Cross-Talk among Intracellular Signaling Pathways Mediates the Diphenyl Ditelluride Actions on the Hippocampal Cytoskeleton of Young Rats

Abstract

In the present report, we showed that diphenyl ditelluride (PhTe)(2) induced in vitro hyperphosphorylation of glial fibrillary acidic protein (GFAP), vimentin and neurofilament (NF) subunits in hippocampus of 21 day-old rats. Hyperphosphorylation was dependent on L-voltage dependent Ca(2+) channels (L-VDCC), N-methyl-d-aspartate (NMDA) and metabotropic glutamate receptors, as demonstrated by the specific inhibitors verapamil, DL-AP5 and MCPG, respectively. Also, dantrolene, a ryanodine channel blocker, EGTA and Bapta-AM, extra and intracellular Ca(2+) chelators respectively, totally prevented this effect. Activation of metabotropic glutamate receptors by (PhTe)(2) upregulates phospholipase C (PLC), producing inositol 1, 4, 5-trisphosphate (IP(3)) and diacylglycerol (DAG). Therefore, high Ca(2+) levels and DAG directly activate Ca(2+)/calmodulin-dependent protein kinase (PKCaMII) and protein kinase C (PCK), resulting in the hyperphosphorylation of Ser-57 in the carboxyl-terminal tail domain of the low molecular weight NF subunit (NF-L). Also, the activation of Erk1/2, and p38MAPK resulted in hyperphosphorylation of KSP repeats of the medium molecular weight NF subunit (NF-M). It is noteworthy that PKCaMII and PKC inhibitors prevented (PhTe)(2)-induced Erk1/2MAPK and p38MAPK activation as well as hyperphosphorylation of KSP repeats on NF-M, suggesting that PKCaMII and PKC could be upstream of this activation. Taken together, our results highlight the role of Ca(2+) as a mediator of the (PhTe)(2)-elicited signaling targeting specific phosphorylation sites on IF proteins of neural cells of rat hippocampus. Interestingly, this action shows a significant cross-talk among signaling pathways elicited by (PhTe)(2), connecting glutamate metabotropic cascade with activation of Ca(2+) channels. The extensively phosphorylated amino- and carboxyl- terminal sites could explain, at least in part, the neural dysfunction associated with (PhTe)(2) exposure.