The aryl hydrocarbon receptor links integrin signaling to the TGF-β pathway

Abstract

Glioblastoma is the most common and aggressive form of intrinsic brain tumor. Transforming growth factor (TGF)-represents a central mediator of the malignant phenotype of these tumors by promoting invasiveness and angiogenesis, maintaining tumor cell stemness and inducing profound immunosuppression. Integrins, which are highly expressed in glioma cells, interact with the TGF-pathway. Furthermore, a link has been described between activity of the transcription factor aryl hydrocarbon receptor (AhR) and TGF-expression. Here we demonstrate that integrin inhibition, using v, 3 or 5 neutralizing antibodies, RNA interference-mediated integrin gene silencing or pharmacological inhibition by the cyclic RGD peptide EMD 121974 (cilengitide) or the non-peptidic molecule GLPG0187, inhibits AhR activity. These effects are independent of cell detachment or cell density. While AhR mRNA expression was not affected by integrin inhibition, AhR total and nuclear protein levels were reduced, suggesting that integrin inhibition-mediated regulation of AhR may occur at a post-transcriptional level. AhR-null astrocytes, AhR-null hepatocytes or glioblastoma cells with a transiently silenced AhR gene showed reduced sensitivity to integrin inhibition-mediated alterations in TGF-signaling, indicating that AhR mediates integrin control of the TGF-pathway. Accordingly, there was a significant correlation of v integrin levels with nuclear AhR and pSmad2 levels as determined by immunohistochemistry in human glioblastoma in vivo. In summary, this study identifies a signaling network comprising integrins, AhR and TGF-and validates integrin inhibition as a promising strategy not only to inhibit angiogenesis, but also to block AhR-and TGF--controlled features of malignancy in human glioblastoma. Here we demonstrate that integrin inhibition, using αv, β3 or β5 neutralizing antibodies, RNA interference-mediated integrin gene silencing or pharmacological inhibition by the cyclic RGD peptide EMD 121974 (cilengitide) or the non-peptidic molecule GLPG0187, inhibits AhR activity.These effects are independent of cell detachment or cell density. While AhR mRNA expression was not affected by integrin inhibition, AhR total and nuclear protein levels were reduced, suggesting that integrin inhibition-mediated regulation of AhR may occur at a posttranscriptional level. AhR-null astrocytes, AhR-null hepatocytes, or glioblastoma cells with a transiently silenced AhR gene showed reduced sensitivity to integrin inhibition-mediated alterations in TGF-β signaling indicating that AhR mediates integrin control of the TGF-β pathway. Accordingly, there was a significant correlation of αv integrin levels with nuclear AhR and pSmad2 levels as determined by immunohistochemistry in human glioblastoma in vivo.In summary, this study identifies a signaling network comprising integrins, AhR and TGF-β and validates integrin inhibition as a promising strategy not only to inhibit angiogenesis, but also to block AhR-and TGF--controlled features of malignancy in human glio...

Induction of Colonic Regulatory T Cells by Mesalamine by Activating the Aryl Hydrocarbon Receptor

“…Given that mesalamine did not affect TGF-β1 mRNA levels and total amounts of TGF-β1 protein, whereas mesalamine increased expression of TSP-1 and integrin αV, genes related to conversion of the latent form of TGF-β1 to the active form, mesalamine might facilitate TGF-β1 activation in the colon via AhR–mediated control of those genes. Consistent with this notion, previous studies suggest that AhR initiates transcription of TSP-1 via activation of the promoter 41 and AhR mediates integrin control of TGF-β signaling 42 . Similarly, a defined mix of Clostridium strains induces colon Tregs, concomitant with increased expression of metalloproteinase 2, 9, and 13, 7 which have been reported to be involved in the activation of TGF-β 25 …”

Role of the aryl hydrocarbon receptor in carcinogenesis and potential as an anti-cancer drug target

“…A subsequent study by this group demonstrated that tryptophan-2,3-dioxygenase-mediated metabolism of tryptophan to give kynurenine was a key pro-carcinogenic event since kynurenine promotes AhR-dependent tumor cell survival and motility (Opitz et al 2011). A recent report indicates that AhR-integrin-TGFβ crosstalk is also involved in glioblastoma (Silginer et al 2016). It is clear that these studies demonstrate a potential clinical role for AhR antagonists in the treatment of glioblastoma.…”

Transcriptional control of O6‐methylguanine DNA methyltransferase expression and temozolomide resistance in glioblastoma

“…), ZH‐161, and ZH‐305 (Silginer et al . ; Stojcheva et al . ) were maintained as sphere (S) cultures in Neurobasal Medium ® supplemented with 2% B‐27 supplement, 1% GlutaMAX (Invitrogen, Life Technologies, Carlsbad, CA, USA), 20 ng/mL epidermal growth factor, 20 ng/mL fibroblast growth factor, and 32 IE/mL heparin.…”