EVIDENCE FOR A 2ND PATHWAY IN THE ACTION MECHANISM OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (TCDD) - SIGNIFICANCE OF AH-RECEPTOR MEDIATED ACTIVATION OF PROTEIN-KINASE UNDER CELL-FREE CONDITIONS

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) when administered directly to a nuclear-free subcellular homogenate of guinea pig adipose tissue, caused a significant rise in protein kinase activities within 1-10 mi n. Such a rapid response was not expected, based on the classic transc riptional mechanism of action for TCDD, i.e. TCDD first binds with its cytosolic Ah-receptor, translocates into the nucleus, dimerizes with ''arnt'' (a nuclear transcription factor), and activates genes contain ing ''xenobiotic-responsive element'' (XRE). The above actions of TCDD on protein kinases were clearly blocked by two specific Ah-receptor b lockers, even under cell- and nucleus-free conditions. TCDD-induced in creases in protein phosphorylation occurred mainly in cytosolic prepar ations (i.e. 100,000 g supernatant) devoid of nucleus, microsomes and plasma membranes and were still observed in the presence of inhibitors of protein phosphatases. Furthermore, TCDD caused a rise in protein t yrosine kinase activity in a purified Ah-receptor preparation, as well as in an isolated heat shock protein 90 complex preparation containin g the Ah-receptor. This activation took place in the presence of actin omycin D and cycloheximide, indicating a portion of TCDD's action that is unrelated to de novo protein synthesis in this process. We have al so obtained evidence indicating that this action of TCDD triggers the protein kinase mediated growth factor signal transduction pathway, suc h as stimulation of mitogen activated protein kinase 2 and tyrosine ki nase activity. These results clearly support the view that the basic a ction pathway for such a TCDD-induced activation of protein kinases is distinctly different from its conventional action pathway involving c hanges in gene transcription in the nucleus.