Differentiation of Mammary Tumors and Reduction in Metastasis Upon Malat1 LncRNA Loss

Genome-wide analyses have identified thousands of long non-coding RNAs (lncRNAs). Malat1 (Metastasis Associated Lung Adenocarcinoma Transcript 1) is among the most abundant lncRNAs whose expression is altered in numerous cancers. Here we report that genomic loss, as well as systemic knockdown of Malat1 using antisense oligonucleotides, in the MMTV-PyMT mouse mammary carcinoma model results in slower tumor growth accompanied by differentiation into highly cystic tumors and a significant reduction in lung metastasis. Further, Malat1 loss results in a reduction of branching morphogenesis in MMTV-PyMT and Her2/neu amplified tumor organoids consistent with the in vivo reduction in lung metastasis. At the molecular level, Malat1 knockdown results in alterations in gene expression and changes in splicing patterns of genes involved in differentiation and pro-tumorigenic signaling pathways. Together, these data indicate that the lncRNA Malat1 regulates critical processes in mammary cancer pathogenesis and represents a promising therapeutic target for inhibiting breast cancer metastasis. Transcriptome profiles of tumors and organoids after Malat1 knockdown using antisense olgonucleotides (ASOs).