Cystic Fibrosis and CFTR Variants

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Questions and Answers

What effect does the F508del variant have on CFTR?

It enhances the chloride channel function.

It causes the instability of NBD 1. (correct)

It has no impact on the protein structure.

It prevents the phosphorylation of the protein.

Which domains are part of the CFTR structure?

Nucleotide-binding domain 1, membrane-spanning domain 1, regulatory domain. (correct)

Membrane-spanning domain 2, regulatory domain, ion-exchange domain.

Nucleotide-binding domain 2, subunit-binding domain, regulatory domain.

Cyclic nucleotide-binding domain, membrane-spanning domain 2, signaling domain.

Why is understanding CFTR variants significant in cystic fibrosis treatment design?

It helps to identify more effective chloride channel blockers.

It provides insights into naturally occurring amino acid changes that affect treatment. (correct)

It allows for the development of gene therapy targeting a single variant.

It simplifies the structural understanding of the protein.

What role does the fourth cytosolic loop (CL4) play in CFTR function?

It contributes to misfolding when mutated. Signup and view all the answers

What is the structural interaction involved in CFTR as revealed by modeling?

Interaction between NBDs and MSDs. Signup and view all the answers

How does the deletion at codon 508 specifically impact CFTR?

It leads to the misfolding of the entire protein structure. Signup and view all the answers

What is the significance of hydrogen bonds formed by F508 in CFTR?

They stabilize the interaction between NBD1 and CL4. Signup and view all the answers

What contributes to the complexity of CFTR variants affecting protein function?

The variety of amino acid substitutions and deletions. Signup and view all the answers

What is the role of ivacaftor in the treatment of cystic fibrosis?

It acts as a CFTR potentiator. Signup and view all the answers

Which mutation is addressed by both lumacaftor and ivacaftor in cystic fibrosis treatments?

F508del mutation Signup and view all the answers

What characteristic of the CFTR gene predominantly causes issues in cystic fibrosis?

Defective intracellular transport and processing Signup and view all the answers

What is a significant effect of temperature on the CFTR protein?

Temperature sensitivity affects CFTR processing. Signup and view all the answers

How do disease-associated mutations in the fourth cytoplasmic loop impact CFTR?

They compromise biosynthetic processing and chloride channel activity. Signup and view all the answers

What defines the disease liability of variants in the CFTR gene?

The degree of protein misfolding they cause. Signup and view all the answers

Which of the following statements about the silent codon change I507-ATC.ATT is true?

It contributes to the severity of CFTR channel dysfunction. Signup and view all the answers

What is a characteristic feature of the CFTR protein associated with the ΔF508 mutation?

Improper folding and transport within the cell. Signup and view all the answers

What mechanism is suggested to be primarily responsible for cystic fibrosis airways disease?

Periciliary liquid layer depletion Signup and view all the answers

Which technology was used to repair CFTR function in cystic fibrosis intestinal stem cell organoids?

CRISPR/Cas9 Signup and view all the answers

What type of stem cells were differentiated into mature airway epithelia in the study by Wong et al.?

Human pluripotent stem cells Signup and view all the answers

Which animal model was developed to investigate the effects of CFTR gene disruption?

Ferrets Signup and view all the answers

What is a major characteristic of conditionally reprogrammed cells mentioned in the studies?

They represent a stem-like state Signup and view all the answers

What specific organ was used in a functional CFTR assay in Dekkers et al.'s study?

Intestine Signup and view all the answers

What was a noteworthy finding in the study involving genetically modified pigs?

They were a model for cystic fibrosis Signup and view all the answers

What functional role does the CFTR protein play in the body?

Regulates ion transport across epithelial cells Signup and view all the answers

Which gene variants have been identified as modifiers affecting the age at onset of diabetes in cystic fibrosis patients?

TCF7L2 Signup and view all the answers

What does the Z allele of SERYINA modify in cystic fibrosis patients?

Risk of cirrhotic liver disease Signup and view all the answers

Which solute carrier gene has been shown to modify lung disease severity in young cystic fibrosis patients?

SLC6A14 Signup and view all the answers

What type of approach increases the yield of significant associations in genome-wide association studies (GWAS) related to cystic fibrosis?

Hypothesis-driven GWAS Signup and view all the answers

Which of the following statements about genetic modifiers in cystic fibrosis is true?

They exhibit pleiotropic effects on the cystic fibrosis phenotype. Signup and view all the answers

What is the role of variants in the SLC26A9 gene in cystic fibrosis patients?

They modify risk for neonatal intestinal obstruction. Signup and view all the answers

Which rare modifier variant is associated with the age at onset of chronic infection with P.aeruginosa?

DCTN4 Signup and view all the answers

Which of the following gene variants is NOT mentioned as a modifier in cystic fibrosis?

TP53 Signup and view all the answers

What is the primary challenge in stabilizing mRNA in vivo against NMD?

