MicroRNA Signature in Waldenstrom Macroglobulinemia

Background. MicroRNAs (miRNAs) constitute a class of small, non-coding, 18–24 nucleotide RNAs, that act as negative regulators of gene expression. By repressing several target mRNAs, mature miRNAs play a pivotal role in regulating development, cell differentiation, apoptosis, and cell proliferation. Moreover, miRNAs have been described to play roles in both solid tumors and hematologic malignancies, however the role of miRNAs in WM has not been yet elucidated.

Methods. We performed miRNA expression profiling of bone marrow-derived CD19+ WM cells, compared to their normal cellular counterparts and validated data by qRT-PCR. In vitro and in vivo functional studies were performed on miRNA-155 knockdown WM cells. Effect of miRNA-155 on signaling cascades have been evaluated by western blot and immunofluorescence. NF-kB activity has been investigated using a DNA-binding enzyme-linked immunosorbent assay-based assay. Gene expression profile analysis has been performed on both miRNA-155 knockdown- and control probe-transfected WM cells in order to identify potential miRNA-155 targeted genes. Finally correlation between miRNA signature and prognosis has been evaluated.

Results. We identified a WM specific miRNA signature characterized by increased expression of miRNA-363*/-206/-494/-155/-184/-542-3p; and decreased expression of miRNA-9* (ANOVA;P< 0.01). Our data showed that miRNA-155 regulates proliferation and growth of WM cells in vitro and in vivo, by inhibiting MAPK/ERK, PI3/AKT, and NF-kB signaling pathways. Potential miRNA-155 target genes were identified using gene expression profiling and included genes involved in cell cycle progression, adhesion, and migration. Importantly, increased expression of the 6 miRNAs significantly correlated with a poorer outcome predicted by the International Prognostic Staging System for WM (P<0.01). We further demonstrated that therapeutic agents commonly used in WM (rituximab, perifosine, bortezomib) alter the levels of the major miRNAs identified, by inducing down-modulation of five increased miRNAs (all but miR-206) and upmodulation of patient-downexpressed miR-9* microRNA.

Conclusion. These data indicate that miRNAs play a pivotal role in the biology of WM; represent important prognostic markers; and provide the basis for the development of new miRNA-based targeted therapies in this disease.