Many of the small, acidic, calcium binding S100 proteins present in the brain specifically map different anatomical regions and cell types and their overexpression is implicated in pathological changes. Similarly to other members of the S100 protein family, calcyclin (S100A6) is expressed in a cell specific manner and is found in subpopulations of neurons and astrocytes in the brain and in epithelial cells and fibroblasts. In this article we review data concerning the cell specific expression of S100 protein genes and present experimental results on the regulation of the calcyclin gene. We have performed promoter deletion studies to locate regions within the calcyclin gene promoter responsible for transcriptional regulation. The results demonstrate that the 3 kb long calcyclin gene promoter lacks a cell specific cis-acting element and drives the expression of the reporter gene also in cells that do not express endogenous calcyclin. The expression is modulated by positive and negative elements acting uniformly in the four different cell lines studied. The first intron of the calcyclin gene was found to have an inhibitory influence on expression regardless of cell type. It was also shown that calcyclin expression can be induced in calcyclin-negative cells by treatment with 5-azacytidine suggesting the involvement of gene methylation in its cell specific expression. The results are discussed in light of the data available on the regulation of other S100 genes.
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