L12 (test 2)

Question 1

what is polarity

Answer 1

A difference in structure, composition or function between the two poles of a cell, such as apical/basolateral in an epithelial cell, axon/dendrites in a neuron

Question 2

what does polarity mean in terms of epithelial cells

Answer 2

In epithelial cells this also means location of a

protein in a specific location (e.g. apical or basolateral) in the cellular membrane.

Question 3

what is the first steep for a cell to become an epithelial cell

Answer 3

when the cell is first formed the protein channels will be scattered randomly (it has not apical and basolateral side)

the first thing that happens is the cell will bind to the basal laminar via hemidesmosomes to help ordinate the cell

Question 4

what 2 things are essential when establishing epithelial cell polarity

Answer 4

cell to basement membrane and cell to cell interactions

Question 5

how do epithelial cells form the epithelium

Answer 5

the founder cell (which is like a stem cell) divides when you get a scratch of something

the new cells will then form connections with the basal laminar through hemidesmosomes

then the new cell will form intercellular connections with neighboring epithelial cells helping to form an enlarged epithelium

Question 6

after hemidesmosome formation, what is the next steep

Answer 6

steep 2 is the first cell to cell interaction through adherence junctions

Question 7

what does the formation of adherence junctions initiate

Answer 7

epithelial formation

Question 8

what if the main filament in adherence junctions

Answer 8

actin

Question 9

what holds adherence junctions together

Answer 9

CAM

Question 10

how do adherence junctions form

Answer 10

1. Nectin proteins make initial cell to cell contact. Nectins on neighbouring cells interact. Ca2+-independent cell adhesion.
2. E-cadherin on one cell forms homodimer with E-cadherin on neighbouring cell pulling the 2 cells tightly together, requires Ca2+.
3. Cytoplasmic tail of E-cadherin binds catenins which links to the actin cytoskeleton.
4. Catenins also link nectin and cadherin complexes to pull all the proteins together to make the AJ.

Question 11

what is the role of nectin in adherence junction formation

Answer 11

1. Nectin proteins make initial cell to cell contact. Nectins on neighbouring cells interact.

Ca2+-independent cell adhesion. doesn’t need Ca

Question 12

what is the role of cadherin in adherence junction formation

Answer 12

2. E-cadherin on one cell forms homodimer with E-cadherin on neighbouring cell pulling the 2 cells tightly together, requires Ca2+.
3. Cytoplasmic tail of E-cadherin binds catenins which links to the actin cytoskeleton.

Question 13

what is the role of Catenins in adherence junction formation

Answer 13

3. Cytoplasmic tail of E-cadherin binds catenins which links to the actin cytoskeleton.
4. Catenins also link nectin and cadherin complexes to pull all the proteins together to make the AJ.

Question 14

Which processes are required for establishing epithelial polarity?

A. Neighbouring cells interacting with each other through
adherens junctions.

B. Connections between epithelial cells and their basement membrane.

C. Nectin proteins from neighbouring cells connecting with each other.

D. All of the above.

Answer 14

D

Question 15

what is steep 3 in the formation of an epithelial cell

Answer 15

small GTP binding protein activation

Question 16

what is steep 4 in the formation of an epithelial cell

Answer 16

activation of polarity complexes

Question 17

how do GTP binding proetins get activated

Answer 17

the formation of AJ recruits many proetins. small GTP binding protein is one of these

Question 18

there are many small GTP binding proetins. we only have to remember the name of one of these. what is it

Answer 18

cdc42

Question 19

what/how do the polarity complexes get activated

Answer 19

steep 4 = activation of polarity complexes

cdc42 (GTP binding protein) activates protein kinase C (aPKC) which helps in the formation/activation of polarity complexes

Question 20

what are the 4 polarity complexes

Answer 20

aPKC, PAR, CRB, SCRIB

Question 21

what do the polarity complexes do

Answer 21

they maintain apical and basolateral polarity

one way they do this via the formations of tight junctions (steep 5)

Question 22

what do tight junctions interact with

Answer 22

apical polarity complexes

Question 23

what do tight junctions act as (3 roles)

Answer 23

Barrier: limits passage of ions and molecules between cells in the paracellular pathway.

Gate: can allow certain solutes to flow through the paracellular pathway.

