Tris (1,3-dichloro-2-propyl) phosphate induces toxicity by stimulating CaMK2 in PC12 cells

Tris (1,3-dichloro-2-propyl) phosphate (TDCIPP) is one of the widely used organophosphorus flame retardants (OPFRs), which are regarded as suitable substitutes for brominated flame retardants (BFRs). Previously, we have validated the toxicity of TDCIPP in PC12 cells owing to the induced alterations in GAP43, NF-H, CaMK2a/2b, and tubulin α/β proteins; however, limited information is currently available on the toxicity and mechanism of TDCIPP. In the present study, cytotoxicity effects were evaluated by exposing PC12 cells to different concentrations of TDCIPP (0-50 μM) for 4 days. To explore the possible mechanisms through which cytotoxicity is induced, changes in intracellular [Ca²⁺ ]_i levels and the activation of calmodulin dependent protein kinase 2 (CaMK2), c-Jun N-terminal kinase (JNK), extracellular regulated protein kinases (ERK1/2), and p38 mitogen-activated protein kinases (MAPK) pathways were evaluated. Furthermore, PC12 cells were pretreated with CaMK2 inhibitor KN93 to investigate the relationship between TDCIPP-induced phosphorylation of CaMK2 and activation of JNK, ERK1/2, and p38 MAPK pathways. Our results indicate that TDCIPP-induced toxicity might be associated with the overload of [Ca²⁺ ]_i levels, increased phosphorylation of CaMK2, and activation of the JNK, ERK1/2, and p38 MAPK pathways, the lattermost of which was further demonstrated to be partially elicited by the CaMK2 phosphorylation.