Two-dimensional characterization of prostatic acid phosphatase, prostatic specific antigen and prostate binding protein in expressed prostatic fluid

Sildenafil citrate induces prostatic hyperplasia in BPH model rats and aged rats

Erectile dysfunction (ED), a prevalent disease among middle-aged and elderly males, significantly impacts both patient and partner quality of life. Phosphodiesterase type 5 inhibitor (PDE5i) represents an effective therapeutic method for ED. Given their widespread global utilization, concerns arise regarding potential reproduction-related problems arising from clinical use. During the extensive development of PDE5i, we speculated that the potential of these inhibitors to variably induce prostatic hyperplasia, but this field remains unexplored. In order to verify the male reproductive toxicity of PDE5i, sildenafil citrate at doses of 5, 10 and 20 mg/kg was administered in BPH model rats and aged rats. Anatomical and pathological analyses indicate a compelling association between sildenafil citrate administration and the promotion of prostatic hyperplasia in both BPH model rats and aged rats. Serum analysis showed that serum prostate-binding protein (PBP) exhibited a non-significant but increasing trend following administration of sildenafil citrate to BPH model rats. Furthermore, significant increase in serum levels of E2 and T, as well as T in dorsal lobe prostate tissue of aged rats, were observed compared to the model control group. These results confirm the hypothesis that sildenafil citrate has reproductive toxicity in males.

Identification of de novo synthesized and relatively older proteins: accelerated oxidative damage to de novo synthesized apolipoprotein A-1 in type 1 diabetes

OBJECTIVE

The accumulation of old and damaged proteins likely contributes to complications of diabetes, but currently no methodology is available to measure the relative age of a specific protein alongside assessment of posttranslational modifications (PTM). To accomplish our goal of studying the impact of insulin deficiency and hyperglycemia in type 1 diabetes upon accumulation of old damaged isoforms of plasma apolipoprotein A-1 (ApoA-1), we sought to develop a novel methodology, which is reported here and can also be applied to other specific proteins.

RESEARCH DESIGN AND METHODS

To label newly synthesized proteins, [ring-(13)C(6)]phenylalanine was intravenously infused for 8 h in type 1 diabetic participants (n = 7) during both insulin treatment and 8 h of insulin deprivation and in nondiabetic participants (n = 7). ApoA-1 isoforms were purified by two-dimensional gel electrophoresis (2DGE) and assessment of protein identity, PTM, and [ring-(13)C(6)]phenylalanine isotopic enrichment (IE) was performed by tandem mass spectrometry.

RESULTS

Five isoforms of plasma ApoA-1 were identified by 2DGE including ApoA-1 precursor (pro-ApoA-1) that contained the relatively highest IE, whereas the older forms contained higher degrees of damage (carbonylation, deamidation) and far less IE. In type 1 diabetes, the relative ratio of IE of [ring-(13)C(6)]phenylalanine in an older isoform versus pro-ApoA-1 was higher during insulin deprivation, indicating that de novo synthesized pro-ApoA-1 more rapidly accumulated damage, converting to mature ApoA-1.

CONCLUSIONS

We developed a mass spectrometry-based methodology to identify the relative age of protein isoforms. The results demonstrated accelerated oxidative damage to plasma ApoA-1, thus offering a potential mechanism underlying the impact of poor glycemic control in type 1 diabetic patients that affects a patient's risk for vascular disease.

Proteomics cataloging analysis of human expressed prostatic secretions reveals rich source of biomarker candidates

Expressed prostatic secretions (EPS) contain proteins of prostate origin that may reflect the health status of the prostate and be used as diagnostic markers for prostate diseases including prostatitis, benign prostatic hyperplasia, and prostate cancer. Despite their importance and potential applications, a complete catalog of EPS proteins is not yet available. We, therefore, undertook a comprehensive analysis of the EPS proteome using 2-D micro-LC combined with MS/MS. Using stringent filtering criteria, we identified a list of 114 proteins with at least two unique-peptide hits and an additional 75 proteins with only a single unique-peptide hit. The proteins identified include kallikrein 2 (KLK2), KLK3 (prostate-specific antigen), KLK11, and nine cluster of differentiation (CD) molecules including CD10, CD13, CD14, CD26, CD66a, CD66c, CD 143, CD177, and CD224. To our knowledge, this list represents the first comprehensive characterization of the EPS proteome, and it provides a candidate biomarker list for targeted quantitative proteomics analysis using a multiple reaction monitoring (MRM) approach. To help prioritize candidate biomarkers, we constructed a protein-protein interaction network of the EPS proteins using Cytoscape (www.cytoscape.org), and overlaid the expression level changes from the Oncomine database onto the network.

