PU.1 Is Identified as a Novel Metastasis Suppressor in Hepatocellular Carcinoma Regulating the miR-615-5p/IGF2 Axis

Invasion and metastasis is the major cause of tumor recurrence, difficulty for cure and low survival rate.Excavating key transcription factors, which can regulate tumor invasion and metastasis, are crucial to thedevelopment of therapeutic strategies for cancers. PU.1 is a master hematopoietic transcription factor and avital regulator in life. Here, we report that, compared to adjacent non-cancerous tissues, expression of PU.1mRNA in metastatic hepatocellular carcinoma (HCC), but not primary HCC, was significantly down-regulated.In addition, levels of PU.1 mRNA in metastatic hepatoma cell lines MHCC97L and MHCC97H were muchlower than in non-metastatic Hep3B cells. Transwell invasion assays after PU.1 siRNA transfection showed thatthe invasion of hepatoma cell lines was increased markedly by PU.1 knockdown. Oppositely, overexpression ofPU.1 suppressed the invasion of these cells. However, knockdown and overexpression of PU.1 did not influenceproliferation. Finally, we tried to explore the potential mechanism of PU.1 suppressing hepatoma cell invasion.ChIP-qPCR analysis showed that PU.1 exhibited a high binding capacity with miR-615-5p promoter sequence.Overexpression of PU.1 caused a dramatic increase of pri-, pre- and mature miR-615-5p, as well as a markeddecrease of miR-615-5p target gene IGF2. These data indicate that PU.1 inhibits invasion of human HCC throughpromoting miR-615-5p and suppressing IGF2. These findings improve our understanding of PU.1 regulatoryroles and provided a potential target for metastatic HCC diagnosis and therapy.