title: Dual transcriptional regulation by runx2 of matrix Gla protein in Xenopus laevis.
abstract: Matrix Gla protein (MGP) is an extracellular mineral-binding protein expressed in several tissues but it only accumulates in bone and calcified cartilage under physiological conditions. Available evidence indicates that it acts as a physiological inhibitor of mineralization. Runx2 is a transcription factor essential for bone formation in mammals, affecting osteoblast and chondrocyte differentiation by regulating key genes crucial for bone and cartilage development. Being an important cartilage-associated gene, MGP is a potential target for Runx2, and thus we have investigated the possible functional interactions between them. In A6 cells, Runx2 was found to modulate MGP transcription and deletion analysis of MGP distal and proximal promoter-luciferase constructs identified cis-regulatory regions. Interestingly, we have also identified a runx2-binding site that mediates transcriptional repression of XlMGP. Mutation of this element, located between -54 and +33 bp, results in 18-fold up-regulation of transcription. Furthermore, and in addition to the previously reported Xlrunx2 types I and II, we have identified three transcripts encoding novel, truncated Xlrunx2 isoforms. Although only type I and type II could transactivate XlMGP, the truncated isoforms identified in this study, which result from alternative splicing, could be involved in negative regulation of MGP expression, as described for other RUNX2 truncated isoforms acting in other target genes. In vivo microinjection of XlMGP promoter constructs and runx2 mRNA confirmed that those promoters are targets for this transcription factor. These data also indicate that MGP is under dual regulation by runx2 through the use of various isoforms and context-dependent formation of transcriptional complexes.
authors.affiliation: University of Algarve, CCMAR, Campus de Gambelas, 8005-139 Faro, Portugal.
authors.forename: Cindy
authors.initials: C
authors.lastname: Fazenda
authors.forename: Brigite
authors.initials: B
authors.lastname: Simões
authors.forename: Robert N
authors.initials: RN
authors.lastname: Kelsh
authors.forename: M Leonor
authors.initials: ML
authors.lastname: Cancela
authors.forename: Natércia
authors.initials: N
authors.lastname: Conceição
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics*; D002460:Cell Line; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000235:genetics*; D005786:Gene Expression Regulation; D016297:Mutagenesis, Site-Directed; D020218:Response Elements / Q000235:genetics*; D014158:Transcription, Genetic; D029867:Xenopus Proteins / Q000235:genetics*; D014982:Xenopus laevis / Q000235:genetics*; D000097568:Matrix Gla Protein
chemical_list: D002135:Calcium-Binding Proteins; D050659:Core Binding Factor Alpha 1 Subunit; D016326:Extracellular Matrix Proteins; D029867:Xenopus Proteins; D000097568:Matrix Gla Protein; C446500:MGP protein, Xenopus