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MitoNews
Mitochondrial Research Bulletin
Published by:
MitoSciences
Advancing Vital Discoveries in Mitochondrial Research
http://www.mitosciences.com
Edited & Moderated by:
Dr. Roderick Capaldi
[email protected]
Volume 01, Issue 05 - May 31, 2005
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Past issues of MitoNews can be found at:
http://www.mitosciences.com/mitonews_archives.html
In This Issue...
RECENT RESEARCH
1. SIRT a link between lifespan and mitochondrial biogenesis
2. MtDNA mutations and cardiomyopathy
3. Resistance to a commonly used cancer drug through
reduced synthesis of the ATP synthase
4. A new drug target for the auto-immune disease lupus:
the ATP synthase
5. Mitochondrial involvement in epilepsy
6. P53 enters the mitochondrion faster than it does the nucleus
7. The crystal structure of the c subunit ring of the
ATP synthase
8. Proteomic analysis of Parkinsons disease
9. Organophosphorus esters cause mitochondrial dysfunction
10. Estrogen produces mitochondrial reactive oxygen species
used for signal transduction
11. OPA1 distribution in retina is consistent with the phenotype
of dominant optic atrophy
12. Krebs cycle changes in old houseflies (and people?)
13. The coenzyme Q synthesizing complex from yeast
14. Cyclooxygenase-2 goes to mitochondria in cancer?
.................................................................
1. SIRT a link between lifespan and mitochondrial biogenesis
Among the proteins identified as involved in increase of
lifespan in lower organisms is Sir2 a NAD-dependent
deacetylase. The mammalian homologue of this protein is
called SIRT1. In the study below, increased expression of
SIRT1 was found to reduce cellular oxygen use by 25%, and
at the same time, alter transcriptional activity of the
mitochondrial biogenesis co-activator PGC1. SIRT1 and PGC1
were shown to associate in a complex by immunoprecipitation
studies. The authors also show that a single amino acid
change in the putative ADP ribosyltransferase site of SIRT1
inhibits its interaction with PGC1. Further data indicate that
SIRT1 probably acts by deacetylating PGC1 to regulate
mitochondrial metabolism.
NEMOTO.S, FERGUSSON. MM & FINKEL.T.
J Biol. Chem.. 280. 16456-60 (2005)
2. MtDNA mutations and cardiomyopathy
Zassenhaus and colleagues has provided several lines of
evidence that accumulation of mtDNA mutations at low levels
(less than 1% total) are found in, and may be causal for,
idiopathic dilated cardiomyopathy and end stage heart failure.
In the paper below, this group now link accumulation of
mutations in mtDNA with increased levels of apoptosis.
They obtained increased levels of mt DNA mutation specifically
in the heart of transgenic mice following the expression of an
error prone mtDNA polymerase. By 8 weeks of age, these mice
had levels of mutation in mtDNA of around 0.01% and all
animals at this stage showed four-chamber cardiac dilation.
There was up-regulation of Bcl2, Bcl-xl and HSP27 along with
other proteins known to inhibit apoptosis. This increased
survival response provided protection against doxorubicin.
The authors conclude that the elevated frequency of mtDNA
mutations triggers the activation of the survival response.
ZHANG.D, MOTTO.JL, CHANG.SW, STEVENS.M,
MIKOLAJCZAK.P & ZASSENHAUS.HP.
Am J. Physiol. Heart. Circ. Physiol. 288. H2476-83 (2005).
3. Resistance to a commonly used cancer drug through
reduced synthesis of the ATP synthase
5-fluorouracyl (5-FU) is widely used in the treatment of
advanced cancers including colorectal cancer but resistance
to the drug is commonly observed. In the study below, the
authors screened for proteins whose expression is altered
by 5-FU using 2D electrophoretic proteomic analysis on
human colon cancer cell lines. They found down regulation
of the alpha subunit of the F1F0ATP synthase in 5-FU resistant
cells compared to controls in their proteomic analysis and then
followed up with Western blotting of several of the ATP synthase
subunits to show that the levels of the complex as a whole was
reduced. This was confirmed by activity measurements.
