Abstract 3992: Roles of ASH1-miR-375 pathway in development of lung cancers with neuroendocrine features

Lung cancers with neuroendocrine (NE) features are often very aggressive, though the underlying molecular mechanisms have not been clearly elucidated. We previously reported that the basic helix-loop-helix protein, achaete-scute homologue 1 (ASH1/ASCL1), a master regulator of pulmonary neuroendocrine cell development, is crucially involved in the pathogenesis of lung cancers with neuroendocrine features (NE-lung cancers). In the present study, we searched for miRNAs regulated by ASH1 in order to gain insight into the involvement of miRNAs downstream of ASH1 in NE-lung cancer pathogenesis. We consequently found that introduction of ASH1 into A549 cells markedly induced miR-375 and down-regulated miR-200b. Interestingly, these two miRNAs inversely affected cell-cell interaction and cell motility, and they together conferred looser cell attachment and a more motile feature. miR-375 was found to be directly transactivated by ASH1. Global gene expression analysis using miR-375-introduced A549 cells and the subsequent pathway analysis using the Ingenuity IPA software revealed altered gene expressions in several cancer-related pathways (e.g., cellular movement and morphology). Interestingly, we also found that miR-375 alone can induce NE differentiation markers in A549 cells and that miR-375 is required to elicit ASH1-indued NE features. In accordance with these findings in vitro, clear induction of NE features as well as enhanced tumor growth was observed in xenografts of A549 cells stably expressing miR-375. We further found that a transcriptional co-activator YAP1 is most significantly repressed by miR-375 through recognition of its two miR-375 binding sites. A positive correlation between ASH1 and miR-375 as well as a negative correlation between miR-375 and YAP1 were observed in lung cancers, indicating the ASH1-miR-375-YAP1 regulatory pathway is indeed functionally implemented in lung cancer cells. In addition, we found that growth-regulatory functions of YAP1 is cell-lineage dependent in lung cancer cell lines. In conclusion, the present study identified the ASH1-miR-375 axis, providing clues for a better understanding of the molecular and cellular biological roles of ASH1-centered microRNA regulatory networks in the pathogenesis of NE-lung cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3992. doi:10.1158/1538-7445.AM2011-3992