Fence: prevent movement of proteins between apical and basolateral domains

Question 24

what happens is you remove ZO proteins from tight junctions

Answer 24

the cells will still maintain their polarity

Question 25

what is steep 5

Answer 25

the formation of tight junctions

Question 26

what is steep 6

Answer 26

positioning of 3 protein polarity complexes

Question 27

what are the 4 different polarity complexes in steep 6 and where are they located

Answer 27

1. PAR complex – apical, near TJ 2. CRB complex – apical, near TJ 3. SCRIB complex – basolateral the 4th one is aPKC

Question 28

what does the a stand for in aPKC

Answer 28

atypical

Question 29

what is aPKC activated by

Answer 29

small GTP binding proteins such as cdc42

Question 30

why is aPKC atypical

Answer 30

aPKC is the only polarity protein that has enzymatic activity. The other polarity proteins are ‘scaffolding’ proteins allowing clusters of proteins to interact together.

Question 31

what does aPKC interact with/phosphorylate

Answer 31

CRB and SCRIB complexes

Question 32

what is mutual exclusion

Answer 32

When phosphorylated the polarity complexes are correctly located in their apical or basolateral domain. therefore when CRB and SCRIB are phosphorylated they stop moving as they are phosphorylated when they are in their correct location

Question 33

what are the 6 steeps of the formation of TJ and epithelial polarity

Answer 33

1. Interactions between neighbouring cells, and between cells and basement membrane. 2. Interaction between cells forms adherens junction. 3. Small GTP proteins (cdc42) activated. 4. Cdc42 activates aPKC - a polarity complex protein. 5. Tight junctions start to form. 6. Positioning of PAR and CRB polarity complexes to apical domain, and SCRIB complex to basolateral domain. Apical-basolateral polarity established.

Question 34

Crumbs defines the basolateral domain and scribble defines the apical domain BECAUSE aPKC is the only polarity complex with enzymatic activity

Answer 34

CRB is apical and SCRIB is basolateral therefore the first statement is false and the second is true

Question 35

what happens to cause epithelial mesenchymal transition (the full process)

Answer 35

when we get a scratch cells need to divide therefore the polarity complexes have to be pulled apart for cell division, then they are reformed, so have to be able to change rapidly this happens when TGF-beta binds to its receptor which leads to the disruption of tight junctions, adherens junctions and polarity complexes in 1 of 2 ways It will directly inhibit the par complex which defines the apical domain. It also will activate proteins called SMADS which when activated translocated into the nucleus. SMADS are transcription facts which lead to an increased expression on snail, zeba and twist. These proteins will downregulate proteins that are important in tight and adherence junction formation. EG snail zeb and twist downregulate - Cadherence - Claudinds - Acculdends - ZO proetins Without these we don't have tight and adherence junction therefore they fall apart (even coming off the basement membrane)

Question 36

what does TGF beta DIRECTLY inhibit

Answer 36

It will directly inhibit the par complex which defines the apical domain.

Question 37

what happens when TGF beta activates SMADS

Answer 37

when activated translocated into the nucleus. SMADS are transcription facts which lead to an increased expression on snail, zeba and twist. These proteins will downregulate proteins that are important in tight and adherence junction formation. EG snail zeb and twist downregulate - Cadherence - Claudins - Occludins - ZO proteins

Question 38

what happens if they cells don't reattach to the basement membrane

Answer 38

metastasis

Question 39

what do mutations in polarity complexes cause

Answer 39

Decreased formation or lack of tight junctions so barrier, gate and fence functions compromised. Changes in cell-cell adhesion and cell movement. Changes in location of apical and basolateral proteins. Cancer (A number of these polarity complexes have been seen to be tumor suppressors )

Question 40

the cells divide when they sense that the epithelial layer is thinner/damaged. what sences this

Answer 40

ZO proteins The ZO proteins will sense this and send transcription factors to the nucleus to stimulate cell division

Question 41

at high cell density what does ZO1 do

Answer 41

ZO1 keeps transcription factors that promote cell division localised to TJs preventing cell division. Epithelia carries out regular functions e.g. absorption/secretion

Question 42

when do epithelial cells become cancerous

Answer 42

Genetic changes in cancer cells of epithelia may promote EMT: cell division increases and loss of epithelial polarity.