Immunoelectron microscopic demonstration of prostatic acid phosphatase in human hyperplastic prostate

Location of prostate-specific membrane antigen in the LNCaP prostate carcinoma cell line

BACKGROUND

Prostate-specific membrane antigen (PSMA) is a novel prostate biomarker overexpressed in poorly differentiated and metastatic prostate carcinomas and apparently upregulated following hormone-ablation therapy. PSMA appears to be a satisfactory target for antibody-directed imaging of prostate carcinomas despite the recent finding that the antigenic epitope recognized by monoclonal antibody (MAb) 7E11-C5 is found in the cytoplasmic domain of this transmembrane glycoprotein [Troyer et al.: Urol Oncol 1:29-37, 1995]. This finding prompted the present investigation to precisely define the cellular location of PSMA in the LNCaP prostate carcinoma cell line, the line used to generate MAb 7E11-C5.

METHODS

Subcellular fractionation, immunofluorescence and immunoperoxidase staining of live and fixed cells, and immunoelectron microscopy were used to determine the localization of PSMA in LNCaP cells.

RESULTS

PSMA was found to be localized at the inner face of the plasma membrane as well as being associated with mitochondria. Staining of LNCaP cells, treated by serum starvation followed by serum stimulation, showed no changes in the typical cytoplasmic staining pattern.

CONCLUSIONS

The data suggest that the PSMA target epitope for antibody-directed imaging with MAb 7E11-C5 only becomes accessible upon apoptosis or necrosis. This further suggests that antibodies directed at the extracellular domain may enhance the sensitivity of antibody-directed imaging and therapy of prostate carcinomas by recognizing surface epitopes of PSMA on living cancer cells.

Immunocytochemical detection and phenotypic characterization of micrometastatic tumour cells in bone marrow of patients with prostate cancer

Monoclonal antibodies (mAbs) specific for cytokeratins are potent probes for the identification of disseminated individual epithelial tumour cells in mesenchymal organs such as bone marrow. We have used a monoclonal antibody (mAB) against cytokeratin 18 (CK18) for the detection of individual metastatic tumour cells in bone marrow aspirates from 84 patients with carcinoma of the prostate. CK18+ cells were detected in a sensitivity of 1 per 8 x 10(5) marrow cells using the alkaline phosphatase anti-alkaline phosphatase (APAAP) system for staining. We were able to detect CK18+ tumour cells in the marrow of 33% of patients with stage N0M0 prostate cancers. The incidence of CK18+ cells showed a significant correlation with established risk factors, such as local tumour extent, distant metastases and tumour differentiation. For further characterization of such cells in patients with prostate cancer, we developed an immunocytochemical procedure for simultaneous labelling of cytokeratin component no. 18 (CK18) and prostate-specific antigen (PSA). In a first step, cells were incubated with a murine mAb against PSA, followed by gold-conjugated goat anti-mouse antibodies. In a second step, a biotinylated mAb to CK18 was applied as primary antibody and subsequently incubated with complexes of streptavidin-conjugated alkaline phosphatase, which were developed with Newfuchsin substrate. The binding of gold-labelled antibodies was visualized by silver enhancement. CK18+ cells co-expressing PSA were found in bone marrow aspirates from 5 out of 14 patients with carcinomas of the prostate. The specificity of CK18 for epithelial tumour cells in bone marrow was supported by negative staining of 12 control aspirates from patients with benign prostatic hyperplasia (BPH).(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical double staining of cytokeratin and prostate specific antigen in individual prostatic tumour cells

