Chondrocytes contain a growth factor that is localized in the nucleus and is associated with chromatin.

Abstract

Bovine scapular and articular chondrocytes were isolated from fresh cartilage and disrupted by sonication. The disrupted cells had the ability to stimulate DNA synthesis and cell division in vitro in chondrocytes and in 3T3 cells. Subcellular fractions were prepared by 2 methods: enucleation with cytochalasin B and cell lysis with Nonidet P-40. After chondrocyte enucleation karyoplasts and cytoplasts were collected, disrupted by sonication and tested for their ability to stimulate DNA synthesis. Over 95% of the cellular growth factor activity was localized in the karyoplast. After chondrocyte lysis in Noniet P-40 over 95% of the growth factor activity was recovered in the nuclear fraction. Chondrocyte chromatin was prepared by low ionic strength detergent treatment of karyoplasts. All of the growth factor activity of the karyoplast was associated with chromatin. The growth factor activity of chondrocytes, cytoplasts, karyoplasts and chromatin was analyzed by gel filtration on Bio-Gel A-0.5 M equilibrated with 4 M guanidine.cntdot.HCl and 5 mM dithiothreitol. Chondrocytes, chondrocyte karyoplasts and chondrocyte chromatin had similar column elution profiles, with MW in the range of 12,000-22,000.