ASGSB 1998 Annual Meeting Abstracts

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DEVELOPMENTAL REGULATION OF COLLAGENASE-3 MRNA IN NORMAL, DIFFERENTIATING OSTEOBLASTS THROUGH THE ACTIVATOR PROTEIN-1 AND THE RUNT DOMAIN BINDING SITES.   N.C. Partridge, R.C. D’Alonzo, and S.K Winchester. Saint Louis University School of Medicine, St. Louis, MO.

Previously, we have shown that collagenase-3 mRNA is developmentally expressed in normal, differentiating rat osteoblasts. Collagenase-3 mRNA is not detectable during osteoblast proliferation (day 5), but expression increases as the osteoblasts begin to differentiate and mineralize an extracellular matrix (days 14 and 21). We demonstrated by nuclear run-on analysis that this increase in expression is due to an increase in transcription of the collagenase-3 gene. Through transient transfection of deletion and mutated collagenase-3 promoter constructs, we demonstrated that the activator protein-1 (AP-1) and runt domain (RD) binding sites are responsible for transcription of the collagenase-3 gene. Mutation of either the AP-1 or the RD binding sites resulted in a loss of collagenase-3 promoter activity. The AP-1 and RD binding sites have been shown to bind members of the activator-protein-1 family of transcription factors and Acute Myelogenous Leukemia (AML) family of transcription factors, respectively. Overexpression of both c-Fos and c-Jun into proliferating osteoblasts or overexpression of osteoblast-specific factor 2 (Osf2) resulted in an increase in collagenase-3 promoter activity. Furthermore, overexpression of c-Fos, c-Jun and Osf2 into osteoblasts resulted in a synergistic increase in collagenase-3 promoter activity. However, mutation of either the AP-1 or the RD binding site resulted in the inability of c-Fos and c-Jun or Osf2 to increase collagenase-3 promoter activity suggesting that both the AP-1 and RD binding sites and proteins are required for expression of collagenase-3 in differentiating osteoblasts. (Supported by NASA: NAG-4538, NCC2-884, and GSRP-98-087).

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