Download Mech133-RvwMolecBasisNeoplasia

Mod #132
Thurs., 05/22/03, 2pm
Dr. Eisenberg
Scott Emerson
Page 1 of 7
Molecular Basis of Cancer (Part 1)
I.
Molecular Basis of Cancer
A. Cancer is cell growth that does not respond to normal regulation
~uncontrolled cell growth
B. Cancer usually arise through a somatic mutation (inherited germline
mutations) leading to change from a protooncogene to oncogene
~tumor suppressor Rb example of inheriting 1 KO (knock out) and then
getting a somatic mutation later on to give the phenotypic appearance of
retinoblastoma
~many tumor suppressor gene dysfunctions inherit one mutation and then
over the course of life may receive a second hit affecting the normal gene
~cancer ususally arrises due to a somatic mutation leading to an
activation/modification of a normal cellular gene and becomes an oncogene
(a gene that can become neoplastic)
C. Protooncogene: the normal cellular gene from which oncogenes are derived
D. Oncogene: any gene that encodes a protein able to malignantly transform cells
E. Nonlethal genetic damage lies at the heart of carcinogenesis
~not enough to kill cell but enough damage to change it to cause
uncontrolled growth
F. Mutations can be caused by:
1. Physical agents (ie. Radiation/UV)
2. Chemical agents (ie. Environmental carcinogens)
3. Biological Agents (ie. Viruses)
4. Basically causing DNA damage that will result in repair and be
reinstituted back into the cycle
5. or….if the damage is not repaired and affects genes of growth
promotion, control of apoptosis, or genes that are cancer suppressor
genes; if affect these can get ulteration/loss that can lead to malignancy
6. Check out Fig. 8-24 on pg 278
II.
Role of Protooncogenes in Cell Growth and Differentiation
A. Protooncogenes are normal cellular genes which code for normal cellular
functions
B. They are typically involved in cellular growth and differentiation
C. Genes play critical roles in one of these two processes
III.
General Concepts
A. Genetic DZ
1. Multifactoral
2. Genetically heterogeneous
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3. Stepwise/sequential process leading to transformation
4. Some of these genes are domanint/some recessive and depends which
class of protooncogenes talking about
B. Transformed or “cancer” phenotype
1. Loss of normal cell-cell interactions (loss of cell-cell inhibition:
uncontrolled proliferation)
2. Loss of normal cell cycle regulation
3. Normally cell replicates a finite # of times before arresting
IV.
Characteristics of Tumor Cells
A. Inappropriately regulated growth producing tumors
1. Benign: localized (ie. Warts)
2. Malignant: capable of spreading, invading, and metastasizing
B. Growth: transformed cell have loss of contact inhibition
C. Aneuploid: abnormal and unstable # of chromosomes, chromo abnormalities
(ie. Translocations and amplifications)
1. aneuploidy is anything outside the normal haploid 23/diploid 46
2. creates instability
3. Burkitt’s lymphoma has translocation (c-myc)
4. Chronic mylogenous leukemia has translocation (c-abl)
5. Amplification (n-myc)
D. Release of transforming growth factors
E. Secrete proteases that digest collagen and other “basal laminaprotiens”
involved in contact inhibition
F. New and altered cell surface protiens
~ie. Receptors that turn on cell without normal ligand
G. Altered gene transcription (ie. Oncogens)
V.
First ID of Oncogenes in Retroviruses
~v-onc: similar between v-onc and normal protooncogene in particular cell
~transformation based on particular insertion into chromosome and then activate
~infections can cause transformation of infected cell
A. Actue Transforming
~has a v-onc into cell causing transformation
~has viral oncogene that is being inserted into cell ultimately leading to
transformation
B. Slow Transforming
~slow due to location importance
~do not have oncogene but due to insertion of virus next to important
cellular oncogene and takes over its expression ultimately resulting in
transformation
~now normal is under the regulation of the elements within the retrovirus
VI.
