ABSTRACT
Regulation of the balance between survival, proliferation, and apoptosis on carcinogenic polycyclic aromatic hydrocarbon (PAH) exposure is still poorly understood and more particularly the role of physiologic variables, including intracellular pH (pH(i)). Although the involvement of the ubiquitous pH(i) regulator Na(+)/H(+) exchanger isoform 1 (NHE1) in tumorigenesis is well documented, less is known about its role and regulation during apoptosis. Our previous works have shown the primordial role of NHE1 in carcinogenic PAH-induced apoptosis. This alkalinizing transporter was activated by an early CYP1-dependent H(2)O(2) production, subsequently promoting mitochondrial dysfunction leading to apoptosis. The aim of this study was to further elucidate how NHE1 was activated by benzo(a)pyrene (BaP) and what the downstream events were in the context of apoptosis. Our results indicate that the mitogen-activated protein kinase kinase 4/c-Jun NH(2)-terminal kinase (MKK4/JNK) pathway was a link between BaP-induced H(2)O(2) production and NHE1 activation. This activation, in combination with BaP-induced phosphorylated p53, promoted mitochondrial superoxide anion production, supporting the existence of a common target for NHE1 and p53. Furthermore, we showed that the mitochondrial expression of glycolytic enzyme hexokinase II (HKII) was decreased following a combined action of NHE1 and p53 pathways, thereby enhancing the BaP-induced apoptosis. Taken together, our findings suggest that, on BaP exposure, MKK4/JNK targets NHE1 with consequences on HKII protein, which might thus be a key protein during carcinogenic PAH apoptosis.
Subject(s)
Apoptosis/drug effects , Benzo(a)pyrene/pharmacology , Hexokinase/biosynthesis , JNK Mitogen-Activated Protein Kinases/metabolism , Sodium-Hydrogen Exchangers/metabolism , Animals , Apoptosis/physiology , Cell Line , Cell Nucleus/metabolism , Enzyme Activation/drug effects , Hydrogen Peroxide/metabolism , Liver/drug effects , Liver/metabolism , MAP Kinase Kinase 4/metabolism , Mitochondria, Liver/drug effects , Mitochondria, Liver/metabolism , Phosphorylation , Rats , Reactive Oxygen Species/metabolism , Sodium-Hydrogen Exchanger 1 , Sodium-Hydrogen Exchangers/biosynthesis , Tumor Suppressor Protein p53/metabolismABSTRACT
Polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (BP) are toxic environmental contaminants known to enhance production of pro-inflammatory cytokines such as IL-1beta. The present study was designed in order to determine whether TNFalpha, another cytokine acting in inflammation, may also constitute a target for these chemicals. Both TNFalpha mRNA and TNFalpha secretion levels were found to be enhanced in human BP-treated macrophages. Dioxin, a contaminant activating the aryl hydrocarbon receptor (AhR) like PAHs, was also shown to increase TNFalpha expression. BP-mediated TNFalpha induction was however not suppressed by AhR antagonists, making unlikely the involvement of the typical AhR signalling pathway. BP-exposure of macrophages did not enhance NF-kappaB DNA binding activity, but it activated the MAP kinase ERK1/2. In addition, the use of chemical inhibitors of extracellular signal-regulated protein kinase (ERK) activation fully abrogated induction of TNFalpha production in BP-treated macrophages. These data likely indicate that PAHs enhance TNFalpha expression in human macrophages through an ERK-related mechanism. Such a regulation may contribute to confer pro-inflammatory properties to these widely-distributed environmental contaminants.
Subject(s)
Benzo(a)pyrene/pharmacology , Environmental Pollutants/pharmacology , Extracellular Signal-Regulated MAP Kinases/physiology , Macrophages/drug effects , Tumor Necrosis Factor-alpha/metabolism , Butadienes/pharmacology , Cells, Cultured , DNA-Binding Proteins/metabolism , Extracellular Signal-Regulated MAP Kinases/antagonists & inhibitors , Flavonoids/pharmacology , Gene Expression/drug effects , Humans , Macrophages/enzymology , Macrophages/immunology , NF-kappa B/metabolism , Nitriles/pharmacology , Polychlorinated Dibenzodioxins/pharmacology , Protein Kinase Inhibitors/pharmacology , RNA, Messenger/analysis , RNA, Messenger/metabolism , Receptors, Aryl Hydrocarbon/antagonists & inhibitors , Tumor Necrosis Factor-alpha/genetics , Up-RegulationABSTRACT
How pH(i) changes, more specifically alkalinization, affect the apoptotic cascade has yet to be determined. The aim of the present work was to test the involvement of mitochondria in the apoptotic cascade triggered by benzo(a)pyrene [B(a)P] and to determine the role of pH(i) changes and p53 relative to mitochondria. Our results indicate that B(a)P-induced apoptosis might rely upon a p53-dependent and a pH-sensitive mitochondrial dysfunction.
