Mutated β-catenin evades a microRNA-dependent regulatory loop

Abstract

hsa-mir-483 is located within intron 2 of the IGF2 gene. We have previously shown oncogenic features of miR-483-3p through cooperation with IGF2 or by independently targeting the proapoptotic gene BBC3/PUMA. Here we demonstrate that expression of miR-483 can be induced independently of IGF2 by the oncoprotein β-catenin through an interaction with the basic helix-loop-helix protein upstream stimulatory transcription factor 1. We also show that β-catenin itself is a target of miR-483-3p, triggering a negative regulatory loop that becomes ineffective in cells harboring an activating mutation of β-catenin. These results provide insights into the complex regulation of the IGF2/miR-483 locus, revealing players in the β-catenin pathway.T he multifunctional protein β-catenin is involved in cell-cell adhesion when it is localized to the cellular membrane (1), and in transcriptional regulation by translocation into the nucleus through the Wnt pathway (2). Wnt signaling is an important molecular pathway required for cellular differentiation, tissue homeostasis, and tissue morphogenesis. Wnt/β-catenin signaling is one of the most commonly activated pathways in cancer, and several Wnt signaling-related gene mutations have been described: adenomatous polyposis coli (APC) and protein phosphatase 2 regulatory subunit A (PPP2R1B) mutations in colorectal cancer (3), AXIN1 mutation in hepatocarcinoma (4), and WTX gene mutations in Wilms' tumor (5), and β-catenin gene (CTNNB1) itself was shown to be mutated (6-8) in the amino-terminal region used for degradation by the GSK3β-APC-AXIN-WTX complex (5, 9). These mutations prevent β-catenin degradation and result in its accumulation in the nucleus, where it acts as a specific transcriptional coactivator of the DNA-binding T-cell factor/lymphoid enhancer factor protein family. Among the targets of this family are important genes involved in tumorigenesis such as MYC, CCND1, CJUN, and FRA1 (10, 11).MicroRNAs (miRNAs) are small noncoding RNAs that modulate gene expression by base pairing to target messenger RNAs (mRNAs) and by inhibiting their translation and/or promoting their degradation (12). MicroRNAs play a critical role in the normal maintenance of fundamental cellular processes, and their deregulation in human neoplasm has been proven to affect a large number of molecular pathways related to cancer (13)(14)(15).Because the miR-483 locus is dysregulated in tumors involving the β-catenin pathway (16-18), we investigated their possible connection.Results miR-483-3p Expression Correlates with the Mutational Status of Wnt/ β-Catenin Genes in Hepatocarcinoma. The Wnt/β-catenin pathway is one of the most important pathways dysregulated in hepatocarcinoma (HCC), colorectal cancer (CRC), and Wilms' tumor (19-21). Because we previously found that miR-483-3p, which is located in intron 2 of the IGF2 gene, is up-regulated in these cancers as well, we investigated the possible involvement of Wnt/β-catenin in miR-483-3p dysregulation.We previously found a positive coefficient of correlation (R) ...

MicroRNA therapy inhibits hepatoblastoma growth in vivo by targeting β‐catenin and Wnt signaling

“…Therefore, our results further strengthen the idea that the regulation of beta‐catenin by miRNAs is linked to p53 signaling 17. We noticed that the exon 3 deletion in HepG2 cells made mutated beta‐catenin more resistant to miRNAs, confirming previous data with miR‐483‐3p in colon cancer cells 18. Such resistance was not measurable in Huh6 cells, which carry a single point mutation in one of the beta‐catenin alleles 8.…”

“…All miRNAs efficiently down‐regulated wild‐type beta‐catenin, but the deleted form was less responsive to miRNAs, especially with miR‐885‐5p and miR‐449b‐3p. Such small RNA‐silencing resistance of deleted beta‐catenin was described for miR‐483‐3p18 and an siRNA against beta‐catenin3 without providing any explanation for this phenomenon. We speculate that a much longer protein half‐life could be a reason for a lower inhibitory effect because exon 3 deletion allows beta‐catenin to escape from proteosomal degradation.…”

“…3B) and inversely correlates with beta‐catenin mRNA in CTNNB1 ‐deleted HBL tumors. These results suggest that the genetic status and transcriptional activity of beta‐catenin is linked to miRNA deregulation in cancer 11, 18, 34. Surprisingly, no inverse correlation was observed between the four decreased miRNAs and the level of total beta‐catenin mRNA in HBL tissues (Supporting Fig.…”

“…1B,C; Supporting Table S2). This selection comprised miR‐885‐5p, which is decreased in HBL tumors,14 and miR‐483‐3p, which regulates beta‐catenin 18. In a second step, we studied the targeting preference of the 26 candidates for the beta‐catenin 5′‐ and/or 3′‐UTR using Tomato‐positive cells expressing GFP with specific UTRs (Fig.…”

“…This characteristic of miRNAs is an advantage for cancer therapy since tumors display specific signaling pathway alterations that can be controlled by single miRNAs 11, 12. Many miRNAs have been reported to target beta‐catenin: mature miRNA (miR)‐200a in human meningioma,16 members of the miR‐34 family in lung and breast carcinomas,17 miR‐483‐3p in breast and colon cancers,18 and miR‐214 in HCC 19. However, it is unknown if one of these miRNAs targets beta‐catenin in HBL.…”