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Fumonisin B1 induces protein kinase C translocation via direct interaction with diacylglycerol binding site
J M Yeung1, H Y Wang, D B Prelusky
1Food Research Division, Food Directorate, Health Protection Branch, Health Canada, Sir Frederick Banting Research Centre, Ottawa, Ontario, Canada.
Abstract:
Fumonisins are carcinogenic to rats and are suspected human carcinogens. However, the mechanism(s) of carcinogenesis of fumonisn B1 (FB1) is poorly understood. Multiple signal transduction pathways such as protein kinase C (PKC) have been shown to play an important role in carcinogenesis. This study was undertaken to evaluate whether FB1 affects PKC activation. Similar to tumor-promoting phorbol ester, phorbol 12-myristate-13-acetate (PMA), PKC is also catalytically activated by FB1. Protein kinase C activity and its redistribution in response to FB1 were determined in rat cerebrocortical slices. Cytosolic and membranous PKC activities were determined by histone phosphorylation in the presence of [gamma-32P]ATP, phosphatidyl-L-serine, PMA, and Ca2+. Distribution of gamma PKC isozyme in the presence of FB1 was also assessed by immunoblotting using affinity purified anti-peptide antibodies. Similar to PMA, FB1 added in vitro to rat cerebrocortical slices facilitated PKC translocation from cytosol to membrane in a concentration-dependent manner. This FB1-induced PKC translocation was inhibited by incubation with the inactive 4 alpha-phorbol 12,13-didecanoate. The effects of FB1 and PMA were neither additive nor synergistic. In addition, PMA and FB1-induced PKC enzyme redistribution were inhibited by pretreating tissues with sphingosine. A concentration-related FB1 attenuation of specific phorbol dibutyrate, [3H]PDBu, binding was also observed when cortical membranes were incubated with either PMA or sphingosine. This is the first report of FB1-induced PKC translocation via a direct action on the diacylglycerol site that also binds phorbol esters. Because phorbol esters are well known tumor promoters, we provide a plausible cellular mechanism to explain the carcinogenicity of FB1.
Insights
Fumonisin B1 (FB1) activates protein kinase C (PKC) and causes its translocation, similar to tumor promoters. This provides a mechanism for FB1
Area of Science:
- Toxicology
- Molecular Biology
- Biochemistry
Background:
- Fumonisins, particularly fumonisin B1 (FB1), are known carcinogens in rats and suspected human carcinogens.
- The precise mechanisms underlying fumonisin-induced carcinogenesis remain poorly understood.
- Signal transduction pathways, including protein kinase C (PKC), are implicated in carcinogenesis.
Purpose of the Study:
- To investigate whether fumonisin B1 (FB1) affects protein kinase C (PKC) activation and translocation.
- To elucidate the cellular mechanisms by which FB1 may contribute to carcinogenesis.
Main Methods:
- FB1's effect on PKC activity and subcellular distribution was assessed in rat cerebrocortical slices.
- PKC activity was measured via histone phosphorylation.
- PKC isozyme redistribution was evaluated using immunoblotting and [3H]PDBu binding assays.
Main Results:
- FB1 induced a concentration-dependent translocation of PKC from the cytosol to the membrane, mirroring the effect of phorbol ester (PMA).
- FB1's action on PKC translocation was inhibited by sphingosine and 4α-phorbol 12,13-didecanoate.
- FB1 competed with phorbol ester binding, suggesting interaction with the diacylglycerol-binding site of PKC.
Conclusions:
- FB1 directly activates and translocates PKC, acting on the same site as phorbol esters.
- This FB1-induced PKC activation provides a plausible cellular mechanism for its carcinogenic activity.
- The findings highlight a critical molecular pathway involved in fumonisin toxicity and carcinogenicity.