Isoenzymes of human prostate acid phosphatase

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.

Homodimer and heterodimer subunits of human prostate acid phosphatase

Human prostatic acid phosphatase (PAP) isoenzymes, designated PAP-A and PAP-B, were isolated from human seminal plasma by sequential affinity chromatography on concanavalin A and L(+)-tartrate, a classic inhibitor of PAP. Both the major PAP-A and the minor PAP-B isoenzymes exhibited a similar molecular mass (100 and 105 kDa respectively), multiple pI values (5.05-5.35 and 5.05-5.12), and substrate and inhibitor specificity. Immunological characterization revealed that PAP-B possesses distinct antigenic determinants, in addition to the common sites shared with PAP-A. SDS/PAGE indicated that both isoenzymes are composed of two subunits of 50 kDa each. At high salt concentration, PAP-B dissociated completely into single subunits of 50 kDa, whereas PAP-A remained intact at 100 kDa. PAP-B was resolved by reverse-phase h.p.l.c. into three components, designated alpha, beta and gamma, each of 50 kDa, at a molar ratio of approx. 2:1:1. PAP-A contained a single component of molecular mass 50 kDa. The single component of PAP-A and the alpha component of PAP-B possessed identical amino acid compositions and N-terminal sequences, which were different from those of the beta and gamma components. These results indicate that human PAP contains three isoforms, alpha 2, alpha beta and alpha gamma. PAP-A, the major isoenzyme, is a homodimer consisting of two identical subunits (alpha 2), and PAP-B, the minor isoenzyme, is a mixture of two heterodimers, consisting of non-identical subunits (alpha beta and alpha gamma).

Grossly elevated serum prostatic acid phosphatase in a patient with carcinoid

We report a case of carcinoid, diagnosed histochemically and biochemically, which was associated with grossly elevated serum prostatic acid phosphatase and normal serum prostate specific antigen.

Radioimmunoscintigraphy of prostate cancer

The development of hybridoma technology has increased research efforts and clinical applications in the area of radioimmunodetection. Despite the many investigative antibodies directed against prostatic tissue or prostate cancer cell lines, only two have been tested in clinical trials. A 111In-labeled antibody directed against prostate-specific antigen, the best available serum tumor marker for prostate cancer, has shown poor sensitivity in limited clinical radioimmunoimaging trials. Monoclonal antibodies against prostatic acid phosphatase have shown better imaging results, particularly at higher antibody doses (greater than or equal to 40 mg). The limitations of this antibody include the poor results in detecting soft tissue lesions, including the primary lesion; the development of human antimouse antibodies in 50% of the patients at doses greater than or equal to 40 mg; the expense of the antibody; and the fact that better results are currently attainable by other less expensive imaging modalities. If and when a more suitable antibody or fragment is developed, the prospect of improved staging and new treatments using immunologic conjugates carrying therapeutic agents may become realities. Until such time, prostatic cancer will be staged with other currently available imaging modalities and conventional therapies with their limitations will remain state of the art.

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.

Genes for tumor markers are clustered with cellular proto-oncogenes on human chromosomes

We have analyzed the relative mapping positions of genes for polypeptides expressed abnormally in tumors (tumor markers) and cellular proto-oncogenes and find a remarkable degree of co-mapping of tumor marker genes with oncogenes in the human karyotype. We propose that aberrant expression of marker genes in tumors may be related to their proximity in the human genome to oncogenes expressed during the development of malignancy, and we suggest ways to test this hypothesis of concerted abnormal gene expression in mammalian tumor cells.

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.

Immunoelectron microscopic demonstration of prostatic acid phosphatase in human hyperplastic prostate

Immunoelectron microscopic studies were done on prostatic tissues obtained from patients with benign hyperplasia. Rabbit IgG-peroxidase conjugate against purified human prostatic acid phosphatase band 2 (HPAP-2) was used for studies. Under the light microscope, the columnar secretory epithelia of prostatic glands showed different intensity and distribution of immunostaining whereas the basal cells were unstained. Under the electron microscope, the secretory epithelial cells often showed electron-dense reaction product in the Golgi apparatus and secretory vesicles and vacuoles, and only sparingly in the cisternae of nuclear envelope and rough ER. Sometimes, fusion of secretory vacuolar membrane and plasma membrane and discharge of the vacuolar contents into the extracellular space were noted. The surfaces of microvilli at the apical portion of the columnar epithelia and the lumen of the glandular acini always showed reaction product. These findings suggest that HPAP-2 may be synthesized in the rough ER and transported to the Golgi apparatus where it is concentrated and transferred to the secretory vesicles and vacuoles. HPAP-2 is finally discharged into the extracellular spaces through exocytosis, a secretory mechanism similar to that of other secretory proteins.

