The hypothesis regarding the importance of proline for hepatoma cells is also supported by the fact that the Huh7.5 cell line is characterized by the conversion of glutamate and ornithine to proline due to the increased transcription of the delta-1-pyrroline-5-carboxylate synthase genes (ALDH18A1) and ornithine aminotransferase (OAT) generating P5C in mitochondria. Here, ALDH18A1 is linked to hepatocellular carcinoma.