscle is mediated by
cGMP-activated protein kinase G
87
tubby gene
involved in control of eating behavior/involvement in obesity
88
Tubby domains
DNA binding domain and a trasncription activation domain
89
What GPCR activate phospholipase C?
Go or Gq coupled receptors
90
PLC on Tubby/PIP2
creates DAG, IP3, and tubby enters nucleus and activates transcription of an unknown gene
91
CREB
links cAMP signals to transcription
92
All genes regulated by cAMP contain this
cis-acting DNA sequence, cAMP-response element (CRE) that binds the phosphorylated form of CRE-binding protein (CREB)
93
GPCR-bound arrestin
activates several kinase cascaddes that control gene expression
94
receptor kinases with intrinsic enzymatic activity
TGFB, RTKs, receptor guanylyl cyclases, receptor phosphotyrosine phosphatases
T-cell receptors
95
tyrosine kinase linked receptors
cytokine receptors and the Jak/STAT pathway
96
TGFB receptors directly activate
Smads
97
BMP
member of TGFB superfamily
98
TGFB1
induce transformed phenotype in some cells
99
Loss of TGFB receptors
leads to growth inhibition (common in tumors)
100
activins and inhibins
TGFB superfamily, affect early development of the genital tract
101
TGFB signaling pathway
activated receptors directly phosphorylate and activate a particular type of Tx fractor, the response depends on the constellation of other Tx factors
102
Role of TGFB signaling
```
Inflammation
• Bone development
• Wound healing
• Growth of fibroblasts
• Growth inhibition in epithelial cells • Embryogenesis
```
103
TGFB secreted as
precursor before mature form
104
TGFB signaling receptors have
serine/threonine kinase activity
105
the most abundant TGFB receptor
RIII a cell-surface proteoglycan also called B-glycan
| concentrates TGFB to cell surface
106
type I and II TGFB receptors
dimeric transmembrane proteins with serine/throenine kinases as part of their cytosolic domains
107
RII
constitutively actve and phos itself in the absence of TGFB
| - phos RI when bound to TGFB
108
Activated Type I TGFB receptors phosphorylate
Smad Tx factors
109
R-Smads
Smad2 or Smad3
110
CoSmad
Smad4
111
Two domains of R-Smads
MH1 and MH2
112
MHI contains
nuclear localization signal (NLS)
113
NLS
required for protein transport to nucleus
114
Importin B
- necessary for nuclear translocation
| binds to NLS other binding domain binds to CoSmad and they go into the nucleus to induce Tx
115
concentration of active smads in the nucleus reflects
activated TGFB receptors
116
What mediated cell-specificity of response to TGFB?
by interaction of Smads with other transcription factors
117
loss of TGFB signaling contributes to
abnormal cell proliferation and malignancy
118
cytokine receptors and receptor tyrosine kinases...
share many signaling features
| - dimer is active and phosphorylates a tyrosine residue
119
cytokines influence
development of many cell types
120
Examples of cytokines
interferon, G-CSF, Epo, interleukins, growth hormone, prolactin
121
IL2
proliferation of T-cells of the immune system
122
IL4
formation of antibody producing Bcells
123
IL6
stress response
124
all cytokines and their receptors
have similar structures and activate similar signaling pathways
- 4 long conserved alpha helices (cytokines)
- dimeric receptors
125
cytokines activate
the Jak/STAT signaling cascade
126
Receptor associated JAK kinases activate
STAT transcription factors bound to a cytokine receptor
127
SH2 and PTB domains bind to
specific sequences surrounding phosphotyrosine residues
128
signaling from cytokine receptors is modulated by
negative signals
129
Short term regulation of cutokine signaling
by SHP1 phosphatase (inactivates JAK)
130
Long term regulation of cytokine signaling
SOCS (in place of JAK) recruits ubiquitin ligase that leads to the degradation
131
receptor tyrosine kinases and
activation of Ras
132
difference between cytokine receptors and receptor tyrosine kinases
receptor tyrosine kinases have intrinsic protein tyrosine kinase activity whereas cytokine have JAK
133
ligands of RTKs
NGF, FGF, PDGF, EGF, insulin
134
activation of RTK stimulates
Ras-MAP kinase pathway (and other pathways)
135
functions of RTK pathways
regulation of cell proliferation and differentiation, promotion of cells survival, and modulation of cellular metabolism
136
ligand bind leads to RTK..
transphosphorylation
137
Ras
a GTPase switch protein alternates between active and inactive states
138
accelerates Ras activation
GEF (guanine nucleotide exchange factor)
139
deactivation of Ras
GAP (GTPase activating protein)
140
What links RTKs to Ras?
An adapter protein and GEF
| GRB2, Sos
141
Binding of Sos Protein to Inactive Ras causes
conformational change that activates Ras
142
MAP kinase
serine/threonine kinase also known as ERK
translocates into the nucleus and phosphorylates many diff proteins including Tx factors that regulate exp of imp cell-cycle and diff-specific proteins
143
MAP Kinase regulates
the activity of many Tx factors controlling early-response genes
144
early-response genes
induced well before cells enter the S phase and replicate their DNA
145
What do tyrosine kinase receptors do?
* Phosphorylate tyrosine residues
| * Provide docking sites for adaptor proteins (i.e. SH2 containing proteins, grb2/sos, cbl, PLC
146
Receptor guanylyl cyclases
* Ligands: ANF and related peptide hormones
| * Receptor: Single TM domain, GC activity in cytosolic domain •Signal transduction: Through formation of cGMP
147
Receptor phosphotyrosine phosphatases
* Ligands: Pleiotrophins and other protein hormones
* Receptors: Intrinsic phosphoTyr phosphatase activity in cytosolic domain
* Inhibited by ligand binding
* Signal transduction: Hydrolysis of phosphoTyr residue on cytosolic domain
148
T-cell receptors
Ligands: Small peptides associated with MHC proteins
•Receptors: Single TM domain, kinase activity in cytosolic domain •Signal transduction: Cytosolic PTKs, PI3K, IP3/DAG, Ras/MAP kinase
149
G protein–coupled receptors
Ligands: Epinephrine, glucagon, serotonin, vasopressin, ACTH, adenosine, and many others (mammals); odorant molecules, light; mating factors (yeast)
Receptors: Seven transmembrane
150
TGF
Ligands: Transforming growth factor
151
Cytokine receptors
Ligands: Interferons, erythropoietin, growth hormone, some interleukins (IL-2, IL-4), other cytokines
Receptors: Single transmembrane
152
Receptor tyrosine kinases
Ligands: Insulin, epidermal growth factor (EGF), fibroblast growth factor (FGF), neurotrophins, other growth factors
Receptor: Single transmembrane