Do Non-viral Tumors Contain Oncogenic DNA Sequences
A. Yes
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B. The answer was provided by experiments involving DNA-mediated gene
transfer (DNA transfection)
C. Many of these transforming sequences have turned out to be homologous to
the ras protooncogene
VII.
ID of Oncogenes in Humans
~DNA mediated gene transfer:
~Cultured tumor cells isolate DNA transfect into NIH/3T3 murine cells 
DNA taken up by cells leads to transformation of some ID foci within
mouse of human oncogens
VIII. Base Substitution
A. Point Mutation
B. EX: ras alleles from transfected human tumor DNA
C. Three amino acid postions involved in activation
D. Basically, have “hot spots” within the ras gene that are more suseptible than
other areas and can ultimately lead to transformation/neoplastic growth
IX.
Levels of Control of Cell Growth
A. Many levels
B. Overall:
~A Growth Factor binds with its Receptor signal transduction to nucleus
transcrition factors activated DNA replication
C. Therefore, you have different levels at which oncogenes/mutations can affect
the signal
D. Growth Factors: sis/PDGF
E. Growth Factor Receptor: erbB/EGFR
F. Intracellular Receptor: erbA/thyroid hormone receptor
G. Intracellular transducer: rel/ser-thr kinase
H. Transcription Factor: fos-jun/AP-1
I. DNA repair: p53/repair activated transcription activator
J. Anti-apoptotic Factor: bcl-2/mitochondrial membrane protein
X.
Nature of Oncogenic Protein
A. Altered protein (ie.n-myc due to amplification and bcl-2 with prolonged cell
life
B. Altered expression of a normal protein
XI.
Role of Protooncogenes in Cell Growth and Differentiation
A. One of several mech. Can convert these protooncogenes to tumorigenic
oncogenes:
1. Mutation
2. Translocation
3. Over expression
4. Inappropriate expression during cell cycle
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5. Should know examples of each of these
XII.
Four Major Classes of Protooncogenes have been ID:
A. Growth promoting protooncogenes
B. Growth-inhibiting cancer suppressor genes (anti-oncogenes)
C. Genes that regulate programmed cell death (apoptosis)
D. Genes that regulate DNA repair
XIII. Protein Products of Oncogenes
A. the binding of a growth factor to its specific receptor on the cell membrane
B. TRANSIENT and LIMITED activation of the growth factor receptor
activates several signal transducing proteins on the inner leaflet of the plasma
membrane
C. Transmission of the transduced signal across the cytosol to the nucleus via 2nd
messangers
D. Induction and activation of nuclear regulatory factors that initiate DNA
transcription
E. Entry and progression of the cell into the cell cycle, resulting ultimately in
division
F. FYI-1: only on for a limited time and effects are only on for a limited time
G. FYI-2: if receptor (R) doesn’t need ligand then constitutively active (no longer
transient)
H. FYI-3: if any control is lost then have chance of transformation
I. FYI-4: if factors that control the cell cycle (positive/negative) are lost then can
disrupt and cause increased cell division
XIV. Growth Factors
~external signal that binds to R
~produced within the cell and if constitutively turned on then always expressing;
cells will automatically keep producing the factor and dividing
~if always expressing factors (meaning way too much) then get constitutive
activaiton (redundant)
XV.
Growth Factor R
A. Too many Rs
B. Irreversible binding to ligand
C. Aberrant activation without ligand
~these can lead to continuous activation and transforming phenotype
XVI. Signal-Transducing Proteins
~inappropriate stimulation due to mutant signal transducer protein produced
(activated even after growth factor has been released)
~ras
~normally transient
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XVII. Nuclear Transcription Proteins
~over production of transcription factor can enter nucleus and bind to DNA
resulting in stimulation of cell growth by activation of transcription
XVIII. Genetic Lesions and Cell Cycle Regulation
A. Factors which normally PROMOTE cell cycle progression
1. Oncogenes
2. Activation produces cell growth
B. Factors which normally SLOW cell cycle
1. Tumor suppressors
2. Inactivation induces cell growth
XIX. Cyclins and CDKs
~Fig. 8-27 pg 284
~Know Rb and its relation to G1 to S (phosph of Rb = G1→S transition)
XX.
