SLC1A4 Promotes Malignant Transformation of Hepatocellular Carcinoma by Activating the AKT Signaling.

Due to the difficulty in early diagnosis and the lack of treatment for advanced disease, the mortality rate of hepatocellular carcinoma (HCC) is high, and the 5-year overall survival rate is low at present. SLC1A4 is a neutral amino acid transporter, but its regulatory role and mechanism in HCC are still unclear. Through analyzing the TCGA database and clinical tissue specimens, this study uncovered the high expression of SLC1A4 in tumor tissues of HCC. Worse more, a high level of SLC1A4 may lead to a poor prognosis of HCC. Mechanically, silencing SLC1A4 inhibited the phosphorylation activation of AKT by suppressing the ubiquitin modification of AKT at lysine 63 and amino acid influx represented by D-serine, decreasing the protein level of β-catenin in the cell nucleus and suppressing the transcriptional activity of c-Myc and EpCAM promoters. As a result, silencing SLC1A4 inhibited the proliferation, migration, and stemness of hepatic cancer cells, which was successfully reversed by the introduction of exogenous AKT. Moreover, epithelial-mesenchymal transition (EMT) in vitro and metastasis potential in vivo of hepatic cancer cells was suppressed by the downregulated SLC1A4 level. In conclusion, SLC1A4 promotes the malignant transformation of HCC through activating signal transduction mediated by AKT. The findings in this study suggested that SLC1A4 may be a diagnostic indicator for the early HCC and a therapeutic target for the advanced HCC.