Effect of in vivo administered 2,3,7,8-tetrachlorodibenzo-p-dioxin on DNA-binding activities of nuclear transcription factors in liver of guinea pigs.

To study the long-term effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the DNA-binding activity of nuclear transcription factors; a single dose of TCDD was injected intraperitoneally to male guinea pigs (1 microgram/kg i.p.). The animals were killed after 1, 2, 10, 20, 28, and 40 days, and DNA-binding activities in liver nuclear fraction were assessed through electrophoretic gel mobility shift assay (EMSA). As expected, the nuclear protein binding to dioxin or xenobiotic response element (DRE or XRE) increased as a result of TCDD's action (1-20 days). In addition, protein binding to 32P-labeled activator protein-1 (AP-1) response element (RE) (1-28 days) and activator protein-2 (AP-2) RE (1-28 days) were all increased by the action of TCDD. On the other hand, TCDD treatment significantly lowered the nuclear protein binding to both specific protein-1 (Sp-1) RE and c-MycRE at all time points (1-40 days). In the case of protein binding to 32P-labeled cAMP response element (CRE), we found two groups of binding bands being affected by TCDD. The intensity of the upper band group decreased, and that of the lower band group increased. As for AP-1 proteins, judging by the results of the Western blotting assay, the level of c-Fos increased while that of c-Jun decreased with TCDD treatment both at day 1 and 28. It is known that the rise in AP-1 and AP-2 activities often results in lowering certain cell differentiation signaling messengers in the nucleus. In agreement with this scenario, binding of C/EBP (CCAAT enhancer binding protein) to its response element site was found to be suppressed for 1 through 28 days. Among hormone receptors, TCDD treatment decreased the binding to retinoic acid RE but increased the binding to thyroid hormone RE.