Mizuo Ando

Transforming mutations of RAC guanosine triphosphatases in human cancers

Members of the RAS superfamily of small guanosine triphosphatases (GTPases) transition between GDP-bound, inactive and GTP-bound, active states and thereby function as binary switches in the regulation of various cellular activities. Whereas HRAS, NRAS, and KRAS frequently acquire transforming missense mutations in human cancer, little is known of the oncogenic roles of other small GTPases, including Ras-related C3 botulinum toxin substrate (RAC) proteins. We show that the human sarcoma cell line HT1080 harbors both NRAS(Q61K) and RAC1(N92I) mutant proteins. Whereas both of these mutants were able to transform fibroblasts, knockdown experiments indicated that RAC1(N92I) may be the essential growth driver for this cell line. Screening for RAC1, RAC2, or RAC3 mutations in cell lines and public databases identified several missense mutations for RAC1 and RAC2, with some of the mutant proteins, including RAC1(P29S), RAC1(C157Y), RAC2(P29L), and RAC2(P29Q), being found to be activated and transforming. P29S, N92I, and C157Y mutants of RAC1 were shown to exist preferentially in the GTP-bound state as a result of a rapid transition from the GDP-bound state, rather than as a result of a reduced intrinsic GTPase activity. Activating mutations of RAC GTPases were thus found in a wide variety of human cancers at a low frequency; however, given their marked transforming ability, the mutant proteins are potential targets for the development of new therapeutic agents.

Leukemic evolution of donor-derived cells harboring IDH2 and DNMT3A mutations after allogeneic stem cell transplantation.

Leukemic evolution of donor-derived cells harboring IDH2 and DNMT3A mutations after allogeneic stem cell transplantation

Cancer‐associated missense mutations of caspase‐8 activate nuclear factor‐κB signaling

Head and neck squamous cell carcinoma (HNSCC) is an aggressive cancer with a 5‐year survival rate of ~50%. With the use of a custom cDNA‐capture system coupled with massively parallel sequencing, we have now investigated transforming mechanisms for this malignancy. The cDNAs of cancer‐related genes (n = 906) were purified from a human HNSCC cell line (T3M‐1 Cl‐10) and subjected to high‐throughput resequencing, and the clinical relevance of non‐synonymous mutations thus identified was evaluated with luciferase‐based reporter assays. A CASP8 (procaspase‐8) cDNA with a novel G‐to‐C point mutation that results in the substitution of alanine for glycine at codon 325 was identified, and the mutant protein, CASP8 (G325A), was found to activate nuclear factor‐κB (NF‐κB) signaling to an extent far greater than that achieved with the wild‐type protein. Moreover, forced expression of wild‐type CASP8 suppressed the growth of T3M‐1 Cl‐10 cells without notable effects on apoptosis. We further found that most CASP8 mutations previously detected in various epithelial tumors also increase the ability of the protein to activate NF‐κB signaling. Such NF‐κB activation was shown to be mediated through the COOH‐terminal region of the second death effector domain of CASP8. Although CASP8 mutations associated with cancer have been thought to promote tumorigenesis as a result of attenuation of the proapoptotic function of the protein, our results now show that most such mutations, including the novel G325A identified here, separately confer a gain of function with regard to activation of NF‐κB signaling, indicating another role of CASP8 in the transformation of human malignancies including HNSCC.

Salvage surgery for local residual or recurrent pharyngeal cancer after radiotherapy or chemoradiotherapy

Local residual or recurrent pharyngeal cancer after definitive radiotherapy (RT) or chemoradiotherapy (CRT) is correlated to poor prognosis. We analyzed the efficacy of salvage surgery for patients with local residual or recurrent pharyngeal cancer after RT or CRT.

