Similarities in mitochondrial ultrastructure of leukemic cells and ethidium-bromide-treated normal cells

Nuclear HMGA1 nonhistone chromatin proteins directly influence mitochondrial transcription, maintenance, and function

We have previously demonstrated that HMGA1 proteins translocate from the nucleus to mitochondria and bind to mitochondrial DNA (mtDNA) at the D-loop control region [G.A. Dement, N.R. Treff, N.S. Magnuson, V. Franceschi, R. Reeves, Dynamic mitochondrial localization of nuclear transcription factor HMGA1, Exp. Cell Res. 307 (2005) 388-401.] [11]. To elucidate possible physiological roles for such binding, we employed methods to analyze mtDNA transcription, mitochondrial maintenance, and other organelle functions in transgenic human MCF-7 cells (HA7C) induced to over-express an HA-tagged HMGA1 protein and control (parental) MCF-7 cells. Quantitative real-time (RT) PCR analyses demonstrated that mtDNA levels were reduced approximately 2-fold in HMGA1 over-expressing HA7C cells and flow cytometric analyses further revealed that mitochondrial mass was significantly reduced in these cells. Cellular ATP levels were also reduced in HA7C cells and survival studies showed an increased sensitivity to killing by 2-deoxy-D-glucose, a glycolysis-specific inhibitor. Flow cytometric analyses revealed additional mitochondrial abnormalities in HA7C cells that are consistent with a cancerous phenotype: namely, increased reactive oxygen species (ROS) and increased mitochondrial membrane potential (Delta Psi(m)). Additional RT-PCR analyses demonstrated that gene transcripts from both the heavy (ND2, COXI, ATP6) and light (ND6) strands of mtDNA were up-regulated approximately 3-fold in HA7C cells. Together, these mitochondrial changes are consistent with many previous reports and reveal several possible mechanisms by which HMGA1 over-expression, a common feature of naturally occurring cancers, may affect tumor progression.

Mitochondrial stress-induced calcium signaling, phenotypic changes and invasive behavior in human lung carcinoma A549 cells

We have investigated mechanisms of mitochondrial stress-induced phenotypic changes and cell invasion in tumorigenic but poorly invasive human pulmonary carcinoma A549 cells that were partly depleted of mitochondrial DNA (mtDNA). Depletion of mtDNA (genetic stress) caused a markedly lower electron transport-coupled ATP synthesis, loss of mitochondrial membrane potential, elevation of steady state [Ca(2+)](c), and notably induction of both glycolysis and gluconeogenic pathway enzymes. Markers of tumor invasion, cathepsin L and TGFbeta1, were overexpressed; calcium-dependent MAP kinases (ERK1 and ERK2) and calcineurin were activated. The levels of anti-apoptotic proteins Bcl2 and Bcl-X(L) were increased, and the cellular levels of pro-apoptotic proteins Bid and Bax were reduced. Both mtDNA-depleted cells (genetic stress) and control cells treated with carbonyl cyanide m-chlorophenylhydrazone (metabolic stress) exhibited higher invasive behavior than control cells in a Matrigel basement membrane matrix assay system. MtDNA-depleted cells stably expressing anti-sense cathepsin L RNA, TGFbeta1 RNA, or treated with specific inhibitors showed reduced invasion. Reverted cells with 80% of control cell mtDNA exhibited marker protein levels, cell morphology and invasive property closer to control cells. Our results suggest that the mitochondria-to-nucleus signaling pathway operating through increased [Ca(2+)](c) plays an important role in cancer progression and metastasis.

Effect of acrylamide toxicity on the ultrastructure of a single cell model Nyctotheroides puytoraci

Acrylamide (ACR), a widely used vinyl monomer, is well known as a neurotoxin to both laboratory animals and man. The experiment reported has demonstrated that ACR induces ultrastructural changes in the parasitic ciliate Nyctotheroides puytoraci, after injecting the host Bufo regularis with 1 mg ACR per toad (single dose). After 1 week of ACR injection, alterations in both nuclear and cytoplasmic organelles were observed. An increase in the number of cisternae of the Golgi complex was visualized which may be due to its division and hence activation. Acrylamide also appeared to cause fusion of mitochondria in the treated trophozoites. Thus trophozoites of these specimens showed a decreased number of irregularly shaped mitochondria with dense matrix and indistinct outer and inner membranes. Such changes may be attributed to a disturbance in mitochondrial protein synthesis. Also, rough endoplasmic reticulum and lysosomes increased in number. The basal cell bodies were degenerated at some sites.

Giant mitochondria in acute lymphocytic leukemia

Giant mitochondria were observed in 2 cases among 28 cases of ALL by electron microscopy. The cristae of the giant mitochondria in the leukemic cells were irregularly arranged, decreased in number, and formed concentric circles. Several morphological abnormalities were also observed in the normal mitochondria. Morphometric analysis of the mitochondria in the 2 patients disclosed that the sizes of mitochondria were well distributed from small to large and thus, the mitochondria could not be divided into different populations. Also, there were no clear differences in the distribution of shape between normal and giant mitochondria. These results suggest that the giant mitochondria were derived from normal mitochondria. Since they were observed before the initial treatment, they did not developed as a result of drug action.

