Additionally, knockout of activating transcription factor 4 (ATF4) [63] reduced, but did not eliminate, the expression of xCT mRNA in murine hepatocytes transformed to hepatocellular carcinoma (HCC) cells [50], implicating the involvement of the amino acid response elements (AAREs) in mediating xCT expression. This evidence concerns the gene SLC7A11 and hepatocellular carcinoma.