lncRNA PCNAP1 predicts poor prognosis in breast cancer and promotes cancer metastasis via miR-340-5p-dependent upregulation of SOX4

The high metastatic rate of breast cancer is the significant cause of its poor prognosis. The long noncoding RNA (lncRNA) proliferating cell nuclear antigen pseudogene 1 (PCNAP1) plays important roles in the initiation and progression of cancers; however, its regulatory function and molecular mechanism in breast cancer metastasis remains unknown. Therefore, we investigated the roles of lncRNA PCNAP1 in breast cancer metastasis by modulating the microRNA (miR)-340-5p/SOX4 axis using quantitative real-time PCR, in vivo mouse models, nucleo-cytoplasmic separation, western blot analysis, scratch assays, Transwell assays, luciferase reporter assays and MS2-RIP, in vitro and in vivo. lncRNA PCNAP1 was found to be upregulated in human breast cancer tissues, and high lncRNA PCNAP1 levels predicted poor overall survival. Function assays showed that knockdown of lncRNA PCNAP1 suppressed the migration and invasion of breast cancer cells in vitro and in vivo. Mechanistically, lncRNA PCNAP1 functioned as a competing endogenous (ce)RNA for miR-340-5p to facilitate the expression of its target gene SRY-box transcription factor 4 (SOX4), promoting migration and invasion of breast cancer cells. Overall, we found that lncRNA PCNAP1 predicted a poor prognosis in breast cancer and promoted cancer metastasis via miR-340-5p-dependent upregulation of SOX4 expression. These results suggest that lncRNA PCNAP1 has potential as an alternative therapeutic target to suppress breast cancer metastasis.