Transformation

Question 1

Anchorage dependence

Answer 1

an increase in proliferation which is seen when cells are allowed to attach to a solid surface - most normal cell cannot grow in suspension (agar, agarose, methylcellulose)

Question 2

Life-span

Answer 2

Cultured normal cells have a limited life-span

Freshly isolated normal cells only proliferate for a short time

Cells stop growing, enlarge and survive for long periods, but do not divide.

Question 3

Growth arrest

Answer 3

Cancer cells avoid replicative senescence to become immortal

Growth arrested cellsacquire a large, flat morphology stain positively for β-galactosidase

Question 4

Cell-cell contact inhibition

Answer 4

Cell contact causes regular alignment & patterning of cells

Cancer cells lose contact inhibition

Question 5

Density inhibition

Answer 5

Confluent cells enter G0/G1 of the cell cycle and arrest their growth

Cancer cells lose density inhibition & divide uncontrollably

Don’t recoil, crawl over, do not go into arrest when confluent → pile up

Question 6

Growth factor dependence

Answer 6

Density inhibition
- mainly due to exhaustion of growth factors
- saturation density is proportional to the serum concentration
- add more serum to dense cultures - growth resumes
- transformed cells reach a higher density because they need less serum
Cancer cells lose growth factor dependence

Question 7

Hallmarks of a cancer cell (Hannah & Weinberg 2000)

Answer 7

1. Sustaining proliferative signaling
   2.Evading growth suppressors
   3.Activating invasion and metastasis
   4.Enabling replicative immortality
   5.Inducing angiogenesis
   6.Resisting cell death

Question 8

Causes of genomic changes

Answer 8

– Inherited (breast cancer)
– Environmental exposure(UV light)
– Pathogens(HPV, cervical cancer)
– Carcinogens (metabolisation lead to active element of carcinogen)
– Mutation, Epigenetics, Deletion, Translocation, Amplification

Question 9

Properties of chemical carcinogens

Answer 9

Most carcinogens are unreactive molecules (e.g. smoking polycyclic hydrocarbons)

These are metabolised to generate an active form (“ultimate carcinogen”)
a conseq. of the body’s attempts to eliminate foreign, lipophilic substances from the body

Question 10

Telomerase

Answer 10

TERT reverse transcriptase, maintain telomere tandem repeats (~15kB)

synthesised telomere repeats from a short RNA template
expressed in germ cells & some stem cells, absent (or very low) in most somatic tissues

Question 11

Induction of DNA-damage response by short/dysfunctional telomeres

Answer 11

1. leads to induction of tumour suppressor p53
2. p53 (TF) induces expression of cyclin-dependent kinase inhibitor (CDKI) ⇒ p21
3. p21 ⇒ causes cell cycle arrest

Question 12

Oncogene

Answer 12

a gene whose expression contributes to the development of cancer

derived from a cellular “proto-oncogene”

Question 13

Function of proto-oncogenes

Answer 13

1. Signal transduction pathways involved in promoting cell growth
2. Regulation of apoptosis
3. Regulation of differentiation
4. Regulation of cellular lifespan

Question 14

Oncogenes cause cancer due to:

Answer 14

1. Over-expression
2. Inappropriate expression
3. Deregulation through mutation
4. Altered specificity/novel function ⇒ result of chromosomal translocation

Question 15

Type of signalling

Answer 15

Local and Paracrine signalling

Question 16

Discovery of Platelet Derived Growth Factor (PDGF)

Answer 16

Discovery in 1970s, when failed to keep cells alive in laboratory setting, use of plasma serume had low proliferation rate due to lack of platelets, supernatant from platelet culture grew better due to platelet containing PDGF

Stimulates the proliferation of fibroblasts, arterial smooth muscle cells, and glial cells

Question 17

Characteristic of PDGF

Answer 17

All PDGF have a common region called Growth factor domain(varying length)

4 PDGF chains assemble into disulphide-bonded dimers via homo- or hetero-dimerization

There are 5 different known isoforms: AA, AB, BB, CC, DD

Question 18

PDGF-A

Answer 18

Ubiquitous
High expression in muscle, pancreas and prostate

Question 19

PDGF-B

Answer 19

Ubiquitous
high expression in placenta

Question 20

PDGF-C

Answer 20

Ubiquitous
high expression in liver, kidney, pancreas and ovary

Question 21

PDGF-D

Answer 21

More restricted none in brain, lung and muscle
Highest expression in heart, pancreas and ovary.

Question 22

Biological activities of PDGF

Answer 22

Embryonic development → kidney, blood vessels, lung , CNS
Adult blood vessels → constriction & relaxation effects
Wound healing
a. stimulates directed migration(chemotaxis) of fibroblasts, white blood cells & smooth muscle cells
b. stimulates production of matrix molecules involved in the healingprocess

Question 23

PDGF & sis (Inappropriate expression)

Answer 23

sis, oncogene of Simian sarcoma virus, was sequenced by Aaronson’s lab in 1983, initially provided no clues to function.

Now known that sis is derived from the gene for B chain of PDGF.

Cells transformed by sis secrete a functional PDGF (B:B homodimer). Only transforms cells with PDGF receptors.

Question 24

Discovery of Epidermal growth factor (EGF) super family

Answer 24

Stanley Cohen & Rita Levi-Montalcini, Nobel Prize(1986)

In 1960s → a group was working on Nerve GF when they observed an unexpected result
Extract of mouse submandibular gland extracts, wiped on mouse embryos
The explanation was that the salivary gland extract contained a growth factor termed as epidermal growth factor, couldstimulate proliferation of epithelial cells in skin & cornea

Salivary gland cells produce & secrete EGF as do cells at the site of a wound, and cells during embryonic development