Global chromatin organizer SATB1 acts as a context-dependent regulator of the Wnt/Wg target genes

Special AT-rich binding protein-1 (SATB1) integrates higher-order chromatin architecture with gene regulation, thereby regulating multiple signaling pathways. In mammalian cells SATB1 directly interacts with β-catenin and regulates the expression of Wnt targets by binding to their promoters. Whether SATB1 regulates Wnt/wg signaling by recruitment of β-catenin and/or its interactions with other components remains elusive. Since Wnt/Wg signaling is conserved from invertebrates to humans, we investigated SATB1 functions in regulation of Wnt/Wg signaling by using mammalian cell-lines and Drosophila. Here, we present evidence that in mammalian cells, SATB1 interacts with Dishevelled, an upstream component of the Wnt/Wg pathway. Conversely, ectopic expression of full-length human SATB1 but not that of its N- or C-terminal domains in the eye imaginal discs and salivary glands of third instar Drosophila larvae increased the expression of Wnt/Wg pathway antagonists and suppressed phenotypes associated with activated Wnt/Wg pathway. These data argue that ectopically-provided SATB1 presumably modulates Wnt/Wg signaling by acting as negative regulator in Drosophila. Interestingly, comparison of SATB1 with PDZ- and homeo-domain containing Drosophila protein Defective Proventriculus suggests that both proteins exhibit limited functional similarity in the regulation of Wnt/Wg signaling in Drosophila. Collectively, these findings indicate that regulation of Wnt/Wg pathway by SATB1 is context-dependent.