Mitogen-activated protein kinases regulate palytoxin-induced calcium influx and cytotoxicity in cultured neurons.
OBJECTIVE
Palytoxin (PLT) is a potent toxin that binds to the Na,K-ATPase. Palytoxin is highly neurotoxic and increases the cytosolic calcium concentration ([Ca(2+)](c)) while decreasing intracellular pH (pH(i)) in neurons (Vale et al., 2006; Vale-Gonzalez et al., 2007). It is also a tumour promoter that activates several protein kinases.


METHODS
The role of different protein kinases in the effects of palytoxin on [Ca(2+)](c), pH(i) and cytoxicity was investigated in cultured neurons.


RESULTS
Palytoxin-induced calcium load was not affected by inhibition of calcium-dependent protein kinase C (PKC) isoforms but it was partially ameliorated by blockade of calcium-independent PKC isozymes. Inhibition of the extracellular signal-regulated kinase (ERK) 2 eliminated the palytoxin-induced rise in calcium and intracellular acidification, whereas inhibition of MEK greatly attenuated the palytoxin effect on calcium without modifying the PLT-evoked intracellular acidification. Blockade of c-Jun N-terminal protein kinases (JNK) somewhat decreased the palytoxin-effect on calcium, whereas inhibition of the p38 mitogen activated protein kinases (MAPKs) delayed the onset of the palytoxin-evoked rise in calcium and acidification. Furthermore, the cytotoxicity of palytoxin was completely blocked by inhibition of ERK 2 and partially prevented by inhibition of MEK. PLT increased phosphorylated ERK immunoreactivity in a concentration-dependent manner.


CONCLUSIONS
MAPKs, specifically ERK 2, link palytoxin cytotoxicity with its effects on calcium homeostasis after inhibition of the Na,K-ATPase. Binding of palytoxin to the Na,K-ATPase would alter signal transduction pathways, even in non-dividing cells, and this finding is related to the potent neurotoxicity of this marine toxin.
Vale
C
C
Departamento de Farmacología, Facultad de Veterinaria, USC, Campus Universitario s/n, Lugo, Spain.
Gómez-Limia
B
B
Vieytes
M R
MR
Botana
L M
LM
D000178:Acrylamides / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology; D003064:Cnidarian Venoms / Q000494:pharmacology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009498:Neurotoxins / Q000633:toxicity*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D000095702:Polyether Toxins
D000178:Acrylamides; D002118:Calcium; D003064:Cnidarian Venoms; D020928:Mitogen-Activated Protein Kinases; D009498:Neurotoxins; D047428:Protein Kinase Inhibitors; C010272:palytoxin; D000095702:Polyether Toxins