Minden Tumor Suppressor genes
Gene conversion
1. DNA polymerase begins replication of chromosome A. 2. DNA pol jumps to template strand of homologous chromosome B. 3. After copying segment of template strand of chromosome B, DNA polymerase jumps back to chromosome A and begins copying again.
two ways hypermethylation can occur
1. Loss of one allele by LOH, and the second allele is inactivated by hypermethylation. This could be followed by duplication of the methylated allele 2. Both alleles could be inactivated independently by hypermethylation
2 types of retinoblastoma
1. Sporadic: No family history. Once the tumor (usually a single tumor in one eye only - unilateral) is removed, that child is at no further risk for cancer 2. Familial: A parent also had the disease. There are usually multiple tumors in both eyes (bilateral retinoblastoma). Even after curing the eye tumor (radiation or surgery) the patient has a greatly increased risk for cancer (usually osteosarcomas - bone cancer).
BRCA1 gene was found to be inactive in ______% of sporadic breast carcinomas, but always through methylation.
10-15%
Tumor suppressors can be divided into two broad types
A. Suppress cell cycle progression (proliferation) or induce differentiation (ex: Rb) B. Inhibit proliferation in response to metabolic imbalances or genomic damage (ex: p53)
When Wnt activates Dishevelled, B-catenin is ________
ACTIVE
______ is a tumor suppressor, frequently associated with colon cancer
APC
In neuroectodermal cells where NF1 is inactive, _____ stays in its active form. In this sense, loss of NF1 mimics it.
Active Ras.
______ is often called familial adenomatous polyposis (FAP). it is associated with an inherited susceptibility to develop colon polyps.
Adenomatous polyposis coli
Inactivation of this gene is associated with breast cancer risk, and to a lesser extent to ovarian cancer risk.
BCRA1
APC signals the degradation of _______, a proliferating protein
Beta catenin
Enterocyte stem cells encounter Wnt factors released by stromal cells near the bottom of the crypt. This keeps ______ levels high in these cells
Beta catenin
The types of mutations that would lead to cancer would be mutations that _____ the migration of colonic epithelial cells.
Block
______ provided some of the first clues for the presence of tumor suppressor genes
Cell fusion experiments
Cells lacking Apc have been shown to have an increase in _______, this results from increases and decreases in chromosome number
Chromosomal instability
Mutations in APC associated with ______ often consist of premature termination of the Apc protein, thereby removing domains that are important for its ability to associate with β-catenin and axin and the resulting _______ of β-catenin.
Colon cancer, degradation
The RASSF1A tumor suppressor gene was found to be hypermethylated on ______ in its promoter, in solid tumors.
CpG islands
Treatment of DNA with bisulphite converts _______, but leaves 5-methylcytosine residues unaffected.
Cytosine to uracil
An oncogene usually ______ cell growth, a tumor suppressor gene usually _______ cell growth
Encourages, inhibits
______ has been used as a marker for Rb
Esterase D
The APC gene is frequently mutated in _____
FAP (familial adenomatous polyposis)
Under normal conditions, HIF-1 transcription factor accumulates to only a very low level and is mostly inactive. This is called a ______
Futile cycle
Ras inactivation is triggered by
GAP and GTP hydrolysis
In ras, you are replacing a _____ for a _____.
Glycine for valine (guanine for thymine)
When in cell cycle is Rb phosphorylated?
Go - unphosphorylated, blocking cell cycle from progressing. G1 - weakly phosphorylated on serine and threonine S - extensively phosphorylated G2 - remains hyperphosphorylated until cell exits mitosis and is then dephosphorylated by type 1 phosphatase
Methylation acts by attracting _____ and thus causing deacetylation and in turn reconfiguring the chromatin. A HDAC inhibitor called _______ reverses deacetylation and thereby reverts the chromatin to a state that favors transcription.
HDAC; TSA
When cells growing adjacent to each other in culture are exposed to a fusogenic agent (such as Sendai virus or polyethylene glycol (PEG)), they initially form a ______ with multiple nuclei.
Heterokaryon
What does bisulfite treatment and PCR tell us?
If the nonmethylated specific primer fails to anneal correctly, and no PCR products occur, the sequence was methylated.
_____ occurs in mitosis rather than meiosis, but at a low frequency
Mitotic recombination
How does loss of heterozygosity occur?
Mitotic recombination Random mutation Gene conversion
This familial cancer is associated with the development of benign tumors of the cell sheaths around nerves.
NF-1
An ______ is a mutant (activated) or overexpressed version of the proto-oncogene, found in cancer.
Oncogene
Hemizygosity
One copy of a gene/allele is deleted.
Stimulates cells important for blood vessels, including endothelial cells, mesenchymal cells, pericytes, and fibroblasts.
PDGF
Methylation can only suppress transcription in the _____ region.
