The relationship between surface protease activity and the rate of cell proliferation in normal and transformed cells

Hepatic and Extrahepatic Sources and Manifestations in Endoplasmic Reticulum Storage Diseases

Alpha-1-antitrypsin (AAT) and fibrinogen are secretory acute phase reactant proteins. Circulating AAT and fibrinogen are synthesized exclusively in the liver. Mutations in the encoding genes result in conformational abnormalities of the two molecules that aggregate within the rough endoplasmic reticulum (RER) instead of being regularly exported. That results in AAT-deficiency (AATD) and in hereditary hypofibrinogenemia with hepatic storage (HHHS). The association of plasma deficiency and liver storage identifies a new group of pathologies: endoplasmic reticulum storage disease (ERSD).

Evaluation of the proteolytic potential of in vitro-cultivated hybridoma and recombinant mammalian cells

The proteolytic potential of culture supernatants derived from recombinant baby hamster kidney (BHK) 21 and mouse-mouse hybridoma cells have been characterized. Several assays using enzyme specific chromogenic artificial peptides, as well as a radioactive test for the detection of the total activity, have been established and were adapted to the special conditions existing in culture media of mammalian cells. Proteolytic activity was detected in human serum albumin containing media which was specific for peptides ending with a terminal arginine. The addition of N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) buffer to the culture media resulted in a significant peptide cleavage potential, supporting the fact that this compound is not recommended as a supplement in animal cell culture media. Medium shock protease activity has been detected in culture supernatants of BHK cells when medium was changed completely, caused by a switch from a serum containing state of growth to a serum-free state of growth which is often used in processes with microcarriers. However, this proteolytic activity showed a transient behaviour whereby its secretion stopped when the cells had adapted to the serum-free medium conditions. Characterization of the proteolytic activities using different specific inhibitors and activators supported the assumption that the proteolytic activity reflects a cell specific composition of proteases which can also change dependent on the culture conditions used.

Alpha 1-antitrypsin as a biomarker in azoxymethane induced intestinal tumors in F344 rats

Alpha 1-antitrypsin (alpha 1AT) has been detected in several human tumors and is thought to be a marker of neoplastic change and progression. As the biology of azoxymethane (AOM) induced intestinal tumors in F344 rats has many characteristics of human intestinal tumors, we have investigated alpha 1AT expression in AOM induced rat intestinal tumors. Nine of 12 colonic carcinomas and 6/8 small intestinal carcinomas had alpha 1AT positive tumor cells. Only 1/11 colonic adenomas and 0/3 small intestinal adenomas contained alpha 1AT. Thus alpha 1AT is a marker of malignancy in this model. Inhibition of carcinogenesis by piroxicam and difluoromethyl ornithine inhibited alpha 1AT expression.

The effects of bestatin, a microbial aminopeptidase inhibitor, on epidermal growth factor-induced DNA synthesis and cell division in primary cultured hepatocytes of rats

We investigated the effects of microbial protease inhibitors, in particular the aminopeptidase inhibitor bestatin, on DNA synthesis and cell division induced by epidermal growth factor (EGF) in hepatocytes. Although bestatin did not significantly affect binding of EGF to hepatocytes, it inhibited EGF-induced DNA synthesis and cell division. DNA synthesis in rat hepatocytes was maximal 24-26 h after EGF addition to the medium. The time required for maximal DNA synthesis was not affected if bestatin was removed less than 12 h after addition, but synthesis was partially inhibited if bestatin was added to the medium several hours after EGF addition, depending on the time of bestatin addition. Our results suggest that bestatin arrests the new cell cycle induced by EGF at about 12 h after the initiation. Considering also our results obtained by employing other protease inhibitors, we concluded that specific proteases play important roles in hepatocyte DNA synthesis and cell division induced by EGF.

