Jerzy Pałka

Prolidase activity in fibroblasts is regulated by interaction of extracellular matrix with cell surface integrin receptors.

Prolidase (EC 3.4.13.9) is a ubiquitously distributed imidodipeptidase that catalyzes the hydrolysis of C‐terminal proline or hydroxyproline containing dipeptides. The enzyme plays an important role in the recycling of proline for collagen synthesis and cell growth. An increase in enzyme activity is correlated with increased rates of collagen turnover indicative of extracellular matrix (ECM) remodeling, but the mechanism linking prolidase activity and ECM is poorly understood. Thus, the effect of ECM‐cell interaction on intracellular prolidase activity is of special interest. In cultured human skin fibroblasts, the interaction with ECM and, more specifically, type I collagen mediated by the β1 integrin receptor regulates cellular prolidase activity. Supporting evidence comes from the following observations: 1) in sparse cells with a low amount of ECM collagen or in confluent cells in which ECM collagen was removed by collagenase (but not by trypsin or elastase) treatment, prolidase activity was decreased; 2) this effect was reversed by the addition of type I collagen or β1 integrin antibody (agonist for β1 integrin receptor); 3) sparse cells (with typically low prolidase activity) showed increased prolidase activity when grown on plates coated with type I collagen or on type IV collagen and laminin, constituents of basement membrane; 4) the relative differences in prolidase activity due to collagenase treatment and subsequent recovery of the activity by β1 integrin antibody or type I collagen treatment were accompanied by parallel differences in the amount of the enzyme protein recovered from these cells, as shown by Western immunoblot analysis. Thus, we conclude that prolidase activity responded to ECM metabolism (tissue remodeling) through signals mediated by the integrin receptor. J. Cell. Biochem. 67:166–175, 1997. Published 1997 Wiley‐Liss, Inc.

Prolidase-dependent regulation of collagen biosynthesis.

Prolidase [EC.3.4.13.9] is a cytosolic imidodipeptidase, which specifically splits imidodipeptides with C-terminal proline or hydroxyproline. The enzyme plays an important role in the recycling of proline from imidodipeptides (mostly derived from degradation products of collagen) for resynthesis of collagen and other proline-containing proteins. The enzyme activity is up-regulated by β1-integrin receptor stimulation. The increase in the enzyme activity is due to its phosphorylation on serine/threonine residues. Collagen is not only structural component of extracellular matrix. It has been recognized as a ligand for integrin receptors, which play an important role in signaling that regulate ion transport, lipid metabolism, kinase activation and gene expression. Therefore, changes in the quantity, structure and distribution of collagens in tissues may affect cell signaling, metabolism and function. Several line of evidence suggests that prolidase activity may be a step-limiting factor in the regulation of collagen biosynthesis. It has been shown in different physiologic and pathologic conditions. It is of great importance during wound healing, inflammation, aging, tissue fibrosis and possibly skeletal abnormalities seen in Osteogenesis Imperfecta. The mechanism of prolidase-dependent regulation of collagen biosynthesis was found at both transcriptional and post-transcriptional levels. In this study, we provide evidence for prolidase-dependent transcriptional regulation of collagen biosynthesis. The mechanism was found at the level of NF-kB, known inhibitor of type I collagen gene expression. Modulation of integrin-dependent signaling by stimulatory (i.e. thrombin) or inhibitory (i.e. echistatin) β1-integrin ligands or by nitric oxide donors (i.e. DETA/NO) affect prolidase at post-transcriptional level. All those factors may represent novel approach to pharmacotherapy of connective tissue disorders.

Serum and tissue level of insulin‐like growth factor‐I (IGF‐I) and IGF‐I binding proteins as an index of pancreatitis and pancreatic cancer

