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in Rat Ventral Prostate during Postnatal Development, after Androgen Ablation, and after Androgen Replacement1
Division of Reproductive Biology, Department of Population Dynamics, The Johns Hopkins University School of Hygiene and Public Health, Baltimore, Maryland 21205
Address all correspondence and requests for reprints to: Dr. Terry R. Brown, Division of Reproductive Biology, Department of Population Dynamics, The Johns Hopkins University School of Hygiene and Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205. E-mail: tbrown{at}jhsph.edu
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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(TGF), are
postulated to mediate androgen action in the rat prostate. In this
investigation, using an immunohistochemical technique, we examined the
cellular and regional expression of TGF in the rat ventral prostate
during postnatal development to adulthood. TGF-immunopositive cells
were located throughout the ductal epithelium from postnatal days
5–20. By day 45 and thereafter, regional variation in TGF
expression became apparent; epithelial cells in the proximal segment
exhibited intense staining, whereas those in the distal segment
exhibited negligible staining. These observations were coincident with
increased serum testosterone concentrations at puberty. To understand
the role of androgen in the expression of TGF in the epithelial
cells of the distal and proximal segments of the adult rat ventral
prostate, androgen was withdrawn by castration, and testosterone
subsequently was administered. Androgen receptor protein expression
decreased after castration and reappeared after androgen replacement in
both the distal and proximal segments. TGF staining was negligible
in epithelial cells of the distal segment of intact adult rats, became
prominent by 7 days after castration, but then diminished after the
administration of testosterone. Western blot analyses revealed the
presence of a specific 30-kDa immunoreactive form of TGF in rat
ventral prostate, and its quantity reflected the staining intensities
observed in the immunohistochemical studies. These results suggest that
TGF expression is negatively regulated by androgen in epithelial
cells of the distal segment. In contrast, staining for TGF in
epithelial cells of the proximal segment did not change with castration
or testosterone administration, suggesting that TGF is not regulated
by androgen in this region of the ventral prostate. In summary, TGF
expression is differentially regulated among epithelial cells localized
in two different regions of the ventral prostate. We hypothesize that
TGF may function as a survival factor for epithelial cells which, as
a consequence of its expression, become androgen independent and thus
escape apoptotic cell death after androgen ablation. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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It is well established that both the growth and maintenance of the prostate gland are androgen-dependent processes (7), but apparently not all epithelial cells are androgen dependent, even though androgen receptors are present in all epithelial cells along the distal-proximal axis in the intact rat (8, 9). In the prostate, androgen receptor expression is under androgenic control (9, 10), with receptor levels decreasing after castration and returning to intact control levels after testosterone replacement (9). We and others demonstrated that withdrawal of androgen from the adult rat by castration induced apoptotic cell death predominantly among epithelial cells in the distal segment, whereas epithelial cells in the proximal segment remained unaffected (11, 12). These results suggested that all prostatic epithelial cells are not equally dependent upon androgen and that there must be some other factor(s) that permits the survival of androgen-independent epithelial cells.
It is widely believed that androgens may not be the direct effectors of
androgen action. For example, androgen has no mitogenic effect on
normal prostate epithelial cells in culture (13). Rather, a number of
soluble growth factors are able to regulate proliferation directly in
these cells (13). Moreover, several polypeptide growth factors have
been postulated to mediate androgen action in the rat prostate
(14, 15, 16, 17, 18). Included among these is transforming growth factor-
(TGF) (18, 19, 20), a 50-amino acid peptide that is related to epidermal
growth factor (EGF) (21). TGF and EGF bind to a common EGF receptor
to initiate their respective biological activities. The binding
affinities of TGF and EGF for this receptor are similar (21).
Although expression of TGF in the ventral lobe of the rat prostate
has been reported in one study (19), another study failed to confirm
these findings (20). However, it is clear that TGF is a
growth-promoting agent of LNCaP, DU-145, and PC-3 cells as well as
benign human prostatic epithelial cells under tissue culture conditions
(22, 23).
