Regulation of miRNA expression by alpha4beta1 integrin-dependent multiple myeloma cell adhesion. Regulation miRNAs in multiple myeloma

The alpha4beta1 integrin plays critical roles in the trafficking of multiple myeloma (MM) cells, and contributes to MM disease progression. Upon attachment to their ligands, integrins can transmit intracellular signals via their associated adaptor and signaling proteins, which could ultimately alter gene expression. MicroRNAs (miRNAs) are key post-transcriptional regulators of tumor progression, and their expression pattern has been associated with MM pathogenesis. Here we used small RNAseq to identify miRNAs whose expression is altered in MM cells specifically attached to the alpha4beta1 ligand CS-1/fibronectin (CS-1/FN). Analysis of the RNAseq data identified 40 miRNAs differentially expressed upon alpha4beta1-dependent MM cell adhesion. Specific upregulation of miR-324-5p, miR-331-3p and miR-424-5p expression in attached cells was confirmed by qPCR following silencing of the alpha4 integrin subunit. Altered miRNA expression upon adhesion to CS-1/FN was dependent on Erk1/2 and PI3K-Akt, but not Src signaling. We show that MM cell attachment to CS-1/FN led to reduced expression of the Hedgehog (Hh) pathway component SMO, a known target of miR-324-5p. Furthermore, miR-324-5p silencing resulted in enhanced SMO expression in adhered cells, suggesting that the alpha4beta1-miR-324-5p-SMO represents an adhesion-controlled miRNA pathway that could regulate the Hh signaling.