The Effect of Chondrocyte Growth Factor on Membrane Transport by Articular Chondrocytes in Monolayer Culture

Abstract

Chondrocyte growth factor (CGF), a contaminant of pituitary glycoprotein hormones, stimulates growth of cultured lapine articular chondrocytes while depressing SO₄-proteoglycan synthesis. To study its effect on membrane transport, NIH-bTSH and two other preparations with comparable CGF activity were employed. In early log phase (36 hr) cultures CGF (64 μg/ml) did not alter thymidine (dThd) uptake during the first 5 min. By 15 min however, TCA-precipitable dThd was 4-fold greater than in controls while the TCA-soluble fraction remained the same. CGF increased deoxy-glucose (DG) uptake in 36-hr old cultures. At 66 hr, CGF reduced DG transport. The transport of cycloleucine (CL) and aminoisobutyric acid (AIB) was reduced by CGF in 36 and 66-hr old cultures. There was a dose dependency between CGF concentration, the lowered uptake of DG, CL and AIB, and cell protein content. The effect of CGF on DG transport and dThd incorporation into DNA was not immediate but required prior exposure of the cells to CGF. CGF did not alter DG transport in rabbit or mouse fibrocytes or Chang liver cells. This and the reported finding that pituitary fibro-blast growth factor (FGF), increases amino acid transport in other cells suggests that the biological specificity of CGF may not be identical to that of FGF. §