P50-associated COX-2 extragenic RNA (PACER) overexpression promotes proliferation and metastasis of osteosarcoma cells by activating COX-2 gene

P50-associated cyclooxygenase-2 (COX-2) extragenic RNA (PACER) is a novel long noncoding RNA that has been found to activate the COX-2 gene, which may function as an oncogene in osteosarcoma. However, the role of PACER and the relationship between PACER and COX-2 in osteosarcoma progression have been unknown until now. Here, we examined the expression levels of PACER in clinical tumor samples and human osteosarcoma cell lines, assessed the functions of PACER in osteosarcoma cell proliferation and invasion, and then explored the mechanism of PACER dysregulation in osteosarcoma. The results showed that PACER was overexpressed in osteosarcoma tissues and cell lines compared with normal tissues and osteoblasts, respectively. PACER knockdown inhibited the proliferation and invasion of human osteosarcoma cells. Downregulation of PACER significantly suppressed the expression of COX-2, and the effects of PACER on cell proliferation and invasion were rescued by COX-2 overexpression. Furthermore, COX-2 activation by PACER was NF-κB-dependent. The regulation of PACER by CCCTC-binding factor (CTCF) was associated with DNA methylation status. Taken together, these findings suggest that PACER promotes proliferation and metastasis of osteosarcoma cells by activating the COX-2 gene and its own expression was influenced by DNA methylation.