Steroid-involved transcriptional regulation of human genes encoding prostatic acid phosphatase, prostate-specific antigen, and prostate-specific glandular kallikrein

Human prostatic acid phosphatase: structure, function and regulation

Human prostatic acid phosphatase (PAcP) is a 100 kDa glycoprotein composed of two subunits. Recent advances demonstrate that cellular PAcP (cPAcP) functions as a protein tyrosine phosphatase by dephosphorylating ErbB-2/Neu/HER-2 at the phosphotyrosine residues in prostate cancer (PCa) cells, which results in reduced tumorigenicity. Further, the interaction of cPAcP and ErbB-2 regulates androgen sensitivity of PCa cells. Knockdown of cPAcP expression allows androgen-sensitive PCa cells to develop the castration-resistant phenotype, where cells proliferate under an androgen-reduced condition. Thus, cPAcP has a significant influence on PCa cell growth. Interestingly, promoter analysis suggests that PAcP expression can be regulated by NF-κB, via a novel binding sequence in an androgen-independent manner. Further understanding of PAcP function and regulation of expression will have a significant impact on understanding PCa progression and therapy.

Structural and functional analysis of human prostatic acid phosphatase

Prostatic acid phosphatase (PAP) is the most abundant phosphatase in human prostate tissue/secretions. It is a clinically important protein for its relevance as a biomarker of prostate carcinoma. Furthermore, it has a potential role in fertilization. We describe here most of the features of PAP including gene regulation, gene/protein structure, functions, its role in tumor progression and evolutionary features. PAP has phosphatase activity and is an extensively studied biomarker of prostate cancer. The major action of PAP is to dephosphorylate macromolecules with the help of catalytic residues (His(12) and Asp(258)) that are located in the cleft between two domains. This article will be of great interest to all those scientists who are working in the area of prostate pathophysiology.

Kallikreins on steroids: structure, function, and hormonal regulation of prostate-specific antigen and the extended kallikrein locus

The 15 members of the kallikrein-related serine peptidase (KLK) family have diverse tissue-specific expression profiles and putative proteolytic functions. The kallikrein family is also emerging as a rich source of disease biomarkers with KLK3, commonly known as prostate-specific antigen, being the current serum biomarker for prostate cancer. The kallikrein locus is also notable because it is extraordinarily responsive to steroids and other hormones. Indeed, at least 14 functional hormone response elements have been identified in the kallikrein locus. A more comprehensive understanding of the transcriptional regulation of kallikreins may help the field make more informed hypotheses about the physiological functions of kallikreins and their effectiveness as biomarkers. In this review, we describe the organization of the kallikrein locus and the structure of kallikrein genes and proteins. We also focus on the transcriptional regulation of kallikreins by androgens, progestins, glucocorticoids, mineralocorticoids, estrogens, and other hormones in animal models and human prostate, breast, and reproductive tract tissues. The interaction of the androgen receptor with androgen response elements in the promoter and enhancer of KLK2 and KLK3 is also summarized in detail. There is evidence that all kallikreins are regulated by multiple nuclear receptors. Yet, apart from KLK2 and KLK3, it is not clear whether all kallikreins are direct transcriptional targets. Therefore, we argue that gaining more detailed information about the mechanisms that regulate kallikrein expression should be a priority of future studies and that the kallikrein locus will continue to be an important model in the era of genome-wide analyses.

Prostate-specific antigen kallikrein and the heart

Currently, there is growing interest regarding prostate-specific antigen (PSA) and the cardiovascular system. Increased PSA serum levels have been reported after prolonged cardiopulmonary resuscitation, cardiac surgery, extracorporeal cardiopulmonary bypass, acute myocardial infarction (AMI) and coronary artery stenting. The possible role of PSA in cardiac events has been questioned due to the finding of PSA decrease during AMI and by the correlation of variation in PSA levels with coronary lesions and occurrence of major adverse cardiac events. Complexed PSA forms and uncomplexed PSA forms are observed in the bloodstream but the increasing formation of irreversible bound PSA seems to be a crucial finding during AMI. Large studies need to be carried out to confirm these preliminary results and to elucidate unclear aspects. These findings present many potential directions for future research including the role of uncomplexed forms of PSA, the possible distribution of PSA in the heart, the relative expression levels in heart disease states, the mode of expression regulation and other potential specific substrates. The journey of PSA investigation could be longer than initially expected.