TGF is present in the epithelial cells of rat prostate (19, 20) and
responds to changes in androgen levels (18, 24). However, until
recently, most structure-function studies, including those examining
TGF, have treated the rodent ventral prostate as a homogeneous
tissue in which cells can be analyzed within random sections or in
tissue homogenates without regard to their location in the prostatic
ductal network (18, 19, 20, 25, 26). Although such studies have provided
important insight, more recent studies have clearly indicated that
there is regional heterogeneity within the ventral lobe of the rodent
prostate with respect to cell type, androgen responsiveness, gene
regulation, and protein synthesis/secretion (1, 4, 6, 27). Herein, we
used immunohistochemistry to examine the types of epithelial cells that
express TGF and the regional localization of these cells within the
ducts of the rat ventral prostate. Firstly, we determined the patterns
of TGF immunostaining in the distal and proximal segments throughout
postnatal development to correlate epithelial cell proliferation and
differentiation with TGF protein expression. We show that TGF is
expressed in both the distal and proximal segments of the ventral
prostate during its early postnatal development, but that in the adult
it is expressed predominantly in the proximal segment. The decrease in
TGF expression in the distal segment during development correlated
with the increasing concentration of serum testosterone at puberty.
Secondly, we investigated whether TGF is differentially regulated by
androgen in the columnar vs. cuboidal epithelial cells of
prostatic ducts from distal and proximal segments, respectively. To
this end, prostatic ducts from castrated and androgen-replaced rats
were examined. Androgen receptors were present in epithelial cell
nuclei of both the proximal and distal prostatic ducts of intact and
castrate-androgen replaced rats, but disappeared from cells in both
segments after castration. TGF staining became prominent in
epithelial cells of the distal segment after androgen withdrawal and
disappeared after androgen replacement. In contrast, staining for
TGF in epithelial cells of the proximal segment did not change with
castration or testosterone administration.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Serum testosterone concentration
Rats were killed, and trunk blood was collected and allowed to
clot for 2 h at room temperature. The serum was separated by
centrifugation and stored frozen (-20 C) until assayed. Serum aliquots
of 100 µl were extracted twice with 4 ml anhydrous ethyl ether, and
the combined extracts were taken to dryness under nitrogen. The
testosterone concentration (nanograms per ml) was determined by RIA
(28). The sensitivity of the assay was 0.02 ng/ml.
Dissection of prostatic lobes
The urogenital complex, containing the bladder, seminal
vesicles, and prostate, was dissected from the abdominal cavity of each
animal and immersed in ice-cold HBSS (Life Technologies, Grand Island,
NY), pH 7.4. The ventral prostatic lobe was separated under a
dissection microscope. In one portion, the tree-like ducts were
physically divided into proximal (arising from the urethra to the first
branch point) and distal (from the first branch point to the distal
tips) segments from the ventral lobe, fixed in 4% neutral buffered
paraformaldehyde for 48 h, and embedded in paraffin. Sections of
4–6 µm were cut, mounted on Vectabond-coated (Vector Laboratories,
Burlingame, CA) glass slides, and stored in a desiccated box at 4 C
until use. Another portion of the ventral lobe was frozen in liquid
nitrogen vapor, embedded in Tissue-Tek OCT compound (Miles, Elkhart,
IN), and stored at -70 C. For Western blot analysis, a portion of a
whole or microdissected ventral prostate (distal and proximal segments)
from intact, castrate, and castrate and testosterone-replaced rats was
flash-frozen in liquid nitrogen and stored at -70 C until use.
Immunohistochemical localization of TGF
Tissue sections were deparaffinized, rehydrated, and digested
with 0.0025% pronase (Sigma Chemical Co., St. Louis, MO) for 15 min at
37 C. Nonspecific binding was blocked by incubation of sections with
10% normal goat serum in PBS for 30 min at room temperature. Mouse
antihuman TGF monoclonal antibody (Ab-2, Oncogene Science,
Uniondale, NY) was used, which cross-reacts with the mature form (5.6
kDa) of rat TGF (29). The antibody was diluted (2 µg/ml) in 0.2%
crystalline grade BSA in PBS, and slides were incubated in a humidified
chamber at 4 C for 16–18 h. The sections were then incubated with
biotinylated goat antirabbit IgG, stained with avidin-biotin-alkaline
phosphatase complex (Vector Laboratories) and Vector red alkaline
phosphate substrate (Vector Laboratories), and counterstained with
0.5% methyl green. Negative control slides were prepared in an
identical manner, except that the primary antibody was replaced with a
similar concentration of purified IgG of the same subtype. TGF
localization was observed by brightfield microscopy, and images were
recorded on Ektachrome 64T film (Eastman-Kodak, Rochester, NY).
