INDUCTION OF NUCLEAR CATECHOL-O-METHYLTRANSFERASE BY ESTROGENS IN HAMSTER-KIDNEY - IMPLICATIONS FOR ESTROGEN-INDUCED RENAL-CANCER

Catecholestrogens are postulated to contribute to carcinogenesis by ca using DNA damage mediated by reactive oxygen species generated during redox cycling between catechol and quinone estrogens, and by quinone e strogens that can form depurinating adducts, The above hypothesis is b ased principally on studies of the cancers that develop in renal corte x of hamsters treated with primary estrogens: Hamster kidney can catal yze 2- and it-hydroxylation of estrogens and support their redox cycli ng, and the kidneys of estradiol-treated hamsters show evidence of oxi dative cellular and DNA damage, Here we used immunocyto-chemisty to te st the postulate that catechol-O-methyltransferase (COMT), the enzyme that can prevent oxidation of catecholestrogens to their quinone deriv atives, would be induced in renal cortex of hamsters treated with estr adiol or ethinyl estradiol, In kidneys of control hamsters, COMT was l ocalized in cytoplasm of epithelial cells of proximal convoluted tubul es, predominantly in the juxtamedullary region where the estrogen-indu ced cancers arise, After 2- or 4-weeks of treatment with either estrog en, COMT was seen in epithelial cells of proximal convoluted tubules t hroughout the cortex, and many cells also showed intense nuclear COMT immunoreactivity, Estradiol-induced renal cancers were negative for CO MT, but were surrounded by tubules with intense cytoplasmic and nuclea r immunostaining, The nucleus-associated COMT was shown by immunoblot analysis to be the soluble form of the enzyme, Using reverse transcrip tion-polymerase chain reaction amplification, hamster kidney COMT was shown to lack the putative nuclear localization signal sequence presen t in human COMT. A second phase II enzyme, CuZn-superoxide dismutase ( CuZnSOD), was shown by immunocytochemistry to remain extranuclear in p roximal convoluted tubules of estrogen-treated hamsters, which indicat es entry of COMT into the nucleus to be selective, The findings are co nsistent with the catechol/quinone estrogen hypothesis of estrogen-ind uced cancer, while the translocation of the enzyme to the nucleus foll owing estrogen treatment suggests a response to a threat to the genome by electrophilic products of catechols.