Regulation of sarco/endoplasmic and plasma membrane calcium ATPase gene expression by calcium in cultured human lens epithelial cells.

Since Ca(2+)-ATPase is a major determinant of calcium homeostasis in the lens, we examined the expression of Ca(2+)-ATPase by calcium. An immortalized human lens epithelial cell line, HLE B-3, was treated with thapsigargin to inhibit sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) releasing calcium from intracellular stores. Isoforms of the plasma membrane Ca(2+)-ATPase (PMCA) and SERCA were quantified by Western blot and quantitative real time reverse transcription polymerase chain reaction. We showed that both PMCA1 and SERCA3 isoform protein and mRNA are upregulated two- to three-fold in thapsigargin-treated HLE B-3 cells in a time and dose-dependent manner. Thapsigargin did not change the protein or mRNA levels of PMCA2, 3, 4 or SERCA2b. Considering the harmful effects of increased intracellular calcium levels, the upregulation of both SERCA and PMCA pumps suggests it is a compensatory mechanism to restore the calcium concentration to the physiological resting level.