Capillary electrophoresis for the investigation of prostate-specific antigen heterogeneity

Prostate-specific antigen (PSA) is a single-chain glycoprotein that is used as a biomarker for prostate-related diseases. PSA has one known posttranslational modification, a sialylated diantennary N-linked oligosaccharide attached to the asparagine residue N45. In this study capillary electrophoresis (CE) was employed to separate the isoforms of seven commercially available free PSA samples, two of which were specialized: enzymatically active PSA and noncomplexing PSA. The free PSA samples examined migrated as four to nine distinct, highly resolved peaks, indicating the presence of several isoforms differing in their oligosaccharide compositions. Overall, the use of CE provides a rapid, reproducible method for separation of PSA into its individual isoforms.

Expression of transmembrane serine protease TMPRSS2 in mouse and human tissues

The purpose of this study was to clarify the expression of TMPRSS2 in mice during development and to compare the tissue distribution of the transcripts in adult mouse and human tissues. Mouse TMPRSS2 cDNA was cloned; the predicted amino acid sequence contains 490 residues sharing 81.4% similarity with human TMPRSS2. According to northern blots, mouse TMPRSS2 is expressed mainly in the prostate and kidney, while human TMPRSS2 is expressed in the prostate, colon, stomach, and salivary gland. In situ hybridization analyses of mouse embryos and adult tissues revealed that TMPRSS2 was expressed in the epithelia of the gastrointestinal, urogenital, and respiratory tracts. Expression was very selective and constant after the gene was turned on during development. Expression of TMPRSS2 was localized in the luminal epithelial cells of the mouse and human prostate. The information presented here will be useful in further studies regarding the function and physiological significance of TMPRSS2.

Two-dimensional electrophoresis of prostate-specific antigen in sera of men with prostate cancer or benign prostate hyperplasia

Prostate-specific antigen (PSA), the main marker for prostate cancer (PCa), is released from the prostate into the blood stream at nanogram level and may increase in PCa and nonmalignant disease such as benign prostate hyperplasia (BPH). More recently, advantage was taken of PSA's ability to bind to protease inhibitors in serum in order to improve discrimination between PCa and BPH, using the free PSA to total PSA ratio. The understanding of this phenomenon at molecular level, which is still unknown, may promise new improvements in the field of diagnostics. For this purpose, we determined the pattern of PSA forms in PCa and BPH sera, using the high resolving power of two-dimensional electrophoresis (2-DE) in conjunction with the high sensitivity of chemiluminescence detection. Serum PSA differs drastically from seminal PSA: apart from complexed forms, serum PSA shows few cleaved forms. Moreover, 2-DE patterns from PCa are relatively homogeneous, whereas patterns from BPH may in some cases present a higher proportion of cleaved forms and in other cases present slightly more basic spots. We therefore demonstrated, for the first time, that an increase in the free to total PSA ratio in BPH cases may be due to cleaved PSA forms (which are enzymatically inactive and unable to bind inhibitors), or possibly related to basic free PSA, which may represent the zymogen forms.

Two-dimensional gel electrophoresis detects prostate-specific antigen–α1-antichymotrypsin complex in serum but not in prostatic fluid

We investigated the interaction between prostate-specific antigen (PSA) and 1-antichymotrypsin (ACT) in prostatic secretions, identifying PSA and ACT in human serum, prostatic fluid, and seminal plasma by two-dimensional gel electrophoresis (2-D PAGE). Both PSA and ACT were detected in all three body fluids, but PSA-ACT complex was detected only in serum. Moreover, the 2-D PAGE Western blot staining profile for ACT from serum differed from that for prostatic fluid or seminal plasma. Incubation of prostatic fluid with purified ACT led to formation of PSA-ACT complex. Incubation of prostatic fluid with purified PSA, however, failed to form the complex, suggesting that the ACT in prostatic fluid was inactive or inhibited. Given that physiological concentrations of zinc inhibited the formation of PSA-ACT complex, we consider zinc a possible physiological inhibitor of the formation of the PSA-ACT complex. These results indicate that the failure to detect the PSA-ACT complex in prostatic fluid could be related to the inactivation of ACT, the presence of inhibitors (e.g., zinc), or simply the PSA:ACT ratio in the fluid.

