Stimulation of DNA synthesis in quiescent rabbit chondrocytes in culture by limited exposure to somatomedin-like growth factors

Authors


  • This paper is dedicated to Professor Emeritus Shiro Akabori on the occasion of his 85th birthday and to Professor Emeritus Yoshiharu Izumi on the occassion of his retirement from Osaka University.

Correspondence to F. Suzuki, Department of Biochemistry, Faculty of Dentistry, Osaka University, 1-8, Yamada-oka, Suita, Osaka 565, Japan

Abstract

Cartilage-derived factor (CDF), extracted from fetal bovine cartilage, and multiplication-stimulating activity (MSA) stimulated DNA synthesis in quiescent rabbit costal chondrocytes in culture under serum-free conditions. As described previously, when added in the presence of fibroblast growth factor (FGF) or epidermal growth factor (EGF) a somatomedin-like growth factor, CDF or MSA, synergistically stimulated DNA synthesis in the cultured chondrocytes. The present study showed that exposure of the cells to MSA or CDF for only the initial 5 h was sufficient for transmission of their full stimulatory effect. Furthermore, the limited exposure did not alter the time course of stimulation of DNA synthesis: [3H]thymidine incorporation into DNA began to increase after 16 h and reached a maximum after 24 h. In contrast to the somatomedin-like growth factors, FGF and EGF were required continuously in the culture medium during traverse of the entire G1 phase for stimulation of DNA synthesis, and the mitogenic effects of FGF and EGF in cultured chondrocytes were stronger than those of CDF and MSA. Synergistic stimulation of DNA synthesis by CDF or MSA in the presence of FGF or EGF could be observed as long as FGF or EGF was continuously present, even when CDF or MSA was withdrawn after the first 5 h of culture. These findings suggest that, in contrast to FGF and EGF, somatomedin-like growth factors affect an early distinct stage in the G1 phase of chondrocytes.

Abbreviations
CDF

cartilage-derived factor

MSA

multiplication-stimulating activity

EGF

epidermal growth factor

FGF

fibroblast growth factor

PDGF

platelet-derived growth factor