Cell-cell adhesion

Question 1

Which transmembrane adhesion protein makes up adherens junctions?

Answer 1

cadherin

Question 2

What is the intracellular cytoskeletal attachment of adherens junctions?

Answer 2

Actin filaments

Question 3

Which transmembrane adhesion proteins make up desmosomes?

Answer 3

cadherin (desmoglein and desmocollin)

Question 4

Which intracellular cytoskeletal attachment makes up desmosomes?

Answer 4

Intermediate filaments

Question 5

Which cadherins are involved in homophilic binding?

Answer 5

classical and desmosomal cadherins (cadherin interacts with same cadherin on another cell)

Question 6

Which cadherins are involved in heterophilic binding?

Answer 6

Fat cadherin (binds to dachsous)
Classical cadherins

Question 7

What ions are cadherin-mediated adhesions dependent on?

Answer 7

calcium

Question 8

What is the structure of cadherin?

Answer 8

Short intracellular domain

Long extracellular domain

5 cadherin repeats linked by short linker segments

Question 9

What happens to cadherin structure in presence of low calcium?

Answer 9

Cadherin becomes flexible and hook-shaped

Question 10

How does calcium stabilise cadherin?

Answer 10

calcium ions bind at interphase between cadherin repeat domains and linker segments

Question 11

Do cadherins bind with low or high affinity? How can it become higher?

Answer 11

Low
Become high affinity through velcro principle.

Question 12

Which protein groups connect cadherins to the actin filaments?

Answer 12

Catenins
Vinvulin

Question 13

What are filopodia?

Answer 13

finger-like protrusions made of actin filaments

Question 14

What do filopodia become after Rac?

Answer 14

Lamellipodia

Question 15

What happens in adherens junctions assembly when Rac is deactivated and Rho is activated?

Answer 15

Formation of parallel bundles of actin filaments.

Formation of myosin bundles (contraction structures)

Question 16

Which desmosome is a key adapter protein linking intermediate filaments to desmosomal cadherins?

Answer 16

desmoplakin

Question 17

What is an important molecule in the transduction of mechanical tension by adherens junctions?

Answer 17

Alpha-catenin

Question 18

During cadherin-cadherin binding, a pulling force occurs between cells.

What do the catenin proteins do at this time?

Answer 18

Extend to unfolded position.

Bind to vinculin.

Vinculin recruits more actin filaments.

Question 19

What is the adhesion belt?

Answer 19

Adherens junctions lining the lumen of gut.
Linked to actin filaments, circling the inner edge of epithelial cells.

Question 20

How does a sheet of epithelial cells become an epithelial tube?

Answer 20

Organised tightening of the adhesion belt.
Invagination of the epithelial sheet.
Pinching off of epithelial tube.

Question 21

What is cadherin-dependent cell-sorting dependent on?

Answer 21

cadherin type
cadherin levels

Question 22

Which cadherin is expressed by neuronal crest cells?

Answer 22

Cadherin 7

Question 23

What are the four main functions of adherens junctions?

Answer 23

Tube structure formation.
Cell sorting.
Dynamic cell-cell adhesion
Signalling platforms

Question 24

How does P120 catenin affect signalling of RhoA, NF-KappaB signalling and MAPK?

Answer 24

Blocks RhoA signaling
Blocks NF-kappaB signaling
Blocks the MAPK pathway

Question 25

What pathway is beta catenin involved in?

Answer 25

Wnt signaling pathway

Question 26

What does contact inhibition of cell proliferation ensure?

Answer 26

Tissue homeostasis

Question 27

During cell density sensing, what protein does alpha catenin bind to?

Answer 27

Scaffold protein 14-3-3 in cell cytoplasm

Question 28

Which protein does alpha-catenin/14-3-3 complex bind in the cytoplasm during cell density sensing?

Answer 28

Yap

Question 29

What is Yap protein?

Answer 29

Transcriptional co-activator Promotes cell growth Can serve as oncogene when deregulated

Question 30

Why does the alpha catenin-14-3-3 complex bind Yap when the cell is well connected via adherens junctions?

Answer 30

Bound Yap remains in the cytoplasm. Prevents it from entering nucleus and promoting cell growth.

Question 31

What does disruption of adherens junctions lead to (regarding Yap)?

Answer 31

The alpha catenin/14-3-3 complex releases Yap. Yap is phosphorylated and enters nucleus.

Question 32

When adherens junctions are disrupted and Yap is allowed to enter the nucleus, what does it bind to?

Answer 32

TEAD transcription factors

Question 33

How is cell proliferation inhibited in hair follicles?

Answer 33

Dermal stem cells in Bulge remain quiescent in G0 until hair needs to be generated. Cell density detected by alpha-catenin-dependent adherens junctions.

Question 34

Which trans-membrane protein is involved in transient cell-cell interactions?

Answer 34

Selectins

Question 35

What are the three types of selectins (and where are they found)?

Answer 35

L-selectins (Leukocytes) P-selectins (platelet) E-selectins (endothelial cells)

Question 36

What are the three main domains of a selectin?

Answer 36

Lectin domain EGF-like domain Cytoplasmic domain

Question 37

What do selectins bind to?

Answer 37

carbohydrates

Question 38

Why are endothelial cells encouraged to express E-selectin during inflammation?

Answer 38

To attract WBCs expressing carbohydrates

Question 39

Why is the adhesion between endothelial cells and leukocytes (via selectins bonding to carbohydrates) weak?

Answer 39

so leukocytes can roll along the endothelial cells surface to site of inflammation.

Question 40

The weak adhesion and rolling of WBCs is selectin-dependent. The switch to strong adhesion is dependent on which protein?

Answer 40

Integrin

Question 41

What are two examples of Immunoglobulin (Ig)-like superfamily CAMs?

Answer 41

NCAM (neural) ICAM (intracellular) - important in WBC binding to endothelial cells

Question 42

What is the main difference between cell-cell adhesion mediated by cadherins vs CAMs?

Answer 42

Calcium is required for cadherin-mediated cell-cell adhesions.