Expression

Ion channels have emerged as new targets for cancer treatment. Here we studied the expression of the alkali-activated potassium channel KCNK5 and the big conductance calcium-activated potassium channel (Slo1) in breast cancer cells.

KCNK5 was found to be expressed in different breast cancer cell lines. Confirming previous results in a microarray study, we found upregulation of KCNK5 by estrogen (E2) in the estrogen receptor a positive breast cancer cells MCF-7 and T47D. This upregulation was correlated with an increase in the amplitude of alkali-activated currents, as assessed by electrophysiology. While confocal microscopy suggested that most of the channels are intracellular in both cell lines, the increase in the currents showed that there are more active channels in the membrane of cells treated with E2. Clofilium, an unspecific blocker of KCNK5, decreased the proliferation and induced apoptosis in breast cancer and non-tumorigenic cells. Clofilium also induced changes in the actin cytoskeleton of T47D cells, characterized by blebbing, and the extension of actin-rich processes. These changes were dependent on extracellular pH, and were not observed in non-tumorigenic and other breast cancer cells. In a more specific manipulation, siRNAs targeting KCNK5 decreased the proliferation of breast cancer and non-tumorigenic cells, and reduced the effect of E2 on the proliferation of T47D cells. KCNK5 siRNAs also reduced the effect of clofilium on the cytoskeleton and potentiated the effects of clofilium on cell viability in T47D cells.

Another channel that has been described in breast cancer cells is Slo1. We observed the expression of Slo1 in different breast cancer cell lines using Western blots and immunofluorescence. On the other hand, using electrophysiological recordings and pharmacological modulators of Slo1, we did not find evidence of the presence of active Slo1 channels in the plasma membrane of most of the cells studied.

We conclude that, while KCNK5 is required for the normal proliferation of breast cancer cells and for the maintenance of the actin cytoskeleton, functional Slo1 channels are absent in the membrane of most breast cancer cells and are less likely to be an effective target for breast cancer treatment.