Molecular and Cell
Biology of Tumors
Lucia Knopfová, PhD.
Prof. RNDr. Jana Šmardová, CSc.
Institute of Experimental Biology
Faculty of Science
MU Brno
Bi9910en
5. Cancer
predisposition genes II
Molecular and Cell
Biology of Tumors
1.  familial cancer syndromes
associated with increased risk
of various malignancies
including myelodysplasia
and acute myeloid
leukemia such as Li-Fraumeni
syndrome
2.  pediatric inherited bone
marrow failure syndromes
such as Fanconi anemia
3.  germline mutations conferring
a specific increased risk of
myelodysplastic syndrome and
acute myeloid leukemia
Hereditary leukemia
Colorectal carcinoma - CRC
Sporadic
Hereditary:
•  Non polyposis
Lynch syndrome
•  Polyposis
Familial adenomatous polyposis (FAP)
Peutz–Jeghers syndrome
Juvenile polyposis syndrome
Hyperplastic polyposis syndrome
Colorectal cancer
•  Only 5-10 % of CRC patients have apparent inherited genetic
predisposition for the cancer.
•  Significant impact of environmental factors, especially diet!
(high-fat, high processed meat, low-fibre).
Historical example: In Japan, there is a low incidence of
colorectal cancer, but high incidence of stomach cancer.
Japanese immigrants in USA (but not Brazil) had higher CRC
risk. Changes in incidence of other cancers too.
Familial adenomatous
polyposis - FAP
•  autosomal dominant inherited condition
•  FAP patients develop numerous adenomatous polyps mainly in
the epithelium of the large intestine. These polyps are benign, though
malignant transformation may occur. Average age of tumor diagnosis in
FAP patients is 40 years..
Polyps formed in FAP patients are histologically similar to sporadic
polyps and individual FAP polyps do not have increased risk of malignant
transformation compared to sporadic polyps. But their high numbers
means that in almost 100 % of FAP patients occur cancer foci.
Weinberg RA. The Biology of Cancer. Garland Science 2007
Familial adenomatous
polyposis
•  Increased risk of other cancers: thyroid, small intestine, stomach and
brain
•  Often „extra-intestinal“ symptoms, such as retinal defects, osteomas,
etc.
•  Usually associated with germinal mutation of tumor suppressor APC
(Adenomatosis Polyposis Coli)
Huge variability among FAP patients, subtypes described:
•  Gardner syndrome – autosomal dominant form of polyposis,
characterized by extra-colonic growths in soft tissues, osteomas,
dental anomalies, …
•  Attenuated FAP – residual APC activity, less polyps (10-100)
•  Turcot syndrome – characterized by combination of neuronal tumors
(glioblastomas, medulloblastomas) and colon tumors (not all cases
of Turcot syndrome is linked with APC mutations)
Formation of adenomatous
polyps in FAP
A. Normal intestinal epithelium:
stem cells, differentiated
cells in the villi
B. - C. Formation of polyps
(from the cells of
proliferative zone):
adenomatous tissue
D. - F. Microadenomas
G. Expansion of a
microadenoma into a
neighboring villus
Bienz M and Clevers H, Cell 103 (2000) 311-320
•  APC gene located at 5q21
•  During cancerogenesis both alleles of APC gene have to be
inactivated
(⇔ frequent „LOH“ 5q)
•  somatic mutations of APC are also key events in development of
sporadic CRC, detected in almost 80 % patients
•  High portion of mutations that lead to the truncated forms of
protein
•  Relation between type of mutation and clinical manifestation iof
disease (between genotype and phenotype)
Familial adenomatous
polyposis
APC and Wnt/β-catenin pathway
Ø  APC is a component
of a cytoplasmic
protein complex that
targets β-catenin for
destruction
Ø  Maintains low levels
of free β-catenin
unless Wnt triggers
mitogenic pathway
(target genes: cmyc,
CCND1)
Weinberg RA. The Biology of Cancer. Garland Science 2007
Structure of APC protein
Fodde R et al, Nat Rev Cancer 1 (2001) 55-66
APC mutations
•  Most APC mutations cause production of truncated proteins that lack
axin or β-catenin binding motifs
•  Germ-line mutations are scattered in 5‘ half of APC gene, somatic
mutations are clustered mainly between codons 1286 and 1513.