Prognostic value of p16 expression irrespective of human papillomavirus status in patients with oropharyngeal carcinoma

OBJECTIVE In a previous study, we reported the value of p16 expression and alcohol consumption in oropharyngeal carcinoma in Japan. We now report the clinical significance of human papillomavirus status and p16 expression in oropharyngeal carcinoma in Japan. METHODS Over a 9-year period, a retrospective case comparison study of the pathology database was conducted at the University of Tokyo to identify tumor samples of oropharyngeal carcinoma. We performed immunohistochemistry for the p16 protein, in situ hybridization for human papillomavirus-deoxyribonucleic acid and polymerase chain reaction for the human papillomavirus-deoxyribonucleic acid oncogene E6 in oropharyngeal carcinoma in Japanese patients. We evaluated the human papillomavirus status in patients with oropharyngeal carcinoma to determine its prevalence and association with prognosis. We defined human papillomavirus(+) and human papillomavirus(-) oropharyngeal carcinoma cohorts as those with and without polymerase chain reaction for the human papillomavirus-deoxyribonucleic acid oncogene E6 or in situ hybridization-human papillomavirus. RESULTS In oropharyngeal carcinoma, the prevalences of p16(+)human papillomavirus(+), p16(+)human papillomavirus(-), p16(-)human papillomavirus(+) and p16(-)human papillomavirus(-) were 32% (48/150), 7% (10/150), 2% (3/150) and 59% (89/150), respectively. Low tobacco and alcohol consumption, tonsil or base of tongue localization, but not age, were associated with p16(+)human papillomavirus(+). Low alcohol consumption was associated with p16(+)human papillomavirus(-). There was a significant difference in overall survival between p16(+)human papillomavirus(-) and p16(-)human papillomavirus(-) (P = 0.03). In multivariate Cox regression models, p16 was the independent prognostic factor, regardless of human papillomavirus status. CONCLUSION p16 expression was a reliable prognostic biomarker regardless of human papillomavirus status.

Clinical Features of Human Papilloma Virus-Related Head and Neck Squamous Cell Carcinoma of an Unknown Primary Site

Purpose: Head and neck squamous cell carcinoma of an unknown primary site (HNSCCUP) is a heterogeneous group of tumors that includes the human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma. To investigate the relationship between HNSCCUP and HPV, we reviewed p16 overexpression and HPV DNA in lymph node metastases and examined their correlation with the primary site and clinical features. Materials and Methods: Thirty-three patients with HNSCCUP were retrospectively studied. Dissected neck metastases were analyzed for p16 overexpression by immunohistochemistry, and the presence of HPV DNA was investigated by in situ hybridization. Results: Of the 33 patients, 8 (24%) exhibited p16 overexpression. p16-positive lymph node metastases contained significantly more HPV DNA and were most frequently associated with occult primary lesions in the oropharynx and a favorable prognosis. Patients with a lower alcohol consumption, only level II/III metastasis, and cystic lymph node metastasis tended to have p16 overexpression. Conclusions: This is the first report on the relationship of HNSCCUP with p16 and HPV DNA status in Asian patients. In total, 24% of the HNSCCUP patients were p16 positive. p16 overexpression in neck metastasis was predictive of both an occult primary lesion in the oropharynx and an association with HPV infection. Alcohol consumption, location, and features of neck metastasis were correlated with p16 expression.

Oncogenic MAP2K1 mutations in human epithelial tumors

The scirrhous subtype of gastric cancer is a highly infiltrative tumor with a poor outcome. To identify a transforming gene in this intractable disorder, we constructed a retroviral complementary DNA (cDNA) expression library from a cell line (OCUM-1) of scirrhous gastric cancer. A focus formation assay with the library and mouse 3T3 fibroblasts led to the discovery of a transforming cDNA, encoding for MAP2K1 with a glutamine-to-proline substitution at amino acid position 56. Interestingly, treatment with a MAP2K1-specific inhibitor clearly induced cell death of OCUM-1 but not of other two cells lines of scirrhous gastric cancer that do not carry MAP2K1 mutations, revealing the essential role of MAP2K1(Q56P) in the transformation mechanism of OCUM-1 cells. By using a next-generation sequencer, we further conducted deep sequencing of the MAP2K1 cDNA among 171 human cancer specimens or cell lines, resulting in the identification of one known (D67N) and four novel (R47Q, R49L, I204T and P306H) mutations within MAP2K1. The latter four changes were further shown to confer transforming potential to MAP2K1. In our experiments, a total of six (3.5%) activating mutations in MAP2K1 were thus identified among 172 of specimens or cell lines for human epithelial tumors. Given the addiction of cancer cells to the elevated MAP2K1 activity for proliferation, human cancers with such MAP2K1 mutations are suitable targets for the treatment with MAP2K1 inhibitors.

