TKT and lung cancer: Additionally, using a GFP-based NHEJ reporter H1299 human lung cancer cell harboring IRES-TK-EGFP DNA integrated in the genome,25 the proportion of EGFP-positive cells was decreased in PHRF1-knockdown cells, but increased in PHRF1-overexpressing cells after I-SceI transfection (Figures 4c and d).