Weinberg RA. The Biology of Cancer. Garland Science 2007
Structure of APC and
mutation frequency
APC mutations
•  Both position and type of second-hit somatic mutation depend
on position of first germ-line mutation!
•  Concrete genotypes are selected during early phases of
cancerogenesis in order to secure „optimal“ levels of free β-catenin,
maximal levels are not desirable because of apoptosis induction!
⇒ Either germinal or somatic mutation preserve at least one specific
(2AA) sequence required for β-catenin down-regulation.
Interdepedence of germ-line
and somatic mutations of APC
Fodde R et al, Nat Rev Cancer 1 (2001) 55-66
Dual function of APC in cell: dual
role in CRC development
APC contributes both to the tumor initiation (conferring the
growth advantage via activation of Wnt-1/β-catenin pathway),
and tumor progression at the later phases via induction of
chromosomal instability.
APC is both „caretaker“ and „gatekeeper“.
Next stages of CRC development
Colorectal carcinomas represent a good model to
study cancerogenesis:
•  Relatively steady and predictable course from small
adenomas (up to 1 cm) to big adenomas and
malignant carcinomas
•  Projection of molecular changes into anatomical and
histological features of each stage
•  model of co-operation between tumor suppressors
and oncogenes
Next stages of CRC development –
activation of K-ras
•  Specific point mutations of
proto-oncogene K-ras or Nras
are present in 50 % of
colorectal adenomas bigger
than 1 cm and in 50 % of late
adenomas/carcinomas
•  Mutations of ras are very
rarely (up to 10 %) found in
smaller adenomas (< 1 cm)
⇒ Mutations of ras occur during
progression of adenomas
(transition between early and
intermediate adenomas)
Kinzler KW and Vogelstein B, Nature Rev Cancer 2 (2002) 673-680
Next stages of CRC development „LOH“
18q
•  Deletions of 18q found in
50 % of late adenomas
and 70 % of carcinomas
•  18q contains gene
SMAD4, alias DPC4
(deleted in pancreatic
cancer)
•  SMAD4 is a component of
TGF-β signaling
Kinzler KW and Vogelstein B, Nature Rev Cancer 2 (2002) 673-680
Next stages of CRC development –
inactivation of p53
•  Loss of 17p („LOH“) is
observed in 75 % of
colorectal carcinomas
•  Loss of 17p rarely detected
in adenomas
⇒ Inactivation of tumor
suppressor p53 is a late
event during development
of CRCs
Kinzler KW and Vogelstein B, Nature Rev Cancer 2 (2002) 673-680
Genetic model of CRC
development
Walther A et al. Nat Rev Cancer. 2009;9(7):489-99.
It takes years for cancer to
develop
Weinberg RA. The Biology of Cancer. Garland Science 2007
Alternative genetic changes
during CRC development
Weinberg RA. The Biology of Cancer. Garland Science 2007
Fodde R et al, Nat Rev Cancer 1 (2001) 55-66
Genetic model of CRC
development
Increasing tolerance to high amounts of β-catenin
β-catenin and colonic crypts
The base of colonic crypts contains selfrenewing
stem cells that have high levels of βcatenin
due to the Wnt signals produced by
surrounding stromal cells
Proliferating undifferentiated
progenitor cells migrate
upwards, Wnt stimulation
weakens, β-catenin is degraded.
Proliferation decreases and cells
achieve differentiated state.
Differentiated cells die after 3-4
days.
In case of mutated APC there are high
levels of β-catenin even without Wnt
signal and undifferentiated cells keep
proliferating and from polyp.
