Lecture 29

Question 1

Which type of focal adhesion junctions tends to be immobile

Answer 1

Low density adhesions

Question 2

Glanzmann’s thrombasthenia is a disease associated with integrins. Discuss the cause and symptoms of this condition

Answer 2

Glanzmann’s thrombasthenia is caused by a mutation in integrin ?IIb?3 that causes symptoms similar to haemophilia. The abnormal integrin impairs platelet function and causes easy bruising and increased likelihood of bruising

Question 3

What part of the actin cytoskeleton involved in cell motility is responsible for membrane tension and the transmission of tension

Answer 3

Actin cortex

Question 4

Focal adhesions act during necrosis, T or F

Answer 4

F – the act during anoikis or attachment-dependent cell death

Question 5

Outline the process of traditional cell migration

Answer 5

The actin-polymerisation-dependant protrusion and the firm attachment of lamellipodium at the leading edge of the cells moves the edge forwards and stretches the actin cortex. Contraction at the rear end of the cell propels the body of the cell forwards to release some of the tension. Finally, new focal adhesions are made at the front and the old ones are disassembled at the back as the cell crawls forwards

Question 6

Which type of focal adhesion junctions are Rac1 and cdc42 dependant

Answer 6

Low density adhesions

Question 7

What is the role of focal adhesion kinase (FAK) in cell adhesion and integrins

Answer 7

FAK is a cytoplasmic protein tyrosine kinase present at cell-matrix junctions in association with the cytoplasmic tails of integrins. It is activated on formation of adhesions but may actually inhibit focal adhesions. FAK is also regulated by the concentration of intracellular Ca2+

Question 8

What three proteins are involved in the maturation of focal adhesions

Answer 8

Actin-binding proteins (ABPs), small G-proteins and myosin

Question 9

What is the name of the complex responsible for nucleation of the actin filament and what is the involvement of Rac

Answer 9

Arp2/3 – stimulated by Rac activity

Question 10

Which termini make up the intracellular and extracellular domains of integrins

Answer 10

The C-terminus forms the intracellular regions of the proteins whilst the N-termini are found in the extracellular domain of the receptors

Question 11

What is the role of endocytosis in cell motility

Answer 11

Endocytosis of a secreted factor alternates the concentration of that factor. In addition, when integrins and other CAMs bind to ligands and extracellular matrix proteins they can be taken into the cell which alters the way the cell subsequently interacts with the extracellular matrix

Question 12

How many different known varieties of integrins are there

Answer 12

24 known integrins (from 18? subunits and 8? subunits)

Question 13

Fibronectin is an extracellular matrix protein that binds to integrins, what sequence is responsible for this binding

Answer 13

RGD – arginine-glycine-aspartate

Question 14

Focal adhesions act through integrins, T or F

Answer 14

T

Question 15

Which proteins and interactions are required for formation of the high density adhesions

Answer 15

RhoA and actin-myosin interactions

Question 16

Explain the role of membrane cycling in cell motility

Answer 16

Membrane endocytosis is occurring constantly around the whole cell. Meanwhile, exocytosis occurs at leading edge leading to an addition of phospholipid bilayer and an increase in the surface area of the membrane. This corresponds to a net membrane addition which could provide a net motive force for cell motility. There is also a net rearwards flow of membrane as membrane is constantly added at leading edge which shifts existing membrane backwards. Therefore, if the membrane is fixed by focal contacts the cell will move forward

Question 17

What is meant by a focal adhesion

Answer 17

Focal adhesions are areas of temporary attachment of a cell to the medium it is moving through

Question 18

What is the proposed difference in timing of the two types of focal adhesions during their maturation

Answer 18

Low density adhesions that are immobile tend to appear earlier, whereas, high density adhesions appear later and are motile

Question 19

Binding of which cations effect the binding of the two integrin glycoproteins

Answer 19

Ca2+ and Mg2+

Question 20

What is the role of fibronectin in migration of the neural crest cells

Answer 20

Fibronectin trails allows neural crest cell migration.

Question 21

To which cytoskeletal element do the majority of integrins bind link to

Answer 21

Actin filaments

Question 22

Signals to dictate cell motility can be soluble or insoluble, give examples of both

Answer 22

Soluble – netrins, insoluble – CAMs

Question 23

Mammalian cell motility is interlinked with adhesion and is mostly actin-based, T or F

Answer 23

T

Question 24

What are the two types of focal adhesion junctions

Answer 24

Low density adhesions and high density adhesions

Question 25

What is the name of the specific motif that integrins bind to on target extracellular matrix proteins

Answer 25

RGD – arginine-glycine-aspartate

Question 26

Integrins are a key class of cell adhesion molecules. Explain the role integrins

Answer 26

Integrins are extracellular matrix receptors present in the membrane of cells. They act to link the extracellular matrix to the cytoskeleton

Question 27

Describe the structure of integrins

Answer 27

Integrins consist of two, non-covalently associated glycoproteins each with an ? and ? subunit.