Regulation by IGF-I and TGF-β1 of swarm-rat chondrosarcoma chondrocytes

The growth factors transforming growth factor-beta 1 and insulin-like growth factor-I influence a wide range of cellular actions, including the growth of several neoplastic cell types. Their role in the regulation of neoplastic chondrocytes remains unclear. We tested the hypotheses that transforming growth factor-beta 1 and insulin-like growth factor-I differentially regulate neoplastic chondrocytes and interact to modulate the mitotic and matrix synthetic activities of neoplastic chondrocytes. We used Swarm-rat chondrosarcoma chondrocytes to investigate the effect of each factor individually and of both factors in combination on [H-3]thymidine incorporation into DNA and on [S-35]sulfate incorporation into glycosaminoglycans. Each factor increased [H-3]thymidine incorporation 2.7-fold; transforming growth factor-beta 1 achieved this effect at a 20-fold lower concentration than insulin-like growth factor-I. In contrast, insulin-like growth factor-I stimulated [S-35]sulfate incorporation 3.5-fold; this was twice the maximal effect of transforming growth factor-beta 1. Transforming growth factor-beta 1 and insulin-like growth factor-I each decreased the proportion of newly synthesized glycosaminoglycans that were retained in the cells and pericellular matrix, indicating that the anabolic effect of these factors is only partly directed toward cell associated matrix production. The mitogenic and matrix synthetic actions of insulin-like growth factor-I and transforming growth factor-beta 1 were synergistic. In concert, they increased [H-3]thymidine incorporation approximately 12-fold, an effect three times greater than the sum of the maximal stimulation achieved by each factor individually. Similarly, transforming growth factor-beta 1 and insulin-like growth factor-I together increased glycosaminoglycan synthesis approximately two times more than the sum of their maximal individual effects. Taken together, these data indicate that these chondrosarcoma chondrocytes are positively regulated by insulin-like growth factor-I and transforming growth factor-beta 1 and that these growth factors interact to augment the mitotic and matrix synthetic actions of the chondrocytes. If supported in human models, the sensitivity to growth factors of these cells suggests that interventions directed toward growth factor inhibition may be of therapeutic value.