Gastric adenocarcinoma and
proximal polyposis of the stomach
(GAPPS)
Li J. et al., Am.J.Hum.Genet. 98: 830-842, 2016
GAPPS is a rare familial gastric cancer syndrome with an autosomal
dominant pattern of inheritance
characterized by:
Ø  fundic gland polyps (FGPs) in proximal part of stomach, some may
be dysplastic, associated with a significant risk of gastric
adenocarcinoma
Ø  Intestines and distal stomach (pylorus) are without polyps (unlike
FAP)
Ø  In 12-84 % of FAP patients develop FGPs
Ø  sporadic FGPs are less frequent, only rarely dysplastic
GAPPS
Ø  autosomal dominant inheritance
Ø  Causal gene located at 5q22 (frequent LOH)
Ø  Whole-exome nad whole-genome sequencing have not found
associated mutations
Ø  Li et al. 2016: analysis of 6 GAPPS families (27 affected individuals)
revealed 3 point mutations in promoter 1B of APC gene, that
consegregated with disease phenotype
Ø  Mutations decreased binding of TF YY1 to APC promoter, leading to
the decreased transcription
Ø  Such mutations are not in FAP!
Ø  promotor 1A is methylated in GAPPS and sporadic FGPs and also in
normal gastric musosis ⇒ transkripts 1B are more abundant in
gastric mucosa!! Colonic cells are „protected“ by expression of
isoform 1A
Li J. et al., Am.J.Hum.Genet. 98: 830-842, 2016
GAPPS
Ø  APC haploinsufficiency is responsible for growth of fundic gland
polyps (FGPs), and loss of the second allele leads to dysplasia
Ø  isoforms 1A and 1B are in frame, but have different N terminus (1B
isoform has one extra exon 1B and lacks exons 2 and 7)
Ø  Specific point mutations in binding site for TF YY1 in
promoter 1B of APC gene causes GAPPS, new and
potentially severe variant of FAP
Li J. et al., Am.J.Hum.Genet. 98: 830-842, 2016
Juvenile polyposis
syndrome
•  autosomal dominant pattern of inheritance
•  The term “juvenile” refers to the type of polyp (juvenile polyp), not age
of manifestation
•  34x higher risk of CRC development; life-long risk of CRC is around
40%; average age at diagnosis of CRC in JPS patients is 44 years
•  Some cases of JPS (approx 20%) are associated with germ-line
mutations of SMAD4 (DPC4) (18q21.1)
TGF-β signaling pathway
•  SMAD proteins are signal
transducers of TGF-β pathway;
TGF-β inhibits growth of many cell
types, resistance to TGF-β is
associated with colorectal tumors.
•  Binding of TGF-β to receptor
leads to phosphorylation of
SMAD2 and/or SMAD3, and
these bind SMAD4 and together
translocate to nucleus. In complex
with other TFs transactivate target
genes (e.g. p21CIP1, p15INK4B, …).
Heteditary non-polyposis colorectal
carcinoma - HNPCC = Lynch syndrome
•  HNPCC represent 2-4 % of all colorectal tumors in western countries
•  Average age of tumor diagnosis in HNPCC patients is 40 years
•  Patients do not have increased numbers of precursor adenomas
•  Lifetime risk of CRC is 50 % for women with HNPCC, for men 80 %
and lifetime risk of uterine cancer is 60 %
•  HNPCC patients are further predisposed to ovarian, stomach,
pancreatic and bladder cancer
•  Cancer risk is associated with mutations of genes involved in MMR
(DNA mismatch repair), tumors are genetically instable and progress
fast
•  somatic mutation in MMR genes (most frequent je methylation of
MLH1) are common in CRC, uterine and stomach cancer, rare in other
cancer types
Heteditary non-polyposis
colorectal carcinoma
•  autosomal dominant inheritance
•  Syndrome is linked with germ-line mutations of genes involved in
mismatch repair:
