case 4 - bowel cancer Flashcards
1
Q
what is the majority of CRCs
A
sporadic
2
Q
what percentage of bowel cancers are FAP
A
1%
3
Q
what surface of the colon do the polyps line
A
the lumen surface of the colon
4
Q
what is HNPCC
A
hereditary non-polyposis colon cancer
5
Q
what is HNPCC
A
hereditary non-polyposis colon cancer
6
Q
what percentage of CRCs are HNPCCs
A
2-3%
7
Q
what is Lynch Syndrome
A
when you are predisposed to other cancers
8
Q
what do these other cancers include
A
ovary, small intestine, urinary tract, skin and brain cancer
9
Q
what is the difference between FAP and HNPCC
A
there are very few polyps in HNPCC but the progression is fast, 2-3 years instead of the 8-10 years in FAP
10
Q
what are FAP and HNPCC
A
both familial forms of cancer
11
Q
what are the hallmarks of cancer
A
evading apoptosis
self sufficiency in growth signals
insensitvity to anti growth signals
sustained angiogenesis
tissue invasion and metastasis
avoiding immune destruction
genomic instability
12
Q
what is the implication gene type for oncogenesis and TSG
A
diploid
13
Q
is is stage G1 in the cell cycle
A
cell is born and each chromosome is a single chromatid
14
Q
what is the S phase of the cell cylce
A
synthesis - DNA replication (replicate the chromosomes)
15
Q
what happens when the S phase is over
A
each chromosome is represented by two sister chromatids
16
Q
what happens after S phase
A
G2
17
Q
what happens after G2
A
mitosis
18
Q
what happens during mitosis
A
division: chromatids get pulled apart in opposite directions, mean that each new cell inherits one copy of each chromosome in them. once they go back to G1, each cell yet again is represented by one chrmoatid
19
Q
what are the steps from gene to tissue
A
- genome
- transcriptome
- proteome - via process of translation
- cell function - biogenesis and metabolism
- tissue architecture - proliferation
20
Q
what happens if there is mutations in these genes
A
we have changes and this affects cell function and proliferation
21
Q
what turns into malignancy
A
hyperplasia
22
Q
what are most tumours made up fo
A
lots of different clones - tumour heterogeneity
23
Q
what does multi step tumorgenesis involve
A
clonal expansion
24
Q
what are oncogenes encoded by
A
viruses that can cause cancer e.g SV40 virus
25
what happens when viral genes are introduced into cells
they have a dominant transformative effect e.g Src, Ras, Myc
26
what is the case of oncogenes
it is sufficient to only have one copy of a mutated gene to cause cancer
27
what are examples of single activating mutations
B catenin and KRAS
28
what are tumour suppressor genes linked with
retinoblastoma and Knudson's two hit hypothesis
29
what is retinoblastoma
a type of cancer that affects children and either comes in a familial or sporadic form
30
what did Knudson notice
that individuals with familial disease had eye tumours bilaterally and were more likely to have other tumours
31
what is retinoblastoma caused by
a mutation on gene 13 (Rb)
32
what happens with indiviudals with familial retinoblastoma
all inherent one mutant copy of this gene
This mutation is recessive but if one cell requires a second copy, Rb function is lost and this not only predisposes them to bilateral eye cancer, but to other cancers as well
33
what type of gene is Rb
a tumour supressor gene
34
what has to happen in sporadic Rb disease
you must first pick up a mutant Rb allelle and then you need a second mutant copy- much more rare event and wont get other cacers
35
what is the basis of Knudson's theory
in familial disease, only one random hit is required but in sporadic disease, two hits are required
36
what do the signalling pathways include;
1. ligands
2. receptors
3. signalling cascade
4. transcription factors
5. alters cellular function and gene expression
37
what are the different types of cell biological processes
growth factor receptors and hormone receptors
Receptor tyrosine kinase
G-protein coupled receptors
Phosphatase
GTpase switches e.g Ras
Cytoplasmic -nucelar shuttling
Serine/threonine phosphorylation cascades
All the elements of transcriptional control
Micro RNAs
Translational control
Sumolyation
(Don’t need to know just be aware)
38
what is RAS
a switch
39
what does ras bind to
GTP
40
what does RAS do to GTP
Ras has GTPase activity, it can hydrolyse GTP
41
what does it hydrolyse GTP to
GDP
42
what does this release
an organic phosphate
43
what happens when ras is bound to GTP
it adopts an active conformation and stimulates downstream pathways
44
what does ras's own GTPase activity turn it into
GDP/RAS complex which is inactive
the GDP is then exchanged for a fresh molecule of GTP
45
what happens when these downstream RAS pathways are active
leads to stimulation of cell proliferation and protein synthesis
46
what happens if there is a single mutation in RASS
locks it in the active form which means these downstream signals continually on, even in the absence of upstream signals. so when RAS is locked on, proliferation is stimulation
47
how many copies of Ras need to be mutated
only one copy of the RAS gene
48
what is Wnt
a secreted factor that promotes proliferation by binding to its receptor
49
what is the Wnt complex made up of
active GSK-3 beta, APC, beta catennin
50
what happens when this Wnt complex is activated
GSK3 beta phosphorylates beta catenin and leads to degradation.
