Inhibition of Collagen Synthesis by$\alpha,\alpha^\prime-Dipyridyl$in Human Skin Fibroblasts in Culture

In human diploid skin fibroblasts in culture we have shown that nonhydroxylated collagen precursors remain in the cell when proline hydroxylation is inhibited by$\alpha, \alpha^\prime-dipyridyl$, a chelator of ferrous ions. The inhibition of proline hydroxylation is reversed by addition of fresh medium containing$50 \mu g$per ml of sodium ascorbate, whereupon nonhydroxylated collagen precursors are hydroxylated within the cell and extruded into the medium. Extrusion of collagen already formed within the cell is not appreciably affected by$\alpha,\alpha^\prime-dipyridyl$inhibition. Under normal conditions collagen is released from the monolayer into the medium within 3 hr of a pulse of$L-\lbrack^{14}C\rbrack proline$. In the presence of$\alpha,\alpha^\prime-dipyridyl$, about 35% of the$L-\lbrack^{14}C\rbrack proline$incorporated into protein is released into the medium within 8 hr as a proline-rich, hydroxyproline-deficient protein; at the same time, approximately 15% of the protein-bound$L-\lbrack^{14}C\rbrack proline$remains in the cell for as long as 12 hr. When proline hydroxylation is restored after 2 and 12 hr of$\alpha,\alpha^\prime-dipyridyl$inhibition, approximately the same amount of hydroxyproline is formed after each time interval in the monolayer. Therefore, nonhydroxylated collagen precursors retained in the cell are not appreciably degraded during at least 12 hr of inhibition by$\alpha,\alpha^\prime-dipyridyl$and are extruded into the medium only upon restoration of hydroxylation.