Organotypic and epidermal-dermal co-cultures of normal human keratinocytes and dermal cells: Regulation of transforming growth factor α, β1 and β2 mRNA levels

Abstract Epidermal-dermal cell-cell interactions are recognized to influence keratinocyte proliferation in vivo as well as in vitro . To study the underlying molecular mechanisms of epithelial-mesenchymal interactions epidermal-dermal cell co-cultures and organotypic cultures were used. Steady-state mRNA levels are described for transforming growth factors (TGF) α, β1 and β2, factors known to stimulate or inhibit the epidermal proliferation rate. In epidermal-dermal monolayer co-cultures TGF α hybridization signals were absent. TGF β1 mRNA was expressed in all cell types (keratinocytes, fibroblasts and microvascular endothelial cells), yet not regulated. In contrast, TGF β2 mRNA was significantly induced in mesenchymal cells when they were co-cultured with keratinocytes. In organotypic cultures epidermal proliferation is dependent on the presence of fibroblasts within the gel. TGF β1 was expressed at low levels in all cell types whereas TGF β2 transcripts were not detectable at all. TGF α mRNA was present in keratinocytes at high levels, independent of epidermal cell proliferation or added epidermal growth factor. These results indicate complex regulative mechanisms for TGF α, β1 and β2 at the mRNA level. However, post-transcriptional steps are involved in the activation of TGF β1 and 2 and also have to be considered.