Immunohistochemical localization of androgen receptor
Frozen tissue sections (5–7 µm) were mounted on
poly-L-lysine-coated glass slides, fixed immediately in
Zamboni’s fixative for 10 min, and washed three times (10 min each
time) in PBS, pH 7.4. Nonspecific binding was blocked by incubation of
sections with 10% normal goat serum in PBS for 30 min at room
temperature. Rabbit polyclonal antibody raised against a synthetic
peptide (near the amino-terminus) specific for the androgen receptor
(Novocastra Laboratories, Newcastle upon Tyne, UK) was diluted (1:50)
in 0.2% crystalline grade BSA in PBS, and slides were incubated in a
humidified chamber at 4 C for 16–18 h. The reaction sites were
visualized by incubating the tissue sections with biotinylated second
antibody, avidin-biotin-peroxidase complex (Vector Laboratories) and
diaminobenzidine reagents (Vector Laboratories). Negative control
slides were prepared in an identical manner, except that the primary
antibody was replaced with similar concentrations of rabbit IgG. The
localization of immunoreactive androgen receptor was observed by light
microscopy (Zeiss, Oberkochen, Germany), and images were recorded on
Kodak Pan film.
Immunoblot analysis
Frozen tissue samples were homogenized in tissue lysis buffer
[10 mM Tris (pH 7.4), 150 mM NaCl, 1% Triton
X-100, 1% deoxycholate, 0.1% SDS, 5 mM EDTA, 1
mM phenylmethylsulfonylfluoride, 1 mM
benzamidine, 0.28 U/ml aprotinin, 50 µg/ml leupeptin, and 0.7 µg/ml
pepstatin] and clarified by centrifugation at 14,000 x
g for 20 min at 4 C. An aliquot of this supernatant was used
for the determination of protein content using the Bio-Rad protein
assay reagent (Bio-Rad Laboratories, Hercules, CA) (30). The remaining
supernatants were mixed (1:1) with 2 x Laemmli buffer [100
mM Tris-HCl (pH 6.8), 200 mM dithiothreitol,
4% SDS, and 20% glycerol], transferred to a boiling water bath for 5
min, rapidly frozen on dry ice, and stored at -70 C until use.
To obtain fluid from ventral prostates of 90-day-old rats, we used our previously described method (31). In brief, the intact ventral lobe was washed in ice-cold Hanks’ Balanced Salt Solution, blotted onto filter paper, nicked in several locations with a sharp blade, placed in a microcentrifuge tube, and spun at 14,000 x g for 20 min to collect the prostatic fluid. The fluid was transferred to a clean tube and stored at -70 C. An aliquot of the fluid was used for the determination of protein content (30). Fifty microliters of 2 x Laemmli buffer were added to 50 µl prostatic fluid and immediately transferred to a boiling water bath for 5 min.
Samples to be analyzed were subjected to SDS-PAGE on a 15% acrylamide
gel, run under reducing conditions, using the system described by
Laemmli (32). After separation, proteins were electrophoretically
transferred to Hybond nitrocellulose membrane (Amersham, Arlington
Heights, IL) according to the method of Towbin et al. (33).
Transfer was accomplished at 500 mA for 2 h at 4 C. The membrane
was initially incubated for 1 h with TBS (20 mM
Tris-HCl, pH 7.6, and 137 mM NaCl) containing 0.01%
Tween-20 and 5% nonfat dry milk to block nonspecific binding and then
incubated for an additional 1.5 h in the presence of TGF
antibody (0.4 µg/ml) with frequent agitation at room temperature. The
membrane was then washed with TBS-0.01% Tween-20, incubated with
horseradish peroxidase-labeled secondary antibody (1:3000 dilution;
Amersham) for 1 h at room temperature, and washed with TBS-0.01%
Tween-20. Antibody-binding sites were visualized on Hyperfilm
(Amersham) by 5-min exposure, using the ECL detection system
(Amersham). High (14.3–200 kDa; Oncogene Science) and low (3.5–29
kDa; Integrated Separation Systems, Natick, MA) molecular mass markers
were run on each gel.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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shows the serum
concentrations of testosterone in Sprague-Dawley rats during postnatal
development, after castration, and after testosterone replacement. The
serum testosterone concentration in 5-day-old intact rats was 0.19
± 0.02 ng/ml, increased to 1.38 ± 0.22 ng/ml by 45 days of age,
and attained the adult level of 2.61 ± 0.92 ng/ml by day 90. The
serum concentration of testosterone in adult rats was reduced to
undetectable levels (<0.02 ng/ml) by 7 days after castration. Seven
days after castration, implantation of 2.5-cm testosterone-filled
SILASTIC capsules for an additional 7 days elevated the serum
testosterone concentration to that in intact adult rats (2.5 ±
0.8 ng/ml).
