TRPM7 is involved in acid-induced necrotic cell death in a manner sensitive to progesterone in human cervical cancer cells

Because intravaginal pH is strongly acidic, it is important to investigate the effects of acidosis on cervical cancer cells. Recently, in response to strong acidosis, human cervical cancer HeLa cells were shown to exhibit necrosis after showing persistent cell swelling induced by Cl- influx. Since cation influx should be accompanied with Cl- influx to drive water inflow causing cell swelling, we here studied on the nature of acidotoxic cation conductance. The mRNA/protein expression was assessed by RT-PCR and Western blotting. Ionic currents were measured by patch-clamping techniques. Cell counting/viability and colorimetric assays were applied to assess proliferation rate and caspase 3/7 activity, respectively. Cell volume and size were measured by electronic sizing and video-microscopic measurements, respectively. Acid exposure enhanced TRPM7 activity endogenously expressed in HeLa cells and exogenously overexpressed in HEK293T cells. Gene silencing of TRPM7 abolished acid-induced cell swelling and necrosis but rather induced activation of apoptotic caspase 3/7 in HeLa cells. Overexpression with the pore charge-neutralizing D1054A mutant suppressed acid-enhanced cation currents, acid-induced cell swelling, and acidotoxic necrosis in HEK293T cells. Progesterone treatment was surprisingly found to suppress molecular and functional expression of TRPM7 and cell proliferation in HeLa cells. Furthermore, in the progesterone-treated cells, acid exposure did not induce persistent cell swelling followed by necrosis but induced persistent cell shrinkage and apoptotic cell death. These results indicate that in the human cervical cancer cells, TRPM7 is essentially involved in acidotoxic necrotic cell death, and progesterone inhibits TRPM7 expression thereby inhibiting acidotoxic necrosis by switching to apoptosis.