RAT OSTEOBLAST AND OSTEOSARCOMA NUCLEAR MATRIX PROTEINS BIND WITH SEQUENCE SPECIFICITY TO THE RAT TYPE-I COLLAGEN PROMOTER

The nuclear matrix mediates the 3-dimensional organization of DNA and supports DNA replication and its transcription. We hypothesize that th e osteoblast nuclear matrix contributes to the transcriptional control of type I collagen (COL1A1) expression. Cis-regulatory elements of th e rat COL1A1 promoter that control osteoblast expression in vivo are b etween -2.3 and -1.67 kilobase pairs (kb) but lie within -3.5 and -2.3 kb in cultured bone cells. This mag result from differences in cell a rchitecture between osteoblasts in tissue and those in vitro. Our aim was to identify osteoblast nuclear matrix proteins (NMPs) that associa ted with sequence-specificity to the COL1A1 promoter. We used osteobla sts from tile rat metaphyseal femur and the rat osteosarcoma cells, RO S 17/2.8. Nuclear matrix and soluble nuclear proteins were obtained as separate subfractions. Gel mobility shift analysis, using fragments o f the COL1A1 promoter, was used to identify DNA-binding proteins in th f nuclear subfractions. A NMP-DNA interaction, NMP3, was observed betw een -2149 and -2106 nucleotide in both osteoblasts and osteosarcoma ce lls. NMP3 was detected between -3518 to -3406 nucleotide. Therefore, o steoblast NMPs recognize sequences in regulatory regions of the COL1A1 promoter and may link cell structure and the transcriptional regulati on of this protein.