Cancer Biology Exam 2

1.) Reproductive Signal: Initiate cell division, can be intracellular or extracellular

2.) Replication of DNA

3.) Segregation: Distribution of DNA into the two new cells

4.) Cytokinesis: Separation of cellular material into the two new cells

Lists the Events of Cell Division

G₁, S, and G₂

When is interphase?

mitotic checkpoint or metaphase checkpoint

The M checkpoint is the same as the..

A spindle assembly checkpoint occurs if a chromosome isn't properly attached to the spindle, checkpoint proteins will halt the cell cycle and inhibit APC.

Explain the metaphase checkpoint or mitosis checkpoint

events, details

For cell division in prokaryotes and eukaryotes, the ______ are the same but the _____ are different.

cell division in prokaryotes, resulting in reproduction of entire single-celled organism

Binary Fission

Two new single-celled organisms

What is the end result in prokaryotic cell division?

External factors (e.g., nutrient concentration and environmental conditions) are reproductive signals

What are examples of reproductive signals for prokaryotic cell division?

Abundant food supplies

What speeds up prokaryotic cell division for many bacteria?

No

Do eukaryotic cells constantly divide when environmental conditions are adequate?

Reproductive signals are related to the needs/function of the entire organism

What are reproductive signals in eukaryotic cell division?

specialized, seldom.

Many cells in multicellular organisms become ______ and ______ divide.

Outside of the cell

Typically the reproductive signal to initiate cell division occurs where?

1.) Growth factors

2.) Growth factor receptors

3.) Intracellular signal transducers

4.) Nuclear transcription factors

What does transduction of growth factor signaling involve?

They link signals outside the cell to intracellular regions.

What do Growth factor receptors link?

Tyrosine, serine, or threonine Kinases

Many Growth factor receptors are what enzymes?

The γ phosphate transferred from ATP/GTP is to hydroxyl groups of specific amino acid in target protein

How do Growth factor receptors phosphorylate the target protein.

Epidermal growth factor (EGF)

What specific growth factor is widely studied in cancer?

Family of tyrosine kinases that respond to EGF

Epidermal growth factor receptor (EGFR) family

1.) EGFR, ErbB1; HER1

2.) ErbB2; HER2; HER2/neu

3.) ErbB3; HER3

4.) ErbB4; HER 4

What are the 4 members of the epidermal growth factor receptor (EGFR) family?

1.) Growth factor binds to receptor

2.) Receptor dimerizes

3.) Autophosphorylation

4.) Activation of intracellular transducers

5.) Activation of Serine/Threonine Kinase Cascade

6.) Regulation of transcription factors for gene expression

What are the steps of EGF signaling?

The extracellular domains of EGFR form a binding pocket that allows for EGF binding.

Explain Step 1 of the EGF Signaling...

EGF binding to the EGFR causes conformational change that reveals dimerization domain. This facilitates binding to another, similar domain after that receptor has also bound to EGF

Explain Step 2 of the EGF Signaling...

homo, hetero

EGFRs can ____dimerize or ____dimerize

Conformational change after ligand binding disrupts intramolecular auto inhibitory interactions. This result is kinase activation: ATP and substrate can now access cytoplasmic catalytic kinase domain. The kinase domain of one receptor phosphorylates other receptor at multiple tyrosines and vice versa.

Explain Step 3 of the EGF Signaling...

substrate proteins

What is phosphorylation necessary for recruiting in EGF signaling?

1.) Additional phosphorylations trigger confirmation change to inhibit ligand binding/kinase activity

2.) Dephosphorylation by tyrosine phosphatases

3.) Kinase domain bound by negative regulators

4.) Receptor endocytosis and degradation

What are the ways in which autophosphorylation can be stopped?

1.) Some phosphorylated tyrosine residues create high-affinity binding sites for SRC homologous domains.

2.) The SH2 domain of Grb2 will bind to phosphorylated tyrosines

3.) The SH3 domian of Grb2 will bind to SOS

4.) SOS will activate RAS in which GDP is removed and replaced with GTP

5.) Farnesylation directs RAS to cell membrane

6.) RAS will activate downstream proteins

Explain Step 4 of the EGF Signaling...

100 amino acids long; SH2 binds to a phosphorylated tyrosine and the amino acids immediately C-terminal to it.

Explain SH2. What is its length? What is its function?