51
what happens when Wnt is bound to this complex
it disrupts this complex, now GSK-3 beta is iz inactive and beta catenin doesnt get degraded and beta catenin builds up in the cell
moves into the nucleus and drive the processes for cell proliferation
52
what is beta catenin
an oncogene
53
what is APC
a tumour supressor gene
54
what are the target genes
cyclin D and myc
55
when is entry into the cell cycle regulated
G1
56
what happens during this period
cells are responsive to mitogenic GFs and to TGF beta
57
what happens once it passes the R point in G1
it is now committed to compete the entire process of the cell cycle
58
what happens if you withdraw stimulatory processes beyond R
the cell cycle will still complete
59
what do CDK4 and 6 bind to
cyclin D
60
what does this complex activate
the cell to drive it through G1
61
what is the CDK2 complex bound to
cyclin E
62
what does CDK2/cyclin E complex trigger
entry into the S phase
63
what does CDK2 also bind to
cyclin A
64
what does this complex do
drives the cell through the S phase
65
what does CDK1 bind to
cyclin B
66
what does this CDK1 cyclin B complex drive
cell into mitosis
67
what happens to the levels of cyclin and the levels of CDK
the levels of cyclin moves up and down but the CDK levels stay relatively the same
68
what is the rise and fall of cyclin crucial to
the regulation of the cell cycle
69
what inhibits the cyclin-CDK complex
CKIs
70
what blocks the activity of multiple CDKs
p21
71
what do growth factors signal
RAS, which along with Wnt signals, signals beta catenin
72
what does RAS signal
fos/jun
73
what does the beta-catenin signal
tcf/lef
74
what do both ras and wnt signal
signal cyclin d1
75
what happens once cyclin D is synthesised
it binds to CDK4, which forms an active protein kinase complex
76
what can this active protein kinase complex phosphorylate
a protein called Rb
77
what happens when rb gets phosphorylated
it lets go of its binding partner E2F
78
what is E2F and what happens once it is liberated
it is a transcription factor and once liberated, it can go onto stimulate the expression of genes like the cyclin E gene
79
what does this expression of cyclin E lead to
the cyclin E- CDK2 complex
80
what can this complex go on to do
phosphorylate Rb which leads to positive feedback cycle
81
what can this cyclin E -CDK2 complex also do
phosphorylates origins of replication to trigger S phase
82
what is Rb in the cell cycle
a break, and if you remove this break then you have uncontrolled replication in the cell cycle (tumour supressor)
83
what happens once the second copy of Rb is hit
the break is lost
84
what is the most important cell cycle checkpoint
p53
85
what is p53
a transcription factor
it is normally degraded
86
what is p53 activated by
'stabilisation'
87
what are the ligases
kinases and ubiquitin ligases
88
what happens once p53 is activated and stabilised
it can lead to
- cell cycle arrest
- DNA repair
- block of angiogenesis
- apoptosis
OR
- senescence
- return to proliferation
89
what is a very important target of p53
the p21 gene which is a cyclin dependent kinase inhibitor which can block the activity of multiple CDKs
90
what does p21 do
puts a block on the cell cycle, giving it enough time to repair and then the cell cycle continues
91
what happens if the damage is too bad to be repaired
p53 leads to apoptosis, and stimulates the expression of Bax etc, which induces cell death
92
what is the guardian of the genome
p53
93
what is the genome being continuously damaged by
xoxidation
Replication errors
UV
X-rays
Chemicals
Mitosis
94
what continuously repairs the genome
BER
NER
Proof reading
NHEJ
HR
Checkpoints
95
what is the very important repair mechanism on the context of colon repair
the mismatch repair and HNPCC
96
how many cases of bowel cancer are there a year
40,000
97
what percentage of people will be alive after their initial diagnosis ten years on
57%
98
what is the abnormal cell growths:
Hyper proliferation
Adenomatous polyps (small)
Adenomatous polyps (large)
Severe dysplasia (precancerous polyp)
Adenocarcinoma - malignant
Invasive cancer - malignant
99
what are the colonic crypts
invaginations where the epithelial sheet has folded back upon itself multiple times
there is an intricate substructure to this structure
100
what kind of cells are there between the Paneth cells in these crypts
rapidly dividing stem cells
101
what do these stem cells produce
produce two daughter cells one stays behind to maintain the stem cell compartment and the other migrates up and out and eventually is shed off at the top of the lumen
102
what is the most important feature of the tissue
it is highly proliferative, and maintained by balancing loss at the top with growth at the bottom
103
what protein do all these stem cells express at the base of the crypts
Lgr5+
104
what is the gene that is responsible for FAP
5q21
105
what does APC stand for
adenomatous polyposis coli and this is the name of 5q21
106
in what percentage of sporadic CRCs is APC mutated in
80-90%
107
what type of gene is APC
tumour suppressor gene
108
what happens to individuals with the disease
they inherit one mutated copy and then the second allele undergoes LOH,
108
what happens to individuals with the disease
they inherit one mutated copy and then the second allele undergoes LOH, APC protein function is lost and tumour suppressor function is lost and then will lead to cancer
109
what happens when Wnt is not bound to its receptor
the APC complex is attacked and beta catenin is targeted for degradation
110
what happens when Wnt signals bind to their receptors
beta-catenin no longer gets phosphorylated and no longer gets degraded, it moves into the nucleus and up regulates cyclin D - proliferation
111
what cells secrete the Wnt signals
the surrounding stromal cells
112
what do the Wnt signals engage with
the stem cells
113
when is proliferation stimulated
when beta catenin is switched on
114
what happens when beta catenin is switched on
the cells then migrate up and out of the crypt and because they are still in close proximity to the Wnt signals they keep on proliferating
115
what happens when they are too far up and far away from the Wnt signals
beta catenin is switched off and gets degraded. the cells stop dividing and disappear out of the top
116
what happens once the cell loses APC function
it is no longer reliant on Wnt signals for proliferation.
