Biochemical characterization of collagens synthesized by intestinal epithelial cell cultures.

Rat intestinal epithelial cells in culture synthesize and secrete several different collagens as identified by biochemical and ultrastructural criteria. These collagens were labeled with [U-14C]proline, separated by DEAE- and CM-cellulose chromatography, and at least four different collagen chains were identified. Two of them, present almost exclusively as fully processed collagens, were alpha 1(I) and alpha 2 chains. The presence of a large excess of alpha 1 (I) chains over the normal ratio for type I collagen indicated that both type I collagen [alpha 1(I)]2 alpha 2 and [alpha 1(I)]3 or type I trimer were present both in the culture medium and in the extracellular matrix. The labeled alpha 1(I) chain had a CNBr peptide pattern superimposable on that of a standard alpha 1(I) chain from rat skin, but the intact radiolabeled chain differed from the standard in its migration on sodium dodecyl sulfate gels and elution position on CM-cellulose column and had a much higher hydroxylysine content. The other two collagen chains were present in the culture medium exclusively as partially processed procollagens. They constituted 60 to 70% of the collagenous proteins and had features corresponding to none of the known collagen types. They were separated by CM-cellulose chromatography and further characterized. Both contained interchain disulfide bonds in the pepsin-resistant portion of the molecule and, after pepsin digestion, eluted from CM-cellulose at lower salt concentrations than standard alpha 1(I) chain. One of them was characterized by a low hydroxyproline content and a high hydroxylysine content, with all the hydroxylysine present as glycosylgalactosyl derivative. The CNBr peptide patterns of these two unknown chains differed from each other, and did not correspond to those of any standard collagen chain examined. They may represent new collagen types specifically present in the intestinal basement membrane.