Tbx3 represses PTEN and is over-expressed in head and neck squamous cell carcinoma

Abstract

BackgroundDespite advances in diagnostic and treatment strategies, head and neck squamous cell cancer (HNSCC) constitutes one of the worst cancer types in terms of prognosis. PTEN is one of the tumour suppressors whose expression and/or activity have been found to be reduced in HNSCC, with rather low rates of mutations within the PTEN gene (6-8%). We reasoned that low expression levels of PTEN might be due to a transcriptional repression governed by an oncogene. Tbx2 and Tbx3, both of which are transcriptional repressors, have been found to be amplified or over-expressed in various cancer types. Thus, we hypothesize that Tbx3 may be over expressed in HNSCC and may repress PTEN, thus leading to cancer formation and/or progression.MethodsUsing immunohistochemistry and quantitative PCR (qPCR), protein and mRNA levels of PTEN and Tbx3 were identified in samples excised from cancerous and adjacent normal tissues from 33 patients who were diagnosed with HNSCC. In addition, HeLa and HEK cell lines were transfected with a Tbx3 expressing plasmid and endogenous PTEN mRNA and protein levels were determined via qPCR and flow cytometry. Transcription assays were performed to demonstrate effects of Tbx3 on PTEN promoter activity. Mann–Whitney, Spearman’s Correlation and Wilcoxon signed-rank tests were used to analyze the data.ResultsWe demonstrate that in HNSCC samples, Tbx3 mRNA levels are increased with respect to their normal tissue counterparts (p<0.001), whereas PTEN mRNA levels are significantly reduced in cancer tissues. Moreover, Tbx3 protein is also increased in HNSCC tissue sections. Over-expression of Tbx3 in HeLa and HEK cell lines causes reduction in endogenous PTEN mRNA and protein levels. In addition, transcription activity assays reveal that Tbx3 is capable of repressing both the basal and induced promoter activity of PTEN.ConclusionsWe show that Tbx3 is up-regulated in tissue samples of HNSCC patients and that Tbx3 represses PTEN transcription. Thus, our data not only reveals a new mechanism that may be important in cancer formation, but also suggests that Tbx3 can be used as a potential biomarker in cancer.

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

“…[6][7][8][9][10][27][28][29][30] This suggests that The levels of TBX3 mRNA expression were analyzed using primers specific to TBX3 and normalized against GUSB. Bars, SEM.…”

“…5 One such mechanism is the ability of TBX3 to override key cell cycle checkpoints to suppress senescence and promote proliferation by transcriptionally repressing the cyclin-dependent kinase inhibitors, p21 WAF1/CIP1/SDII (hereafter referred to as p21) and p14 ARF . 6,7 TBX3 also promotes proliferation of head and neck squamous carcinoma cells by directly repressing the tumor suppressor PTEN 8 and embryonic stem cells by up-regulating Zscan4 to elongate telomeres as well as through repressing NFjBIB and p14 ARF . 9,10 In light of these findings it appears that the role of TBX3 in cancer may, in part, be linked to its ability to regulate the cell cycle, which suggests that its levels and transcriptional activity may have to be tightly regulated during this process.…”

The T-Box transcription factor 3 in development and cancer

“…For example, an inverse correlation between the mRNA and protein levels of TBX3 and the tumour suppressor PTEN was identified in HNSCC cells (55). PTEN is a negative regulator of the phosphoinositide 3-kinase/ Protein kinase B (PI3K/AKT) pathway and suppresses oncogenic processes such as proliferation, cell survival and migration (56).…”

“…PTEN is a negative regulator of the phosphoinositide 3-kinase/ Protein kinase B (PI3K/AKT) pathway and suppresses oncogenic processes such as proliferation, cell survival and migration (56). Importantly, TBX3 can directly repress PTEN by binding a 132 bp DNA region within its promoter (55). Interestingly, the authors found that this region of the PTEN promoter does not contain a T-element and thus speculated that TBX3 may repress PTEN by either interacting with transcriptional corepressors or by interfering with positive activators of PTEN.…”

TBX3 (T-box 3)

“…TBX3 has been described to function as a transcriptional repressor and to date was shown to directly repress p14, p21, E-cadherin and phosphatase and TENsin homolog (PTEN) Hoogaars et al, 2008;Rodriguez et al, 2008;Burgucu et al, 2012). While in vitro assays have suggested that TBX3 is capable of transcriptional activation, it has not yet been shown to activate any physiologically relevant target genes.…”