mTOR controls lysosome tubulation and antigen presentation in macrophages and dendritic cells

1a. What is the difference between a phagosome and a lysosome?

phagosome - vesicle made by phagocytes during phagocytosis

lysosome - organelles with acidic and enzymatically active lumen for molecular digestion

1b. Lysosomes are a family of organelles, what distinguishes each family?

degrade different types of molecules using different enzymes

phagolysosomes - digest microbes/apoptotic bodies from host tissue

major histocompatibility complex class II compartment - delivers antigens to plasma membrane → t cell recognition

lytic granules - kill virally infected cells

2. What is meant by tubular formation of the lysosome?

microtubules provide a scaffold for kinesin and dynein to alter the shape of lysosomes - long and dynamic shape -maximise surface area for transport

3. Discuss the TLR receptors, what are the different ligands that bind to the members of the TLR family. What does the TLR’s stimulate in the APC?

Toll-like receptor 4

ligand: lipopolysaccharide (LPS) from pathogens

triggers MyD88-independent pathway aand MyD88-dependent pathway (that can activate PI3K-Akt pathway)

4. Describe the PI3-K Akt pathway. What does this pathway control in the APC?

PI3K → ^ AKT (prosurvival signal) → P TSC1/2 → v Rheb → ^ mTORC1 → ^ mTORC2 → AKT

5. Interpret and explain the results from Figure 1.

Cells treated with LPS showed tubular formations of the lysosome, except with also treated with MyD88 or PI3K inhibitors, with p < 0.001 → MyD88 pathway in implicated in TL biogenesis

6. Explain the role of MyD88.

activates PI3K-Akt pathway & activates IRAK1/4 and TRAF6 → IkB degraded & NF-kB translocated to nucleus → pro-inflammatory cytokines

7. What is the functional difference between macrophage and bone marrow derived dendritic cell (BMDC)?

phagocytosis vs antigen presentation

8. What does both Fig 2A and 3A show about S6K? Explain.

since LPS activates Akt and, in turn, mTORC1, it activates p70 S6K too.

9. Interpret Fig 5 C & D in terms what activates mTOR. What does torin1 treatment prove?

LPS activates mTOR, while rapamycin and torin inhibits mTOR activity, preventing lysosome tubulation.

10. Interpret the data of Fig 3, E & F.

when mTOR is silenced, lysosome tubulation decreases - sustained over time

11. Discuss the data that shows the relationship between AMPK and mTOR.

AMPK activation opposes mTOR activation → v TL

12. Discuss the relationship between LPS mediated tubulation and autophagy, Fig 6.

tubulation requires mTOR activation, autophagy is triggered by mTOR inhibition, so this pathway is not responsible for LT

13. Explain Fig 8, in terms of the immune response.

mTOR moves MHCII to the cell surface in APCs that absorb viral/other material - more presenting capacity