Organotypic and epidermal-dermal co-cultures of normal human keratinocytes and dermal cells: Regulation of transforming growth factor alpha, beta1 and beta2 mRNA levels.

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) alpha, beta1 and beta2, factors known to stimulate or inhibit the epidermal proliferation rate. In epidermal-dermal monolayer co-cultures TGF alpha hybridization signals were absent. TGF beta1 mRNA was expressed in all cell types (keratinocytes, fibroblasts and microvascular endothelial cells), yet not regulated. In contrast, TGF beta2 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 beta1 was expressed at low levels in all cell types whereas TGF beta2 transcripts were not detectable at all. TGF alpha 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 alpha, beta1 and beta2 at the mRNA level. However, post-transcriptional steps are involved in the activation of TGF beta1 and 2 and also have to be considered.