Overexpression of TNFα induces premature senescence and mitochondrial dysfunctions in melanoma cells in vitro

Background: Tumor necrosis factor alpha (TNFα) is a pleiotropic cytokine with both anti-tumorigenic and pro-tumorigenic activity, affecting tumor cell biology, balance between cell survival and death. Final effect of TNFα is dependent on type of malignant cells, with potential to arrest cancer progression and change the tumor microenvironment to the tumor suppressive conditions.

Methods: In order to investigate diverse changes in cellular and molecular biology upon the TNFα influence in vitro, we engineered malignant melanoma cell line A375 stably expressing this cytokine.

Results: Under the TNFα overexpression, significant upregulation of proinflammatory cytokine IL6 gene was observed. Melanoma cells A375/hTNFα displayed increased autophagy on day 3, followed by premature senescence on day 6. Both processes seem to be interconnected, following earlier apoptosis induction and deregulation of mitochondrial functions. We documented altered mitochondrial status, lowered ATP production, lowered mitochondrial mass, and changes in mitochondrial morphology. Overexpression of TNFα was not linked with significant affection of the subpopulation of cancer stem-like cells (CSCs) in vitro. However, we could demonstrate a decrease by up to 50% of aldehyde dehydrogenase (ALDH) activity, which is linked to the stemness phenotype.

Conclusions: Our in vitro study of direct TNFα influence provides complex report of cellular processes initiated in malignant melanoma cells. Despite high overexpression of TNFα protein in engineered tumor cells, the subpopulation of CSCs responsible for tumor growth initiation remained unaffected, and probably is not directly linked with the loss of tumorigenic potential.