Mitochondria Of Breast Cancer Cells Research Articles

Part III. Molecular changes induced by high nitric oxide adaptation in human breast cancer cell line BT-20 (BT-20-HNO): a switch from aerobic to anaerobic metabolism

Nutrient deprivation and reactive oxygen species (ROS) play an important role in breast cancer mitochondrial adaptation. Adaptations to these conditions allow cells to survive in the stressful microenvironment of the tumor bed. This study is directed at defining the consequences of High Nitric Oxide (HNO) exposure to mitochondria in human breast cancer cells. The breast cancer cell line BT-20 (parent) was adapted to HNO as previously reported, resulting in the BT-20-HNO cell line. Both cell lines were analyzed by a variety of methods including MTT, LDH leakage assay, DNA sequencing, and Western blot analysis. The LDH assay and the gene chip data showed that BT-20-HNO was more prone to use the glycolytic pathway than the parent cell line. The BT-20-HNO cells were also more resistant to the apoptotic inducing agent salinomycin, which suggests that p53 may be mutated in these cells. Polymerase chain reaction (PCR) followed by DNA sequencing of the p53 gene showed that it was, in fact, mutated at the DNA-binding site (L194F). Western blot analysis showed that p53 was significantly upregulated in these cells. These results suggest that free radicals, such as nitric oxide (NO), pressure human breast tumor cells to acquire an aggressive phenotype and resistance to apoptosis. These data collectively provide a mechanism by which the dysregulation of ROS in the mitochondria of breast cancer cells can result in DNA damage.

Mitochondrial dynamics regulates migration and invasion of breast cancer cells

Mitochondria are highly dynamic and undergo constant fusion and fission that are essential for maintaining physiological functions of cells. Although dysfunction of mitochondria has been implicated in tumorigenesis, little is known about the roles of mitochondrial dynamics in metastasis, the major cause of cancer death. In the present study, we found a marked upregulation of mitochondrial fission protein dynamin-related protein 1 (Drp1) expression in human invasive breast carcinoma and metastases to lymph nodes. Compared to non-metastatic breast cancer cells, mitochondria also were more fragmented in metastatic breast cancer cells that express higher levels of total and active Drp1 and less mitochondrial fusion protein 1 (Mfn1). Silencing Drp1 or overexpression of Mfn1 resulted in mitochondria elongation or clusters, respectively, and significantly suppressed metastatic abilities of breast cancer cells. In contrast, silencing Mfn proteins led to mitochondrial fragmentation and enhanced metastatic abilities of breast cancer cells. Interestingly, these manipulations of mitochondrial dynamics altered the subcellular distribution of mitochondria in breast cancer cells. For example, silencing Drp1 or overexpression of Mfn1 inhibited lamellipodia formation, a key step for cancer metastasis, and suppressed chemoattractant-induced recruitment of mitochondria to lamellipodial regions. Conversely, silencing Mfn proteins resulted in more cell spreading and lamellipodia formation, causing accumulation of more mitochondria in lamollipodia regions. More importantly, treatment with a mitochondrial uncoupling agent or ATP synthesis inhibitor reduced lamellipodia formation and decreased breast cancer cell migration and invasion, suggesting a functional importance of mitochondria in breast cancer metastasis. Together, our findings show a new role and mechanism for regulation of cancer cell migration and invasion by mitochondrial dynamics. Thus targeting dysregulated Drp1-dependent mitochondrial fission may provide a novel strategy for suppressing breast cancer metastasis.

Abstract 467: Mitochondrial dynamics regulates migration and invasion of breast cancer cells

