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