Early dissemination of malignant cells is the main cause for metastatic relapse in patients with solid tumours. By use of monoclonal antibodies (mAbs) specific for cytokeratins, disseminated individual epithelial tumour cells can now be identified in mesenchymal organs such as bone marrow. Further to characterize such cells in patients with prostate cancer, an immunocytochemical procedure was developed for simultaneous labelling of cytokeratin component no. 18 (CK18) and prostate specific antigen (PSA). In a first step, cells were incubated with mAb ER-PR8 against PSA and secondary gold-conjugated goat anti-mouse antibodies. In a second step, biotinylated mAb CK2 to CK18 was applied as primary antibody and subsequently incubated with complexes of streptavidin-conjugated alkaline phosphatase, which were developed with the Newfuchsin substrate. The binding of gold-labelled antibodies was visualized by silver enhancement. The sensitivity and specificity of the technique was demonstrated on cryostat sections of hyperplastic prostatic tissue, and cytological preparations of LNCaP prostatic tumour cells. Double staining was restricted to cells derived from the secretory epithelium of the prostate. Cross-reactivity between both detection systems was excluded by several controls, including the use of unrelated antibodies of the same isotype and the staining of CK18+/PSA- HT29 colon carcinoma cells. CK18+ cells co-expressing PSA were found in bone marrow aspirates from 5 out of 13 patients with carcinomas of the prostate, a finding that is consistent with the relative fraction of double-positive LNCaP cells. The specificity of CK18 for epithelial tumour cells in bone marrow was supported by negative staining of 12 control aspirates from patients with benign prostatic hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroids inversely affect the biosynthesis and secretion of human prostatic acid phosphatase and prostate-specific antigen in the LNCaP cell line

In order to elucidate the mechanism of androgen-regulation of genes expressed only in the prostate gland, the effects of steroid hormones on the biosynthesis and secretion of human prostatic acid phosphatase (PAP) and prostate-specific antigen (PSA) were studied in the human prostatic carcinoma cell line, LNCaP. This cell line produces PAP and PSA, both of which were found to be similar to the proteins purified from and located in human prostatic tissue, as shown by Western blot analysis. The synthetic androgen, R1881, regulated the biosynthesis of these two important tumour marker proteins inversely: the amount of PSA released into the medium was increased to 506% +/- 100 of the control levels, while that of PAP was decreased to 26% +/- 3, in 7 days. These effects were dependent on the concentration of the steroid in the growth medium. The androgen-dependent changes observed in the amounts of the secreted proteins were correlated with alterations in their intra-cellular levels. LNCaP cells were found to have very different capacities for secreting PAP and PSA. Whereas the measurable, cellular amounts of PSA and PAP were of similar magnitudes, much larger amounts of PSA than PAP were secreted into the medium. PSA was also found to be more stable than PAP in the culture medium of the LNCaP cells. Other steroids could elicit effects on PAP and PSA biosynthesis similar to those induced by R1881, and the combined effects of effective concentrations of these steroids were undistinguishable from those caused by each one of them separately, suggesting that all these compounds compete for binding to the same modified androgen receptors of the LNCaP cells. Thus, our results confirm the observations of the altered nature of the LNCaP androgen receptors, and demonstrate the ability of these ligands to produce changes in the expression of androgen-dependent prostatic genes. The fact that the changes observed at the protein level were accompanied by increased levels of PSA mRNAs and by decreased levels of PAP mRNA in steroid-treated cells, suggests that one of the targets of androgen and steroid action in the regulation of these genes is at the mRNA level.

