Overexpression of latent transforming growth factor-β binding protein 1 (LTBP-1) in dioxin receptor-null mouse embryo fibroblasts

Abstract

The aryl hydrocarbon receptor (AhR) is a transcriptional regulator of genes involved in xenobiotic metabolism. Increasingly clear is also the role of the AhR in the control of cell growth and proliferation. By analyzing differential patterns of gene expression between wild-type (AhR+/+) and null (AhR–/–) mouse embryo fibroblasts (MEF), we have identified latent transforming growth factor-β binding protein 1 (LTBP-1) as a negatively AhR-regulated gene in the absence of xenobiotics. Ltbp-1 mRNA and protein expression were markedly increased in AhR–/– MEF. Furthermore, secreted LTBP-1 was elevated in the culture medium and the extracellular matrix of AhR-null MEF. Actinomycin D inhibited Ltbp-1 mRNA overexpression, suggesting regulation at the transcriptional level. AhR activation by dioxin (TCDD) downregulated Ltbp-1, again suggesting an AhR-regulated mechanism. Treatment of AhR+/+ MEF with transforming growth factor-β(TGF-β) downregulated AhR and, simultaneously, increased Ltbp-1, further supporting the role of this receptor in LTBP-1 expression. AhR–/– conditioned medium had higher levels of active and total TGF-β activity, suggesting a role for LTBP-1 in maintaining extracellular TGF-β concentrations. TGF-β did not appear to directly regulate Ltbp-1 given that addition of TGFβ neutralizing antibody or TGFβ protein to AhR–/– MEF had no effect on Ltbp-1 expression. AhR–/– MEF had lower levels of matrix metalloproteinase 2 (MMP-2) activity, which could not be attributable to MMP-2 mRNA downregulation or MMP-inhibitors Timp-1 and Timp-2 overexpression. These data identify LTBP-1 as one of the few AhR-regulated genes not involved in xenobiotic metabolism and also support the implication of the AhR in controlling TGFβ activity and cell proliferation.

Chronic TCDD exposure results in the dysregulation of gene expression in splenic B-lymphocytes and in the impairments in T-cell and B-cell differentiation in mouse model

“…Consistent with the increased percentage of B cells, the most up-regulated pathway was that of lymphocyte proliferation (Z-score 2.5), with the specific B cell proliferation pathway also up-regulated (Z-score 1.1). Another set of up-regulated pathways included the pathways for invasion, migration, and movement of cells, consistent with the growing body of evidence that supports the roles of AhR in cell growth, movement and proliferation, as well as in the regulation of TGF-β activity Fernandez-Salguero, 2010;Gomez-Duran et al, 2009;Kerkvliet, 2009a;Santiago-Josefat et al, 2004). The pathway regulating the apoptosis of cancer cells was the most down-regulated, consistent with the established lymphomagenic potential of TCDD.…”

Aryl hydrocarbon receptor inhibition downregulates the TGF-β/Smad pathway in human glioblastoma cells

“…AhR has been reported earlier, for example, for embryo fibroblasts and primary hepatocyte cultures using the paradigm of AhR null mice (Santiago-Josefat et al, 2004;Zaher et al, 1998). Regulators of TGF-b signaling have been reported earlier to function abnormally, and thus influence the progression of tumors such as glioblastoma (Miyazono et al, 2003;Seoane et al, 2004).…”

“…Importantly, AhR and TGF-b signaling pathways are known to cross-regulate each other in a cell type-specific manner (Chang et al, 2007;Wolff et al, 2001). Moreover, latent TGF-b-binding protein-1 (LTBP-1), a protein that has been characterized as crucial in the process of TGF-b activation in gliomas (Tritschler et al, 2009), is a transcriptional target of AhR (Corchero et al, 2004;Santiago-Josefat et al, 2004). Altogether, the possible interplay of these important factors led us to study the role of AhR in glioma cells in more detail.…”

Dioxin Receptor Expression Inhibits Basal and Transforming Growth Factor β-induced Epithelial-to-mesenchymal Transition

“…Washed beads were then used for immunoblotting. SDS-PAGE and immunoblotting were performed as described (9,31).…”