Evidence for phosphorylation of proteoglycans in chick embryo cartilage cells

Somatomedin C (SM) stimulates the incorporation of /sup 35/SO/sub 4/ into glycosaminoglycans in chick cartilage cells. Medium from cell cultures contain increased amounts of /sup 35/SO/sub 4/-labeled proteoglycan when the cells are stimulated by (SM). When these cells are incubated with /sup 32/P(PO/sub 4/), /sup 32/P is incorporated into material that is precipitate from the medium by cetylpyridinum chloride (CPC). The /sup 32/P incorporation is also stimulated by SM. Following digestion by DNase and RNase, 6 to 14% of the /sup 32/P remains precipitable by CPC and chromatographs at the void volume of Sephadex G-25 columns. After digestion with chondroitinase ABC approximately 70% of the /sup 32/P chromatographs at the column volume, indicating a significant reduction in the molecular weight of the material containing /sup 32/P. 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.