Promotor
_____ are used for mapping genes
RFLPs - restriction fragment length polymorphisms
The _____ has a single point mutation, compared with wild-type (proto-oncogene). This is mutated in many human cancers.
Ras oncogene
In many cases the resulting heterokaryon is non-tumorigenic, indicating that The cancer alleles are _______
Recessive
When Rb is bound to E2F and DP1, transcription is _______.
Repressed
_______ is a potent inducer of cell cycle arrest in many epithelial cells
Retinoic Acid
Gene conversion occurs during the ___ phase of DNA replication.
S phase
_____ consist of a single base-pair change in a restriction site.
SNPs
_____ is the use of bisulphite treatment of DNA to determine its pattern of methylation.
Sodium Bisulfite treatment
Perform _______ and ______ to determine if there was a LOH
Southern blot, gel electrophoresis
Stimulates growth of a variety of cell types including epithelial cells.
TGF-Alpha
Treatment of breast cancer cells with _____ can restore sensitivity to RA.
TSA
Advantages of ubiquitination
Unidirectional - cannot be reversed Rapid Fine-tuning Localized Site-specific
Causes growth of endothelial cells (blood vessel cells)
VEGF
The main function of ______ is to foster destruction of a subunit of a transcription factor called hypoxia-inducible factor-1 (HIF-1)
VHL tumor suppressor gene
_______ is a hereditary predisposition to the development of a variety of tumors, including clear-cell carcinomas of the kidney, pheochromocytomas (adrenal gland) and hemangioblastomas (blood vessel tumors) of the central nervous system and retina
Von Hippel-Lindau Disease
How does p21 suppress the cell cycle?
When DNA damage occurs, p53 levels increase and activate the p21 gene. P21 protein then binds to CDK1 and cyclin, and there can be no progression from G1 to S.
How does Rb suppress the cell cycle
When Rb is bound to E2F and DP1, transcription is repressed. This happens at the G1 phase.
When Rb is phosphorylated, transcription is _______
activated.
For an oncogene, mutations that involve _______ cause cancer For a tumor suppressor gene, mutations that cause _____ cause cancer.
activation, inactivation
if VHL is not present or not functional, HIF-1 transcription factor can not ever be targeted for destruction. It is ________, and the target genes can be activated any time.
always active
Loss of Apc could lead to _____ due to _____ chromosome segregation.
aneuploidy (incorrect number of chromosomes); improper
Patients with NF sometimes have "______ spots", areas of hyper- pigmentation on the skin, and benign lesions on the iris
café au lait
The _______ contains replicating stem cells near the bottom. Cells further up are more differentiated with a specialized functions
colonic crypt
In methylation, a _____ is methylated
cytosine
If cyclin D levels _____, Rb is dephosphorylated and active
decrease
P21 P15 P27 and P16 ______ CDKs
downregulate
Methylation is considered ______ because it does not alter DNA sequence.
epigenetic
What is loss of heterozygosity
genes become homogenous for bad copy [two alleles lacking differences at a particular region]
Loss of ______ in the Rb gene causes cancer
heterozygosity
β-catenin levels are _____ in the stem cells in the crypt
high
Under _______ conditions, proline hydroxylase fails to oxidize the two prolines on HIF-1α (because it depends on normal O2 levels), and VHL fails to bind and target HIF-1α for destruction. HIF-1α levels will ______.
hypoxic; increase
Chromosomal instability is due to ______. It can lead to _______ of too many chromosomes
inappropriate segregation of chromosomes during mitosis; Accumulation
The ______ specific primer will only bind to sequences that are methylated (after sodium bisulfate treatment), and will therefore only result in a PCR product if the sequence is methylated
methylation
If the heterokaryon is ______, the cancer cells are recessive.
non-tumorgenic
For oncogenes, mutations on _______ are sufficient to cause cancer, whereas for tumor suppressor genes, mutations must occur on ______
one allele; both alleles
The promoter of ______ was found to be methylated in 44% of normal bronchial epithelial cells cultured from current and former smokers, but not at all those of people who had never smoked.
p16INK4A
Increased levels of CDK4 may lead to increased _______ of Rb
phosphorylation
Ras activation is triggered by ____
phosphorylation of GDP via GEF.
loss of APC causes cells to stay crypt cells and to _______. This also gives them a chance to develop other mutations, such as Ras mutations.
proliferate excessively
Under normal O2 conditions, _______ converts one or both prolines on HIF-1α to hydroxyproline residues.
proline hydroxylase
A _______ is a normal cellular gene, that is associated with cancer only if it is improperly activated (usually by overexpression, mutation, or gene translocation).
proto-oncogene
Restriction enzymes cut DNA at defined short sequences known as ______
restriction sites
A _______ gene only causes cancer if it is inactivated or deleted. In this way, it can be considered the opposite of an oncogene.
tumor suppressor
The mechanism by which VHL causes degradation of Hif1α is by _____
ubiquitylation