Binding of aflatoxins to the 20S proteasome: effects on enzyme functionality and implications for oxidative stress and apoptosis.
Aflatoxins (AF) are contaminants of improperly stored foods; they are potent genotoxic and carcinogenic compounds, exerting their effects through damage to DNA. They can also induce mutations that increase oxidative damage. The goal of this study was to evaluate the possibility that a third mechanism could be involved in the carcinogenic action of aflatoxins, namely, direct binding to key enzymes involved in the regulatory pathways of the cell cycle, thereby modulating enzyme functionality. The 20S constitutive and immunoproteasome peptidase and proteolytic activities were assayed in the presence of aflatoxins B1, G1 and M1. All three toxins activated multiple peptidase activities of the proteasome. Aflatoxin (AF) M1 was the most potent activator of proteasome activity, while the constitutive 20S proteasome was specifically stimulated by AFG1. Furthermore, the effects of AFB1 on cultured hepatoma cells were investigated and the various proteasomal activities determined with cell lysates were differently affected. Taking into account the key role of the proteasome in cellular defense against oxidative stress, the carbonyl group content and the activities of antioxidant enzymes in cell lysates were analyzed. The proapoptotic effect of AFB1 was also investigated by measuring caspase-3 activity and cellular levels of p27 and IkappaBalpha.
Amici
Manila
M
Department of Molecular, Cellular and Animal Biology, University of Camerino, I-62032 Camerino (MC), Italy.
Cecarini
Valentina
V
Pettinari
Assuntina
A
Bonfili
Laura
L
Angeletti
Mauro
M
Barocci
Simone
S
Biagetti
Massimo
M
Fioretti
Evandro
E
Eleuteri
Anna Maria
AM
D016604:Aflatoxin B1 / Q000378:metabolism / Q000494:pharmacology; D016607:Aflatoxin M1 / Q000378:metabolism / Q000494:pharmacology; D000348:Aflatoxins / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002364:Caseins / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D018384:Oxidative Stress / Q000187:drug effects*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding
D000348:Aflatoxins; D002364:Caseins; D018809:Proliferating Cell Nuclear Antigen; C413374:p27 antigen; D016607:Aflatoxin M1; D016604:Aflatoxin B1; D053148:Caspase 3; D046988:Proteasome Endopeptidase Complex