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Advances in Brief |
Departments of Urology [S H M., C Y F Y.] and Biochemistry and Molecular Biology [W Z.], Mayo Graduate School, Mayo Foundation, Rochester, Minnesota 55905
| ABSTRACT |
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| Introduction |
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| Materials and Methods |
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Western Blot Analysis.
LNCaP cells were plated in 10-cm dishes at 9 x 105 cells/dish in RPMI 1640 (Mediatech, Herndon, VA) and 5% FCS (Biofluids, Rockville, MD). After 48 h, the cells were treated with 1.0 nM Mib and varying concentrations of resveratrol. After 24 h, cells were collected according to Santa Cruz Biotechnology research applications. Protein levels were measured with a DC protein assay (Bio-Rad, Hercules, CA). Ten µg of protein were loaded into precast 412% NuPage gels (Novex, San Diego, CA), run with 4-morpholinepropanesulfonic acid buffer and transferred according to the manufacturers instructions onto a nitrocellulose membrane (Bio-Rad, Hercules, CA). A Ponceau S stain was performed for total protein staining and visualized on a digital camera. The membranes were blocked overnight at 4°C in TBST [20 mM Tris-HCl (pH 8.0), 137 mM NaCl, and 0.1% Tween 20] and 5% dry milk. The membranes were washed three times for 10 min each with TBST. Primary antibody for AR and p21 (PharMingen, San Diego, CA) at a 1:2000 dilution was incubated at room temperature for 1 h. The membranes were washed three times for 10 min each with TBST. Antimouse horseradish peroxidase secondary antibody (Amersham, Piscataway, NJ) used at a 1:10,000 dilution was also incubated for 1 h at room temperature. The membranes were washed again, and Renaissance chemiluminescence (DuPont NEN, Boston, MA) was used according to the manufacturers instructions.
Transient Transfections.
LNCaP cells were plated in 60-mm dishes until they reached a confluency of 5070%. Cells were transiently transfected as described previously with the appropriate constructs (7)
. After 24 h, the cells were treated with 50, 100, or 150 µM resveratrol with or without Mib. Whole-cell extracts were prepared, and a luciferase assay was performed according to the manufacturers instructions (Promega) for the PSA promoter/luciferase or AR promoter/luciferase transfection. The hK2 ARE/minimal thymidine kinase promoter/CAT transfection used the CAT ELISA from Boehringer Mannheim as per the instructions. CMV-
-gal expression vector and parental vectors (pGL3 and pBLCAT2) as controls were also included in the above transfections.
-gal activity was assayed for normalization purposes (7)
. Each transfection was done three times, and SDs were calculated.
Northern Blots.
LNCaP cells were treated with varying amounts of resveratrol, 1 nM Mib as indicated, and RNA was collected by the guanidine isothiocyanate method (8)
. An RNA gel was run and transferred onto a nylon membrane according to the GeneScreen protocol by New England Nuclear. Fifteen µg of total RNA were loaded in each lane. cDNAs for ARA70 and glyceraldehyde-3-phosphate dehydrogenase were used as probes labeled with [32P]dCTP by random priming. The hybridization was performed according to Clontech protocols with ExpressHyb hybridization solution. The films were autoradiographed at -70°C.
Hoechst 33258 Staining for Apoptosis.
LNCaP cells were seeded at 9 x 105 cells/10-cm dish for 48 h. Cells were then treated with 1 nM Mib and 0, 50, 100 or 200 µM of resveratrol for 24 and 32 h. Then the plates were treated with Hoechst 33258 (15 µg/ml in PBS) for 5 min at 37°C. Cells were washed carefully in PBS twice and visualized by fluorescence microscopy using an Axioplan II microscope (Zeiss, Inc.). An appropriate excitation filter was used (365 nm excitation; 420 nm emission). The number of apoptotic cells per 500 total cells were counted and expressed as a percentage of the total. A cell was counted as being apoptotic if nuclear fragmentation and chromatin condensation was observed (9)
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| Results and Discussion |
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We have demonstrated that resveratrol can inhibit the expression of the AR and its functions, including gene induction and cell proliferation. To further ascertain that resveratrol has a broad effect on androgen-regulated genes, Northern or Western analysis was performed to see whether different classes of the androgen-regulated genes are affected. Fig. 3c
shows that the AR-specific coactivator ARA70 mRNA level is decreased with resveratrol treatment. The graph shows the normalization data as a percentage of the Mib-treated control. It seems that the maximal reduction of ARA70 mRNA is achieved at 100 µM resveratrol. It has been suggested that the decrease in ARA70 could affect AR-mediated gene expression and cellular processes (12, 13, 14)
. Therefore, it is possible that the repression of the expression of ARA70 may further enhance the inhibitory effects of resveratrol on androgen action.
