Increased calmodulin levels in psoriasis and low Ca++ regulated mouse epidermal keratinocyte cultures

Calcium has been shown to regulate the proliferation of epidermal keratinocytes in vitro. We became interested in the role of the calcium binding protein, calmodulin, in hyperproliferative, low calcium regulated keratinocytes in vitro and in the in vivo hyperproliferative state, psoriasis. Calmodulin levels were measured by radioimmune assay in neonatal mouse keratinocytes grown in 0.02 mM calcium (hyperproliferative) and 1.2 mM calcium (normal) media, and in cells that had been grown in low calcium medium and then switched to normal calcium. On a whole culture basis the normal cells had more calmodulin than the low calcium cells. However, when low calcium monolayers were compared to the normal basal monolayer, the low calcium hyperproliferative cells had more calmodulin. Cells that were switched from 0.02 mM calcium to 1.2 mM calcium showed increasing calmodulin levels over time. Psoriatic plaques contained 2-3 times more calmodulin than the skin of normal controls when examined on a per micrograms of DNA, per micrograms of protein, and per gram of wet weight basis. Adjacent uninvolved psoriatic skin also had significantly elevated calmodulin levels in all data bases except per microgram of protein/cm2. These data suggest that increased calmodulin levels are associated with epidermal hyperproliferation and/or with the state of differentiation.