Department of Environmental Health Sciences, Johns Hopkins Medical Institutions, Baltimore, MD 21205, USA.
The broad spectrum of biological responses associated with exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) is believed to be due to the alteration in expression of TCDD-inducible genes. The aim of this study was to investigate the effects of TCDD on the in vivo tissue-specific expression of the recently identified TCDD-inducible cytochrome P450 CYP1B1 [Sutter et al. (1994) J. Biol. Chem., 269, 13092-13099] in Sprague-Dawley rats. We cloned the 5.0 kb rat homolog of CYP1B1 from a TCDD-treated rat liver cDNA library and showed that the rat and human CYP1B1 predicted amino acid sequences are 80% identical. RNA hybridization analysis showed that CYP1B1 is constitutively expressed in the adrenal glands and also in the testes of untreated rats. This tissue distribution suggests that CYP1B1 may be a physiological steroid hydroxylase. Seventy-two hours post-administration of 25 micrograms/kg body wt TCDD by gavage, steady-state levels of the 5.1 kb CYP1B1 RNA were increased > 50-fold in liver, and to a lesser extent in kidneys, lung, heart and ovaries. Average CYP1B1 RNA levels were significantly higher in the kidneys and livers of TCDD-treated females than in those from similarly treated males. In contrast, no significant sex-difference was observed in the levels of CYP1A1 in these tissues in TCDD-treated animals. In Sprague-Dawley rats, TCDD is a more potent hepatocarcinogen in females than in males. The induction of CYP1B1 in TCDD rat liver may be a contributing factor to the carcinogenic action of this persistent environmental pollutant.