Abstract Mitochondrial structure is dynamically regulated by fusion and fission events that are essential for maintaining physiological functions of cells. Although dysfunction of mitochondria has been implicated in tumorigenesis, little is known about the roles of mitochondrial dynamics in metastasis, the major cause of cancer death. In the present study, we found that mitochondria were more fragmented in metastatic breast cancer cells that express higher levels of mitochondrial fission protein dynamin-related protein 1 (Drp1) and less mitochondrial fusion protein 1 (Mfn1). Silence of Drp1 or overexpression of Mfn1 resulted in mitochondria elongation and significantly suppressed metastatic abilities of breast cancer cells. In contrast, silence of Mfn proteins led to mitochondrial fragmentation and enhanced metastatic abilities of breast cancer cells. Interestingly, these manipulations of mitochondrial dynamics had no significant effects on overall mitochondrial bioenergetics but altered the subcellular distribution of mitochondria in breast cancer cells. Silence of Drp1 or overexpression of Mfn1 inhibited lamellipodia formation, a key step for cancer metastasis, and suppressed chemoattractant-induced recruitment of mitochondria to lamellipodial regions. Conversely, silence of Mfn proteins caused accumulation of more mitochondria in lamollipodia regions with higher mitochondrial membrane potential, an indication of higher ATP synthesis. Treatment with the ATP uncoupling agent m-chlorophenylhydrazone (CCCP) or mitochondrial ATP synthesis inhibitor oligomycin A caused disappearance of lamellipodia and decreased breast cancer cell migration and invasion. Together, our findings show a new mechanism for regulation of cancer cell migration and invasion by mitochondrial dynamics. Thus targeting mitochondrial dynamics may provide a novel strategy for suppressing breast cancer metastasis. This work was supported by the National Institutes of Health (CA125661), State of Nebraska Research Fund (Grant LB595), the National Natural Science Foundation of China (31100973) and the National Basic Research Program (2010CB833701, 2012CB934003). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 467. doi:1538-7445.AM2012-467

Abstract 75: Electron transport chain-dependent oxygen consumption in metastatic breast cancer cells

Abstract Although mitochondrial ATP-production deficiency has been historically implicated to account for the Warburg effect or “aerobic” glycolysis in cancer cells, recent observations indicate the presence of functionally competent mitochondria in cancer cells. We hypothesized that a lung-metastatic breast cancer cell line with intact mitochondrial membrane potential would exhibit mitochondria-dependent oxygen consumption. A murine breast cancer cell line (4T1) was used to evaluate mitochondrial membrane potential by JC-1 fluorescence microscopy. Oxygen consumption by cancer cells in suspension was determined using a dissolved oxygen meter. Fluorescence microscopy of JC-1 red aggregates indicated the presence of highly polarized mitochondria in 4T1 cells, suggesting that these cells are capable of oxidative phosphorylation. Oxygen consumption rate of 4T1 cells suspended in 10 mM glucose-containing medium equilibrated with 21% oxygen (258 µM dissolved oxygen) at 25°C was 2.98 nmol/min/million cells (Control). Oxygen consumption was significantly enhanced by carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), a mitochondrial uncoupler (7.88 nmol/min/million cells, p<0.05 vs. Control). Myxothiazol (a respiratory chain complex III inhibitor) inhibited the oxygen consumption (0.75 nmol/min/million cells; p<0.05 vs. Control), indicating the presence of a functional electron transport chain. A nitric oxide donor also inhibited oxygen consumption (0.84 nmol/min/million cells; p<0.05 vs. Control). These data indicate the presence of oxidative phosphorylation-competent mitochondria in breast cancer cells. We conclude that cancer cells possess respiration-capable mitochondria and their “aerobic” glycolysis may not reflect a compensatory mechanism for ATP generation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 75.

Development of phenotypic indexes for the description of morphological injury in breast cancer cell mitochondria

e22055 Background: Mitochondriopathy has been recently rekindled as new cancer theory. We report on structural damage of breast-infiltrating ductal carcinoma (IDC) mitochondria characterised by reduced expression levels of the oxidative phosphorylation system (OXPHOS). Methods: Mitochondria from HMC-1 (human mammary carcinoma) and HMEC (human mammary epithelial cell) cultures, traced by Mitotracker, were assayed for OXPHOS expression levels using cryo-immunoelectron microscopy (CIEM) quantitative labelling and fluorescence immunolabelling on unfractionated HMC-1 and HEMC cells. Convolution degeneration was established by transmission electron microscopy (TEM). Twenty different cell sections for both HMC-1 and HEMC cells, including 65 and 72 mitochondria, respectively, were randomly recorded and quantitatively analyzed for the percentage of area occupied by intact cristae to provide a grading of mitochondrial damage (cristae loss index). Results: Depressed expression levels were detected for all HMC-1 OXPHOS complexes by CIEM. Normalized labelling density (HEMC/HMC-1), expressed as colloidal gold particles/mitochondrial area (ρ) provided the following values: 1.77 for the NADH-ubiquinone oxidoreductase complex I NDUFS3; 1.86 for the succinate- dehydrogenase complex II SDH-B protein; 1.63 for the ubiquinol cytochrome c reductase complex III UQCRC2; 4.88 and 1.58 for the cytochrome-oxidase complex IV (CO) subunit I and IV, respectively; 2.70 for the ATP-synthase complex V F1β protein. Fluorescence immunolabelling confirmed CIEM quantitative data. MitoTracker's co-staining showed altered membrane potential and permeability. Injury grading was categorised assigning three levels of morphological damage: i) severe, ii) moderate, iii) slight, corresponding to 0 % (6.2 % and 1.4 % for HMC-1 and HMEC, respectively), 1–50 % (21.5 % and 2.8 % for HMC-1 and HMEC, respectively) and 51–75 % (44.6 % and 15.3 % for HMC-1 and HMEC, respectively) of area occupied by intact cristae (p<0.0001, χ2Test). The entire HMC-1 mitochondrial damage resulted 3.7 times higher than that observed for HMEC cells (72.3HMC-1 %/19.5HMEC %). Conclusions: New phenotypic harm indexes for IDC cell mitochondria might provide new hallmarks in breast cancer cell biology. No significant financial relationships to disclose.

