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
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Mentions: HERP1 is a transcriptional repressor abundantly expressed in the developing vascular system (Nakagawa et al., 2000; Iso et al., 2001a, b). HERP1 has been shown to physically associate with SRF and inhibit SM differentiation by interfering with SRF binding to CArG box (Doi et al., 2005). Because both HERP1 and Olfm2 interact with SRF with opposite effects on SM differentiation, we hypothesize that TGF-β induction of Olfm2 promotes SM differentiation through inhibition of HERP1 expression or HERP1 binding to SRF. Indeed, TGF-β induced time-dependent suppression of HERP1 but up-regulated Olfm2 expression (Figure 7, A and B). Of importance, Olfm2 overexpression decreased HERP1 mRNA expression (Figure 7C), whereas knockdown of Olfm2 effectively attenuated TGF-β–induced blockade of HERP1 expression (Figure 7, D and E). These data suggest that Olfm2 mediated suppression of HERP1 by TGF-β. To determine whether Olfm2 affects HERP1 interaction with SRF, we performed CoIP assay in cells where Olfm2 expression was blocked. We found that TGF-β treatment inhibited HERP1-SRF interaction. However, knockdown of Olfm2 restored the HERP1 binding to SRF that was suppressed by TGF-β, indicating that Olfm2 mediated the TGF-β–induced dissociation of HERP1 from SRF (Figure 7, F and G). These data demonstrate that Olfm2 regulates TGF-β–induced SM differentiation by removing the inhibitory effect of HERP1, that is, releasing SRF from HERP1.
Affiliation: Department of Physiology and Pharmacology, University of Georgia, Athens, GA 30602.