β-Catenin/LEF-1 transcription complex is responsible for the transcriptional activation of LINC01278.

Background: Our previous study shows that LINC01278 inhibits the malignant proliferation and invasion of papillary thyroid carcinoma (PTC) cells by regulating the miR-376c-3p/DNM3 axis. However, the regulation mechanism of LINC01278 expression in PTC cells is still unclear.

Methods: The luciferase reporter and ChIP assays were used to confirm the binding of LEF-1 to the putative promoter site of LINC01278 gene. The RNA immunoprecipitation and RNA pulldown were used to determine the enrichment of LINC01278 in β-catenin protein. The proteasome inhibitors (MG132) was used for detecting the β-catenin ubiquitination-proteasome degradation. Wnt/β-catenin specific agonists (LiCI), inhibitors (WiKI4) and TOP/FOP-flash reporter assay were used for detecting the activation of Wnt/β-catenin signal. Western blot was used to detected the expression of target proteins.

Results: The online PROMO algorithm determines a putative LEF-1 binding site on LINC01278 promoter, the LEF-1 binds to the putative promoter site of LINC01278 gene, and β-catenin enhances the binding of LEF-1 to the LINC01278 gene promoter. Furthermore, LINC01278 negatively regulated the protein accumulation of β-catenin in the cytoplasm, into nucleus, and ultimately inhibited the transcription of downstream target genes activated by Wnt/β-catenin signal. The results of RNA immunoprecipitation and RNA pulldown proved the direct binding of LINC01278 to β-catenin protein. In addition, the combination of LINC01278 and β-catenin promotes the β-catenin ubiquitination-proteasome degradation.

Conclusion: In summary, we found the transcriptional activation of LINC01278 by the β-catenin/LEF-1 transcription factor, and the negative feedback regulation of LINC01278 onβ-catenin signal.