miR‐29a inhibition normalizes HuR over‐expression and aberrant AU‐rich mRNA stability in invasive cancer

Abstract

The activities of RNA-binding proteins are perturbed in several pathological conditions, including cancer. These proteins include tristetraprolin (TTP, ZFP36) and HuR (ELAVL1), which respectively promote the decay or stability of adenylate-uridylate-rich (AU-rich) mRNAs. Here, we demonstrated that increased stabilization and subsequent over-expression of HuR mRNA were coupled to TTP deficiency. These findings were observed in breast cancer cell lines with an invasive phenotype and were further confirmed in ZFP36-knockout mouse fibroblasts. We show that TTP–HuR imbalance correlated with increased expression of AU-rich element (ARE) mRNAs that code for cancer invasion genes. The microRNA miR-29a was abundant in invasive breast cancer cells when compared to non-tumourigenic cell types. When normal breast cells were treated with miR-29a, HuR mRNA and protein expression were up-regulated. MiR-29a recognized a seed target in the TTP 3′ UTR and a cell-permeable miR-29a inhibitor increased TTP activity towards HuR 3′ UTR. This led to HuR mRNA destabilization and restoration of the aberrant TTP–HuR axis. Subsequently, the cancer invasion factors uPA, MMP-1 and MMP-13, and cell invasiveness, were decreased. The TTP:HuR mRNA ratios were also perturbed in samples from invasive breast cancer patients when compared with normal tissues, and were associated with invasion gene expression. This study demonstrates that an aberrant ARE-mediated pathway in invasive cancer can be normalized by targeting the aberrant and functionally coupled TTP–HuR axis, indicating a potential therapeutic approach. Copyright © 2013 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Systematic Analysis of AU-Rich Element Expression in Cancer Reveals Common Functional Clusters Regulated by Key RNA-Binding Proteins

“…The mRNAs of TTP and HuR contain AU-rich elements, and their proteins are capable of regulating their own expression in an AREmediated manner (17)(18)(19)(20). In addition, we identified a TTP-HuR axis in which TTP reduces HuR mRNA and translation (18,21). Furthermore, TTP mRNA levels can be reduced by the high cellular levels of the miR-29a in invasive breast cancer (22).…”

“…The TTP/HuR mRNA ratios were computed since the balance of these RNAbinding proteins can influence the expression of certain AREmRNAs (21). We tested the correlation of the TTP/HuR mRNA ratio with the expression patterns of the 414 ARE-mRNAs using the fit model; the result was significant, R 2 ¼ 0.98 (P < 0.001; Pearson correlation with Fisher test of significance; Fig.…”

“…Cotransfection with RPS23-linked RFP was performed in HEK293 using Lipofectamine 2000 (Invitrogen). The induced expression of HA-tagged TTP and myc-tagged HuR were used as outlined previously (4,5,21).…”

“…Furthermore, TTP mRNA levels can be reduced by the high cellular levels of the miR-29a in invasive breast cancer (22). The inhibition of miR-29a using a cell-permeable anti-miR-29a peptide-nucleic acid can normalize the TTP-HuR axis, which leads to a reduction in the levels of ARE-mRNAs in breast cancer cells (21).…”

Comparison of gene regulatory networks of benign and malignant breast cancer samples with normal samples

“…Zinc finger protein 36 (ZFP36) is a tandem CCCH zinc-finger RNA-binding protein that regulates the stability of certain AU-rich element mRNAs involved in breast cancer-related processes (Al-Souhibani et al, 2010). ZFP36 gene defects will cause an imbalance in the cellular steady state, leading to over-expression of cancer genes and cancer cell metastasis (Al-Ahmadi et al, 2013). Yin Yang 1 (YY1) is highly expressed in various types of cancers and regulates tumorigenesis through multiple pathways.…”