7 - Growth Factors, Oncogenes, and Cancer Flashcards
1
Q
What decisions do cells make in the cell cycle?
A
Whether to proceed to S phase, wait at G1 phase, or stop at G0 phase
2
Q
What helps determine the decision in the cell cycle?
A
Cell signaling
3
Q
What was used to study how cell signaling was involved in the cell cycle?
A
By studying unregulated cell signaling and cell growth (cancer)
4
Q
What are some properties of malignant cells?
A
Not responsive to influences that normally cause cells to stop growth and division
5
Q
What conditions will cause normal cells to stop growing?
A
Lack of growth factors, and when cells touch neighboring cells
6
Q
What is contact inhibition?
A
Stopping of cell growth when it touches other cells
7
Q
What do normal cells look like in a dish?
A
Thin monolayer
8
Q
What do malignant cells look like in a dish?
A
Clumps (foci)
9
Q
What is the phenotype of normal fibroblasts?
A
Flat, many extensions, contact inhibition
10
Q
What is the phenotype of malignant fibroblasts?
A
Rounded, few extensions, no contact inhibition
11
Q
What is tumorigenesis?
A
The development of a malignant tumor
12
Q
How does cancer start?
A
Uncontrolled proliferation of a single cell
13
Q
How does tumorigenesis occur?
A
Through a cumulative progression of genetic alterations
14
Q
What happens to cells as they progress through tumorigenesis?
A
Cells become less responsive to growth regulation, and better able to invade normal tissues
15
Q
What is the first step of tumorigenesis?
A
Formation of a benign tumor
16
Q
What is a benign tumor?
A
A tumor composed of cells that proliferate uncontrollably but cannot metastasize
17
Q
What does it mean to metastasize?
A
Leave ECM to go to the bloodstream (spread)
18
Q
What are the genes involved in carcinogenesis responsible for?
A
Cell cycle regulation, cell adhesion, and DNA repair
19
Q
Why is the sequence of when genes mutate important in cancer?
A
Sequence influences how the cancer develops
20
Q
What did Peyton Rous do?
A
Isolated the first tumor-causing animal virus
21
Q
True or false: Peyton Rous received the Nobel Prize shortly after his discovery of Rous sarcoma virus
A
False: it took nearly 50 years after his discover in 1911 to receive the Nobel Prize in 1966
22
Q
What happened in the 1960s that helped in studying cancer?
A
Molecular biology was being used to understand how viruses contain genetic material, which could be used to infect mammalian cells
23
Q
What led to the identification of many cancer causing genes in humans?
A
Investigations of abnormal cell growth due to viral infection
24
Q
What did Baltimore, Dulbecco, and Temin discover about viruses?
A
They have RNA (not DNA) as genetic material, and had reverse transcriptase (RNA -> DNA)
25
What did Varmus and Bishop do?
Discovered the first oncogene, src
26
What is an oncogene?
A gene that creates oncology (cancer)
27
How was it proven that src caused tumors?
Adding vsrc led to a tumor, and removing vsrc stopped tumor growth
28
True or false: normal cells also contain src
True: c-src is a proto-oncogene
29
What is a proto-oncogene?
A gene that could become an oncogene when mutated
30
What is the origin of oncogenes in viruses?
Viruses take this DNA information from hosts
31
What did Erikson, Sefton, and Hunter do?
Study what src did
32
How was the function of src discovered?
Used radioactive ATP, and a 2D gel to find the difference between v-src lines and normal cell lines
33
What was different in the v-src 2D gel compared to the normal 2D gel?
Only tyrosine was phosphorylated by src
34
What was the conclusion of the 2D gels of v-src and normal cell lines?
Src was a tyrosine kinase
35
What is the function of src?
Tyrosine kinase
36
How much more active is v-src compared to c-src?
3x more
37
What was the significance of finding the function of src?
First evidence that protein kinases may play a role in cell growth
38
What cell signaling pathways are regulated by proto-oncogenes and tumor suppressor genes?
Apoptosis, proliferation, immortalization, and senescence
39
What is immortalization involved with?
The regulation of telomerase
40
What is senescence?
Cells are metabolically active but are non-dividing
41
What do proto-oncogenes do?
Promote cell survival / proliferation
42
What mutations occur with proto-oncogenes in cancer?
Gain of function mutations (unregulated cell growth / proliferation)
43
What do tumor suppressor genes do?
Inhibit cell survival or proliferation
44
What mutations occur with tumor suppressor genes in cancer?
Loss of function mutations (allow unregulated cell growth / proliferation)
45
What do caretaker genes do?
Repair or prevent DNA damage
46
What mutations occur with caretaker genes in cancer?
Loss of function mutations (allow mutations to accumulate)
47
Why does cancer increase as you age?
More time to accumulate mutations
48
What is colon cancer a good example of?
Cancers can have very specific sequences of mutations to develop
49
What is the structure of c-src?
Kinase domain (binds to ATP), C-terminal SH2 domain, and N-terminal SH3 domain
50
What does SH2/SH3 stand for?
src homology 2/3 domains
51
How is c-src inhibited?