Proteinases and their inhibitors in cells and tissues

A large body of evidence has been assembled to indicate the substantial importance of proteolytic processes in various physiological functions. It has recently become clear too that endo-acting peptide bond hydrolases provisionally characterized and classified at present as serine, cysteine, aspartic and metallo together with unknown catalytic mechanism proteinases sometimes act in cascades. They are controlled by natural proteinase inhibitors present in cells and body fluids. In the first part of the present monograph the author was concerned to present an overview on the morphological and physiological approach to localization, surveying reaction principles and methods suitable for visualization of proteolytic enzymes and their natural and synthetic inhibitors. In the second part the roles played by proteinases have been summarized from the point of view of cell biology. The selection of earlier and recent data reviewed on the involvement of proteolysis in the behavior of individual cells reveals that enzymes, whether they be exogeneous or intrinsic, can be effective and sensitive modulators of cellular growth and morphology. There exists a close correlation between malignant growth and degradation of cells. It appears likely that as yet unknown or at least so far inadequately characterized factors that influence the survival or the death of cells may turn out to be proteinases. The causal role of extracellular proteolysis in cancer cell metastases, in stopping cancer cell growth and in cytolysis remains for further investigated. Ovulation, fertilization and implantation are basic biological functions in which proteolytic enzymes play a key role. The emergence of new approaches in reproductive biology and a growing factual basis will inevitably necessitate a reevaluation of present knowledge of proteolytic processes involved. The molecular aspects of intracellular protein catabolism have been discussed in terms of the inhibition of lysosomal and/or non-lysosomal protein breakdown. Peptide and protein hormone biosynthesis and inactivation are still at the centre of interest in cell biology, and a number of proteinases have been implicated in both processes. A number of conjectures partly based on the author's own work have been discussed which suggest the possibility of the involvement of proteolysis in exocytosis and endocytosis. The author's optimistic conclusion is that through the common action of biochemists, cell biologists, cytochemists, and pharmacologists the mystery of cellular proteolysis is beginning to be solved.

Cell-layer-associated proteolytic cleavage of the telopeptides of type I collagen in fibroblast culture

In human skin fibroblast cultures a fraction of the procollagen that was processed to collagen and remained in the cell layer was further proteolytically modified by removal of both N- and C-terminal telopeptides. The proteolytic activity was associated with the cell layer, since secreted collagens were found always to contain intact telopeptides. The inclusion of neutral polymers, which caused the accumulation of the collagen in the cell layer [Bateman, Cole, Pillow & Ramshaw (1986) J. Biol. Chem. 261, 4198-4203], made the telopeptide cleavage more apparent in those cells which expressed the proteolytic activity. The extent of this cleavage was variable from cell culture to cell culture and between experiments with the same fibroblast line. The proteolytic activity was pH-dependent; cleavage was greatest at a culture-medium pH of 7.5 and 8.0 and was completely inhibited at a culture-medium pH of 7.0 and 6.5. The activity was significantly inhibited by soybean trypsin inhibitor, an elastase-specific inhibitor (N-acetylalanylalanylprolylvalylchloromethane) and the thrombin inhibitor hirudin. This cell-associated proteolytic activity may play a role in collagen degradation by removing the telopeptides, which are the primary sites of collagen cross-linking, thus destabilizing the collagen matrix sufficiently to render it susceptible to further proteolytic breakdown.

Proteolytic enzymes and arachidonic acid metabolites produced by MRC-5 cells on various microcarrier substrates

Human diploid fibroblasts were cultured on microcarriers made from DEAE-dextran, denatured collagen, DEAE-dextran linked to denatured collagen, and glass. Cells grown on these four substrates were examined for the production of proteolytic enzymes and arachidonic acid metabolites. Culture fluids from cells grown on the DEAE-dextran microcarriers contained the highest amounts of proteolytic enzyme activity. Both plasminogen-independent and plasminogen-dependent fibrinolytic activities were present and the plasminogen-dependent activity seemed to result from the presence of both urokinase and tissue plasminogen activator. Culture fluid from the cells grown on the glass microcarriers contained the least amount of protease activity, and nearly all of the plasminogen-activator activity seemed to be of the urokinase type. Protease activity in the culture fluids of cells grown on the other two substrates were intermediate. With regard to arachidonic acid metabolites, cells grown on the DEAE-dextran microcarriers produced the highest amounts of cyclooxygenase products but very low levels of lipoxygenase metabolites. Cells grown on the other three substrates produced comparable amounts of various cyclooxygenase products (lower than that produced by cells on the DEAE-dextran substrate). Cells grown on the glass microcarriers also produced detectable amounts of two lipoxygenase metabolites--leukotriene B4 and leukotriene C4. Inasmuch as both proteolytic enzymes and arachidonic acid metabolites regulate basic cell properties, the differential amounts of these metabolites observed in the culture fluids on the various substrates may contribute to the biological differences that exist on these substrates.

