Antioxidants (Basel) 2026 Jun 10;156:. doi: 10.3390/antiox15060740.

Nitric Oxide, Reactive Oxygen Species, and Focal Adhesion Kinase Mediate Anoikis Resistance in A375 and SK-MEL-28 Human Melanoma Cells.

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Melanoma is a highly aggressive and invasive form of skin cancer that arises from the uncontrolled growth of melanocytes. It is characterized by early spread through the lymphatic system and metastasis. The success of metastasis is linked to the ability of melanoma and other cancer cells to resist anoikis, a type of cell death that occurs when cells lose their adhesion to the extracellular matrix. Redox signaling plays an essential role in anoikis resistance. The balance between intracellular levels of nitric oxide (NO) and the reactive oxygen species (ROS) O2- and H2O2 stimulate signaling pathways related to proliferation and survival or cell death. A375 and SK-MEL-28 human melanomas cell lines, representing primary melanoma and lymph node metastatic melanoma cells, respectively, under suspension and adherent culture conditions were used to investigate the redox regulation of anoikis resistance. Both cell lines express the three isoforms of nitric oxide synthases (NOS) and NADPH oxidase 4 (NOX4) as endogenous sources of NO and ROS, respectively. When A375 cells in suspension were treated with the pan-NOS inhibitor L-NAME, their viability decreased. The treatment resulted in a decrease in FAK phosphorylation at Tyr397 and in ERK 1/2 phosphorylation. The expression of FAK, ERK 1/2, β-actin, and α-tubulin were significantly reduced. Treatment with L-NAME led to an increase in the expression of the metalloprotease MMP-9. SK-MEL-28 cells in suspension and treated with the NOX4 inhibitor, GKT36901, exhibited reduced viability. This was accompanied by the inhibition of FAK phosphorylation at Tyr397, ERK 1/2 phosphorylation, and a reduction in the expression of FAK, ERK 1/2, β-actin, and α-tubulin, with a slight elevation in the expression of MMP-9. Migration and invasion were strongly inhibited in A375 cells upon treatment with L-NAME, while treatment with GKT36901 had a marginal effect on the migration and invasion capacities of SK-MEL-28 cells. In summary, melanoma cells employ nitrosative and oxidative stress to shield themselves from anoikis. Nitric oxide was essential for melanoma cells at the primary site for resisting anoikis, while H2O2 contributed to anoikis resistance in metastatic melanoma cells.

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