Cell Migration, Barrier Fn/Epithelial Cells

Question 1

Usual steps in cell migration

Answer 1

(1) Receipt of stimulus
(2) Actin-mediated protrusion of one side of cell
(3) Formation of integrin-based adhesions
(4) Creation of stress fibers (short, branched actin and long, straight actin filaments)
(5) Contraction of lagging end

Question 2

Types of cell protrusions

Answer 2

(1) Filopodia
(2) Lamellipodia
(3) Pseudopodia

Question 3

Filopodia

Answer 3

• Happens in growth cones and fibroblasts

- Long bundled actin filaments

Question 4

Lamellipodia

Answer 4

• Epithelial cells and fibroblasts

- Branched actin at leading edge

Question 5

Pseudopodia

Answer 5

• Neutrophils

- Stubby projections

Question 6

What assembles in lamellipodia? How?

Answer 6

Arp2/3 complexes (forms branched filaments at leading edge). As filaments form, ATP–> ADP making it a target for cofilin (depolymerizer)

Question 7

Cell organelle position during migration (leading vs. lagging end)

Answer 7

ER and Golgi towards leading edge, nucleus near lagging end

Question 8

General overview of neutrophil migration

Answer 8

(1) Chemoattractant activates GPCR
(2) GPCR activates Gi and G12/13
(3) Gi creates PIP3 which activates Rac (which supports actin polymerization at leading edge
(4) G12/13 induces RhoA (which directs lagging edge actin/myosin-mediated contraction

Question 9

What does Rac do?

Constitutive Rac activation leads to?

Answer 9

It directs actin polymerization by activating various downstream targets. Controls leading edge.

Leads to lamellipodia everywhere

Question 10

What does Rho do?

Answer 10

It facilitates contraction by activating Rho kinase (ROCK) and other proteins. Controls lagging edge.

Question 11

Focal complexes? Do? Mature into?

Answer 11

Anchor actin at the leading edge. Mature into stronger focal adhesions at the end of stress fibers. These disassemble at lagging edge

Question 12

What controls focal adhesion assembly and disassembly and how?

Answer 12

PIP gradient. PIP3 is higher at the leading edge while PIP2 is higher at lagging edge. Due to gradient of PTEN (phosphatase that converts PIP3 to PIP2)

Question 13

Selectins

Answer 13

Type of lectin specific for cells in bloodstream. Lectins are cellular adhesion molecules. Bind to sugar moieties and polymers. Binding triggers activation of integrins (stronger binding)

Question 14

Types of epithelium

Answer 14

Simple, stratified, pseudostratified

Squamous, cuboidal, columnar, transitional

Question 15

Epithelial cells are polar. Explain

Answer 15

Have apical surface facing lumen, basal surface facing basal lamina, and two lateral surfaces facing adjacent cells. Different proteins found within each membrane.

Question 16

Vectorial transport: basal membrane

Answer 16

Na+/K+ pumps

Question 17

Epithelial cells in small intestine use what to bring glucose in?

Answer 17

Use glucose/Na+ symporter (SLGT1) to bring glucose from the gut lumen into the cell. They then rely on GLUT2 to allow glucose to exit cell on basolateral side. Na leaves via Na/K ATPase at basolateral side.

Question 18

Cholera triggers diarrhea how?

Answer 18

By excessive activation of the CFTR transporter, causing excessive Cl- influx into intestine. Result of ion channels on basal membrane making the membrane potential negative.

Question 19

Protein sorting in epithelial cells

Answer 19

Proteins generally localized into basal membrane. Trans-Golgi network is what sends proteins to apical or basal surface.

Question 20

Transcytosis

Answer 20

Protein moving from one membrane to another

Question 21

Epithelial polarity achieved by both _____mechanisms. Examples of latter?
Inhibition of these lead to?

Answer 21

• Extrinsic and intrinsic.
• Intrinsic signals that direct polarity include:

(1) PAR complex: activates WASp to stimulate acting polymerization (Par3 recruits Par6 and aPKC which recruit CDC42, which activates WASp)
(2) Crumbs complex: localizes to tight junctions on lateral membranes
(3) Scribble complex: localizes to lateral membranes and regulates cell-cell contacts
- Inhibition of these lead to cancer – thought to be tumor suppressors.

Question 22

Epithelial adhesive interactions

Answer 22

(1) Tight jxns (zona occludens): seals gap between cells, control solute/solvent mvmt between compartments. Made of claudins, occludins, JAM, ZO1/2
(2) Adherens jxns (zonula adherens): sticks cells together. Made of cadherins and caterins
(3) Desmosomes: “spot welds”, most often in skin. Made of cadherins
(4) Gap jxns: permit transport of materials from cell to cell
(5) Hemidesmosomes: connect cell to basal lamina

Question 23

Adherens cadherins

Desmosome cadherins

Answer 23

• Bind end to end and require Ca2+ to stably connect. Link to intracellular actin
• Also require Ca2+ but link to intermediate filaments in cell

Question 24

Beta cadenin

Answer 24

Part of junctional complexes but also acts as trx factor in Wnt signaling cascade

Question 25

Wnt signaling cascade (canonical)

Answer 25

(1) Wnt binds Frizzled
(2) Frizzled recruits adaptor proteins
(3) These inactivate the destruction complex, which normally degrades free beta-catenin
(4) Beta-catenin translocates into nucleus and promote trx of Wnt-targeted genes

Question 26

Wnt signaling (noncanonical)

Answer 26

(1) Different Wnt family protein binds Frizzled.
(2) Leads to increased intracellular Ca2+
(3) Activates Rho and Rac
(4) Stimulates JNK signaling, which regulates actin and MT dynamics and thus cell shape