LOSS OF GAP-JUNCTIONS FROM DDT-TREATED RAT-LIVER EPITHELIAL-CELLS

The mechanism by which the liver tumor promoter 1,1-bis(p-chlorophenyl )-2,2,2-trichloroethane (DDT) inhibits gap junctional intercellular co mmunication (GJIC) in WB-F344 rat liver epithelial cells could involve gap junction loss and/or decreased gap junction channel permeability. We examined these two possibilities in the present study. Immunohisto chemical studies using antibodies specific to connexin43, the major ga p junction protein expressed by these cells, revealed that gap junctio n number and size were reduced during exposure to DDT. The reductions in gap junctions (33-91%) correlated with dose-dependent (1-10 mu M) a nd time-dependent (0.5-4 h) decreases in cell-to-cell fluorescent dye- coupling (64-85%), as well as cellular levels of phosphorylated connex in43. These effects were reversible following removal of the tumor pro moter from the culture medium, although cycloheximide reduced the leve l of gap junction reformation. The losses in gap junctions were not du e to decreased connexin43 gene expression since steady-state levels of connexin43 mRNA were not similarly affected by DDT. Fenarimol (10 mu M), a structural analog of DDT, did not inhibit GJIC and had no effect on gap junction structure or connexin43 expression. These data sugges t that the inhibition of GJIC by DDT resulted from the removal of gap junctions from the plasma membrane and their degradation rather than s imply a decrease in their permeability.