Risk of off-target effects Signup and view all the answers

What has been documented in clinical trials of PTC suppressors for CFTR?

Modest recovery of CFTR function in nasal epithelia Signup and view all the answers

Which approach seems viable in augmenting CFTR function after PTC suppression?

Augmenting with ivacaftor Signup and view all the answers

What are cryptic splice sites associated with in the context of RNA splicing variants?

Activation that can increase normally spliced RNA transcript Signup and view all the answers

Which type of variants are proving particularly difficult to treat despite manipulation of splicing factors?

Variants altering canonical nucleotides in splice sites Signup and view all the answers

What might occur when successful readthrough of a PTC incorporates a non-native amino acid?

Altered protein processing and function Signup and view all the answers

What alternative strategy can be used to stabilize transcripts with PTCs?

Induction of the unfolded protein response Signup and view all the answers

What is required for the successful synthesis of a full-length protein in the context of PTC variants?

Readthrough of the PTC Signup and view all the answers

Study Notes

Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)

The F508del mutation is a common cause of Cystic Fibrosis (CF) resulting in defective processing and altered chloride channel function of CFTR.
The F508del mutation can be categorized into at least three classes.
Other missense variants are also known to cause defective processing and altered chloride channel function of CFTR.
The understanding of the diverse effects caused by CFTR variants is crucial for designing molecular treatments for CF.
CFTR consists of three main motifs:
- Nucleotide-binding domains 1 (NBD1) and 2 (NBD2) which interact with ATP.
- Membrane-spanning domains 1 (MSD1) and 2 (MSD2) which anchor the protein in the membrane.
- The regulatory domain (R domain) which is rich in phosphorylation sites.
The F508del mutation is known to destabilize NBD1, although the mechanism by which this localized structural defect leads to misfolding of the entire protein was not clear for a long time.
Missense mutations outside the NBD1 domain, specifically in the fourth cytosolic loop (CL4) within MSD2, also contribute to protein misfolding.
Modelling based on the atomic structure of related proteins and cysteine crosslinking experiments revealed an interaction between the NBDs and MSDs of CFTR.
The F508del mutation occurs at an interface between NBD1 and CL4, and appears to form hydrogen bonds with arginine at codon 1070 (R1070).

Modifiers of Cystic Fibrosis Phenotype

Genome-wide approaches are useful for identifying pathways that modify disease severity in CF.
Variants in four genes associated with type 2 diabetes risk in the general population (TCF7L2, CDKAL1, CDKN2A/B, and IGF2BP2) were found to modify the age of diabetes onset in CF.
The Z allele of SERPINA1, which causes a-1 antitrypsin deficiency and is related to emphysema and liver disease risk, modifies the risk of cirrhotic liver disease in CF.
Variants in SLC26A9, encoding a chloride and bicarbonate channel interacting with CFTR, influence the risk of neonatal intestinal obstruction and diabetes.
Solute carriers associated with the risk of neonatal intestinal obstruction also influence lung disease severity in young CF patients (SLC9A3 and SLC6A14) and age at the initial infection with P. aeruginosa (SLC6A14).
Hypothesis-driven GWASs revealed that proteins residing in the same cellular location as CFTR are enriched for modifiers of neonatal intestinal obstruction.
Exome sequencing has identified rare modifier variants in DCTN4, encoding a dynactin protein involved in autophagy, which are associated with the age of onset of chronic infection with P. aeruginosa.

Therapeutic Strategies for Cystic Fibrosis

Most premature termination codon (PTC) variants trigger RNA degradation through nonsense-mediated RNA decay (NMD).
Counteracting NMD to stabilize mRNA in vivo is challenging due to potential off-target effects.
Readthrough of the PTC is required for synthesis of a full-length protein. Compounds derived from aminoglycosides have shown some success in suppressing nonsense variants in CFTR.
Clinical trials of PTC suppressors have reported modest recovery of CFTR function in the nasal epithelium, but lung function improvement has not been documented.
The incorporation of a non-native amino acid during readthrough can affect protein processing and function.
Combining PTC suppression with ivacaftor augmentation of CFTR function might be a viable approach to overcome the therapeutic threshold.
Strategies like induction of the unfolded protein response could potentially attenuate NMD, stabilizing transcripts with PTCs and enabling readthrough.
Variants leading to aberrant RNA splicing pose unique challenges.
- Suppressing variants that activate cryptic splice sites can significantly increase the amount of normally spliced RNA transcript and protein.
- Treating variants altering canonical nucleotides in splice sites remains difficult, although manipulating splicing factors (U1 small nuclear RNA) and the splicing process (trans-splicing) shows promise.
Rearrangement variants require replacement of one or more exons or the entire CFTR coding sequence.

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Description

Explore the mechanisms and effects of the F508del mutation in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). This quiz delves into the structural motifs of CFTR and their relation to chloride channel function. Understanding these aspects is essential for advancing molecular treatments for Cystic Fibrosis.