Further evidence for a cell surface proteinase essential to the growth of cultured fibroblasts

Specific antibodies and protein proteinase inhibitors will inhibit cell-surface proteinase activity on human fibroblasts and cause a concomitant inhibition of DNA synthesis and of cell multiplication. An insolubilized proteinase inhibitor also inhibits cell multiplication. The same reagents partially inhibit the multiplication of mouse L cells, both in monolayer and suspension culture, and inhibit the mitogenic effect of epidermal growth factor (EGF) on both types of cell.

Induction of differentiation in human myeloid leukemic cells by proteolytic enzymes

Exogenous serine proteases were found to induce differentiation in human myeloid leukemic cells from either in vitro established long-term cell lines or in primary cultures of cells derived directly from patients with acute myeloid leukemia. Exposure of the human promyelocytic cell line HL-60 to trypsin, chymotrypsin, or elastase induced the appearance, within 3-6 days, of neutrophilic granulocytes defined by their morphology, their ability to reduce nitroblue tetrazolium, and their efficient phagocytosis of latex particles. Upon further incubation monocyte-like cells appeared. While these cells developed into fully mature macrophages other types of cells disappeared and on day 12 the culture consisted of a pure macrophage population. The inducing effect could be observed when the enzyme was presented alone, whereas a synergistic effect was noted when the protease was added in the presence of subthreshold concentrations of chemicals known to induce differentiation in this cell line such as dimethylsulfoxide, retinoic acid, butyric acid, or hexamethylene bisacetamide. Optimal induction of differentiation by trypsin required a 48 hr continuous exposure to the enzyme. When the protease was removed earlier no appreciable differentiation was noticed. The protease-induced differentiation involved a direct interaction with the cells and was not due to a proteolytic cleavage of a serum component because it could be obtained in serum-free cultures. The enzymatic activity of the protease was needed for its effect on cell maturation: Addition of protease inhibitors such as soybean-trypsin inhibitor or trasylol completely blocked differentiation induced by the proteases but had no effect on differentiation induced by the other inducers. It is still to be determined whether a proteolytic process is a general molecular event in cell differentiation or induction by chemicals involves a mechanism different from that initiated by exogenous proteases.

Plasminogen activator activity in differentiating leukemia cells

Plasminogen activator (PA) activity of human promyelocytic leukemia cell line HL-60 was assayed by following the conversion of plasminogen to plasmin and the plasmin-mediated hydrolysis of 14C-labeled globin. When HL-60 cells were induced to differentiate into macrophages by 12-O-tetradecanoyl-phorbol-13-acetate (TPA), cell-associated PA activity and secretion of PA into the conditioned medium increased profoundly. PA activity increased earlier and as a result of lower concentrations of TPA than the ability of the cells to adhere. Exposure to 10(-6)M dexamethasone did not prevent TPA-induced adherence and produced a slight inhibition of cellular PA activity. These findings imply that TPA-induced differentiation of HL-60 cells to macrophage-like cells is associated with induction of PA activity.