Morphologic and regulatory aspects of prostatic function

Current concepts of the structural and functional organization of the human prostate are presented and are related to endocrine principles which have been studied in experimental animals. Based on embryological and histological studies, the internal structure of the human prostate gland is divided into four subdivisions: 1. the anterior nonglandular fibromuscular stroma. 2. the periurethral portion, 3. the peripheral zone, and 4. the central zone. The central zone which accounts for 25% of the gland, is formed by a wedge-shaped group of ducts, arising close to the orifices of the ejaculatory ducts and is surrounded by the peripheral zone (75% of the gland). The functional interdependence and relationship between the stroma and the epithelium observed during embryological development, postnatal maturation and under certain pathological conditions, has led to the concept of a functional prostatic unit, which is useful for the explanation of prostatic growth and the expression of specific genes. There is growing evidence of a functional heterogeneity within the prostatic secretory duct system, with a concentration of estrogen-sensitive cells close to the urethra, and a relatively long persistence of undifferentiated nonsecretory acini at the peripheral tips of the gland ducts close to the dorsal capsule until late puberty. Secretory and proliferative activities of the gland are strictly androgen-dependent. Of particular importance with respect to glandular and stromal proliferation are the recent reports on the presence of different growth factors in the prostate. Hormonally induced imbalances in the system of growth factor production, androgen- and estrogen-dependence and general ageing of the cells have to be taken into consideration in understanding various prostatic pathologies such as benign prostatic hyperplasia and prostate cancer.

Improved immunohistochemical detection of prostatic acid phosphatase by a monoclonal antibody

A monoclonal antibody with high affinity to acid phosphatase isoenzyme 2 (Ab-AcP2) was selected to examine its binding to different normal and tumor tissues using the indirect immunohistochemical method. Both mature prostatic epithelial cells in the prostate and the highly dedifferentiated prostatic cancer cells in the bone marrow showed strong binding to the antibody. Among nonprostatic tissues, only bone marrow, breast, and kidney showed trace staining in some specimens. The specificity of Ab-AcP2 was much better than that of the polyclonal antibody to acid phospatase previously reported. When the antibody to the prostate-specific antigen (Ab-PSA) was used, weak background staining was often encountered, and weak to moderate stains were seen in the prostatic stroma, bone marrow, lung, skin, and melanoma.

Relationship of prostatic acid phosphatase localization in human prostate by a monoclonal antibody with the Gleason grading system

Prostatic acid phosphatase (PAP) was localized in human prostate with a monoclonal antibody prepared against PAP isoenzyme II to determine patterns of its expression in normal, hyperplastic (BPH), and cancerous glands. The monoclonal antibody reacted with both isoenzymes II and IV in immunoblot studies. Formalin-fixed, paraffin-embedded tissue was used from patients who had not been treated with hormones or chemotherapy. In normal glands and BPH, there was marked variation in the intensity of PAP staining in morphologically otherwise similar epithelial cells. There was similar heterogeneity of staining in the adenocarcinomas. Rough quantification of the intensity patterns in the clinical groups indicated a slight shift to more intense staining in BPH and well-differentiated carcinomas but a progressive decline in the PAP staining in the moderately and poorly differentiated tumors. This decrease in intracellular staining with decreasing differentiation is not inconsistent with the clinical observation that serum levels of acid phosphatase generally increase with higher grade and disseminated tumors, since the enzyme is simply more accessible to the circulatory system in those cases. The same decrease may explain the few disseminated tumors that are not associated with elevated serum levels.

Cytochemistry and biochemistry of acid phosphatases VII: Immunohistochemistry of canine prostatic acid phosphatase

Acid phosphatase (E.C. 3.1.3.2.) has been isolated from canine prostatic gland homogenates by gel permeation chromatography (AcA34 or G150), by affinity chromatography (con A-Sepharose), or by using fluid phase liquid chromatography (FPLC) using Superose 12 and Mono P columns. Acid phosphatase-enriched fractions were submitted to analytical SDS-PAGE or to analytical isoelectric focusing. A protein with a molecular weight of 30 kD (on SDS gels) was used for immunization of rabbits. The antiserum produced was cross-reactive with prostatic acid phosphatase (canine and human) as shown by immunoblotting. When applied to paraffin or plastic sections of normal canine prostate, a positive immunoreaction was found exclusively in the secretory cells. In experimentally altered glands (castration and/or hormone treatment), a varying pattern of immunoreactive cells was found. In canine prostatic carcinomas, intensively reacting cell clusters were found along with nonreactive cells. The antiserum was also slightly cross-reactive with the respective human antigen, but the cross-reactivity of an antiserum prepared against human prostatic secretory acid phosphatase with canine prostatic acid phosphatase was far more pronounced.

