Possible molecular targets of halogenated aromatic hydrocarbons in neuronal cells

Halogenated aromatic hydrocarbon including polychlorinated biphenyls (PCBs) are persistent and bioaccumulative environmental toxicants, Although healt h effects associated with exposure to these chemicals, including motor dysf unction and impairment in memory and learning, have been identified, their molecular site of action is unknown. Previous study from this laboratory de monstrated that, while ortho PCBs perturbed intracellular signaling mechani sms including Ca2+ homeostasis, receptor-mediated inositol phosphate produc tion and translocation of PKC, non-ortho PCBs did not. Since PKC signaling pathway is implicated in the modulation of motor behavior, as well as learn ing and memory, and the roles of PKC are isoform-specific, we have now stud ied the effects of two structurally distinct PCBs on isoforms of PKC in cer ebellar granule cell culture model, Cells were exposed to 2,2'-dichlorobiph enyl (ortho PCB; 2,2'-DCB) or 4,4'-dichlorobiphenyl (non-ortho PCB; 4,4'-DC B) for 15 min, respectively, and subsequently fractionated and immunoblotte d against the selected PKC monoclonal antibodies (alpha, gamma, delta, epsi lon, lambda, iota), While 2,2'-DCB induced a translocation of PKC-alpha [cy tosol (% control): 54 +/- 12 at 25 muM and 66 +/- 10 at 50 muM; membrane (% control): 186 +/- 37 at 25 muM and 200 +/- 48 at 50 muM] and -epsilon [cyt osol (% control): 92 +/- 12 at 25 muM and 97 +/- 15 at 50 muM; membrane (% control): 143 +/- 23 at 25 muM and 192 +/- 24 at 50 muM] from cytosol to me mbrane fraction in a concentration-dependent manner, 4,4'-DCB had no effect s. 2,2'-DCB induced translocation of PKC-alpha was blocked by pretreatment with sphingosine, suggesting a possible role of sphingolipid pathway. Altho ugh reports on implication of PKC-gamma with learning and memory are relati vely extensive, the expression of this particular isoform in the primary ce rebellar granule cells was below the detectable level. PKC-delta, -lambda a nd -iota were present in these cells, but were not altered by PCB exposure, These results suggest that the effects of 2,2'-DCB on PKC is isoform-depen dent and PKC-alpha as well as PKC-epsilon may be target molecules for ortho -PCBs in neuronal cells.