Overexpression of a human prostate-specific glandular kallikrein, hK2, in E. coli and generation of antibodies

The genomic and the cDNA clones of human glandular kallikrein (hK2), a member of the kallikrein family, have been isolated; however, the hK2 protein has not yet been identified and characterized. The deduced sequence of hK2 is highly homologous to prostate specific antigen (PSA), a widely accepted prognostic indicator of prostate carcinoma. Also, hK2 mRNA, like PSA mRNA, is exclusively expressed in prostatic epithelia. These two properties make hK2 a potentially useful marker for studying prostate cancer. In this paper, we describe for the first time the overexpression of the entire hK2 protein (pre-pro hK2:pphK2) in the E. coli system. Our system yields high levels of authentic pphK2 (as determined by partial amino acid sequence analysis) comprising about 40% of total cellular protein. pphK2 was purified to near homogeneity by preparative SDS/PAGE and used to generate anti-pphK2 antibodies in rabbits. The antibodies recognize the recombinant hK2 protein and a major band of approximately 34 kDa in seminal fluid.

Analysis of prostatic fluid: evidence for the presence of a prospective marker for prostatic cancer

In an endeavor to identify marker(s) for prostatic cancer, proteins in prostatic fluids were analyzed by two-dimensional (2-D) gel electrophoresis. The fluids were obtained from five males who had no prostate lesions and five patients each with benign prostatic hyperplasia (BPH) and prostatic carcinoma (PCA). The specimens were collected directly over a mixture of protease inhibitors and centrifuged, and the supernatants were lyophilized and solubilized in sodium dodecyl sulfate mix. Identical amounts of proteins were pooled according to donors' prostate disease and the resulting samples were subjected to 2-D gel analysis employing the ISO-DALT system. The electrophoretograms were developed by silver or double stain. The samples of each group exhibited distinctive profiles with the exception of similar relative positions of major protein spots. A predominant protein occurring as several charge variants was consistently present in prostatic fluids of patients with PCA. This protein appeared to be a previously unknown constituent that we have called protein D (molecular weight approximately 22 kDa and isoelectric point approximately 4), and was undetectable in the fluids of "normal" men and patients with BPH. An analysis of pooled, unprocessed urine from PCA patients revealed that perhaps this protein is excreted in urine in very low quantities. These results strongly suggest that the potential of this protein as a marker for prostatic cancer should be further explored.

Prostate-specific antigen and human glandular kallikrein: two kallikreins of the human prostate

Prostate-specific antigen (PSA) is a 33 kD protein synthesized in the epithelial cells of the prostate gland. It is a serine protease that belongs to the subgroup of kallikreins, among which it is very similar to a putative enzyme called human glandular kallikrein (hGK-1). Although the hGK-1 enzyme remains to be characterized in vivo, the hGK-1 gene is expressed in the same prostatic epithelial cells as the PSA gene. Expression of the PSA gene is under complex control and the steady-state level of PSA mRNA is increased by androgens, and decreased by epidermal growth factor and activation of protein kinase C. This suggests the existence of several regulatory elements within the cis-acting control elements of the PSA gene. As a seminal serine protease, PSA has been shown to digest the high molecular weight seminal vesicle protein, seminogelin. However, it is likely that this does not constitute the only natural substrate of PSA, as PSA has been shown to degrade insulin-like growth factor-binding protein-3. Serum PSA concentrations are frequently increased in patients with prostatic cancer, but this is also the case in patients with benign prostatic hyperplasia. Thus, PSA measurements alone are not useful as a screening tool for undiagnosed prostatic cancer. However, serum PSA concentrations can be successfully used together with other methods in diagnosing prostatic diseases and in monitoring the successfulness of treatments for prostatic cancer.

