Isolation and characterization of androgen-dependent non-histone chromosomal protein from dorsolateral prostate of rats

Targeting strategies of adenovirus‑mediated gene therapy and virotherapy for prostate cancer (Review)

Prostate cancer (PCa) poses a high risk to older men and it is the second most common type of male malignant tumor in western developed countries. Additionally, there is a lack of effective therapies for PCa at advanced stages. Novel treatment strategies such as adenovirus-mediated gene therapy and virotherapy involve the expression of a specific therapeutic gene to induce death in cancer cells, however, wild-type adenoviruses are also able to infect normal human cells, which leads to undesirable toxicity. Various PCa-targeting strategies in adenovirus-mediated therapy have been developed to improve tumor-targeting effects and human safety. The present review summarizes the relevant knowledge regarding available adenoviruses and PCa-targeting strategies. In addition, future directions in this area are also discussed. In conclusion, although they remain in the early stages of basic research, adenovirus-mediated gene therapy and virotherapy are expected to become important therapies for tumors in the future due to their potential targeting strategies.

Upstream stimulatory factor 2, a novel FoxA1-interacting protein, is involved in prostate-specific gene expression

The forkhead protein A1 (FoxA1) is critical for the androgenic regulation of prostate-specific promoters. Prostate tissue rescued from FoxA1 knockout mice exhibits abnormal prostate development, typified by the absence of expression of differentiation markers and inability to engage in secretion. Chromatin immunoprecipitation and coimmunoprecipitation studies revealed that FoxA1 is one of the earliest transcription factors that binds to prostate-specific promoters, and that a direct protein-protein interaction occurs between FoxA1 and androgen receptor. Interestingly, evidence of the interaction of FoxA1 with other transcription factors is lacking. The upstream stimulatory factor 2 (USF2), an E-box-binding transcription factor of the basic-helix-loop-helix-leucine-zipper family, binds to a consensus DNA sequence similar to FoxA1. Our in vitro and in vivo studies demonstrate the binding of USF2 to prostate-specific gene promoters including the probasin promoter, spermine-binding protein promoter, and prostate-specific antigen core enhancer. Furthermore, we show a direct physical interaction between FoxA1 and USF2 through the use of immunoprecipitation and glutathione-S-transferase pull-down assays. This interaction is mediated via the forkhead DNA-binding domain of FoxA1 and the DNA-binding domain of USF2. In summary, these data indicate that USF2 is one of the components of the FoxA1/androgen receptor transcriptional protein complex that contributes to the expression of androgen-regulated and prostate-specific genes.

Non-competitive androgen receptor inhibition in vitro and in vivo

Androgen receptor (AR) inhibitors are used to treat multiple human diseases, including hirsutism, benign prostatic hypertrophy, and prostate cancer, but all available anti-androgens target only ligand binding, either by reduction of available hormone or by competitive antagonism. New strategies are needed, and could have an important impact on therapy. One approach could be to target other cellular mechanisms required for receptor activation. In prior work, we used a cell-based assay of AR conformation change to identify non-ligand inhibitors of AR activity. Here, we characterize 2 compounds identified in this screen: pyrvinium pamoate, a Food and Drug Administration-approved drug, and harmol hydrochloride, a natural product. Each compound functions by a unique, non-competitive mechanism and synergizes with competitive antagonists to disrupt AR activity. Harmol blocks DNA occupancy by AR, whereas pyrvinium does not. Pyrvinium inhibits AR-dependent gene expression in the prostate gland in vivo, and induces prostate atrophy. These results highlight new therapeutic strategies to inhibit AR activity.

A small composite probasin promoter confers high levels of prostate-specific gene expression through regulation by androgens and glucocorticoids in vitro and in vivo

Transient transfection studies have shown that the probasin (PB) promoter confers androgen selectivity over other steroid hormones, and transgenic animal studies have demonstrated that the PB promoter will target androgen, but not glucocorticoid, regulation in a prostate-specific manner. Previous PB promoters either targeted low levels of transgene expression or became too large to be conveniently used. The goal was to design a PB promoter that would be small, yet target high levels of prostate-specific transgene expression. Thus, a composite probasin promoter (ARR2PB) coupled to the bacterial chloramphenicol acetyltransferase reporter (ARR2PBCAT) was generated and tested in prostatic and nonprostatic cell lines and in a transgenic mouse model. In PC-3, LNCaP, and DU145 prostate cancer cell lines, the ARR2PB promoter gave basal expression and was induced in response to androgen and glucocorticoid treatment after cotransfection with the respective steroid receptor. Basal expression of ARR2PBCAT in the nonprostatic COS-1, MCF-7, ZR-75-1, and PANC-1 cell lines was very low; however, CAT activity could be induced in response to androgens and glucocorticoids when cells were cotransfected with either the AR or GR. In contrast to the transfection studies, ARR2PBCAT transgene expression remained highly specific for prostatic epithelium in transgenic mice. CAT activity decreased after castration, and could be induced by androgens and, in addition, glucocorticoids. This demonstrates that the necessary sequences required to target prostate-specific epithelial expression are contained within the composite ARR2PB minimal promoter, and that high transgene expression can now be regulated by both androgens and glucocorticoids. The ARR2PB promoter represents a novel glucocorticoid inducible promoter that can be used for the generation of transgenic mouse models and in viral gene therapy vectors for the treatment of prostate cancer in humans.

