Posttranslational modifications in the biosynthesis of type IV collagen by a human tumor cell line

Abstract

Factors responsible for the high extent of intracellular posttranslational modifications in type IV collagens were studied in a cultured human tumor cell line, HT-1080 [neoplastic fibrosarcoma]. These cells do not synthesize any detectable amounts of interstitial collagens but produce type IV collagen at a high rate, corresponding to about 1/3 of the production of interstitial collagens by cultured human skin fibroblasts. Prolyl 4-hydroxylase activity was lower in the HT-1080 cells than in human skin fibroblasts with a rough correlation between this enzyme activity and the rate of 4-hydroxyproline formation in these 2 cell types. The differing extents of the respective modifications could largely be explained by differences in the activities of lysyl hydroxylase and the hydroxylysyl glycosyltransferases between the 2 cell types. No difference was found in prolyl 3-hydroxylase activity even though the extent of 3-hydroxylation of proline residues was about 6-fold in the type IV collagens. In experiments where the HT-1080 cells were studied in suspension, a lag of about 100 min was found before the secretion of type IV collagen from the cells became linear. Pulse-chase experiments in suspension indicated that all the intracellular enzyme reactions proceeded for about 40 min, presumably due to the slow triple-helix formation in type IV collagens. This slow helix formation apparently contributed to the high extent of all the intracellular modifications but was not a major factor.