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Molecular Cell Biology > Signaling > Flashcards

Signaling Flashcards

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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

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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)

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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.

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4
Q

effector proteins

A

carry out the final response or function in a particular process

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5
Q

Why do cells communicate?

A
  1. Regulation of metabolite function
  2. Growth and differentiation
  3. Synthesis and secretion of proteins
  4. Composition of intracellular and extracellular fluids
  5. Neuronal signaling
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6
Q

How do cells communicate?

A

ligands, receptors, signaling molecules and second messengers, target proteins

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7
Q

ligands

A

Any molecule that binds to a specific site on a protein or other molecule

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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)

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9
Q

types of ligands

A

small molecules (amino acid or lipid derivatives, acetylcholine), peptides, proteins, steroids, retinoids, thyroxine* (*hydrophobic, bind intracellular receptors)

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10
Q

contact-dependent signaling

A

requires cells to be in direct membrane-membrane contact

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11
Q

paracrine signaling

A

depends on signals that are released into the extracellular space and act LOCALLY on neighboring cells

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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

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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

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14
Q

autocrine

A

act on self - ligand produced by target cell, common in tumor cells

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15
Q

major classes of ligands

A

hormones, GFs, neurotransmitters (NT), pheromones, changes in metabolite concentration

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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)
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17
Q

receptor-ligand interactions

A

have effector specificity

  • weak non-covalent forces (ionic, VDW, hydrophob)
  • molecular complementarity
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18
Q

effector specificity

A

mediates a specific cellular response

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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

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20
Q

IP3

A

inositol 1,4,5-triphosphate (structure 13-7)

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21
Q

binding assay

A

receptors are detected and measured by their ability to bind radioactive ligands to cells or to cell fragments

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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…

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23
Q

other important second messengers

A

Ca2+, and inositol phospholipids (phosphoinositides) - embedded in cellular membranes

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24
Q

GTPase switch proteins

A

guanine nucleotide-binding proteins turned “on” when bound to GTP and “off” when bound to GDP

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25
Q

guanine nucleotide-exchange factor (GEF)

A

inactive to active

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26
Q

GTPase-accelerating protein (GAP)

A

enhances GTP hydrolysis (active to inactive)

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27
Q

Two classes of GTPase switch proteins

A
  1. trimeric (large) G proteins - directly bind to receptors

2. monomeric (small) G proteins (like Ras or Ras-like) - indirectly bind

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28
Q

Activation of PKA

A

by 4 cAMP

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29
Q

Phosphoinositides

A

PI->PIP->PIP2->DAG+IP3

can promote activation of proteins involved with actin remodeling, endocytosis, and vesicle fusion

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30
Q

Phospholipase C activation

A

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

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31
Q

protein kinase

A

add phosphate

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32
Q

two types of protein kinase

A
  1. add phosphate to the hydroxyl on tyrosine

2. add phosphate to hydroxyl on serine and threonine

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33
Q

phosphatases

A

remove phosphate

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34
Q

PDZ domains

A

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

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35
Q

Src homology domains

A

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
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36
Q

protein clustering

A 
lipid rafts (caveolae)
marked by presence of caveolin
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37
Q

clathrin

A

mediates endocytosis

coast form the donor membrane to produce a vesicle

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38
Q

Types of receptors

A
  1. G-protein coupled receptors
  2. Cytokine receptors
  3. Receptor tyrosine kinases
  4. TGFb receptors
  5. Hedgehog (Hh)
  6. Wnt receptors
  7. Notch receptors
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39
Q

What are GPCRs coupled to?

A

signal-transducing trimeric G proteins

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40
Q

What are the 3 subunits of signal-transducing G proteins?

