KCl depolarization increases HIF-1 transcriptional activity via the calcium-independent pathway in SGC7901 gastric cancer cells.

BACKGROUND

Hypoxia-inducible factor 1alpha (HIF-1alpha) has been reported to be expressed aberrantly in gastric cancer cells. Stability and transactivation of HIF-1 were associated with the change of intracellular calcium. We hypothesized that KCl depolarization may modulate HIF-1 activity in gastric cancer cells through calcium involvement.

METHODS

HIF-1alpha expression and its transcriptional activity were determined in SGC7901 gastric cancer cells treated with KCl and/or CoCl2 under normoxia. KCl induced change in the intracellular free calcium concentration and its effect on HIF-1 activity was investigated subsequently.

RESULTS

Exposure of SGC7901 cells to KCl (50 mM) could induce HIF-1alpha expression and its nucleus accumulation under normoxic conditions, reaching the peak at 8 and 2 h, respectively. KCl could also induce transactivation of the HIF-1 reporter gene and its target gene VEGF secretion at 8 h. Further experiments confirmed that depolarization of SGC7901 cells with KCl caused an increase in intracellular free calcium concentration. Chelation of intracellular calcium by BAPTA [1,2-bis (2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid] induced HIF-1alpha accumulation and HIF-1 activity. However, elevation of cytosolic calcium level by ionomycin, a calcium ionophore, failed to induce HIF-1 transcriptional activity.

CONCLUSIONS

KCl depolarization would act through the calcium-independent pathway leading to enhanced HIF-1 transcriptional activity in gastric cancer cells.