Previously we have found deregulation of collagen metabolism in human pancreatitis and pancreatic cancer tissues. Insulin‐like growth factor‐I (IGF‐I) is known to stimulate collagen biosynthesis through interaction with IGF‐I receptor. IGF‐I binding proteins (BPs) regulate the activity of IGF‐I. We investigated whether serum and tissue IGF‐I and IGF‐BPs as well as tissue IGF‐I receptor expression may reflect disturbances of collagen metabolism in patients with pancreatitis and pancreatic cancer. In pancreatitis tissue, a significant increase in IGF‐I and IGFBP‐3 content was accompanied by a distinct increase in IGF‐I receptor expression, compared to control pancreas tissue. In contrast, serum from patients with pancreatitis did not show significant increases in IGF‐I and IGFBP‐3 levels, however, significant increases in IGFBP‐1 level (2.5 fold). Moreover, a distinct decrease in radioactive IGF‐binding to the BPs, compared to control serum, was found. Pancreatic cancer tissue and serum of patients with pancreatic cancer showed significant increases in IGF‐I, IGFBP‐3 and IGFBP‐1 content, accompanied by dramatic increases in IGF‐I tissue receptor expression, compared to controls. In serum of patients with pancreatic cancer distinct increases in radioactive IGF‐binding to 46 kDa BP, compared to control serum, were observed. The data suggest that disturbances in tissue collagen metabolism during pancreatic diseases may result from deregulation of IGF‐I homeostasis and that elevated serum levels of IGF‐I, IGFBP‐3 and IGFBP‐1 may serve as markers of pancreatic cancer.

Enhanced prolidase activity and decreased collagen content in breast cancer tissue

Adherent interactions between integrins and extracellular matrix (ECM) proteins play an important role in tumorigenicity and invasiveness. The major component of ECM is collagen that plays a central role in the interaction with integrins. The expression of certain collagenases (gelatinases) by tumour cells is one of the characteristic features of the so‐called metastatic phenotype, presumably by breaking down ECM barriers as well by altering the ECM–cell interaction. Although extracellular collagenases initiate the breakdown of collagen, the final step of collagen degradation is catalysed by intracellular prolidase. Collagen deposition, gelatinolytic and prolidase activities, expression of β1‐integrin receptor and their possible relationships were studied in seven operable breast cancer cases. In breast cancer tissue, we have found significant decrease in the amount of collagen. The decrease in collagen deposition in breast cancer tissue was accompanied by increase in the tissue gelatinolytic and prolidase activities. Simultaneously, a slight decrease in the expression of β1‐integrin receptor in breast cancer tissue was observed. These results suggest that alteration in collagen metabolism in breast cancer tissue may reflect tissue remodelling, characteristic for invasive phenotype of cancer cells. Increased gelatinolytic and prolidase activities in breast cancer tissue may enhance stromal matrix degradation and thus may promote metastatic dissemination. On the basis of the data, it seems that compounds endowed with gelatinolytic and prolidase inhibitory activities may be considered as a potential drug candidates for breast cancer therapy.

Inhibition of collagen and DNA biosynthesis by a novel amidine analogue of chlorambucil is accompanied by deregulation of β1-integrin and IGF-I receptor signaling in MDA-MB 231 cells

A novel amidine analogue of chlorambucil N-(2-(4-(4-bis(2-chloroethyl)aminophenyl)butyryl)aminoethyl)-5-(4-amidinophenyl)-2-furanecarboxamide hydrochloride (AB(1)), and the parent drug were compared for their effects on collagen and DNA synthesis in breast cancer MDA-MB 231 cells. IC(50) values for chlorambucil and its amidine analogue for collagen synthesis were found to be about 44 and 19μM, respectively. Increased ability of AB(1) to suppress the protein synthesis, compared to chlorambucil, was found to be related to an inhibition of prolidase activity and expression. The phenomena were probably a result of disruption of β(1)-integrin and the insulin-like growth factor-I (IGF-I) receptor mediated signaling caused by this compound. Expression of β(1)-integrin receptor, as well as focal adhesion kinase pp125(FAK) (FAK), growth-factor receptor-bound protein 2 (GRB2), son of sevenless protein 1 (Sos1) and phosphorylated mitogen activated protein kinases (MAPK), extracellular-signal-regulated kinase 1 (ERK(1)) and kinase 2 (ERK(2)) but not Src and Shc proteins was significantly decreased in cells incubated for 24h with 10μM AB(1), compared to controls. Chlorambucil in the same conditions did not evoke any changes in expression of all these signaling proteins, as shown by Western immunoblot analysis. In addition, AB(1) revealed a higher antiproliferative activity than chlorambucil, accompanied by a stronger down-regulation of IGF-I receptor expression. The results were confirmed by [(3)H]thymidine incorporation assay. Incubation of the cells with 10μM AB(1) for 12 and 24h contributed to a decrease in DNA synthesis by about 33 and 46% of the control values, respectively, while in case of chlorambucil by about 23 and 29%, respectively. These data suggest that the amidine analogue of chlorambucil (AB(1)) disturbs MDA-MB 231 cell metabolism more potently than does the parent drug, chlorambucil. The mechanism of this phenomenon may be due to its stronger suppression of β(1)-integrin and IGF-I receptor signaling.

