Expression of BUB1 protein in gastric cancer correlates with the histological subtype, but not with DNA ploidy or microsatellite instability.

During mitosis, the spindle checkpoint delays the onset of anaphase until all chromosomes have attached properly to the mitotic spindle, preventing chromosome missegregation. BUB (budding uninhibited by benzimidazole) 1 is one of the key components of this checkpoint. BUB1 mutations are rare in cancer tissues and no mutations have been identified in gastric cancer. In mice, immunodepletion of BUB1 abolished the spindle checkpoint. Thus, aberrant expression of BUB1 protein could impair mitotic checkpoint function, resulting in aneuploidy, a common phenomenon in gastric cancer. In the present study, an antibody was generated against BUB1 and its expression was studied in gastric cancer tissue sections (n = 80) by immunohistochemistry. Nuclear BUB1 expression was found in all gastric cancer cases. The proportion of tumour cells expressing BUB1 was significantly greater in diffuse-type than in intestinal-type gastric carcinoma (p < 0.001). No correlation was found between BUB1 expression and deoxyribonucleic acid (DNA) ploidy, microsatellite instability or any other histopathological parameters investigated. To the authors' knowledge, this is the first study of BUB1 protein expression in gastric cancer tissues. Different BUB1 protein expression levels in intestinal- and diffuse-type gastric cancer may provide further evidence of a potential link between different genetic pathways and morphological phenotype in gastric carcinogenesis. However, further studies are needed to establish whether there is an association between BUB1 protein expression level and mitotic spindle checkpoint function in gastric cancer.

Diagnostic value of nucleolar organizer regions (AgNORs) in brush biopsies of suspicious lesions of the oral cavity.

OBJECTIVE: The aim of this retrospective study was to report on the diagnostic accuracy of AgNOR-analysis as an adjunctive diagnostic tool of conventional oral exfoliative cytology taken from suspicious lesions in our clinic. STUDY DESIGN: Cytological diagnoses obtained from brush biopsies of macroscopically suspicious lesions of the oral mucosa from 75 patients (final diagnoses: 53 histologically proven squamous cell carcinomas, 11 leukoplakias and other inflammatory oral lesions) and from 11 patients with normal mucosa as a negative control group were compared with histological and/or clinical follow-ups. Five smears were doubtful and seven suspicious for tumor cells in the cytologic report. Number of AgNOR's were counted in 100 squamous epithelial cell-nuclei per slide after silver-restaining. RESULTS: Sensitivity of our cytological diagnosis alone on oral smears for the detection of squamous carcinomas was 92.5%, specificity 100%, positive predictive value was 100% and negative 84.6%. The best cut-off value of the mean number of AgNOR dots per nucleus distinguishing benign from malignant cells was 4.8. The percentage of nuclei with more than three AgNORs had a cut-off level of 70%. Applying these methods to twelve doubtful or suspicious cytological diagnoses we were able to correctly establish the diagnosis of malignancy in ten cases of histologically proven cancers and to reveal benignity in two histologically proven cases. Thus we achieved a positive and negative predictive value of 100% each. CONCLUSIONS: Smears from brushings of visible oral lesions, if clinically considered as suspicious for cancer, are an easily practicable, non-invasive, painless, safe and accurate screening method for detection of oral cancerous lesions. We conclude that AgNOR-analysis may be a useful adjunct to other methods in routine cytological diagnosis of oral cancer that can help to solve cytologically suspicious or doubtful cases.

Overexpression of the mitotic checkpoint genes BUB1, BUBR1, and BUB3 in gastric cancer--association with tumour cell proliferation.

The mitotic spindle assembly checkpoint modulates the timing of anaphase initiation in response to improper alignment of chromosomes at the metaphase plate. The BUB gene family encodes proteins which are part of a large multi-protein kinetochore complex and which are believed to be key components of the checkpoint regulatory pathway. Failure of this surveillance system can lead to genomic instability and could be responsible for the increased incidence of aneuploidy in gastric cancer. Since mutations of BUB genes have not been identified in gastric cancer to date, altered BUB expression levels may significantly impair mitotic checkpoint function. To explore this possibility, the expression levels of BUB1, BUBR1, and BUB3 were determined in 43 gastric carcinomas and corresponding normal gastric mucosa by reverse transcription-polymerase chain reaction (RT-PCR). Gene expression levels were compared with histopathological parameters and DNA ploidy, as well as with proliferative activity, measured by Ki-67 mRNA expression. To the authors' knowledge, this is the first study to investigate the expression levels of mitotic checkpoint genes together with DNA ploidy in gastric cancer. BUB1 was overexpressed in 84%, BUBR1 in 68%, and BUB3 in 79% of gastric cancers. This study also revealed that all three genes were simultaneously overexpressed in 61% of the tumours and that there was a statistically significant positive correlation between overexpression of BUB1, BUBR1 or BUB3 and Ki-67 expression (p < 0.001). Eighty-one per cent of the tumours were classified as aneuploid. However, no correlation was found between ploidy and BUB transcript expression levels. These results suggest that inactivation of the mitotic checkpoint genes BUB1, BUBR1, and BUB3 by epigenetic silencing does not seem to play a role in gastric carcinogenesis. The strong correlation of BUB expression level and tumour cell proliferation suggests that BUB overexpression is a proliferation-dependent phenomenon in gastric cancer. However, overexpression due to lack of normal BUB protein function or due to a yet unknown additional BUB function has to be considered.