Rat probasin: structure and function of an outlier lipocalin

Probasin (PB) occurs both as a secreted and a nuclear protein that is abundantly expressed in the epithelial cells of the rat prostate. A genomic clone of 17.5 kb gene was isolated from a rat liver genomic library, determining that the probasin gene was comprised of seven exons where the splice donor/acceptor sites conformed to the GT/AG consensus sequence. The exon number and size are remarkably similar to those of aphrodisin, rat alpha(2)-urinary globulin and major urinary protein, outlier members of the lipocalin superfamily. In addition, alignment of the deduced amino acids determined that the probasin gene also contains the glycine-X-tryptophan (G-X-W) motif similar to that of human retinol serum binding protein which binds retinol, and the C-X-X-X-C motif also found in insect lipocalins that bind pheromones. The cysteine residues in exons 3 and 6 are conserved, predicting a secondary structure of eight beta-sheets and the alpha-helix commonly seen in the lipocalin superfamily. Unique PB characteristics include a large genomic fragment (17.5 kb compared to the 3-5 kb seen in other lipocalin genes) and an isoelectric point (pI) of 11.5 which is very basic compared to that of the other more acidic lipocalins. Functionally, PB gene expression is regulated by androgens and zinc in the epithelial cells of the rodent prostate. The 5'-flanking region of probasin contains two androgen receptor binding sites that allow androgen-specific gene expression as well as prostate-specific elements that target and maintain high levels of transgene expression in several PB transgenic mouse models.

Isolation and characterization of mouse probasin: An androgen-regulated protein specifically expressed in the differentiated prostate

BACKGROUND

The development and growth of the prostate gland is regulated, in part, by a variety of steroid and polypeptide growth-factor hormones. As a consequence of hormone action, the prostate gland will produce a number of tissue-restricted gene products. Characterization of the regulation, expression, and function of genes encoding prostate-specific proteins is critical to our understanding of prostate biology. Probasin is a prostate-specific gene originally isolated from the rat and has been exploited as a marker of prostate differentiation and to elucidate androgen action. Furthermore, a number of transgenic mouse models of prostate cancer have been established based on the regulatory elements derived from the rat probasin gene. In this report, we describe the isolation and characterization of the mouse probasin ortholog to further facilitate studies related to hormone action in the prostate and the generation and characterization of novel autochthonous models of prostate cancer.

METHODS

Mouse probasin cDNA was isolated from a phage library, and the DNA sequence was determined. The predicted protein sequence was used to generate specific oligonucleotide primers and antibodies. Probasin protein and RNA expression were examined by immunobloting, immunohistochemistry, and RT-PCR, in normal mouse prostate tissue and tumor tissues derived from the autochthonous "transgenic adenocarcinoma of the mouse prostate" (TRAMP) model. Regulation of probasin expression in response to surgical castration and hormone supplementation was also characterized.

RESULTS

Several points of evolutionary sequence conservation were identified between mouse and rat probasin, especially in the 3' untranslated region. Specific polyclonal antibodies were generated to peptide fragments, and the temporal and spatial pattern of probasin expression was examined. The expression of probasin was primarily localized to the apical membrane of differentiated secretory epithelium. Probasin mRNA and protein were absent from the poorly differentiated tissue of TRAMP tumors. Probasin was found to be androgen-regulated. In contrast to data from studies on rat probasin, no postcastration rebound of mouse probasin mRNA was observed.

CONCLUSIONS

Probasin is a marker of differentiation and androgen action in the mouse prostate, and strong sequence conservation between mouse and rat probasin supports an essential role for this gene in the biology of the prostate gland. Isolation and characterization of mouse probasin will facilitate further development and analysis of autochthonous mouse models of prostate cancer.

Regulation of a bifunctional mRNA results in synthesis of secreted and nuclear probasin

Probasin, a rat prostatic protein, is statistically related to members of a protein family that includes serum, cellular, and nuclear proteins. In vivo, probasin appears both in the secretions and in the nucleus of prostatic epithelial cells. Using primer extension and S1 nuclease protection assays we detected only one probasin mRNA. Thus, the localization of this protein to two separate cellular regions must be encoded by this one mRNA. Furthermore, in vitro translation of synthetic probasin mRNA demonstrated that a protein containing a signal peptide and a protein lacking a signal peptide were synthesized by initiation at different AUG codons. These data are consistent with a mechanism of translational regulation of a eukaryotic bifunctional mRNA.