Collagen metabolism disturbances are accompanied by an increase in prolidase activity in lung carcinoma planoepitheliale

One of the consequences of neoplastic transformation is deregulation of tissue collagen metabolism. Although metalloproteinases initiate the breakdown of collagen in lung carcinoma, the final step of collagen degradation is mediated by prolidase (E.C.3.4.13.9). We investigated whether prolidase activity could reflect disturbances of collagen metabolism in human lung carcinoma planoepitheliale (Ca pl.). Ten human lung Ca pl. and 10 samples of normal lung parenchyma were compared with respect to prolidase activity and expression (western immunoblot), the content of collagen and collagen degradation products (free and bound hydroxyproline determination), β1 integrin subunit expression (western immunoblot) and collagenolytic activity (zymography). An increase in collagen content (66%, P < 0.05), free proline pool (50%, P < 0.05) and collagenolytic activity was accompanied by a significant increase in the prolidase activity (106%, P < 0.05) and its expression in Ca pl. No differences were found between Ca pl. and the control lung tissue with respect to β1 integrin expression. Prolidase activity may reflect disturbances in tissue collagen metabolism in lung Ca pl. and it may, therefore, serve as a sensitive marker of the disease.

Fibroblast chemotaxis and prolidase activity modulation by insulin-like growth factor II and mannose 6-phosphate.

Chemotactic locomotion of fibroblasts requires extensive degradation of extracellular matrix components. The degradation is provided by a variety of proteases, including lysosomal enzymes. The process is regulated by cytokines. The present study shows that mannose 6-phosphate and insulin-like growth factor II (IGF-II) enhance fibroblast chemotaxis toward platelet-derived growth factor (PDGF). It is suggested that lysosomal enzymes (bearing mannose 6-phosphate molecules) are involved in chemotactic activity of the cells. The suggestion is supported by the observation that a-mannosidase and cathepsin D inhibitor - pepstatin are very potent inhibitors of fibroblast chemotaxis. Simultaneously, mannose 6-phosphate stimulates extracellular collagen degradation. The final step in collagen degradation is catalyzed by the cytosolic enzyme - prolidase. It has been found that mannose 6-phosphate stimulates also fibroblast prolidase activity with a concomitant increase in lysosomal enzymes activity. The present study demonstrates that the prolidase activity in fibroblasts may reflect the chemotactic activity of the cells and suggests that the mechanism of cell locomotion may involve lysosomal enzyme targeting, probably through IGF-II/mannose 6-phosphate receptor.

The potential mechanism for glutamine-induced collagen biosynthesis in cultured human skin fibroblasts.

Although glutamine (Gln) is known as an important stimulator of collagen biosynthesis in collagen-producing cells, the mechanism and endpoints by which it regulate the process remain largely unknown. Intermediates of Gln interconversion: glutamate (Glu) and pyrroline-5-carboxylate (P5C) stimulate collagen biosynthesis in cultured cells but evoke different maxima of collagen biosynthesis stimulating activity at different times of incubation. P5C was found to be the most potent stimulator of collagen biosynthesis after 6 h of incubation (approx. three-fold increase); after 12 h, it induced increase in collagen biosynthesis to 260%, while at 24 h, the process was decreased to approximately 80% of control values. Glu induced increase in collagen biosynthesis to approximately 180%, 400% and 120% of control values, after 6, 12 and 24 h, respectively, suggesting that after 12 h of incubation, Glu was the most potent stimulator of collagen biosynthesis. Glu was also the most potent stimulator of type I procollagen expression at this time. After 6, 12 and 24 h incubation, Gln induced collagen biosynthesis to approximately 112, 115 and 230% of control values, respectively. Since prolidase is known to be involved in collagen metabolism, the enzyme activity assay was performed in fibroblasts cultured in the presence of Gln, Glu and P5C. While Gln and Glu required 24 h for maximal stimulation of prolidase activity, P5C induced it after 6-12 h. The data suggest that P5C induced collagen biosynthesis and prolidase activity in a shorter time than Gln and Glu. We considered that P5C directly stimulates the processes, while Gln acts through its intermediate-P5C. Reduction of P5C to proline is coupled to the conversion of glucose-6-phosphate (G6P) to 6-phospho-gluconate, catalyzed by G6P dehydrogenase. We have found that dehydroepiandrosterone (DHEA), a potent inhibitor of G6P dehydrogenase, inhibited a stimulatory effect of P5C on collagen synthesis, expression of type I collagen and prolidase activity. Our results postulate a potential mechanism of glutamine-induced collagen biosynthesis through its intermediate - P5C. P5C-dependent activation of nucleotide biosynthesis, prolidase activity and P5C conversion into proline may contribute to the stimulation of collagen biosynthesis.

