Stimulation of c- ras expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Abstract

A series of in vivo and in vitro experiments were conducted to determine the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) administered on the expression of c- ras. Differences in c- ras expression between control and TCDD treated groups were determined by immunoassay of p21 ras protein, or indirectly measured by the specific binding of 3H-GTP to hepatic plasma membrane preparations. Intraperitoneal injection of sublethal doses of TCDD significantly elevated (P<0.05, Student t test) levels of hepatic p21 ras protein in Sprague-Dawley rats and TCDD sensitive C57BL/6J mice. Such an increase occurred at an early stage of poisoning in the C57BL/6J mice. The earliest increase was detectable 6 h after dosing, and the difference became statistically significant by 12 and 24 h after dosing. TCDD treatment increased levels of a 21Kd protein found in the in vitro translation products of RNA purified from guinea pig liver. This protein was identified as a c- ras protein based upon its ability to bind GTP, precipitation by a polyclonal antibody against the ras Ha and Ki proteins and subsequent SDS-PAGE which showed a single protein band of ≈21Kd.