Transformation Flashcards
Anchorage dependence
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)
Life-span
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.
Growth arrest
Cancer cells avoid replicative senescence to become immortal
Growth arrested cellsacquire a large, flat morphology stain positively for β-galactosidase
Cell-cell contact inhibition
Cell contact causes regular alignment & patterning of cells
Cancer cells lose contact inhibition
Density inhibition
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
Growth factor dependence
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
Hallmarks of a cancer cell (Hannah & Weinberg 2000)
- Sustaining proliferative signaling
2.Evading growth suppressors
3.Activating invasion and metastasis
4.Enabling replicative immortality
5.Inducing angiogenesis
6.Resisting cell death
Causes of genomic changes
– Inherited (breast cancer)
– Environmental exposure(UV light)
– Pathogens(HPV, cervical cancer)
– Carcinogens (metabolisation lead to active element of carcinogen)
– Mutation, Epigenetics, Deletion, Translocation, Amplification
Properties of chemical carcinogens
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
Telomerase
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
Induction of DNA-damage response by short/dysfunctional telomeres
- leads to induction of tumour suppressor p53
- p53 (TF) induces expression of cyclin-dependent kinase inhibitor (CDKI) ⇒ p21
- p21 ⇒ causes cell cycle arrest
Oncogene
a gene whose expression contributes to the development of cancer
derived from a cellular “proto-oncogene”
Function of proto-oncogenes
- Signal transduction pathways involved in promoting cell growth
- Regulation of apoptosis
- Regulation of differentiation
- Regulation of cellular lifespan
Oncogenes cause cancer due to:
- Over-expression
- Inappropriate expression
- Deregulation through mutation
- Altered specificity/novel function ⇒ result of chromosomal translocation
Type of signalling
Local and Paracrine signalling
Discovery of Platelet Derived Growth Factor (PDGF)
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
Characteristic of PDGF
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
PDGF-A
Ubiquitous
High expression in muscle, pancreas and prostate
PDGF-B
Ubiquitous
high expression in placenta
PDGF-C
Ubiquitous
high expression in liver, kidney, pancreas and ovary
PDGF-D
More restricted none in brain, lung and muscle
Highest expression in heart, pancreas and ovary.
Biological activities of PDGF
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
PDGF & sis (Inappropriate expression)
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.
Discovery of Epidermal growth factor (EGF) super family
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
