Effects of redox modulation on quiescin/sulfhydryl oxidase activity of melanoma cells.

Secreted quiescin/sulfhydryl oxidase (QSOX) is overexpressed in many tumor cell lines, including melanoma, and is usually associated with a pro-invasive phenotype. Our previous work described that B16-F10 cells enter in a quiescent state as a protective mechanism against damage generated by reactive oxygen species (ROS) during melanogenesis stimulation. Our present results show that QSOX activity was two-fold higher in cells with stimulated melanogenesis when compared to control cells. Considering that glutathione (GSH) is one of the main factor responsible for controlling redox homeostasis in cells, this work also aimed to investigate the relationship between QSOX activity, GSH levels and melanogenesis stimulation in B16-F10 murine melanoma cell line. The redox homeostasis was impaired by treating cells with GSH in excess or depleting its intracellular levels through BSO treatment. Interestingly, GSH-depleted cells without stimulation of melanogenesis kept high levels of viability, suggesting a possible adaptive mechanism of survival even under low GSH levels. They also showed lower extracellular activity of QSOX, and higher QSOX intracellular immunostaining, suggesting that this enzyme was less excreted from cells and corroborating with a diminished extracellular QSOX activity. On the other hand, cells under melanogenesis stimulation showed a lower GSH/GSSG ratio (8:1) in comparison with control (non-stimulated) cells (20:1), indicating a pro-oxidative state after stimulation. This was accompanied by decreased cell viability after GSH-depletion, no alterations in QSOX extracellular activity, but higher QSOX nucleic immunostaining. We suggest that melanogenesis stimulation and redox impairment caused by GSH-depletion enhanced the oxidative stress in these cells, contributing to additional alterations of its metabolic adaptive response.

The metabolic response of Araucaria angustifolia embryogenic cells to heat stress is associated with their maturation potential.

Araucaria angustifolia is a critically endangered species and its distribution can be affected by an increase in temperature. In this study, we evaluated the effects of heat stress (30°C) on Araucaria angustifolia cell lines responsive (SE1) and non-responsive (SE6) to the development of somatic embryos. The viability of both cell lines was reduced by heat stress and mitochondria were the organelles most affected. Heat stress for 24h increased the reactive oxygen species (ROS) levels in SE1 cells, followed by a reduction at 48 and 72h. In SE6 cells, an increase occurred after 24 and 48h of stress, returning to control levels at 72h. H2 O2 levels were increased after 24h for both SE1 and SE6 cells, being higher for SE6. Interestingly, at 48 and 72h, H2 O2 levels decreased in SE1 cells, while in SE6, the values returned to the control levels. The respiration of SE6 cells in the presence of oxidisable substrates was inhibited by heat stress, in agreement with the high lipid peroxidation levels. The AaSERK1 gene was identified in both cultures, with greater expression in the SE1 line. Heat stress for 24 and 48h increased gene expression only in this cell line. The activity of peroxidase, superoxide dismutase and enzymes of the glutathione/ascorbate cycle was increased in both cell lines subjected to heat stress. Catalase activity was increased only in SE6 cells at 72h of exposure. These results show that responsive SE1 cells can modulate ROS levels more efficiently than SE6 when these cells are stressed by heat. This ability may be related to the maturation capacity of these cells.