PO-124 PTTG and PBF functionally interact with P53 and predict overall survival in head and neck cancer

Research output: Contribution to journalAbstract

External organisations

  • University of Birmingham, Birmingham.

Abstract

Introduction: Worldwide,~6 87 000 new cases of head and neck cancer are diagnosed annually with more than 3 80 000 deaths. Dysregulation of the tumour suppressor p53 is common in head and neck squamous cell carcinoma (HNSCC) especially in aggressive tumours. TP53 is mutated in 50%–80% of HNSCC but relatively little is understood about the biological and clinical impact of proto-oncogenes that regulate p53. Here, we show that proto-oncogenes pituitary tumour transforming gene 1 (PTTG) and its interacting partner PBF cooperate to regulate p53 activity in HNSCC. In addition, we probe TCGA data and reveal that PTTG and PBF represent new and useful prognostic indicators.

Material and methods: PTTG/PBF expression was determined in matched (tumour/normal) HNSCC tissue (n=24). p53 expression and function was assessed in 92-VU-040T [wild-type TP53 (wtTP53)] and 93-VU-147T [mutant TP53 (mTP53)] cells with lentiviral shRNA ablation of PTTG and PBF. Expression of PTTG, PBF and p53-target genes, as well as patient overall survival (OS), was analysed using HNSCC TCGA data.

Results and discussions: HNSCC tissue revealed significant upregulation of PTTG (1.9-fold, p<0.05) and PBF mRNA (1.6-fold, p<0.01), which was consistent with expression in a larger TCGA dataset (n=520). We found a striking correlation between PTTG and a panel of 129 p53-target genes in HNSCC TCGA data (wtTP53: 82%; mTP53: 53%, p<0.05). In contrast, PBF expression correlated with fewer p53-target genes (wtTP53: 18%; mTP53: 31%, p<0.05). In agreement, there were significant mRNA changes in PTTG- and PBF-depleted HNSCC cells for key p53-responsive genes such as BCL2. Co-immunoprecipitation studies confirmed that PTTG and PBF are specific interactors of p53 in HNSCC. PTTG retained the ability to bind p53 in the absence of PBF, but the degree of interaction was significantly attenuated (PBF-depleted 92-VU-040T cells: 0.25±0.06 fold, p<0.001) suggesting that PBF facilitates binding of PTTG to p53. Half-life studies showed that PTTG and PBF inhibit p53 stability, with joint over-expression giving the most pronounced decrease in p53 protein stability (~13 fold, p<0.001). Subsequent analysis of TCGA HNSCC patients with mTP53 and high tumoural PBF/PTTG showed poorer overall survival (p<0.05, median OS=28.98 months) than those with low PBF/PTTG (median OS=71.16 months).

Conclusion: These findings provide compelling evidence that PTTG and PBF cooperate to dysregulate p53 in HNSCC which results in greater impairment of p53-dependent signalling and contributes towards worse clinical outcomes.

Details

Original languageEnglish
Pages (from-to)A69-A69
Number of pages1
JournalESMO Open
Volume3
Issue numberSuppl. 2
Early online date29 Jun 2018
Publication statusPublished - 1 Jul 2018