Dual effects of ouabain on the regulation of proliferation and apoptosis in human umbilical vein endothelial cells: involvement of Na(+)-K(+)-ATPase α-subunits and NF-κB.

PURPOSE: To elucidate the effect of ouabain on the regulation of proliferation and apoptosis of HUVECs and involvement of different Na(+)-K(+)-ATPase α-subunits and NF-κB.
METHODS: HUVECs were isolated by collagenase perfusion, and MTT assays and cell cycle analysis were performed to study proliferation. NF-κB expression and function were examined by immunohistochemical staining and western blotting. Na(+)-K(+)-ATPase activity was determined by measuring released ouabain inhibitable inorganic phosphate (Pi). The expression of different α-subunits was investigated by real RT-PCR, western blotting and cell immunofluorescence.
RESULTS: 0.3 nM ouabain treatment for 0.5 h triggered the proliferation of HUVECs, peaking at 1-2 h. At 1.8 nM for 0.5 h, ouabain induced an increase of cell proliferation for a short time, and then triggered a decrease after 1 h. Cell cycle analysis show that 37% of HUVECs were in G2/M phase of the cell cycle following incubation with 1.8 nM ouabain, compared with 18% with 0.3 nM ouabain. NF-κB activity was assessed by western blot analysis of IκB expression, which was significantly reduced with 0.3 nM ouabain treatment; there was no different between 1.8 nM ouabain treatment and untreated cells. Na(+)-K(+)-ATPase activity in HUVECs was markedly reduced after treatment with 0.3 nM and 1.8 nM ouabain. Real RT-PCR and western blotting indicated that Na(+)-K(+)-ATPase α1-subunit mRNA expression levels increased after 0.3 nM ouabain treatment and decreased after 1.8 nM ouabain treatment. However, α2- and α3-subunit mRNA decreased after 0.3 nM ouabain treatment and increased after 1.8 nM ouabain treatment.
CONCLUSION: Ouabain at different concentrations caused dual effects on proliferation and apoptosis in HUVECs.