MicroRNAs (miRNAs) are noncoding small RNAs that regulate gene expression. Expression profiles of miRNAs are useful to improve classification, diagnosis, and prognostic information of specific human malignancies, including lung cancer. We sought to uncover miRNAs preferentially repressed or over-expressed in pre-malignant and malignant lung lesions in recently described transgenic cyclin E mice. These transgenic mice expressed in the lung under control of the human surfactant C promoter wild-type or proteasome degradation-resistant cyclin E species. These mice developed pulmonary dysplasia and adenocarcinoma, recapitulating pre-malignant and malignant lung lesions frequently found in lung cancer patients. Comprehensive miRNA microarray analyses were conducted using independently harvested normal and malignant lung tissues from these transgenic mice. A cluster of miRNAs was preferentially repressed in transgenic lung cancers versus normal lung tissues including: miR-34c, miR-145, miR142-5p, and other miRNAs previously associated with lung carcinogenesis. Expression profiles were independently validated by semi-quantitative and real-time polymerase chain reaction assays. In transgenic mice, single cell expression profiles were studied in pre-malignant and malignant lung lesions by in situ hybridization assays. Concordant results were obtained after analyses of paired normal-malignant human lung tissues representing each histopathologic subtype of non-small cell lung cancer. To address functional roles of repressed miRNAs, novel lung cancer cell lines were derived from murine transgenic wild-type (ED-1 cells) or proteasome-degradation resistant (ED-2 cells) cyclin E expressing lung cancers. ED-1 and ED-2 cells each caused lung adenocarcinomas to form after tail-vein injections into syngeneic FVB mice. Engineered over-expression of each basally repressed miRNA in ED-1 as well as in ED-2 cells markedly (P < 0.001) repressed cell growth. Anti-miR co-transfections antagonized these effects. A mechanism for this growth suppression was found by showing cyclin E, a predicted miR-34c bioinformatic target, was significantly repressed in miR-34c transfectants. Other miRNAs were selected for knock-down in ED-1 and ED-2 cells by virtue of their high basal expression in these cells as well as in murine transgenic lung cancers and human lung cancers versus normal lung tissues. Knock-down of candidate oncogenic miRNAs repressed lung cancer cell growth, which was antagonized by over-expression of the same miRNA. Experiments are underway in miRNA transfected ED-1 cells to assess in vivo tumorigenicity in FVB mice. Taken together, these studies uncovered candidate tumor suppressive and oncogenic miRNAs. We propose these miRNAs are molecular pharmacologic targets for lung cancer therapy and chemoprevention.

Citation Information: Cancer Prev Res 2008;1(7 Suppl):A135.

Seventh AACR International Conference on Frontiers in Cancer Prevention Research-- Nov 16-19, 2008; Washington, DC