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antibody (Upstate Biotechnology, Lake
Placid, NY) were spotted onto a nitrocellulose membrane and probed with
the TGF antibody, only the TGF was detected (data not shown). To
further evaluate the specificity of the TGF antibody, purified
recombinant TGF and tissue extracts from ventral prostate of intact
and castrated rats were analyzed by Western blot. Figure 1A shows that purified recombinant TGF
was detected as a band of 5.6 kDa, whereas a single protein band of
approximately 30 kDa was detected in tissue extracts from ventral
prostate of intact and castrated rats. When the TGF antibody was
preincubated with 1 µg purified TGF, the TGF-immunoreactive
bands were undetectable or greatly reduced in intensity (Fig. 1B).
Similar results were obtained when the TGF antibody was preincubated
in the presence of 100 µg protein equivalent from ventral prostate
tissue extracts of castrated rats (data not shown). Using various
amounts of purified recombinant TGF, we observed that the lower
limit for detection of the protein by Western blot was approximately
25–30 ng (data not shown).
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during postnatal
development of the ventral prostate), and on day 10, when the epithelial
cells were organized as a tube with a small lumen (Fig. 2B), cells that
were immunopositive for TGF were located throughout the ductal
epithelium. On day 20, epithelial cells in the distal segment were
columnar (Fig. 2C), whereas the proximal epithelial cells appeared
cuboidal (Fig. 2D). The epithelial cells of the distal segment stained
for TGF expression, and an abundance of highly stained secretory
material was present within the lumen. The cuboidal epithelial cells of
the proximal segment also were intensely stained, but there was no
staining within the lumen. By day 45, however, regional specificity of
staining became apparent. Columnar epithelial cells in the distal
segment exhibited negligible staining for TGF, although staining of
luminal secretions remained intensely positive (Fig. 2E). In contrast,
the cuboidal epithelial cells in the proximal segment continued to
exhibit intense staining for TGF (Fig. 2F). Throughout the period of
postnatal development until day 45, stromal cells did not stain for
TGF.
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in the epithelial cells of distal and proximal
segments of adult rat ventral prostate, we examined androgen receptor
protein expression in intact, castrate, and castrate plus
androgen-replaced rats. In the intact adult rat, epithelial cells of
the distal and proximal segments showed intense nuclear staining for
androgen receptor (Fig. 3, A and B). In
both segments, some stromal cells were also androgen receptor positive
(Fig. 3, A and B). As expected, nuclear androgen receptor staining
intensity decreased dramatically in epithelial and stromal cells in
both distal and proximal segments 7 days after castration (Fig. 3, C
and D). However, 7 days after testosterone administration to castrated
rats, nuclear androgen receptor staining reappeared in the columnar
epithelial cells of the distal segment (Fig. 3E) and cuboidal
epithelial cells of the proximal segment (Fig. 3F). At this time,
androgen receptor immunoreactivity was evident again in some stromal
cells in both the distal and proximal segments (Fig. 3, E and F).
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in the ventral prostate
of adult intact, castrate, and castrate plus testosterone-replaced
rats
staining seen on day 45 became more striking. Thus, the distal segment
contained columnar epithelial cells, which, as on day 45, exhibited
little TGF staining (Fig. 4A). In a
few of these cells, TGF was localized at the supranuclear region,
but unlike the situation on day 45, the luminal contents stained
variably for TGF. In contrast, cuboidal epithelial cells in the
proximal segment stained intensely (Fig. 4B).