117
what does this mean
it means that as it migrates up, it can still proliferate, even in the absence of the Wnt signals. so now the APC mutants move up beyond the zone of Wnt signalling, they just dont care
118
what stays on even if there are no Wnt signals and explain how the hyperproliferative zone comes to be
beta catenin - the cells dont differentiate, they keep on proliferating and they dont finish migrating, forming a hyperproliferative zone of cells when normally no division would take place
119
where do normal epithelial cells proliferate
only proliferate at the bottom when they are close to the secreted Wnt signals.
120
what is the difference to this in APC mutants
B-catenin is stabilised even in the absence of Wnt signals, cyclin D is synthesised, driving proliferation even when the cells have migrated beyond the normal proliferative zone
121
how many CRCs have beta catenin mutations
10-20%
122
what kind of mutation is a beta catenin mutation
single point mutation that stops it being phsophorylated - stops it being degraded.
123
what is an obligate step in colon cancer
deregulation of the Wnt pathway
124
where is the HNPCC gene found
found on chromosome 2p
125
what is the mismatch repair
error in newly made strand
binding of mismatch proofreading proteins
DNA scanning detects nick in new DNA strand
strand is removed
repair DNA synthesis
126
what is silenced by methylation in around 15% of sporadic CRCs
MLH1 promotor is silenced
127
what is the mutator phenotype of mismatch repair
mutation of MHL1 does not cause cancer.
but rather, by losing MSH2, or MLH1 function, the mutation rate goes up and that accelerates the accumulation in traditional tumour suppressor and oncogenes
128
what is mutated in about 90% of mismatch repair CRCs
the TGF beta receptor is mutated
129
what can we see when we sequence genes
whole genome - CNV
Exome - mutations
Promoter methylation
RNA - global gene expression profiling
Proteomics (protein level) - net effect of how mutations and changes in gene expression manifest
130
what are the hyper mutated colon cancers
the mismatch repair colon cancers
80% dont have mismatch repair defectd
131
what do the hyper mutated tend to be
diploid i.e the CNV is low
132
what do the non hypermutated tend to exhibit
CIN and therefore are aneuploid i.e the CNV is high
133
what are the specific mutations
APC, p53, and K-ras
134
what is the novel b catenin mutation
29 cases
deletions
spanning exon 3
135
what is the novel APC mutations
35 cases
upstream of exon 9
slicing defect
protein truncation
136
where are mutant proteins expressed
on the cell surface
137
what are these mutant proteins recognised by
T cells
138
what do tumour cells also express
PD-L1 which suppresses T cells
139
what can antibodies do
block the PD-1 interaction
140
what does this reuslt in
some cancers will benefit greatly from antibody therapies and given immune checkpoint inhibitors to resolve this inteaction
141
what is the antibody which blocks PD1
Pembrolizumbab
142
what are the 3 mutation subtypes
POLE ultra mutated <1%
MSI - hyper mutated due to micro satellite instability - 9% (mis match repair defect)
MSS - micro satellite stable - 90% (but high CNV due to CIN)
143
what kind of target is the Wnt pathway
an obligate and early target, either via APC or beta catenin
144
what tumours are prioritised for immune checkpoint therapy
MSI tumours
145
what are liquid biopsies
tumours shed cells and DNA into the blood
Minimally invasive and relative inexpensive biopsy
Advances in detection technology e.g NGS, mass spec
146
what are the benefits of liquid biopsies
early detection
Predictive biomarkers
Monitor response to therapy
