Reduced expression of the let-7 microRNAs in human lung cancers in association with shortened postoperative survival.

In this study, we report for the first time reduced expression of the let-7 microRNA in human lung cancers. Interestingly, 143 lung cancer cases that had undergone potentially curative resection could be classified into two major groups according to let-7 expression in unsupervised hierarchical analysis, showing significantly shorter survival after potentially curative resection in cases with reduced let-7 expression (P = 0.0003). Multivariate COX regression analysis showed this prognostic impact to be independent of disease stage (hazard ratio = 2.17; P = 0.009). In addition, overexpression of let-7 in A549 lung adenocarcinoma cell line inhibited lung cancer cell growth in vitro. This study represents the first report of reduced expression of let-7 and the potential clinical and biological effects of such a microRNA alteration.

Gene expression-based, individualized outcome prediction for surgically treated lung cancer patients.

Individualized outcome prediction classifiers were successfully constructed through expression profiling of a total of 8644 genes in 50 non-small-cell lung cancer (NSCLC) cases, which had been consecutively operated on within a defined short period of time and followed up for more than 5 years. The resultant classifier of NSCLCs yielded 82% accuracy for forecasting survival or death 5 years after surgery of a given patient. In addition, since two major histologic classes may differ in terms of outcome-related expression signatures, histologic-type-specific outcome classifiers were also constructed. The resultant highly predictive classifiers, designed specifically for nonsquamous cell carcinomas, showed a prediction accuracy of more than 90% independent of disease stage. In addition to the presence of heterogeneities in adenocarcinomas, our unsupervised hierarchical clustering analysis revealed for the first time the existence of clinicopathologically relevant subclasses of squamous cell carcinomas with marked differences in their invasive growth and prognosis. This finding clearly suggests that NSCLCs comprise distinct subclasses with considerable heterogeneities even within one histologic type. Overall, these findings should advance not only our understanding of the biology of lung cancer but also our ability to individualize postoperative therapies based on the predicted outcome.

Frequent and histological type-specific inactivation of 14-3-3sigma in human lung cancers.

One isoform of the 14-3-3 family, 14-3-3sigma, plays a crucial role in the G2 checkpoint by sequestering Cdc2-cyclinB1 in the cytoplasm, and the expression of 14-3-3sigma is frequently lost in breast cancers. This loss of expression is thought to cause a G2 checkpoint defect, resulting in chromosomal aberrations. Since lung cancers frequently carry numerous chromosomal aberrations, we examined the DNA methylation status and expression level of the 14-3-3sigma gene in 37 lung cancer cell lines and 30 primary lung tumor specimens. We found that small cell lung cancer (SCLC) cell lines frequently showed DNA hypermethylation (9 of 13 lines, 69%), and subsequent silencing of the 14-3-3sigma gene. Among non-small cell lung cancers (NSCLC), large cell lung cancer cell lines showed frequent hypermethylation and silencing of 14-3-3sigma (4 or 7 lines, 57%). In contrast, in other NSCLC cell lines, hypermethylation occurred very rarely (1 of 17 lines, 6%). All eight primary SCLC specimens examined also showed a loss or significant reduction in 14-3-3sigma expression in vivo, while a loss or reduction of 14-3-3sigma expression was very rare in primary NSCLC specimens (1 of 22 tissues, 5%). This is the first description that indicates lung cancers frequently show significant inactivation of the 14-3-3sigma gene mainly due to DNA hypermethylation in SCLC, but rarely in NSCLC, suggesting involvement of the 14-3-3sigma gene in lung tumorigenesis in a histological type-specific manner.

Identification of frequent G(2) checkpoint impairment and a homozygous deletion of 14-3-3epsilon at 17p13.3 in small cell lung cancers.

Accumulating evidence suggests that a coordinately controlled G(2) checkpoint prevents cells with damaged DNA from entering mitosis, thus playing an important role in the maintenance of chromosomal integrity. In the study presented here, we identified a homozygous deletion of the 14-3-3epsilon gene, which resides within a previously identified, commonly deleted region at 17p13.3 in lung cancers, in two small cell lung cancer cell lines that originate from distinct metastatic sites of the same patients. The introduction of 14-3-3epsilon induced significantly restored G(2) checkpoint responses, which resulted in the reduction of mitotic cells as well as of aberrant mitotic figures in the X-ray-irradiated 14-3-3epsilon-null small cell lung cancer cell line. Interestingly, we also found that the G(2) checkpoint response is frequently impaired to various degrees in a large fraction of small cell lung cancer cell lines. These findings suggest the possible involvement of the perturbed G(2) checkpoint in the pathogenesis of this aggressive form of human lung cancers.