Ouabain-Induced Cell Death and Survival. Role of α1-Na,K-ATPase-Mediated Signaling and [Na ⁺] _i/[K ⁺] _i-Dependent Gene Expression

Ouabain is of cardiotonic steroids (CTS) family that is plant-derived compounds and is known for many years as therapeutic and cytotoxic agents. They are specific inhibitors of Na,K-ATPase, the enzyme, which pumps Na⁺ and K⁺ across plasma membrane of animal cells. Treatment of cells by CTS affects various cellular functions connected with the maintenance of the transmembrane gradient of Na⁺ and K⁺. Numerous studies demonstrated that binding of CTS to Na,K-ATPase not only suppresses its activity but also induces some signal pathways. This review is focused on different mechanisms of two ouabain effects: their ability (1) to protect rodent cells from apoptosis through the expression of [Na⁺]_i-sensitive genes and (2) to trigger death of non-rodents cells (so-called «oncosis»), possessing combined markers of «classic» necrosis and «classic» apoptosis. Detailed study of oncosis demonstrated that the elevation of the [Na⁺]_i/[K⁺]_i ratio is not a sufficient for its triggering. Non-rodent cell death is determined by the characteristic property of "sensitive" to ouabain α1-subunit of Na,K-ATPase. In this case, ouabain binding leads to enzyme conformational changes triggering the activation of p38 mitogen-activated protein kinases (MAPK) signaling. The survival of rodent cells with ouabain-«resistant» α1-subunit is connected with another conformational transition induced by ouabain binding that results in the activation of ERK 1/2 signaling pathway.

Keywords: Na,K-ATPase; cardiotonic steroids; cell death; gene expression; intracellular Na+ and K+; intracellular signaling; ouabain.