Reversible inhibition of in vitro epithelial cell proliferation by 2,3,7,8-tetrachlorodibenzo- p-dioxin

Abstract

Subconfluent cultures of a mouse epithelial cell line, which after prolonged subculturing exhibited an elevated saturation density as compared to the original cell line, were treated with 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD). Cultures of cells with or without TCDD grew at equal rates until confluency was reached. At confluency, cultures treated with as little as 10 −11 m TCDD showed a decline in cell proliferation relative to controls as demonstrated by cell enumeration and supported by reduced [ 3H]thymidine incorporation (both by liquid scintillation spectrometry of whole culture and autoradiography of individual cells). After 14 days of exposure, the saturation density of the treated culture was about 50% of the control culture. This TCDD-induced, increased sensitivity to density-dependent inhibition of replication (DDIR) was accompanied by a change from a fusiform morphology in the high-saturation-density control cells to a flat cobblestone appearance in the treated low-saturation-density cells. The nondividing cultures treated for 14 days with 10 −11 m TCDD had the same viability as control cultures. Upon trypsin suspension and reseeding, these formerly quiescent cultures were again capable of growing to high cell density and of again showing susceptibility to TCDD-induced changes in cell growth and morphology. Evidence is presented to suggest that this reversible increase in sensitivity to DDIR and the morphological change are not a consequence of cell growth inhibition. This system may provide the basis for an in vitro model to study the effect of TCDD on the control of replication of these cells.