Cellular control of macromolecular synthesis: rates of synthesis of extracellular macromolecules during and after depletion by papain

Abstract

Papain was administered in doses of 1$\cdot $6, 8$\cdot $0 or 80$\cdot $0 $\mu $g/ml. of synthetic medium for 24 h to 11- to 12-day embryonic chicken tibiae grown in organ culture. This treatment caused: (1) a decrease in length and weight, (2) loss of cells and total protein, (3) little change in hydroxyproline content, and (4) release of large amounts of glycosaminoglycans. When subcultured and allowed to recover in normal medium for periods of up to 144 h the explants increased in length and weight and partially replaced the lost material. In response to the depletion of the glycosaminoglycans, primarily chondroitin sulphate and keratan sulphate, from the extracellular matrix the cells of the treated explants synthesized both precursor hexosamine and the requisite polymerized glycosaminoglycans more rapidly than control explants. This increased rate of synthesis occurred whether or not the glycosaminoglycans were incorporated into the matrix; indeed, during recovery after treatment with the 80 $\mu $g/ml. dose the tissue was unable to accept the newly synthesized macromolecules even though the matrix was very deficient in these substances, and the glycosaminoglycans were released into the medium. Large amounts of the monomer precursors of hexosamine also were released into the medium before they could be assembled into the polymer glycosaminoglycans. The results showed that the cell compensates for its loss of extracellular material by increased synthesis of the depleted macromolecules; after treatment with 8$\cdot $0 $\mu $g/ml. the rate of production of hexosamine was over three times that of the control explants.