A novel Cpa3-Cre; miR-9∆fl/∆fl mouse reveals a functional role for miR-9 in promoting a mast cell invasive phenotype via upregulation of CMA1

The purpose of this study was to investigate the biologic consequences of miR-9 overexpression in normal mast cells and interrogate the mechanisms by which mir-9 enhances invasion. We generated a transgenic mouse line carrying a floxed-STOP-miR-9 transgene (miR-9∆fl/∆fl) and crossed it with Cpa3-Cre transgenic mice in which Cre recombinase expression is restricted largely to mast cells and basophils, by the carboxypeptidase A3 (Cpa3) promoter. RNA-seq revealed a unique transcriptional profile associated with miR-9 overexpression in BMCMCs, notably up-regulation of mast cell-restricted proteases CMA1 and MCP6 involved in extracellular matrix remodeling. Targeting of the transcriptional corepressor SIN3A by miR-9 enhanced CMA1 expression, indicating a novel regulatory pathway through which miR-9 upregulates CMA1 expression, thereby promoting an invasive phenotype. These data support a role for miR-9 in mast cell invasive properties and provide a mechanism through which dysregulation of miR-9 in mast cells may contribute to pathologic conditions involving mast cell-mediated tissue remodeling. Bone marrow-cultured mast cells (BMCMCs) were generated from age- and sex-matched Cpa3-Cre and Cpa3-Cre;miR-9∆fl/∆fl mice. RNA-seq was performed at the OSUCCC Genomics Shared Resource using the Illumina HiSEq-2500 instrument at a depth of ∼70 million paired-end, 50bp long, strand-specific reads per sample. Statistical analysis relative to mRNA expression data was performed using DESeq2 Software. Differential gene expression was determined by one-way ANOVA and p-values of <0.0001 were considered statistically significant.