The effects of the organochlorine (OC) liver
tumor promoter heptachlor epoxide (HE; 0, 0.1, 1, 10, and 50 microM) 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 Ca2+ in the endoplasmic reticulum (ER) store,
connexin43 (
Cx43), PLCgamma(1), nPKCvarepsilon, 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 PLCgamma(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 nPKCvarepsilon or
Cx43. Further, with the lower HE dosages, particulate PLCgamma(1) and nuclear
AP-1 were positively modulated by HE after 1 h versus 3 or 72 h for nPKCvarepsilon and
Cx43. Ca2+ store depletion was probably the third most sensitive parameter, after
AP-1 and PLCgamma(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 PLCgamma(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.