Mucoepidermoid carcinoma of the thyroid gland showing marked ciliation suggestive of its pathogenesis

Mucoepidermoid carcinoma of the thyroid gland is a rare tumor first described by Rhatigan et al. in 1977. Its pathogenesis is still controversial. With regard to its most likely origin, some authors have suggested that it arises directly from follicular epithelium whereas others have proposed that it arises from ultimobranchial body (diverticulum from the fourth pharyngeal pouch) remnants, also known as solid cell nests (SCN). Herein is reported a unique case of thyroid mucoepidermoid carcinoma. The patient, a 67‐year‐old man, presented with a non‐tender thyroid mass and vocal cord fixation. The tumor was poorly defined, necessitating subtotal thyroidectomy with composite resection of the adjacent structures. Pathologically, the tumor cells had characteristics of mucoepidermoid carcinoma, along with layers of columnar cells showing marked ciliation resembling respiratory‐type epithelium, suggesting that this rare tumor had originated from SCN. p63 immunopositivity in the tumor provided additional evidence for the pathogenesis.

Recurrent cancer of the parotid gland: how well does salvage surgery work for locoregional failure?

Purpose: Many articles have discussed the clinical features of previously untreated parotid cancer, but the clinical characteristics and treatment of recurrent parotid cancer have not yet been fully described. Materials: We retrospectively reviewed 20 patients with recurrent parotid cancer and analyzed the therapeutic strategies and the prognostic factors. Results: Twelve patients (60%) underwent definitive surgery, including 3 who underwent skull base surgery. The 5-year overall survival (OS) and 5-year disease-free survival (DFS) in the surgery group were 66.7 and 64.1%. In the definitive surgery group, the presence of lymph node metastasis and high-grade malignant histopathology were associated with a poor prognosis (p < 0.01). On the other hand, the presence of facial palsy at presentation, the surgical margin, the time of relapse and the T stage did not affect the DFS in our series. Conclusions: The results suggest that aggressive definitive surgery may be justified for the treatment of recurrent parotid cancer. The presence of lymph node metastasis and the histopathological malignancy grade are poor prognostic factors for OS and DFS.

High-throughput resequencing of target-captured cDNA in cancer cells.

The recent advent of whole exon (exome)‐capture technology, coupled with second‐generation sequencers, has made it possible to readily detect genomic alterations that affect encoded proteins in cancer cells. Such target resequencing of the cancer genome, however, fails to detect most clinically‐relevant gene fusions, given that such oncogenic fusion genes are often generated through intron‐to‐intron ligation. To develop a resequencing platform that simultaneously captures point mutations, insertions–deletions (indels), and gene fusions in the cancer genome, we chose cDNA as the input for target capture and extensive resequencing, and we describe the versatility of such a cDNA‐capture system. As a test case, we constructed a custom target‐capture system for 913 cancer‐related genes, and we purified cDNA fragments for the target gene set from five cell lines of CML. Our target gene set included Abelson murine leukemia viral oncogene homolog 1 (ABL1), but it did not include breakpoint cluster region (BCR); however, the sequence output faithfully detected reads spanning the fusion points of these two genes in all cell lines, confirming the ability of cDNA capture to detect gene fusions. Furthermore, computational analysis of the sequence dataset successfully identified non‐synonymous mutations and indels, including those of tumor protein p53 (TP53). Our data might thus support the feasibility of a cDNA‐capture system coupled with massively parallel sequencing as a simple platform for the detection of a variety of anomalies in protein‐coding genes among hundreds of cancer specimens. (Cancer Sci 2012; 103: 131–135)