MicroRNA miR-24 enhances tumor invasion and metastasis by targeting PTPN9 and PTPRF to promote EGF signaling.

MicroRNAs are known to play regulatory roles in gene expression associated with cancer development. We analyzed levels of the microRNA miR-24 in patients with breast carcinoma and found that miR-24 was higher in breast carcinoma samples than in benign breast tissues. We generated constructs expressing miR-24 and studied its functions using both in vitro and in vivo techniques. We found that the ectopic expression of miR-24 promoted breast cancer cell invasion and migration. In vivo experiments in mice indicated that the expression of miR-24 enhanced tumor growth, invasion into local tissues, metastasis to lung tissues and decreased overall mouse survival. In the miR-24-expressing cells and tumors, EGFR was highly phosphorylated, whereas expression of the phosphatases tyrosine-protein phosphatase non-receptor type 9 (PTPN9) and receptor-type tyrosine-protein phosphatase F (PTPRF) were repressed. We confirmed that miR-24 could directly target both PTPN9 and PTPRF. Consistent with this, we found that the levels of phosphorylated epidermal growth factor receptor (pEGFR) were higher whereas the levels of PTPN9 and PTPRF were lower in the patients with metastatic breast carcinoma. Ectopic expression of PTPN9 and PTPRF decreased pEGFR levels, cell invasion, migration and tumor metastasis. Furthermore, we found that MMP2, MMP11, pErk, and ADAM15 were upregulated, whereas TIMP2 was downregulated; all of which supported the roles of miR-24 in tumor invasion and metastasis. Our results suggest that miR-24 plays a key role in breast cancer invasion and metastasis. miR-24 could potentially be a target for cancer intervention.

MnSOD and Cyclin B1 Coordinate a Mito-Checkpoint during Cell Cycle Response to Oxidative Stress.

Communication between the nucleus and mitochondrion could coordinate many cellular processes. While the mechanisms regulating this communication are not completely understood, we hypothesize that cell cycle checkpoint proteins coordinate the cross-talk between nuclear and mitochondrial functions following oxidative stress. Human normal skin fibroblasts, representative of the G2-phase, were irradiated with 6 Gy of ionizing radiation and assayed for cyclin B1 translocation, mitochondrial function, reactive oxygen species (ROS) levels, and cytotoxicity. In un-irradiated controls, cyclin B1 was found primarily in the nucleus of G2-cells. However, following irradiation, cyclin B1 was excluded from the nucleus and translocated to the cytoplasm and mitochondria. These observations were confirmed further by performing transmission electron microscopy and cell fractionation assays. Cyclin B1 was absent in mitochondria isolated from un-irradiated G2-cells and present in irradiated G2-cells. Radiation-induced translocation of cyclin B1 from the nucleus to the mitochondrion preceded changes in the activities of mitochondrial proteins, that included decreases in the activities of aconitase and the mitochondrial antioxidant enzyme, manganese superoxide dismutase (MnSOD), and increases in complex II activity. Changes in the activities of mito-proteins were followed by an increase in dihydroethidium (DHE) oxidation (indicative of increased superoxide levels) and loss of the mitochondrial membrane potential, events that preceded the restart of the stalled cell cycle and subsequently the loss in cell viability. Comparable results were also observed in un-irradiated control cells overexpressing mitochondria-targeted cyclin B1. These results indicate that MnSOD and cyclin B1 coordinate a cross-talk between nuclear and mitochondrial functions, to regulate a mito-checkpoint during the cell cycle response to oxidative stress.

Direct oxidation of 2',7'-dichlorodihydrofluorescein by pyocyanin and other redox-active compounds independent of reactive oxygen species production.

Formation of dichlorofluorescein (DCF), the fluorescent oxidation product of 2',7'-dichlorodihydrofluorescein (DCFH2), in cells loaded with the latter compound is often used to detect ROS formation. We previously found that exposure of DCFH2-loaded A549 cells to the Pseudomonas aeruginosa secretory product pyocyanin results in DCF formation, consistent with ROS production. However, since pyocyanin directly accepts electrons from NAD(P)H, we hypothesized that pyocyanin might directly oxidize DCFH2 to DCF without an ROS intermediate. Incubation of DCFH2 with pyocyanin rapidly resulted in DCF formation, the rate of which was proportional to the [pyocyanin] and was not inhibited by SOD or catalase. Phenazine methosulfate, a pyocyanin analog, was more effective than pyocyanin in generating DCF. Mitoxantrone and ametantrone also produced DCF. However, menadione, paraquat, plumbagin, streptonigrin, doxorubicin, daunorubicin, and 5-iminodaunorubicin did not. Pyocyanin, phenazine methosulfate, mitoxantrone, and ametantrone also oxidized dihydrofluorescein and 5- (and 6-) -carboxy-2',7'-dichlorodihydrofluorescein, whereas dihydrorhodamine was oxidized only by pyocyanin or phenazine methosulfate. Under aerobic conditions, the interaction of DCFH2 with pyocyanin or phenazine methosulfate (but not mitoxantrone or ametantrone) produced superoxide, as detected by spin trapping. Direct oxidation of the fluorescent probes needs to be controlled for when employing these compounds to assess ROS formation by biological systems exposed to redox active compounds.

MiR-93 enhances angiogenesis and metastasis by targeting LATS2.

