dieldrin and chaetoglobosins

The purpose of the present study was to identify the biochemical mechanism(s) of the preventative and reversal effects of Chaetoglobosin K (ChK), a bioactive natural product, on inhibition of gap junction-mediated communication and connexin phosphorylation by the tumor promoting organochlorine compounds, lindane, and dieldrin.. A fluorescent dye transfer assay was used to quantify gap junction-mediated communication and sensitivity to lindane and dieldrin. Analyses of connexin 43, PKC, ERK, GSK-3beta, Raf, and Akt kinase phosphorylation were performed by Western blotting.. Pre-incubation of astroglial cells with 10 microM ChK prevented inhibition of dye transfer by lindane and dieldrin, which correlates with stabilization of the connexin 43 P2 isoform, and addition of ChK after lindane or dieldrin reversed the inhibitory effect, which correlated with re-appearance of the P2 isoform. Using phosphorylation site-specific antibodies, we demonstrated that lindane, dieldrin, and ChK all activated p44/42 ERK, but only ChK activated Akt kinase. ChK also activated a downstream effector of Akt, GSK-3beta, and activation of both kinases was inhibited by Wortmannin. Wortmannin also blocked ChK's ability to prevent dieldrin-induced inhibition of gap junction-mediated communication between RG-2 cells.. ChK's protective effects, both preventative and reversal, on lindane and dieldrin inhibition of gap junction-mediated communication are associated with stabilization and reappearance of the connexin 43 P2 phosphoform and may be mediated by the Akt pathway.

Topics: Animals; Astrocytes; Cell Communication; Cell Survival; Cells, Cultured; Connexin 43; Dieldrin; Dose-Response Relationship, Drug; Hexachlorocyclohexane; Indole Alkaloids; Neuroprotective Agents; Phosphorylation; Proto-Oncogene Proteins c-akt; Rats; Signal Transduction

Innumerable toxic substances present in the environment inhibit gap junctions, intercellular membrane channels that play fundamental roles in coordinated function of cells and tissues. Included are persistent organochlorine compounds, which pose health risks to humans and animals owing to their widespread use, bioaccumulation, and ability to inhibit gap junction channel-mediated intercellular communication in liver, lung, skin, heart, and brain cells. In this study, the organochlorine xenobiotics dieldrin and endosulfan, at micromolar concentrations, were found to inhibit gap junction-mediated intercellular communication and induce hypophosphorylation of connexin 43 in cultured rat astrocytes, the predominant cell type in the brain coupled through gap junctions. This inhibition of gap junctional communication was substantially reduced by preincubation with chaetoglobosin K (ChK), a bioactive natural produce previously shown to have ras tumor suppressor activity. Chaetoglobosin K also prevented dieldrin and endosulfan-induced hypophosphorylation of connexin 43 and prevented dieldrin-induced connexin 43 plaque dissolution in both astrocytes and cultured liver epithelial cells. The results suggest that stabilization of the native, phosphorylated form of connexin 43 by ChK may contribute to its ability to prevent organochlorine-induced inhibition of gap junction-mediated communication and dissolution of gap junction plaques within the plasma membrane.

Topics: Animals; Astrocytes; Cell Communication; Cell Line; Cell Survival; Cerebral Cortex; Connexin 43; Dieldrin; Endosulfan; Gap Junctions; Hepatocytes; Indole Alkaloids; Indoles; Insecticides; Mycotoxins; Phosphorylation; Rats; Rats, Inbred F344