p53-Inducible Micrornas 192 and 215 Regulate p53 Expression and IGF1 Axis in Multiple Myeloma.

Abstract 1973

Poster Board I-996

Multiple myeloma (MM) is an incurable neoplastic disease of B cell origin, affecting 50,000 patients in the United States, occurring in approximately 16,000 new individuals each year. In MM, mutation or deletion of p53 is rarely detected at diagnosis, although both become more frequent in advanced disease. Therapeutic activation of p53 might therefore be particularly suitable for the treatment of MM. The discovery of microRNAs (miRNAs) has revealed a new level of regulation of protein expression. We have shown that an altered miRNA expression profile plays a role in the malignant transformation of plasma cells (PCs); we recently published the first comprehensive global microRNA expression profiles of MM, monoclonal gammopathy of undetermined significance (MGUS) and contrasted these expression patterns with that of normal plasma cells (PCs). Now we have used nutlin-3a, a recently developed small-molecule activator of p53, that efficiently disrupts the p53-MDM2 interaction, to profile a p53 miRNA activation pathway in the MM1s cell line. Results of the analysis have shown differential expression of 46 individual miRNAs after p53 activation, 14 showing up-regulation and 32 showing down-regulation. We confirmed our data by qRT-PCR in p53 wild type and mutated MM cell lines and in primary MM cells. Our results confirm published results; after p53 stabilization we found up-regulation of the miR-34a, but we also detected strong up-regulation of several other miRNAs. In fact we found that p53 induces two additional, mutually related clusters of miRNAs, leading to the up-regulation of miR-192, miR-194, and miR-215. The same miRNAs were detected at high levels in normal plasma cells (n.3) but were severely reduced in many untreated MM samples (n.22). Here we characterize the promoter and the p53 activation site for miR-192-194 cluster on chromosome 11(q13.1) but we have also confirmed the previous published p53 consensus site for miR-215-194 cluster on chromosome 1(q41) in multiple myeloma cells. Furthermore we found that miR-192 and its cousin miR-215 but not miR-194 can each contribute to enhanced CDKN1A/p21 levels, colony suppression, cell cycle arrest in multiple myeloma cells acting directly on p53 regulation. On the other hand, we define that IGF-1 and IGFR are direct targets of miR-192-215. In fact the re-expression of these miRNAs in multiple myeloma cells blocks their migration through both endothelial barriers and associated bone marrow stroma. Our data suggest that downstream signaling in the p53 pathway is functional in MM cells and able to induce miRNAs that play a pivotal role in cell cycle progression, mobility and invasive properties of these cells. These studies provide the basis for the development of new miRNA-targeted therapies for MM.