Is it all just an Akt - you’d be SMAD to believe it! Role of TGFβ1 in oral cancer metastasis

Abstract

Introduction: TGFβ1 activates both SMAD and non-SMAD dependent signalling pathways but their role in oral cancer cell migration and metastasis is little known. The aim of this research was to investigate the role of TGFβ1-induced signalling pathways in oral cancer cell migration and to establish whether the inhibition of the associated pathway may be a suitable target for chemotherapeutic drug design to control oral cancer cell metastasis. Materials and Methods: SDS-PAGE and Western blot techniques were used to investigate the expression and phosphorylation status of TGFβ1induced key signalling molecules such as, SMAD, Akt and MAPK in normal keratinocytes and oral cancer cells. Gap closure and scatter assays were employed to study the effect of TGFβ1 on cell migration. Akt and MAPK inhibitors were also used to explore the role of associated signalling pathways in TGFβ1-induced cell migration. Phosphorylation of Akt, MAPK and SMAD were analysed by immunofluorescence in TGFβ1-induced migrated cells. Results: TGFβ1 stimulated the phosphorylation of SMAD, Akt and MAPK in both normal keratinocytes and oral cancer cells. The level of phosphorylation, however, depended upon cell type, time of exposure to and concentration of TGFβ1. TGFβ1-stimulated cancer cell migration both as single cells (EMT, epithelial to mesenchymal transition) and as a sheet of cells. Inhibitor assays confirmed that cancer cell migration is phosphorylated-Akt dependent. However, TGFβ1 did not stimulate migration as a sheet of cells, but EMT of normal keratinocytes which was phosphorylated-MAPK dependent. Conclusion: TGFβ1-induced oral cancer cell migration was dependent on the Akt signalling pathway. From this study, we propose that blocking the Akt pathway may inhibit oral cancer metastasis and could have potential in translating this research into clinical practice.

Head and Neck Cancer Metastasis and the Effect of the Local Soluble Factors, from the Microenvironment, on Signalling Pathways: Is It All about the Akt?

“…TGFβ has been shown to activate Akt, leading to cell migration in prostate cancer [ 44 ]. TGFβ1 stimulates the phosphorylation of SMAD (Sma and Mad proteins), MAPK, and Akt in head and neck cancer but stimulated the migration of cancer cells in an Akt-dependent manner [ 45 ]. In prostate cancer, CXCR4 is overexpressed, and a loss of the tumour suppressor PTEN was reported to activate Akt and regulate the CXCL12/CXCR4 signalling pathway in metastasis [ 46 ].…”

<strong>Oral Tumour Cell Migration and the Effect of the Local Soluble Factors from the Microenvironment on Signalling Pathways. Is It All about the Akt? </strong>

“…TGFβ has been shown to activate Akt, leading to cell migration in prostate cancer [27]. TGFβ1 stimulates the phosphorylation of SMAD, MAPK and Akt in oral cancer, but stimulated the migration of oral cancer cells in an Akt-dependent manner [28]. In prostate cancer, CXCR4 is overexpressed and loss of the tumour suppressor PTEN was reported to activate Akt and regulate the CXCL12/CXCR4 signalling pathway in metastasis [29].…”

Role of Akt/Protein Kinase B in Cancer Metastasis

“…Akt has been reported to be abundant in the nucleus in many cancer cells yet, the mechanism of translocation, biological importance and activity has not yet been established [165]. Published data from our group also revealed that EGF (Epidermal Growth Factor), TGFα (Transforming Growth Factor α), TGFβ1(Transforming Growth Factor β1) and NGF (Nerve Growth Factor) can stimulate head and neck cancer cell migration and a specific PI3k/Akt pathway inhibitor such as PI103 or MK2206 can effectively block growth factor-induced cell migration [166,167]. Study from our research group also suggested that receptor tyrosine kinase inhibitors such as Gefitinib and Erlotinib inhibited the migration of head and neck cancer cells by inhibiting both Akt and MAPK phosphorylation [168].…”