Distribution of prostatic acid phosphatase isoenzymes in normal and cancerous states

We have studied the IEF (isoelectric focusing) profiles and the sedimentation characteristics of intracellular and secretory prostatic acid phosphatase (PAP) in normal and cancerous states. IEF studies show a similar relative distribution of tartrate inhibitable pI 4.9 (approximately 80%) and 5.6 (approximately 20%) forms of this enzyme in normal as well as cancerous prostate. The same IEF profile is obtained regardless of whether an enzymatic or RIA method is utilized for detection of PAP. Of these two isoenzymes, only the form of pI 4.9 predominates in prostatic and seminal fluids and in Stage IV serum. Sedimentation analysis shows that the purified enzyme is exceptionally stable since it retains an S020,w value of 5.7 at low concentrations (ng/ml). While only the 5.7S form is observed in normal and cancerous tissues as well as in prostatic fluid, analysis of Stage IV serum reveals an additional form at 8.7S. Control experiments suggest that the 8.7S form is not induced by non-specific association with normal serum proteins or by the inhibitor tartrate. Our results suggest that: (a) of the two major isoenzymes in tissue, only the pI 4.9 isoenzyme predominates in secretion, (b) this relationship of intracellular to secretory forms is unaltered in the transition from normal to cancerous tissue, and (c) the utility of PAP as a tumor marker is derived at least in part by the intrinsic stability of the 5.7S form. The significance of the 8.7S form is unknown at the present time, but it does not distort the clinical (RIA) measurement of PAP in serum.

Induction of acid phosphatase synthesis in canine prostatic epithelial cells in vitro

The increase in acid phosphatase (AP) activity in cultured canine prostatic epithelial cells was investigated as a biochemical marker of in vitro cellular differentiation. The enzyme was studied in secretory and non-secretory epithelial cell populations obtained from control and cycloheximide-treated cultures over a period of 3 weeks and compared to the AP present in tissue and cellular extracts from normal canine prostates. The progressive increase in AP activity with the duration of culture was strongly inhibited by cycloheximide in both cell populations. The degree of inhibition was more pronounced late in the culture when AP activity increased at a faster rate in secretory cells. Cycloheximide inhibited protein biosynthesis by 70-80% as evidenced by a reduction in the incorporation of amino acids into acid-insoluble material. However, the specific activities of AP in the cellular extracts were similar in control and cycloheximide-treated cultures and increased sharply by 3-4-fold in the secretory cells after 12 days of culture. When extracts derived from control and cycloheximide-treated cells of various duration were submitted to electrophoresis in polyacrylamide gels (PAGE), a unique pattern of three bands of AP activity with Rf values of 0.18, 0.27 and 0.38 was obtained. In controls the AP activity in the band with an Rf of 0.18 increased preferentially during the culture period and was more important quantitatively in secretory cells. In cycloheximide-treated cultures the increase of AP activity associated with the band with an Rf of 0.18 was more strongly inhibited. The addition of tartrate to the staining mixture inhibited all three bands of AP activity. Similar results were obtained when extracts derived from freshly dispersed cells as well as from normal canine prostatic tissue were submitted to PAGE; the AP activity was resolved into 3 bands with Rf values of 0.15-0.18, 0.23-0.27 and 0.33-0.38; all three bands were inhibited by the addition of tartrate and the first band was predominant. Thus, the increase in AP activity in prostatic epithelial cells in a culture medium supplemented with serum and deprived of sex steroids is due to the de novo synthesis of a major form of the enzyme by the secretory cells.

Comparison of prostatic and nonprostatic acid phosphatase

Electrophoresis and ion-exchange column chromatography were used to separate the wide varieties of acid phosphatases with different biological and clinical significance. Band 0 was very strong in ascitic cells with many autophagic vacuoles, indicating a role in autophagic function. Band 1 was a membrane-bound acid phosphatase, seen mainly in the microsomal fraction. Band 3 was the major lysosomal acid phosphatase of all nonprostatic tissues. Bands 2 and 4 were antigenically identical to each other, and were observed in unusually high amounts in the prostate. The different electrophoretic mobility between bands 2 and 4 was due to their carbohydrate content. Band 5 was a characteristic enzyme of the osteoclast. The tartrate-sensitive enzymes included bands 0 through 4. Only band 5 was tartrate resistant. The tartrate-resistant acid phosphatase of erythrocytes was not detected by the electrophoresis method. Clinical applications were seen for both bands 2 and 5. Band 2 was a secretory enzyme, normally secreted into the seminal plasma. Band 2 was absorbed into the blood circulation in some prostatic cancer patients. A small amount of bands 2 and 4 was observed in nonprostatic tissues. The diagnostic value of band 2 resulted from its extremely high concentration in the prostate. Band 5 was not observed in the normal prostate. A high concentration of band 5 was observed in hairy cells, Gaucher cells, and osteoclasts. The serum level of band 5b was an indicator of osteoclastic activity in the bone. Elevation of band 5b in serum was observed in normal children during physiological bone growth, in Gaucher's disease, and in malignancies metastasized to bone.

