Ken-ichi Aoyama

Frequent mutations in NOTCH1 ligand-binding regions in Japanese oral squamous cell carcinoma.

Recent studies showed that head and neck squamous cell carcinoma (HNSCC) including oral squamous cell carcinoma (OSCC) of Caucasian, Chinese and Indian patients frequently have NOTCH1 mutations. We found eight of 84 OSCC in Japanese patients have point mutations (9.5%) correspond to the ligand binding region of NOTCH1 protein. Two set of them are the same mutations and all mutations are non-synonymous G>A transitions. In addition, median disease-free survival is significantly longer in patients with NOTCH1-mutated tumors as compared to those without the mutation (P<0.05). The protein structure simulation based on X-ray crystallography indicated that new p.A465T mutation leads to a conformational change of NOTCH1 ligand binding domain as well as the p.G481S mutant NOTCH1 with a loss of flexibility around this residue. These results suggest that NOTCH1 mutation occurs frequently in Japanese OSCC in the vicinity of the ligand binding region and, these mutations cause downregulation of the NOTCH1 function.

Kikuchi-Fujimoto disease with 18f-fludeoxyglucose uptake in cervical lymph nodes on dual-time-point imaging positron emission tomography/computed tomography mimicking malignant disease

Kikuchi-Fujimoto disease (KFD) is a benign but self-limiting disorder. However, KFD is often misdiagnosed as a malignant disease. Although 18F-fludeoxyglucose (FDG) uptake on dual-time-point imaging (DTPI) positron emission tomography (PET)/computed tomography (CT) is useful in distinguishing malignant from benign disease, the latter sometimes mimics malignancy on DTPI PET/CT, resulting in a misdiagnosis. Here, we describe the case of a 30-year-old woman who complained of cervical lymphadenopathy. PET showed increased FDG uptake in multiple lymph nodes, with a maximum standardized uptake value (SUVmax) of 19.0 in the early phase to 21.8 in the late phase. A biopsy was performed, and pathological examination revealed KFD. KFD with FDG uptake in lymph nodes on DTPI PET/CT is rare and difficult to be distinguished from a malignant disease.

A mutation in NOTCH1 ligand binding region detected in patients with oral squamous cell carcinoma reduces NOTCH1 oncogenic effect

NOTCH1 is known as an oncogenic or tumor suppressive gene in solid cancer. NOTCH1 mutations in oral squamous cell carcinoma (OSCC) frequently occur near the ligand-binding region. These mutations change the domain structure of this protein and affect the ligand binding activity. When NOTCH1 is activated by ligand binding, NOTCH1 intracellular domain (NICD) is cleaved from the cell membrane. This study investigated the functional change induced by a NOTCH1 mutation detected in OSCC clinical samples using stable transformant analysis. HEK293 cell lines expressing NOTCH1 wild-type (WT cells) or p.A465T NOTCH1 (A465T cells) were established. NOTCH1 expression was analyzed by flow cytometry, western blotting, and immunofluorescence using an anti-human NOTCH1 antibody. mRNA expression levels in WT and A465T cells were determined by quantitative real-time PCR (qPCR). Cell proliferation was analyzed by using cell growth assays and a xenograft tumor assay. Flow cytometry indicated that NOTCH1 expression on the cell membrane was lower in A465T cells than that in WT cells. NOTCH1 and NICD were both detected by western blot in WT and A465T cells. The immunofluorescence signal for NICD was detected in the nucleus of WT cells, while it was localized mainly in the cytoplasm of A465T cells. HES1 and HEY1 mRNA expression levels were lower in A465T than in WT cells. The cell growth of WT cells was significantly higher than that of HEK293 cells (3-fold, P<0.01), while that of A465T cells was significantly lower than that of HEK293 cells (37%, P<0.01). In a xenograft model, the tumor cell implantation rate of WT cells was 80%, while that of A465T cells was 0%. This study indicates that NOTCH1 acts as an oncogene and that the NOTCH1 mutation (p.A465T) in the ligand-binding region causes the loss of tumorigenicity by downregulating the NOTCH1 pathway.