The Change Of NOTCH1 Signaling In Oral Squamous Cell Carcinoma And Its Clinical Significance

【Objective】 NOTCH is highly conserved among species through evolution, and plays an important role in development. Its role in tumor also complicated, because it can function both as an oncogene and a tumor suppressor alike depending on the cell context. In head and neck cancer, the exact role of NOTCH remains largely unknown. But recently some studies observed a surprisingly high NOTCH1 mutation(15-20%) in head and neck cancer, only lower than TP53 mutation. These studies also indicated NOTCH1 as a tumor suppressor in head and neck cancer, which differs from its role in T cell acute lymphocytic leukemia(T-ALL), where it plays as an oncogene. Based on the fact that ethnicity may indicate different genetic background in common tumors that affects clinical outcome and response to therapy. It is of great importance and significance to explore the NOTCH1 mutation status in Chinese oral cancer patients.PRESENILIN1(PS1), which is important in NOTCH signaling activation, is reported to inversely modulate epidermal growth factor receptor(EGFR) expression in development. The expression of PS1 in oral cancer and its role in EGFR signaling pathway were also detected in this study. 【Methods and Materials】 Fifty-one primary oral squamous cell carcinoma tissue sample block with formalin fixed and paraffin embedded from Chinese patients and 46 of their matched normal tissues were collected for genomic DNA. By using Ion-torrent platform we sequenced the whole exons of NOTCH1 and TP53 gene. After collecting the somatic mutations of these samples, we analyzed the correlation between NOTCH1 mutation and clinical characteristics and survival. We also performed immunohistochemistry and realtime RT-PCT to detect the expression of PS1 in oral cancer. By using siRNA targeting PS1, we detected the effect of PS1 knockdown on the proliferation and apoptosis of oral cancer cell lines and the relationship between PS1 knockdown and EGFR pathway in oral cancer.【Results】There were 156 NOTCH1 single nucleotide variants altogether, including 35 missense mutations and 7 nonsense mutations, distributed in 22 of the 51(43.1%) samples. What was different from previous reports was that there were 12 mutations that might serve as gain-of-function mutations. NOTCH1 mutation was associated with decreased overall survival(P = 0.0042) and disease-free survival(P = 0.001). Like cervical lymph node metastasis, NOTCH1 mutation can also independently predicts a decreased survival(risk ratio, 3.445; 95% CI, 1.611 to 7.369, P = 0.001). All 15 patients with both NOTCH1 mutation and nodal metastasis recurred or metastasized within 2 years after surgery.There were 21 missense mutations and 4 nonsense mutations in TP53 gene, distributed in 21 patients(41%). There were no association between TP53 mutation and any clinical characteristics.PS1 expression was elevated in oral cancer cell lines and in primary oral cancer tissues. PS1 down-regulation resulted in cell growth inhibition and apoptosis. What is unexpected is that its expression correlated with EGFR to some extent, and down-regulation of PS1 inhibited EGFR expression level and EGFR-STAT pathway. 【Conclusions】NOTCH1 mutation is more common and complicated in Chinese oral squamous cell carcinoma and associates with shorter survival. The complexity of the mutation spectrum underscores the importance of individualized therapeutic approach for Chinese patients with this type of cancer. Combined with the elevated PS1 expression and its correlation with EGFR, we conclude that change in NOTCH signaling plays an important role in the development of oral squamous cell carcinoma.