SIGNIFICANCE OF TCDD-INDUCED CHANGES IN PROTEIN-PHOSPHORYLATION IN THE ADIPOCYTE OF MALE GUINEA-PIGS

The chemical TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) at very low co ncentrations has been found to cause a rapid rise in protein phosphory lation activities in the extranuclear fraction (i.e., cytosol and cell ular membranes) of the adipose tissue from male guinea pigs. The effec t occurred both in vivo and when TCDD was added to adipose in tissue c ulture (in situ). To study the cause for such a TCDD-induced biochemic al change, isolated adipose tissues were treated with TCDD in conjunct ion with various diagnostic agents known to affect protein synthesis ( actinomycin D and cycloheximide) and protein phosphorylation activitie s (genistein). The stimulatory effect of TCDD on protein phosphorylati on was not totally abolished by actinomycin D; however, cycloheximide and genistein partially suppressed the effect of TCDD. Such an action of TCDD was accompanied by a quick rise in ras GTP binding activity as well as a rise in phosphorylation of nuclear c-myc protein product wi thin 10 minutes after TCDD addition, indicating that TCDD is likely to activate the signal transduction pathway for growth factors. In view of the absence of an inhibitory action of actinomycin D and the short time required for TCDD to induce these changes, we have formulated a w orking hypothesis that stimulation of protein phosphorylation activiti es by TCDD may not be mediated by a transcriptional process. To test t his possibility, an extranuclear fraction was obtained from the homoge nate of adipose tissue, and the effect of TCDD was studied in vitro ce ll-and nucleus-free conditions. It was found that TCDD was capable of activating protein phosphorylation activity under cell free conditions even in the absence of nuclei. Such an action of TCDD is dependent on the action of the Ah receptor.