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BIO 317 > 13 - Signaling Mechanisms Regulating Cytoskeletal Dynamics I > Flashcards

13 - Signaling Mechanisms Regulating Cytoskeletal Dynamics I Flashcards

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1
Q

What mediates the morphological changes of cells during cell polarization?

A

The cell cytoskeleton

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2
Q

What makes up the cytoskeleton?

A

Microtubules and microfilaments

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3
Q

How is the actin cytoskeleton formed?

A

By monomers of actin forming large oligomers

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4
Q

What is needed for actin monomers to bind together?

A

ATP

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5
Q

What is the structure of actin filaments?

A

A double helix

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6
Q

True or false: actin filaments have directionality

A

True: they have a plus end and a minus end

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7
Q

What happens at the plus end of actin?

A

More monomers of actin are added

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8
Q

What higher order structures are possible with actin filaments?

A

Branching, binding together, etc.

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9
Q

True or false: the actin cytoskeleton is a static structure

A

False: it is highly dynamic

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10
Q

How is the actin cytoskeleton dynamic?

A

It can polymerize or degrade based on the needs of the cell

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11
Q

What is the significance of the actin cytoskeleton being dynamic?

A

Allows for large morphological changes in the cell

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12
Q

What happens at the minus end of actin?

A

The actin filaments get degraded by enzymes

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13
Q

What does aPKC do?

A
  1. Phosphorylates and activates crucial downstream targets for polarization
  2. Facilitates formation of actin cytoskeleton rearrangement
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14
Q

How does PAR-3 regulate cytoskeletal remodeling?

A

By regulating Rac-1 and recruiting a ring of F-actin

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15
Q

How does PAR-3 regulate tight-junction assembly?

A

By localizing to the site, and recruiting other proteins

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16
Q

What will be the phenotype of epithelial cells if PAR-3 and PAR-6 were deleted?

A

A mix of basal and apical features, thus destroying any unique features

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17
Q

How is PAR-3 and PAR-6 localized in the neurons during development?

A

All around the neurites in stage 2, but only in the axon in stage 3

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18
Q

What is the significance of PAR-3 and PAR-6 being localized in the axon in stage 3?

A

They play a later role in axon development (compared to LKB1)

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19
Q

What happens when PAR-3 is overexpressed in neurons?

A

They develop multiple axons

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20
Q

What happens if aPKC is deleted from neurons?

A

They do not develop axons

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21
Q

What does PAR-6 interact with?

A

aPKC, PAR-3, and Cdc42-GTP

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22
Q

What GTPases are found in the positive feedback loop of axon development?

A

Cdc42 and Rac-1

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23
Q

What are GTPases?

A

GTP-hydrolyzing enzymes, that depend on GTP hydrolysis for their function

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24
Q

What functions do GTPases regulate?

A

Migration, development, trafficking, and regulation of cytoskeletal dynamics

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25
Q

When is a GTPase inactive?

A

When bound to GDP

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26
Q

When is GTPase active?

A

When bound to BTP

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27
Q

What helps activate a GTPase?

A

GEF

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28
Q

What helps inactivate a GTPase?

A

GAP

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29
Q

How do GEFs work?

A

Exchange bound GDP for GTP (activate)

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30
Q

How do GAPs work?

A

Increase rate of GTP hydrolysis of GTPase (inactive)

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31
Q

True or false: PAR-6 is always bound to Cdc42

A

False: it is only bound when Cdc-42 is active (GTP bound)

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32
Q

What does Cdc-42 regulate?

A

The localization of the scaffold proteins (PAR-3 and PAR-6) to the apical domain

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33
Q

When happens if Cdc-42 is inactivated?

A

Delocalization of scaffold proteins (PAR-3 and PAR-6)

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34
Q

How does Cdc-42 mediates apical domain polarization?

A

Through remodeling of the actin cytoskeleton and tight junctions

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35
Q

What is TIAM-1?

A

The GEF for Rac-1

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36
Q

What is the GEF for Rac-1?

A

TIAM-1

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37
Q

Where does TIAM-1 bind to?

A

PAR-3

38
Q

When does PAR-3 and PAR-6 mediate cytoskeletal remodeling?

A

When PAR-3 is activated by Rac-1

39
Q

What does Rac-1 do?

A

Recruits F-actin for cytoskeletal remodeling via activation of PAR-3

40
Q

What happens when TIAM-1 is inactivated?

A

Collapse of apical domain architecture

41
Q

What is the “crux” of the positive feedback loop in neuronal development?

A

PI3K

42
Q

What does PI3K stand for?

A

Phosphoinositide 3-kinase

43
Q

What type of protein is PI3K?

A

A serine/threonine kinase

44
Q

How can PI3K be activated?

A
  1. Association with phosphorylated RTKs
  2. Binding to active, GTP-bound Ras
  3. Binding to other GTPases such as Rac-1
45
Q

What pathways does PI3K act in?

A

Cell growth, cell survival, translation, organelle biogenesis, organelle localization, and cytoskeleton regulation

46
Q

Where does PI3K act?

A

At the cell surface

47
Q

Why is PI3K a critical regulator of the cell surface?

A

This is where it is localized when it is activated

48
Q

What is the structure of PI3K?

