Evidence for phosphorylation of proteoglycans in chick embryo cartilage cells

Somatomedin C (SM) stimulates the incorporation of 35SO4 into glycosaminoglycans in chick cartilage cells. Medium from cell cultures contain increased amounts of 35SO4-labeled proteoglycan when the cells are stimulated by (SM). When these cells are incubated with 32P[PO4], 32P is incorporated into material that is precipitate from the medium by cetylpyridinum chloride (CPC). The 32P incorporation is also stimulated by SM. Following digestion by DNase and RNase, 6 to 14% of the 32P remains precipitable by CPC and chromatographs at the void volume of Sephadex G-25 columns. After digestion with chondroitinase ABC approximately 70% of the 32P chromatographs at the column volume, indicating a significant reduction in the molecular weight of the material containing 32P. Based on these data, the phosphate is in proteoglycan. Medium from control cells not stimulated by somatomedin also contains material that is qualitatively the same. These data would suggest that like many other biological processes, phosphorylation may be an important regulatory event in proteoglycan biosynthesis