Autoinhibition. SH3 domain binds to proline rich sequence, inhibiting kinase domain, and Phospho-Y527 binds to SH2 domain to inhibit kinase domain
52
How does SH3 inhibit c-src?
Binds to proline rich sequences to inhibit kinase domain
53
How does SH2 inhibit c-src?
Binds to Phospho-Tyr527 to inhibit kinase domain
54
What happens when Tyr527 in c-src is phosphorylated?
Binds to SH2 domain, inhibiting c-src
55
What happens when Tyr527 in c-src loses a phosphate?
Releases SH2 and SH3, activating the kinase
56
What is the difference in protein structure between c-src and v-src?
No Y527
57
What is the difference in genes between c-src and v-src?
v-src is a C-terminal truncation mutation
58
Why is v-src always active?
It has no Y527 to bind to SH2 to inhibit the kinase domain. Thus, it is always active
59
What question was raised by studying how viruses caused cancer?
If viruses use genetics to cause cancers, can human genes do the same thing?
60
How can a proto-oncogene be mutated into an oncogene?
Through mutation in coding sequence, gene amplification, or chromosome rearrangement
61
How does a mutation in the coding sequence affect a proto-oncogene?
Produces hyperactive protein in a normal amount
62
How does a gene amplification affect a proto-oncogene?
Normal protein is overproduced
63
How does a chromosome rearrangement affect a proto-oncogene?
Can be either a hyperactive protein, or overproduced
64
How can a chromosome rearrangement create a hyperactive protein from an oncogene?
Nearby regulatory DNA sequence
65
How can a chromosome rearrangement create overproduced proteins from an oncogene?
Fusion to an actively transcribed gene
66
What did Robert Weinberg do?
Discover human cancer genes
67
What techniques did Robert Weinberg use?
Insert human oncogene into mouse fibroblasts
68
What was required to perform Weinberg's studies?
1980's technology to introduce DNA into cells
69
How does DNA transfection work?
Add smaller and smaller fragments of cancer DNA until the gene is cloned
70
What is a phage?
A virus that infects bacteria
71
How were phages used in Weinberg's studies?
Each phage had a segment of DNA to be injected into E. Coli
72
How come you only get a single gene at a time with DNA transfection?
It is an inefficient process, so only a small proportion of cells take up the cut DNA (and the right DNA)
73
How was the human DNA separated from mouse DNA in Weinberg's studies?
By using an Alu probe
74
What are Alu sequences?
Repetitive DNA sequences found in humans, and not mice
75
How were Alu sequences used in Weinberg's studies?
Used to probe the human oncogene from the mouse DNA
76
What protein did Weinberg discover?
Ras
77
What is ras?
A small monomeric G-protein
78
What does ras do?
Activate downstream responses when bound to GTP, inactive when bound to GDP
79
What is the difference between ras and other G-proteins, such as Gs?
Ras is monomeric, and Gs is trimeric
80
What is the significance of ras in cancer?
Ras is mutated in many cancers
81
What is needed for ras to properly function?
GEFs and GAPs
82
What are the GEFs for trimeric G-proteins?
The receptors themselves
83
What does an inhibitory ras mutation do?
Can't bind to GEF to exchange GDP for GTP, thus staying inactive
84
What does an excitatory ras mutation do?
Blocks ability of GAP / ras to hydrolyze GTP into GDP, thus staying active
85
What are some downstream effectors of ras?
Raf, MEK/MAP kinases, etc.
86
Generally, what does ras signal for?
Proliferation (stimulate cell cycle)
87
What are the characteristics of ras oncoprotein?
Higher affinity for GTP, and lower GTPase activity (stuck in "on" position)
88
True or false: growth factor is needed for oncogenic ras to function
False: no growth factor is needed since ras is always on
89
What happens when src* is active or ras* is active?
Cells divide
90
What happens when src* is active and ras* is inhibited?
Cells do not divide
91
What happens when src* is inhibited and ras* is active?
Cells divide
92
What is the simplest relationship between src* and ras*?
src -> ras (downstream in a common signaling pathway)
93
What is the GEF for ras?
SOS
94
What is the GAP for ras?
RasGAP
95
What is the problem with src -> ras?
Normally, src is not the major upstream effector of ras
96
When does src -> ras?
When src is mutated to be constantly active (phosphorylate things it shouldn't)
97
What does src activate (when it is mutated)?
SOS (GEF for ras)
98
What did Stanley Cohen do?
Looked at growth factors to find upstream effectors of ras
99
What does EGF stand for?
Epidermal growth factor
100
What happens when EGF is added to a cell?
The cell will divide
101
What happens when EGF and anti-ras is added to a cell?
The cell will not divide
102
What is the conclusion of adding EGF and anti-ras to a cell?
EGF and ras must be in the same pathway (ras inhibition stopped growth factors)
103
What does EGFR stand for?
Epidermal growth factor receptor
104
What is EGFR?
A receptor tyrosine kinase that can autophosphorylate
105
How many membrane passes are in EGFR?
One transmembrane region
106
How does EGFR work?
Binding of a ligand causes dimerization, which activates receptors through autophosphorylation
107
What happens once a tyrosine kinase receptor is activated?
