Project Summary/Abstract Aberrantly high expression of the long noncoding RNA (lncRNA) Malat1 is strongly associated with lung adenocarcinoma (LUAD) progression and poor patient prognosis and has been pursued as a potential therapeutic target. However, these correlative observations do not reveal whether the aberrant expression of Malat1 is a driver of tumorigenesis and what are the mechanisms by which Malat1 overexpression promotes disease progression. In preliminary studies, we developed an innovative CRISPR activation (CRISPRa) system that successfully models Malat1 overexpression in patient-derived cell lines and autochthonous murine models of LUAD. Strikingly, we uncovered that tumor-specific overexpression of Malat1 at the time of tumor initiation is sufficient to accelerate the progression of murine LUAD to aggressive and metastatic disease, demonstrating that Malat1 overexpression is a driver of cancer development. We further determined that Malat1 overexpression leads to pleiotropic effects on the tumor microenvironment through the altered expression of cytokines and stromal factors. Based on these promising findings, our central hypothesis is that progressive accumulation of Malat1 in LUAD drives the development of aggressive disease through the activation of a metastasis-promoting gene expression program and the establishment of a pro-metastatic tumor microenvironment. In Aim 1, we describe our use of advanced, temporally controlled mouse models to clarify the stage of tumorigenesis when overexpression of Malat1 promotes tumor progression, the requirement for sustained Malat1 overexpression, and the window of opportunity when downregulation of Malat1 may have a therapeutic impact. Aim 2 seeks to investigate the non-cell autonomous effects of Malat1 overexpression in the establishment of a pro-metastatic niche. We propose to perform detailed characterization of Malat1-dependent changes in the tumor stroma at different stages of tumorigenesis as well as use genetic models to explore the contributions of candidate secreted factors, such as inflammatory cytokines. Finally, Aim 3 outlines our plans to elucidate the molecular mechanism by which overexpressed Malat1 alters the expression of tumor microenvironment effectors. We propose to utilize state-of-the-art molecular biology approaches and work with long-term collaborators, who are experts in bioinformatics and chemical biology, to determine whether Malat1 overexpression affects target genes at the transcriptional or post-transcriptional level, through dominant negative or gain-of-function mechanisms, and through direct or indirect activities. In summary, this proposal outlines a highly innovative experimental and conceptual framework for dissecting the poorly understood role of overexpressed Malat1 as a driver in LUAD. Beyond Malat1, the broad significance of this work lies in its potential to elucidate how aberrantly expressed lncRNAs modulate cancer development and to uncover whether ...