Lecture 14 - Protein trafficking in epithelia 3

Question 1

What is required to specifically traffic apical proteins?

Answer 1

Binding proteins as trafficking to apical membrane is saturable

Question 2

What are the 3 models for protein exocytosis in epithelial cells?

Answer 2

1. Direct route
2. Indirect route
3. Random sorting

Question 3

What is the direct route model for protein exocytosis in epithelial cells?

Answer 3

Proteins are sorted in TGN into apical or basolateral bound vesicles. Once in vesicles the proteins go straight to their appropriate membrane

Question 4

What is the in direct route model for protein exocytosis in epithelial cells?

Answer 4

1. All proteins exocytosed to one membrane
2. Proteins retrieved from membrane (endocytosis) and trafficked to endosome
   3a. Apical proteins trafficked to apical membrane
   3b. Basolateral proteins trafficked to basolateral membrane

Question 5

What is the in random sorting route model for protein exocytosis in epithelial cells?

Answer 5

1. Proteins trafficked to either membrane randomly
2. Proteins retrieved from membrane (endocytosis) and trafficked to endosome
   3a. Apical proteins redirected to apical membrane
   3b. Basolateral proteins redirected to basolateral membrane

Question 6

What is the exocyst believed to aid in?

Answer 6

The exocyst is believed to aid in the trafficking of basolateral proteins via the lateral membrane

Question 7

Which statement about protein sorting and targeting in epithelia is CORRECT?
A. The exocyst is the site for delivery of proteins to the basolateral membrane.
B. Experimental evidence shows that the trans-Golgi network can sort apical and basolateral proteins into separate vesicle populations.
C. In the indirect sorting pathway all proteins are first delivered to the same membrane domain.
D. All of A, B and C are correct

Answer 7

D. All of A, B and C are correct

Question 8

Endocytosis of transmembrane proteins occurs through interaction with the AP2 complex BECAUSE the transmembrane proteins contain amino acid sequences such as YXXϕ.

Answer 8

A. Both statements true and causal.

Question 9

What specfic adaptin is found in the plasma membrane clathrin-coated pits?

Answer 9

AP2

Question 10

What are endocytosis motifs bound by?

Answer 10

clathrin-binding adaptins

Question 11

What four subunits make up AP2?

Answer 11

α and β adaptins
μ2 adaptin
σ2 subunits

Question 12

What does the α and β adaptin subunit of AP2 bind to?

Answer 12

Clathrin

Question 13

What does the μ2 adaptin subunit of AP2 bind to?

Answer 13

YXXϕ

Question 14

What are examples of tyrosine based amino acid motifs?

Answer 14

YXXϕ
NPXY

Question 15

What is an example of hydrophobic amino acid motifs?

Answer 15

LL

Question 16

What happens to basolateral transferrin receptor (TfR) once endocytosed?

Answer 16

Once ligand-bound transferrin is endocytosed to
basolateral sorting endosome, it is trafficked on to common endosome. From here the TfR is either recycled back to basolateral membrane or trafficked through the late endosome to the lysosome for degradation

Question 17

What is the endocytosis and recycling or
degradation of apical ENaC?

Answer 17

Once ENaC is ubiquitinated and endocytosed, it is trafficked through apical sorting endosome to the common endosome. From here either:
* Ubiquitin removed and recycled back to apical membrane
* Ubiquitin remains and is trafficked to late endosome and onto the lysosome for degradation

Question 18

What is the steps of endocytosis in epithelia?

Answer 18

1. Protein is endocytosed to applicable sorting endosome (apical protein to apical sorting endosome)
2. Endocytosed material (apical and basolateral) goes to the common endosome
3. Proteins recycled back to corresponding membrane

Question 19

How are apical proteins believed to be recycled back to the apical membrane?

Answer 19

Via an apical recycling endosome

Question 20

What amino acid motifs are found on ENaC subunits?

Answer 20

ENaC subunits have YXXϕ motifs and are monoubiquitinated

Question 21

What amino acid motifs are found on CFTR?

Answer 21

CFTR has YXXϕ and LL motifs

Question 22

What amino acid motifs are found on Na+/K+ ATPase subunits?

Answer 22

Na+/K+ ATPase subunits have YXXϕ and LL motifs

Question 23

What is the transcytosis of the immunoglobulin A receptor (IgAR)?

Answer 23

1. IgAR endocystosed from basolateral
   membrane and trafficked to basolateral sorting endosome
   2 & 3. Trafficked on to apical recycling endosome through common endosome
2. IgAR exocytosed to apical membrane