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expression in rat ventral prostate by androgen
was examined in 90-day-old rats. In contrast to the situation in the
intact adult, in which epithelial cells of the distal segment were
negligibly stained for TGF, 7 days after castration these cells
expressed high levels of TGF (Fig. 4C
), but appeared cuboidal rather
than tall columnar as in intact animals. Cells in the proximal segment
were positive, as was the case before castration (Fig. 4D). Seven days
after testosterone administration to castrated rats, columnar
epithelial cells reappeared in the distal segment (Fig. 4E), coincident
with which TGF staining disappeared from the cells of this segment.
In contrast, cuboidal epithelial cells in the proximal segment
continued to express TGF (Fig. 4F). Stromal cells were devoid of
staining throughout the experimental manipulations.
Western blots of immunoreactive TGF in the ventral prostate of
adult intact, castrate, and castrate plus testosterone-replaced
rats
As we have seen regional differences in TGF immunohistochemical
localization in rat ventral prostate and its regulation by androgen, we
also employed Western blots to semiquantitatively determine the levels
of TGF expression and to identify the immunoreactive protein(s)
present in the microdissected distal and proximal segments of the
ventral prostate of adult intact, castrate, and castrate plus
testosterone-replaced rats. A single immunoreactive protein of
approximately 30 kDa was detected in all tissue extracts prepared from
the ventral prostate (Fig. 5). The level
of TGF was lower in the distal segment than in the proximal segment
of intact rats (Fig. 5A). Seven days after castration, TGF levels
increased in the distal segment, but after testosterone replacement for
7 days, TGF levels in the distal segment declined to the intact
control level. By contrast, TGF levels in the proximal segment did
not change after castration or the subsequent administration of
androgen.
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antibody reacted with the secretory products in the
prostatic lumen of several tissue sections, shown in Figs. 2 and 4, we
were interested to determine whether TGF was secreted into the
prostatic lumen, and if so, whether the immunoreactive protein was the
same as that seen in tissue extracts. Figure 5B shows that prostatic
fluid also contains a 30-kDa TGF protein, and therefore, the
immunoreactive protein observed in the lumen of prostatic sections by
immunohistochemistry is consistent with the protein expressed within
epithelial cells. |
Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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is expressed throughout the
development of the ventral prostate, from postnatal day 5 to adulthood.
This result corroborates the observation by Cunha and his associates
that TGF messenger RNA is present in the neonatal rat prostate (34).
However, our results differ from the previous study of Taylor and
Ramsdell (19), in which a sheep polyclonal antiserum directed against
the mature TGF 50-amino acid sequence was used for the localization
of TGF in rat ventral prostate during its postnatal development
(days 8–42). They did not detect TGF immunoreactivity in the
ventral prostate of 10- and 21-day-old rat pups, although it was
present in prostatic epithelial cells at 28 and 35 days of age (19). In
contrast to this previous study (19), we found TGF immunoreactivity
in the epithelial cells throughout postnatal development (days 5–45)
in both distal and proximal segments using a mouse monoclonal antiserum
specific for the mature form of TGF (29).
During postnatal development, the rat ventral prostate attains a highly
branched, convoluted, tree-like structure, with regional differences in
cellular architecture along the prostatic ducts. The regional cellular
heterogeneity cannot be appreciated by examination of random sections.
The dissection method we used enabled us to visualize both the distal
and proximal segments. In this regard, the regional variability in
TGF protein expression in the prostatic ducts was particularly
noteworthy; with developmental age, staining intensity became more
prominent in the proximal, but disappeared from the distal, segment. It
seems likely that the contradictory results of previous studies,
reporting either the presence of TGF in epithelial cells of the
adult ventral prostate (19) or its absence (20), may have resulted from
the examination of different regions of the ventral lobe.
Regional variation in TGF staining became strikingly apparent in the
adult rat ventral prostate. We found that TGF protein expression
appeared almost exclusively in the cuboidal epithelial cells of the
proximal segment, with very little in the columnar epithelial cells of
the distal segment. In contrast, both cuboidal and columnar epithelial
cells in these segments stained positively for nuclear androgen
receptor. Therefore, we asked whether TGF was regulated differently
by androgen in epithelial cells of the proximal and distal segments
despite the apparent ubiquitous expression of androgen receptor? In the
distal segment, castration resulted in high levels of TGF expression
in the epithelial cells, and the administration of physiological levels
of testosterone reduced this expression. In striking contrast, androgen
levels had no effect on the prominent TGF expression in the proximal
segment. These results suggest that TGF is negatively regulated by
androgen in epithelial cells of the distal segment, which is consistent
with a recent study that reported the induction of TGF messenger RNA
in the ventral lobe after castration (18), but in contrast, TGF
expression in epithelial cells of the proximal segment appears not to
be regulated by androgen. It is apparent that different regulatory
mechanisms determine TGF expression that are cell type and/or
segment specific.