Study of activities of arginase, hexosaminidase, and leucine aminopeptidase in prostate fluid

Our previous studies demonstrated that extracts of the cancerous prostate tissues exhibit increased activities of arginase and hexosaminidase and decreased activity of leucine aminopeptidase. In an endeavor to devise a reliable, noninvasive and cost effective method for the diagnosis of prostate carcinoma, prostate fluids collected from 123 patients were analyzed for arginase, hexosaminidase, and leucine aminopeptidase. Based on the clinical diagnoses, the patients were divided into four groups: 13 men with chronic prostatitis, 29 with no recognized prostatic lesions, 63 with benign prostatic hyperplasia, and 18 with prostate cancer. The prostate fluids had no detectable arginase activity. The means of the total (units/mL) and the specific activities (units/mg of protein) of hexosaminidase and leucine aminopeptidase varied, albeit there were no significant differences in the four groups of patients recruited in this study. It was concluded that the profiles of enzymes in prostate fluids might differ from that in the secreting prostate tissues and that the results of enzyme analysis in prostate fluids for the diagnosis of cancer should be interpreted with caution.

Regulation of prostatic carcinoma cell proliferation and secretory activity by extracellular matrix and stromal secretions

Previous studies from our laboratory have shown that reconstituted basement membrane and stromal secretory products are important regulators of benign prostatic epithelial cell growth and differentiation. In the present study we evaluated the impact of extracellular matrix (ECM) and soluble stromal secretory products on the proliferation and secretory activity of the androgen-responsive prostatic carcinoma cell line LNCaP. In these studies, dihydrotestosterone (DHT) was a potent mitogen for LNCaP cells cultured on plastic or on type I collagen. The growth response to DHT was greatly attenuated when LNCaP cells were grown on prostatic stromal ECM. Cells grown on stromal ECM also exhibited clustered morphology compared to the monolayer growth observed on plastic and secreted elevated levels of prostate specific antigen (PSA) and prostatic acid phosphatase (PAP). These findings indicate that cultivation of LNCaP on stromal ECM will promote the expression of differentiated functions. In additional studies, stromal cell conditioned medium (SCM) significantly increased PSA/PAP secretion by LNCaP cells in the presence of 10 nM DHT. The enhancement of DHT-induced PSA/PAP secretion by SCM was most pronounced when LNCaP cells were grown on stromal ECM. SCM did not significantly alter LNCaP proliferation. These studies indicate that prostatic stromal ECM and soluble secretory products will promote differentiated function in cultured LNCaP cells. In addition, we show that DHT can act as either a growth or differentiation-promoting stimulus depending on the presence of stromal factors.

Variations in 3H-diisopropylfluorophosphate binding proteins in human seminal plasma

We have characterized the electrophoretic pattern and variations in 3H-diisopropylfluorophosphate (DFP)-binding proteins in human seminal plasma from normal men and from 103 patients attending the infertility clinic of our hospital. This study shows that 34 kDa prostate-specific antigen (PSA) is the major 3H-DFP-binding protein and that two other ubiquitous bands of 100 and 60 kDa are also present in seminal plasma from all the men studied. Additional bands of 92, 50-54 (doublet) and 38 kDa were also observed in some patients. The 38 kDa band was shown to be a highly glycosylated form of PSA. Further complexity was demonstrated by two-dimensional gel electrophoresis in the 27-30 kDa range of the gels since at least 10 major spots and rows of spots were seen. The concentration of these spots, including PSA, was extremely variable, as was their pattern of inhibition by various active site inhibitors of serine-proteases; these variations were not correlated with any specific sperm characteristics. With the exception of PSA, the proteins have not been identified. Their distribution suggests that most of them are exclusively of prostatic origin although a few could also derive from the seminal vesicles or blood. Future studies will be aimed at determining the nature of these proteins and their potential usefulness in andrology.

Generation and characterization of monoclonal antibodies to prostate secretory protein

Monoclonal antibodies (MAbs) were produced against a highly purified preparation of prostate secretory protein (PSP) isolated from normal seminal plasma. Fifteen antibodies were selected for further evaluation based on their strong reactivity and specificity for PSP. All the MAbs had a specificity for prostate epithelial cells and none reacted to any of a variety of normal tissues as determined by immunoperoxidase staining. Six of the MAbs were selected for further immunohistochemical evaluation based on their ability to recognize different antigenic determinants. Using competitive binding immunoassays, a variety of overlapping specificities were observed with at least 2 distinct epitopes identified. Although some staining variability was noted, the 6 antibodies, in general, gave the same pattern of tissue reactivity. Both the normal prostate and the benign prostate hyperplastic ductal epithelial cells stained intensely, with 78 to 100% and 50-100% of the cells staining, respectively. The number and often the staining intensity of the tumor cells decreased as the tumor became more undifferentiated. Approximately 40 to 100% and 15 to 70% of the tumor cells stained in the moderately-differentiated and well-differentiated carcinoma tissues, respectively, whereas either no staining was observed or less than 20% of the tumor cells stained in the poorly-differentiated and undifferentiated tumors. Most of the metastatic prostate tumors showed either no staining or scattered staining in a few cells (i.e., less than 20%).