Oligomycin strongly antagonized 5FU induced suppression
of cell proliferation, while reduced levels of subunit d achieved
by siRNA treatment increased cell viability in the presence of
the drug. The authors conclude that down regulation of ATP
synthase could be a bioenergetic signature of colorectal
carcinomas and may lead to the cellular events responsible
for 5-FU resistance.
SHIN.YK, YOO.BC, CHANG.HJ, JEON.E, HONG.SH, JUNG.MS,
LIM.BJ & PARK.JG.
Cancer Res. 65. 3162-70 (2004)
EDITORS NOTE. The authors focus on mitochondrial ATP
synthase but regular readers of these synopses will know that
this same complex is found on the plasma membrane of cells,
particularly cancer cells (see the brief review of mitochondria
and cancer in the MitoSciences website). Probably, the
presence of ATP synthase and other mitochondrial enzymes
on the plasma membranes of cells involves fusion between
the organelle membranes(s) and the PM.
4. A new drug target for the auto-immune disease lupus:
the ATP synthase
Current drugs for the treatment of lupus are quite toxic and
several groups have been looking for novel drug targets for
treating this disease. In the paper below, Glick and colleagues
show that Bz-423, a 1,4 benzodiazepine, is a promising new
drug which suppresses disease in lupus prone mice by killing
selectively the pathogenic lymphocytes through apoptosis.
It increases apoptosis via a reactive oxygen signaling pathway.
Phage display screening identified the ATP synthase subunit
OSCP as the binding site for the compound. This is supported
by the lowered sensitivity to Bz 423 when the levels of OSCP
are reduced by RNA interference methods.
JOHNSON.KM, CHEN.X, BOITANO.A, SWENSON.L,
OPIPARI.AW.Jr & GLICK.GD.
Chem. Biol. 12. 485-96 (2005)
EDITORS NOTE. OSCP or oligomycin sensitivity conferring
protein is a misnomer. This polypeptide is a part of one of the
2 stalks that join the F1 to F0 parts of the complex. It is not
the binding site for oligomycin, which binds in the F0 part.
5. Mitochondrial involvement in epilepsy
There is evidence that mitochondrial dysfunction and resulting
increased oxidative stress is involved in a number of
neurological conditions. In the paper below, exciting data are
provided that links respiratory chain deficiency and specific
alterations in the Rieske non-heme iron protein of Complex III
with epilepsy. Proteomic analysis of rats with drug induced
epilepsy showed a modified variant of the Rieske protein
altered in isoelectric point in the hippocambus of epileptic
animals. There was also a selective expression of this same
protein in the subgranular neurons of the dorsal dentate
gyrus, a region implicated in neurogenesis. The modified
form of the Rieske protein, not yet fully characterized, was
lost when animals were allowed to revert to normal, implying
loss of the modification or degradation of the altered subunit.
The authors suggest that the modification is an oxidative
reaction based on previous work linking iron overload to the
condition.
JUNKER.H, SPATE.K, SUOFU.Y, WALTHER.R, SCHWARZ.G,
KAMMER.W, NORDHEIM.A, WALKER.LC, RUNGE.W,
KESSLER.C & POPA-WAGNER.A.
Epilepsia. 46. 339-43 (2005)
6. P53 enters the mitochondrion faster than it does the nucleus
There are several studies to show that the tumor suppressor
gene p53 is targeted to mitochondria as well as the nucleus.
