The long non-coding RNA NEAT1 promotes sarcoma metastasis by regulating RNA splicing pathways.

Soft tissue sarcomas (STSs) are rare malignancies showing lineage differentiation toward diverse mesenchymal tissues. Half of all high-grade STSs develop lung metastasis with a median survival of 15 months. Here we use a genetically engineered mouse model (GEMM) that mimics undifferentiated pleomorphic sarcoma (UPS) to study the molecular mechanisms driving metastasis. High-grade sarcomas were generated with Cre recombinase technology using mice with conditional mutations in Kras and Trp53 (KP) genes. After amputation of the limb bearing the primary tumor, mice were followed for the development of lung metastasis. Using RNA sequencing (RNA-Seq) of matched primary KP tumors and lung metastases, we found that the long non-coding RNA (lncRNA) Neat1 is significantly upregulated in lung metastases. Furthermore, NEAT1 RNA in situ hybridization of human UPS showed that NEAT1 is upregulated within a subset of lung metastases compared to paired primary UPS. Remarkably, CRISPR/Cas9 mediated knockout of Neat1 suppressed the ability of KP tumor cells to colonize the lungs. To gain insight into the underlying mechanisms by which the lncRNA Neat1 promotes sarcoma metastasis, we pulled down Neat1 RNA and used mass spectrometry to identify interacting proteins. Interestingly, most Neat1 interacting proteins are involved in RNA splicing regulation. In particular, KH-Type Splicing Regulatory Protein (KHSRP) interacts with Neat1 and is associated with poor prognosis of human STS. Moreover, depletion of KHSRP suppressed the ability of KP tumor cells to colonize the lungs. Collectively, these results suggest that Neat1 and its interacting proteins which regulate RNA splicing are involved in mediating sarcoma metastasis. Implications: Understanding that lncRNA NEAT1 promotes sarcoma metastasis at least in part through interacting with the RNA splicing regulator KHSRP may translate into new therapeutic approaches for sarcoma.