Multiple collagen gene expression with type III predominance in rat mucosal keratinocytes

Collagen synthesis in serially propagated cultures of rat mucosal keratinocytes (line RTK-I) was investigated. Analysis of biosynthetically labeled cell and media proteins retrieved after limited pepsin digestion revealed seven or eight collagen chains originating from four distinct collagens (types I, III, IV, V). Type III collagen was identified as the predominant species based on its electrophoretic and chromatographic behavior in the reduced and unreduced states, on the peptide pattern generated by limited cleavage with CNBr and with trypsin, and on the immunofluorescent detection of intracellular, collagen type III-reactive material. Evidence for the synthesis of two type IV collagen chains (155 k and 160 k after limited pepsin digestion) was provided by immunofluorescent and electrophoretic studies. Type V collagen was revealed by immunofluorescence, and two, possibly three, component chains were resolved in native type V collagen isolated from the harvest medium. Type I collagen, identified by comigration with authentic carriers, was a constant but quantitatively variable synthetic product. This study provides evidence that keratinocytes produce collagens normally found in mesenchymal matrices (type I and III) in addition to collagens characteristic of basement membranes (type IV) and of pericellular structures (type V). These findings reveal a hitherto unrecognized complexity and heterogeneity of the collagens synthesized by a highly differentiated epithelial cell type.