PTH-RESPONSIVE OSTEOBLAST NUCLEAR MATRIX ARCHITECTURAL TRANSCRIPTION FACTOR BINDS TO THE RAT TYPE-I COLLAGEN PROMOTER

In connective tissue, cell structure contributes to type I collagen ex pression. Differences in osteoblast microarchitecture may account for the two distinct cis elements regulating basal expression, in vivo and in vitro, of the rat type I collagen alpha 1(I) polypeptide chain (CO L1A1). The COL1A1 promoter conformation may be the penultimate culmina tion of osteoblast structure. Architectural transcription factors bind to the minor groove of AT-rich DNA and bend it, altering interactions between other trans-acting proteins. Similarly, nuclear matrix (NM) P roteins bind to the minor groove of AT-rich matrix-attachment regions, regulating transcription by altering DNA structure. We propose that o steoblast NM architectural transcription factors link cell structure t o promoter geometry and COL1A1 transcription. Our objective was to ide ntify potential osteoblast NM architectural transcription factors near the in vitro and in vivo regulatory regions of the rat COL1A1 promote r. Nuclear protein-promoter interactions were analyzed by gel shift an alysis and related techniques. NM extracts were derived from rat osteo sarcoma cells and from rat bone. The NM protein, NMP4, and a soluble n uclear protein, NF: both bound to two homologous poly(dT) elements wit hin the COL1A1 in vitro regulatory region and proximal to the in vivo regulatory element. These proteins bound within the minor groove and b ent the DNA. Parathyroid hormone increased NP/NMP4 binding to both pol y(dT) elements and decreased COL1A1 mRNA in the osteosarcoma cells. NP /NMP4-COL1A1 promoter interactions may represent a molecular pathway b y which osteoblast structure is coupled to COL1A1 expression. (C) 1998 Wiley-Liss, Inc.