THE TISSUE-SPECIFIC NUCLEAR MATRIX PROTEIN, NMP-2, IS A MEMBER OF THEAML CBF/PEBP2/RUNT DOMAIN TRANSCRIPTION FACTOR FAMILY - INTERACTIONS WITH THE OSTEOCALCIN GENE PROMOTER/

The nuclear matrix protein, NMP-2, was originally identified as an ost eoblast-specific DNA-binding complex localized exclusively to the nucl ear matrix. NMP-2 was shown to recognize two binding, sites, site A (n t -605 to -599) and site B (nt -441 to -435), in the rat bone-specific osteocalcin gene promoter. This study shows that the NMP-2 binding si tes A and B as well as a third NMP-2 binding site (nt -135 to -130) co nstitute a consensus sequence, (T)(A)G(C)(T)GGT, and represent an AML- 1 recognition motif. AML-1 is a member of the AML transcription factor family which is associated with acute myelogenous leukemia and binds to the sequence TG(C)(T)GGT via its DNA-binding runt domain. Electroph oretic mobility shift assays reveal that a component of NMP-2 is a mem ber of the AML/PEBP2/runt domain transcription factor family based on cross-competition with AML-1 consensus oligonucleotide. Limited immuno reactivity of NMP-2 with a polyclonal N-terminal AML-1 antibody and in ability of the AML-1 partner protein CBF-beta to form complexes with N MP-2 indicate that NMP-2 is not identical to AML-1 but represents a va riant AML/PEBP2/runt domain protein. Western and Northern blots reveal the presence of multiple AML-related proteins and AML-1 transcripts i n several osseous cell lines. Furthermore, our results indicate that A ML family members may selectively partition between nuclear matrix and nonmatrix compartments. Because proteins that contain a runt domain a re implicated in tissue-specific transcriptional regulation, our resul ts support the concept that the nuclear matrix mediates osteoblast-spe cific expression of the osteocalcin gene.