Project: Research project

Project Details


DESCRIPTION (Applicant's Description) Studies of the role of estrogens
(Es) in the etiology of breast cancer have focused on their receptor-
mediated actions as mitogens. However, such actions of Es can not
fully explain either laboratory or epidemiological data. However,
Es can undergo P450-mediated metabolic activation to generate
electrophilic species which are known initiators of carcinogenesis.
This concept has evolved from studies of the biogenesis and
characteristics of 2- and 4-hydroxylated catechol metabolites of Es
(2- and 4-OH-CEs) which may damage DNA via oxygen free radicals
generated by redox cycling of CEs or by causing depurinating adducts
via their quinone metabolites. The mechanisms involved are analogous
to those by which xenobiotic procarcinogens undergo P450-mediated
metabolic activation to proximal carcinogens. The overall
hypothesis states that 2- and 4-OH-CEs generated in the gland, in
particular 4-OH-CEs, are important determinants of P450-
mediated Es role in carcinogenesis, in particular, in the early
initiating stages of the disease. According to this postulate P450s
which can generate CEs and their quinone derivatives and support
redox cycling of CEs provide an interface between chemical and
hormonal carcinogenesis, since these forms of P450 Es are
inducible by xenobiotics. The relevance of this postulate to breast
cancer is supported by recent cytochemical findings that all of the
forms of P450 required for such a mechanism are, in fact, expressed
in ductal epithelial cells in the normal human breast, that is, in
the cells of origin of most breast cancers. The forms of P450
identified include P45O1A1 and 3A4 which can catalyze formation of
2-OH-CEs and redox cycling of CEs, as well as recently identified
P4501B1 which, in its dioxin-inducible form in MCF-7 cells, is an
E-4-hydroxylase. This is the first P450 known which generates 4- OH-CEs
preferentially, the class of CEs which the investigator proposes may
play a special role in carcinogenesis since they are potent long acting
Es and may be less readily inactivated than 2-OH-CEs. The specific
goal of proposed experiments is to determine if the constitutive form
of P4501B1 expressed in human mammary gland, like that induced by
dioxins in cultured cells, is an E- 4-hydroxylase and the extent to
which its sequence conforms to that induced by dioxin. Probes for
screening cDNA libraries from human breast parenchyma will be obtained
by polymerase chain reaction applied to reverse transcripts
(RT/PCR) to RNA prepared from the same tissue and using asymmetrical
primers based on the conserved sequences used to identified P4501B1 in
human breast by in situ hybridization. The libraries will be screened
with RT/PCR amplified probes to obtain full length sequence for P4501B1
which will then be used to produce P4501B1 protein in yeast expression
vector for analysis for E-2- and E-4-hydroxylase activities. The
investigator proposes to measure E-2- and 4- hydroxylase activity in
samples of normal human breast parenchyma and assess the contribution
made to these activities by different forms of P450 using specific
antibodies. These studies may provide new information relevant to the
etiology of breast cancer and focus attention on factors in normal
human breast that may contribute in particular to early, initiating
stages of carcinogenesis.
Effective start/end date9/30/959/29/96


  • National Cancer Institute

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