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

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.