A

alpha beta gamma

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41
Q

Galpha subunit

A

GTPase switch protein that alternative between active and inactive (GDP)

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42
Q

effector proteins of GPCR

A

membrane bound ion channels or enzymes that catalyze formation of 2nd messengers (camp, dag, ip3)

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43
Q

Major classes of trimeric G-proteins

A

s, i, olf, q, o, t

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44
Q

Transduction of signal by GPCR from extracellylar hormones to associated effector proteins

A
  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
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45
Q

How to measure the GPCR-mediated dissociation of trimeric G proteins?

A

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)

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46
Q

all epinephrine receptors

A

GPCRs

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47
Q

stimulatory G protein (Gs)

A

activates adenylyl cyclase (makes cAMP)

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48
Q

functional expression assay

A

can identify a cDNA encoding a cell-surface receptor

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49
Q

inhibitory G protein (Gi)

A

inhibits adenylyl cyclase

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50
Q

What structure of GPCR is important for interactions between a receptor and its coupled G protein?

A

C3 loop between zlpha helices 5 and 6

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51
Q

x-ray crystallographic analysis

A

pinpointed the regions in Gsalpha-GTP that interact with adenylyl cyclase

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52
Q

cAMP-dependent protein kinase

A

protein kinase A

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53
Q

virtually all effects of cAMP are mediated through…

A

protein kinase A

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54
Q

structure of inactive PKA

A

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
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55
Q

residues that PKA phosphorylates

A

serine or threonine

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56
Q

first cAMP mediated cellular response -

A

release of glucose from glycogen

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57
Q

glycogen synthase

A

UDP-glucose to glycogen

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58
Q

degradation of glycogen

A

catalyzed by glycogen phosphorylase

glucose 1 phosphate

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59
Q

how does epinephrine enhance conversion of glycogen to G1P

A

inhibiting glycogen synthesis, stimulating glycogen degradation
- stimulates an increase in cAMP and PKA activation

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60
Q

PKA inhibition of glycogen synthesis

A

phosphorylates glycogen synthase

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61
Q

PKA stimulation of gygogen degradation

A

indirectly phosphorylating glycogen phosphorylase kinase (GPK) which phophorylates and activates glycogen phophorylase

62
Q

removes phophate residues from inactive glycogen synthase and active glycogen phosphorylase kinase and glycogen phosphorylase

A

phophoprotein phosphatase

63
Q

PKA regulated of phosphoprotein phosphatase

A

low camp levels, inactive PKA does not phosphorylate an inhibitor
synthesis of glycogen*

64
Q

amplification of signal through GPCR pathway

A

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
Q

B-arrestin

A

cytosolic protein that binds to receptors extensively phosphorylated by BARK (cannot activate Gs)
-also binds to clathrin/AP2–>endocytosise

66
Q

What does B-arrestin bind to for endocytosis?

A

clathrin and AP2

67
Q

what does B-arrestin bind to for activation of MAP kinase cascade?

A

cSRC, leading to phosphorylation of key transcription factors

68
Q

What does b-arrestin bind to activate c-Jun kinase cascade?

A

AJK-1, MKKY,JNK-1

69
Q

A kinase associated proteins (AKAPs)

A

localize PKA isoforms to specific subcelllular regions, therby restricting cAMP-dependent responses to these locations

70
Q

mAKAP in heart muscle

A

anchors PKA and cAMP phosphodiesterase (PDE)

negative feedback loop provides close local control of the cAMP level

71
Q

PDE

A

phosphodiesterase attaches to mAKAP near PKA to create a negative feedback loop for cAMP level control

72
Q

Ion channel regulation by GPCRs

A

direct mechanism: muscarinic acetylcholine

indirect: Gt-coupled receptors

73
Q

cardiac muscarinic acetylcholine receptors activate

A

a G protein that opens a K+ channel

74
Q

Gt-coupled receptors are activated

A

by light

75
Q

rhodopsin

A

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
Q

the trimeric G protein coupled to rhodopsin

A

transducin (Gt) - found only in rod cells

77
Q

absorption of light by rhodopsin leads to

A

closing of ion channels

less neurotransmitter release

78
Q

structural change in rhodopsin

A

11-cis to all trans - activates Gt

79
Q

activation of rhodopsin induces

A

closing of cGMP-Gated Cation channels

80
Q

cGMP

A

the key transducing molecule linking activated opsin to the closing of cation channels in rod-cell plasma membrane

