Non-dioxin-like organic toxicant PCB153 modulates sphingolipid metabolism in liver progenitor cells: its role in Cx43-formed gap junction impairment.
The non-dioxin-like environmental toxicant 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153), member of a group of persistent organic pollutants wide-spread throughout the environment, reduces gap junction intercellular communication (GJIC), an event possibly associated with tumor promotion. Since very few studies have investigated the signaling effectors and mode(s) of action of PCB153, and it is known that the gap junction (GJ) protein Cx43 can be regulated by the bioactive sphingolipid (SL) sphingosine 1-phosphate (S1P), this in vitro study mainly addresses whether SL metabolism is affected by PCB153 in rat liver epithelial WB-F344 cells. PCB153 treatment obtained significant changes in the S1P/ceramide (Cer) ratio, known to be crucial in determining cell fate. In particular, an increase in S1P at 30 min and a decrease of the bioactive lipid at 3 h were observed, whereas Cer level increased at 1 h and 24 h. Notably, a time-dependent modulation of sphingosine kinase (SphK), the enzyme responsible for S1P synthesis, and of its regulators, ERK1/2 and protein phosphatase PP2A, supports the involvement of these signaling effectors in PCB153 toxicity. Electrophysiological analyses, furthermore, indicated that the lipophilic environmental toxicant significantly reduced GJ biophysical properties, affecting both voltage-dependent (such as those formed by Cx43 and/or Cx32) and voltage-independent channels, thereby demonstrating that PCB153 may act differently on GJs formed by distinct Cx isoforms. SphK down-regulation alone induced GJIC impairment, and, when combined with PCB153, the acute effect on GJ suppression was additive. Moreover, after enzyme-specific gene silencing, the SphK1 isoform appears to be responsible for down-regulating Cx43 expression, while being the target of PCB153 at short-term exposure. In conclusion, we provide the first evidence of novel effectors in PCB153 toxic action in rat liver stem-like cells, leading us to consider SLs as potential markers for preventing GJIC deregulation and, thus, the tumorigenic action elicited by this environmental toxicant.
Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research Unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy.
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Pierucci
Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research Unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy.
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Frati
Department of Experimental and Clinical Medicine, Section of Physiological Sciences, University of Florence, Viale GB Morgagni 63, 50134, Florence, Italy.
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Squecco
Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research Unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy.
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Lenci
Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research Unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy.
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Vicenti
Veterinary Research Institute, Hudcova 70, 62100, Brno, Czech Republic.
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Slavik
Department of Experimental and Clinical Medicine, Section of Physiological Sciences, University of Florence, Viale GB Morgagni 63, 50134, Florence, Italy.
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Francini
Veterinary Research Institute, Hudcova 70, 62100, Brno, Czech Republic.
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Machala
Department of Experimental and Clinical Biomedical Sciences "Mario Serio", Research Unit of Molecular and Applied Biology, University of Florence, Viale GB Morgagni 50, 50134, Florence, Italy. elisabetta.meacci@unifi.it.
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Meacci
D000818:Animals; D002478:Cells, Cultured; D018031:Connexin 43 / Q000378:metabolism*; D004147:Dioxins / Q000633:toxicity; D004594:Electrophysiology / Q000379:methods; D017629:Gap Junctions / Q000187:drug effects* / Q000502:physiology; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D008246:Lysophospholipids / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011078:Polychlorinated Biphenyls / Q000633:toxicity*; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D013107:Sphingolipids / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism; D000099157:Sphingosine Kinase
D018031:Connexin 43; D004147:Dioxins; D008246:Lysophospholipids; D048052:Mitogen-Activated Protein Kinase 3; D017853:Phosphotransferases (Alcohol Group Acceptor); D011078:Polychlorinated Biphenyls; D054648:Protein Phosphatase 2; D013107:Sphingolipids; D013110:Sphingosine; D000099157:Sphingosine Kinase; C580592:Gja1 protein, rat; C060506:sphingosine 1-phosphate; C014024:2,4,5,2',4',5'-hexachlorobiphenyl
Connexin 43; Environmental toxicant non-dioxin-like PCB153; Gap junctions; PP2A; Sphingosine-1-phosphate