Integrated biophotonics approach for noninvasive and multiscale studies of biomolecular and cellular biophysics

In the crowded cellular milieu, biological processes require coordinated intermolecular interactions, conformational changes, and molecular transport that span a wide range of spatial and temporal scales. This complexity requires an integrated, noninvasive, multiscale experimental approach. Here, we develop a multimodal fluorescence microspectroscopy system, integrated on a single platform, to gain information about molecular interactions and their dynamics with high spatio-temporal resolution. To demonstrate the versatility of our experimental approach, we use rhodamine 123-labeled mitochondria in breast cancer cells (Hs578T), verified using differential interference contrast (DIC) and fluorescence (confocal and two-photon) microscopy, as a model system. We develop an assay to convert fluorescence intensity to actual concentrations in intact, individual living cells, which contrasts with conventional biochemical techniques that require cell lysates. In this assay, we employ two-photon fluorescence lifetime imaging microscopy (FLIM) to quantify the fluorescence quantum yield variations found within individual cells. Functionally driven changes in cell environment, molecular conformation, and rotational diffusion are investigated using fluorescence polarization anisotropy imaging. Moreover, we quantify translational diffusion and chemical kinetics of large molecular assemblies using fluorescence correlation spectroscopy. Our integrated approach can be applied to a wide range of molecular and cellular processes, such as receptor-mediated signaling and metabolic activation.

Oxidative metabolism dysfunction and morphological damage in breast cancer cell mitochondria

22200 Background: Mitochondria are cell energy and signalling source, generating ATP and regulating apoptosis. Altered mitochondrial functions have been identified as causative or contributing fact...

Alteration of expression levels of the oxidative phosphorylation system (OXPHOS) in breast cancer cell mitochondria

Mitochondria are dynamic intracellular organelles playing a central role in cell metabolism by generating ATP, through the oxidative phosphorylation system (OXPHOS). Altered mitochondrial functions have been identified as causative or contributing factors in some degenerative diseases and are becoming crucial to understanding cancer mechanisms. We report on distinct expression differences between mitochondria of normal and breast-infiltrating ductal carcinoma (IDC) cells. Mitochondria isolated from HMC (human mammary carcinoma) and HMEC (human mammary epithelial cell) cultures were assayed for expression levels of the multi-protein OXPHOS complexes using Western blot and densitometric analyses. Depressed expression levels were detected for all HMC OXPHOS complexes. Drastic signal reduction was observed for the succinate-dehydrogenase complex II iron-sulphur protein SDH-B (3.38%), while decreasing was reported for the NADH-ubiquinone oxidoreductase complex I Fe-S protein 3 NDUFS3 (32.78%) and the ubiquinol-cytochrome c reductase complex III protein 2 UQCRC2 (50.34%). A significant signal dropping was detected for the ATP-synthase complex V F(1)beta subunit (18.07%). For the cytochrome-oxidase complex IV (CO), near-depletion of the mitochondrial-encoded COI (4.37%) and no apparent variation of the COIV (97.26%) subunits were observed. CO and ATP-synthase were also assayed by cryo-immunoelectron microscopy (CIEM) on unfractionated HMC and HEMC cell mitochondria. COI and F(1)beta differential expression, invariance of COIV levels were corroborated, while HMC mitochondria morphology deterioration was highlighted. MitoTracker Red and fluorescence immunolabelling merging confirmed CIEM data. MitoTracker Red and Green co-staining showed mitochondria membrane property modulation. These data describe bioenergetic and phenotypic alterations of IDC cell mitochondria, possibly providing new cancer hallmarks.

