Ouabain-Induced Alterations of the Apical Junctional Complex Involve α1 and β1 Na,K-ATPase Downregulation and ERK1/2 Activation Independent of Caveolae in Colorectal Cancer Cells

Abstract

Studies have reported that Na,K-ATPase interacts with E-cadherin to stabilize (AJs) and regulate the expression of claudins, the main proteins present in the tight junction (TJ) in epithelial cells containing caveolae. However, the role of this ATPase in the regulation of the AJ and TJ proteins in colorectal cancer cells as well as the molecular events underlying this event in a caveolae-independent system remain undefined. In the present study, we used ouabain, a classic drug known to inhibit Na,K-ATPase, and Caco-2 cells, which are a well-established human colorectal cancer model that does not exhibit caveolae. We demonstrated that ouabain treatment resulted in a reduction of the β1 Na,K-ATPase protein and cell redistribution of the AJ proteins E-cadherin and β-catenin, as well as the α1 Na,K-ATPase subunit. Furthermore, ouabain increased claudin-3 protein levels, impaired the TJ barrier function and increased cell viability and proliferation during the early stages of treatment. Additionally, the observed ouabain-induced events were dependent on the activation of ERK1/2 signaling; but in contrast to previous studies, this signaling cascade was caveolae-independent. In conclusion, our findings strongly suggest that α1 and β1 Na,K-ATPase downregulation and ERK1/2 activation induced by ouabain are interlinked events that play an important role during cell-cell adhesion loss, which is an important step during the tumor progression of colorectal carcinomas.

Na/K Pump and Beyond: Na/K-ATPase as a Modulator of Apoptosis and Autophagy

“…The N -terminus is located in the cytoplasm, whereas the C -terminus (glycosylated) is located in the extracellular medium [ 33 ]. This glycoprotein is considered regulatory and is involved in the stabilization of the enzymatic complex in the plasma membrane, the affinity of the pump for potassium and sodium ions, and adhesion processes through E -cadherin [ 39 , 40 , 41 , 42 ]. Three β-subunit isoforms (β1, β2 and β3) have been identified.…”

Targeting Na+/K+‐translocating adenosine triphosphatase in cancer treatment

“…The β ‐subunit of the sodium‐potassium pump dimerizes to a neighbouring β ‐subunit to enhance the cell‐to‐cell adhesion through β ‐ β bridges. As the expression of the β ‐subunit decreases, the protein expression of E‐cadherin also decreases . E‐cadherin is a vital protein in EMT and the prevention of cell invasion; the decreased activity in E‐cadherin allows for the promotion of β ‐catenin, which leads to EMT and cancer invasion and metastasis …”

“…As the expression of the b-subunit decreases, the protein expression of E-cadherin also decreases. 22 E-cadherin is a vital protein in EMT and the prevention of cell invasion; the decreased activity in Ecadherin allows for the promotion of b-catenin, which leads to EMT and cancer invasion and metastasis. 21 Snail, zinc finger protein SNAI1, is another key protein that acts as a regulator by suppressing E-cadherin.…”

On the Many Actions of Ouabain: Pro-Cystogenic Effects in Autosomal Dominant Polycystic Kidney Disease

“…Ouabain prevents the growth of medulloblastoma and glioblastoma cells and tumors [ 109 , 110 , 111 ]. Other effects of ouabain on cancer cells include the increase in proliferation of human colorectal Caco-2 cells, reduction of cell viability of adrenocortical cells, promotion of cell cycle arrest and apoptosis of liver HepG2 cells, and the decrease in growth of human pancreatic cells xenografted in nude mice [ 112 , 113 , 114 ].…”