Tumor suppressive activity of PIWI-interacting RNA in human fibrosarcoma mediated through repression of RRM2.

P-element induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are a promising class of small regulatory RNAs, earlier believed to control transposable elements (TEs) activity in germlines are now reported in somatic and cancer cells. The aberrant expression of piRNAs has been documented in various cancers wherein they modulate tumorigenesis either as oncogenes or tumor suppressors by curbing target gene expression. However, there is no report yet on the association of piRNAs in fibrosarcoma, an early metastatic lethal tumor. For the first time, we reported a piRNA, piR-39980 in fibrosarcoma and investigated its potential role in malignancy by employing several methods such as qRT-PCR, MTT assay, transwell invasion and migration assay, wound healing assay, flow cytometric cell cycle analysis, Annexin V-PE apoptosis assay, AO/EB dual staining assay, and chromatin condensation assay. We observed that piR-39980 significantly attenuated proliferation, migration, invasion, and colony forming ability as well as induced apoptotic cell death of HT1080 fibrosarcoma cells when transiently overexpressed with its piRNA mimics. The dual luciferase reporter assay confirmed that piR-39980 promotes apoptosis and inhibits proliferation in fibrosarcoma by repressing RRM2 through direct targeting at its 3'UTR through extensive sequence complementary binding, unlike microRNA targeting. In summary, this study revealed that piR-39980 has a strong anti-tumor effect and hence could be a promising RNA-based therapeutic agent for the malignancy of fibrosarcoma.