Lecture 5: Cancer

Question 1

What type of mutations cause cancer and description

Answer 1

1. Point mutations:The mutation of one or a small number ofbaseswithin agene. Changes in the codons of the DNA can affect whichamino acidsare linked together to make proteins, and so can affect the whole cell.
2. Chromosomal mutations:Changes in the positions of the genes within a chromosome – the genes may be duplicated, deleted or their positions may be changed around.All of these mutations have the potential to produce problems in the individual, because they may result in the formation of a different protein that does not function properly in the cell.
3. Whole chromosome mutations:These usually occur in meiosis, when a whole chromosome is lost or duplicated in the gametes.
4. Damage toDNAcaused by harmful substances in the environment, such as the chemicals in tobacco smoke andultravioletrays from the sun
   5.Inherited

Question 2

Factors increasing risk of cancer development

Answer 2

Smoking
Chemicals
UV
Viruses
Cell dividing 
Genetic

Question 3

Cell division steps

Answer 3

1. G1 = duplication of cell contents (except chromosomes)
   2.S = duplication of chromosomes to form 2 sister chromatids for every chromosome
   3.G2 = double checking and any repair if errors
   4.Mitosis
   PPMATC

Prophase = chromosome condense, spindle fibres appear
Prometaphase = chromosome condense and spindle fibres attach
metaphase= chromosomes allign
anaphase = sister chromatids diverge to opposite ends of cell
Telophase = chromosome decondense, spindle fibres disappear, nuclear membrane forms
Cytokinesis = cytoplasm divides

Question 4

What is the restriction point?

Answer 4

occurs in the G1 phase. Metabolic changes prepare the cell for division. At a certain point - the restriction point - the cell is committed to division and moves into the S phase.

Question 5

MItosis vs meiosis main difference

Answer 5

mitosis is the process of making new body cells to form two identical daughter cells. Meiosis is the type of cell division that creates egg and sperm cells.

Question 6

Cell division process with the specific cyclins and CDKS in each step with the restriction points

Answer 6

G1 to S = Cyclin E/CDK2
S to G2 = Cyclin A/CDK2
G2 to M = Cyclin B/ CDK1
M to G1 = Cyclin D/CDK2

Restriction sites:
End of G1
End of G2 and before cell division in mitosis.

Question 7

Purpose of restriction points
and the the examples of three restriction points with specific cyclins and CDK’s

DRAW DIAGRAM

Answer 7

This is where the complexes of cyclin and CDK bind together and allow the cell to continue through the cell cycle.

G1 = Cyclin E/CDK2 bound
G2= Cyclin B/ CDK1 (mitotic cyclin and mitotic CDK
M = anaphase -promoting complex

Question 8

2 major roles of regulator

Answer 8

1. detecting and repairing damaged DNA

2. preventing uncontrolled cell division.

Question 9

two key classes of regulatory molecules

Answer 9

Cyclin (regulator subunit) and CDK (catalytic subunit)

Question 10

Is cyclin OR CDK synthesised in cell and have catalytic activity?

and their overall function once bound together

Answer 10

Cyclins are synthesized in the cell cycle and have no catalytic activity.

CDKs are found within the cell and only active once bound with cyclins.

Cyclins and CDKs work together to phosphorylate and activate (or inactivate) target proteins in the following steps of the cell cycle.

Question 11

Function of S cyclin-CDK complex

Answer 11

S cyclin-CDK complexes ..
1. phosphorylate proteins in pre-replication complexes, therefore activating them

2. prevent new unwanted complexes from forming
3. ensure only one copy of each genome

Question 12

Function of mitotic cyclin-CDK complex

Answer 12

Mitotic cyclin-CDK complexes

1. initiate mitosis by stimulating the proteins involved in the processes of mitotic spindle creation and chromosome condensation

Question 13

Function of Cyclin D and CDK2

Answer 13

phosphorylate retinoblastoma (Rb). When this happens, the Rb protein breaks away from the Rb/E2F pathway and activates E2F.

