APEX1 and lung cancer: The following proximity ligation assays were then successfully carried out to validate the identified APE1-interacting proteins within cells: i) SFPQ (splicing factor, proline- and glutamine-rich), DHX9 (DEAH-box helicase 9) and hnRNPK (heterogeneous nuclear ribonucleoprotein K) in HeLa cells (Fig. 2C and Supplementary Figs. S1 and S2); ii) hnRNPA2/B1 in the JHH-6 hepatocellular carcinoma cell line31 (Supplementary Fig. S1B); iii) SFPQ in the A549 lung cancer cell line (Supplementary Fig. S1C)32.