Transcriptional activation of the human prostatic acid phosphatase gene by NF-kappaB via a novel hexanucleotide-binding site

Human prostatic acid phosphatase (PAcP) is a prostate epithelium-specific differentiation antigen. Cellular PAcP functions as a neutral protein tyrosine phosphatase and is involved in regulating androgen-promoted prostate cancer cell proliferation. Despite the fact that the promoter of the PAcP gene has been cloned, the transcriptional factors that regulate PAcP expression remain unidentified. This article describes our analyses of the promoter of the PAcP gene. Deletion analyses of the promoter sequence up to -4893 (-4893/+87) revealed that a 577 bp fragment (-1356/-779) represents the unique positive cis-active element in human prostate cancer cells but not in HeLa cervix carcinoma cells. Interestingly, the 577 bp fragment contains a non-consensus nuclear factor kappaB (NF-kappaB)-binding site that is required for NF-kappaB up-regulation in prostate cancer cells, while NF-kappaB failed to have the same effect in HeLa cells. Conversely, inhibition of the NF-kappaB pathway stopped p65 NF-kappaB activation of the p1356 promoter activity. Gel shift and mutation analyses determined that AGGTGT (-1254/-1249) is the core sequence for NF-kappaB-binding and activation. Biologically, tumor necrosis factor-alpha (TNF-alpha) activated endogenous PAcP expression in LNCaP human prostate cancer cells. The data collectively indicate that NF-kappaB up-regulates PAcP promoter activity via its binding to the AGGTGT motif, a novel binding sequence located inside the cis-active enhancer element in human prostate cancer cells.

Tissue-specific expression of the prostatic acid phosphatase promoter constructs

Human prostatic acid phosphatase (hPAP) is intensely expressed in epithelial cells of the prostate gland following puberty. Its regulatory regions were analyzed in transgenic mice and cell line transfections, in order to clarify the mechanisms of tissue-specific gene expression. A construct containing the sequence of hPAP between the nucleotides -734 and +467 in front of the CAT reporter gene was significantly expressed in the prostate of transgenic mice, while the proximal promoter -734/+50 alone achieved low levels of CAT mRNA in all tissues analyzed. Five homologous sequences (A-E) for our previously identified prostatic GAAAATATGATA DNA-binding site were found in the area. The competitive reactions in electrophoretic mobility shift assays suggested that the same nuclear factor binds to the GAAAATATGATA and the sites C and E. The importance of the intronic area +57/+467 on the androgen-activated expression in prostatic cells was shown by the reporter construct containing heterologous promoter.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

Identification and characterization of regulatory elements of the human prostatic acid phosphatase promoter

Human prostatic acid phosphatase (PAcP) is a prostate epithelium-specific differentiation antigen. The cellular form of PAcP functions as a neutral protein-tyrosine phosphatase, and is involved in regulating prostate cell growth. Although some information on the PAcP gene structure has been obtained, little is known regarding the cis- and trans-acting factors that regulate its expression. Due to the biological importance of PAcP, we investigated the regulation of its expression. A region upstream of the PAcP gene from -2899 to +87 base pairs was linked to the coding sequence of the chloramphenicol acetyltransferase (CAT) gene. Sequential deletions of the sequence between -2899 and -205 revealed that, in addition to the basic promoter, the region between -1258 and -779 represents a positive regulatory element. This -1258/-779 fragment could enhance the PAcP promoter activity in PC-3 and DU 145 human prostate cancer cells, but not in non-prostate cancer cells, including WI-38 lung diploid cells, A-431 epidermoid carcinoma cells, and HeLa cervix epitheloid carcinoma cells. Furthermore, this cis-element together with the promoter sequence could drive a high level of expression of green fluorescent protein (GFP) in PC-3 cells, but not in HeLa cells. The prostate-specific expression was further examined by injecting naked plasmid DNA into the prostate and the hamstring muscle of mice. The fluorescence pattern clearly showed that the level of GFP expression is consistently higher in prostate cells than in muscle cells of the intact animal. The data collectively indicate that region between -1258 and -779 is involved in governing the cell type-specific expression of the PAcP gene.

Combination of dexamethasone and a somatostatin analogue in the treatment of advanced prostate cancer

The local microenvironment at the sites of cancer metastases protects tumour cells from anticancer drug-induced apoptosis via mechanisms, such as soluble growth factors and cytokines. The concept of antisurvival factor (ASF) therapy as a component of anticancer treatments aims at neutralising the protective effect conferred upon cancer cells by the survival factor(s) derived by the local microenvironment, in order to enhance the sensitivity and/or reverse the resistance of tumour cells to other anticancer therapeutic strategies. Herein, we review the translation of this concept from ex vivo studies to clinical applications in the setting of prostate cancer refractory to androgen ablation (stage D3). At this stage, which predominantly involves bone metastases, insulin-like growth factor 1 (IGF-1) production (either growth hormone (GH)-dependent or GH-independent) can protect tumour cells from apoptosis, despite the significant suppression of androgens. The application of the ASF therapeutic concept involves the combination of dexamethasone (which suppresses GH-independent IGF-1) and somatostatin analogue (which suppresses endocrine, GH-dependent IGF-1) with the pro-apoptotic effect of the testicular androgen suppression by sustained use of LHRH analogues. In stage D3, patients who had failed anti-androgen withdrawal, chemotherapy and also had several other adverse prognostic features, the ASF-based combination achieved durable objective responses and major symptomatic improvement, paving the way for future applications of this approach. The ASF-based combination therapy illustrates a novel paradigm in cancer treatment: anti-tumour treatment strategies may not only aim at directly inducing cancer cell apoptosis, but can also target the tumour microenvironment and neutralise the protection it confers on metastatic cancer cells. The favourable toxicity profile of this therapeutic approach calls for its testing in a randomised controlled setting in metastatic prostate cancer and, conceivably, in other IGF-1-responsive malignancies.