The androgen-dependent rat prostate protein, probasin, is a heparin-binding protein that co-purifies with heparin-binding growth factor-1

Rat prostate extracts contain an abundant 20-22 kilodalton heparin-binding protein with near identical chromatographic properties, but only 0.2-1% of the mitogenic activity, of bovine brain heparin-binding growth factor-1 (acidic fibroblast growth factor). Amino terminal amino acid sequence (met-met-thr-asp-lys-asn-leu-lys-lys-lys-ile-glu-gly-asn-trp-arg-thr-val -tyr- leu-ala-ala-ser-?-val-glu-lys-ile-asn-glu-gly-ser-pro) and immunochemical analysis revealed that the protein is identical to the androgen-dependent protein "probasin".

Protein profiles of benign hypertrophic prostate: stroma-abundant distribution of BPH-associated nonhistone proteins

Mechanically isolated epithelium and stroma from benign hypertrophic prostates were highly pure on the basis of histochemical and biochemical criteria. By electrophoretic analyses, whole cellular and nuclear proteins were compared among whole tissues, epithelium, and stroma. The characteristic protein profiles of benign hypertrophic prostates were reflected in the electrophoretic patterns of the stroma. Two-dimensional gel electrophoretic patterns of the epithelium were different from those of the stroma with exception of about 18 major spots that were common to both fractions. Of the protein species separated, 35K/6.7 (molecular weight/pI) and 36K, which was composed of two species with pI of 4.4 and 4.6, were abundant in the epithelium and stroma, respectively. Nuclei prepared from whole tissues of benign hypertrophic prostates contained three kinds of nonhistone proteins (NHP) closely associated with benign prostatic hypertrophy (BPH); 42 K-NHP, 55 K-NHP and 190 K-NHP. Electrophoretic analysis of the nuclear proteins revealed that all the BPH-associated nonhistone proteins were abundantly distributed in the nuclei of the stroma.

Growth factors in the prostate

Certain local tissue factors, such as growth factor, in addition to androgens, are involved in the prostate growth. The prostate contains two types of growth factors capable of stimulating DNA synthesis in BALB/3T3 cells. They were divided into low affinity (LoA) type and high affinity (HiA) type by a different affinity for heparin-Sepharose. HiA-type growth factor is further classified into acidic HiA and basic HiA types. Acidic HiA type could be purified from the Dunning tumor (R 3327), a rat prostatic adenocarcinoma, and has a molecular weight of about 19,000 and a pI of about 3.8. Basic HiA type could be isolated from the tissues of human benign prostatic hypertrophy and has a molecular weight of about 12,000 and a pI of about 10.5. They are inactivated by heat and acid treatments. Acidic HiA type appears to be involved in growth of the rat prostate epithelium, and LoA type growth factor is possibly relevant to reproductive physiology because of its coexistence with "probasin," a major secretory protein in the dorsolateral prostate having a strong affinity for spermatozoa.

The occurrence of extended acidic sequences in nonhistone chromosomal proteins

Nonhistone chromosomal proteins and soluble cytoplasmic proteins from rat liver were treated with a combination of proteases and chemical reagents which split a variety of peptide bonds but do not attack sequences consisting predominantly or exclusively of acidic amino acid residues. Analysis of the resulting digests by gel filtration chromatography and column electrophoresis demonstrated that, relative to cytoplasmic proteins, nonhistone chromosomal proteins are rich in highly charged, acidic peptides up to 12 residues in length, but rarely contain very long peptides consisting exclusively of acidic residues such as are found in the nonhistone chromosomal proteins HMG1 and HMG2.

Lobe-specific distribution of a 20,000-dalton nonhistone protein in the dorsolateral prostate of rats

