AP-1, NFκB, and ERK Activation Thresholds for Promotion of Neoplastic Transformation in the Mouse Epidermal JB6 Model

• Published in: Environmental health perspectives 2002-09, Vol.110 (9), p.865-870
• Main Authors: Suzukawa, Kazumi, Weber, Thomas J., Colburn, Nancy H.
• Format: Article
• Language: English
• Subjects: Animals; Cancer; Carcinogenesis; Carcinogens; Cell Culture Techniques; Cell growth; Cell Transformation, Neoplastic; Dose response relationship; Dose-Response Relationship, Drug; Environmental health; Epidermal cells; Mice; Mitogen-Activated Protein Kinases - pharmacology; Mutagens - adverse effects; NF-kappa B - pharmacology; Risk Assessment; Signal Transduction; Skin - cytology; Transcription Factor AP-1 - pharmacology; Transformed cell line; Tumors
• ISSN: 0091-6765; 1552-9924
• DOI: 10.1289/ehp.02110865

The promotion-sensitive mouse epidermal JB6 cells (clone 41) have been used to identify the tumor-promoting activity of various compounds. Because treatment by tumor promoters [12-O-tetradecanoylphorbol-13-acetate (TPA), epidermal growth factor (EGF), or tumor necrosis factor alpha (TNFα)] transforms clone 41 cells to anchorage-independent and tumorigenic phenotypes, they are considered to be undergoing late-stage tumor promotion. Here we address the question of how much activation of transformation-relevant transcription factors [activator protein-1 (AP-1), ternary complex factors (TCFs), or nuclear factor κB (NFκB)] is required for transformation response and how much tumor promoter produces significant risk of transformation. Stable transfectants harboring a reporter construct with an AP-1 response element, serum-response element (SRE), or NFκB response element were established. We examined the relationship between concentration of tumor promoters, key signaling events, and activation of the transcription factors. A concentration of > 0.2 nM TPA or 0.12 ng/mL (0.02 nM) EGF produced a significant increase in transformation response as well as in extracellular signal-regulated protein kinase (ERK), SRE, or AP-1 activation. Treatment with > 0.4 U/mL (2.35 pM) TNFα increased NFκB activity and transformation response in a dose-dependent manner. However, transformation response decreased at > 33 U/mL TNFα due to a cytotoxic response. These findings suggest that the signaling pathway leading to the activation of ERK, TCF, and AP-1 proteins constitutes a major factor determining the risk of tumor promotion by TPA or EGF. Cell toxicity in addition to NFκB activation should be considered in predicting TNFα-induced transformation response.