CuCl₂-dependent regulation of a HRE-driven reporter gene. CHO chinese hamster ovary (A) and Hep3B human hepatoma (B-C) cell lines stably transfected with an HRE-containing luciferase reporter gene were treated for 24 hours with the CuCl₂ (A-B) or CuCl (C) concentrations indicated. (A-B) MTT assays were used to assess Cu²⁺ toxicity. Shown are mean values ± SEM of n = 3 (all MTT assays), n = 7 (hypoxic Hep3B), n = 8 (normoxic Hep3B), or n = 10 (CHO) independent experiments. (C) A representative experiment performed in quadruplicate is shown as mean values ± SEM.