Lysosomal isozyme patterns in ethylnitrosourea-induced brain tumors

Isozyme patterns for five acid hydrolases, acid phosphatase (AP), aryl-sulfate (AS), beta-glucuronidase (beta-Glu), N-acetylglucosaminidase (NAG) and beta-galactosidase (beta-Gal), were studied in isolated lysosomes from ethylnitrosourea (ENU)-induced gliomas and compared with normal and newborn rat brains. With polyacrylamide gel electrophoresis (PAGE), AP was separated into three bands, acidic (A), intermediate (B) and basic (C). In tumors and newborn brains there was a decrease in A and C but a significant increase in B. For NAG the acidic form was elevated by 9-19% in tumors, while newborn brains showed a 19% decrease. Even though the band intensities of beta-Glu in tumors and newborn brains were increased, the relative distribution remained similar to normal brain. With isoelectric focusing, five hydrolases were separated into four to five distinct forms. In ENU-induced gliomas the intensities of all peaks were considerably increased, but in most cases the number of isozymes remained the same. In tumors the isoelectric points were shifted towards the acidic side and smaller peaks in the basic regions merged into more acidic peaks. This effect was especially evident for AP and Gal. In the cases of AS, beta-Glu and NAG, consistently more activity was associated with acidic peaks than with the basic ones. Our data indicates that there is a significant increase in acidic forms of some of the lysosomal hydrolases studied in ENU-induced brain tumors.

Activity and isoenzymes of acid phosphatase in human B-cell lymphomas of low-grade malignancy: a novel aid in the classification of malignant lymphoma

Activity and isoelectric focusing (IEF) pattern of lysosomal acid phosphatase (E.C.3.1.3.2.) were investigated in 55 cases of low-grade malignant B-cell lymphoma, classified as chronic B-lymphocytic leukemia (B-CLL), centroblastic/centrocytic follicular lymphoma (CB/CC), lymphoplasmacytic/lymphoplasmacytoid lymphoma (Immunocytoma, IC), and plasmacytoma (PC), applying the criteria of the Kiel classification. The results show (1) that the four lymphoma types present a characteristic range of enzyme activity in an increasing order: B-CLL, BC/CC, IC, and PC. B lymphocytes, germinal center cells, and plasmacytes are the main constituents of these lymphomas. This sequence might reflect one possible mode of B-cell transformation into plasmacytes traversing an amplification stage in germinal centers under normal conditions. (2) All cases showed the basic IEF pattern of normal B lymphocytes with 12 bands localized in three regions between pH 6.1 and 3.9. This finding supports the B-cell origin and the close phenotypical relationship among the investigated lymphomas. (3) The IEF patterns of B-CLL and CB/CC did not differ from that of normal B lymphocytes, whereas two additional isoenzymes were encountered in cases of IC and seven in PC; this suggests that the higher enzyme activity of IC and PC is at least partly due to the appearance of "new" isoenzymes. The results support the validity of the underlying classification and indicate the individually, B-cell origin, and close relationship among the four lymphoma entities investigated.

Lysosomal acid phosphatase: activity and isoenzymes in separated normal human blood cells

The present study was devised to investigate the activity and isoenzymes of lysosomal acid phosphatase in individual normal human blood cells, including the T- and B-population of lymphocytes, with the aim to contribute to the classification of haematopoietic neoplasias on the basis of cell specific isoenzyme patterns. Platelets, erythrocytes, granulocytes, monocytes and T-lymphocytes were isolated from blood by gradient centrifugation or immune adsorption. B-lymphocytes were obtained from human tonsils. After purity control and isolation of lysosomes the concentration of acid phosphatase was assayed using the conventional spectrophotometric method. Isoenzymes were separated by isoelectric focusing on polyacrylamide thin layer slabs. Monocytes revealed the highest activity with 14 mU/10(7) cells, about three times more than granulocytes. T-lymphocytes showed an activity of 2.85 mU/10(7) cells and B-lymphocytes of 1.83 mU/10(7) CELLS. The lowest activity was found in platelets with 0.08 mU/10(7) cells. Granulocytes showed 12 isoenzyme bands, whilst the number for monocyte, B-lymphocytes, T-lymphocytes and platelets were respectively 11, 12, 1 and 4 isoenzyme bands. Thus it became evident that the different blood cell populations can be distinguished on the basis of their acid phosphatase isoenzyme pattern.