cell signalling part 2

1.

A cell line expresses both GPCR and RTK for growth factor signalling. Experiments:

• GPCR agonist treatment → Increase in cAMP but no MAPK activation.

• RTK ligand treatment → Strong MAPK activation.

• When both ligands are added simultaneously, MAPK activation is much stronger than RTK alone.

Question:

• Which mechanism explains the synergy between GPCR and RTK?

• What role does PKA/PKC play in this synergy?

• How would MAPK activation change if GPCR signalling was blocked by pertussis toxin?

2.

A researcher investigates signalling via an RTK mutant. Experimental observations:

1. Ligand binding and receptor dimerization occur normally.

2. Receptor autophosphorylation is absent.

3. Grb2 and PI3K do not bind.

4. MAPK pathway is inactive.

5. However, Akt is still phosphorylated when cells are co-treated with IGF-1 (a different RTK ligand).

Question:

• Explain why MAPK signalling is blocked in the mutant receptor but Akt signalling can still occur.

• Which phenomenon does this highlight in cell signalling?

• Predict what would happen if both receptors (EGFR + IGF-1R) are inhibited simultaneously.

3. A novel drug inhibits phospholipase C. Which pathway is most directly affected?

4. In Wnt signalling, addition of Wnt ligand but destruction complex is intact. Which outcome?

5. A patient with loss-of-function mutation in Gsα will most likely have:

6. Which mutation is most likely to result in uncontrolled cell proliferation?

7. In NF-κB pathway, which molecule acts as the inhibitor under resting conditions?

8. Which signalling pathway involves γ-secretase–mediated cleavage?

9. Activation of GPCRs can indirectly activate RTKs via:

10. Which experiment best shows direct protein–protein interaction in signalling?

11. In TGF-β signalling, SMAD2/3 phosphorylation occurs but transcription does not. What is the most likely cause?

12. Insulin signalling activates PI3K-Akt. When PI3K is inhibited, glucose uptake is blocked, but MAPK signalling remains. Interpretation?

13. Which signalling event is directly regulated by ubiquitination?

14. Which would be a result of cholera toxin action?

15. A receptor tyrosine kinase mutant lacks intracellular kinase domain. Its ligand binds normally. What happens?

16. Which experimental tool best helps in tracing real-time Ca²⁺ signalling?

17. If ERK is constitutively active, treatment with Raf inhibitor will cause:

18. In Wnt signalling, APC mutation results in:

19. A patient has mutation in GPCR that prevents GTP hydrolysis on Gα. What will happen?

20. In NF-κB signalling, knockout of NEMO (IKKγ subunit) will lead to:

21. If caffeine inhibits phosphodiesterase, what will happen in GPCR–cAMP signalling?

22. A researcher uses a dominant-negative receptor mutant lacking kinase activity. What is observed?

23. Ras-MAPK signalling is terminated by:

24. In Hedgehog signalling, absence of Hedgehog ligand causes:

25. Which second messenger is generated by phospholipase C action?

26. Rapamycin inhibits mTOR. Which cellular process will be most directly affected?

27. Constitutively active β-catenin mutation is most strongly associated with:

28. Which is NOT a feature of Notch signalling?

29. Which of the following is an example of ligand-independent activation of RTKs?

30. In PI3K-Akt signalling, deletion of PTEN causes:

31. A mutation in Ras makes it insensitive to GAP proteins. Which is the most likely outcome?

32. In a GPCR signalling experiment, forskolin is used. Its effect?

33. A drug blocks phosphodiesterase (PDE). If applied to GPCR–cAMP signalling cells:

34.

Cells lacking Sos protein are tested for RTK signalling. Observation:

• No Ras activation

• No MAPK activation

• PI3K activation intact

Interpretation:

35. In TGF-β signalling, mutation in SMAD4 results in:

36. Insulin receptor activates PI3K-Akt pathway. If PI3K inhibitor is applied:

37.

In Hedgehog signalling:

• Knockout of Patched → constitutive activation of Smoothened

• Knockout of Smoothened → no Gli activation even in presence of Hedgehog

This proves:

38. A Ras mutant is locked in GDP-bound state. Which event will occur?

39. In a signalling study, inhibiting proteasome prevented degradation of IκB, but β-catenin also accumulated in the same cells. Which conclusion is most logical?

40.

An experiment was performed with cells lacking calmodulin. Upon stimulation with a hormone that normally increases intracellular Ca²⁺:

• Ca²⁺ levels rise normally

• Ca²⁺-dependent kinases remain inactive

This indicates:

41. A GPCR activates both adenylate cyclase and phospholipase C. Which is the most likely mechanism?

42. A mutant JAK protein is able to bind the cytokine receptor but cannot phosphorylate STAT proteins. However, STAT phosphorylation is rescued when constitutively active Ras is introduced. Which interpretation is correct?

43. Cells treated with IKK inhibitor are exposed to TNF-α. Experimental outcome:

44.

In Wnt signalling, knockdown of Axin shows the following:

• β-catenin accumulates in cytoplasm and nucleus

• TCF/LEF target genes are constitutively expressed

• Addition of Wnt ligand has no further effect

Which conclusion is correct?

45. Inhibition of PI3K in a cancer cell line leads to reduced Akt phosphorylation but increased ERK phosphorylation. This demonstrates:

46. Researchers observed that overexpression of β-arrestin leads to reduced cAMP signalling but enhanced MAPK activation via GPCR. This suggests:

47.

A novel growth factor "GFX" binds to its RTK receptor. In cells treated with a tyrosine kinase inhibitor, the following are observed:

1. Receptor dimerization occurs normally.

2. Grb2 recruitment is absent.

3. PI3K activation is abolished.

4. MAPK phosphorylation does not occur.

Which is the correct interpretation?