Jian Q. Feng

BONE MORPHOGENETIC PROTEIN 2 (BMP-2) ENHANCES BMP-3, BMP-4, AND BONE CELL DIFFERENTIATION MARKER GENE EXPRESSION DURING THE INDUCTION OF MINERALIZED BONE MATRIX FORMATION IN CULTURES OF FETAL RAT CALVARIAL OSTEOBLASTS

Normal bone formation is a prolonged process that is carefully regulated and involves sequential expression of growth regulatory factors by osteoblasts as they proliferate and ultimately differentiate. Since this orderly sequence of gene expression by osteoblasts suggests a cascade effect, and BMP-2 is capable of initiating and maintaining this effect, we examined the effects of BMP-2 on expression of other BMPs and compared these effects with the expression pattern of bone cell differentiation marker genes in primary cultures of fetal rat calvarial (FRC) osteoblasts. To examine the gene expression profile during bone cell differentiation and bone formation, we also examined the effects of rBMP-2 on bone formation in vivo and in vitro. rBMP-2 stimulated bone formation on the periosteal surface of mice when 500 ng/day rBMP-2 was injected subcutaneously. When rBMP-2 was added to primary cultures of FRC osteoblasts, it accelerated mineralized nodule formation in a time and concentration-dependent manner (10–40 ng/ml). rBMP-2 (40 ng/ml) enhanced BMP-3 and -4 mRNA expression during the mineralization phase of primary cultures of FRC osteoblasts. Enhancement of BMP-3 and -4 mRNA expression by rBMP-2 was associated with increased expression of bone cell differentiation marker genes, alkaline phosphatase (ALP), type I collagen, osteocalcin (OC), osteopontin (OP), and bone sialoprotein (BSP). These results suggest that BMP-2 enhances expression of other BMP genes during bone cell differentiation. BMP-2 may act in a paracrine fashion in concert with other BMPs it induces to stimulate bone cell differentiation and bone formation during remodeling.

Structure and sequence of mouse bone morphogenetic protein-2 gene (BMP-2): Comparison of the structures and promoter regions of BMP-2 and BMP-4 genes

Screening of a mouse spleen genomic DNA library with mouse BMP-4 and BMP-2 cDNA probes led to the isolation of mouse BMP-2 gene. This gene contains approximately 11 kb transcription unit and 3 exons. The deduced protein has 394 amino acids. The C-terminal amino acid mature coding region is identical to that of the human BMP-2. Comparison of mouse BMP-2 and BMP-4 gene shows little similarity in exon/intron structure, although the mature coding peptide regions of both genes share over 90% identity at the amino acid level.