title: A correction: inhibitory activity in the conditioned medium of embryonic chick bones is due to thymidine.
abstract: Earlier studies from this laboratory suggested that embryonic chick bones in organ culture released into the culture medium a specific inhibitor of bone cell proliferation as defined by inhibition of [3H]TdR incorporation into DNA. Dialysis and membrane ultrafiltration experiments suggested that the inhibitory substance (IS) had a molecular weight between 6000 and 14,000. However, subsequent studies on the purification of IS have revealed that the inhibitory activity in bone-conditioned medium is of lower molecular weight and has several properties in common with thymidine (TdR): (1) IS coeluted with [3H]TdR upon gel filtration chromatography on Sephadex G-10. (2) IS bound to charcoal but not to cation or anion exchange resins. (3) Bone-conditioned medium decreased incorporation of [3H]TdR into the free [3H]TdR pool of cells in monolayer culture. (4) Conditioned medium inhibited [3H]TdR incorporation into [3H]thymidine monophosphate in a reaction catalyzed by thymidine kinase. The equivalent concentration of TdR in conditioned medium as estimated by thymidine kinase assay was sufficient to account for the reduction in [3H]TdR incorporation into bone cell DNA. No evidence was found for a specific inhibitor of bone cell proliferation other than TdR. Hence we conclude that the inhibitory effect of IS is due to dilution of [3H]TdR by nonradioactive TdR. Furthermore, media conditioned by several tumor cell lines also contained a low-molecular-weight component which inhibited [3H]TdR incorporation. The results suggest that organ- and cell-conditioned media can contain significant concentrations of TdR which can artifactually inhibit [3H]TdR incorporation in cell proliferation assays.
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002606:Charcoal; D002642:Chick Embryo; D002850:Chromatography, Gel; D003470:Culture Media; D004247:DNA / Q000096:biosynthesis; D008970:Molecular Weight; D009924:Organ Culture Techniques; D013936:Thymidine / Q000378:metabolism / Q000494:pharmacology*; D013937:Thymidine Kinase / Q000378:metabolism
chemical_list: D003470:Culture Media; D002606:Charcoal; D004247:DNA; D013937:Thymidine Kinase; D013936:Thymidine