[Two proteins from the nuclear matrix bind osteopontin gene promoter]

DNA transcription and replication are organized by the nuclear matrix. It has been recently shown that the osteocalcin gene promoter binds specifically two proteins, NMP-1 and NMP-2 (nuclear matrix proteins 1 and 2), from cell line ROS 17/2.8 (Bidwell et al., 1993). Osteocalcin in one of the proteins taking part in extracellular matrix mineralization during osteogenic differentiation. Osteopontin gene is also active at the late stages of osteogenesis, so we supposed that its promoter could be bound to the nuclear matrix as well. Among the nuclear matrix proteins of ROS 17/2.8 we have found a protein factor which binds the promoter region of the osteopontin gene specifically with the help of gel shift assay. Two proteins with isoelectric points of pH > 8.0 and mol. masses of 38 and 43 kDa, respectively, have been purified by affinity chromatography with the promoter region of osteopontin attached to cellulose. The mol. masses of the revealed proteins are similar to those of already characterized NMP-2 (38 kDa) and one of subunits of heterodimer NMP-1 (43 kDa). Computer analysis shows that the binding sites for these proteins exist in the osteopontin gene promoter region. So, it is very likely that we dealt with the same proteins. A further investigation could lead to characterization of a group of nuclear matrix attached osteogenic-specific transcriptional factors.