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PHSL233 TEST 2 > Lecture 12 - Protein trafficking 1 > Flashcards

Lecture 12 - Protein trafficking 1 Flashcards

1. define polarity, why is poalrity important? how are epithelia made? 2. State the components of the three protein polarity complexes. 3. describe in general terms, how epithelial cell polarity is established?

1
Q

What is polarity?

A
  • difference in structure, composition or function between two poles of a cell, such as apical/basolateral in an epithelial cell, axon/dendrites in a neuron.
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2
Q

what does polarity mean in epithelial cells?

A

In epithelial cells this also means the location of a protein in a specific location (apical/basolateral) in the cellular membrane.

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3
Q

what do the epithelial cells have?

A

Epithelial cells develop distinct apical and basolateral domains as an epithelia forms

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4
Q

why do epithelial cells need polarity?

A

proteins must be sorted and directed to apical and basolateral membranes for ion transport pathways of epithelial cells to function

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5
Q

epithelial cells function

A
  • essential for epithelia to transport ion/molecules
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6
Q

where are the proteins sorted?

A

they are sorted or trafficked to the basal or lateral membrane and they sit there to work

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7
Q

other function of polarity on epithelial cells

A

essential for epithelia to transport ions/ molecules

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8
Q

how are ion channels and pumps arranged to allow absorption or secretion in epithelia?

A

CFTR : secreting chloride and is in the apical membrane

ENaC : absorption of sodium through apical membrane

Na/K/ATPase in the basolateral membrane

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9
Q

methods for studying how an epithelia forms

A

studies have been performed in 2-dimensional cell culture models of epithelia e.g. (Madin Darby canine kidney cells)

growth on a petri dish

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10
Q

model for development of a 3D epithelia- Development of MDCK cell cysts in culture

A
  • MDCK cells grown in a 3D matrix (similar to extracellular matrix)
  • Apical surface contacts lumen, lateral membrane contacts other cells, basal membrane contacts the matrix
  • a ‘cyst’ forms
  • organoids (growing whole like organs with many growth factors)
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11
Q

why is Development of Epithelia important?

A
  • cell-basement membrane and cell-cell interactions are necessary to establish epithelial cell polarity

a series of cells join together to create a apical and basal lateral membranes

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12
Q

calcium switch assay in epithelial cell model

A
  • cells maintained in calcium- free media, Na/K/ATPase is randomly distributed.
  • upon calcium addition, tight junctions form and Na, K ATPase is found on basolateral membrane.
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13
Q

how do the cells know to only secrete basement membrane proteins onto the BL side?

A

the calcium addition

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14
Q

epithelial cells forming an epithelium

A

stem ( or founder) cells divides, then forms contacts with the basal lamina and with its neighbours.

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15
Q

what are the first cell-cell interaction?

A

adherens junctions

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16
Q

what does the formation of adherens junctions form?

A

it initiates epithelia formation

they are the first junction formed when the cells touch each other, they are just below the tight junctions.

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17
Q

CAMs

A

cell adhesion molecules

E-cadherin and nectins

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18
Q

nectin proteins

A
  • make initial cell-cell contact. nectins on neighbouring cells interact. calcium independent cell adhension.
19
Q

E-cadherin

A

E-cadherin of one cell forms homodimer with E-cadherin

on neighbouring cell. It requires calcium.

20
Q

tail of E-cadherin

A

binds catenins which links to the actin cytoskeleton

21
Q

catenins

A

they also link nectins and cadherin complexes to pull all the proteins to make the adheren junctions.

22
Q

which processes are required for establishing epithelial polarity?

A
  • neighbouring cells interacting with each other through adherens junctions
  • connections between epithelial cells and their basement membrane
  • nectin proteins from neighbouring cells connecting with each other
23
Q

Step 3 of epithelium formation

A

small GTP binding protein activation

24
Q

step 4 of epthelium formation

A

activation of polarity complexes

25
Q

what happens after the formation of adherens junctions?

A

form small GTP - binding proteins (cdc42) are activated. acts as a molecular switch

activation of aPKC

polarity complexes form

26
Q

cdc42

A

one of the GTP - binding proteins

27
Q

what does cdc42 do?

A

it coordinates multiple pathways necessary for polarity in epithelia

  • tight junctions
  • actin cytoskeleton
  • microtubules
  • protein trafficking
  • gene transcription
  • Activation of aPKC and formation of polarity complexes
28
Q

what is the step 5 of epithelium formation?

A

Tight junction formation

Tight Junction components interacts with apical polarity protein complexes.

29
Q

what is ZO and what does it do?

A

zonula occludens proteins and they link to the cytoskeleton.

30
Q

what is the step 6 of formation of epithelium?

A

positioning of three protein polarity complexes

31
Q

what are three protein polarity complexes?

A
  1. PAR complex - apical, near tight junction
  2. CRB complex - apical, near tight junction
  3. SCRIB complex - basolateral
32
Q

when cant the epithelial be polarised?

A

if the complexes are in the wrong place

33
Q

aPKC

A
  • atypical protein kinase C activated by cdc42
  • only polarity protein that is enzymetic activity as otheres are scaffolding proteins allowing clusters of proteins to intract together.
  • interacts and phosphorylates the CRB and SCRIB complexes
34
Q

mutual exclusion

A

when the phosphorylated the polarity complexes ae correctly located in their apical or basolateral domain.

35
Q

summary of formation of tight junctions and epithelial polarity

A
  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. postioning of PAR and CRB polarity complexes to apical domain, and SCRIB complex to basolateral domain.
  7. Apical-basolateral polarity established.
36
Q

mutations in polarity complex proteins cause

A
  • decreased formation or lack of tight junctions so barrier, gate and fence fuctions compromised
  • changes in cell- cell adhesion and cell movement
  • changes in location of apical and basolateral proteins
37
Q

normal epithelium

A

fully polarised AJ AND TJ

this structure inhibits cell division pathways, and promotes differentiation

  • high cell density - ZO1 keeps transcription factors that promote cell division localised to TJ preventing cell division. epithelial carries out regular functions such as absorption and secretion.
38
Q

wound healing/damage

A

low cell density - transcription factors that promote cell division move from TJ to nucleus to stimulate cell division

(sensing a gap so it needs to repair with new cells)

39
Q

cancer pathophysiology of epithelium

A

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

40
Q
A
41
Q
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42
Q
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43
Q
A

PHSL233 TEST 2 (2 decks)

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