L13

Question 1

what are MVBs?

Answer 1

• multi-vesicular bodies
• have intralumenal vesicles (inward budding)
• form of late endosome
• when cargo is sorted for degradation

Question 2

what is inward budding being done by?

Answer 2

• ESCRT proteins

- (4 protein groups (0,1,2,3)

Question 3

what is ubiquitination ?

Answer 3

Reversible post-translational modificaiton by adding of ubiquitin molecules

Question 4

what is the signal that facilitates transport from the EE to the LE?

Answer 4

MONOUBIQUITINATION

Question 5

WHAT IS HRS?

Answer 5

A component of ESCRT0 which recognises and binds to mono-ubiquitination

Question 6

what is a FYVE domain?

Answer 6

domain found in proteins which bind to PIP3

e.g. the hrs domain of ESCRT0

Question 7

what does ESCRT stand for?

Answer 7

endosomal sorting complexes required for transport

Question 8

what does vsp4 do?

Answer 8

strips ESCRT proteins from membrane once process is complete

Question 9

what do ESCRT protiens do?

Answer 9

cause inward membrane bending and cutting (scisson) (signal is mono-ubiquitination)which allows formation of ILV which form MVB
- MVB can then fuse with lysosome - degradation

Question 10

give the different types of ESCRT proteins and their roles

Answer 10

• ESCRT0 - recoginition of monoubiquitination by the hrs domain
• ESCRT1 - assembles to recruit/activate ESRCT2
• ESCRT2 - oligermerisation and recruitment of ESCRT3
• ESCRT3 - cargo concentration and deubiquitination

VSP4 (ATPase) - mediates pinching off step of inward membrane and dissociates ESCRTS from membrane

Question 11

what do mutations in the ESCRT somplexes give rise to?

Answer 11

• cancer

- overexpression results in malignancy

Question 12

how do virsuses bud out of cells?

Answer 12

use ESCRT complexes for retrovirla budding

-escrt complexes could be a target for viruses?

Question 13

give some of the roles of endocytosis

Answer 13

• signal attenutation (take in signal)
• signal regulation
• removal of products from cell surface for recycling/degradation

Question 14

what 2 endocytic pathways can tgfB go through?

Answer 14

• clathrin dependent endocytosis (needs this pathway in order to signal and enter ER(shown by using EEA1))
• calveolae - doesn’t signal via this route (degraded)

Question 15

How do we know that tgfB has to enter the cell via clathrin dependent endocytosis in order to signal?

Answer 15

• if dynamin is inhibited (required in clathrin dep pathway)- transcription of downstream targets of tgfB is inhibited
• If calveolae pathway is inhibited transcription of tgfB downstream targets increases (more endocytosis occurs via CDE)

Question 16

what is the function of TGFb?

Answer 16

cellular growth and differentiation

Question 17

what does tgfB activation lead to?

Answer 17

• phosphorylation of smad 2
• smad 2 (tf) tranlocated to nucleus
• smad 2 transcription requires SARA (FYVE domain)(PIP3 required) as SARA recruits Rsmad - required to go into nucleus

TGFb has to be in endosomes in order to signal

Question 18

giev some components that have a FYVE domain

Answer 18

FYVE domain in proteins which bind PIP3

• Hrs
• Sara
• EEA1

Question 19

what is required for tgfB signalling?

Answer 19

• needs to enter via CME as can only signal if in endosomes

- needs to phosphorylate Smad2 (transcription requires SARA(promotes R-SMAD) - (FYVE comain so PIP3 also required))

Question 20

what are signalosomes?

Answer 20

areas where receptors are clustered together to provide efficient signalling

Question 21

how does EGF concentraiton determine the endocytic route of EGF?

Answer 21

• low EGF concentration - high CDE (signalling)
• high EGF concentration - high calveola (degradation)

-ubiquitination is signal to switch between pathways