<i>OBSCN</i> restoration via <i>OBSCN-AS1</i> long-noncoding RNA CRISPR-targeting suppresses metastasis in triple-negative breast cancer.

Abstract

Mounting evidence implicates the giant, cytoskeletal protein obscurin (720 to 870 kDa), encoded by the <i>OBSCN</i> gene, in the predisposition and development of breast cancer. Accordingly, prior work has shown that the sole loss of <i>OBSCN</i> from normal breast epithelial cells increases survival and chemoresistance, induces cytoskeletal alterations, enhances cell migration and invasion, and promotes metastasis in the presence of oncogenic KRAS. Consistent with these observations, analysis of Kaplan-Meier Plotter datasets reveals that low <i>OBSCN</i> levels correlate with significantly reduced overall and relapse-free survival in breast cancer patients. Despite the compelling evidence implicating <i>OBSCN</i> loss in breast tumorigenesis and progression, its regulation remains elusive, limiting any efforts to restore its expression, a major challenge given its molecular complexity and gigantic size (~170 kb). Herein, we show that <i>OBSCN-Antisense RNA 1</i> (<i>OBSCN-AS1</i>), a novel nuclear long-noncoding RNA (lncRNA) gene originating from the minus strand of <i>OBSCN</i>, and <i>OBSCN</i> display positively correlated expression and are downregulated in breast cancer biopsies. <i>OBSCN-AS1</i> regulates <i>OBSCN</i> expression through chromatin remodeling involving H3 lysine 4 trimethylation enrichment, associated with open chromatin conformation, and RNA polymerase II recruitment. CRISPR-activation of <i>OBSCN-AS1</i> in triple-negative breast cancer cells effectively and specifically restores <i>OBSCN</i> expression and markedly suppresses cell migration, invasion, and dissemination from three-dimensional spheroids in vitro and metastasis in vivo. Collectively, these results reveal the previously unknown regulation of <i>OBSCN</i> by an antisense lncRNA and the metastasis suppressor function of the <i>OBSCN-AS1/OBSCN</i> gene pair, which may be used as prognostic biomarkers and/or therapeutic targets for metastatic breast cancer.