The Ca2+/Mn2+-transporting SPCA2 pump is regulated by oxygen and cell density in colon cancer cells

The mammalian SPCA1 and SPCA2 ATPases localize in membranes of the secretory pathway and transport ions of Ca2+ and Mn2+. The role of tissue-specific SPCA2 isoform, highly expressed in lungs, mammary gland and gastrointestinal tract, is poorly understood. To elucidate the function of SPCA2, we studied human colon cancer HCT116 cells, grown under ambient and decreased O-2 levels. We found that in contrast with other Ca2+-ATPase isoforms the expression of SPCA2 was up-regulated under hypoxia (3% O-2), in both adherent (2D) and spheroid (3D) cultures. In spheroids, experiencing lowest O-2 levels (30-50 mu M, measured by phosphorescence lifetime imaging microscopy), we observed lower staining with reactive oxygen species (ROS)-specific fluorescent probe, which correlated with increased SPCA2. However, SPCA2 expression was up-regulated in cells exposed to reactive oxygen and nitrogen species donors, and when grown at higher density. We noticed that the culture exposed to hypoxia showed overall increase in S phase-positive cells and hypothesized that SPCA2 up-regulation under hypoxia can be linked to Mn2+-dependent cell cycle arrest. Consequently, we found that SPCA2-transfected cells display a higher number of cells entering S phase. Altogether, our results point at the important role of SPCA2 in regulation of cell cycle in cancer cells.