Up-regulation of mitochondrial antioxidation signals in ovarian cancer cells with aggressive biologic behavior

Objective: Recently, a high frequency of mutations in mitochondrial DNA (mtDNA) has been detected in ovarian cancer. To explore the alterations of proteins in mitochondria in ovarian cancer, a pair of human ovarian carcinoma cell lines (SKOV3/SKOV3.ip1) with different metastatic potentials was examined. Methods: Cancer cells SKOV3.ip1 were derived from the ascitic tumor cells of nude mice bearing a tumor of ovarian cancer cells SKOV3. SKOV3.ip1 exhibited a higher degree of migration potential than its paired cell line SKOV3. The proteins in the mitochondria of these two cells were isolated and separated by 2-D gel electrophoresis. The differently expressed proteins were extracted and identified using matrix assisted laser desorption ionisation/time-of-flight/time-of-flight (MALDI-TOF/TOF), and finally a selected protein candidate was further investigated by immunohistochemistry (IHC) method in nude mice bearing tumor tissues of these two cells. Results: A total of 35 spots with different expressions were identified between the two cells using 2D-polyacrylamide gel electrophoresis (PAGE) approach. Among them, 17 spots were detected only in either SKOV3 or SKOV3.ip1 cells. Eighteen spots expressed different levels, with as much as a three-fold difference between the two cells. Twenty spots were analyzed using MALDI-TOF/TOF, and 11 of them were identified successfully; four were known to be located in mitochondria, including superoxide dismutase 2 (SOD2), fumarate hydratase (FH), mitochondrial ribosomal protein L38 (MRPL38), and mRNA turnover 4 homolog (MRTO4). An increased staining of SOD2 was observed in SKOV3.ip1 over that of SKOV3 in IHC analysis. Conclusions: Our results indicate that the enhanced antioxidation and metabolic potentials of ovarian cancer cells might contribute to their aggressive and metastatic behaviors. The underlying mechanism warrants further study

Post–Cytochrome c Protection from Apoptosis Conferred by a MAPK Pathway in Xenopus Egg Extracts

In response to many different apoptotic stimuli, cytochrome c is released from the intermembrane space of the mitochondria into the cytoplasm, where it serves as a cofactor in the activation of procaspase 9. Inhibition of this process can occur either by preventing cytochrome c release or by blocking caspase activation or activity. Experiments involving in vitro reconstitution of apoptosis in cell-free extracts of Xenopus laevis eggs have suggested that extracts arrested in interphase are susceptible to an endogenous apoptotic program leading to caspase activation, whereas extracts arrested in meiotic metaphase are not. We report here that Mos/MEK/MAPK pathways active in M phase–arrested eggs are responsible for rendering them refractory to apoptosis. Interestingly, M phase–arrested extracts are competent to release cytochrome c, yet still do not activate caspases. Concomitantly, we have also demonstrated that recombinant Mos, MEK, and ERK are sufficient to block cytochrome c–dependent caspase activation in purified Xenopus cytosol, which lacks both transcription and translation. These data indicate that the MAP kinase pathway can target and inhibit post–cytochrome c release apoptotic events in the absence of new mRNA/protein synthesis and that this biochemical pathway is responsible for the apoptotic inhibition observed in meiotic X. laevis egg extracts