Ly. Kong et al., Frequency and molecular analysis of hprt mutations induced by estradiol inChinese hamster V79 cells, INT J ONCOL, 17(6), 2000, pp. 1141-1149
The natural hormone estradiol (E-2) induces tumors in rodents and various t
ypes of DNA damage in vitro, and in vivo, but has not been mutagenic in bac
terial or mammalian assays. Recent reports of chromosomal and genetic lesio
ns induced by E-2 has led us to re-examine the mutation frequency and molec
ular alterations of the hypoxanthine-guanine phosphoribosyltransferase (hrp
t) gene in Chinese hamster V79 cells. E-2 at both physiological and pharmac
ological concentrations (10(-11), 10(-10), and 10(-7), 10(-6) M) significan
tly increased the mutation frequency of the hrpt gene by 2.57-, 3.35-, 2.63
-, and 8.78-fold, respectively, compared to the controls, while 10(-13), 10
(-12), 10(-9), or 10(-8) M E-2 induced little change (less than or equal to
0.93-fold). PCR and a molecular analysis of the hprt coding sequence identi
fied genetic lesions in the cDNA and/or genomic DNA in 15 of the 21 picked
E-2-induced mutants (71%). Simple base substitutions, such as T-->G or T-->
A transversions, were the most common mutations (8/21 or 38%) and frequentl
y occurred at 122 bp or 407 bp of the hprt coding sequence. Deletion mutati
ons were detected in 6 of the 21 clones (29%). An A-->G and a C-->T transit
ion and a four-base insertion (TATT) were identified each in one mutant clo
ne. A RT-PCR analysis demonstrated an abundant expression of the estrogen r
eceptor-alpha (ER alpha). However, ICI 182,780, an antagonist of ERa, acted
in an additive manner with E-2 and increased the hrpt mutation frequency.
In conclusion, E-2 induces a low frequency of mutations (deletions and poin
t mutations) in V79 cells, which is consistent with the weak carcinogenic a
ctivity of this hormone. The mutagenic effects of E-2 in V79 cells are not
mediated by the ER alpha..