Long non-coding RNA LOC554202 modulates chordoma cell proliferation and invasion by recruiting EZH2 and regulating miR-31 expression
Chordoma is a rare malignant bone tumour arising from notochordal remnants. Long non-coding RNA LOC554202, as the host gene of miR-31, contributes to various cancer developments. However, little is known about the biological function of LOC554202 in chordoma. Here, the relationship between LncRNA LOC554202, miR-31 and EZH2 was elucidated in chordoma. The levels of LOC554402, miR-31, EZH2, RNF144B, and epithelial-mesenchymal transition (EMT) markers were measured in chordoma tissues and the chordoma cell lines via quantitative real-time PCR (qRT-PCR) or Western blot. FISH assay demonstrated the LOC554402 expression in chordoma tissues. The chordoma cell lines, U-CH1 and JHC7, were transfected with siRNA or miRNA mimics and analysed for cell proliferation ability, apoptosis, cell migration, and invasion. RNA pull down, RIP assay, and Luciferase Reporter Assay were used to analyze the interaction between LOC554202 and EZH2. Animal tumour xenografts were generated, and qRT-PCR was performed to investigate EZH2, miR-31, and RNB144B expression on tumour growth in vivo. We found elevated expression of LOC554202 was associated with a decreased level of miR-31 in cancer tissues. Knockdown of LOC554202 or overexpression of miR-31 suppressed the proliferation, migration, and invasion of chordoma cells. Unexpectedly, EZH2 as a binding protein of LOC554202, and it was positively regulated by LOC554202, leading to the reduced expression of miR-31. Furthermore, the impaired function of miR-31 restored expression of the oncogene RNF144B and maintained the metastasis-promoting activity in vitro. The results in vivo confirmed the anti-tumour effects of knockdown of LOC554202, which inhibited EZH2/miR-31 to activate the oncogene RNF144B. Our results suggest that LOC554202 may play an important role in the progression of chordoma by the direct upregulation of EZH2 and indirect promotion of RNF144B via miR-31.