Induction of an epithelial to mesenchymal transition in human immortal and malignant keratinocytes by TGF‐β1 involves MAPK, Smad and AP‐1 signalling pathways

Abstract

Recent data indicate that transforming growth factor-beta1 (TGF-beta1) can act to promote tumour progression in the late stages of carcinogenesis. The mechanism by which this occurs is unknown although a ligand-induced epithelial-mesenchymal transition (EMT) is thought to be important. In this study, we demonstrate that active Ras is required for TGF-beta1-induced EMT in human keratinocytes and that epidermal growth factor (EGF) can substitute for mutant Ras. EMT was reversed by the removal of TGF-beta1. Under conditions of TGF-beta1-induced EMT, cells were growth inhibited by the ligand resulting in G1 arrest. In cells containing normal Ras, TGF-beta1-activated ERK and p38 mitogen-activated protein kinases (MAPKs), and levels of activation were further increased by co-treatment with EGF. Inhibition of MAPK pathways and Smad2/3 signalling blocked the induction of EMT by TGF-beta1. Further, inhibition of the AP-1 transcriptional complex by [6]-Gingerol, or by the ectopic expression of JDP2, blocked TGF-beta1-induced EMT and conversely, stimulation of AP-1 by 12-O-tetradecanoylphorbol 13-acetate (TPA) substituted for EGF in the induction of EMT by TGF-beta1 in cells containing normal Ras. The presence of oncogenic Ras, the treatment of cells with EGF, or the treatment of cells with TPA to activate AP-1, potentiated TGF-beta1-induced Smad-dependent transcription, an effect that was attenuated by the inhibition of MAPKs and AP-1. The results demonstrate that active Ras and TGF-beta1 co-operate to reversibly induce EMT in human keratinocytes by mechanisms that involve MAPKs, Smad2/3 and AP-1. Further we demonstrate that MAPK/AP-1 signalling enhances Smad transcriptional activity under conditions associated with TGF-beta1-induced EMT.

Targeting TGF-β Signaling for Therapeutic Gain

“…However, during tumor progression, the normal function of TGF-b as a homeostatic negative regulator of cellular proliferation is blunted by activation of oncogenes. Moreover, TGF-b1 expression is sequentially elevated by multiple mechanisms during the progression of multistage carcinogenesis from tumor initiation through to metastasis (Oft et al 2002)-for example, by oncogene-driven AP-1 transcription factor binding to and activation of the TGFB1 gene promoter (Kim et al 1989;Weigert et al 2000;Davies et al 2005) and by latent TGF-b activation within a protease-rich TME (Leitlein et al 2001). Tumor and patient are therefore bathed in excess TGF-b, contributing to an immunosuppressed state.…”

“…It has been postulated that SMIs penetrate tumor tissue more easily than antibodies, and this may be true in highly dysplastic tumors, such as pancreatic carcinoma. However, the anti-TGF-b antibody, fresolimumab, was shown to be efficaciously delivered to glioblastoma cells in a clinical setting, presumably owing to breakdown of the blood brain barrier in this neoplastic tissue (Den Hollander et al 2015).…”

Fra‐1 regulates vimentin during Ha‐RAS‐induced epithelial mesenchymal transition in human colon carcinoma cells

“…12,13 AP-1 can also promote invasion and the transition of tumor cells from an epithelial to a mesenchymal morphology, which is one of the early steps in tumor metastasis. 14 Components of AP-1 have also been shown to stimulate EMT. 15 These oncogenic properties of AP-1 are primarily dictated by the dimer composition of the AP-1 family proteins and their posttranscriptional and posttranslational modifications.…”

Activation of Bone Morphogenetic Protein Signaling by a Gemini Vitamin D3 Analogue Is Mediated by Ras/Protein Kinase Cα

“…Many studies of cross-talk between Ras and TGF-h/Smad signaling have been described during the last decade (31)(32)(33)(34)(35). Yue et al (31) reported that TGF-h activated the Ras/MAPK pathway required for the autocrine TGF-h production and Smad1 regulation.…”

“…Ras was also suggested as a mediator of pleiotropic TGF-h1 signaling in developing neurons (32). The activation of Ras/MAPK or the presence of oncogenic Ras was shown to enhance TGF-hinduced epithelial-mesenchymal transition (33,34). More importantly, it has been shown that 1a,25(OH) 2 D 3 regulates the MAPK pathway by activating Ras/RAF-1 signaling in muscle cells and in myeloid leukemic cells (17,18).…”