Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and young adults. It is characterized by the expression of one or several muscle-specific genes including MyoD, myogenin, and desmin and thought to be derived from deregulated muscle progenitor cells. microRNAs (miRNAs) are a class of post-transcriptional regulators involved in various cellular processes and developmental events. Dysregulated expression of miRNAs is associated with a variety of diseases, including RMS. In our current study, we found that the expression level of miR-203 was drastically reduced mainly due to promoter hypermethylation in two RMS-derived cell lines (i.e., RD and Rh30) and a large fraction of RMS biopsies. Re-expression of miR-203 in both RD and RH30 cells promoted partial myo...[ Read more ]

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and young adults. It is characterized by the expression of one or several muscle-specific genes including MyoD, myogenin, and desmin and thought to be derived from deregulated muscle progenitor cells. microRNAs (miRNAs) are a class of post-transcriptional regulators involved in various cellular processes and developmental events. Dysregulated expression of miRNAs is associated with a variety of diseases, including RMS. In our current study, we found that the expression level of miR-203 was drastically reduced mainly due to promoter hypermethylation in two RMS-derived cell lines (i.e., RD and Rh30) and a large fraction of RMS biopsies. Re-expression of miR-203 in both RD and RH30 cells promoted partial myogenic differentiation and inhibited cell proliferation both in vitro and in vivo. p63, a member of the p53 tumor suppressor family, and Leukemia inhibitory factor receptor (LIFR) were found to be key direct targets of miR-203 in these RMS cells. We showed that p63 positively regulated the Notch pathway by stimulating the expression of Jagged1, while LIFR was required for the activation of the JAK1/STAT1/STAT3 pathway. Re-expression of miR-203 in RMS cells led to the down regulation of both the Notch and the JAK1/STAT1/STAT3 pathways, which promote myogenic differentiation.

To identify additional tumor suppressive miRNAs that are down regulated by promoter hypermethylation in RMS, we treated both RD and Rh30 cells with 5'-azacytidine and performed quantitative PCR-based microRNA screening. Among positive hits we identified, we selected miR-515-5p for further in-depth analysis. The GTPase activating protein (SH3 domain) binding protein 2 (G3BP2) gene was found to be a direct target of miR-515-5p.Although G3BP2 has been found to be over-expressed in tumors, its role in tumorigenesis remains unclear. Work is underway to further characterize its role in RMS.

Collectively, we have identified two new tumor suppressive miRNAs that are down regulated in RMS mainly by promoter hypermethylation. They would serve as new targets for therapeutic treatment of RMS in the future.