Endoplasmic Reticulum Stress Due to Altered Cellular Redox Status Positively Regulates Murine Hepatic CYP2A5 Expression

Abstract

Murine hepatic cytochrome P450 2A5 (CYP2A5) is uniquely induced by a variety of agents that cause liver injury and inflammation, conditions that are typically associated with downregulation of P450s. We hypothesized that induction of CYP2A5 occurs in response to hepatocellular damage resulting in endoplasmic reticulum (ER) stress. Treatment of mice in vivo and mouse hepatocytes in primary culture with the CYP2A5 inducer pyrazole resulted in overexpression of the ER stress biomarker glucose-regulated protein (GRP) 78. Treatment of primary hepatocytes with ER stress activators thapsigargin, tunicamycin, and trans-4,5-dihydroxy-1,2-dithiane (DTT ox ) and the calcium ionophore A23187 (calcimycin) resulted in elevated GRP78 mRNA levels; however, only the reducing agent DTT ox induced levels of CYP2A5 mRNA, protein, and coumarin 7-hydroxylase activity. To test the hypothesis that CYP2A5 induction is due to liver injury resulting from altered cellular redox status, we demonstrated that CYP2A5 induction, elevated serum alanine aminotransferase, and oxidative protein damage occur concurrently in pyrazole-treated mice. Pyrazole also induced the expression of cytosolic ␣ and class glutathione S-transferase expression both in vivo and in primary mouse hepatocytes. Moreover, treatment of hepatocytes with the redox cycling quinone menadione resulted in overexpression of CYP2A5 and GSTM1 mRNA. Finally, pretreatment of hepatocytes with the antioxidants N-acetylcysteine and vitamin E attenuated pyrazole-mediated increases in CYP2A5 mRNA levels. These findings clearly indicate that induction of mouse hepatic CYP2A5 during liver injury occurs via a novel mechanism involving ER stress due to altered cellular redox status.

Cytochrome P450 2A5 and bilirubin: Mechanisms of gene regulation and cytoprotection

“…The mechanism of the unique regulation of Cyp2a5 during these conditions is unclear and remains to be investigated. The one demonstrated mechanism that is common in these conditions is, in part, oxidative stress (Kirby et al, 1994b;Chomarat et al, 1997;Nebert et al, 2000;Cheung et al, 2003;Gilmore et al, 2003;Gilmore and Kirby, 2004;Su and Ding, 2004;Weng et al, 2005;Chen and Siddiqui, 2007;Fisher et al, 2009;De-Oliveira et al, 2010). Furthermore, these conditions appear to be associated with increased serum bilirubin levels (Bonacini, 2004;Malaguarnera et al, 2005;Richardson et al, 2006b;Hansen, 2010).…”

“…Furthermore, these conditions appear to be associated with increased serum bilirubin levels (Bonacini, 2004;Malaguarnera et al, 2005;Richardson et al, 2006b;Hansen, 2010). (Pellinen et al, 1993) Chloroform Anesthetic/Teflon (Camus et al, 1996) Cocaine Topical anesthetic (Pellinen et al, 1994a(Pellinen et al, , 1994b) Ethanol Fuel, beverage, and antiseptic (Lu et al, 2010) Phenobarbital Barbiturate and anticonvulsant (Hahnemann et al, 1992;Salonpää et al, 1994) Pyrazole Precursor for various medicines (Juvonen et al, 1985;Nichols and Kirby, 2008 (Cai et al, 2002) Buthionine sulfoximine Drug used in chemotherapy to reduce levels of glutathione (Gilmore et al, 2003) pregnenolone 16a-carbonitrile (PCN) Pregnane X receptor (PXR) agonist or antiglucocorticoid (Cai et al, 2002) Rifampicin Bactericidal antibiotics (Donato et al, 2000) Trans-4,5-dihydroxy-1,2-dithiane (DTTox) Intramolecular disulfide form of dithiothreitol; reducing agent (Gilmore and Kirby, 2004) (Montero et al, 1999) Bilirubin Bilirubin (BR) is the end product of heme catabolism, and heme is found in hemoglobin or other hemoproteins such as cytochromes, catalase, and a small pool of unbound free heme (Roy-Chowdhury et al, 2007). BR consists of a tetrapyrrole ( Figure D1).…”

“…Hepatic CYP2A5 protein expression was analyzed by western blot analysis as described previously (Gilmore and Kirby, 2004) …”

Ethanol Induction of CYP2A5: Permissive Role for CYP2E1

“…Increased expression of CYP2A5 occurs during viral, fulminant, or bacterial hepatitis, in certain tumors, and after treatment with a variety of hepatotoxins and heavy metals (Jounaïdi et al, 1994;Abu-Bakar et al, 2004;De-Oliveira et al, 2006;Lämsä et al, 2010). Induction of CYP2A5 has been suggested to occur in response to hepatocellular damage and to endoplasmic reticulum stress (Gilmore and Kirby, 2004). Depending on the inducer, the activation of hepatic CYP2A5 can occur via transcriptional and post-transcriptional mechanisms (Abu-Bakar et al, 2004, 2007Gilmore and Kirby, 2004).…”

Strain-Specific Effects of Alachlor on Murine Olfactory Mucosal Responses

“…TOXICOLOGIC PATHOLOGY (Salonpaa et al, 1994;Kojo et al, 1998;Gilmore and Kirby, 2004), CYP2A5 levels were not increased in C57BL/6J mouse liver following chronic alachlor treatment. We also evaluated levels of 2 cytochrome P450 proteins implicated in alachlor metabolism in humans, namely CYP3A4 and CYP2B6, using antibodies that recognize the murine proteins.…”