MicroRNA-33b suppresses the proliferation and metastasis of hepatocellular carcinoma cells through the inhibition of Sal-like protein 4 expression

Abstract

MicroRNAs (miRNAs or miRs) have been found to participate in the development and malignant progression of human cancers by negatively mediating the expression of their target genes. Recently, miR33b has been reported to be involved in multiple types of human cancer, including hepatocellular carcinoma (HCC). However, the underlying regulatory mechanisms of miR33b in HCC cell growth and metastasis remain largely unclear. In the present study, RT-qPCR revealed that miR33b was significantly downregulated in HCC tissues compared to their matched adjacent normal tissues. Moreover, the miR33b level was significantly lower in advanced-stage HCC (stages T3-T4) compared to early-stage HCC (stages T1-T2). Furthermore, it was also downregulated in the HCC cell lines, LH86, HepG2, LMH and PLHC-1, when compared with the THLE-3 normal human liver cells. We further demonstrated that the overexpression of miR33b led to a significant decrease in the proliferation, migration and invasion of HepG2 and LH86 cells. Luciferase reporter assay identified Sal-like protein 4 (SALL4) as a target gene of miR33b, and its protein expression was negatively regulated by miR33b in HepG2 and LH86 cells. Moreover, the restoration of SALL4 expression markedly reversed the inhibitory effect of miR33b overexpression on the proliferation, migration and invasion of HepG2 and LH86 cells, indicating that SALL4 is involved in miR33b-mediated malignant phenotypes of HCC cells. Furthermore, we found that SALL4 was significantly upregulated in HCC tissues compared to their matched adjacent normal tissues, and its increased expression was significantly associated with the advanced malignancy of HCC. Moreover, SALL4 was also upregulated in HCC cell lines compared to the THLE-3 normal human liver cells. Finally, we found that the SALL4 expression inversely correlated with the miR33b level in HCC tissues. On the whole, the findings of our study demonstrate that miR33b suppresses the proliferation and metastasis of HCC cells through the inhibition of SALL4 expression. Therefore, miR33b/SALL4 may become a potential therapeutic target for the treatment of HCC.