L12 - Oncogenes Flashcards by Jack Corston

What quantity of tumours are induced by viruses

Minority

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How many genes do viral genomes have

Few genes

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What can be said about the few genes that viruses do contain

They are enough to drive the tumour phenotype

Extremely potent genes which perturb the complex regulatory circuit of the host cells that they infext

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RSV

Rous Sarcoma Virus

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How was the carcinogenic agent in RSV discovered

Chicken with sarcoma in breast
Sarcoma removed and ground with sand
Collect filtrate that had passed through a fine-pore filter
Inject filtrate into a young chicken
Observe the formation of a sarcoma in the injected chicken

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What are foci

Clusters of tumour cells which appear after infection

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Describe the morphology of the foci and how they grow

Rounded cells that grow one on top of the other

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What characteristics of the foci is similar to the cells of the tumour

Have similar metabolism

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Define cell transformation

Converstion of a normal cell into a cancer cell

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Describe the transmission of the cancer between the cells of the foci

Transformed phenotype was transmitted from the initially infected cells to its descendents

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What is a TS RSV mutant

RSV virus which carries a temperature sensisitve mutation

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Describe how the TS RSV mutant functions

Proteins are able to function at the permissive temperature (37) if raised about this the proteins don’t have TW function

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What can be said of the dependence of the transformed phenotype on the virus

Viral transforming gene is required to initiate and maintain the transformed phenotype of the infected cells

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Properties of transformed cells

Altered morphology 
Loss of contact inhibition 
Ability to grow w/o attachment 
Ability to proliferate indefintely 
Reduced requirement for MGFs 
High saturation density 
Inability to halt proliferation in the absence of GFs 
Increased uptake of glucose 
Tumorigenicity

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How many genes in the RSV virus

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What are the four genes in RSV

Gag, Pol, Env, C

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What is the effect of the removal of Gag, Pol and Env

Virus is unable to replicate but is still able to transform other cells

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What is the effect of the removal of X

Virus is able to replicate but is unable to induce cell transformation

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The single gene required for transformation is known as

Src

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How many genes are required for replication of the RSV virus

Gag, pol and env

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What is the derivations behind the name Src

Ability to induce a sarcoma in the chicken

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What can be used to understand the origin and functions of Src especially useful to be able to follow it in infected cells

Src specific DNA probe

Src when it is normally found in organisms is known as

C-Src

What type of Src is found in viruses

What can it act as

V-Src

Potent oncogene

What is an oncogene

Gene which is able to transform a normal cell into a tumour one

What type of gene is C-src What is it a precurrsor to

Proto-oncogene Precursor of an active oncogene

What are the two hypothesies to describe how oncogenes become activated

Through endogenous retroviruses | Induction through mutants

Describe how you would be able to identify wether chemicall transformed cells are able to carry mutated genes

TRANSFECTION STUDIES Chemically transform mouse fibroblasts Isolate DNA - transfect using calcium phosphate Inject into normal mouse fibroblasts Formation of a focus of morphologically transformed cells Injection of morphologically transformed cells into mouse host Formation of a tumour

What was the overall conclusion of the transfection studies

Donor tumour DNA carried by one or several genetic elements is able to convert a normal cells into a tumorigenic one

Oncogenes detected by transfection were derived from ____

Pre-existing normal cellualr genes which lack previously lacked oncogenic function - similar scenario to the viral oncogenes

Give an example of an oncgoene detected in human bladder carcinoma

H-Ras

Is H-Ras expressed through gene amplification

No - mutation present in only the one copy

What is the mutation which must occur in order for h-Ras to become oncogenic

Point mutation at residue 12 Glycine --> Valine

Describe the method which is used to identify the sequence which has changed

Creation of hybrids - 1/2 and 1/2 of the known cancer and normal If the hybride can transform you know thar THE CANCER HALF CONTAINS THE MUTATED SEQUENCE Perform again

What are the 3 Ras proteins What do they have in common

H, K and N Ras | Point mutations are able to convert from protooncogenes to oncogenes

Describe the cycling seen in small GTPases

cycle between the active form - with GTP bound AND The inactive form with GDP bound

What is required to activated Ras

GEF

What is required to cause a cessation in the signalling of Ras

GAPS

What is significant about Ras G12V (Glycine --> Valine at position 12)

It is unable to hydrolyse GTP Protein is consituitively active

In the presence of no growth factor describe the activity of the Ras G12V

ONCOGENIC RAS No growth factor but mutant RAS is always ON Leading to cell division and proliferation

What are the four immediate downstream targets of Ras

RAF PI3K RALGDS PLC

How many mechanisms are there which would lead to the activation of the myc oncogene

What are the three mechanisms leading to oncogenic transformation of myc

1) Expression driven by normal promoter but gene is amplifyed 2) Chromosomal translocation 3) Pro-virus integration causing an insertional mutagenesis

How does Expression driven by normal promoter but gene is amplifyed arise?

More than 2 copies => high levels of gene product

What can be said about the prognosis of myc at the various copy levels

With a higer myc copy number the prognosis for patients is worse

How many chromosomal translocation cause oncogenic activation of Mtc

C-myc would be under the control of a foreign promoter | **Most common to have Myc expressed under a Ig (immunoglobin) promoter

During a chromosomal translocation is there any change to the strucutre of myc

NO Strucutall normal but is expressed at high ammounts

Wht type of lymphoma is caused by a chromosomal translocation affecting myc

Burkitt lymphoma

What is ALV

Avian leukosis virus

Describe how pro-virus integration may lead to elevated myc expression

Virus integrates immeidatly adjacent to the myc gene so expression of myc is now driven by the active viral promoter leads to an INCREASE IN GENE PRODUCT

Describe how changes in the EGF receptor may form ocogenees

Trucation of the EC ligand bidning domain results in a consituitively active receptor

What is the normal structure and mechanism of activation of the EGF receptor

EC ligand binding domain - when a growth factor binds here the IC domain is able to signal

What are 4 ways in which EGF signalling could be manipulated to oncogenic levels

Over expression of EGF ligand Overexpression of the receptor Ligand independent dimerisation (dimerisation in the absence of ligand biinding) Mutations resulting in the formation of a constituitvelt active receptor