c-Myc Acts as a Competing Endogenous RNA to Sponge miR-34a, in the Upregulation of CD44, in Urothelial Carcinoma

Abstract

MicroRNAs (miRNAs) have been shown to play a crucial role in the progression of human cancers, including urothelial carcinoma (UC), the sixth-most common cancer in the world. Among them, miR-34a has been implicated in the regulation of cancer stem cells (CSCs); however, its role in UC has yet to be fully elucidated. In this study, bioinformatics and experimental analysis confirmed that miR-34a targets CD44 (a CSC surface marker) and c-Myc (a well-known cell cycle regulator) in UC. We found that, surprisingly, most UC cell lines and patient samples did express miR-34a, although epigenetic silencing by promoter hypermethylation of miR-34a expression was observed only in UMUC3 cells, and a subset of patient samples. Importantly, overexpression of c-Myc, a frequently amplified oncogene in UC, was shown to upregulate CD44 expression through a competing endogenous RNA (ceRNA) mechanism, such that overexpression of the c-Myc 3′UTR upregulated CD44, and vice versa. Importantly, we observed a positive correlation between the expression of c-Myc and CD44 in clinical samples obtained from UC patients. Moreover, overexpression of a dominant-negative p53 mutant downregulated miR-34a, but upregulated c-Myc and CD44, in UC cell lines. Functionally, the ectopic expression of miR-34a was shown to significantly suppress CD44 expression, and subsequently, suppression of cell growth and invasion capability, while also reducing chemoresistance. In conclusion, it appears that aberrant promoter methylation, and c-Myc-mediated ceRNA mechanisms, may attenuate the function of miR-34a, in UC. The tumor suppressive role of miR-34a in controlling CSC phenotypes in UC deserves further investigation.

Multifunctional Roles of miR-34a in Cancer: A Review with the Emphasis on Head and Neck Squamous Cell Carcinoma and Thyroid Cancer with Clinical Implications

“…Among miRNAs involved in the ceRNA network, miR-34a occupies an important position, which was documented recently in several studies [ 28 , 29 , 30 , 31 ]. Some miR-34a targets have been recently shown to control the function of miR-34a through the ceRNA mechanism.…”

“…Similarly, lnc015192 and lncRNA FEZF1-AS1 act as miR-34a sponges to upregulate ADAM1 expression in breast cancer cells and Notch-1 in glioblastoma, respectively, and, thereby, promoting cancer cell migration [ 29 , 30 ]. C-mycRNA targeting miR-34a acts as a ceRNA and upregulates CD44 expression in urothelial carcinoma [ 31 ].…”

The correlation of epithelial-mesenchymal transition-related gene expression and the clinicopathologic features of colorectal cancer patients in Taiwan

“…The expression of CD44 may be regulated by other epigenetic or posttranslational mechanisms. A recent research in urothelial cancer showed that overexpression of c-Myc upregulates CD44 through a miR-34a -mediated competing endogenous RNA mechanism [ 23 ]. Up to now, the role of CD44 and its variants in EMT is still controversial.…”

<p>ARPP-19 Mediates Herceptin Resistance via Regulation of CD44 in Gastric Cancer</p>

“…26,34,35 We herein demonstrated that CD44 was regulated by ARPP-19 and mediated Herceptin resistance of human HER2-positive gastric cancer cells. Plenty of literatures demonstrated that CD44 played oncogenic roles in various human cancers, [36][37][38][39][40] gastric cancer included. [41][42][43] Furthermore, CD44 was a famous mediator to regulate cancer stem cell-like properties.…”