MicroRNA expression profiles in plexiform neurofibromas and malignant peripheral nerve sheath tumors derived from the same neurofibromatosis type 1 patient

Malignant peripheral nerve sheath tumors (MPNST) are aggressive cancers that occur spontaneously (sporadic MPNST) or from pre-existing, benign plexiform neurofibromas in neurofibromatosis type 1 (NF1) patients. MPNSTs metastasize easily, are resistant to therapeutic intervention and are frequently fatal. The molecular changes underlying the transition to malignancy in the NF1 setting are incompletely understood. Here we investigate the involvement of microRNAs in this process. Using an RT-PCR platform microRNA expression profiles were determined from a unique series of archival paired samples of plexiform neurofibroma and MPNST. At least 90 differentially expressed microRNAs (p<0.025; FDR<10%) were identified between the paired samples. Most microRNAs (91%) were found downregulated and 9% of the microRNAs were upregulated in MPNST. Based on the fold changes and statistical significance three downregulated microRNAs (let-7b-5p, miR-143-3p, miR-145-5p) and two upregulated microRNAs (miR135b-5p and miR-889-3p) were selected for further functional characterization. Their expression levels were validated in a relevant cell line panel and a series of unpaired fresh frozen tumor samples containing plexiform neurofibromas, atypical neurofibromas and MPNSTs. As part of the validation process we also determined and analyzed microRNA expression profiles of sporadic MPNSTs observing that microRNA expression discriminates NF1-associated and sporadic MPNSTs emphasizing their different etiologies. The involvement of microRNAs in tumorigenesis and cancer progression was examined in NF1-derived MPNST cell lines through modulating microRNA levels by transient transfection of microRNA mimics or inhibitors. The effects of microRNAs on cellular proliferation, migration, invasion and Wnt/ẞ-catenin signaling were determined. Our findings indicate that, some of the selected microRNAs affect migratory and invasive capabilities and Wnt signaling activity. It was observed that the functional effects upon microRNA modulation are distinct in different cell lines. From our study we conclude that miRNAs play essential regulatory roles in MPNST facilitating tumor progression. To study the involvement of microRNAs in the malignant transition of benign plexiform neurofibromas into MPNST, we determined the microRNA expression profiles of a unique series of nine paired plexiform neurofibromas and MPNST samples. Each plexiform neurofibroma / MPNST pair was derived from the same neurofibromatosis type 1 (NF1) patient. MicroRNA expression profiles were determined from 18 archival formalin-fixed paraffin-embedded (FFPE) tumor samples (9 plexiform neurofibromas and 9 NF1-derived MPNSTs). TaqMan® Low Density Array (TLDA) Human MicroRNA Cards (A card v2.0, B card v3.0; Applied Biosystems/Thermo Fisher Scientific) were used. The microRNA expression profiling data was used for a comparison between the benign plexiform neurofibromas and the MPNST in order to determine differentially expressed microRNAs.