Abstract
Epigenetic abnormalities are common in hematologic malignancies, including multiple myeloma, and their effects can be efficiently counteracted by a class of tumor suppressor miRNAs, named epi-miRNAs. Given the oncogenic role of histone deacetylases (HDAC) in multiple myeloma, we investigated whether their activity could be antagonized by miR-29b, a well-established epi-miRNA. We demonstrated here that miR-29b specifically targets HDAC4 and highlighted that both molecules are involved in a functional loop. In fact, silencing of HDAC4 by shRNAs inhibited multiple myeloma cell survival and migration and triggered apoptosis and autophagy, along with the induction of miR-29b expression by promoter hyperacetylation, leading to the downregulation of prosurvival miR-29b targets (SP1, MCL-1). Moreover, treatment with the pan-HDAC inhibitor SAHA upregulated miR-29b, overcoming the negative control exerted by HDAC4. Importantly, overexpression or inhibition of miR-29b, respectively, potentiated or antagonized SAHA activity on multiple myeloma cells, as also shown in vivo by a strong synergism between miR-29b synthetic mimics and SAHA in a murine xenograft model of human multiple myeloma. Altogether, our results shed light on a novel epigenetic circuitry regulating multiple myeloma cell growth and survival and open new avenues for miR-29b-based epi-therapeutic approaches in the treatment of this malignancy. Mol Cancer Ther; 15(6); 1364-75. ©2016 AACR.
Highlights
Multiple myeloma is a plasma cell malignancy characterized by a high genetic complexity and molecular heterogeneity [1]
HDAC4 is a direct target of miR-29b in multiple myeloma cells On the basis of the role of miR-29b as epi-miRNA in human cancer, we interrogated microRNA Data Integration Portal, applying the high precision quality filter, to identify histone deacetylases (HDAC) potentially targeted by miR-29b
To validate the regulation of HDAC4 by miR29b, we first used the 30 untranslated region (UTR) of HDAC4 cloned into an expression vector downstream of the luciferase reporter gene, which was cotransfected into KMS11 cells together with synthetic miR-29b mimics or scrambled oligonucleotides (NC); levels of miR-29b 24 hours after transfection are shown in Fig. 1A. miR-29b mimics reduced the activity of the reporter but did not regulate the 30 UTR of HDAC4 devoid of the predicted miR-29b target site, demonstrating that miR-29b regulates HDAC4 mRNA (Fig. 1B)
Summary
Multiple myeloma is a plasma cell malignancy characterized by a high genetic complexity and molecular heterogeneity [1]. A subclass of TSmiRNAs, named epi-miRNAs, is emerging as novel epigenetic regulators, which target and downregulate the expression of DNA methyltransferases (DNMT), histone deacetylases (HDAC), or components of the polycomb repressor complexes, representing relevant tools to revert epigenetic aberrations. Studies showed that HDACs influenced the expression of several genes involved in cancer initiation and progression. MiR-29b/HDAC4 Epigenetic Loop in Multiple Myeloma and vorinostat (SAHA) and romidepsin (FK228 or FR901228) have been FDA approved for the treatment cutaneous T-cell lymphoma, whereas panobinostat was recently approved for multiple myeloma treatment [20, 21]. We here evaluated the effectiveness of miR-29b in counteracting aberrant HDAC activity and whether its expression might be in turn controlled through acetylation in multiple myeloma. We can anticipate that our findings strengthen the central role of miR-29b as an epigenetic modulator and provide the rationale for novel miR-29b– based epi-therapeutic approaches in multiple myeloma
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
