title: A network connecting Runx2, SATB2, and the miR-23a~27a~24-2 cluster regulates the osteoblast differentiation program.
abstract: Induced osteogenesis includes a program of microRNAs (miRs) to repress the translation of genes that act as inhibitors of bone formation. How expression of bone-related miRs is regulated remains a compelling question. Here we report that Runx2, a transcription factor essential for osteoblastogenesis, negatively regulates expression of the miR cluster 23a∼27a∼24-2. Overexpression, reporter, and chromatin immunoprecipitation assays established the presence of a functional Runx binding element that represses expression of these miRs. Consistent with this finding, exogenous expression of each of the miRs suppressed osteoblast differentiation, whereas antagomirs increased bone marker expression. The biological significance of Runx2 repression of this miR cluster is that each miR directly targets the 3' UTR of SATB2, which is known to synergize with Runx2 to facilitate bone formation. The findings suggest Runx2-negative regulation of multiple miRs by a feed-forward mechanism to cause derepression of SATB2 to promote differentiation. We find also that miR-23a represses Runx2 in the terminally differentiated osteocyte, representing a feedback mechanism to attenuate osteoblast maturation. We provide direct evidence for an interdependent relationship among transcriptional inhibition of the miR cluster by Runx2, translational repression of Runx2 and of SATB2 by the cluster miRs during progression of osteoblast differentiation. Furthermore, miR cluster gain of function (i.e., inhibition of osteogenesis) is rescued by the exogenous expression of SATB2. Taken together, we have established a regulatory network with a central role for the miR cluster 23a∼27a∼24-2 in both progression and maintenance of the osteocyte phenotype.
authors.affiliation: Department of Cell Biology and Cancer Center, University of Massachusetts Medical School, Worcester, MA 01655, USA.
authors.forename: Mohammad Q
authors.initials: MQ
authors.lastname: Hassan
authors.forename: Jonathan A R
authors.initials: JA
authors.lastname: Gordon
authors.forename: Marcio M
authors.initials: MM
authors.lastname: Beloti
authors.forename: Carlo M
authors.initials: CM
authors.lastname: Croce
authors.forename: Andre J
authors.initials: AJ
authors.lastname: van Wijnen
authors.forename: Janet L
authors.initials: JL
authors.lastname: Stein
authors.forename: Gary S
authors.initials: GS
authors.lastname: Stein
authors.forename: Jane B
authors.initials: JB
authors.lastname: Lian
mesh_terms: D000818:Animals; D001665:Binding Sites; D002454:Cell Differentiation / Q000235:genetics*; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000235:genetics; D025461:Feedback, Physiological; D053263:Gene Regulatory Networks; D036961:Matrix Attachment Region Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism; D005810:Multigene Family; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D010012:Osteogenesis / Q000235:genetics; D011485:Protein Binding; D051381:Rats; D012097:Repressor Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D036961:Matrix Attachment Region Binding Proteins; D035683:MicroRNAs; C534062:Mirn23b microRNA, mouse; C529080:Mirn24 microRNA, mouse; C540674:Mirn27 microRNA, mouse; D012097:Repressor Proteins; C493716:Runx2 protein, mouse; C501473:SATB2 protein, mouse; D014157:Transcription Factors