Mononuclear cell supernatants inhibit prolyl hydroxylation.

The effect of phytohemagglutinin(PHA)-activated human peripheral mononuclear cell supernatant (AS) on collagen production by human fibroblasts was examined. The AS inhibited collagen production in a dose- and time-dependent manner. Labeling and pulse chase experiments showed that it did not block collagen secretion, but a greater proportion of molecules synthesized in its presence accumulated within the cells. Amino acid analysis showed that when labeling was done at 24 degrees C prolyl hydroxylation in fibroblasts exposed to the AS was reduced to two-thirds of the cultures treated with control supernatant (CS), however it was not different at 37 degrees C. These results indicate that the AS inhibits collagen hydroxylation, that the un-(under)hydroxylated collagen molecules are degraded at physiological temperature and that suppression of collagen hydroxylation may be a mechanism by which the AS inhibits collagen production.