Recently, it has been reported that p21Waf1/Cip1, a cyclin-dependent kinase inhibitor, is also an androgen up-regulated gene (15)
. p21 has been reported as a powerful cell proliferation inhibitor or cell death facilitator (16)
. On the other hand, in many cases it has been shown that this protein can protect cells from death (17)
, and reducing its intact protein levels may enhance apoptosis (16)
. The authors of the above report (15)
suggested that the increase in p21 by androgens may facilitate LNCaP cell proliferation. A Western blot of LNCaP cells treated with 0, 100, or 200 µM resveratrol for p21 protein was performed. Fig. 4a
shows that resveratrol indeed decreases p21 in a dose-dependent manner. Our study seems to suggest that the reduction of p21 by resveratrol may be at least in part because of the repression of AR. Moreover, the higher the concentrations of resveratrol, the more profound effects it has on p21 levels. This may not solely be from the repression effect on the AR. Also, it will be interesting to determine whether any other factors can be affected by resveratrol that subsequently reduce the expression of p21.
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To study whether the effects of resveratrol are reversible, LNCaP cells were treated with resveratrol for 24 h, and then the treated medium was removed and fresh medium was added. Fig. 4c
shows that with up to the 100 µM concentration of resveratrol, the growth-inhibitory effects on the cells can be reversed (P = 0.06). However, at 150 µM, the cells are still inhibited and similar to effects without medium removal (P < 0.05). Because these studies were conducted without Mib, it shows that at high concentrations, resveratrol could inhibit cell growth.
Androgens are important regulators of the prostate gland. Androgens are so essential in the carcinogenesis of prostate cancer that it does not develop unless a man produces and uses androgens (18 , 19) . One important question not yet addressed is whether resveratrol is able to accumulate in tissues such as the prostate at concentrations as high as 100 and 200 µM. No conclusive human studies have been executed. Other chemically related compounds, such as green tea polyphenols, appear in the blood stream at relatively low concentrations after oral administration (20) . Their in vitro concentrations to achieve biological effects are often much higher than those in plasma. However, their in vivo administration seems to be able to show certain biological effects, as predicated in the in vitro system. For example, in a very recent report (21) , green tea polyphenols seem to show a repressive effect on androgen action in mice. Further study of in vivo effects of resveratrol on the expression of the AR and subsequent androgen action will clarify this question. Nevertheless, in this study we have shown a novel aspect of resveratrol that presents as a potent inhibitor for androgen action in prostate cancer cells. We showed that the inhibition of androgen action by resveratrol is mediated via the reduced expression of several important genes such as AR, ARA70, and p21. This study strongly suggests that resveratrol can modulate AR-mediated action in the prostate. It has the potential to become a chemopreventive and/or chemotherapeutic agent for prostate cancer.
| FOOTNOTES |
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1 This study is supported in part by NIH Grant CA70892 and United States Army Medical Research and Material Command Grant DMAD 17-98-107-523 ![]()
2 To whom requests for reprints should be addressed, at Department of Urology and Biochemistry/Molecular Biology, Mayo Clinic/Foundation, Guggenheim Building 1742B, 200 First Street SW, Rochester, MN 55905. Phone: (507) 284-9247; Fax: (507) 284-2384. ![]()
3 The abbreviations used are: AR, androgen receptor; Mib, mibolerone; hK2, human glandular kallikrein-2; PSA, prostate-specific antigen; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; ARE, androgen response element; CAT, chloramphenicol acetyltransferase;
-gal,
-galactosidase. ![]()
Received 7/21/99. Accepted 10/18/99.
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