Term
| What part of the nucleus is responsible for supporting the envelope and the attachment of DNA networks? |
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Definition
| The nuclear lamina underlying the inner nuclear membrane |
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Term
| What are the primary symptoms associated with Laminopathies? |
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Definition
Remember, laminopathies involved mutations in the lamin A gene.
Symptoms include muscle wasting, locomotion issues, fat redistribution and CV problems. |
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Term
| Provide a molecular interpretation of how LMNA -/- mutations can lead to laminopathies. |
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Definition
LMNA produces Lamin A and C via alternate splicing.
Knockout mice have symptoms of laminopathies as well as abnormal cell nuclei (also seen in human fibroblasts).
Disorganized cytoskeletal desmin filaments (intermediate filaments) in affected cardiomyocytes have also been detected. |
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Term
| What cells normally alter nuclear shape to limit mechanical stress upon diapedesis? |
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Definition
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Term
| What is Quantitative Nuclear Morphometry used for in clinical settings? |
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Definition
| Nuclear morphology characterization to test for cancer tumor staging and other diseases |
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Term
| What is imported/exported through a typical nuclear pore complex (NPC)? |
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Definition
Import- histone proteins (free diffusion)
Export – ribosome complexes (pore must dilate through action of nucleoporins, b/c NPC is >9nm)
**Proteins are not unfolded here** |
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Term
| How do nuclear localization signals (NLS) and nuclear export signals (NES) differ? |
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Definition
1) NLS is 8-18 basic-AA sequence that can be interrupted by unrelated AA
2) NES is Leucine or isoleucine rich
3) Neither are claved during translocation and proteins are not unfolded as they pass through the NPC |
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Term
A patient presents with hair loss ,diminished sub-c fat, CV disease and skeletal malformations in the 1st year of life.
1) What disease are they suffering from and how is it caused?
2) What treatment options exist? |
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Definition
Hutchinson-Gilford progeria syndrome (HGPS)
1) Short answer:LaminA mutations lead to incorrect processing of gene product. C-terminal farnesyl group is kept on too long, altering nuclear structure.
Full Explanation: LaminA mutations (usually small deletions) cause errors in proteolytic processing of gene product, and produce a truncated progerin/LAD50 product instead.
Farnesyltransferase enzymes usually add a farnesyl group on the C-terminus of the gene product that is lost upon cleavage. However, mutations causes the farnesyl group to be maintained, which alters nuclear function and structure.
2) Farnesyltranserase inhibitors (FTIs) have worked to reverse phenotype in mice. |
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Term
| From a genomic screen, you determine that a patient has a mutation in the Karyopherin-alpha gene. Why might you be concerned? |
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Definition
Protein access through the nuclear pore complex!
Karyopherin-alpha binds the NLS of proteins translocating through the nuclear pore complex (NPC).
If Karyopherin-alpha cannot bind the NLS, than Karyoperin-beta cannot bind K-alpha, and the target protein will not make it through the nucleus. |
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Term
| How is cargo that has translocated into the nucleus through the nuclear pore complex released? |
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Definition
Ran!
Remember, Ran becomes "activated" into its GTP-bound form in the nucleus in a GEF-dependent manner, where it acts to dissociate molecular cargo that has been brought in by the Karyopherin proteins.
Aside- In the cytoplasm, GTP-Ran is hydrolyzed and "inactivated" via the action of GTPase-activating proteins (GAPs) to become GDP-Ran. |
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Term
| How is the nuclear localization of steroid hormone receptors regulated? |
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Definition
In their un-liganded form, steroid receptor complex-associated "chaperone" proteins often mask the NLS of the receptor.
When steroids bind to these receptors, these chaperones dissociate, and the nuclear localization signal is exposed. |
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Term
| How does NF-AT regulate gene expression in activated T-cells? |
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Definition
1) T-cells are activated, increasing intracellular calcium
2) Calcium activates calcineurin (phosphatase), which dephosphorylates NF-AT and exposes the NLS
3) NF-AT is imported to the nucleus, where it activates genes. |
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Term
| What are 4 types of nuclear-transport regulation? |
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Definition
1) Steroids (receptor-chaperone masking NLS)
2) Post-translational Modification (phosphorylation of NF-AT in T-cells)
3) Direct Proteolysis (SREBP with LDL-receptors)
4) Indirect Proteolysis (NF-kB activation/IKB cleavage) |
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Term
| Provide a molecular interpretation of the sensitivity of LDL-receptor expression to cholesterol levels. |
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Definition
1) When cellular cholesterol is high, SREBP exits as a 125KDa ER-associated protein.
2) When cellular cholesterol is low, SREBP is cleaved, releasing a 68 KDa protein that translocates to the nucleus via its NLS, and acts as at transcription factor to up-regulate LDLR expression. |
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Term
| How is Nf-kB-mediated gene expression regulated? |
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Definition
Indirect proteolysis.
Upon stimulation, phosphorylation of IKB (bound to NF-KB) leads to its degradation, thereby exposing the NLS of NF-kB and allowing it to translocate to the nucleus. |
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