Expression of epidermal integrins in human organotypic keratinocyte cultures

In organotypic coculture of human epidermal keratinocytes (HEK) or follicular outer root sheath (ORS) cells with human dermal fibroblasts, a stratified epithelium develops which in many regards resembles interfollicular epidermis. The epithelium growing on type I collagen gels in the absence of a performed basement membrane itself produces only low or moderate amounts of laminin and collagen type IV, so that a well-structured basement membrane cannot be formed. This results in loose and insufficient anchoring of basal cells in the collagen gel, frequently leading to cleft formation at the junction. Because integrins are important receptors for cell-cell and cell-matrix adhesion of keratinocytes which under certain circumstances may also influence epidermal differentiation, we studied their expression under this culture condition which provides adhesional stress but leaves epidermal differentiation largely unaltered. The localization of integrins differed markedly from that in normal epidermis or normal outer root sheath since all integrin chains were polarized to the epithelium-collagen I interface. Thus, not only the alpha 6 and beta 4-chains showed preferential expression at the basal attachment site of keratinocytes as in normal epidermis, but also the alpha 2-, alpha 3-, beta 1-chains which in normal epidermis under "steady state" conditions appear primarily involved in cell-cell interaction of keratinocytes and are preferentially expressed at the lateral sides of their plasma membranes. Interestingly, the altered expression of integrins in organotypic cultures is not accompanied by significant disturbances in terminal differentiation.