The differences in TGF expression in the distal and proximal
segments suggest region-specific roles for TGF in the adult ventral
prostate. A definitive function for TGF in the prostate has not yet
been established, although it is postulated to play a role in autocrine
growth regulation of epithelial cells. For example, overexpression of
TGF in a number of organs, including the anterior lobe (coagulating
gland) of the prostate, was shown to result in tissue enlargement,
primarily due to epithelial cell hyperplasia (35, 36), suggesting that
TGF acts as a mitogen. In addition, Cunha and his colleagues have
shown a profound inhibition of androgen-dependent prostatic ductal
morphogenesis and growth in serum-free organ cultures of neonatal rat
prostates using a neutralizing antibody to TGF (34). This would
predict that TGF should be expressed primarily in the distal segment
where cell proliferation is most prominent, but, as we observed, it is
not.
How, then, does the proposed mitogenic function of TGF relate to its
high level of expression in the proximal segment? We propose that
TGF may have the ability to protect epithelial cells from death, in
addition to a role in cell proliferation. In fact, it has been shown in
cell culture that TGFß1-induced cell death can be counterbalanced by
mitogenic factors such as basic fibroblast growth factor and EGF (37, 38). Perhaps this is a role that TGF plays in the proximal segment
of the ventral prostate. Indeed, our unpublished results show that the
cell survival factor, Bcl-2, is expressed predominantly in the proximal
segment, but staining intensity increases in the distal segment after
castration. We suggest that epithelial cells in the proximal segment
may express several factors, including TGF, to aid in their
survival, as these cells are required for tissue renewal.
In fact, we found that TGF protein expression appeared in all
surviving epithelial cells of the distal segment by 7 days
postcastration. Our previous results demonstrated that cell death
(apoptosis) was maximal by 2–3 days after castration, resulting in a
60% loss of cells by 1 week (12). Thus, the absence of TGF
expression in the epithelial cells of the distal segment before seven
days postcastration (data not shown) is correlated with the loss of
cells, whereas TGF expression after 7 days postcastration is
correlated with the survival of the remaining epithelial cells, now of
a cuboidal type. This interpretation is consistent with observations in
the proximal segment in which all epithelial cells are TGF positive,
and very little cell death occurs in response to androgen withdrawal
(12). Taken together, these observations make it reasonable to suggest
that TGF may protect epithelial cells from death.
Similar to our immunohistochemical results, our Western blot analysis
demonstrated a region-specific increase in the level of TGF after
castration and a decrease in TGF level after androgen replacement to
castrated rats. However, the immunoreactive protein detected in the
prostatic tissue extracts had a molecular mass of approximately 30 kDa
and was not the 5.6-kDa protein representing the mature form of TGF,
although the antibody we used reacts with both mature and precursor
forms of TGF. Because we estimated the sensitivity of our TGF
Western blot system to be in the range of 25–30 ng, only small amounts
of the mature form of TGF must be present in rat ventral prostate.
However, higher molecular mass forms of TGF are not unusual and have
been reported previously. For example, higher molecular mass forms
comprised the predominant TGF activity extracted from lysates or
supernatants of human rhabdomyosarcoma (18 kDa) (39), melanoma (22.5
kDa) (40), mammary carcinoma cells (30 and 68 kDa) (41), human
platelets (24 kDa) (42), the urine of cancer patients (30 kDa) (43),
human prostate carcinoma cells (18 kDa) (23), rat hepatocellular
carcinoma cells (18–21 kDa) (44), and rat submandibular gland (15–20
kDa) (45). Several of these higher molecular mass forms of TGF have
been tested and found to have biological activity (41, 44, 46, 47, 48).
