Olfactomedin 2, a novel regulator for transforming growth factor-β-induced smooth muscle differentiation of human embryonic stem cell-derived mesenchymal cells.
Bottom Line: Olfm2 also inhibited HERP1 expression.Moreover, blockade of Olfm2 expression inhibited TGF-β-induced SRF binding to SM gene promoters in a chromatin setting, whereas overexpression of Olfm2 dose dependently enhanced SRF binding.These results demonstrate that Olfm2 mediates TGF-β-induced SM gene transcription by empowering SRF binding to CArG box in SM gene promoters.
Affiliation: Department of Physiology and Pharmacology, University of Georgia, Athens, GA 30602.Show MeSH
Related in: MedlinePlus
Mentions: Because SRF binding to CArG box is crucial for SM gene transcription and Olfm2 mediated SRF release from HERP1, we sought to determine whether Olfm2 plays a role in SRF binding to SM marker gene promoter. Previous studies showed that SRF binding to CArG box is functionally important for SM22α promoter activity both in vitro and in vivo (Miano, 2003; McDonald et al., 2006). We thus performed chromatin immunoprecipitation (ChIP) assays to determine whether Olfm2 affects SRF binding to this CArG box. As shown in Figure 8A, SRF weakly bound to the CArG box of SM22α promoter in a basal state. TGF-β treatment significantly enhanced the binding (Figure 8, A and B), consistent with previous studies (Hautmann et al., 1999). Knockdown of Olfm2, however, significantly diminished TGF-β–enhanced SRF binding to the promoter (Figure 8, A and B), suggesting that Olfm2 is essential for SRF binding to SM marker promoter. Moreover, ectopic expression of Olfm2 in TGF-β–untreated cells dose dependently enhanced SRF binding to SM22α promoter (Figure 8, D and E). To determine whether this is a common mechanism for Olfm2 to regulate SRF targets in SM differentiation, we tested the Olfm2 effect on SRF binding to another SM promoter, SMMHC promoter, and observed similar results as with SM22α promoter (Figure 8, A–F). These data demonstrate that Olfm2 is a novel factor facilitating SRF binding to SM gene promoter, a key event for SM differentiation.
Affiliation: Department of Physiology and Pharmacology, University of Georgia, Athens, GA 30602.