Differential expression of the HsKin17 protein during differentiation of in vitro reconstructed human skin

In eukaryotic cells, various proteins homologous to the E. coli RecA protein are involved in the elimination of DNA damage. These proteins contribute to the repair of double-strand breaks and to genetic recombination. The mouse Kin17 protein is recognised by antibodies directed against the RecA protein. Kin17 has a zinc-finger domain allowing binding to curved DNA stretching over illegitimate recombination junctions. In the present study, we identified the human counterpart of the mouse Kin17 protein (named HsKin17) in skin cells. We employed an in vitro reconstructed skin model composed of an epidermal sheath lying on a dermal matrix with human fibroblasts embedded in rat collagen type I. The maturation programme (proliferation versus differentiation) of keratinocytes was highly dependent on stromal cells. Immunohistochemical staining of frozen sections obtained from skin specimens was monitored by an interactive laser cytometer. In this way we analysed protein levels in both dermal and epidermal compartments. After having characterised the epithelium, we focused our attention on HsKin17 expression. We detected HsKin17 in human keratinocytes. HsKin17 protein levels increased in proliferating epithelial keratinocytes after 7 days of culture. After 2 weeks of culture, epidermal sheaths acquired most of the differentiated features of mature epithelium. At this time, HsKin17 protein dropped below measurable levels in the stratum corneum, and diminished in nucleated cells. This study showed that HsKin17 is expressed in human reconstructed epithelium under conditions of hyperproliferation.