Therefore, it is reasonable to propose that the 30-kDa TGF of rat
ventral prostate would be biologically active. Moreover, similar to
many human carcinomas, normal rat ventral prostate also secretes a
higher molecular mass form of TGF in the prostatic fluid. Because
there are no reports that show the mature form (5.6 kDa) or any other
molecular mass forms of TGF in rat prostate or in prostatic fluid to
be biologically active, it will be interesting to determine whether
further processing of the 30-kDa TGF is required for its biological
activity. It will be of interest to investigate whether the 30-kDa form
of TGF is biologically equipotent and/or resistant to proteolytic
degradation compared with mature TGF, and whether lobe-specific or
age-dependent changes occur in the processing of TGF to
differentially affect its activity in different regions of the
prostate.
Our understanding of the regional cellular heterogeneity in the prostatic ductal system is more clear than before, as we now recognize that in the same ductal system in which all prostatic epithelial cells are exposed to the same level of circulating androgen, all cells (columnar vs. cuboidal) are not responding in the same manner. These observations suggest that the effect of androgen on the epithelial cells of prostatic ducts may vary profoundly based on their regional localization. Whether similar regional heterogeneity in stromal cells exists in the prostatic ducts is not known at this point and will be the subject of future investigation.
In summary, our results show for the first time that regional
heterogeneity in the expression of TGF in epithelial cells exists in
the rat ventral prostate. Although androgen receptors are present in
epithelial cells of the proximal segment, these cells appear to be
minimally androgen dependent based upon their survival after androgen
ablation. We speculate that TGF expression may be indicative of
epithelial cell androgen independence. Our findings suggest a possible
role for TGF in the androgen-independent growth of prostatic cells
in diseases such as cancer and benign prostatic hyperplasia, even as
serum testosterone levels decrease with age and androgen ablation
therapy is implemented.
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Footnotes |
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Received January 23, 1998.
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 K. G. Rajesh, S. Sasaguri, R. Suzuki, and H. Maeda Antioxidant MCI-186 inhibits mitochondrial permeability transition pore and upregulates Bcl-2 expression Am J Physiol Heart Circ Physiol, November 1, 2003; 285(5): H2171 - H2178. [Abstract] [Full Text] [PDF]
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 K. G. Rajesh, S. Sasaguri, Z. Zhitian, R. Suzuki, R. Asakai, and H. Maeda Second window of ischemic preconditioning regulates mitochondrial permeability transition pore by enhancing Bcl-2 expression Cardiovasc Res, August 1, 2003; 59(2): 297 - 307. [Abstract] [Full Text] [PDF]
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 P. P. Banerjee, S. Banerjee, and T. R. Brown Bcl-2 Protein Expression Correlates with Cell Survival and Androgen Independence in Rat Prostatic Lobes Endocrinology, May 1, 2002; 143(5): 1825 - 1832. [Abstract] [Full Text] [PDF]
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 F. Vinals and J. Pouyssegur Transforming Growth Factor {beta}1 (TGF-{beta}1) Promotes Endothelial Cell Survival during In Vitro Angiogenesis via an Autocrine Mechanism Implicating TGF-{alpha} Signaling Mol. Cell. Biol., November 1, 2001; 21(21): 7218 - 7230. [Abstract] [Full Text] [PDF]
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P. P. Banerjee, S. Banerjee, and T. R. Brown Increased Androgen Receptor Expression Correlates with Development of Age-Dependent, Lobe-Specific Spontaneous Hyperplasia of the Brown Norway Rat Prostate Endocrinology, September 1, 2001; 142(9): 4066 - 4075. [Abstract] [Full Text] [PDF]
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S. Banerjee, P. P. Banerjee, and T. R. Brown Castration-Induced Apoptotic Cell Death in the Brown Norway Rat Prostate Decreases as a Function of Age Endocrinology, February 1, 2000; 141(2): 821 - 832. [Abstract] [Full Text] [PDF]
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 S. Nandi, P. P. Banerjee, and B. R. Zirkin Germ Cell Apoptosis in the Testes of Sprague Dawley Rats Following Testosterone Withdrawal by Ethane 1,2-Dimethanesulfonate Administration: Relationship to Fas? Biol Reprod, July 1, 1999; 61(1): 70 - 75. [Abstract] [Full Text]
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P. P. Banerjee, S. Banerjee, J. M. Lai, J. D. Strandberg, B. R. Zirkin, and T. R. Brown Age-Dependent and Lobe-Specific Spontaneous Hyperplasia in the Brown Norway Rat Prostate Biol Reprod, November 1, 1998; 59(5): 1163 - 1170. [Abstract] [Full Text]
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