The calmodulin content of normal and leukaemic lymphocytes

Calcium/calmodulin regulation of the proliferation of human epidermal keratinocytes, dermal fibroblasts and mouse B16 melanoma cells in culture

We have investigated the relationship between extracellular calcium, intracellular calmodulin and proliferation in normal keratinocytes. Keratinocyte proliferation and its sensitivity to calmodulin antagonists was compared with that of normal human dermal fibroblasts and neoplastic mouse B16 melanoma cells. Keratinocytes were similar to fibroblasts in showing reduced proliferation in low (0.15 mM) calcium medium and unlike B16 cells which continued to proliferate until calcium was reduced to submicromolar levels. Intracellular calmodulin was significantly higher in rapidly dividing keratinocytes in normal (1.15 mM) calcium medium than in slower dividing cells in low (0.15 mM) calcium. Fibroblasts and B16 cells maintained similar calmodulin levels in both low and normal calcium media. Calmodulin antagonists inhibited proliferation of all three cell types equally. Thus, keratinocyte calmodulin seems related to the proliferative state of the cell (unlike fibroblast calmodulin) and calmodulin antagonists may be of use in controlling the hyperproliferation of the psoriatic epidermis.

An extracellular role for calmodulin-like activity in cell proliferation

1. Addition of extracellular pure pig brain calmodulin was found to modulate DNA synthesis and cell proliferation in K562 human leukaemic lymphocytes. At lower cell densities calmodulin significantly stimulated [3H]thymidine uptake; at higher densities it decreased it. 2. A protein biochemically indistinguishable from calmodulin was detected in the cell-conditioned media of rapidly dividing K562 cells. The concentration of calmodulin-like activity found in the conditioned media of these and a range of other normal and neoplastic cells (250-1636 ng/ml) was of the same order as would stimulate DNA synthesis in subconfluent cells. 3. Amounts of extracellular calmodulin-like activity and immunoreactivity varied during cell growth from low to high density, a peak of extracellular calmodulin preceding DNA synthesis in synchronized K562 cells. Extracellular calmodulin concentrations did not correlate with the presence of lactate dehydrogenase in the medium. 4. Inhibition of extracellular calmodulin activity by calmodulin antagonist immobilized on agarose beads, or by antibody to calmodulin, significantly decreased DNA synthesis. 5. These data strongly suggest that calmodulin or a very closely related protein can influence mitosis through an extracellular mechanism.