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Identification and characterization of a prostate-specific androgen-independent protein-binding site in the probasin promoter.

ABSTRACT: In this study we investigated the combination of transcription factors and proteins binding to the proximal part of the prostate-specific probasin (PB) promoter. Using DNaseI in vitro footprinting, several protected regions were identified on the proximal PB promoter (nucleotides -286 to +28 relative to the transcription start site) when nuclear extracts from LNCaP, a human prostate cancer cell line, were used. Four of the protected areas were observed only when LNCaP nuclear extracts treated with synthetic androgen (10 nM R1881) were used. Two other regions, referred to as FPI and FPII, showed protection regardless of the presence or absence of androgen. When DNaseI footprinting was done using other prostate and non-prostate nuclear extracts, protection of the FPII region was only seen in prostate cell lines. These androgen-independent regions were further tested for tissue and binding specificity using the electrophoretic mobility-shift assay. Eight complexes formed with the FPI probe while four complexes were observed with the FPII probe on incubation with the tested nuclear extracts. Methylation protection assays reveal that prostate cancer cell lines yield slightly different protection patterns for some of the protein complexes formed with non-prostate-derived cell lines, suggesting the presence of prostate-enriched or -exclusive proteins. Site-directed mutagenesis of the protected nucleotides within FPII resulted in a significant reduction in expression from the PB promoter. Identification of proteins binding to the FPII region revealed the participation of nuclear factor I (NF-I) or a closely related protein, although other unknown proteins are also involved. Defining the DNA and protein components that dictate prostate-specific expression of the PB promoter in an androgen-independent manner would provide a strong basis for the design and development of a gene therapy for systemic treatment of androgen-independent prostate cancer.

SUBMITTER: Yeung LH

PROVIDER: S-EPMC1223328 | biostudies-other | 2003 May

REPOSITORIES: biostudies-other

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Project description:BackgroundClooxygenase-2 (COX-2) expression is overexpressed in human prostate cancer, and aberrant methylation of the COX-2 promoter has also been elucidated. However, how the methylation of CpG islands at COX-2 regulates its expression in prostate cancer is still unclear. We will determine the methylated 5' CpG island of the COX-2 gene and its role in the expression of COX-2 in prostate androgen-dependent and androgen-independent cancer cells, LNCaP and DU145.MethodsWe used western blotting and quantitative reverse transcription polymerase chain reaction (qRT-PCR) to confirm the COX-2 expression in prostate cancer cell lines, including LNCaP (androgen-dependent) and DU145 (androgen-independent) cells. To investigate whether the COX-2 expression was regulated by the methylation status of the 5' CpG island, we treated LNCaP and DU145 cells with the DNA methylation inhibitor, 5-aza-2'-deoxycytidine, and determined COX-2 expression in the treated/untreated cells by western blotting and qRT-PCR. Subsequently, bisulfite sequencing was performed to study the methylation sites in the treated/untreated cells. The effects of 5-aza-2'-deoxycytidine to cell proliferation, cell migration and cell cycle process in DU145 and LNCaP cells were determined using Cell Counting Kit-8 (CCK-8) assay, transwell assay and flow cytometry, respectively.ResultsThe results revealed that the expression of COX-2 in androgen-dependent LNCaP cells was 5.44-fold (in protein level) and 2.46-fold (in mRNA level) higher than that in androgen-independent DU145 cells. After 5-aza-2'-deoxycytidine treatment, COX-2 expression in DU145 cells was elevated significantly, but no change was found in LNCaP cells. The A and C regions of the COX-2 CpG island exhibited reduced methylation along with that an increased expression of COX-2 was noted in DU145 cell after 5-aza-2'-deoxycytidine treatment. Also, the treatment with 5-aza-2'-deoxycytidine inhibited cell proliferation, cell migration and influenced the cell cycle progression in both DU145 and LNCaP cells.ConclusionsOur results reveal that androgen receptor (AR)-dependent/independent prostate cancer cell lines exhibit different regulation of methylation in COX-2 that regulate its expression. Additionally, 5-aza-2'-deoxycytidine treatment of DU145 and LNCaP cells inhibits their ability of tumor progression.

Project description:A solid-phase radioimmunoassay was developed to measure the level of the androgen-dependent spermine-binding protein (SBP) in the cytosol fraction of the rat ventral prostate during endocrine manipulation. The concentration of SBP and immunologically cross-reacting material (CRM) in the ventral prostate was at least 5000 times higher than the level of CRM detected in rat serum or cytosol from other rat tissues. Cytosol from the ventral prostate of intact rats was separated by DEAE-cellulose chromatography into three major fractions of CRM. One of these fractions corresponded to the elution position of SBP. Cytosol prepared from rats 48 h after castration lacked SBP and one of the two other fractions of CRM. This loss coincided with an increase in CRM in the remaining fraction. No significant difference was detected in the total level of CRM when intact and 48 h-castrated rats were compared. Injection of rats with 5 alpha-dihydrotestosterone (DHT) immediately after castration prevented these changes in the profile of CRM. Several proteins cross-reacting with antibodies to purified SBP were detected in cytosol by using an immunoblot procedure. The highest-Mr band corresponded to SBP. The effect of short- and long-term castration and subsequent DHT treatment on CRM was studied by using the immunoblot technique. Short-term castration (2 days) led to the disappearance of CRM coinciding with SBP (Mr 35 000-38 000) and an increase in smaller forms of CRM (Mr 24 000 and 22 000). Injection of rats with DHT 2 days after castration led to the reappearance of CRM corresponding to SBP, which returned to normal levels within 4 to 5 days of treatment. Long-term castration (up to 14 days) led to a gradual disappearance of all CRM; subsequent DHT treatment led to the reappearance of all forms of CRM and normal levels were attained within 5 days. We have identified SBP and the various forms of CRM as a secretory product of the rat ventral prostate by immunohistochemical staining and by DEAE-cellulose fractionation of prostatic fluid. Prostatic fluid is rich in proteolytic activity and these proteinases may be responsible for processing SBP to small forms of CRM.

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Identification and characterization of a prostate-specific androgen-independent protein-binding site in the probasin promoter.

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