GAP JUNCTION ENDOCYTOSIS AND LYSOSOMAL DEGRADATION OF CONNEXIN43-P2 IN WB-F344 RAT-LIVER EPITHELIAL-CELLS TREATED WITH DDT AND LINDANE

Treatment of WB-F344 rat liver epithelial cells with DDT (1,1-bis(p-ch lorophenyl)-2,2,2-trichloroethane) or lindane induces a loss of gap ju nction plaques and a decrease in the phosphorylated gap junction prote in connexin43-P2 (Cx43-P2), which is associated with the plaques, In t his study we have considered several mechanisms, The loss of junctiona l plaques could be due to disaggregation of junctional particles or to endocytosis of the plaques, while the loss of Cx43-P2 could be due to dephosphorylation or degradation. Immunohistochemical analyses of DDT - or lindane-treated cells revealed a reduction in plasma membranous C x43-positive gap junction plaques coincident with the appearance of Cx 43-positive punctate cytoplasmic structures, The cytoplasmic Cx43-posi tive structures eventually disappeared after 4 h treatment. Diffuse Cx 43-positive plasma membranous staining was not seen following DDT or l indane treatment, Western blot analyses of these cells indicated that Cx43-P2 decreased in a time-dependent manner that paralleled the disap pearance of gap junction plaques from the plasma membrane, The loss of Cx43-P2 was not due to dephosphorylation, since no increase in non-ph osphorylated (Cx43-NP) or other phosphorylated (Cx43-P1) forms of the protein were evident, The decrease in Cx43-P2 and the disappearance of cytoplasmic Cx43-positive structures were prevented by colchicine and chloroquine, which suggests that Cx43-P2-containing plaques were inte rnalized and degraded in lysosomes, In addition, two small (similar to 18 and similar to 22 kDa) bands appeared in Western blots coincident with the loss of Cx43-P2 and may be degradation products of the protei n, These immunohistochemical and biochemical data strongly suggest tha t the loss of gap junction plaques and of Cx43-P2 in WB-F344 cells tre ated with DDT and lindane were due to endocytosis of the plaques and d egradation of Cx43-P2 in lysosomes.