Plasminogen activator in prostatic tumors of Nb rats

Altered expression of extracellular matrix and proteinases in Noble rat prostate gland after long-term treatment with sex steroids

BACKGROUND

Interactions between the epithelial cells and stromal tissues, which include the epithelial basement membrane, extracellular matrix, inducible factors, and various cell types, are believed to play a significant role in prostate gland carcinogenesis. Remodeling of extracellular matrix and degradation of basement membrane are the prerequisites for tumor cell invasion, and these changes are correlated with the expression of various proteinases.

METHODS

The present study examined the alterations of epithelial basement membrane, extracellular matrix, and proteinase activities in the Noble rat prostate gland after long-term treatments with androgen and estrogen (T+DES or T+E(2) for 4-12 months) by histochemistry, immunohistochemistry, electron microscopy, and gelatin-gel zymography.

RESULTS

After hormonal treatments, defects of epithelial basement membranes, such as focal disruption, diffuse staining and multilayering, were observed by histochemistry and immunohistochemistry in the dysplastic and neoplastic lesions induced in the lateral (LP) and ventral prostates (VP) but not in dorsal prostate (DP). An increase in the amount of extracellular matrix components, including hyaluronan (HA), chondroitin sulfate proteoglycan (CSPG) and tenascin, in the stroma of hormone-treated LP and VP was revealed by histochemistry and immunohistochemistry. Positive immunolabeling of matrix metalloproteinases 2 (MMP-2) and 9 (MMP-9) was detected in the fibromuscular layer surrounding the adenoma and adenocarcinoma induced in LP and VP after treatments with steroids for over 9-12 months. Zymography also detected an increase in activities of proteinases of apparent MW 120, 90, 86 and 68 kDa in the hormone-treated LP and VP, and these proteinases were characterized as metalloproteinases. In addition, two serine proteinases of MW 100 and 30 kDa were identified as being overexpressed in the hormone-treated LP and VP. Compared to LP and VP, there was no significant change in the proteinase activities in the hormone-treated DP.

CONCLUSIONS

The present study demonstrated that the epithelial basement membrane and stromal extracellular matrix were altered in dysplastic and neoplastic Noble rat prostates. Since HA and CSPG (or their complexes) are highly anionic molecules, their increased accumulation in the altered prostatic stroma would tend to hydrate this tissue. This would create an environment more favorable for tumor growth and invasion. These morphological changes were also correlated with the concurrent increase in gelatinolytic proteinase activities induced in these prostates. The results suggest that the remodeling of the stromal tissue might play a role in the early stage of prostate carcinogenesis as shown in the Noble rat model.

Density dependent polarized secretion of a prostatic epithelial cell line

The polarized secretions (apical/basal) of newly synthesized total protein and proteases from prostatic epithelial sheets of PA-III cells grown in dual compartment chambers were investigated at various cell densities and culture conditions. PA-III cells grown in a serum free defined medium (SFDM) form morphologically polarized monolayers of epithelial cells. These cells secreted their 35S-methionine labeled total protein in a predominantly apical direction (apical/basal ratio, 4-8 fold), with a lesser proportion of protein secreted apically at lower cell densities of the PA-III cell monolayer. PA-III cells grown in 5% fetal calf serum (FCS) are morphologically squamous, comparable to the anaplastic phenotype, and exhibited an inversion of polarized total protein secretion (apical/basal ratio, 0.4-0.9 fold), with an increased proportion of total protein secreted in a basal direction at lower cell densities. Since the culture of PA-III cells in FCS may approximate the anaplastic phenotype we investigated the polarized secretion of proteases from these cells at various cell densities, and compared them with the secretory pattern of protease secretion from polarized PA-III cells cultured in SFDM. At lower cell densities of the PA-III cells grown in FCS the polarity of protease secretion was inverted such that metalloproteinases, tissue type plasminogen activator, and a 72 kD gelatinase were secreted in a predominantly basal direction, as well as urokinase and a gelatinase of 26 kD that were secreted more or less equally into the apical and basal compartments of the chambers. On the other hand, for cultures of PA-III cells grown in SFDM the aforementioned proteases exhibited predominantly an apically directed polarity of secretion. These results suggest that the anaplastic phenotype characterized by a loss of polarized structure may also be characterized by a functional loss or inversion of polarized secretion. The consequences of such a loss or inversion of polarized secretion would be to increase the localized concentrations of proteases along the basal domain of cells thereby facilitating degradation of the basement membrane and interstitial tissue in vivo.