Distribution of an androgen-dependent, 20,000-dalton nonhistone protein with a pI of about 11.5 (20K-NHP) was examined by electrophoretic techniques. Nuclei of the brain, liver, spleen, skeletal muscle, lung, and thymus of rats contained a negligible amount of 20K-NHP, whereas 20K-NHP was distinctly detectable, in different relative amounts, in the nuclei of the male accessory sex organs, with the dorsolateral prostate having the highest relative content (100%), followed by the coagulating gland (approximately equal to 16%), the ventral prostate (approximately equal to 6%), and the seminal vesicle (approximately equal to 2%). There were heterogeneous distributions of cytosol components, acid phosphatase isozymes, and nonhistone proteins in the dorsolateral prostate. Zinc was localized in the lateral lobe, and fructose and glucose were in the dorsal lobe. Cytosol proteins with pI 7.5, 8.2, and 8.5 were abundant in the dorsal lobe, and proteins with pI 7.4 and 8.0 in the lateral lobe. Acid phosphatase isozymes with pI 7.1, 7.4, 7.7, and 8.0 were abundantly distributed in the lateral lobe. Of the nonhistone proteins, 20K-NHP showed the highest content both in the lateral lobe and in the dorsal lobe. It was found that 20K-NHP was more abundantly distributed in the lateral lobe (maximally four times higher) than in the dorsal lobe. The heterogeneous distribution of 20K-NHP in the dorsolateral prostate was strikingly similar to that of zinc. It appears, therefore, that 20K-NHP is closely related to dorsolateral prostate zinc content.

Localization of prostatic basic protein ("probasin") in the rat prostates by use of monoclonal antibody

Isolated nuclei of the rat prostates contain a unique androgen-dependent basic protein, "probasin". Despite that it was hardly detectable in the cytosol centrifugally prepared from the prostates, immunofluorescent histological analysis of whole tissues using monoclonal antibody, which was raised against probasin purified from the nuclei, revealed that probasin was abundantly localized in the lumen and acinal regions of the epithelium, but hardly in the nuclei. Previous extraction of secretory fluid from the prostates caused about 60% decrease in the probasin content of isolated nuclei. These suggest that probasin was originally a secretory component in the prostates, being redistributed from the secretory fluid and granule into nuclei during fractionation of subcellular components.

Comparison of subcellular proteins of normal prostate, benign prostatic hypertrophy, and prostatic cancer: presence of BPH-associated nonhistone proteins

Proteins in the cytosol, postnuclear particulate, and nuclear fractions from seven specimens of normal prostate from bladder cancer patients, 14 specimens of benign hypertrophic prostate (BPH), and three specimens of cancerous prostate were analyzed and compared by SDS-polyacrylamide slab gel electrophoresis. Abundant protein species in the cytosol fractions were 60K (species having a molecular weight of about 60,000) and 42K; their relative contents were about 35% for 60K and about 12% for 42K. In the postnuclear particulate fraction, 42K was the most abundant (about 10% of the total). The contents of these major protein species were similar in specimens of normal and diseased prostates. In addition, there are marked similarities in the electrophoretic patterns for all the protein (24-29 species) in the cytosol and postnuclear particulate fractions of the human prostate, except for four minor species in the cytosol fraction. Of the nuclear proteins, the content of core histones (H2A, H2B, H3, and H4) was fundamentally similar among all the specimens, whereas the content of H1 histone was different from one specimen to another. The most remarkable and significant difference was that the 42K-NHP (nonhistone protein having a molecular weight of about 42,000), 55K-NHP, and 190K-NHP concentrations were significantly higher in BPH than in normal and cancerous prostates.

Differences in nonhistone protein changes in rat ventral and dorsolateral prostate during sexual maturation

Age-related changes of chromosomal proteins in the dorsolateral and ventral prostates of rats from 6 to 31 weeks of age were studied by SDS-polyacrylamide gel electrophoresis. A nonhistone protein having a molecular weight of about 20,000 (20K-NHP), abundantly localized in the dorsolateral prostate, increased rapidly in content during the early stage of sexual maturation (6-11 weeks of age) in association with increases of serum testosterone concentration and prostatic tissue weight. Serum testosterone concentration decreased after week 11 and then remained constant until week 31. In contrast, the 20K-NHP content continued to increase after 11 weeks of age in the dorsolateral prostate, but not in the ventral prostate. The rapid increase of 20K-NHP in the dorsolateral prostate during the early stage of sexual maturation could not be attained in immature rats (5 weeks of age) by injection of excess amounts of androgens and/or prolactin for a week. But the 20K-NHP content in the ventral prostate of rats treated with testosterone propionate was almost the same as that of mature rats.

Changes of an androgen-dependent nuclear protein during functional differentiation and by dedifferentiation of the dorsolateral prostate of rats

Nuclei of the dorsolateral prostate of rats contain a large amount of androgen-dependent non-histone protein (20K-NHP) (mol. wt. not equal to 20,000; pI not equal to 11.5) (Matuo et al. (1]. Its content in the nuclei increased most markedly during 4-8 weeks of age, when functional differentiation of the prostate was most active on the basis of the changes of major cytosol proteins and zinc. Nuclei of the Dunning tumors originating in the dorsolateral prostate were found to lack 20K-NHP regardless of androgen dependency, indicating the disappearance of the 20K-NHP from the nuclei by dedifferentiation. These suggest that the 20K-NHP is an important nuclear protein for differentiation of the dorsolateral prostate cells.