EXAM 3 STARTS: Cell adhesion

Question 1

how do cells define their capacity for adhesive interactions

Answer 1

by selectively expressing plasma membrane receptors with limited ligan-binding activity

Question 2

how are receptors expressed

Answer 2

mostly genetically but sometimes by extracellular stimuli

Question 3

what is the second principle of adhesion

Answer 3

many adhesion proteins bind one main ligand and many ligands bind a single type of receptor

Question 4

what makes the integrin family of receptors an exception to one-to-one pairing

Answer 4

they bind more than one ligand and some ligands, such as fibronectin, bind more than one integrin. they also bind ahdesion proteins on the surface of other cells including Ig-CAMs and one cadherin

Question 5

describe how cadherins prefer to bind and what does binding require

Answer 5

prefer to bind themselves so they promote the adhesion of like cells. it requires Ca2+

Question 6

describe how selectins bind

Answer 6

anionic polysaccharides like those on mucins. generally these interactions bind together two different types of cells

Question 7

describe how Ig-CAMs bind

Answer 7

they bind other cell surface adhesion proteins. may occur between the same or different cell types

Question 8

how do cells modulate adhesion

Answer 8

by controlling the surface density, state of aggregation, and state of activation of their adhesion receptors

Question 9

what does surface density reflect

Answer 9

level of synthesis, partitioning of adhesion molecules between the plasma membrane and intracellular storage compartments

Question 10

how can cells sort themselves

Answer 10

according to the type and level of cadherins they express

Question 11

what are cadherins

Answer 11

calcium dependent adhesion molecules

Question 12

what do cadherins do

Answer 12

establish and maintain intercellular connections
- spatial segregation of cell types

Question 13

what anchors cadherins into the cell

Answer 13

a complex of proteins called catenins

Question 14

what forms the adherens junctions

Answer 14

cadherin-catenin complex

Question 15

where do catenins bind

Answer 15

the actin cytoskeleton of the cell

Question 16

how well do cell surface adhesion proteins bind their ligands

Answer 16

weakly in comparison to other molecular interactions

Question 17

what do rapid, reversible binding of ligands (transient adhesion) allow for

Answer 17

-white blood cells to roll along the endothelium of blood vessels
- fibroblasts to migrate through CT

Question 18

where do many adhesion receptors interact

Answer 18

within the cytoskeleton inside the cell

Question 19

what do adapter proteins link

Answer 19

cadherins and integrins to actin filaments or intermediate filaments

Question 20

what is the purpose of adapter protein linkage of cadherins and integrins to actin filaments or intermediate filaments

Answer 20

provide mechanical continuity from cell to cell in muscles and epithelia, allowing them to transmit forces and resist mechanical disruption

Question 21

what does the association of ligands and adhesion receptors activate

Answer 21

intracellular signal transduction pathways, leading to changes in gene expression, cellular differentiation, secretion, motility, receptor activation and cell division

Question 22

how do cells attach to the underlying extracellular matrix

Answer 22

-focal adhesions- attach the actin cytoskeleton to fibers of fibronectin
- hemidesmosomes- connect intermediate filaments to basal laminae

Question 23

where are integrin-containing cell matrix junctions found

Answer 23

highly motile cells such as keratinocytes and in immobile strongly adherent cells such as epithelila
- weakly adherent

Question 24

where are hemidesmosomes found

Answer 24

mainly on the basal surface of epithelial cells

Question 25

what do hemidesmosomes do

Answer 25

firmly anchor epithelial cells to underlying basal lamina

Question 26

what does the cytosolic side of a hemidesmosome consist of

Answer 26

a plaque composed of adapter proteins which are attached to the ends of keratin filaments

Question 27

what is integrin alpha6beta4 localized to and what does it bind to

Answer 27

localized to hemidesmosomes and binds to plectin within the plaques and to laminin

Question 28

how do cell-matrix junctions increase the overall rigidity of epithelial tissues

Answer 28

by interconnecting the intermediate filaments of the cytoskeleton with the fibers of the basal lamina

Question 29

where is E-cadherin expressed

Answer 29

on all early mammilian embryonic cells, even at the 1-cell stage. later- restricted to epithelial tissues of embryos and adults