•  MSH2 (first identified; 2p15-16, 106 kDa)
•  MLH1 (3p21; 85 kDa)
- these two account for more than 90 % of HNPCC
•  PMS2 (7p22; 96 kDa)
•  MSH6 (2p16) – cause different phenotype
- these two only minor HNPCC
•  PMS1 (2q31)
•  MSH3 (5q11-q12)
- only rarely present as germ-line mutations
•  MLH3 (14q24.3)
DNA mismatch repair
•  MMR is in focus of cancer research after discovery of sporadic
CRC tumors with large changes in poly(A) regions of their
genomes; later identified changes in poly(CA) repetitive
sequences and this phenomenon was termed microsatellite
instability (MSI)
•  microsatellite DNA is prone to mismatch errors during
replication, because during synthesis of short tandem repetitions
the newly synthesized chain may slide and shift against DNA
template :
thus e.g. A7 → A6 or A8
Impact of mutations in MMR
genes
„oncogenic“ mutations that are secondary to defects in MMR
(microsatellite instability - MSI) may occur in any gene;
described e.g. in APC gene, gene encoding receptor II for
TGFß (TGFßRII; 10A DNA sequence encoding 3 lysines), BAX
(gene contains DNA sequence of 8G - codons 38-41), in MMR+
tumors there are frequent insertions and deletions of 1 nt –
typically associated with wt p53
Example of impact of MMR
defects: mutation of TGF-βRII
TGF-βRII is frequently
mutated in CRC with MSI
There is a microsatellite of
10A. Often deletion of 1 or
2 A → non-sense mutation
→ premature stop codon →
absence of C-terminal
kinase domain ⇒
resistance to TGFβ
signaling.
(mutated protein has 129 or
161AA instead of 565 AA)
Peutz-Jeghers syndrome - PJS
•  autosomal dominant syndrome (Peutz 1921; Jeghers 1949)
•  Characterized by dark blue or dark brown pigmented freckling,
especially around the mouth and on the lips, fingers, or toes
(fade with age) and growth of hamartomatous polyps in small
instestine, colon, stomach
•  Polyps may progress into malignant tumors
•  Predisposed for other cancers pancreatic,
gastrointestinal,
bilateral breast carcinomas
Peutz-Jeghers syndrome
•  PJS causally associated with mutations of LKB1 (STK11, Liver
Kinase B1) gene (19p13.3)
•  LOH present in smaller fraction of hamartomatous polyps and in 70
% of malignant tumors of PJS patients → haploinsufficiency of LKB1
triggers growth of hamartomas
•  LKB1 mutations are rare in sporadic tumors
•  Germ-line mutations of LKB1 are in 70 % of affected families, thus
existence of other gene causing PJS is suspected
•  Penetrance is high (93%); average age of detection of malignant
tumor is 43 years
•  LKB1 is serine-threonine protein kinase present in nucleus and
cytosol
•  Most mutations result in complete loss of LKB1 protein, point
mutations inactivate kinase activity
Expression of LKB in small
intestine
•  Stem cells are at the base of colonic crypts, they produce progenitor cells and
these migrate upward (a smaller fraction also in opposite direction to the
base), differentiate and die by apoptosis after 3-5 days
•  High expression of LKB1 is at the top of the vili and base of crypts – in cells
undergoing apoptosis
Yoo LI et al, Nature Rev Cancer 2 (2002) 673-680
LKB1 function
•  LKB1 is expressed in cells undergoing apoptosis;
•  In apoptotic cells LKB1 is translocated to mitochondria
→  protein LKB1 probably involved in apoptosis regulation
•  Some studies demonstrated absence (low frequency) of TP53
mutations in tumors harbouring LKB1 mutations – indicates
functional crosstalk between LKB1 and p53 (apoptosis?)
