miR-31 and miR-17-5p levels change during transformation of follicular lymphoma.

The 30% of patients whose indolent follicular lymphoma transforms to aggressive diffuse large B-cell lymphoma (DLBCL) have poor survival. Reliable predictors of follicular B-cell lymphoma transformation to DLBCL are lacking, and diagnosis of those that will progress is challenging. MicroRNA, which regulates gene expression, has critical functions in the growth and progression of many cancers and contributes to the pathogenesis of lymphoma. Using 5 paired samples from patients who presented with follicular lymphoma and progressed to DLBCL, we identified specific microRNA differentially expressed between the two. Specifically, miR-17-5p levels were low in follicular lymphoma and increased as the disease transformed. In contrast, miR-31 expression was high in follicular lymphoma and decreased as the lymphoma progressed. These results were confirmed in additional unpaired cases of low-grade follicular lymphoma (n = 13) and high-grade follicular lymphoma grade 3 or DLBCL (n = 17). Loss of miR-31 expression in DLBCL was not due to deletion of the locus. Changes in miR-17-5p and miR-31 were not correlated with immunophenotype, genetics, or status of the MYC oncogene. However, increased miR-17-5p expression did significantly correlate with increased expression of p53 protein, which is indicative of mutant TP53. Two pro-proliferative genes, E2F2 and PI3KC2A, were identified as direct messenger RNA targets of miR-31, suggesting that these may contribute to follicular lymphoma transformation. Our results indicate that changes in miR-31 and miR-17-5p reflect the transformation of follicular lymphoma to an aggressive large B-cell lymphoma and may, along with their targets, be viable markers for this process.