The T-box transcription factor, TBX3, is a key substrate of AKT3 in melanomagenesis

Abstract

The AKT3 signalling pathway plays a critical role in melanoma formation and invasion and components of this signalling cascade are therefore attractive targets for the treatment of malignant melanoma. Recent evidence show that the embryonically important TBX3 transcription factor is upregulated in a subset of melanomas and plays a key role in promoting melanoma formation and invasion, in part by repressing the cell adhesion molecule E-cadherin. We have identified TBX3 as a key substrate of AKT3 in melanomagenesis. Briefly, using site-directed mutagenesis and in vitro kinase assays, we have identified the AKT3 target site at serine residue 720 in the TBX3 protein and show that this site is phosphorylated in vivo. Importantly, we show by western blotting, immunofluorescence, reporter, migration and invasion assays that the phosphorylation at S720 promotes TBX3 protein stability, nuclear localization, transcriptional repression of E-cadherin, and its role in cell migration and invasion. Our results identify a novel signalling and transcriptional network linking AKT3, TBX3 and E-cadherin during melanoma migration and invasion and reveals TBX3 as a potential target for anti-metastatic therapeutics.

The T-Box transcription factor 3 in development and cancer

“…While there are instances where the three Akt isoforms are able to compensate for each other, recent research show that their tissue expression patterns and functions are different (99,100). The PI3K/Akt pathway is activated in 70% of all melanoma cases and Peres et al reported that TBX3 is a substrate and effector of this pathway in melanoma (69). Consistent with other reports, the authors demonstrated that Akt3 is the predominant isoform activated in a panel of human melanoma cell lines.…”

“…This repression was shown to be physiologically relevant because when TBX3 was silenced in metastatic melanoma cells, E-cadherin levels increased. Furthermore, TBX3 is transcriptionally indirectly upregulated by the oncoprotein BRAF V600E, which is constitutively activated in 50% of melanomas, and is a substrate and effector of AKT3, which is activated in ~70% of advanced stage melanomas where it plays a critical pro-invasive role (68,69). Importantly, TBX3 was shown to repress E-cadherin downstream of both these pathways to promote migration and invasion of melanoma cells.…”

The T-Box factor TBX3 is important in S-phase and is regulated by c-Myc and cyclin A-CDK2

“…49,50 The ¡2186-base pair TBX3-luciferase plasmid was modified to introduce point mutations by site-directed mutagenesis using the Stratagene QuikChange system. Successful introduction of the mutation was confirmed by sequencing.…”

T-box 3 overexpression is associated with poor prognosis of non-small cell lung cancer

“…A mutation of Tbx3 was demonstrated to be closely associated with the pluripotency of embryonic stem cells and the invasiveness of cancer (6). In resectable pancreatic carcinoma (7), melanoma (8), bladder cancer (9) and colorectal cancer (10), Tbx3 was revealed to be overexpressed and associated with poor prognosis of cancer. Recently, Tbx3 was reported to serve a key role in melanoma migration and invasion by acting as a key substrate of protein kinase B and thus inducing the repression of E-cadherin (8).…”

“…In resectable pancreatic carcinoma (7), melanoma (8), bladder cancer (9) and colorectal cancer (10), Tbx3 was revealed to be overexpressed and associated with poor prognosis of cancer. Recently, Tbx3 was reported to serve a key role in melanoma migration and invasion by acting as a key substrate of protein kinase B and thus inducing the repression of E-cadherin (8). Additionally, Tbx3 is involved in the anti-proliferative event mediated by the transforming growth factor β1 signaling pathway by repressing the oncogenic Tbx2 in human breast epithelial MCF-12A cells (11).…”