Question 30

where is P-cadherin expressed

Answer 30

trophoblast cells ( placental cells of the mammilian embryo that contact the uterine wall) and on the uterine wall epithelium

Question 31

what does P cadherin do

Answer 31

facilitates the connection of the embryo to the uterus

Question 32

what do protocadherins do

Answer 32

separate the notochord from the other mesodermal tissues during xenopus gastrulation

Question 33

where is N-cadherin expressed

Answer 33

first on mesodermal cells in the gastrulating embryo as they lose their E-cadherin expression. also highly expressed on cells of the developing CNS

Question 34

what does EP-cadherin do

Answer 34

critical for maintaining adhesion between the blastomeres of the xenopus blastula and is required for the normal movements of gastrulation

Question 35

what are protocadherins

Answer 35

calcium dependent adhesion proteins that differ from the classic cadhering in that they lack connections to the cytoskeleton through catenins

Question 36

what is homophilic binding

Answer 36

-cadherin joins cells together by binding same type of cadherin example: E-cadherins will stick best to other cells with E-cadherin and will sort out from cells containing N-cadherin

Question 37

how can cadherins be restricted in their expression

Answer 37

spatially

Question 38

what are the functions of the basal lamina

Answer 38

- molecular filter -cell barrier - molecular scaffolding to aid in regeneration after injury

Question 39

how does the basal lamina act as a molecular filter

Answer 39

retaining proteins in the blood while filtering toxic substances into the urine

Question 40

how does the basal lamina act as a cell barrier (example)

Answer 40

ameloblasts and odontoblasts separated by a BM during tooth development

Question 41

what does vinculin do when interacting with Arp2/3

Answer 41

at focal adhesions the leading edge promotes protrusion of the membrane

Question 42

what does vinculin do in traction force generation

Answer 42

links integrins to the actin cytoskeleton and bears the forces exerted during motility

Question 43

how does vinculin interact with PIP2

Answer 43

induces a conformational change that reduces vinculin interaction with actin, therby promoting the disassembly of focal adhesions

Question 44

how do t-cells use cell adhesion receptors

Answer 44

in process of antigen presentation

Question 45

how does mechanical tension activate signaling pathways at adhesion sites

Answer 45

exposure of cryptic sites, tension can affect protein conformation to expose protein binding sites or sites for kinases or other protein modifications

Question 46

how does RhoA regulate adhesion maturation through Rock and mDia

Answer 46

-adhesion of fibronecting activates RhoA through p115/RhoGEF and LARG, leading to rock mediated myosin stimulation. -GEF-H1, LARG, and mDia are recruited and promote actin polymerization -B1 and alphav integrin subtypes cooperate to regulate RhoA signaling and adhesion maturation

Question 47

how do cells transition to a motile state

Answer 47

de-adhesion of cells from the ECM by inhibition of cell-matrix interactions and by destruction of matrix components

Question 48

what do the main class of disintegrins contain

Answer 48

integrin-binding RGD sequence in ECM proteins

Question 49

what do disintegrins do

Answer 49

bind to integrins on the surface of cells and competitively inhibit binding of cells to matrix components

Question 50

what does the secondary class of disintegrins contain

Answer 50

2 proteases: ADAMs and MMPs

Question 51

what are ADAMs and what do they do

Answer 51

membrane bound proteases that catalyze shedding of transmembrane proteins -soluble enzyme that cleaves non-fibrillary ECM proteins

Question 52

what do tight junctions do

Answer 52

seal gap between epithelial cells

Question 53

what do adherens junctions do

Answer 53

connect actin filaments between cells

Question 54

what do desmosomes do

Answer 54

connects intermediate filaments between cells

Question 55

what do gap junctions do

Answer 55

allow passage of small water soluble molecules from cell to cell

Question 56

what do hemidesmosomes do

Answer 56

anchor intermediate filaments in cell to ECM

Question 57

what are the cell- cell junction types and what is their transmembrane adhesion protein

Answer 57

adherens and desmosome and cadherin

Question 58

what are the cell-matrix junction types and what is their transmembrane adhesion protein

Answer 58

actin-linked cell-matric adhesion and hemidesmosomes and they use integrins