Tumour suppressor genes Flashcards
What is the two hit hypothesis?
Both alleles must be mutated for a cell to become cancerous.
What happens if there is a germline mutation?
All cells in the developing embryo are heterozygous.
What is loss of heterozygosity?
The process leading to inactivation of the second copy of a tumor suppressor gene.
What is chromosomal nondisjunction?
The failure of homologous chromosomes or sister chromatids to separate properly during cell division.
What can result from chromosomal nondisjunction?
Hemizygosity or duplication of chromosomes or chromosome arms.
What is mitotic recombination?
Replacing one allele with another, effectively deleting the wild type.
What is gene conversion?
Directly replacing one allele with a copy of another, leading to homozygosity of mutation.
How can loss of heterozygosity (LOH) be detected?
Through somatic cell hybridization (SCH).
What is the process of somatic cell hybridization?
Introduce potential suppressor gene into malignant cell line, mix normal cells with tumor cells, and use polyethylene glycol (PEG) to induce cell fusion.
What is the result of somatic cell hybridization?
Hybrid cells appear normal, but some spontaneously reverse, resulting in a reversal of malignant phenotype.
Example: 5q allele loss in early adenomas of FAP, caused by mutations in APC gene.
What is restriction fragment length polymorphism (RFLP)?
Variations in DNA sequence of homologous chromosomes at individual restriction endonuclease sites.
What are the steps in RFLP analysis?
Isolate the DNA, use cleavage enzymes to chop it, view results via southern blot.
What is the role of CDKs in the cell cycle?
CDKs regulate phosphorylation of cyclins.
What are the three interphase CDKs?
CDK2, CDK4, CDK6.
What is the role of cyclins in the cell cycle?
Cyclins regulate the cell cycle through their degradation, which leads to inactivation of CDKs.
What triggers the onset of S phase?
Increasing levels of Cyclin E-CDK2.
What initiates S phase reduction?
Reduction of Cyclin E-CDK2 levels by Fbxw7.
What regulates the completion of S phase?
Cyclin A-CDK2.
What triggers the end of the cell cycle?
Inactivation of CDK1 and decreasing Cyclin B levels.
What are the main checkpoints in the cell cycle?
Restriction point in G1, S checkpoint, G2 checkpoint, M checkpoint.
What is the role of p21?
Inhibits CDK2 and CDK4/6 involved in progression of G1 to S.
What regulates p21 expression?
p53.
What is the TP53 gene?
Located on chromosome 17p, it is the most frequently altered gene in human tumors.
What is the structure of p53?
Contains a DNA binding domain, transactivation domain, oligomerization domain, C-terminal regulatory domain, NLS, and proline-rich domain.
What activates p53?
DNA damage results in activation of ATM and ATR kinases.
What happens when p53 is activated?
It regulates cell proliferation, promotes DNA repair, apoptosis, cell differentiation, and blocks angiogenesis.
How is p53 regulated?
Rapidly degraded by ubiquitin ligase MDM2; its half-life is 6-20 minutes.
What is the role of FBXW7?
It is a receptor subunit of E3 ligase of the ubiquitin-proteasome system.
What happens when FBXW7 is mutated?
It cannot bind to FBXW7 associated proteins, leading to uncontrolled cell growth.
What is the structure of Rb1?
Located on chromosome 13, it has a central ‘spacer’ or ‘pocket’ domain.
What regulates Rb1?
Phosphorylation by multiple CDKs and other S/T kinases.
What is the function of Rb1?
Regulates interaction with E2F transcription factors, critical for cell cycle progression.
What are other tumor suppressors mentioned?
WT1, MTS-1, MEN-1, NF-1, P21RAS, NM23, KAI1, BRCA-1, BRCA-2, FHIT, DBC2.
