Note: LNCaP cells refer to prostate cancer cells.
Down-Regulation of Prostate-specific Antigen Expression by Finasteride through Inhibition of Complex Formation between Androgen Receptor and Steroid Receptor-binding Consensus in the Promoter of the PSA Gene in LNCaP Cells
cancerres.aacrjournals.org/cgi/reprint/57/4/714
As a specific competitive inhibitor of 5a-reductase, an intracellular
enzyme that converts testosterone to dihydrotestosterone, finasteride is
being extensively used for the treatment of benign prostatic hyperplasia
and in experimental settings for prostate cancer. In this study, we showed that finasteride markedly inhibited prostate-specific antigen (PSA) secretion and expression.
The promoter of the PSA gene contains several well-known cis-regula
tory elements. Among them, steroid receptor-binding consensus (SRBC)
has been identified as a functional androgen-responsive element. Our
previous study showed that PSA was not only present in conditioned
medium of the PSA-positive LNCaP cells but was also detectable in small
amounts in PSA-negative cell lines, PC-3 and DU-145 (L. G. Wang et ci,
OncoL Rep., 3: 911—9171,996).
A strong correlation between binding of nuclear factors to SRBC and the level of PSA present in the conditioned medium and cell extracts was found in these three cell lines, whereas no such correlation with binding was obtained using Spi oligonucleotide as a probe. Binding of LNCaP cell nuclear proteins to SRBC was diminished when the cells were exposed to 25 @tMfinasteride, at which concentration 50% of both PSAmRNA and protein were inhibited. As a major component of DNA-protein complexes, the level of androgen receptor was dramatically decreased in the cells treated with finasteride.
Our data indicate that inhibition of complex formation between SRBC
and nuclear proteins due to the remarkable decrease in the level of
androgen receptor plays a key role in the down-regulation of PSA gene
expression by finasteride in LNCaP cells.
“… To understand whether the decrease of PSA protein is due to the
changes of rates of the transcription or the translation of the protein,
the mRNA of PSA was determined in LNCaP cells after treatment
with finasteride. As shown in Fig. 4, the very pronounced decreasein
the level of PSA mRNA was observed in a dose-dependent manner
after exposure of LNCaP cells to finasteride for 72 h that accurately
paralleled the decrease in the amount of PSA protein. This result
suggests that the regulation of PSA gene expression by finasteride
was, at least in part, in the transcriptional level.”
“…Fig. 8 shows the effect of androgen antibody on the formation of the
binding complexes and the effect of finasteride on the level of AR in
the cells. Complexes were significanfly diminished when the nuclear
extracts were preprecipitated with AR antibody, whereas no changes
were observed when the histone Hi antibody proteins were used (Fig.
8A). This finding provides additional evidence that the AR plays a key
role in the formation of the binding complexes and confirms the
previous mechanism as outlined by Luke and Coffey (17). After
treatment with various concentrations of finasteride, the AR levels in
the cell extracts of LNCaP cells were remarkably decreased in a
dose-dependent manner (Fig. 8B). As documented in the Fig. 8C,
following the treatment of LNCaP cells with 25um with finasteride, AR
levels in cellular extracts were decreased to approximately 50% of
baseline without significant cytotoxicity.”
"…Our result provides additional evidence that AR is a major component of SRBC-protein complexes. This finding paralleled the observed decrease of the AR level in the cells treated with finasteride. Thus, lack of formation of SRBC-protein complexes due to the decrease in the level of AR may play a key role in the down-regulation of PSA gene expression by finasteride."