The study below examines the temporal nature of the
translocation of this regulator of gene expression. P53 is
activated by reactive oxygen species-generating agents. Its
translocation was measured in skin epidermal cells following
treatment with the tumor promoter
12-O-tetradeconylphorbol-13-acetate (TPA). P53 entered
mitochondria within 10 min, compared to 1hr for the nucleus
following TPA application. The authors show that once inside
the organelle p53 interacts with Mn superoxide dismutase,
consistant with observed reduction of the superoxide
scavenging activity of this enzyme. P53 entry into the nucleus
also resulted in up-regulation of bax, but at 15hr following
drug exposure. Activation of p53 transcriptional activity could
be prevented by application of MnTE-2-PyP(5+) a SOD mimetic
ZHAO.Y, CHAISWING.L, VELEZ.JM, BATINIC-HABERLE.I,
COLBURN.NH, OBERLEY.TD & ST CLAIR. DK.
Cancer Res 65. 3745-50 (2005)
7. The crystal structure of the c subunit ring of the
ATP synthase
There have been several crystal structures of parts of the
F1F0ATP synthase, notably for the F1 part as isolated from
several bacterial, plant and animal sources. An NMR structure
of c subunit monomers is available as is a low resolution
structure of the c subunit ring from yeast. Now Dimroth and
colleagues have obtained a 2.4angstrom structure of the c
subunit ring isolated away from the rest of the F1F0 of the
organism Ilyobacter tartaricus. It now appears that the number
of c subunits in the ATP synthase complex is variable with 9 or
10 in yeast, 14 in chloroplasts, 12 in E coli and 11 in I tartaricus.
The high resolution structure described in the paper below shows
the c ring of this last organism is an hourglass shaped cylinder
with 11 fold symmetry. As crystallized, this structure contains 11
sodium ions each bound through 2 C terminal helices and 1 N
terminal helix of the monomers, located at the region where
there is a bend in these helices, near the middle of the structure.
MEIER.T, POLZER.P, DIEDERICHS.K, WELTE.W. & DIMROTH.P.
Science 308. 659-62 (2005)
8. Proteomic analysis of Parkinsons disease
A hallmark of Parkinsons disease is the generation of Lewy
bodies, and it is now believed that these structures are
aggregates of synuclein and other proteins generated through
oxidative stress induced by mitochondrial dysfunction. To test
the mitochondrial involvement the authors of the study below
used nonbiased quantitative proteomics with isotope-coded
affinity tag to compare the mitochondrial profiles in the
substancia nigra of mice treated chronically with MPTP and
control untreated mice. Of the more than 300 proteins identified
in the analysis, 100 displayed significant changes in relative
abundance. One of these is DJ-1 a mutation in which has
been implicated in familial PD. DJ-1 was shown to colocalize
with alpha synuclein.
JIN.J, MEREDITH.GE, CHEN.L, ZHOU.Y, XU.J, SHIE.FS,
LOCKHART.P & ZHANG.J
Brain Res. Mol. Brain Res. 134. 119-38 (2005)
9. Organophosphorus esters cause mitochondrial dysfunction
In the study below, the effect of organophosphorus esters, a
known neurotoxicant, was examined in SH-SY5Y neuroblastoma
cells as well as dorsal root ganglia cells from chick embryos.
These common environmental toxins were found to reduce ATP
synthesis by lowering respiratory chain functioning, predominantly
at complex I. Loss of mitochondrial functioning in the neuronal
cell line was also evident from the loss of the mitochondrial
specific staining by the dye tetramethylrhodamine.
MASSICOTTE.C, KNIGHT.K, VAN DER SCHYF.CJ,
JORTNER.BS & EHRICH.M.
Neurotox Res. 7 203-17 (2005)
10. Estrogen produces mitochondrial reactive oxygen species
used for signal transduction
Several lines of evidence show that 17beta-estrdiol enters
mitochondria. In the article below, evidence is presented that
the estrogen induces reactive oxygen species within the
organelle, probably H2O2. Confocal microscopy indicates
that this ROS production is within perinuclear mitochondria.
The authors propose that the mitochondrially-generated ROS
they describe explains the oxidative damage and subsequent
cancer-causing genetic mutations seen with elevated
concentrations of estrogens.
FELTY.Q, XIONG.WC, SUN.D, SARKAR.S, SINGH.KP,
PARKASH.J & ROY.D.