Phospho-tyrosines act as docking sites for other proteins to continue signal
108
What binds to activated EGFR?
SOS (and GRB2)
109
What does GRB2 do?
Coupled SOS to phospho-tyrosines on activated EGFR
110
True or false: receptor tyrosine kinases can only act in one pathway
False: the many phospho-tyrosines can act as docking sites for proteins in many pathways at once
111
True or false: multiple receptor tyrosine kinase pathways are independent
False: they can also converge
112
What gene encodes EGFR?
erb-B
113
What does erb-B do?
Encode for EGFR
114
What does v-erb-B look like?
Partial deletion
115
What does v-EGFR look like?
No extracellular ligand binding site
116
Why is v-EGFR always activated?
No extracellular domain leads to receptors being always dimerized, and thus activated
117
What does EGF activate?
EGFR
118
What are some oncogenes in the receptor tyrosine kinase / ras / MAP kinase cascade?
sis (PDGF, growth factor), erb-B (EGFR, receptor), ras (G-protein, and modulators), raf (MAPKKK, kinase), transcription factors (myc, fos, jun, ets)
119
What do many proto-oncogenes encode for?
Cell surface receptors
120
What mutation effects will lead to constitutive activation of receptor tyrosine kinases?
Ligand-independent dimerization, or overproduction
121
What is Her2?
A receptor tyrosine kinase
122
What is the difference in structure between c-Her2 and v-Her2?
c-Her2 has a val, while v-Her2 has a gln
123
What is the significance of the val-gln mutation in Her2?
Keeps receptors dimerized, and thus keeps signal on
124
What can be used to treat oncogenic receptors?
Monoclonal antibodies
125
What can receptor tyrosine kinases signal for?
Cell growth, cytoskeleton, anchorage-dependent growth, contact inhibition, metabolism, etc.
126
What is the first step of cancer?
Initiation (a mutation gives one cell an advantage)
127
What is the second step of cancer?
Promotion (a second mutation increases the advantage)
128
What is the third step of cancer?
Progression (chromosomal instability, invasive)
129
What does Gleevec do?
Binds to oncogenic kinase through competitive inhibition
130
What was the first discovered tumor suppressor gene?
Retinoblastoma
131
What does RB stand for?
Retinoblastoma
132
What is RB?
A tumor suppressor gene
133
What is sporadic RB?
Two separate mutations leading to loss of RB
134
What is familial RB?
One allele passed from parent, and another allele mutated, leading to loss of RB
135
How can a cancerous phenotype be suppressed (for RB)?
By adding wild-type RB
136
What strategies are being used to combat cancer?
Immunotherapy, targeting cancer proteins, angiogenesis
137
What is passive immunotherapy?
Uses patient's own antibodies to respond to tumor cells
138
What is active immunotherapy?
Uses patient's own immune system to target malignant cells
139
How does active immunotherapy work?
Have cells display tumor proteins to be marked by immune system
140
What is angiogenesis?
Formation of new blood vessels
141
Why do tumors need angiogenesis?
Constant division is metabolically costly (needs nutrients through vasculature)
142
What signal is used in angiogenesis?
VEGF
143
How does mutating RasGAP (structurally) interact with Ras?
Mutated RasGAP cannot bind to ras to increase its GTPase activity, thus keeping ras GTP-bound and always on
144
What do cancer drugs impact?
Any rapid growth
145
What is meant by "collateral damage" (for cancer drugs)?
Many cancer drugs have side effects that need to be taken into consideration
146
Why do adverse reactions arise from monoclonal antibody therapies?
Immune system is recruited, which can lead to many reactions
147
True or false: Gleevac works for all receptors that it is meant for
False: there can be changes in the receptor that make it resistant to Gleevac (desensitization)
148
Are oncogene mutations dominant or recessive?
Dominant
149
Why are oncogene mutations dominant?
One copy is enough to keep the signal turned on (only one copy is needed to be mutated for an effect)
150
Are tumor suppressor gene mutations dominant or recessive?
Recessive
151
Why are tumor suppressor gene mutations recessive?
One copy is enough to keep the signal turned off (need both copies mutated for an effect)
152
How can src activate SOS when overactive, and not under normal conditions?
Localization can be overcome with active mutations (overlapping and intersecting pathways)
153
True or false: monoclonal antibody therapy is constant
True: you need to keep having treatment to keep the cells under control
154
What environmental conditions often lead to cancer?
DNA damage (radiation, ultraviolet light, etc.)
155
True or false: cancer treatment is unprediactable
True: therapies are often very personalized
156
True or false: c-src is a major upstream affector of ras
False: it normally does not activate SOS
157
True or false: v-src is a major upstream affector of ras
True: v-src is always on, which makes it able to activate SOS
158
Why is it unlikely to reverse the mutation of c-src to v-src?
The truncation means that part of the gene is missing
159
How do cancer cells avoid treatment?
Rapid division with an unstable genome leads to many mutations
160
How does telomerase impact cancer cells?
Have just enough to maintain telomeres (not significantly longer) and maintain immortality
