(c) The competitive p62 activity against Keap1 was measured by luciferase assay. The expression plasmids for Nrf2, Keap1 and p62 wild-type (w.t.) or its mutants were transfected into Hepa1 cells along with pNqo1-ARE reporter plasmid and pRL-TK as an internal control. At 36 h after transfection, the luciferase activity was measured in accordance with the instructions provided by the manufacturer. Assays were performed twice in triplicate. Data are means and s.d. for six determinations. 