81
Q

light absorption induces (enzyme)

A

cGMP phosphodiesterase which hydrolyzes cGMP to 5’GMP

82
Q

rod cells adapt to

A

varying levels of ambient light

83
Q

cleavage of PIP2

A

by PLC to generate DAG and IP3 (IP3/DAG pathway)

84
Q

inositol 1,4, 5-triphosphate triggers release

A

of calcium ions from the endoplasmic reticulum which then activated protein kinaseC with DAG

85
Q

DAG activates

A

PKC which regulates many other proteins

86
Q

signal-induced relaxation of vascular smooth muscle is mediated by

A

cGMP-activated protein kinase G

87
Q

tubby gene

A

involved in control of eating behavior/involvement in obesity

88
Q

Tubby domains

A

DNA binding domain and a trasncription activation domain

89
Q

What GPCR activate phospholipase C?

A

Go or Gq coupled receptors

90
Q

PLC on Tubby/PIP2

A

creates DAG, IP3, and tubby enters nucleus and activates transcription of an unknown gene

91
Q

CREB

A

links cAMP signals to transcription

92
Q

All genes regulated by cAMP contain this

A

cis-acting DNA sequence, cAMP-response element (CRE) that binds the phosphorylated form of CRE-binding protein (CREB)

93
Q

GPCR-bound arrestin

A

activates several kinase cascaddes that control gene expression

94
Q

receptor kinases with intrinsic enzymatic activity

A

TGFB, RTKs, receptor guanylyl cyclases, receptor phosphotyrosine phosphatases
T-cell receptors

95
Q

tyrosine kinase linked receptors

A

cytokine receptors and the Jak/STAT pathway

96
Q

TGFB receptors directly activate

A

Smads

97
Q

BMP

A

member of TGFB superfamily

98
Q

TGFB1

A

induce transformed phenotype in some cells

99
Q

Loss of TGFB receptors

A

leads to growth inhibition (common in tumors)

100
Q

activins and inhibins

A

TGFB superfamily, affect early development of the genital tract

101
Q

TGFB signaling pathway

A

activated receptors directly phosphorylate and activate a particular type of Tx fractor, the response depends on the constellation of other Tx factors

102
Q

Role of TGFB signaling

A 
Inflammation
• Bone development
• Wound healing
• Growth of fibroblasts
• Growth inhibition in epithelial cells • Embryogenesis
103
Q

TGFB secreted as

A

precursor before mature form

104
Q

TGFB signaling receptors have

A

serine/threonine kinase activity

105
Q

the most abundant TGFB receptor

A

RIII a cell-surface proteoglycan also called B-glycan

concentrates TGFB to cell surface

106
Q

type I and II TGFB receptors

A

dimeric transmembrane proteins with serine/throenine kinases as part of their cytosolic domains

107
Q

RII

A

constitutively actve and phos itself in the absence of TGFB

- phos RI when bound to TGFB

108
Q

Activated Type I TGFB receptors phosphorylate

A

Smad Tx factors

109
Q

R-Smads

A

Smad2 or Smad3

110
Q

CoSmad

A

Smad4

111
Q

Two domains of R-Smads

A

MH1 and MH2

112
Q

MHI contains

A

nuclear localization signal (NLS)

113
Q

NLS

A

required for protein transport to nucleus

114
Q

Importin B

A
  • necessary for nuclear translocation

binds to NLS other binding domain binds to CoSmad and they go into the nucleus to induce Tx

115
Q

concentration of active smads in the nucleus reflects

A

activated TGFB receptors

116
Q

What mediated cell-specificity of response to TGFB?

