Proliferation in low calcium medium as a marker for malignancy: an apparent exception among human carcinoma cells

The proliferative capacity of 2 human carcinoma cell lines, C-4I and C-4II which have a reduced ability to form colonies in low calcium (0.02 mM) medium, was compared with that of other tumor cells (C-33) which were characteristically calcium-independent, and with non-tumorigenic cells. In low calcium medium the C-4 lines continued to incorporate [3H]thymidine but few cells reached metaphase. Under the same conditions DNA synthesis of non-tumorigenic cells was reduced, while C-33 cells proliferated as efficiently as in standard medium. These results indicate the possibility of multiple sites for proliferation arrest in low calcium medium, and the necessity to follow-up colony-forming assays with [3H]thymidine incorporation tests when proliferation in low calcium medium is used as a marker for malignancy.