Characterization of gelatin-degrading metalloproteinase activities of the Dunning rat prostate tumor grown in nude mice

Proteinase activities in the Dunning R-3327 prostatic tumor grown in nude mice and the dorsal lobe of the normal Copenhagen rat prostate were characterized using gelatin-containing SDS-polyacrylamide gel electrophoresis. Calcium-stimulated activities of approximately 33, 42, 64, 71, 76, 85, 98, 115, and 120 Kd as well as a 91 Kd calcium-independent proteinase were detected in the tumor, whereas the dorsal prostate showed calcium-dependent activities of approximately 62 and 80 Kd and a calcium-independent activity much greater than 120 Kd. The zymographic calcium-dependent proteinase patterns in the other rat prostatic lobes (a 62 Kd proteinase in the anterior lobe; 59, 62, and 67 Kd forms in the ventral lobe; and 52, 62, and 72 Kd activities in the lateral lobe) were distinctive from that of the tumor and of the dorsal lobe. The calcium-dependent and -independent proteinases of the tumor were active over a broad range of pH values with optimal activity near pH 8.0-8.4. The calcium-dependent activities were inhibited by EDTA and EGTA. Barium and strontium could partially substitute for calcium. The calcium-independent activities were not affected by these chelators nor by the proteinase inhibitors benzamidine, epsilon-aminocaproic acid, tranexamic acid, hydrocinnamic acid, or iodoacetate. Similarly, the metalloproteinase activities were not affected by the latter inhibitors. There was little change in the predominant molecular forms (64, 71, and 76 Kd) of proteinase following castration of tumor-bearing nude mice; however, the 98 Kd calcium-dependent activity decreased and the 91 Kd calcium-independent activity increased as a result of this treatment.

Plasminogen activator activities in the ventral and dorsolateral prostatic lobes of aging Fischer 344 rats

Plasminogen activator (PA) activities were measured in extracts of ventral and dorsolateral prostate lobes in Fischer 344 (F344) rats of different ages. Ventral prostates of 30-month-old animals demonstrated widespread epithelial atrophy, some foci of inflammation, intraglandular atypical hyperplasia and/or adenocarcinoma, and a marked increase in PA activities compared with younger animals. Both low- and high-molecular-weight forms of activator were found in zymograms and both forms of activator showed an increase at 30 months. However, the PA activity of the aged rats showed a greater resistance to amiloride inhibition, suggesting a greater relative increase in the tissue-type activator activity than that of urokinase. These changes were not observed in the dorsolateral prostate. The lobe-specific changes in activator activity appear related to dysplasia/neoplasia and not aging.

Increased activity of plasminogen activators during involution of the rat ventral prostate

Plasminogen activator was measured in the ventral prostates of non-castrated, castrated, and androgen-treated rats to determine whether changes in this activity correlated with the process of glandular involution. While the activity was very low in cytosolic extracts from the prostates of non-castrated rats, 2 days following castration the plasminogen activator activity increased in a near-linear fashion such that by day 7 it was 10-fold higher in terms of specific activity (per mg of protein) and cellular concentration (per mg of DNA). During this interval there was a rapid decrease in the cell population of the prostates. Treatment of the 7-day castrated rats with the potent androgen, dihydrotestosterone, both reduced the plasminogen activator activity and restored the cell number in a dose-related manner. Gel electrophoretic analysis revealed two major bands of plasminogen activator activity in the cytosolic extracts from 4- and 7-day castrated rats, plus additional minor bands in samples from 10- and 14-day castrated rats. Approx. 10% of the cellular concentration of plasminogen activator activity was recovered in association with an 18000g pellet fraction from the prostates; this fraction showed less heterogeneity of the plasminogen activator forms as observed by gel electrophoresis. Inhibitor studies indicated that the 18000g pellet fraction from the prostates of non-castrated rats possessed some plasminogen activator inhibitor activity, but the relative concentration of the inhibitor activity was small. We conclude that the involution of the prostate is probably associated with increased synthesis of plasminogen activators through a de-repression process which may involve loss of androgen receptors.

Plasminogen activator activity in human prostate and breast tumors: relationship to steroid receptors

Using a fluorometric assay based on the activation of human plasminogen, plasminogen activator (PA) activity was measured in cytosolic and lysosomal extracts prepared from normal, benign hyperplastic (BPH), and carcinomatous human prostates. In all three types of prostatic tissue, the lysosomal extracts had much higher concentrations of PA activity than did the cytosolic extracts. The mean PA activity in lysosomal extracts of the carcinomatous prostates was 170% and 85% higher than that measured in normal and BPH prostates, respectively (Student's t-test, p less than .05). With prostatic carcinoma and BPH specimens there was an inverse (negative) relationship between lysosomal PA activity and the nuclear concentration of androgen-receptors (correlation coefficient, -0.84). By comparison in specimens of human breast tumors, there were weakly positive correlations between PA activity and either estrogen (ER) or progestin (PR) receptors (correlation coefficients of + 0.23 and + 0.54, respectively). While as a group ER+, PR+ breast tumors had higher PA activity that ER+, PR- or ER-, PR- tumors, the differences were not statistically significant (Student's t-test, p greater than .05). Thus in breast tumors, it is uncertain whether high levels of PA activity are indicative of hormonal dependence. However, our findings with prostatic tumors infer that in contrast, high concentrations of this enzyme may reflect a malignant phenotype characterized by a decrease in both androgen responsiveness and differentiation.