Question 14

Function of Cyclin E and CDK2

Answer 14

move the cell from the G1 to the S phase of the cell cycle. Promote expression of S cyclins and enzymes that DNA replication requires and degrade S phase inhibitors via ubiquitination

Question 15

Function of Cyclin B and CDK1

Answer 15

move it from the G2 to the M phase, and also cause the breakdown of the nuclear envelope so that mitosis can begin.

Question 16

What are the role and example of regulatory inhibitors

Answer 16

Inhibitory proteins include CDK inhibitory proteins (the CIP family) and kinase inhibitory proteins (the KIP family).

They alter the G1 phase of the cell cycle by inactivating cyclin-CDK complexes.

More inhibitors include the INK4a/ARF family (which bond to CDK-4, preventing degradation and halting the G1 phase)

Question 17

Define Proto-oncogene, oncogene and tumor suppressor gene

Answer 17

Proto-oncogene:
A gene which regulates cell proliferation, growth and differentiation. It codes for proteins which promote cell cycle progression, eg RAS and MYC.

oncogene: A mutated form of a proto-oncogene which causes the production of proteins which cause the cell to multiply all the time (hyperactive proteins, eg RAS creating too many cyclins and MYC promotes too much cell growth, surivival and activity). POS regulator of cell cycle

Tumor suppressor gene:
Code for proteins which allow for cell arrest, DNA repair and cell apoptosis. NEG regulator of cell cycle

Question 18

2 ways in which Proto-oncogene, oncogene and tumor suppressor gene cause CANCER

Answer 18

Low tumor suppressor genes

High oncogenes

Question 19

Describe RAS and MYC functions as proto-oncogenes and oncogenes and the effects of this

Answer 19

RAS:
The RAS gene is located in cell DNA and creates the protein RAS located below plasma membrane next to the growth factor receptor. If a cell goes through the cell cycle it releases growth factor. This binds to the growth factor receptor and activates the RAS protein. This creates a series of intracellular phosphorylation reactions and forms a transciption protein. This binds to the DNA and transcribes the DNA to formulate cell growth proteins (cyclins and CDK’s). These RAS proteins are inactive and only active when the growth factor is present.

IF mutated then the RAS gene makes RAS proteins which are always activated and thus constant intracellular phosphorylation reactions and transciption proteins and thus overproducing these CDK and cyclins causing the cell to bypass the restriction points

MYC:
This gene codes for proteins that aid in cell growth, activity and survival. SO mutation to MYC gene means that the cell has MORE growth, activity and survival making it more cancerous

THESE mutated forms cause the proto-oncogenes to oncogenes causing uncontrolled cell growth

Question 20

Tumour suppressor genes function as proto-oncogenes and ongogenes

Answer 20

If a cell is damaged at a checkpoint (G1) then the cells DNA releases p53 proteins which act as transcription factor. This makes proteins for cell arrest (proteins that inhibit cyclins and CDK’s thus inhibiting cell cycle to allow for DNA repairs to be completed), apoptosis (if DNA can not be fixed), repairs DNA.

IF MUTATED
Then these proteins can not occur and there is no arrest of damaged DNA in cells causing these cells to proliferate and the checkpoitns to be irrelevant

Question 21

Types of cancers

Answer 21

Carcinomas
A carcinoma begins in the skin or the tissue that covers the surface of internal organs and glands.
They are the most common type of cancer. Examples of carcinomas includeprostate cancer,breast cancer,lung cancer, andcolorectal cancer.

Sarcomas
Asarcomabegins in the tissues that support and connect the body. A sarcoma can develop in fat, muscles, nerves, tendons, joints, blood vessels, lymph vessels, cartilage, or bone.

Leukemias
Leukemia is a cancer of the blood.
4 main types of leukemia areacute lymphocytic leukemia,chronic lymphocytic leukemia,acute myeloid leukemia, andchronic myeloid leukemia.

