EFFECT OF MULTIPLICATION-STIMULATING ACTIVITY ON DNA AND PROTEIN-SYNTHESIS IN CULTURED FETAL RAT CALVARIA

Multiplication-stimulating Activity (MSA), a peptide closely related to somatomedin, was examined for its effects on bone formation and sulfation activity in vitro. To study the effect of MSA on bone formation, we examined its effects on the incorporation of3H-thymidine into DNA,3H-uridine into RNA, and3H-proline into collagenase-digestible (CDP) and noncollagen protein (NCP), as well as DNA content in 21-day fetal rat calvaria cultured for 24 h periods. MSA caused a dose-dependent stimulation of the incorporation of3H-thymidine into DNA at concentrations of 1 to 3 μg/ml, increased the total DNA content, and had no effect on3H-uridine incorporation. The effect on3H-thymidine incorporation appeared and was maximal at 12 h and was sustained for 24 h. After 24 h of treatment, MSA, 1 to 3 μg/ml, caused a 25 to 60% stimulation on the incorporation of3H-proline into CDP and NCP. The effect was not specific for CDP, and there was no increase in the percent collagen synthesized. In contrast, insulin, 10 n M, increased the labeling of CDP by 95% but had a small effect on NCP and did not affect DNA synthesis. Insulin did not diminish the MSA effect on CDP and NCP labeling but slightly decreased its effect on thymidine incorporation. Cortisol inhibited DNA synthesis, but MSA was effective in its presence and cortisol did not affect the stimulatory effect of MSA on CDP or NCP. Histological sections showed a sixfold increase in the mitotic index after colcemid arrest in MSA-treated bones. MSA, 0.1 to 5 μg/ml, also stimulated the incorporation of35S into pig costal cartilage in culture. Our studies indicate that MSA stimulates DNA, collagen, and noncollagen protein synthesis in bone cultures and stimulates sulfate incorporation into cartilage. © 1979 Springer-Verlag.