Migration and invasion of drug-resistant lung adenocarcinoma cells are dependent on mitochondrial activity

A small proportion of cancer cells have stem-cell-like properties, are resistant to standard therapy and are associated with a poor prognosis. The metabolism of such drug-resistant cells differs from that of nearby non-resistant cells. In this study, the metabolism of drug-resistant lung adenocarcinoma cells was investigated. The expression of genes associated with oxidative phosphorylation in the mitochondrial membrane was negatively correlated with the prognosis of lung adenocarcinoma. Because the mitochondrial membrane potential (MMP) reflects the functional status of mitochondria and metastasis is the principal cause of death due to cancer, the relationship between MMP and metastasis was evaluated. Cells with a higher MMP exhibited greater migration and invasion than those with a lower MMP. Cells that survived treatment with cisplatin, a standard chemotherapeutic drug for lung adenocarcinoma, exhibited increased MMP and enhanced migration and invasion compared with parental cells. Consistent with these findings, inhibition of mitochondrial activity significantly impeded the migration and invasion of cisplatin-resistant cells. RNA-sequencing analysis indicated that the expression of mitochondrial complex genes was upregulated in cisplatin-resistant cells. These results suggested that drug-resistant cells have a greater MMP and that inhibition of mitochondrial activity could be used to prevent metastasis of drug-resistant lung adenocarcinoma cells.

Aldehyde dehydrogenase is used by cancer cells for energy metabolism

We found that non-small-cell lung cancer (NSCLC) cells express high levels of multiple aldehyde dehydrogenase (ALDH) isoforms via an informatics analysis of metabolic enzymes in NSCLC and immunohistochemical staining of NSCLC clinical tumor samples. Using a multiple reaction-monitoring mass spectrometry analysis, we found that multiple ALDH isozymes were generally abundant in NSCLC cells compared with their levels in normal IMR-90 human lung cells. As a result of the catalytic reaction mediated by ALDH, NADH is produced as a by-product from the conversion of aldehyde to carboxylic acid. We hypothesized that the NADH produced by ALDH may be a reliable energy source for ATP production in NSCLC. This study revealed that NADH production by ALDH contributes significantly to ATP production in NSCLC. Furthermore, gossypol, a pan-ALDH inhibitor, markedly reduced the level of ATP. Gossypol combined with phenformin synergistically reduced the ATP levels, which efficiently induced cell death following cell cycle arrest.

Down syndrome critical region 1 enhances the proteolytic cleavage of calcineurin

Down syndrome critical region 1 (DSCR1), an oxidative stress-response gene, interacts with calcineurin and represses its phosphatase activity. Recently it was shown that hydrogen peroxide inactivates calcineurin by proteolytic cleavage. Based on these facts, we investigated whether oxidative stress affects DSCR1-mediated inactivation of calcineurin. We determined that overexpression of DSCR1 leads to increased proteolytic cleavage of calcineurin. Convertsely, knockdown of DSCR1 abolished calcineurin cleavage upon treatment with hydrogen peroxide. The PXIIXT motif in the COOH-terminus of DSCR1 is responsible for both binding and cleavage of calcineurin. The knockdown of overexpressed DSCR1 in DS fibroblast cells also abrogated calcineurin proteolysis by hydrogen peroxide. These results suggest that DSCR1 has the ability to inactivate calcineurin by inducing proteolytic cleavage of calcineurin upon oxidative stress.