Effects of heptachlor epoxide on components of various signal transduction pathways important in tumor promotion in mouse hepatoma cells: Determination of the most sensitive tumor promoter related effect induced by heptachlor epoxide

Abstract

The effects of the organochlorine (OC) liver tumor promoter heptachlor epoxide (HE; 0, 0.1, 1, 10, and 50 μM) on several cellular tumor promoter-sensitive parameters were studied in mouse 1c1c7 hepatoma cells in an effort to identify the most sensitive biomarker for OC promoter exposure and the critical pathway and target of OC promoters. The levels of Ca 2+ in the endoplasmic reticulum (ER) store, connexin43 (Cx43), PLC γ 1, nPKC ε, and AP-1 DNA binding in nucleus were studied to screen for effects induced by submicromolar HE levels. While all the parameters tested elicited effects, particulate PLC γ 1 and AP-1 DNA binding were found to be the most sensitive parameters affected by HE on both dose and temporal bases. Their levels were increased with 10- to 100-fold lower HE concentrations than were required to affect nPKC ε or Cx43. Further, with the lower HE dosages, particulate PLC γ 1 and nuclear AP-1 were positively modulated by HE after 1 h versus 3 or 72 h for nPKC ε and Cx43. Ca 2+ store depletion was probably the third most sensitive parameter, after AP-1 and PLC γ 1. These results suggest the tyrosine kinase growth factor receptor pathway is the probable critical pathway for HE-induce tumor promotion with the critical target most likely being upstream of PLC γ 1 and AP-1. This work also demonstates that upon exposure to a tumor promoter such as HE, many hepatocellular effects or changes result, suggesting that a cellular-program shift occurs similar to that described by the resistant hepatocyte model after exposure to a carcinogen or enzyme inducer.