Here we report that miR-93, a miRNA in the miR-106B~25 cluster, a paralog of the miR-17-92 cluster, was significantly upregulated in human breast carcinoma tissues. We stably expressed miR-93 in the MT-1 human breast carcinoma cell line and found that tumors formed by the miR-93 cells contained more blood vessels than those formed by the control cells. Co-culture experiments indicated that the MT-1 cells displayed a high activity of adhesion with endothelial cells and could form larger and more tube-like structures with endothelial cells. Lung metastasis assays were performed in a mouse metastatic model, and it was found that expression of miR-93 promoted tumor cell metastasis to lung tissue. In cell culture, expression of miR-93 enhanced cell survival and invasion. We examined the potential target that mediated miR-93's effects and found that the large tumor suppressor, homology 2 (LATS2) was a target of miR-93. Higher levels of LATS2 were associated with cell death in the tumor mass. Silencing LATS2 expression promoted cell survival, tube formation and invasion, while ectopic expression of LATS2 decreased cell survival and invasion. These findings demonstrated that miR-93 promoted tumor angiogenesis and metastasis by suppressing LATS2 expression. Our results suggest that the inhibition of miR-93 function may be a feasible approach to repress tumor metastasis.

Pseudomonas aeruginosa pyocyanin directly oxidizes glutathione and decreases its levels in airway epithelial cells.

Production of pyocyanin enhances Pseudomonas aeruginosa virulence. Many of pyocyanin's in vitro and in vivo cytotoxic effects on human cells appear to result from its ability to redox cycle. Pyocyanin directly accepts electrons from NADH or NADPH with subsequent electron transfer to oxygen, generating reactive oxygen species. Reduced glutathione (GSH) is an important cellular antioxidant, and it contributes to the regulation of redox-sensitive signaling systems. Using the human bronchial epithelial (HBE) and the A549 human type II alveolar epithelial cell lines, we tested the hypothesis that pyocyanin can deplete airway epithelial cells of GSH. Incubation of both cell types with pyocyanin led to a concentration-dependent loss of cellular GSH (up to 50%) and an increase in oxidized GSH (GSSG) in the HBE, but not A549 cells, at 24 h. An increase in total GSH, mostly as GSSG, was detected in the culture media, suggesting export of GSH or GSSG from the pyocyanin-exposed cells. Loss of GSH could be due to pyocyanin-induced H(2)O(2) formation. However, overexpression of catalase only partially prevented the pyocyanin-mediated decline in cellular GSH. Cell-free electron paramagnetic resonance studies revealed that pyocyanin directly oxidizes GSH, forming pyocyanin free radical and O(2)(-). Pyocyanin oxidized other thiol-containing compounds, cysteine and N-acetyl-cysteine, but not methionine. Thus GSH may enhance pyocyanin-induced cytotoxicity by functioning as an alternative source of reducing equivalents for pyocyanin redox cycling. Pyocyanin-mediated alterations in cellular GSH may alter epithelial cell functions by modulating redox sensitive signaling events.

Subcellular localization of Pseudomonas pyocyanin cytotoxicity in human lung epithelial cells.

The Pseudomonas aeruginosa secretory product pyocyanin damages lung epithelium, likely due to redox cycling of pyocyanin and resultant superoxide and H(2)O(2) generation. Subcellular site(s) of pyocyanin redox cycling and toxicity have not been well studied. Therefore, pyocyanin's effects on subcellular parameters in the A549 human type II alveolar epithelial cell line were examined. Confocal and electron microscopy studies suggested mitochondrial redox cycling of pyocyanin and extracellular H(2)O(2) release, respectively. Pyocyanin decreased mitochondrial and cytoplasmic aconitase activity, ATP levels, cellular reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide, and mitochondrial membrane potential. These effects were transient at low pyocyanin concentrations and were linked to apparent cell-mediated metabolism of pyocyanin. Overexpression of MnSOD, but not CuZnSOD or catalase, protected cellular aconitase, but not ATP, from pyocyanin-mediated depletion. This suggests that loss of aconitase activity is not responsible for ATP depletion. How pyocyanin leads to ATP depletion, the mechanism of cellular metabolism of pyocyanin, and the impact of mitochondrial pyocyanin redox cycling on other cellular events are important areas for future study.

The Pseudomonas secretory product pyocyanin inhibits catalase activity in human lung epithelial cells.

Pyocyanin, produced by Pseudomonas aeruginosa, has many deleterious effects on human cells that relate to its ability to generate reactive oxygen species (ROS), such as superoxide and hydrogen peroxide. Human cells possess several mechanisms to protect themselves from ROS, including manganese superoxide dismutase (MnSOD), copper zinc superoxide dismutase (CuZnSOD), and catalase. Given the link between pyocyanin-mediated epithelial cell injury and oxidative stress, we assessed pyocyanin's effect on MnSOD, CuZnSOD, and catalase levels in the A549 human alveolar epithelial cell line and in normal human bronchial epithelial cells. In both cell types, CuZnSOD and MnSOD were unaltered, but over 24 h pyocyanin significantly decreased cellular catalase activity and protein content. Pyocyanin also decreased catalase mRNA. Overexpression of MnSOD in A549 cells prevented pyocyanin-mediated loss of catalase protein, but catalase activity still declined. Furthermore, pyocyanin decreased catalase activity, but not protein, in A549 cells overexpressing human catalase. These data suggest a direct effect of pyocyanin on catalase activity. Addition of pyocyanin to catalase in a cell-free system also decreased catalase activity. Mammalian catalase binds four NADPH molecules, helping maintain enzyme activity. Spin-trapping data suggest that pyocyanin directly oxidizes this NADPH, producing superoxide. We conclude that pyocyanin may decrease cellular catalase activity via both transcriptional regulation and direct inactivation of the enzyme. Decreased cellular catalase activity and failure to augment MnSOD could contribute to pyocyanin-dependent cytotoxicity.