nuclear transport disease

Q: What is the function of the HIV Rev protein?

A: It binds the RRE and exports unspliced or partially spliced HIV RNA.

Q: Where is the RRE located?

A: On an RNA structure within an intron of HIV RNA.

Q: What signal allows Rev to enter the nucleus?

A: A Nuclear Localization Signal (NLS).

Q: What method was used to study Rev export in Xenopus oocytes?

A: Nuclear microinjection followed by nuclear/cytoplasmic fractionation.

Q: What did the Xenopus assay show about Rev export?

A: Rev moves from the nucleus to the cytoplasm over time.

Q: What does Leptomycin B inhibit?

A: CRM1/exportin-1.

Q: How does LMB affect Rev nuclear export?

A: It blocks Rev export

Q: Does LMB affect importin-α export?

A: No

Q: What motif does Rev use to bind CRM1?

A: A leucine-rich Nuclear Export Signal (NES).

Q: What technique demonstrated direct binding between Rev NES and CRM1?

A: Yeast two-hybrid assay.

Q: What happens when the leucines in the Rev NES are mutated?

A: CRM1 binding is abolished.

Q: What conformational change allows CRM1 to bind NES cargo?

A: Ran-GTP binding opens the hydrophobic NES-binding cleft.

Q: How does LMB inhibit CRM1 at the molecular level?

A: It covalently modifies Cys528 in the NES-binding groove.

Q: Why is CRM1 a target in cancer therapy?

A: Overactive CRM1 exports tumor suppressors

Q: What are SINE compounds?

A: Selective Inhibitors of Nuclear Export designed to inhibit CRM1 with less toxicity.

Q: What is the FDA-approved CRM1 inhibitor?

A: Selinexor (KPT-330).

Q: What mutation confers resistance to CRM1 inhibitors?

A: CRM1 Cys528 mutation.

Q: Where is NFAT located at resting calcium levels?

A: In the cytoplasm.

Q: What causes NFAT to enter the nucleus?

A: Increased calcium activates calcineurin

Q: How does phosphorylation affect NFAT localization?

A: Phosphorylated → cytoplasm; dephosphorylated → nucleus.

Q: Which drugs inhibit NFAT nuclear import?

A: Calcineurin inhibitors (e.g.

Q: What genetic mutation causes ALS/FTD?

A: G4C2 repeat expansion in C9orf72.

Q: What organism was used to model C9orf72 toxicity?

A: Drosophila.

Q: How does increasing repeat length affect Drosophila eyes?

A: Longer repeats cause severe degeneration.

Q: What pathway repeatedly modifies repeat toxicity?

A: Nucleocytoplasmic transport (Ran/RanGAP pathway).

Q: What happens to Ran localization in disease models?

A: Ran becomes mislocalized from nucleus to cytoplasm.

Q: What effect does RanGAP overexpression have?

A: It rescues toxicity and reduces degeneration.

Q: What structure does expanded G4C2 RNA form?

A: RNA G-quadruplexes.

Q: How do G-quadruplexes disrupt transport?

A: They bind/sequester RanGAP

Q: What additional toxic products come from the repeat?

A: Dipeptide repeat proteins via RAN translation.

Q: What are the two main mechanisms of C9orf72 toxicity?

A: RNA-mediated sequestration of transport factors and dipeptide repeat protein toxicity.