•  LKB1 also induces cell cycle arrest, probably via p21WAF1/Cip1
Result of defects in repair of DSBs
for genetic stability
NHEJ - nonhomologous end joining
SSA - single-strand annealing
HR - homologous recombination
Venkitaraman AR, Cell 108: 171-182, 2002
Physiological DSBs
•  meiotic recombination
•  Gene (gene segments) rearrangements in
immunoglobulin and T- and B-cell receptor genes
(V(D)J recombination)
Protein network involved in DSBs
repair by homologous
recombination
•  these proteins control
genome integrity
•  Their germ-line
mutations predispose
to cancer
Blue arrows:
phosphorylation
Wang JYJ, Nature 405: 404-405, 2000
Ataxia – Telangiectasia (A-T)
•  autosomal recessive pattern of inheritance
•  Prevalence around 1:40.000 (USA); frekvention of carriers
(heterozygots) around 1%
•  progressive neurodegenerative disease: impairs certain areas of
the brain (cerebellum), causing difficulty with movement and
coordination (ataxia)
•  Endocrine dysfunctions
•  Dysfunctions of immune system
•  Sterility, premature aging
•  Sensitivity to ionizing radiation (X-rays and gamma rays),
topoisomerase inhibitors
•  Defects in repair of DSBs = increased risk of cancer
Ataxia telangiectasia
Predisposition to cancer development:
•  Approx 38 (25) % of AT patients develop tumor during lifetime mostly
(85 %) T-lymphomas and CLL - chronic lymphocytic
leukemia, but also higher risk of stomach cancer,
medulloblastomas, gliomas, tumors of urinary trackt,
Choi M et al. 2016, DOI: 10.1158/1535-7163.MCT-15-0945
Ataxia telangiectasia: gene
•  Located at chromosome 11 (11q22.3), 66 exons
•  Expressed in all tissues
•  More than 250 (167) different mutations of ATM described, common
are truncated forms
•  Mutation type affects phenotype
Weinberg RA: The Biology of Cancer. GS, 2007
ATM mutation spectra
Choi M et al. 2016, DOI: 10.1158/1535-7163.MCT-15-0945
Frekvention of somatic mutations of
ATM in different cancers
Choi M et al. 2016, DOI: 10.1158/1535-7163.MCT-15-0945
Ataxia telangiectasia: protein
•  3506 AA, 370 kDa
•  serine/threonine protein kinase, C-terminus high homology with PI3K
kinase (PIKK family „PI3K-like protein kinases“: PIRK, ATM, ATR,
DNA-PKs, TRRAP,..)
•  Activated by double stranded breaks in DNA (DSBs) induced e.g. by
ionizing radiation (not UV), topoisomerase inhibitors
•  Activation of ATM is primary and direct reaction to DSBs (but not the
only one); later other ATM-independent pathways are triggered
Substrates
•  phosphorylates p53 at ser15 → stabilization and activation
•  phosphorylates MDM2 at min 2 sites → release of p53 from MDM2
•  Other substrates, e.g. Chk2, c-Abl, BRCA1, NBS1, FANCD2 and
others
ATM-dependent pathways
Rotman G and Shiloh Y, Oncogene 18 (1999) 6135-6144
ATM function in repair of
DSBs
Choi M et al. 2016, DOI: 10.1158/1535-7163.MCT-15-0945
ATM function
In response to ds breaks in DNA:
•  Induce cell cycle arrest (prevent replication of damaged DNA)
•  Induce repair of DSB: besides other mechanisms also by direct
inetraction with RAD51 (RAD51 interacts with BRCA1 and
BRCA2)
Its function is reflected in clinical symptoms of A-T: germ cell that
undrego meiosis (and meiotic recombination) and maturing
lymphocytes undergoing V(D)J recombination are more
sensitive to the ATM mutations (⇒ sterility, immunodefficiency,..)
Protein network involved in DSBs
repair by homologous
recombination
•  these proteins control
genome integrity
•  Their germ-line
mutations predispose
to cancer
Blue arrows:
phosphorylation
Wang JYJ, Nature 405: 404-405, 2000
Nijmegen breakage syndrome
- NBS
•  similar symptoms as for A-T: growth defects, endocrine dysfunction,
immunedeficiency, sensitivity to radiation, predisposition to cancer,
mainly B-lymphomas (in 40 % of patients by the age 20
•  Distinct from A-T: microcephaly, mental retardation
•  Also similar phenotypes at cellular levels: associated with defects in
DSB repair.