50 amino acids long, and binds to residues on partner proteins

Explain SH3. What is its length? What is its function?

1 SH2 and 2 SH3 domains

What domains does Grb2 have? How many of each?

SOS

What protein does SH3 interact with?

A guanine nucleotide exchange factor that activates RAS in which the GDP bound is released and a GTP binds.

What is SOS?

GTP-binding proteins that can activate serine/threonine kinases. Examples include N-RAS, H-RAS, K-RAS.

What are RAS proteins? What are examples?

Farensylation, a farnesyl group, or lipid group is added to the RAS which allows RAS to bind to the cell membrane

What directs RAS to the cell membrane? How?

RAS is inactivated when bound to GDP and activated when bound to GTP.

Explain when RAS is inactivated and activated.

This can now interact with downstream proteins

When RAS is bound to GTP, what does this allow?

Catalyze the hydrolysis of GTP to GDP to terminate signal. RAS proteins have intrinsic GTPase activity for self-regulation.

Explain GTPase activating protein (GAPs). Where is GTPase located on RAS proteins?

RAS recruits Raf to the cell membrane, which causes a conformational change to Raf, which activates it.

How does RAS activate Raf?

It activates Serine or threonine kinase Raf

Once RAS is bound to GTP, what kinase does it activate?

1.) RAS activates the Raf kinase, which carries the signal away from the membrane and Raf phosphorylates MEK

2.) MEK will phosphorylate MAPK

3.) MAPK will phosphorylate transcription factors which activates them, allowing them to regulate the expression of genes.

Explain Step 5 of the EGF Signaling...

MAPKKK

What is another term for Raf?

MAPKK

What is another term for Mek?

A tyrosine and serine/threonine kinase that phosphorylates MAPK

What is the function of MEK? What kind of kinase is it?

A serine/threonine kinase which phosphorylates MEK.

What is the function of Raf? What kind of kinase is it?

Mitogen-activated protein kianse, a family of serine/threonine kinases that phosphorylate transcription factors to regulate their activity.

What is the function of MAPK? What kind of kinase is it?

1.) AP-1 transcription factors - which are involved in growth, differentiation, and death. Phosphorylation of Fos alters DNA-binding activity

2.) Myc family of transcription factors - which regulate expression of genes important for proliferation. MAPK targets N-ras and p53.

What transcription factors does MAPKs regulate? What is targed and what occurs when phosphorylated?

They are enzymes that phosphorylate a hydroxyl group on specific amino acids. Tyrosine kinase and serine/threonine kinases are the two main types.

Explain what protein kinases are and Explain the two main protein kinases.

Cell cycle progression, signal transduction, and transcription

What are protein kinases involved in?

Proto-oncogne; Helps transmit signal from recptor to inside the cell

What is the Ras family?

Tumor suppresor gene. lines stress different cellular responses.

What is p53?

Stress: DNA Damage

Cellular Responses: Cell Cycle Arrest and DNA Repair

For p53, what is an example of a stress and what are examples of cellular respones?

Tumor suppressor gene, inhibits cell cycle progression

Explain Retinoblastoma gene...

Intracellular tyrosine kinase with SH2 and SH3 domains

What is SRC?

Activated EGFR interacts with SH2 domain of SRC to induce cell proliferation

How does Activated EGFR induce cell proliferation?

Focal adhesion kinase interacts with SH2, which is important for cell shape, adherence, and motility.

Explain FAK and its function.

When Tyr-530 is phosphorylated and binds to the SH2 domain.

How is SRC inactivated?

Mutated gene whose protein product is produced in higher quantites/has increase activity.

Explain briefly oncogenes

dominant

Oncogenes act in a ________ manner.

Any normal gene that can be activated to become oncogenic

Explain proto-oncogenes.

100, 20

How many oncogenes and tumor suppressor are identified respectively?

structural and functional changes

In regards to oncogenes, point mutations/deletions in coding sequences cause what...

overexpression of genes

In regards to oncogenes, point mutations/deletions in regulatory sequences caused..

fusion proteins with novel functions

In regards to oncogenes, chromosomal translocations caused..

aberrant expression

In regards to oncogenes, insertional mutagenesis caused by viral integration caused..

During cell division, ecDNA can be distributed randomly between the two daughter cells.

