No abstract

Progress in understanding the biology of multiple myeloma (MM), a plasma cell malignancy, has been slow. The discovery of microRNAs (miRNAs), a class of small noncoding RNAs targeting multiple mRNAs, has revealed a new level of gene expression regulation. To determine whether miRNAs play a role in the malignant transformation of plasma cells (PCs), we have used both miRNA microarrays and quantitative real time PCR to profile miRNA expression in MM-derived cell lines (n ‫؍‬ 49) and CD138؉ bone marrow PCs from subjects with MM (n ‫؍‬ 16), monoclonal gammopathy of undetermined significance (MGUS) (n ‫؍‬ 6), and normal donors (n ‫؍‬ 6). We identified overexpression of miR-21, miR-106bϳ25 cluster, miR181a and b in MM and MGUS samples with respect to healthy PCs. Selective up-regulation of miR-32 and miR-17ϳ92 cluster was identified in MM subjects and cell lines but not in MGUS subjects or healthy PCs. Furthermore, two miRNAs, miR-19a and 19b, that are part of the miR-17ϳ92 cluster, were shown to down regulate expression of SOCS-1, a gene frequently silenced in MM that plays a critical role as inhibitor of IL-6 growth signaling. We also identified p300-CBP-associated factor , a gene involved in p53 regulation, as a bona fide target of the miR106bϳ25 cluster, miR-181a and b, and miR-32. Xenograft studies using human MM cell lines treated with miR-19a and b, and miR-181a and b antagonists resulted in significant suppression of tumor growth in nude mice. In summary, we have described a MM miRNA signature, which includes miRNAs that modulate the expression of proteins critical to myeloma pathogenesis.PCAF ͉ SOCS-1 ͉ tumor suppressor gene ͉ MGUS ͉ plasma cells

Summary In multiple myeloma (MM), an incurable B-cell neoplasm, mutation or deletion of p53 is rarely detected at diagnosis. Using small-molecule inhibitors of MDM2, we provide evidence that miR-192, 194 and 215, which are down-regulated in a subset of newly diagnosed MMs, can be transcriptionally activated by p53 and then modulate MDM2 expression. Furthermore, ectopic re-expression of these miRNAs in MM cells increases the therapeutic action of MDM2 inhibitors in vitro and in vivo by enhancing their p53-activating effects. In addition, miR-192 and 215 target the IGF pathway, preventing enhanced migration of plasma cells into bone marrow. The results suggest that these miRNAs are positive regulators of p53 and that their down-regulation plays a key role in MM development.

By transactivating expression of miRNAs that repress expression of the ZEB1 and ZEB2 transcription factors, p53 inhibits the epithelial–mesenchymal transition.