•  Cause by mutation of NBS1 (nibrin, 8q21)
•  autosomal recessive inheritance
Nijmegen breakage syndrome -
NBS
•  protein NBS1 (nibrin) forms trimeric
complex with (MRE11 and RAD50) that
interacts with damaged DNA (DSBs)
•  NBS1 function as a „sensor“ – if absent,
MRE11-RAD50 complex is not recruited to
DSBs – and also as effector – contributes
to the repair
•  MRE11 is mutated in rare genetic disorder
called ATLD (AT-like-disorder)
•  MRE11 is nuclease, at DSBs it degrades nt
of one strand leaving single strand
overhangs
•  around 10 % breast cancer is hereditary, out of that 50 % is
associated with mutations of BRCA1 and BRCA2
•  Breast cancer genetic predisposition is caused by other germ-line
mutations: TP53, PTEN, LKB1 (5-10%) and possibly other genes
(40%)
Ø  somatic mutations of BRCA genes are less frequent in sporadic
tumors.
Hereditary Breast and Ovarian
Cancer syndrome (HBOC)
BRCA1, BRCA2
Ø  No homologues in yeast and Drosophila – „late“ in evolution
Ø  BRCA1: discovered in 1994; locus 17q21.31; 22 exons
Ø  BRCA2: discovered in 1994/1995; locus 13q12.3; 27 exons
Ø  Encode large proteins that are expressed in many tissues and
localized mostly in nucleus
Ø  Significant function in protection of genome integrity, but their
functions are not identical!!
Ø  „caretakers“, preserve genome integrity
Venkitamaran, Cell. 2002;108(2):171-82.
BRCA1, BRCA2 in DNA damage
response
Homologous recombination
Chen C. editor,. New Research Directions in DNA Repair. 2013;
Available from: http://dx.doi.org/10.5772/46014
RAD51: a recombinase that
catalyzes the homology
search and the strand
exchange with a homologous
sequence and thus ensures
the accurate repair of the
DSB.
Model of BRCA2 function
Wilson JH, Science. 2002;297(5588):1822-3.
Interacts with RAD51 and
regulate its level and
activity.
Ø DSBs activate ATM or ATR
Ø ATM/ATR phosphorylate thus
activate complex BRCA2-
RAD51
Ø activated RAD51 loads onto
damaged ss DNA and activates
homologous recombination;
release from repaired DNA
strands is associated with
dephosphorylation of the
complex
BRCA1 function
Ø  More difficult to identify exact function of BRCA1:
•  In DNA regions with DSBs high turnover of chromatin
modifications and protein composition
•  Appears fast at DSB sites, substrate of kinases ATM, ATR, ChK2,
interacts with SWI/SNF, HDAC/HATs,...
Ø  Interacts with MRE11/RAD50/NBS1 complex (MRN), inhibits
nuclease MRE11, and thus regulates lenght of ss overhangs
Ø  Interacts with DNA helicase BLM
Ø  Interacts with proteins MSH2 and MSH6 that participate in DNA
mismatch repair
Ø  BRCA1 colocalizes with protein encoded by FANCD2 (mutated in
Fanconi anemia)
BRCA1 function
Ø  Difficult to define the exact function of BRCA1 (based on
interaction partners)
Ø  Responsible for correct assembly of repair complexes at
the sites of DSBs – it functions as a scaffold
Model of BRCA1 function
Venkitamaran, Cell. 2002;108(2):171-82.
Link between BRCA1 mutations and
mutations of other genes
Ø  Mutations of both alleles of BRCA1 or BRCA2 is lethal for cells, their
survival is secured by mutations of some checkpoint genes, e.g.
P53
Ø  Timeline: germ-line mutation of BRCA → inactivation of p53 →
mutation of second allele of BRCA.
Frequency of p53 mutations is higher in tumors with BRCA mutations
(and other mutation spectra).
•  Similar effects as p53 mutations may have mutations of genes
associated with spindle checkpoint (metaphase-to-anaphase
transition): Bub1, BubR1.
Ø  Mutations of BRCA1 and 2 survive only mammary and ovarian cells
due to the anti-apoptotic effect of estrogens.
