REGULATION BY 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (TCDD) OF THE DNA-BINDING ACTIVITY OF TRANSCRIPTIONAL FACTORS VIA NUCLEAR-PROTEIN PHOSPHORYLATION IN GUINEA-PIG ADIPOSE-TISSUE

2,3,7,8-Tetrachloro-p-dioxin (TCDD) induced a modest stimulation of nu clear protein phosphorylation in explant tissue cultures in 10 min, fo llowed by a substantial decrease in the level of total protein phospho rylation activity in the nucleus. Curiously, this TCDD-induced decline in nuclear protein phosphorylation was accompanied by an increase in cytosolic and extranuclear protein phosphorylation activity. One of th e main causes for such a decrease in the protein phosphorylation activ ity in the nucleus appears to be related to some increase in protein p hosphatase activities as judged by the counteractions of okadaic acid and Na3VO4 to the above effect. In addition, TCDD induced changes in n uclear protein kinase activities as well. Manganese-stimulated protein kinase was found to be the predominant type of nuclear protein phosph orylating activity affected by TCDD, with 60% of the total activity du e to heparin-sensitive casein kinase II (CK II), a major nuclear prote in kinase. The level of CK II activity in the nuclear protein preparat ion from adipose tissue of TCDD-treated guinea pigs (1 mu g/kg) in the presence of 100 nM heparin was only 35% of the control value after 24 hr. In addition, TCDD was found to increase the protein kinase C and microtubule-associated protein 2 kinase activities as early as 15 min after treatment in isolated adipose tissues in culture. Under in situ incubation conditions with explant tissues in culture, TCDD rapidly en hanced the DNA binding activity of the transcriptional factor AP-1, wh ereas the same treatment reduced c-Myc DNA binding activity. Genistein a specific protein tyrosine kinase inhibitor, abolished the stimulato ry effect of TCDD on AP-1 binding activity, but not on DNA binding act ivity of c-Myc. Phorbol ester (TPA) increased the binding activity of AP-1 and c-Myc, as expected. However, TCDD in combination with TPA cau sed a slight reduction in binding activity of both transcriptional fac tors. On the other hand, in the presence of forskolin, the stimulatory effect of TCDD on AP-1 binding activity and the inhibitory effect on c-Myc were still apparent. Okadaic acid almost abolished the binding a ctivity of c-Myc, whereas in combination with TCDD a stimulatory effec t was found. These observations are consistent with the idea that TCDD regulates the DNA binding activity of AP-1 and c-Myc mainly through m odulating their states of phosphorylation by altering protein kinase a nd phosphatase activities.