Extra-cellular calcium concentration regulates the expression of skin calcium binding protein (SCaBP) in mouse keratinocyte cultures.

Abstract

We have recently demonstrated the presence of a calcium binding protein in rat skin (SCaBP) [6-8 , 10]. This protein is located in the cytosol of the basal layer [10]. SCaBP shares many of the properties of other intracellular calcium binding proteins. Thus it has a low molecular weight (12,000 daltons) is acidic in nature and has an amino-acid composition very similar to that of other calcium binding proteins. It has a high content of phenylalanine and there are striking homologies in the amino-acid sequence between this protein and others, particularly parvalbumin. Like parvalbumin each molecule of this protein binds two calcium ions with high affinity (107 M 1) [9]. There are however differences in the amino acid sequence and calcium binding properties of these proteins [9]. Because of these differences, antiserum raised against SCaBP does not crossreact with intestinal CaBP, calmodulin, parvalbumin or the $100 protein [6, 8-10] . The function of SCaBP is not known but it is found in the basal layer of all malpighian epithelia thus far examined [10]. Recently, it has been shown that the pattern of growth and differentiation of mouse epidermal cells in culture is shifted in favour of continued proliferation by reducing the calcium concentration of the medium below 0.1 mM. Under such conditions, the epidermal cells grow as monolayer, have a high mitotic rate and can be maintained in culture for prolonged periods. The cells nevertheless retain the potential to differentiate when incubated with higher calcium concentrations. Thus the extracellular calcium concentration regulates epidermal growth and differentiation in cell culture [5].