Nuclear Factor κB p65 Regulates Synovial Sarcoma Development through a DGCR8-Dependent Signaling Pathway

Synovial sarcoma (SS) is a malignant soft tissue sarcoma. Our previous study revealed that miR-9-5p aggravates SS development. The aim of current study is to explore the mechanism that regulating miR-9-5p expression in SS progression. RIP assay is performed to analyze the combination of DiGeorge syndrome critical region gene 8 (DGCR8) and nuclear factor κB (NF-κB) p65 with primary (pri)-miR-9-1, pri-miR-9-2 and pri-miR-9-3. Co-IP is used to detect the combination of DGCR8 and NF-κB p65. Cell proliferation and apoptosis are analyzed using colony formation assay and flow cytometry, respectively. NF-κB p65 and miR-9-5p are evaluated in SS tumors and they are positively correlation. In SS cells, NF-κB p65 increasing promotes mature miR-9-5p expression, but inhibits pri-miR-9-1/3 expression. NF-κB p65 silencing results in opposite effects. Altering NF-κB p65 level did not affect the expression of pri-miR-9-2. The binding of DGCR8 and pri-miR-9-1/3 are attenuated by NF-κB p65 silencing. The combination of NF-κB p65 and DGCR8 is weakened by RNase treatment or NF-κB p65 silencing. The inhibition of NF-κB p65 to pri-miR-9-1/3 expression and the promotion of NF-κB p65 to miR-9-5p expression are rescued by DGCR8 silencing. Functional experiment results revealed that NF-κB p65 overexpression promotes SS cell proliferation and suppresses cell apoptosis, but there are rescued by miR-9-5p silencing or DGCR8 silencing. Overall, NF-κB p65 contributes the processing of pri-miR-9-1/3 into mature miR-9-5p in a DGCR8-dependent manner. Meantime, NF-κB p65 promotes SS cell proliferation and inhibits SS cell apoptosis by promoting miR-9-5p expression. Our data provided a novel evidence for miR-9-5p serving as a promising target for SS therapy, and proposed a novel regulatory mechanism for SS development.