To determine whether the Insig1/2 loop 1 peptide regulates the interaction between PCK1 and Insig1/2 in tumor cells, we treated Huh7 and Hep3B HCC cells with this peptide fused with a fragment of transactivator of transcription (TAT) peptide to facilitate plasma membrane penetration,[17] resulting in ≈100% tumor cells internalizing the peptide (Figure S1c, Supporting Information). Here, INSIG1 is linked to hepatocellular carcinoma.