Superfund Research Program

Antioxidant Protection by Hyperbilirubinemia in Toxicity and Disease

Project Leader: Robert H. Tukey
Grant Number: P42ES010337
Funding Period: 2000-2017

Project-Specific Links

Final Progress Reports

Year:   2016  2009  2004 

Cellular signaling mechanisms coordinate the movement and underlie the regulatory events associated with a chemical induced toxic response.  Last year Dr. Tukey’s research team published (Chen S. et al, JBC 278, 19526, 2003) a link between MAP kinase p38 dependent phosphorylation and cellular protection when cells are exposed to the benzo[a]pyrene metabolite B[a]P-7,8,-dihydrodiol.  The initiation of apoptosis following B[a]P-7,8-dihydrodiol treatment results from activation of the Ah receptor and metabolism of B[a]P-7,8-dihydrodiol to the ultimate carcinogen, B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE-2).  This report was the first to document the activation of the Ah receptor by B[a]P-dihydrodiol but more importantly cellular protection by p38.

This work has now led to recent findings where the researchers show that Erk kinase inhibitors were unable to prevent B[a]P-7,8-dihydrodiol induced apoptosis, leading them to speculate that Erk kinases are linked to regulation of the Ah receptor. Cotreatment of hepa1c1c7 cells with TCDD and Erk kinase inhibitors PD98059, U0126 or SL327 led to enhanced nuclear accumulation of Ah receptor, but with a reduced capacity to complement TCDD induction of Cyp1a1.  This is explained in part by the ability of Erk kinase inhibitors to alter the steady-state levels of cellular Ah receptor, a result that leads to a dramatic induction in detectable receptor levels.  These changes in cellular Ah receptor levels are associated with delayed degradation of the Ah receptor, since TCDD initiated degradation is reversed when cells are co-treated with TCDD and Erk kinase inhibitors. Erk kinase is linked to Ah receptor expression, as demonstrated by reductions in total Ah receptor levels following overexpression of constitutively active MEK1.  In addition, Erk kinase activity modulates the transcriptional response, since MEK1 overexpression enhances TCDD initiated transactivation potential of the receptor.  Thus, Erk kinase activity facilitates ligand initiated transcriptional activation while targeting the Ah receptor for degradation. Immunoprecipitation experiments of the Ah receptor indicate that Erk kinase activity is associated with the receptor.  Interestingly, the carboxyl region of the Ah receptor is associated with the transactivation region as well as the site for ubiquitination, indicating that Erk kinase dependent phosphorylation targets the carboxyl region of the receptor.