The diagnostic and prognostic utility of prostate-specific antigen for diseases of the breast

Although prostate-specific antigen (PSA) is the most valuable tumor marker for the diagnosis and management of prostate carcinoma, it is widely accepted that PSA is not prostate specific. Numerous studies have shown that PSA is present in some female hormonally regulated tissues, principally the breast and its secretions. In this review, we summarize the findings of PSA in the breast, and focus on its potential for clinical applications in breast disease. PSA is produced by the majority of breast tumors and is a favorable indicator of prognosis in breast cancer. Low levels of PSA are released into the female circulation, and while the level of serum PSA is elevated in both benign and malignant breast disease, the molecular form of circulating PSA differs between women with and without breast cancer. These findings indicate that PSA may have potential diagnostic utility in breast cancer. PSA may also have a clinical application in benign breast disease, as both the level and molecular form of PSA differ between Type I and II breast cysts. High levels of PSA have been reported in nipple aspirate fluid (NAF) and recent studies have shown that the concentration of PSA in NAF is inversely related to breast cancer risk, indicating that NAF PSA may represent a clinical tool for breast cancer risk assessment. Thus, PSA represents a marker with numerous potential clinical applications as a diagnostic and/or prognostic tool in breast disease.

Glucocorticoid receptor down-regulates c-Jun amino terminal kinases induced by tumor necrosis factor alpha in fetal rat hepatocyte primary cultures

The effect of dexamethasone on Jun N-terminal kinase (JNK) activity was assayed by using fetal hepatocytes in primary culture. The addition of tumor necrosis factor alpha (TNF-alpha) caused an increase in JNK in a dose- and time-dependent manner. We show that activation of JNK by this extracellular signal is inhibited by dexamethasone in a dose-dependent fashion. This inhibitory effect was observed in cells treated for 10 minutes with dexamethasone in the presence of protein phosphatase inhibitors such as orthovanadate or okadaic acid, or in cells previously treated with actinomycin D. Glucocorticoid receptor (GR) can be precipitated with the fusion protein, GST-c-Jun (1-79), bound to agarose beads. However, the inhibitory effect of glucocorticoids on JNK activity was also observed using ATF-2 as substrate. In addition, dexamethasone inhibits JNK phosphorylation induced by TNF-alpha. Finally, we show that GR can also be phosphorylated in tyrosine residues in response to TNF-alpha and epidermal growth factor (EGF) upon ligand-binding. Our results suggest that the anti-inflammatory effect of glucocorticoids on the inflammatory pathways induced by TNF-alpha can be explained, at least in part, by modulating JNK activity through a direct protein-protein interaction; the JNK phosphorylation and tyrosine-phosphorylation state of GR may be regulatory steps also involved in that effect.

Human Kallikrein 2 (hK2) and prostate-specific antigen (PSA): two closely related, but distinct, kallikreins in the prostate

Recent studies on human kallikrein 2 (hK2) have revealed striking similarities and significant differences with the closely related kallikrein PSA. Both PSA and hK2 are primarily localized to the prostate and share close structural similarities. Although both kallikreins are produced by the same secretory epithelial cells in the prostate, hK2 is associated more with prostate tumors than PSA and is highly expressed in poorly differentiated cancer cells. The potent trypsin-like activity of hK2 contrasts with the weak chymotrypsin-like activity of PSA. The inactive precursor form of PSA, proPSA, is converted rapidly to active PSA by hK2, suggesting an important in vivo regulatory function by hK2 on PSA activity. The high homology between hK2 and PSA results in significant cross-reactivity to hK2 by polyclonal and some monoclonal antibodies to PSA. Future studies on both PSA and hK2 need to take into account this potential for cross-reactivity. Specific monoclonal antibodies to hK2 have now demonstrated that serum levels of hK2, like PSA, are correlated with prostate cancer. The production of hK2 protein in active protease form and specific monoclonal antibodies to the hK2 antigen will allow extensive future studies delineating the physiological and clinical utility of this new prostate antigen.

Cloning and analysis of the promoter activity of the human prostatic acid phosphatase gene

Human prostatic acid phosphatase (PAP) has been proposed to be a prostate-epithelium differentiation antigen and its expression can be regulated by androgen. Nevertheless, the regulatory mechanism at the molecular level is not completely understood. In this communication, we demonstrated the tissue-specific expression of PAP in the normal prostate epithelium. Furthermore, results of nuclear run-on experiments indicated that androgen could regulate the transcriptional rate of the PAP gene. This mode of regulation was modulated by cell density. To investigate the transcriptional regulation, we cloned and characterized a 1.4- kilobase (kb) fragment of DNA that flanks the 5' region of the PAP gene from LNCaP human prostate carcinoma cells. The results demonstrated that this 1. 4-kb DNA fragment can drive a chloramphenicol acetyltransferase (CAT) gene expression in LNCaP cells. Also, the promoter activity was inversely correlated with the growth of those cells.