Apoptosis
~know what causes it and what blocks it (bcl-2)
~bcl-2 can block cell death due to over production and lead to inappropriate
longevity of cell
XXI. Localization and Function of Proto-oncogense
~be familiar with where oncogenes are
~ras is involved in signal transduction and resides within the inner cell membrane
and signal activates other process that give rise to DNA transciption
XXII. Selected Oncogens
~KNOW the tables present in PPs (except hst-1)
~sis: platelet derived growth factor
~bcr-1/2: familial breast cancer
~erb-B2: breast carcinoma
~similar to table 8-7 on pg 279
XXIII. Mechanism of Activation of Cellular Protooncogenes
A. 2 broad categories of change that can occur which result in the transformation
of the protooncogene into neoplastic oncogenes
1. Changes in the structure of the gene, resulting in the synthesis of an
abnormal gene product having an aberrant function
2. Changes in the regulation of gene expression, resulting in enhanced or
inappropriate production of normal growth-promoting protein (wrong
time, overexpression, continuous expression….)
XXIV. Activation of ras Protooncogene by mutation (prototype)
A. ras is a signal transducer
B. activation of R stimulates ras (binds GTP)
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C. normally ras-GTP is hydrolyzed by intrinsic GTPase activity (back to rasGDP/inactive form)
D. NF-1/GAP enhances this GTPase activity
E. When have a dominant mutation in ras you lose this GTPase activity and GTP
remains bound (loss of GAP stimulation/activation of normal GTPase to
hydrolyze GTP)
F. Therefore you have a continuously activated ras which leads to increased
cytoplasmic kinase activity and DNA synthesis
G. Cause of neurofibromatosis-1 (b/c lose the NF-1’s ability to turn off ras)
H. Mutations can take place within the ras protein or in GAP
XXV. Activation by Translocation
A. Burkitt’s Lymphoma is a translocation of the myc gene of C8 to the Ig heavy
chain control region on C14
~Myc oncogene now under the control of the heavy chain regulation and
thus have inappropriate activation/expression of myc protein
B. Chronic Mylogenous Leukemia (CML) is a translocation of the abl oncogene
on C9 to the bcr (breakpoint cluster region) on C22
~This actually creates a fusion gene (Philadelphia Chromosome): abl-bcr
~Because of this you will get increased tyrosine kinase activity
XXVI. PH1 Translocation at the Molecular Level
A. Creates of chimeric fusion protein (with altered activity) due to translocation
B. Abl of C9 inserts itself within a breakpoint of bcr on C22 making the fusion
Philadelphia Chromosome (abl-bcr)
C. Number of different exons within the bcr that breakage can occur
D. Varying expression depending on where the able inserts
~within CML have 2 phases: 1)Chronic 2)Blast…..
~amount of time someone stays within the chronic phase is associated
where within the bcr the breakage occurs
~if occurs more 3’ then people move into the blast phase quicker
XXVII. Oncogenes Activated by Translocation
A. CML: t(9;22)
~c-able/bcr oncogene
B. Burkitt’s Lymphoma: t(8;14)
~c-myc oncogene
C. B cell Lymphoma: t(14;18)
~bcl-2 oncogene
~increases the life-span of B cells which increases mutation probability
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XXVIII. Amplification of the N-myc in Neuroblastoma
A. Increased amplification of n-myc
B. Changes banding pattern (don’t see bands within the amplification; called the
HSR: homogenous staining region)
C. Double Minutes: little clusters of amplified n-myc genes
D. Associated with neuroblastoma
“It begins to appear that everything one does to gain a livelihood or for pleasure is
fattening, immoral, illegal, or, even worse, oncogenic” -Robbins
Fade to black….