Hereditary Breast and Ovarian
Cancer syndrome
•  About 1 in 300-800 women has mutation in either BRCA1 or
BRCA2 gene
•  prophylactic mastectomy (a surgery to remove one or both
breasts) reduces breast cancer risk from 85% to 1-5%
(remaining risk may be connected with residual mammary tissue
after surgery)
•  prophylactic adnexectomy (removal of ovaries and fallopian
tubes) reduces risk of ovarian cancer from 60% (BRCA1
mutation carriers) or 20% (BRCA2 mutation carriers) to 1-5%
•  Surgery is recommended at age 35-40 years
•  Removal of ovaries may diminish the risk of breast cancer by 50
% thanks to the estrogen depletion
Foretová L.: Dědičný syndrom nádorů prsu a ovaria, Medical Tribune XI, 24.3.2015
Breast carcinoma in men
•  Mutations of RAD51B (SNP 17q24.1) enhance risk of breast
cancer in men by 50%
•  around 10 % of patients have BRCA2 mutation, mutations of
BRCA1 are not present in men with breast carcinoma
•  Breast carcinoma in men and women is presumably quite
different clinical entity
Orr N. 2012, Nat Genet 44: 1182-1184
RecQ helicases
•  Family of RecQ helicases (5 in human) contribute to the control of
genome stability: they catalyze separation of complementary strains
of DNA using energy from ATP hydrolysis
•  Family RecQ helicases comprises:
BLM (RECQ2) (Bloom syndrome)
WRN (RECQ3) (Werner syndrome)
RECQ4 (Rothmund-Thompson
syndrome - RTS)
- all syndromes are associated
with enhanced cancer risk
Bloom syndrome - BS
•  Very rare autosomal recessive disease
•  Predisposition to cancer development
•  typical facial feature and thin voice
•  Small stature
•  Sensitivity to sunlight
•  common Diabetes mellitus
•  Sterility (reduced fertility)
•  Immunodeficiency
Bloom syndrome
•  Caused by mutation in BLM gene (15q26.1)
•  Autosomal recessive pattern of inheritance, heterozygots are
without any symptoms
•  BLM mutations are generally very rare in population, more
common amongst people of Ashkenazi Jewish background
(carrier is 1 in 110 people, specifically mutation blmAsh: 6-bp
deletion and 7-bp insetion in exon 10)
•  In other populations not specific mutations, may be of many
types: missense, frameshift, nonsense, splice-site
•  Tumors in BLM patients have high chromosomal instability
Tumors in BS patients
•  High frequency (benign and malignant)
•  Wide range of tumor types (acute leukemias, lymphomas, lung,
colorectal, skin, breast, cervical cancer, etc)
•  Very early onset (average age at diagnosis is 24.7 years)
•  high frequency of multiple primary tumors
Ø  Cancer is the most frequent cause of death
Werner syndrome - WS
•  rare autosomal recessive disease, global incidence
rate 1:220.000 - 1.000.000 (incidence in Japan and
Sardinia is higher)
•  Till adulthood normal phenotype. Then onset of rapid
premature aging: premature graying of hair, hair
loss, wrinkling, prematurely aged faces with beaked
noses, skin atrophy, loss of fat tissues
•  Increased risk cancer (30x): common non-epithelial
tumors: soft tissue sarkomas, osteosarcomas,
melanomas, thyroid cancer...
