A novel component of epidermal cell-matrix and cell-cell contacts: transmembrane protein type XIII collagen.

Type XIII collagen is a short chain collagen which has recently been shown to be a transmembrane protein. The purpose of this study was to elucidate the presence and localization of type XIII collagen in normal human skin and cultured keratinocytes. Expression of type XIII collagen was demonstrated in normal human skin and epidermis at the RNA level using reverse transcription followed by polymerase chain reaction and at the protein level using western blotting and indirect immunofluorescence labeling. Immunolabeling of epidermis revealed type XIII collagen both in the cell-cell contact sites and in the dermal-epidermal junction. In cultured keratinocytes type XIII collagen epitopes were detected in focal contacts and in intercellular contacts. The results of this study show very little colocalization of type XIII collagen and desmosomal components at the light microscopic level. Thus, these results suggest that type XIII collagen is unlikely to be a component of desmosomes. Instead, the punctate labeling pattern of type XIII collagen at the cell-cell contact sites and high degree of colocalization with E-cadherin suggests that type XIII collagen is very likely to be closely associated with adherens type junctions, and may, in fact, be a component of these junctions.