Explain inheritance of ecDNA during cell division...

compact, accessible

Compared to chromosomal DNA, ecDNA is less _______/more __________.

retroviruses

Discovery of oncogenes came from studies of...

RNA, provirus

Retrovirses inject _____ into host and end up with a __________.

The DNA form of a retrovirus that results from reverse transcription

What is a provirus?

randomly

Retroviruses integrate DNA _________ into the host genome.

The translation of viral RNA produced viral proteins needed for synthesis of new viral particles.

The translation of viral RNA produces...

fragments of genes from host genome at sites of integration.

When the viral DNA is later copied or removed, it can acquire...

Integration is when a retrovirus inserts a copy of its genetic material into the host cell's DNA.

Explain integration for retroviruses.

c-src

Which host gene did Rous Sarcoma Virus (RSV) acquire a truncated form of?

Rous discovered that a virus could cause sarcoma in chickens, leading to the identification of its viral cancer-causing gene, v-src.

How did Rous discover the v-src gene?

Discovered c-src, a normal cellular proliferating gene similar to viral v-src that can cause cancer when altered or abnormally activated. This discovery helped establish the concept of oncogenes.

Explain How Bishop and Varmus connected the c-src gene to the v-src gene.

Stimulates epithelial cells around wound edge to proliferate and repair damage.

Platelet-derived growth factor (PDGF)

PDGF

What was one of the first identified proto-oncogenes?

The oncogene results in PDGF staying in the cytoplasm rather than secreted. This causes PDGF to interact with the newly forming PDGF receptors in the Rough ER or Golgi Apparatus, signaling to be inappropriately activated, leading to unregulated cell growth.

The oncogene form of PDGF causes what to occur to PDGF? What does this cause?

EGFR oncogene is truncated form of EGFR, which doesn't have an extracellular domain

What is the difference between EGFR oncogene and the proto-oncogene form?

The EGFR oncogenic activation of receptor tyrosine kinases occurs through mutations that cause constitutive tyrosine activation, dimerization, and altered substrate activity.

Explain constitutive activation in regards to EGFR of the tyrosine kinase.

Ras

What is the most commonly mutated oncogene?

GTPase, GTP, GDP

The mutation of RAS results in the loss of ______ activity, so RAS-___ can't be inactivated to RAS-___.

B-Raf point mutation. This results in constitutive kinase activity and insensitivity to feedback mechanisms.

What point mutation is common in melanoma? What does this result in?

Nuclear threonine kinase involved in DNA damage-induced apoptosis.

Explain ABL

A chromosomal translocation places ABL next to BCR. The BCR-ABL fusion protein is maintained in the cytoplasm, which causes kinase activity constitutively active in cytoplasm, which causes access to different substrates.

Explain how the Philadelphia chromosome formation causes an increased risk of leukemias and lymphomas.

This mutation results in truncation and eliminates a motif involved in mRNA instability. Thus, mRNA has a longer half-life, ultimately leading to inappropriate increase in transcription of AP-1 regulated genes.

What happens to a mutation in the Fos protein?

kinase

Many specific ______ inhibitors have been created, although the catalytic domains are very similar when active.

Herceptin, it is used for treatment of metastatic breast cancers that over express ErbB2.

What is Herceptin used in treatment for?

It is humanized monoclonal antibody that binds extracellular domain of ErbB2, which increases receptor degradation, inhibition of angiogenesis, and recruitment of immune cells resulting in cytotoxicity.

Explain the function of Herceptin.

Directed against tyrosine kinase activity of EGFR family receptors. It competes for binding of ATP. The initial response rate is high, but drug resistance is common due to additional mutations.

Explain the function of Tarceva.

Tarceva and Herceptin

What are two examples of treatments for EGFR?

Gleevec

What is used to Target BCR-ABL?

95

__% of CML patients express BCR-ABL fusion protein.

chronic myeloid leukemia

What is CML?

This drug binds to ATP-binding pocket of the catalytic domain of ABL. It is very succesfull in treatment of early-stage CML, but mutations lead to relapse.

Explain the function of Gleevec. What can it treat?

A theory that states that some cancer cells become highly dependent on some specific oncogenes to survive and keep growing.

Oncogene addiction

No

Has Ras targeting been successful?

Yes, Drug resistance due to mutations or switching to different kinase for constitutive growth signals

Has there been success with target of downstream effectors in the Ras pathway? How would drug resistance occur?