A

by interaction of Smads with other transcription factors

117
Q

loss of TGFB signaling contributes to

A

abnormal cell proliferation and malignancy

118
Q

cytokine receptors and receptor tyrosine kinases…

A

share many signaling features

- dimer is active and phosphorylates a tyrosine residue

119
Q

cytokines influence

A

development of many cell types

120
Q

Examples of cytokines

A

interferon, G-CSF, Epo, interleukins, growth hormone, prolactin

121
Q

IL2

A

proliferation of T-cells of the immune system

122
Q

IL4

A

formation of antibody producing Bcells

123
Q

IL6

A

stress response

124
Q

all cytokines and their receptors

A

have similar structures and activate similar signaling pathways

  • 4 long conserved alpha helices (cytokines)
  • dimeric receptors
125
Q

cytokines activate

A

the Jak/STAT signaling cascade

126
Q

Receptor associated JAK kinases activate

A

STAT transcription factors bound to a cytokine receptor

127
Q

SH2 and PTB domains bind to

A

specific sequences surrounding phosphotyrosine residues

128
Q

signaling from cytokine receptors is modulated by

A

negative signals

129
Q

Short term regulation of cutokine signaling

A

by SHP1 phosphatase (inactivates JAK)

130
Q

Long term regulation of cytokine signaling

A

SOCS (in place of JAK) recruits ubiquitin ligase that leads to the degradation

131
Q

receptor tyrosine kinases and

A

activation of Ras

132
Q

difference between cytokine receptors and receptor tyrosine kinases

A

receptor tyrosine kinases have intrinsic protein tyrosine kinase activity whereas cytokine have JAK

133
Q

ligands of RTKs

A

NGF, FGF, PDGF, EGF, insulin

134
Q

activation of RTK stimulates

A

Ras-MAP kinase pathway (and other pathways)

135
Q

functions of RTK pathways

A

regulation of cell proliferation and differentiation, promotion of cells survival, and modulation of cellular metabolism

136
Q

ligand bind leads to RTK..

A

transphosphorylation

137
Q

Ras

A

a GTPase switch protein alternates between active and inactive states

138
Q

accelerates Ras activation

A

GEF (guanine nucleotide exchange factor)

139
Q

deactivation of Ras

A

GAP (GTPase activating protein)

140
Q

What links RTKs to Ras?

A

An adapter protein and GEF

GRB2, Sos

141
Q

Binding of Sos Protein to Inactive Ras causes

A

conformational change that activates Ras

142
Q

MAP kinase

A

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
Q

MAP Kinase regulates

A

the activity of many Tx factors controlling early-response genes

144
Q

early-response genes

A

induced well before cells enter the S phase and replicate their DNA

145
Q

What do tyrosine kinase receptors do?

A
  • Phosphorylate tyrosine residues

* Provide docking sites for adaptor proteins (i.e. SH2 containing proteins, grb2/sos, cbl, PLC

146
Q

Receptor guanylyl cyclases

A
  • Ligands: ANF and related peptide hormones

* Receptor: Single TM domain, GC activity in cytosolic domain •Signal transduction: Through formation of cGMP

147
Q

Receptor phosphotyrosine phosphatases

A
  • 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
Q

T-cell receptors

A

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
Q

G protein–coupled receptors

A

Ligands: Epinephrine, glucagon, serotonin, vasopressin, ACTH, adenosine, and many others (mammals); odorant molecules, light; mating factors (yeast)
Receptors: Seven transmembrane

150
Q

TGF

A

Ligands: Transforming growth factor

151
Q

Cytokine receptors

A

Ligands: Interferons, erythropoietin, growth hormone, some interleukins (IL-2, IL-4), other cytokines
Receptors: Single transmembrane

152
Q

Receptor tyrosine kinases

A

Ligands: Insulin, epidermal growth factor (EGF), fibroblast growth factor (FGF), neurotrophins, other growth factors
Receptor: Single transmembrane

Molecular Cell Biology (5 decks)

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