miR-4510 blocks hepatocellular carcinoma development through RAF1 targeting and RAS/RAF/MEK/ERK signalling inactivation.

BACKGROUND: Therapeutic outcomes using the multikinase inhibitors, sorafenib and regorafenib, remain unsatisfactory for patients with advanced hepatocellular carcinoma (HCC). Thus, new drug modalities are needed. We recently reported the remarkable capacity of miR-4510 to impede the growth of HCC and hepatoblastoma through Glypican-3 (GPC3) targeting and Wnt pathway inactivation.

METHODS: To identify new targets of miR-4510, we used a label-free proteomic approach and reported down-regulation of RAF proto-oncogene serine/threonine-protein kinase (RAF1) by miR-4510. Because the tumourigenic role of RAF1 in HCC is controversial, we further studied RAF1:miR-4510 interactions using cellular, molecular as well as functional approaches and a chicken chorioallantoic membrane (CAM) xenograft model.

RESULTS: We found an increase in RAF1 protein in 59.3% of HCC patients and a specific up-regulation of its transcript in proliferative tumours. We showed that miR-4510 inactivates the RAS/RAF/MEK/ERK pathway and reduces the expression of downstream targets (ie c-Fos proto-oncogene [FOS]) through RAF1 direct targeting. At a cellular level, miR-4510 inhibited HCC cell proliferation and migration and induced senescence in part by lowering RAF1 messenger RNA (mRNA) and protein expression. Finally, we confirmed the pro-tumoural function of RAF1 protein in HCC cells and its ability to sustain HCC tumour progression in vitro and in vivo.

CONCLUSIONS: In this work, we confirm that RAF1 acts as an oncogene in HCC and further demonstrate that miR-4510 acts as a strong tumour suppressor in the liver by targeting many proto-oncogenes, including GPC3 and RAF1, and subsequently controlling key biological and signalling pathways among which Wnt and RAS/RAF/MEK/ERK signals.