lncRNA TUG1 Promotes Cisplatin Resistance by Regulating CCND2 via Epigenetically Silencing miR-194-5p in Bladder Cancer

Taurine-upregulated gene 1 (TUG1) has been involved in tumorigenesis of several human cancers, but its precise biological role in bladder cancer remains largely elusive. In this study, we found that TUG1 was upregulated in bladder cancer and the expression of TUG1 was positively and negatively correlated with CCND2 and miR-194-5p, respectively. MiR-194-5p expression was frequently decreased through promoter hypermethylation, while it was epigenetically increased following cisplatin and 5-aza-2′-deoxycytidine (5-Aza-DC) treatment. Furthermore, knockdown of TUG1 attenuated the expression of epigenetic regulator Enhancer of zeste homolog 2 (EZH2), and it alleviated the promoter hypermethylation of miR-194-5p and induced its expression. Increased miR-194-5p expression or decreased TUG1 expression significantly sensitized bladder cancer cells to cisplatin, inhibited the proliferation, and induced apoptosis. Besides, CCND2 was a direct target of miR-194-5p, while miR-194-5p was regulated by TUG1. CCND2 could partially restore the tumor-suppressive effects on cell proliferation and cisplatin resistance following TUG1 silencing. Additionally, TUG1 expression was correlated with clinical stage, lymphatic metastasis, and patient prognosis. In conclusion, TUG1 promotes bladder cancer cell growth and chemoresistance by regulating CCND2 via EZH2-associated silencing of miR-194-5p. Our study may be conducive to elucidating the molecular mechanism of and providing novel therapeutic target and biomarker for bladder cancer.