Molecular cloning of cDNA for human prostatic acid phosphatase

A human liver cDNA library in lambda gt11 was screened with polyclonal antiserum to human acid phosphatase isoenzyme 2a/4. About eleven positive clones have been obtained. Two clones, lambda Hap21 and lambda Hap22 were further characterized: clone lambda Hap21 contained a 0.8-kb cDNA insert and clone lambda Hap22 a 1.8-2.0-kb insert. XbaI digestion of lambda Hap22 generated two fragments of 1.0 and 0.9 kb. BglII digestion resulted in a 1.2-kb fragment and several smaller fragments of undetermined size. Clone lambda Hap22 contained all the genes carried by lambda gt11(lac5cI857nin5Sam100) and the 2-kb insert. An Escherichia coli(lambda Hap22) lysogen was generated, and its acid phosphatase activity was approximately ten-fold higher than that in the control nonlysogenic lysate. Western-blot analysis of total proteins present in this E. coli(lambda Hap22) lysate revealed that the non-induced lambda Hap22 prophage directed the synthesis of an approx. 175-kDa protein. This protein was recognized by antibody to the human acid phosphatase isoenzyme 2a/4 and anti-beta-galactosidase and was produced only upon induction with IPTG. These results indicated that lambda Hap22 carried a major portion of the gene coding for the human acid phosphatase isoenzyme 2a and/or 4 and this protein fragment of acid phosphatase was sufficient to manifest enzymatic activity.

Immunoultrastructural demonstration of prostatic acid phosphatase isoenzyme 2 in prostatic carcinoma

Human prostatic acid phosphatase isoenzyme 2 (HPAcP-2) was isolated from semen. This purified enzyme was immunized to rabbit to produce polyclonal antibodies. The specificity of the antibodies was tested by Western blot transfer method. Rabbit IgG-peroxidase conjugate was prepared from the antiserum and used to localize HPAcP-2 in prostatic carcinoma. It was found that in the tumor glandular acinus the normal basal cells were replaced by tumor cells containing reaction product. In the tumor cells, the reaction product was seen in the cisternae of rough endoplasmic reticulum (ER) and Golgi apparatus. The secretory vesicles which contained reaction product-stained granules and some amorphous material were seen to fuse with the apical plasma membrane and discharged their content into the glandular lumen. On the other hand, some secretory vesicles in the tumor cells facing to the basement membrane also discharged their similar content into the extracellular spaces. Reaction product-stained granules were found in the interstitial spaces surrounding the tumor cells. These findings suggest that HPAcP-2 is synthesized on the bound ribosomes and discharged into the cisternae of rough ER. The molecules are transported to the Golgi cisternae. After concentration and packaging, HPAcP-2 molecules are then transferred to the secretory vesicles, and discharged into the glandular lumen and to the extracellular spaces. The isoenzyme released in the extracellular space may reach the blood stream through the interstitial spaces or the lymphatic system, resulting in the elevation of serum HPAcPase level in some prostatic cancer patients.

Monoclonal antibody specific to acid phosphatase isoenzyme 4

Prostatic acid phosphatase isoenzyme 4 was purified by ion exchange column chromatography, followed by high pressure liquid chromatography. The highly purified enzyme was used to produce monoclonal antibody from immunized BALB/c mice. The antibody was specific to isoenzyme 4, with negligible affinity to isoenzyme 2. The specificity of the monoclonal antibody was evaluated by Western blot analysis and by inhibition of radioimmunoassay. Immunohistochemistry method using the antibody to isoenzyme 2 showed heavy staining on the cell surface in contrast to the even staining throughout the cytoplasm when monoclonal anti-isoenzyme 4 was used. These results reflect the secretory nature of isoenzyme 2 and the non-secretory nature of isoenzyme 4.