alpha-ENaC is a functional element of the hypertonicity-induced cation channel in HepG2 cells and it mediates proliferation.
The molecular correlate of hypertonicity-induced cation channels (HICCs) and their role in proliferation vs. apoptosis is a matter of debate. We report in this paper that, in whole-cell patch-clamp recordings, hypertonic stress (340-->450 mosM) reversibly increased the Na(+) conductance of HepG2 cells from 0.8 to 5.8 nS. The effect was dose-dependently inhibited by flufenamate and amiloride, known blockers of HICCs, with some 50% efficiency at 300 muM. In parallel, both drugs decreased HepG2 cell proliferation [in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and with automatic cell counting]. Small interfering RNA (siRNA) silencing of the alpha-subunit of the epithelial Na(+) channel (ENaC) reduced hypertonicity-induced Na(+) currents to 60%, whereas the rate of HepG2 cell proliferation was approximately half of that of the control. Moreover, alpha-ENaC siRNA inhibited the regulatory volume increase of HepG2 cells (measured with scanning acoustic microscopy) by 60%. In florescence-activated cell sorting measurements, silencing of alpha-ENaC led to a significant decrease in the G1 and an increase in the G2/M phase of the cell cycle, whereas the S phase was not changing. Finally (determined by a caspase 3/7 assay), HICC inhibition by flufenamate and silencing of alpha-ENaC increased the rate of apoptosis in HepG2 cells. It is concluded that alpha-ENaC is one functional element of the HICC in HepG2 cells and that the channel is an important mediator of cell proliferation; likewise, HICC blockage shifts the system from a proliferative into a rather apoptotic one. This is the first report of a role of alpha-ENaC in cell proliferation.
Bondarava
Maryna
M
Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227, Dortmund, Germany.
Li
Tongju
T
Endl
Elmar
E
Wehner
Frank
F
D006528:Carcinoma, Hepatocellular / Q000473:pathology* / Q000503:physiopathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating; D014882:Water-Electrolyte Balance
D053503:Epithelial Sodium Channels