title: p53 and MDM2 are involved in the regulation of osteocalcin gene expression.
abstract: Osteocalcin (OC) is a major noncollagenous bone matrix protein and an osteoblast marker whose expression is limited to mature osteoblasts during the late differentiation stage. In previous studies we have shown osteosarcomas to lose p53 function with a corresponding loss of osteocalcin gene expression. Introduction of wild type p53 resulted in re expression of the osteocalcin gene. Using gel shift and chromatin immunoprecipitation assays, we have identified a putative p53 binding site within the rat OC promoter region and observed an increase in OC promoter activity when p53 accumulates using a CAT assay. The p53 inducible gene Mdm2 is a well-known downstream regulator of p53 levels. Our results showed a synergistic increase in the OC promoter activity when both p53 and MDM2 were transiently overexpressed. We further demonstrate that p53 is not degraded during overexpression of MDM2 protein. Increased OC expression was observed with concomitantly increased p53, VDR, and MDM2 levels in ROS17/2.8 cells during treatment with differentiation promoting (DP) media, but was significantly decreased when co-treated with DP media and the small molecule inhibitor of MDM2-p53 interaction, Nutlin-3. We have also observed a dramatic increase of the OC promoter activity in the presence of p53 and Mdm2 with inclusion of Cbfa-1 and p300 factors. Our results suggest that under some physiological conditions the oncoprotein MDM2 may cooperate with p53 to regulate the osteocalcin gene during osteoblastic differentiation.
authors.affiliation: Department of Biochemistry, Chicago College of Osteopathic Medicine, Midwestern University, Downers Grove, IL 60515, USA.
authors.forename: Hankui
authors.initials: H
authors.lastname: Chen
authors.forename: Kevin
authors.initials: K
authors.lastname: Kolman
authors.forename: Natalie
authors.initials: N
authors.lastname: Lanciloti
authors.forename: Michael
authors.initials: M
authors.lastname: Nerney
authors.forename: Emily
authors.initials: E
authors.lastname: Hays
authors.forename: Chet
authors.initials: C
authors.lastname: Robson
authors.forename: Nalini
authors.initials: N
authors.lastname: Chandar
mesh_terms: D000818:Animals; D001665:Binding Sites; D045744:Cell Line, Tumor; D050659:Core Binding Factor Alpha 1 Subunit / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D050881:E1A-Associated p300 Protein / Q000494:pharmacology; D005786:Gene Expression Regulation; D016158:Genes, p53; D007093:Imidazoles / Q000494:pharmacology; D010006:Osteoblasts / Q000378:metabolism*; D015675:Osteocalcin / Q000235:genetics* / Q000378:metabolism; D010012:Osteogenesis; D010879:Piperazines / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D051736:Proto-Oncogene Proteins c-mdm2 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D004268:DNA-Binding Proteins; D007093:Imidazoles; D010879:Piperazines; D016159:Tumor Suppressor Protein p53; D015675:Osteocalcin; C482205:nutlin 3; D050881:E1A-Associated p300 Protein; C494362:Ep300 protein, rat; D051736:Proto-Oncogene Proteins c-mdm2