Lymphomas.
Lymphoma is a cancer that begins in the lymphatic system.
There are 2 main types of lymphomas:Hodgkin lymphoma andnon-Hodgkin lymphoma

Question 22

Tumor antigens examples and description

Answer 22

1. Self antigens (on healthy tissues)
2. Tumor assosciated antigens (Overexpression of self antigens, differientation antigens and cancer testis antigens) Antigens derived from genes overexpressed in tumours comprise a class of normal self-proteins which are minimally expressed by healthy tissues but constitutively overexpressed in cancer cells as a result of their malignant profile.
3. Tumor specific Antigens
   (neoanitgens, oncoviral antigens)

Question 23

Tumour antigen examples: Viral, differentiation, cancer-germline, overexpressed and mutated

Answer 23

Viral antigens are only expressed in virus-infected cells.

Differentiation antigens are encoded by genes with tissue-specific expression.

Cancer germline genes are expressed in tumours or germ line cells owing to whole-genome demethylation.

Some genes are overexpressed in tumours as a result of increased transcription or gene amplification. The resulting peptides are upregulated on these tumours but also show a low level of expression in some healthy tissues.

However, mutated genes may yield a mutant peptide (neoantigen), which is recognized as non-self by immune cells.

Question 24

Immune response to tumour main roles

Answer 24

Protect the host from virus-induced tumours by eliminating or suppressing viral infections

Specifically identify and eliminate tumour cells on the basis of their expression of tumour-specific antigens or molecules induced by cellular stress in timely manner

Question 25

Cancer immunoediting process

Answer 25

Ehrlich, 1909 The immune system regulates cancer development and protects the host from neoplastic diseases. Burnet and Thomas Introduced cancer immunosurvalliance hypothesis. The interface between cancer and immune system Dual effects of the immune system Protect against tumor development and capacity to promote tumour growth.

Question 26

3 steps of immunoediting and description

Answer 26

1) . Elimination represents cancer immunosurveillance (thymus dependent cells of the body constantly surveyed host tissues for nascently transformed cells) 2) equilibrium is the period of immune-mediated latency after incomplete tumour destruction in the elimination phase 3) escape refers to the final out- growth of tumours that have outstripped immunological restraints of the equilibrium phase.

Question 27

Describe the elimination phase

Answer 27

Original concept: The immune system detects and eliminates tumour cells Complete When all tumour cells are successfully eradicated Incomplete: When only some of the tumour cells are eradicated and this causes dynamic equilibrium that can develop between the immune system and the developing tumour.

Question 28

Describe the equilibrium phase

Answer 28

Dynamic Phase Immune cells and their cytokines exert relentless selection pressure on the tumour cells Is it enough? Many of the original tumour cell variants are eliminated but new variants may arise which carry new mutations Resistance to immune attack: tumour cells eventually resist the hosts immunological seige and a new tumour cell population emerges

Question 29

Describe the escape phase

Answer 29

Immune system is no longer able to constrain tumour growth and there is progressive tumour growth The ability of cancer to evade the protective network of the immune system is often considered a hallmark of cancer The multitude of mechanisms which cancer uses to the evade the immune system is wide

Question 30

Cancer immunoediting is now considered a process composed of 3 phases:

Answer 30

elimination, or cancer immune surveillance; equilibrium, a phase of tumor dormancy where tumor cells and immunity enter into a dynamic equilibrium that keeps tumor expansion in check; escape, where tumor cells emerge that either display reduced immunogenicities or engage a large number of possible immunosuppressive mechanisms to attenuate antitumor immune responses leading to the appearance of progressively growing tumors

Question 31

Example of a mechanism of 'escape'

Answer 31

These variants may eventually evade the immune system by a variety of mechanisms, expanding in an uncontrolled manner and becoming clinically detectable in the escape phase. Other factors that may contribute to escape is T cell exhaustion, in which they have increased expression of inhibitory moleculaes such as PD-1 on their surface. In addition, tumour cells may have increased expression of PD-L1 which bind to PD-1 and thus shutting down the T cell response.

Question 32

Immune evasion mechanisms of tumor cells

Answer 32

Reduced immunogenecity Resistance to immune mediated killing subversion of the immune response