Transcript the story of APC

The story of APC and
the Wnt pathway
The story of APC and
the Wnt pathway
Signal Transduction Pathways
Important for development and homeostasis.
All involved in Cancer.
RTK
Wnt
TGF-β
Hedgehog
Notch
2007 Estimated US Cancer Deaths*
Lung & bronchus
31%
Men
Women
289,550 270,100
26%
Lung & bronchus
Prostate
9%
15%
Breast
Colon & rectum
9%
10%
Colon & rectum
Pancreas
6%
6%
Pancreas
Leukemia
4%
6%
Ovary
Liver & intrahepatic
bile duct
4%
4%
Leukemia
3%
Esophagus
4%
Non-Hodgkin
lymphoma
Urinary bladder
3%
3%
Uterine corpus
Non-Hodgkin
lymphoma
3%
2%
Brain/ONS
2%
Kidney
3%
Liver & intrahepatic
bile duct
23%
All other sites
All other sites
24%
ONS=Other nervous system.
Source: American Cancer Society, 2007.
Colon cancer is the second
leading cause of cancer deaths
in the U.S.
(> 50,000 deaths per year)
150,000 cases diagnosed per year
(i.e., your chances are 1/18)
Colorectal cancer
Early detection is the key
>90% 5 year survival with early detection
60% if it has spread locally
<10% if it has metastasized
Polyps, the first stage
In tumor development
Data from ACS
Figure 2.15a The Biology of Cancer (© Garland Science 2007)
Colorectal cancer treatment
1. Surgical removal of tumor
2. This can be followed by either
Radiation or chemotherapy (fluorouracil)
3. Chemotherapy also used to
slow the progress of metastatic disease
Data from ACS
Colon cancer genetics
95% of cases sporadic (no genetic history)
HNPCC 3% of all cases.
Defects in mismatch repair.
Familial adenomatous polyposis (FAP)
1% of all colon cancers
Familial Adenomatous Polyposis (FAP)
300-1000 polyps by age 30
http://www.clevelandclinic.org/reg
istries/inherited/fap.htm
Figure 7.22 The Biology of Cancer (© Garland Science 2007)
Inheriting FAP-related mutations dramatically increases
your risk of developing colorectal cancer.
93% colorectal cancers by age 50
100% colorectal cancers lifetime risk
0.2% colorectal cancers by age 50
6% colorectal cancers lifetime risk
Until recently the only treatment
was to surgically remove the colon
Treatment with an aspirin-like drug
called celecoxib (a COX2 inhibitor)
led to a 25% reduction in polyp number ,
and the remaining polyps shrank.
The hope is this will allow doctors to
delay surgery till later in life
Steinbach et al.
New England Journal of Medicine 342, 1946 (2000)
Figure 7.23 The Biology of Cancer (© Garland Science 2007)
Adenomatous Polyposis Coli (APC)
Not to be confused with:
APC (anaphase-promoting complex)
APC (antigen-presenting cell)
nor with:
Armoured Personnel Carrier
The American Pie Council (APC)
committed to preserving America's
pie heritage
We have positioned and cloned a gene
What is the next step?
looks like……..
NOTHING!!
mutated in FAP
and in 70% of sporadic
cases of colon cancer
dominant inheritance
but cancer involves two
mutated copied
tumor suppressor
gene
APC mutations are
the earliest event
in the development
of the tumor
Tell me who are your friends and I will tell you who you are.
If we don’t know what APC is doing, let’s find binding partners
APC
cell extract
First, immunoprecipitation
Thermo Scientific
co-immunoprecipitation
Thermo Scientific
Fishing with APC
Colon cancer
WT
cell line
?
first,
immunoprecipitation
APC
Fishing with APC
Colon cancer
WT cell line
co-immunoprecipitation
p95= -catenin
What is -catenin?
Drosophila is a segmented animal.
The different parts and organs in the body are derived from a
total of 14 embryonic segments.
Each segment is composed of rows of cells.
Each segment is polarized in the anterior-posterior axis.
The cuticle in each segment
has a hairy anterior part and
a naked posterior part.
In other words, cells from
the different halves of the
segment have different
fates.
Genetics is the Key Tool for Understanding Drosophila
Development
Christiane NussleinVolhard
Nobel prize in
physiology and
medicine 1995
Eric Wieschaus
The wild-type body
is segmented
and each segment
has a unique identity
and thus produces
distinctive structures
The Heidelberg screen
2 young scientists
1 microscope
1 year
26,978 flies
139 new genes
Wieschaus and NüssleinVolhard removed single
genes (random
mutagenesis) and looked
for effects on the body plan
In some of the mutants: no naked cuticle
wild type
mutant
The name of the mutant: armadillo
armadillo was cloned
armadillo = -catenin
1. adherens junctions (wait till Thursday..)
2. cytoplasmic/nuclear
Dr. Mark Peifer
-catenin and TCF form a bipartite transcription factor
armadillo is not the only mutant without a naked cuticle
wild type
arm
(and others)
-catenin and TCF form a bipartite transcription factor
-catenin is phosphorylated by GSK-3 for degradation
In the absence of APC,
levels of Armadillo/  -catenin rise dramatically
wild-type
APC mutant
Rosin-Arbesfeld, Nature 00
McCartney, Dev 06
APC is a complex protein
bind to Armadillo
15 AA
rpts
20 AA
rpts
Mutation
Cluster
Region
bind to Axin
armadillo is not the only mutant without a naked cuticle
wild type
arm
(or wingless)
Signal Transduction Pathways
Important for development and homeostasis.
RTK
Wnt (wingless)
TGF-β
Hedgehog
Notch
Wingless/Wnt regulates Armadillo/  catenin stability and promotes specific
cell fates.
Back to Colon Cancer
A quick look at colon architecture
differentiated villus
cells
As cells migrate
away from the
crypt, they
differentiate.
proliferating
cells
Wnt
crypt
The genes turned on by Wnt signaling
are expressed in crypts
and those that are turned off are
expressed in villi
Gene turned ON by Wnt
Hans Clevers
Gene turned OFF by Wnt
The effect on p21 expression is indirectly mediated by
the transcription factor c-myc.
Transcription of the myc gene is directly regulated
By TCF/beta-catenin.
As cells migrate
away from the
crypt, they
differentiate.
Let’s put this together
to form a picture of normal colon biology
and how it is perturbed by APC mutations
loss of function
As cells migrate
away from the
crypt, they
differentiate.
Stromal cells send Wnt signals.