Demonstration of the role of prostate-specific antigen in semen liquefaction by two-dimensional electrophoresis

Two-dimensional protein profiles of human semen, prostatic fluid, and seminal vesicle fluid were compared to demonstrate changes in the protein composition of human semen before and after liquefaction. Semen specimens were obtained from a volunteer. Prostatic fluid specimens were collected by rectal massage from patients visiting a urology clinic. Samples of seminal vesicle fluid were collected by needle aspiration from isolated seminal vesicles, which were removed at surgery. All specimens were prepared and processed according to the ISO-DALT system for separation of proteins in two-dimensional gels. Following electrophoresis, protein spots in the gels were visualized by silver staining. Prostatic fluid and seminal vesicle fluid showed their characteristic protein profiles. The protein profile of human semen contained specific proteins of both prostatic fluid and seminal vesicle fluid. One major group of proteins in seminal vesicle fluid (Mw 28,000-68,000 daltons), designated as seminal vesicle-specific antigen, was observed in freshly ejaculated human semen, but disappeared from the two-dimensional profile when the ejaculate was allowed to stand at room temperature for 30 min. When prostatic fluid or prostate-specific antigen was mixed with seminal vesicle fluid and incubated at 37C for 30 min, the seminal vesicle-specific antigen also disappeared from the two-dimensional profiles. The findings indicate that seminal vesicle-specific antigen, a group of predominant proteins in seminal vesicle fluid, is the structural component of seminal coagulum, and that prostate-specific antigen is the enzyme which digests seminal vesicle-specific antigen and liquifies semen coagulum.

Looking for human glandular kallikrein-1 in the prostate

Based on recent studies indicating that human glandular kallikrein-1 (hGK-1) mRNA was present in the prostate, we have undertaken to determine whether the prostate contained trypsin-like proteases with properties compatible with those deduced from hGK-1 gene nucleotide sequence. The first series of experiments showed that only minimal levels of trypsin-like enzymatic activity, determined with synthetic substrates, were present in chromatographic fractions of prostatic glycoproteins having a molecular weight in the range expected for hGK-1, i.e., 25,000-35,000. Because of this, we used [3H]diisopropylfluorophosphate (DFP) labeling alone or in the presence of various serine-protease inhibitors to identify trypsin-like proteases in the prostate. Two-dimensional gel electrophoresis of prostatic glycoproteins showed the presence of minor spots of 18-32 kDa. These spots were slightly more acidic than were those of prostate specific antigen (PSA) and were completely inhibited by preincubation with tosyl lysine chloromethyl ketone and p-nitrophenyl-p-guanidobenzoate in contrast to PSA spots that were not affected by these treatments. When a similar procedure was applied to total cytosolic proteins instead of glycoproteins, an additional 30 kDa DFP binding protein was observed. This relatively abundant protein was much more acidic than was PSA and was not inhibited by any of the protease inhibitors tested. In conclusion, this study has permitted us to demonstrate the presence of two sets of proteins that have physicochemical properties compatible with those that can be deduced from the information contained in the hGK-1 gene.

Enzymatic and electrolytic profiles of human semen

Chemical parameters comprising urea and creatinine nitrogen, cations (Na+, K+, and Ca2+), chloride, phosphorus, protein, cholesterol and enzymes, aminotransferases, alkaline and prostatic acid phosphatases, gamma-glutamyltransferase, creatine kinase, and lactate dehydrogenase were ascertained for semen from groups A (vasectomized), B (oligospermic), and C (normospermic) men, 19 to 55 years of age. Of the parameters, the vasectomized group underwent definite depressions in potassium ion, alkaline phosphatase, aspartate aminotransferase, gamma-glutamyltransferase, and lactate dehydrogenase as compared with the normospermic group; the last three enzymes and, possibly, the urea-creatinine ratio were decreased for the oligospermic group vs. the normospermic men. In the comparison of groups A and B, only the decrements in alanine aminotransferase and lactate dehydrogenase were statistically significant. In corroboration of past reports, CK-BB comprised the main isoenzyme of semen creatine kinase.