Quantitative evaluation of leukemic mitochondria with a computer-controlled image analyzer

Mitochondria from 25 patients with acute lymphoblastic leukemia (ALL) and 25 patients with acute myelogenous leukemia (AML) were compared in terms of their number, area, and shape index using a computer-controlled image analyzer. The number of mitochondria was greater in the AML than in the ALL patients. However, their size, as measured in electron micrographic profiles was similar in the two groups, in disagreement with conventional reports that mitochondria are small in granulocytes but large in lymphocytes. Two ALL patients had giant mitochondria. The mitochondria of the ALL cells were more irregular than those of the AML cells, and furthermore, within the ALL group, the degree of the irregularity was greater in those with a poor prognosis than in those in longstanding remission. The number of mitochondria was significantly greater in B-cell ALL than in null cell and T-cell ALL.

Intramitochondrial lamellar bodies in acute myeloblastic leukemia

Intramitochondrial lamellar bodies were observed in three cases of acute myeloblastic leukemia. Two of the patients had M1 leukemia and the remaining patient M4 leukemia, by the FAB classification. In all three cases neoplastic cells contained dilated mitochondria that varied in size and shape and contained decreased numbers of cristae. Some mitochondria contained lamellar structures that resembled myelin figures and, occasionally, primary granules; these structures were more conspicuous in the central portion of the mitochondria. Regardless of the proliferating cell type (lymphoblasts, myeloblasts, or monoblasts), there are common ultrastructural changes that represent abnormal metabolic function, such as disorders of intramitochondrial protein synthesis. The exact meaning of these findings is not known; adequate interpretation will require further investigation of the biology of these neoplastic processes.

The inhibition of mitochondrial DNA replication in vitro by the metabolites of benzene, hydroquinone and p-benzoquinone

Rat liver mitochondria incubated with the metabolites of benzene, p-benzoquinone or 1,2,4-benzenetriol, showed a dose-dependent inhibition of [3H]dTTP incorporation into mtDNA with median inhibitory concentrations of 1 mM for each compound. Benzene and the metabolites phenol, catechol and hydroquinone did not inhibit at concentrations up to 10 mM. Similarly, incubation of p-benzoquinone or hydroquinone with rabbit bone marrow mitochondria showed a dose-dependent inhibition of mtDNA synthesis with 50% inhibition at 1 mM and 10 mM, respectively. That these metabolites inhibit mitochondrial replication was evidenced by the fact that [3H]dTTP incorporation into characteristic 38S, 27S and 7S mitochondrial replication intermediates was decreased by the quinones, as analyzed on 5-20% neutral sucrose velocity gradients. p-Benzoquinone, hydroquinone and 1,2,4-benzenetriol inhibited the activity of partially purified rat liver mtDNA polymerase gamma using either activated calf thymus DNA or poly(rA) X p(dT)12-18 as primer/template, with 50% inhibitory concentrations of 25 microM, 25 microM and 180 microM, respectively. Preincubation of the metabolites with polymerase gamma or primer/template, followed by removal of the unreacted metabolite by gel filtration, indicated that inhibition resulted from interaction of the metabolites with the enzyme, rather than with the template. Binding appeared to involve a sulfhydryl residue on the enzyme since the binding of [14C]hydroquinone was prevented by N-ethylmaleimide. The ability of hydroquinone or p-benzoquinone to inhibit binding of [14C]hydroquinone to the enzyme suggests that the compounds bind to a common site or are converted to a common intermediate. Inhibition of, or changes in, replication in mitochondria of bone marrow cells by hydroquinone and p-benzoquinone may explain the changes in the mitochondrial genome observed in marrow stem cells in acute myelogenous leukemia and may suggest a mechanism for benzene leukemogenesis.

Inhibition of RNA synthesis by benzene metabolites and their covalent binding to DNA in rabbit bone marrow mitochondria in vitro

Mitoplasts from rabbit bone marrow cells in vitro incubated with benzene metabolites showed a concentration-dependent inhibition of mitochondrial RNA synthesis. The 50% molar inhibitory concentration for each metabolite was determined to be p-benzoquinone, 2 X 10(-6); phenol, 2.5 X 10(-5); hydroquinone, 5 X 10(-5); catechol, 2 X 10(-3); benzene, 1.6 X 10(-2). Activated metabolites of radiolabeled benzene covalently bound to mitochondrial DNA in vitro. Labeled deoxynucleosides, enzymatically produced from DNA isolated from mitoplasts prelabeled in DNA with [3H]dGTP and exposed to [14C]benzene in vitro, were chromatographed on a Sephadex LH-20 column to obtain deoxynucleoside-adducts. The elution profiles indicated that mtDNA contained seven deoxyguanosine-adducts. A similar experiment in which the mtDNA was prelabeled with [3H]dATP indicated that two deoxyadenosine-adducts of mtDNA were formed from benzene in vitro. Tentative identification of several deoxyguanosine-adducts indicates that p-benzoquinone, hydroquinone, phenol, and 1,2,4-benzenetriol produced from benzene form adducts with guanine.