Yoji Hayashita

MicroRNAs (miRNAs) are small noncoding RNAs, thought to be involved in physiologic and developmental processes by negatively regulating expression of target genes. We have previously reported frequent down-regulation of the let-7 miRNA family in lung cancers and, in the present study, assessed alteration in a panel of 19 lung cancer cell lines. As a result, we found for the first time that the miR-17-92 cluster, which comprises seven miRNAs and resides in intron 3 of the C13orf25 gene at 13q31.3, is markedly overexpressed in lung cancers, especially with small-cell lung cancer histology. Southern blot analysis revealed the presence of increased gene copy numbers of the miRNA cluster in a fraction of lung cancer cell lines with overexpression. In addition, we were able to show predominant localization of C13orf25 transcripts within the nucleus and introduction of the expression construct of the miR-17-92 cluster, but not the putative open reading frame of C13orf25, enhancing lung cancer cell growth. These findings clearly suggest that marked overexpression of the miR-17-92 cluster with occasional gene amplification may play a role in the development of lung cancers, especially in their most aggressive form, small-cell lung cancer, and that the C13orf25 gene may well be serving as a vehicle in this regard.

It has been suggested that attenuation of the decatenation G(2) checkpoint function, which ensures sufficient chromatid decatenation by topoisomerase II before entering into mitosis, may contribute to the acquisition of genetic instability in cancer cells. To date, however, very little information is available on this type of checkpoint defect in human cancers. In this study, we report for the first time that a proportion of human lung cancer cell lines did not properly arrest before entering mitosis in the presence of a catalytic, circular cramp-forming topoisomerase II inhibitor ICRF-193, whereas the decatenation G(2) checkpoint impairment was present independently of the impaired DNA damage G(2) checkpoint. In addition, the presence of decatenation G(2) checkpoint dysfunction was found to be associated with diminished activation of ataxia-telangiectasia mutated in response to ICRF-193, suggesting the potential involvement of an upstream pathway sensing incompletely catenated chromatids. Interestingly, hypersensitivity to ICRF-193 was observed in cell lines with decatenation G(2) checkpoint impairment and negligible activation of ataxia-telangiectasia mutated. These findings suggest the possible involvement of decatenation G(2) checkpoint impairment in the development of human lung cancers, as well as the potential clinical implication of selective killing of lung cancer cells with such defects by this type of topoisomerase II inhibitor.

Thymidine phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD) are the major catabolic enzymes of 5-FU. In this study, we analyzed the concentration of TP and DPD in non-small cell lung cancer tissue by enzyme-linked immunosorbent assay. We measured the TP and DPD levels in 25 adenocarcinoma tissues and 25 squamous cell carcinoma tissues. The mean TP concentration in non-small cell lung cancer tissue was statistically higher than that of normal lung tissue as was the mean DPD concentration. The ratio of the TP level to DPD level in tumor tissue was higher in squamous cell carcinoma than in adenocarcinoma. No significant difference could be detected between the TP level, DPD level, or TP/DPD level and the tumor size or lymph node metastasis. In conclusion, chemotherapy with 5-FU may be more effective in squamous cell lung cancer patients than lung adenocarcinoma patients from the result of the ratio of TP to DPD.

Supplementary Figure from A Polycistronic MicroRNA Cluster, <i>miR-17-92</i>, Is Overexpressed in Human Lung Cancers and Enhances Cell Proliferation