| Zinc-Finger E-box binding protein (ZEB)-1 (Zfhx1a, AREB6, deltaEF1), encoded by the gene tcf8, is a transcription factor that binds to E-box sequences in regulatory regions of its target genes to either repress or activate transcription. ZEB1 induces the epithelial-to-mesenchymal transition (EMT) during development and cancer progression. The most prominent phenotype of tcf8 null mice is abnormal skeletal development, and ZEB1 inhibits differentiation of mesenchymal precursors into chondrocytes and osteoblasts; however, little is known about the transcriptional regulation of tcf8 throughout these processes. The transcription factor Runx2 is a master regulator of skeletal formation, making it a likely candidate to regulate expression of tcf8 in this tissue. Seven putative Runx binding sites are present in the tcf8 proximal promoter, and we hypothesized that Runx2 regulates tcf8 activity by binding to one or more of these sites. Reporter-based assays indicate that Runx2 either represses or activates transcription of tcf8 in a cell type-dependent manner and that this activity is mediated through a region between -164 and -112 relative to the translation start site. Furthermore, Runx2 was found to cooperate synergistically with the transcription factor LEF-1 to activate transcription of tcf8 in Cos7 cells. Given that LEF-1 mediates the effects of the canonical Wnt signaling pathway, the effect of the Wnt3a on tcf8 expression was examined in the C2C12 mesenchymal precursor cell line, where an induction of endogenous tcf8 was observed. These data provide the first evidence for regulation of tcf8 by Runx2 and suggest that Runx2 may interact with LEF-1 to mediate the effects of Wnt signaling on expression of tcf8. |
