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Differential regulation of c‐ fos expression in estrogen‐induced hamster renal tumors compared with kidney not due to creation of an estrogen‐response element by point mutation in the gene's flanking sequence
Author(s) -
Sarabia Stephen F.,
Liehr Joachim G.
Publication year - 1999
Publication title -
molecular carcinogenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.254
H-Index - 97
eISSN - 1098-2744
pISSN - 0899-1987
DOI - 10.1002/(sici)1098-2744(199904)24:4<255::aid-mc3>3.0.co;2-c
Subject(s) - biology , hamster , microbiology and biotechnology , estrogen receptor , kidney , point mutation , estrogen , hormone response element , response element , gene , gene expression , mutant , endocrinology , genetics , promoter , cancer , breast cancer
The conversion of a palindromic sequence, GGTCTnnnAGACC, in the 5′‐flanking region of the murine c‐ fos proto‐oncogene into a functional estrogen‐response element by a single base change into GGTC A / G nnnAGACC has previously been postulated [Nawaz et al., 1993] as a possible mechanism of the induction of tumors by estrogens. This attractive hypothesis has been investigated in estradiol‐induced Syrian hamster kidney tumors, in H‐301 kidney tumor cells (a cell line derived from the Syrian hamster tumor), and in normal kidney tissue. The c‐ fos gene is differentially regulated by a classical estrogen receptor–mediated process in tumors, whereas in the acutely treated kidney, estradiol induces c‐ fos expression independent of estrogen‐receptor function. In this study, we identified in the 5′‐flanking region of the hamster kidney c‐ fos gene the sequence AGTCCnnnAGACC, which closely resembled but did not appear to function as an estrogen‐response element. No mutations were detected in this sequence or in the 5′‐flanking region of c‐ fos genes from three different primary tumors and from H‐301 tumor cells. To rule out the possibility of a low copy number of mutant alleles in a tumor sample, polymerase chain reaction‐based single‐strand conformation polymorphism analysis was performed on 372 base pairs of the 5′‐flank of the c‐ fos gene (−367 to +5 base pairs relative to the transcription start point). Nine different kidney tumor DNA samples and five normal kidney tissue samples (controls) produced an identical pattern of DNA bands, suggesting a lack of natural polymorphisms and mutations in this region of the c‐ fos gene. Acute treatment of hamsters with 17β‐estradiol for 6 h significantly induced renalc‐ fos mRNA expression, whereas control levels of c‐fos were restored by co‐treatment with estradiol and either N‐acetyl‐ L ‐cysteine or α‐naphthoflavone. We concluded that the previously observed change in regulatory control of c‐ fos expression in kidney versus estradiol‐induced tumors does not involve the creation of a functional estrogen‐response element by single point mutation in the 5′‐flanking region of the gene. Additionally, c‐ fos expression in estradiol‐treated hamster kidneys appears to be mediated by free radicals generated by the catechol metabolites of estradiol and not by the activation of any estrogen receptor. Mol. Carcinog. 24:255–262, 1999. © 1999 Wiley‐Liss, Inc.