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Cell Theme 2 and 3 > Weisel - Cell Adhesion > Flashcards

Weisel - Cell Adhesion Flashcards

1
Q

Functions of cell junctions:

A

Tight junctions - selective permeability
Anchoring junctions - cytoskeleton-cytoskeleton connections
Gap junctions - cell cell communication
Selective cell-cell adhesion and cell sorting?
Cell adhesion receptor clustering?

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2
Q

Anchoring junctions

A

Cell-cell: e.g. cadherins

Cell-matrix: e.g. integrins

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3
Q

Occluding junctions

A

Between epithelial cells - e.g. claudins

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4
Q

Channel forming junctions

A

Connexins or innexins

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5
Q

Actin attachment sites

A

Adherens junctions - cellcell

Focal adhesions - cellmatrix

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6
Q

Intermediate filament attachment sites

A

Desmosomes - cellcell

Hemidesmosomes - cellmatrix

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7
Q

Occluding junctions

A

Tight junctions - vertebrates only

Septate junctions - invertebrates only

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8
Q

Channel forming junctions

A

Gap junctions - animals

Plasmodesmata - plants

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9
Q

Tight junction

A

Seals gap between epithelial cells, at the top

These form a selective permeability barrier across epithelial cell sheets, helsp cells withstand stresses

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10
Q

Adherens junction

A

Next one down, connects actin filament bundle in one cell with that in the next cell

A CONTINUOUS ADHESION BELT PRESENT IN EPITHELIAL CELLS - CONNECTING BUNDLES OF ACTIN FILAMENTS FROM CELL TO CELLS.
Adhesion proteins may be cadherins.

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11
Q

Desmosome

A

Connects intermediate filaments in one cell to those in the next cell

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12
Q

Gap junction

A

Allows passage of small water soluble stuff

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13
Q

Hemidesmosome

A

Anchors intermediate filaments to the ECM

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14
Q

Actin linked cell matrix, anchoring junctions

A

Actin-linked cell matrix adhesion anchors actin filaments in cell to ecm

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15
Q

Which junctions are stable and which are labile?

A

Tight/occluding junctions are stable
Some anchoring junctions as well
Others are labile

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16
Q

How does selective cell-cell adhesion occur ? (binding types

A
  1. homophilic binding
  2. heterophilic binding
  3. binding thorugh extracellular linker molecule
17
Q

How was the presence of tight junctions shown?

A

Electron dense tracer was added to the surface of the cell and it did not go beyond where the tight junction was. it could not cross.

You can also visualize using freeze fracture which allows you to see the channels

18
Q

What proteins form tight junctions?

A

Claudins and occludins - small proteins with 4 transmembrane helices and both N- and O-terminal ends in the cytoplasm and extracellular loops that interact in a homophilic manner.

19
Q

Purpose of anchoring junctions?

A

Form a strong membrane spanning structure.

20
Q

2 main components of anchoring junctions?

A
  1. Intracellular anchor proteins - form a plaque on cytoplasmic face of the membrane and connect the adhesion membrane protein to the cytoskeleton
  2. Transmembrane adhesion proteins - cytoplasmic domain that binds to anchor protein and extracellular domain that binds to another cells adhesion protein or to ECM.
21
Q

Cell adhesion molecules

A

Cadherins
Ig-superfamily CAMs
Mucin like CAMs
Integrins

22
Q

Cadherins

A

main adhesion molecules holding cells together in early embryonic tissues, expressed in virtually all cells.

Calcium dependent

Form homodimers in the cell membrane - extracellular domain of one cadherin dimer binds the identical dimer on the adjacent cell. Ca2+ makes them rigid.

5 repeats (extracellularly) separated by Ca2+ binding sites 
Crystal structure of a single repeat resembles an Ig Domain.

Cadherins can be coupled to actin via alpha and beta catenins.

23
Q

Integrins

A

Cell adhesion proteins that link to the cytoskeleton or cell-cell. Importnat for cell-cell junction. There is an alpha and beta subunit but lots of combinations (and for instance beta 3 integrin can be joined to a different alpha subunit..) lots of combinations!
Platelets can be used to study integrins…
Integrin aIIbBeta3 is missing and does not bind to fibrinogen in glanzmann’s thrombasthenia.
Activation of integrin leads to conformtional change that binds ligand.

24
Q

How can you study integrin?

A

Make nanodisks, each one with a single integrin in the membrane. Look at different conformations of the integrin. Mostly you see bent and resting conformation but in presence of tailin you see unfolded open form. Resting conformation - bent form. Active conformation - open form.

25
Q

Assay for cell-cell adhesion

A

Take isolated cells and put them on a plate and see if they aggregate. Block with appropriate antibody first. Melanoma cells have lost E-cadherin and gained N-cadherin.

26
Q

Optical trapping experiment? / optical tweezers

A

If you shine a beam of light you can actually use force from that light to trap things.
This comes in useful if you have a ligand on one surface and receptor molecule on the other surface. You can move the beam and moved the trapped bead and touch it to the pedestal and then measure the bead’s position in the trap. If there is a ligand receptor bond, it will take force to break the bond and you can measure the force needed to break the bond.

27
Q

P-selectin

A

Present on platelets and endothelial cells that have been activated by inflammatory response. This mediates leukocyte adhesion and rolling…

28
Q

Ig Superfamily - CAMS

A

Mediates calcium independent cell cell adhesion. Weaker than those mediated by cadherins.
CAMs used during development and regeneration.
There are different forms of N-CAM (neural cell adhesion molecule) present in many cells. they are made of ig domains and fibronectin type iii domains and they interact via homophilic binding.

29
Q

Gap junctions allow for

A

Electrical coupling
Metabolite sharing
Embryogenesis - cooperative assembly of cells following same pathway. In early embryo, cells are coupled to each other electrically. Granulosa cells also communicate each other this way.

30
Q

How could we visualize gap junctions

A

Freeze fracture is one way

31
Q

Can gap junction permeability be regulated?

A

Yes - in general decreaes of cytosolic ph or increases of ca2+ decrease gap junction permeability which is likely a damage control response.

32
Q

Vinculin

A

Anchor protein, located at focal adhesions, where actin bundles terminate at the membrane.

33
Q

How do we study clustering of adhesion receptors in the membrane?

A

We can do it with FRET - 2 fluorescence labels, one excites the other.
You can use this to determine if 2 molecules in a cell are close to each other. There has to be overlap between emission wavelength of protein 1 and excitation of fluorophore 2.
Or use BRET - which is a fret variation that uses bioluminescent luciferase.

34
Q

Adhesion mediated signaling

A
  • REceptor occupancy - binding cause signal transduction across cell membrane
  • Receptor clustering - junctional complexes
  • REceptor tensioning - binding to an immobilized ligand allows myosin contraction to tension linkages from ligand to actin.

Cell Theme 2 and 3 (7 decks)

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