•  Caused by mutation of WRN gene, located 8p12
•  WRN mutations are mostly non-sense or frameshift ⇒
truncated proteins
•  WRN protein contributes to repair of DNA damage
resulting from chronic oxidative stress, WRN is
important in dealing with oxidative DNA damage that
underlies normal aging Penisi E, Science 272 (1996) 193-194
Rothmund-Thompson
syndrome - RTS
•  autosomal recessive inheritance
•  Some RTS patients have mutation in RECQL4, located
8q24.3
•  RECQL4: DNA helicase – problems during initiation of
replication
•  Characterized by defects in skin pigmentation, hair
loss, skeletal defects
•  Associated with increased cancer risk, common
osteosarcomas, but also other tumors with early onset
(before age 25 y)
Fanconi anemia - FA
•  autosomal recessive syndrome, very rare: common
growth retardation, pigmentation defects,
microcephaly, etc (heterogenous disease)
•  Bone marrow failure syndrome leading to the
congenital hematopoietic abnormalities
•  Cancer predisposition, mostly: leukemia (AML),
hepatocellular carcinoma,
•  FA is rare, somatic mutations of „FA cluster“ also in
some sporadic cancers – impaired response to DNA
damage
Fanconi anemia
•  11 genes (FANCA to FANCL) causing: no sequence homology,
linked by functional interplay
•  Encoding components of single tumor suppressor pathway and form
nuclear complex FA that is required for activation of key protein
FANCD2
Ø  FANCD2 is monoubiquitinated in response to DNA damage,
together with other proteins (BRCA1 and BRCA2) is localized in
sites of DBSs, participates in homologous recombination
•  At cellular level is for FA characteristic sensitivity
to DNA crosslink agents
Skin cancer
•  Melanomas: originate from transformation of
melanocytes, cells producing
•  Other skin tumors:
- about 80 % represent basal cell carcinoma, remaining
20 % squamous cell carcinomas
Xeroderma pigmentosum - XP
•  Rare autosomal recessive syndrome
•  Incidence rate 1:1.000.000 in USA and Europe and around
1:100.000 in Japan and north Africa
•  High sensitivity to UV: Xeroderma (dry skin), irregular dark spots
on the skin,severe sunburn, about 1000x increased risk of
„sunlight-induced“ skin cancer*, also predisposition to leukemias
and gastric, brain, lung cancer
•  In some patients (18%) associated with neurologic problems
(hearing loss, poor coordination, etc)
* XP patients have higher risk for both melanomas (5%) and
other skin cancers (squamous and basal cell derived) (95%)
Xeroderma pigmentosum
•  90% of tumors appear at head, face and neck – skin
highly exposed to sunlight
•  Average age of tumor diagnosis is 8 years (for
sporadic tumors – not XP- average age is 60)
•  Associated with germ-line mutations in one of 7 XP
genes: XP-A to XP-G
•  Proteins endoded by these genes contribute to
nucleotide excision repair (NER) as a part of
multiprotein complex
•  protein XP-V (POLH) encodes (error-prone) DNA
polymerase pol-η – can replicate DNA over the lesion
(→ 8 genes causally involved with XP syndrome)
•  No therapy, prevention of UV exposure
Model of NER
NER is required for enzymatic
removal of damaged nucleotides
(common for bulky lesions such
as thymine dimers induced by UV)
and their replacement.
NER is mediated by multiprotein
complex (of 24 subunits)
7 subunits encoded by XP genes
(A, B, C, D, E, F, G), mutations
cause different types of
Xeroderma pigmentosum (type
A..).
8th type (Type V) caused by XPV
mutation – defects „by-pass (errorprone)
polymerase“ pol-η.
von Hippel-Lindau (VHL)
syndrome
•  VHL (pVHL)
Hereditary diffuse gastric
cancer
•  CDH1 (E-cadherin)
Secondary malignant neoplasias
(SMN) induced by therapy
•  Increasing numbers of patients (especially pediatric) that survive
many years after treatment with cytotoxic therapy.
•  Most common SMNs are sarcomas of bone and soft tissues
•  Radiation therapy is frequently the cause of SMNs.
•  Young age and low dose of radiation therapy increases risk of
thyroid cancer
•  Women that underwent radiation therapy of Hodgkin lymphoma
often develop breast cancer with increasing age
•  Patients that received alkylating agents and inhibitors of
topoisomerase II have higher risk of secondary leukemias
Secondary malignant neoplasias
(SMN) induced by therapy
Interation of therapy with genetic predispositions is critical:
RB (retinoblastom): sarkomy, melanomy
•  NF1 (neurofibromas): neurofibrosarkomas, AML, JMML, gliomy
•  RB (retinoblastoma): sarkomas, melanomas
•  Sensitivity to ionizing radiation: AT, NBS, BS, WS
•  Sensitivity to UV: XP, BS
•  Sensitivity to alkylating agents: FA
⇒  Therapy must be carefully considered especially in patients
with genetic predispositions!!!
Thank you for attention!