Lecture 20 - Regulation of Gene Expression and Oncogenes

What are 4 methods of regulation in gene expression (eukaryotes)

1. Gene dosage

2. Transcription factors, epigenetics (promoter and histone modification)

3. mRNA stability, miRNAs (RNA interference)

4. Protein modification

What are 3 examples of histone modification/epigenetics?

1. Tightly packed DNA is NOT expressed

2. Acetylation of histones → loosening of the nucleosomes allows for transcription to take place

3. Incorrect modifications of histones is associated with some cancers

What two things contribute to mRNA stability?

1. Poly A tail length

2. 3’ untranslated region

What two roles does RNA interference (RNAi) have?

1. Gene expression regulation through microRNAs (miRNAs)

2. Destroys viral RNA (Short interfering RNAs)

What are the steps to RNA interference in the lab

1. Double stranded RNA synthesized in vitro with RNA polymerization of both DNA strands

2. Injected or transfected into cells

3. One inside knocks out or knocks down gene expression

What are two types of post transcriptional level gene expression regulation

1. Polypeptide degradation

2. Pre-version of protein that has to be processed before it is active

What does preinsulin do in gene expression regulation?

Endopeptidase activates insulin peptide by cutting off a section

What are the characteristics of cancer cells?

1. Unregulated cell division

2. Formation of masses in cell culture instead of a monolayer

3. No stable bonding with neighboring cells

4. Disorganized cytoskeleton

5. Unusual cell surface proteins

6. Aneuploid (abnormal chromosome number)

7. Frequent chromosome level abnormalities (deletions, duplications, translocations)

What are 4 causes of cancer?

1. Carcinogens

2. Radiation

3. Viruses

4. Random

What are 4 pieces of evidence for a genetic basis of cancer?

1. Clonally inherited → All descendent cells are cancerous

2. VIruses can induce cancer

3. Agents known to cause mutations can induce cancer

4. Cancers tend to run in families

Cyclin concentration

Determines whether cell moves into different stages of the cell cycle. When low, cyclin detaches from the CDK and inhibits enzyme kinase activity

Describe the steps of cell cycle

1. Start checkpoint in G1 is controlled by D-type cyclin and CDK4

2. IF cyclin D/CDK4 complex is present, then commit to S phase and cell division

3. IF complex is disrupted by proteins that prevent complex forming, it will remain in G1

What are reasons for a cell to remain in the G1 phase?

1. Low nutrient levels

2. DNA damage - wait for repair (Cancer cells do NOT wait for repair)

What makes cancer cells checkpoints deregulated?

1. Mutations in cyclin or CDK genes

2. Mutations in genes encoding the proteins that respond to specific cyclin/CDK complexes

3. Mutations in proteins that regulate complex formation

What is Rous Sarcoma virus?

Cell-free extract from tumors can cause tumors in new host

What 4 genes are in the ROus Sarcoma virus?

1. gag - capsid protein

2. pol - reverse transcriptase, integrase

3. env - viral envelope protein

4. v-src - protein kinase

What does the presence of v-src indicate?

Not present = no tumor

Retroviruses

Genome is composed of RNA and the DNA integrates into the host genome. They are transcribed to prpoduce new virus proteins