TCDD causes stimulation of c-ras expression in the hepatic plasma membranes in vivo and in vitro.
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 p21ras 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 less than 0.05, Student t test) levels of hepatic p21ras 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 hr after dosing, and the difference became statistically significant by 12 and 24 hr after dosing. In contrast, TCDD tolerant DBA/2J mice had only a marginal increase in hepatic p21ras protein which did not become statistically significant even at 24 hr host-dosing. TCDD evoked increases in hepatic p21ras protein of C57BL/6J mice were accompanied by the increase in the specific binding of GTP to hepatic plasma membranes. Column chromatography of solubilized rat hepatic membrane proteins on sephadex G-50 showed TCDD administration increased levels of a 3H-GTP binding protein with MW of approximately 21 Kd. 3H-GTP binding in total hepatic membranes was also elevated (P less than 0.05, Fisher PLSD multiple comparison test) 6 hr and 24 hr after dosing of C57BL/6J mice, but as expected the effect of TCDD was not as conspicuous as that found in the plasma membrane. TCDD treatment increased levels of a 21 Kd 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 rasHa and Ki proteins and subsequent SDS-PAGE which showed a single protein band of approximately 21 Kd.
Tullis
K
K
Department of Environmental Toxicology, University of California, Davis 95616.
Olsen
H
H
Bombick
D W
DW
Matsumura
F
F
Jankun
J
J
D016475:3T3 Cells; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004285:Dogs; D015870:Gene Expression / Q000187:drug effects*; D011905:Genes, ras / Q000187:drug effects*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006168:Guinea Pigs; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D014176:Protein Biosynthesis; D016283:Proto-Oncogene Proteins p21(ras) / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000302:isolation & purification; D051381:Rats; D017207:Rats, Sprague-Dawley
D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D006160:Guanosine Triphosphate; D016283:Proto-Oncogene Proteins p21(ras)