Biochemistry 44. 6900-09 (2005)
11. OPA1 distribution in retina is consistent with the phenotype
of dominant optic atrophy
Autosomal dominant optic atrophy is the most common form
of hereditary optic neuropathy. Retinal ganglion cells and
optic nerve degeneration occurs progressively during the
first decade of life. The protein defective in this disease is
OPA1 (Optic atrophy type 1), a dynamin related GTPase
involved in mitochondrial fusion fission events and overall
maintainance of the mitochondrial network and genome.
In the paper below the authors have examined the distribution
of OPA1 in various cell types that make up the retina and optic
nerve. The protein is expressed in the ganglion cell layer,
outer plexiform layer, inner nuclear layer and the inner plexiform
layer. In the ganglion cell layer OPA1 is expressed
predominantly in retinal ganglion cells. It is in low amount or
absent in astrocytes and oligodendrocytes. The data are
consistant with the selective vulnerability of retinal ganglion
cells to OPA1 loss.
JU.WK, MISAKA.T, KUSHNAREVA.Y, NAKAGOMI.S,
AGARWAL.N, KUBO.Y, LIPTON.SA & BOSSY-WETZEL.E.
J Comp. Neurol. 488. 1-10 (2005).
12. Krebs cycle changes in old houseflies (and people?)
In the study below, flight muscle mitochondria of houseflies were
used to gauge the effects of aging on citric cycle enzymes. Young,
medium aged and old flies were collected (the old ones cannot fly
and are presumably easier to catch!). Maximal activities of each
of the Krebs cycle enzymes were measured in each set of flies.
Only aconitase activity was altered, reaching 56% of normal in
the old flies. The authors conclude that the observed reduction
in aconitase activity is likely to contribute to the decline in
efficiency of mitochondrial bioenergetics and result in secondary
effects including accumulation of redox-active iron.
YARIAN.CS & SOHAL.RS.
J.Bioenerg.Biomembr. 37. 91-96 (2005)
EDITORS NOTE. Aconitase is heavily modified by oxidative
stress and its activity decline is often used to measure the l
evels of reactive oxygen species in cells.
13. The coenzyme Q synthesizing complex from yeast
At least eight genes encoding polypeptides Coq1-Coq8 are
required for coenzyme Q biosynthesis in yeast. In the paper
below, evidence is presented from Blue Native Gel
electrophoresis and gel filtration chromatography that these
polypeptides are a part of a complex of at least 700kDa.
Co-precipitation of biotinylated forms of some of the
polypeptides is also used to support the concept that the
coQ biosynthesis machinery forms a large complex.
MARBOIS.B, GIN.P, FAULL.KF, POON.WW, LEE.PT,
STRHAN.J,.SHEPHERD.JN & CLARKE CF.
J.Biol.Chem. 280. 20231-38 (2005)
14. Cyclooxygenase-2 goes to mitochondria in cancer?
Cyclooxygenase-2 (the other COX-2!) is generally considered
as a protein of the nuclear envelope, endoplasmic reticulum
and plasma membrane. In the study below the authors
examined the localization of this enzyme in cancer cells
including lung, colon, breast and hepatocellular cancer cells
using confocal microscopy. They found co-localization of
COX-2 with heat shock protein 60 i.e to mitochondria.
COX-2 was not localized to mitochondria in fibroblasts.
The mitochondrial localization of this protein was confirmed
by immunoblotting after cell fractionation. Cells with high
mitochondrial COX-2 were highly resistant to arachidonic
acid and H2O2-induced apoptosis while fibroblasts were
highly susceptible. Finally treatment of cells with a selective
COX-2 inhibitor resulted in loss of resistance to apoptosis.
The authors propose that mitochondrial COX-2 in cancer
cells confers resistance to apoptosis by reducing
proapoptotic arachidonic acid.
LIOU.JY, ALEKSIC.N, CHEN.SF, HAN.TJ, SHYUE.SK & WU.KK.
Exp. Cell Res 306. 75-84 (2005)
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