Insulin-like growth factor I-dependent regulation of prolidase activity in cultured human skin fibroblasts

Prolidase [E.C.3.4.13.9] is a cytosolic exopeptidase that catalyses the hydrolysis of C-terminal proline containing dipeptides or tripeptides. The enzyme plays an important role in the recycling of proline for collagen synthesis. Increase in enzyme activity is correlated with increased rates of collagen turnover but the mechanism and endpoints by which this enzyme is regulated remain largely unknown. We have found that insulin-like growth factor-I (IGF-I), potent stimulator of collagen biosynthesis, induces prolidase activity in cultured human skin fibroblasts. Supporting evidence comes from the following observations: (1) Serum of fasted rats, (IGF-I, 72 ± 16 ng/ml) showed about 50% reduced ability to stimulate prolidase activity and collagen biosynthesis in confluent fibroblasts in comparison to the effect of control rat serum (IGF-I, 168 ± 29). (2) An addition of IGF-I (100 ng/ml) to fasted rat serum restored its ability to stimulate prolidase activity and collagen biosynthesis to control values. (3) In confluent human skin fibroblasts, cultured for 48 h with serum free medium prolidase activity was decreased to 50% of control cells, cultured in the presence of normal rat serum. Supplementation of serum free medium with EGF, PDGF and IGF-I (factors that can replace growth promoting activity of serum) stimulated prolidase activity to control values while the medium deprived IGF-I had no such effect. (4) The relative differences in prolidase activity due to specific treatment of confluent cells with above growth factors were accompanied by parallel differences in the amount of the enzyme protein recovered from these cells as shown by western immunoblot analysis. Thus we conclude that prolidase activity is regulated by IGF-I in confluent fibroblasts.

Estrogenic and antiestrogenic effects of raloxifene on collagen metabolism in breast cancer MCF-7 cells

We compared the effects of different concentrations of raloxifene (1 ,4 and 10 μM) on collagen biosynthesis ,gelatinolytic and prolidase activities and matrix metalloproteinase (MMP) expression (MMP-2 and MMP-9) in estradiol-stimulated (2 nM) breast cancer MCF-7 cells. Raloxifene inhibited in a dose-dependent manner the proliferation of MCF-7 cells ,independently of the presence or absence of estradiol in the growth medium. Raloxifene at concentrations of 1 μM and 4 μM inhibited collagen biosynthesis by about 10-fold and prolidase activity by about 50% ,while at a concentration of 10 μM it inhibited these processes by only about 25%. This phenomenon was accompanied by differences in gelatinolytic activity and MMP (MMP-2 and MMP-9) expression as demonstrated by zymography and Western immunoblot analysis, respectively. In estrogenstimulated MCF-7 cells ,cultured in the presence of 1 μM raloxifene ,a dramatic increase in the activity of both collagenases was found. In contrast ,addition of raloxifene at a concentration of 10 μM to the medium of the cells resulted in restoration of gelatinolytic activity to that found in control cells. Similarly ,but at both doses (1 and 10 μM) ,raloxifene was able to reduce MMP-2 expression in the cells. However ,when used alone (without estradiol) a concentration of 1 μM raloxifene strongly stimulated MMP-2 expression ,while at a concentration of 10 μM the effect was not observed. In the case of MMP-9 ,only trace amounts of this gelatinase were detected ,although in contrast to MMP-2 ,an increase in its expression was noticed at a concentration of 10 μM raloxifene. The data raise the possibility that in estrogen-stimulated MCF-7 cells ,raloxifene at low concentrations (1 and 4 μM) evokes antiestrogenic effect on collagen biosynthesis and prolidase activity on the one hand ,and an estrogenic effect on gelatinolytic activity on the other ,while at higher concentrations (about 10 μM) it evokes an estrogenic effect on collagen biosynthesis and prolidase activity, and an antiestrogenic effect on gelatinolytic activity. Our data suggest that the effects of raloxifene on collagen synthesis ,prolidase and metalloproteinase activities in breast cancer may explain its role in the prevention of breast cancer development.