Collagen synthesis by human amniotic fluid cells in culture: characterization of a procollagen with three identical proα1(I) chains

Abstract

Second trimester human amniotic fluid [AF] cells synthesize and secrete a variety of collagenous proteins in culture. F cells (amniotic fluid fibroblasts) are the most active biosynthetically and synthesize predominantly type I with smaller amounts of type III procollagen. Epithelioid AF cells (the predominating clonable cell type) synthesize a type IV-like procollagen and a procollagen with 3 identical pro.alpha. chains, structurally and immunologically related to the pro.alpha.1 chains of type I procollagen. The latter procollagen, when cleaved with pepsin and denatured, yields a single non-disulfide-bonded .alpha. chain that migrates more slowly than F cell or human skin .alpha.1(I) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis but coelutes with these chains from carboxymethylcellulose. The major cyanogen bromide produced peptides demonstrate a similar behavior relative to peptides derived from .alpha.1(I). The collagen is characterized by an increased solubility at neutral pH and high ionic strength, relative to type I collagen. The amino acid composition of the pepsin-resistant .alpha. chain is essentially identical with that of human .alpha.1(I), except for marked increases in the content of 3- and 4-hydroxyproline and hydroxylysine. These increased posttranslational modifications apparently are responsible for the unusually slow migration of this collagen and its cyanogen bromide peptides on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The procollagen has been assigned the chain composition (pro.alpha.1(I)]3. Like type I procollagen, [pro.alpha.1(I)]3 undergoes a time-dependent conversion in the medium and cell layer to procollagen intermediates and .alpha. chains. The production of [pro.alpha.1(I)]3 probably reflects the state of differentiation and/or embryologic derivation of AF cells rather than a characteristic of the fetal phenotype, since F cells do not synthesize significant amounts of the procollagen.