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ROS-Generating Mitochondrial
DNA Mutations Can Regulate
Tumor Cell Metastasis.
Kaori Ishikawa, et al. Science. 2008; 661–664
Adviser : Chin-Tin Chen
Speaker: Yi-Chen Tsai D98B47402
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Cancer
The 5-year relative survival rate is 98% for breast cancer patients
with localised disease and only 26% for those with distant-stage
disease.
(Ries et al, 2006)
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Mitochondria of tumor cells have been reported to differ
functionally and morphologically from those of normal cells.
Normal gastric cell line
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Gastric cancer cell line
(Kim, 2007)
Mitochondrion – “cellular power plants”
Membrane-enclosed organelle found in most eukaryotic cells
inner membrane
 Perform the redox reactions of oxidative phosphorylation
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Generate ATP
Electron transport chain couples a chemical reaction between an
electron donor (such as NADH) and an electron acceptor (such as O2)
to the transfer of H+ ions across a membrane, through a set of
mediating biochemical reactions.
These H+ ions are used to produce
adenosine triphosphate (ATP), the main
5 energy intermediate in living organisms.
(Wallace, 1999)
Many chemical carcinogens have been shown to bind
preferentially to mtDNA rather than to nuclear DNA.
(Allen and Coombs, 1980)
High frequencies of homoplasmic mutations in mtDNA
of tumors rather than in mtDNA of normal tissues of
the same patients.
(Fliss, 1978)
Preferential accumulation of mutated mtDNAs in tumor
cells.
(Gallardo, 2006)
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Are mtDNA mutations involved in oncogenic
transformation of normal cells to develop tumors?
mtDNA was considered to be the major cellular target of
chemical carcinogens, and resultant creation of mutations
in mtDNA could be responsible for oncogenic transformation
of normal cells to develop tumors.
(Shay and Werbin, 1987)
？
Tumorigenicity
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mtDNA mutation
Nuclear but not mitochondrial genome involvement in 3methylcholanthrene (MCA)-induced expression of tumori(Hayashi et al., 1989)
genicity.
nucleus
Mitochondrion
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Normal cell
MCA-induced tumor cell
No Tumorigenicity
Still express
tumorigenicity
Maternal inheritance of mtDNA
Mitochondria are normally inherited exclusively from the mother.
Only
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Tumorigenicity
Mother
Offspring
With cancer
？
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However, there has been no statistical evidence for the
presence of maternal inheritance of tumor development.
Mitochondrial defect disease
In humans, complex I defects caused by mtDNAs with
pathogenic mutations and the resultant overproduction
of ROS are reported to be associated with the pathogenesis
in Leber’s hereditary optic neuropathy (LHON).
According to the statistical analysis, the patients with LHON
develop cancers that are already metastatic.
(Wallace, 1999)
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Motive
Mitochondrion
Tumorigenicity
？
mtDNA mutation
Metastasis
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Are mtDNA mutations involved in malignant
progression of tumor cells to develop metastasis?
High metastatic cells showed significant reduction of
complex I (NADH dehydrogenase) activity.
P29
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A11
B82
B82M
P29
A11
B82
B82M
Complex I consists of subunits encoded by both nuclear
(Wallace, 1999)
DNA and mtDNA.
Difficulty of excluding possible involvement
of nuclear DNA mutations in these processes
mtDNA exchange technology
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mtDNA exchange technology
Nuclear DNA P29 P29
P29 A11
mtDNA
A11 A11
P29 A11
The mtDNA of high metastatic cells is therefore likely to harbor
a mutation(s) responsible for complex I defects.
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Does the mtDNA that induce metastasis in tumor cells also
induce tumor development in normal cells?
Nuclear DNA P29 P29
P29 B82M
mtDNA
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B82 B82
B82 A11
NIH NIH NIH
NIH A11 B82M
NIH3T3, normal cell
Nuclear
mtDNA
DNA
B82
B82
B82
A11
NIH
NIH
NIH
A11
NIH
B82M
These mutations do not control the development of tumorigenicity,
at least in nontransformed NIH3T3 cells.
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P29
A11
G13997A mutation
B82
B82M
13885insC mutation
Complex I defects
？
Metastasis
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ND6 gene mutation
NADH dehydrogenase subunit 6
How does Complex I defects regulate metastasis, and
which nuclear genes (if any) are involved in this process?
A11 cells, but not P29 cells, show resistance to hypoxiainduced apoptosis, accompanied by up-regulation of
antiapoptotic MCL-1 (myeloid cell leukemia–1).
(Takasu, 1999)
A11 cells showed higher expression levels of two genes
associated with neoangiogenesis, HIF-1α (hypoxia-inducible
factor–1α) and VEGF (vascular endothelial growth factor), in
comparison with P29 cells.
(Koshikawa, 2006)
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Nuclear DNA P29
P29
mtDNA
P29 A11 A11
A11 P29 A11
The mutated mtDNA and the resultant complex I defects induce
up-regulation of the MCL-1, HIF-1α, and VEGF genes and are
associated with high metastatic potential.
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Mitochondrion
ND6 gene mutation
NADH dehydrogenase subunit 6
Complex I defects
ROS production
(Koshikawa, 2006)
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？
Nuclear-coded genes
related to metastasis
？
Nuclear-coded genes
ROS production
Nuclear DNA
mtDNA
P29
A11
ROS scavenger
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ROS scavenger
Treatment of the cybrids with ROS scavenger in cell culture
reduced the amount of ROS.
Nuclear DNA P29
A11
mtDNA
ROS scavenger
ROS scavenger
Cells
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Treatment of the cybrids with ROS scavenger in cell culture
down-regulated MCL-1
reduced theirROS
metastatic
potential
ROS and
scavenger
scavenger
in mouse models.
Mitochondrion
ND6 gene mutation
NADH dehydrogenase subunit 6
Complex I defects
ROS production
？
Metastasis
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Nuclear-coded genes
related to metastasis
Nuclear DNA P29
A11
mtDNA
Cells
Down-regulation of MCL-1 in P29mtA11 cybrids by small
interfering RNA also suppressed their metastatic potential.
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Mitochondrion
ND6 gene mutation
NADH dehydrogenase subunit 6
Complex I defects
ROS production
Metastasis
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Nuclear-coded genes
related to metastasis
Can contribution of mtDNA to tumor cell metastasis be
extended to human tumors?
Human cell lines
Cell type
Metastatic potential
human breast cancer
HeLa
MDAMB231 human breast cancer
Low
High
Nuclear DNA HeLa
MDAMB231
mtDNA
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Can contribution of mtDNA to tumor cell metastasis be
extended to human tumors?
HeLa
Nuclear DNA HeLa
HeLa MDAMB231
mtDNA
Cells
Transfer of mtDNA from human cancer cells expressing high
metastatic potential into low metastatic cells induces complex
I defects, increased ROS production, and high metastatic
potential.
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Summary
Mitochondrion
ND6 gene mutation
NADH dehydrogenase subunit 6
Complex I defects
ROS production
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Metastasis
Nuclear-coded genes
related to metastasis
Discussion
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Mitochondrion
Discussion
mtDNA
mutation
Metastasis
Resolve the question
Why does the patients with LHON develop cancers that are
already metastatic?
Conventional mitochondrial theories
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ROS-mediated genetic instability is responsible for aging,
age-associated disorders.