A

Regulatory domain (p85) and catalytic domain (p110)

49
Q

What is the p85 domain of PI3K made up of?

A

SH2, SH3, and proline-rich regions

50
Q

What is the significance of the structure of the p85 domain of PI3K?

A

Many protein-binding domains for regulation of its activity

51
Q

What does PI3K do once it is activated?

A

Convert PIP2 into PIP3

52
Q

What is PIP2?

A

Phosphatidylinositol 4,5-bisphosphate

53
Q

What is PIP3?

A

Phosphatidylinositol 3,4,5-trisphosphate

54
Q

What does PTEN do?

A

Converts PIP3 into PIP2

55
Q

What is the role of PTEN?

A

Negative regulation of PI3K pathway

56
Q

What type of molecules are PIP2 and PIP3?

A

Lipid second messengers

57
Q

True or false: PIP3 is a stable second messenger

A

False: it is quickly degraded by PTEN

58
Q

What type of protein is PTEN?

A

A phosphatase

59
Q

What does PIP3 activate?

A

Akt, and the rho family of GTPases

60
Q

What is another name for Atk?

A

PKB (protein kinase B)

61
Q

What do the rho GTPases activate?

A

PI3K

62
Q

What is the significance of rho GTPases activating PI3K?

A

This creates a positive feedback loop (PI3K –> PIP3 –> rho GTPases –> PI3K)

63
Q

What is a PH domain?

A

Pleckstrin homology domain

64
Q

What is the purpose of a PH domain?

A

Allow binding to PIP3 to regulate activity

65
Q

How does Akt get activated?

A

By binding to PIP3, being recruited to the cell surface, and being further phosphorylated by PKD

66
Q

How does Akt get phosphorylated by PKD?

A

PKD is activated and recruited to the cell surface by PIP3

67
Q

What pathways are downstream of Akt?

A
  1. Inhibition of apoptosis and promotion of cell survival
  2. Activation of translation (through mTOR)
  3. Activation of small GTPases
68
Q

How does PAR-3 get recruited to the cell membrane?

A

By binding to PIP2

69
Q

Besides PAR-6 and aPKC, what is bound to PAR-3?

A

TIAM-1, PIP2, and PTEN (and oligomers)

70
Q

Why does PAR-3 bind to PTEN?

A

PTEN creates more PIP2, leading to stronger anchoring of PAR-3 to the cell membrane

71
Q

How does PAR-3 get recruited to the tight junctions?

A

By associated with proteins that are critical components of the tight junctions

72
Q

What is the full scaffold complex seen in cell polarization?

A

PAR-6 binds with aPKC, Cdc-42-GTP, and PAR-3. PAR-3 binds with TIAM-1/Rac-1-GTP, PIP2, PTEN, and PAR-6

73
Q

What is the full, major positive feedback loop in polarization?

A

PI3K –> Cdc-42 –> aPKC/PAR-3/PAR-6 –> TIAM-1/Rac-1 –> PI3K

74
Q

What are some example of rho GTPases activated by PI3K (and PIP3)?

A

Rac-1 and Cdc-42

75
Q

What is the significance of PI3K activating rho GTPases?

A

This creates a positive feedback loop, thus leading to continuous signaling

76
Q

Why does PAR-3 bind to PIP2 and not PIP3?

A

PIP3 concentrations are kept fairly low, as a means of negative regulation of PI3K

77
Q

True or false: TIAM-1 and Rac-1 are found in physical association when they are both in the scaffold

A

True: Rac-1 associated with the GEF through a physical association

78
Q

True or false: PAR-6 can oligomerize, similar to PAR-3

A

True: this leads to robust signaling through recruitment of many scaffolds

79
Q

True or false: many of the signaling determinants in polarization only function in that pathway

A

False: many are also upstream of cell growth and survival, development, organelle biogenesis, etc.

80
Q

What is needed to regulate positive feedback loops?

A

Negative feedback

81
Q

How can negative regulation be exerted in the cell?

A

GAPs, PDEs, and phosphatases

82
Q

What do GAPs negatively regulate?

A

GTPases

83
Q

What do PDEs negatively regulate?

A

cAMP (and its downstream activators)

84
Q

What do phosphatases negative regulate?

A

Kinases (and their products, such as PIP3)

85
Q

In terms of polarization, which regulation is more well understood?

A

Positive regulation (as opposed to negative regulation)

86
Q

What is the phenotype of neurons with deleted PI3K?

A

No axons, but also no healthy neurites, smaller cells, not as healthy

87
Q

Why do neurons that have deleted PI3K not look healthy?

A

PI3K is involved in cell growth and survival as well as neuronal polarization

88
Q

What is the conclusion of the experiments that deleted PI3K from neurons?

A

Deleting PI3K may not be the best way to look at the question of neuronal development (is it just because the neurons are sick?)

89
Q

Why is deleting PI3K not the best way to study neuronal development?

A

Not sure if the phenotype is due to the kinase, or just that the neurons are not surviving well

90
Q

Where is aPKC located when it is not bound to PAR-3 and PAR-6?

A

All over the cell

91
Q

What do the experiments about inhibiting PI3K suggest about its interactions with the neurites?

A

PI3K may be involved in proper neurite formation

BIO 317 (27 decks)

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