Functional estrogen receptors in the mitochondria of breast cancer cells.

Steroid hormones have been reported to indirectly impact mitochondrial functions, attributed to nuclear receptor-induced production of proteins that localize in this cytoplasmic organelle. Here we show high-affinity estrogen receptors in the mitochondria of MCF-7 breast cancer cells and endothelial cells, compatible with classical estrogen receptors ERalpha and ERbeta. We report that in MCF-7, estrogen inhibits UV radiation-induced cytochrome C release, the decrease of the mitochondrial membrane potential, and apoptotic cell death. UV stimulated the formation of mitochondrial reactive oxygen species (mROS), and mROS were essential to inducing mitochondrial events of cell death. mROS mediated the UV activation of c-jun N-terminal kinase (JNK), and protein kinase C (PKC) delta, underlying the subsequent translocation of Bax to the mitochondria where oligomerization was promoted. E2 (estradiol) inhibited all these events, directly acting in mitochondria to inhibit mROS by rapidly up-regulating manganese superoxide dismutase activity. We implicate novel functions of ER in the mitochondria of breast cancer that lead to the survival of the tumor cells.

TAT-mediated protein transduction and targeted delivery of fusion proteins into mitochondria of breast cancer cells

The protein transduction domain (PTD) from the HIV-1 TAT protein has been widely utilized to deliver biologically active macromolecules, including full-length proteins, into a variety of cell types in vitro and in vivo. Without additional targeting signals, the intracellular localization of the proteins delivered in this fashion appears to be cytoplasmic, nuclear or, as recently reported, endosomal. In this study, we show that the presence of the mitochondrial targeting signal (MTS) from hMnSOD on the N-terminus of TAT-fusion proteins directs them into mitochondria of breast cancer cells. We generated and purified fusion proteins containing GFP (MTS-GFP-TAT) or Exonuclease III (MTS-ExoIII-TAT) from Escherichia coli. The results of Western blots of subcellular fractions and fluorescent microscopic analyses revealed efficient protein transduction and mitochondrial localization of the fusion proteins. Specific exonuclease activity was found in the mitochondrial extracts isolated from MTS-ExoIII-TAT transduced cells. This increased exonuclease activity reduced the repair of mtDNA damage following oxidative stress. This diminished mtDNA repair led to a decrease in survival of breast cancer cells. Thus, the present study demonstrates the applicability of this new approach for intramitochondrial targeting of TAT-fusion proteins capable of modulating mitochondrial function and cell survival.

The expression of Exonuclease III from E. coli in mitochondria of breast cancer cells diminishes mitochondrial DNA repair capacity and cell survival after oxidative stress

The ability to sensitize cancer cells to radiation would be highly beneficial for successful cancer treatment. One mode of action for ionizing radiation is the induction of cell death through infliction of extensive oxidative damage to cellular DNA, including mitochondrial DNA (mtDNA). The ability of cells to repair mtDNA and otherwise maintain the integrity of their mitochondria is vital for protection of the cells against oxidative damage. Because efficient repair of oxidative damage in mtDNA may play a crucial role in cancer cell resistance, interference with this repair process could be an effective way to achieve a radiation sensitive phenotype in otherwise resistant cancer cells. Successful repair of DNA is achieved through a precise and highly regulated multistep process. Expression of excessive amounts of one of the repair enzymes may cause an imbalance of the whole repair system and lead to the loss of repair efficiency. To study the effects of changing mtDNA repair capacity on overall cell survival following oxidative stress, we expressed a bacterial repair enzyme, Exonuclease III (ExoIII) containing the mitochondrial targeting signal of manganese superoxide dismutase, in a human malignant breast epithelial cell line, MDA-MB-231. Following transfection, specific exonuclease activity was found in mitochondrial extracts. In order to examine the effects on repair of oxidative damage in mtDNA, cells were exposed to the enzyme xanthine oxidase and its substrate hypoxanthine. mtDNA repair was evaluated using quantitative Southern blot analysis. The results revealed that cells expressing ExoIII in mitochondria are deficient in mtDNA repair when compared with control cells that express ExoIII without MTS. This diminished mtDNA repair capacity rendered MDA-MB-231 cells more sensitive to oxidative damage, which resulted in a decrease in their long-term survival following oxidative stress.