Login to Access Video or Poster Abstract: MP98-08
Sources of Funding: NIH/NCI CA165980, CA177665, CA112557, and NIH/NIEHS ES000260

Introduction

MEG3 is a long non-coding RNA (lncRNA) transcribed from putative tumor suppressor locus 14q32 that is frequently silenced epigenetically in human bladder cancer. The biological consequences of MEG3 silencing in bladder cancer cells remain poorly defined. This study was designed to understand the effects and the underlying mechanisms of MEG3 down-regulation in bladder cancer biology.

Methods

Full-length lncRNA MEG3 and its controls were stably transfected into human bladder cancer cell lines, T24T and UMUC3, that were originally derived from high-grade, muscle-invasive bladder cancers. The effects of MEG3 expression on bladder cancer cells including proliferation and invasion were accessed. RNA immunoprecipitation was used to identify the binding between MEG3 and miR-27a. RNA binding-site point-mutation experiments and luciferase reporter assay were used to study 3’-UTR activity of PHLPP2 and the promoter activity of c-Myc, respectively.

Results

We found that stable expression of MEG3, but not its controls, in T24T and UMUC3 cells strongly inhibited human bladder cancer cell proliferation and invasion. MEG3 exerted these anti-tumor effects by binding specifically to microRNA, miR-27a, and competing its binding for the mRNA of PHLPP2, a tumor suppressor that inhibits the AKT pathway. By so doing, MEG3 markedly reduced the activity of miR-27a and in turn increased the protein translation of PHLPP2. As a consequence, the upregulated PHLPP2 decreased c-Jun phosphorylation at Ser63/73, and inhibited c-Myc transcription, thus reducing the invasiveness of bladder cancer cells.

Conclusions

We demonstrate for the first time that MEG3, transcribed from a gene locus with recurrent epigenetic silencing in human bladder cancer, is a putative tumor suppressor. MEG3 acts as a competing endogenous RNA (ceRNA) that binds miR27a releasing its inhibition on tumor suppressor PHLPP2, the latter of which inhibits oncogenes/invasion-promoters c-Jun and c-Myc. Silencing of MEG3 reverses all these tumor-suppressive effects and leads to bladder cancer cell proliferation and invasion.

Funding

NIH/NCI CA165980, CA177665, CA112557, and NIH/NIEHS ES000260