The fusion gene LRP1–SNRNP25 drives invasion and migration by activating the pJNK/37LRP/MMP2 signaling pathway in osteosarcoma

Abstract

Through transcriptome sequencing, we previously identified a new osteosarcoma-specific, frequent fusion gene, LRP1–SNRNP25, and found that it played an important role in tumor cell invasion and migration. However, the specific mechanism remains unclear. In this article, whole-genome sequencing further confirmed that the LRP1–SNRNP25 fusion gene is formed by fusion of LRP1 exon 8 and SNRNP25 exon 2. In vitro, scratch and Transwell assays demonstrated that the migration and invasion abilities of LRP1–SNRNP25-overexpressing osteosarcoma cells were significantly increased. To explore the molecular mechanism of the LRP1–SNRNP25 fusion in affecting osteosarcoma cell migration and invasion, we evaluated the migration and invasion-related molecular signaling pathways by western blotting. Some migration- and invasion-related genes, including pJNK and MMP2, were upregulated. Coimmunoprecipitation–mass spectrometry showed that 37LRP can interact with pJNK. Western blotting confirmed that LRP1–SNRNP25 overexpression upregulates 37LRP protein expression. Immunofluorescence staining showed the intracellular colocalization of LRP1–SNRNP25 with pJNK and 37LRP proteins and that LRP1–SNRNP25 expression increased the pJNK and 37LRP levels. Coimmunoprecipitation (co-IP) confirmed that LRP1–SNRNP25 interacted with pJNK and 37LRP proteins. The pJNK inhibitor SP600125 dose-dependently decreased the pJNK/37LRP/MMP2 levels. After siRNA-mediated 37LRP knockdown, the MMP2 protein level decreased. These two experiments proved the upstream/downstream relationship among pJNK, 37LRP, and MMP2, with pJNK the farthest upstream and MMP2 the farthest downstream. These results proved that the LRP1–SNRNP25 fusion gene exerts biological effects through the pJNK/37LRP/MMP2 signaling pathway. In vivo, LRP1–SNRNP25 promoted osteosarcoma cell growth. Tumor growth was significantly inhibited after SP600125 treatment. Immunohistochemical analysis showed that the pJNK, MMP2, and Ki-67 protein levels were significantly increased in tumor tissues of LRP1–SNRNP25-overexpressing cell-injected nude mice. Furthermore, lung and liver metastasis were more prevalent in these mice. In a word, LRP1–SNRNP25 promotes invasion, migration, and metastasis via pJNK/37LRP/MMP2 pathway. LRP1–SNRNP25 is a potential therapeutic target for LRP1–SNRNP25-positive osteosarcoma.