Effect of calcium deprivation on the proliferation and ultrastructure of cultured human carcinoma cells.

The ability of cells to proliferate in the presence of low extracellular calcium levels has been proposed as a marker for malignancy. To further evaluate this marker, the effects of extracellular calcium deprivation on proliferation and morphology in culture were examined in eight tumorigenic lines derived from human cancers. With calcium reduced from 1.8 mM (HCM) to 0.02 mM (LCM), the colony-forming ability remained unchanged in five lines, increased in line SK-BR-3, decreased partially in line C-4II, and was reduced to the level of nontumorigenic cells (by approximately 90%) in line C-4I. This atypical response of C-4I could not be accounted for by the presence of a subpopulation of nontumorigenic cells. In contrast to nontumorigenic cell, sparsely seeded C-4I cells adapted to growth in LCM with time. Like nontumorigenic cells, C-4I cells grew efficiently in LCM if seeded at high densities, suggesting that conditioned medium compensated for calcium depletion. The four tumorigenic lines with the least organized growth patterns in HCM changed least in shape, intercellular associations, cell surface, and cytofilaments upon exposure to LCM. Line C-4I, which in HCM expressed characteristics of stratified squamous epithelium, underwent the most drastic changes, including a redistribution of tonofilaments from the peripheral cytoplasm and contact regions to a perinuclear position. The results support the concept that most tumorigenic lines have reduced calcium requirements for proliferation. Exceptions, as illustrated by the limited colony-forming ability in LCM of the C-4I cells, may be related to the retention of a requirement for growth factors.