Lecture 5: Proto-Oncogene Activation in Malignancy

Question 1

Origins of Cellular Oncogenes

Answer 1

The result of proto-oncogene activation
-Viral origin, identified by virtue of structural homology to retroviral oncogenes
-Cellular origin: Don’t have viral oncogene

Question 2

Origins of Viral Oncogenes

Answer 2

-RNA Viruses
-DNA Viruses

Question 3

Tumor Addiction to Proto-Oncogene

Answer 3

Tumor cells require cell oncogenes to be active

Question 4

Truncated Receptors

Answer 4

A growth factor receptor missing its extracellular domain, causing it to emit unregulated signals into the cell.

Question 5

Growth factor receptor

Answer 5

Cytoplasmic domain that when extracellular growth factors bind, the intracellular portion releases signal into the cell to stimulate cell growth.

Question 6

RAS Oncogene

Answer 6

Causes On/Off function to deactivate, leaving only “ON” allowing unrestricted cell growth. Associated with colorectal cancer

Question 7

MYC Oncogene

Answer 7

Amplification causes increased function of MYC causing increased and uncontrolled DNA replication. Often linked with colorectal cancer.

Question 8

RAS Normal Gene

Answer 8

Controls the signaling pathways of cells by acting as an “On/Off” switch for protein production. Master controller of cell growth and differentiation.

Question 9

MYC Normal Gene

Answer 9

Amplifies function of RNA copying in genes and involved in metabolism. Acts as the “Master regulator” of 37 genes

Question 10

Three biological roles of proto-oncogenes

Answer 10

-Stimulates cell division
-Inhibiting cell differentiation
-Prevention of apoptosis

Question 11

3 phases where proto-oncogene transcription is observed

Answer 11

1. Embryogenesis
2. During stimulus of mitosis
3. Regeneration of lost tissue

Question 12

4 pathways of proto-oncogene conversion to oncogene

Answer 12

1. Nucleotide substitution
2. Gene fusion
3. Enhancer hijacking
4. Focal amplification

Question 13

Non-random amplification and deletions of chromosomal regions

Answer 13

Each cancer type has a characteristic gene amplification and deletion affecting a specific set of chromosomal regions.

Question 14

Neuroblastoma amplification and deletion region

Answer 14

Have changes in the copy numbers of genes in chromosomes 1 and 17. Corresponding changes in the levels of the transcripts expressed by these genes.

Question 15

Measurable changes in the copy of genes were found to be paralleled by changes in mRNA Expression

Answer 15

When DNA copy number of a chromosomal region was increased or reduced, there was a parallel change in the level of corresponding RNA.

Question 16

Sufficiency in evoking tumorigenicity

Answer 16

The activation of s single copy of an oncogene is often enough

Question 17

Exception from DNA mutation sufficiency

Answer 17

C-MYC may become upregulated and help drive tumorigenesis without mutations in either the coding region or regulatory region of its own genes.

Question 18

Level’s of c-MYC in expressed proteins can be inappropriately increased by

Answer 18

1. Epigenetic factors
2. Increased stability of oncoprotein
3. Deregulated upstream signaling revealed when looking for changes in coding sequences in oncogene.

Question 19

Chromosomal Translocations

Answer 19

Pieces of a chromosome are exchanged which can lead to proto-oncogene activation.

Question 20

Philadelphia Chromosome Translocation

Answer 20

Translocation between chromosome 9 and chromosome 22 cause formation of oncogenic BCR-ABL fusion protein with novel structure and function.

Question 21

BCR-ABL protein

Answer 21

Causes out of control CML growth and division

Question 22

CML Symptoms

Answer 22

-Fatigue
-Weight loss
-Night Sweats
-Low-grade fever
-Left upper quadrant pain

Question 23

Chronic Vs. Acute Stage CML

Answer 23

-Chronic stage: Moderate increase in granulocytes
-Acute stage: Leukemic cells produced in vast numbers

Question 24

c-ABL proto-oncogene characteristics and functions

Answer 24

-Ubiquitously expressed
-Cytoplasmic & nuclear forms
-Nuclear: DNA damage
-Cytoplasmic: Adhesions and proliferation

Question 25

Protocol for karyotype preparation in leukemic patient

Answer 25

Bone marrow extraction from pelvic bone followed by metaphase arrest and hypotonic treatment to fixate, spread, and band under microscope

Question 26

Insertional Mutagenesis

Answer 26

Slowly transforming retroviruses activate proto-oncogenes by inserting their genomes adjacent to these cellular genes

Question 27

Cellular transformation by proto-oncogene

Answer 27

Proposed that mutations in the cellular homologies of these genes could transform cells in the absence of any viral involvement

Question 28

Explanation for the diversity of transforming retroviruses

Answer 28

Retroviruses might be carrying kidnapped cellular proto-oncogenes and may be using these acquired genes to transform infected cells

Question 29

Cellular transformation by retroviruses

Answer 29

Retroviral oncogenes could rapidly transform cells and that the viruses had acquired these genes from the genomes of mammalian and avian cells they infected.

Question 30

Cellular transformation by chemical carcinogens

Answer 30

Weinberg and Cooper showed that transfection with DNA of cells transformed by chemical carcinogens can cause cancerous transformation in normal cells. Implies cooperation of cellular genes in the absence of viral genes.

Question 30

How would you test the hypothesis that RAS mutations contribute to cell transformation

Answer 30

1. Inject mice with pro-nucleus of fertilized zygote
2. Implant embryo into pseudopregnant females
3. Screen offsprings for carrying the gene.

Question 31

pBKI0-Ras transgenic mice

Answer 31

Ras expression is tissue specific because Ras expression is under the control of pBKI0 promoter, expressed in skin basal cells of mice

Question 32

RAS-Activation Pathways

Answer 32

Growth Factor -> Interaction with receptor -> Intracellular signaling -> Activations of kinases -> New transcription factors -> Expressions of various genes

Question 33

Kirsten rat sarcoma viral oncogene homologue.

Answer 33

One of the most highly mutated oncogenes in human cancer, occurring in 95% of pancreatic, 50% colorectal, and 32% lung adenocarcinomas and other tumors.

Question 34

Chromosomal Translocation in Burkitt’s Lymphoma

Answer 34

Translocation between chromosome 8 and 14. Resulting myc ongogene initially makes structurally normal Myc protein in abnormally high amounts.

Question 35

______ gene is often amplified in childhood neuroblastoma

Answer 35

N-Myc

Question 36

Oncogene addiction

Answer 36

Introduced by Bernard Weinstein to describe the depedency of certain tumor cells on a single activated oncogenic protein or pathway to maintain malignant properties. This occurs despite the likely accumulation of multiple loss-of-function mutations that contribute to tumorigenicity.

Question 37

Non-oncogene addiction

Answer 37

Proper functioning of non-mutated genes has been shown to enhance the survival of many cancers