Alpha 1-antitrypsin, alpha 1-antichymotrypsin, and alpha 2-macroglobulin in human gastric carcinomas: a retrospective immunohistochemical study

One hundred twenty-six gastric carcinomas (68 advanced cancers and 58 early cancers) were examined immunohistochemically for alpha 1-antitrypsin (AAT), alpha 1-antichymotrypsin (ACT), and alpha 2-macroglobulin (AMG) within tumor cells. The incidence of these three protease inhibitors was markedly higher in advanced than in early cancers, regardless of the histologic type of gastric carcinoma. In advanced cancers the incidence of both AAT and AMG was significantly higher in well-differentiated adenocarcinomas than in poorly differentiated adenocarcinomas, but no difference was observed in the expression of ACT between these two types of advanced carcinomas. Eighty per cent of the AAT-positive advanced carcinomas had ACT, and 40 per cent of these tumors also contained AMG. The two-year survival rates clearly indicated that well-differentiated adenocarcinomas with AAT have worse prognoses than well-differentiated adenocarcinomas without AAT, but there was no relation between the expression of ACT or AMG and prognosis. These results strongly suggest that the presence of protease inhibitors in gastric carcinomas is related to the invasive growth of the tumors and that AAT is a tissue tumor marker of well-differentiated adenocarcinomas of the stomach. It may also serve as a biologic marker of high malignancy in patients with these gastric cancers.

Antibody affinity chromatography of human proteinases and related proteins

Antibodies specific for a purified proteinase from the cell-surface of human leukocytes were used to prepare an antibody affinity chromatography column. This column bound a variety of proteins from extracts of human cells and tissues and from human body fluids, indicating that proteins immunologically related to the leukocyte proteinase are widespread in the human body. For human urine and a human fibroblast extract, a single protein species with serine proteinase activity was eluted from the column in each case. Small quantities of a heterogeneous protein fraction were also weakly bound to the column from an extract of mouse submaxillary glands.

Membrane proteinases from normal and neoplastic tissues in man and the rat

Plasma membranes were purified from rat liver, muscle and sarcoma tissues and from human liver and hepatoma tissues. The plasma membranes all contained DFP-sensitive, neutral proteolytic activity. Plasma membranes from all normal tissues contained a single DFP-binding protein of apparent molecular weight 68,000. Only the plasma membranes from tumour tissue contained a plasminogen activator; the DFP-binding proteins from these membranes were more diverse than those from the normal samples. The rat liver plasma membrane proteinase was purified. It was a labile enzyme sensitive to inhibition by DFP and by calcium ions, and with a broad substrate specificity. A similar protein was the sole DFP-binding protein in rat liver microsomes. This and the properties of the enzyme suggested a possible role in the processing and secretion of newly-synthesized protein.

Alpha-1-antitrypsin immunoreactivity in gastric carcinoid

Alpha-1-antitrypsin (AAT) was demonstrated in tumour cells in three out of five cases of gastric carcinoma showing the histological characteristics of carcinoid tumour. It was also detected in normal stomach mucosa, but was not found in 10 cases of adenocarcinoma of intestinal or mucous cell type. The AAT-positive tumour cells were argyrophilic, PAS-positive and were negative for pancreatic and gastric hormones. These findings suggest a possible malignant proliferation of alpha-1-antitrypsin-containing cells in the stomach.

The binding and processing of plasminogen by Balb/c 3T3 and SV3T3 cells

The binding and processing of plasminogen by Balb/c 3T3 and SV3T3 cells was studied using 125I-labeled canine plasinogen. Throughout a 3-day period, 125I-plasminogen in the incubation medium bound to the cells and was degraded, first to intermediate-sized macromolecules that were the same size as the large (74,600-dalton) and small (25,000-dalton) chains of active plasmin, and to smaller fragments including 3-iodo-L-tyrosine. Binding to SV3T3 cells was independent of the protease-dependent morphological change (PDMC) characteristic of these and many other transformed cells. The SV3T3, and to a somewhat lesser extent, the 3T3 cells, both accumulated and released into the incubation medium 3-iodo-L-tyrosine, a terminal lysozymal digestion product. The results of a sublethal cell-surface trypsinization assay suggest that the cell-associated plasminogen was primarily bound to the surfaces of the 3T3 and SV3T3 cells while the macromolecular degradation products including active plasmin were inside the cells. The rate of 125I plasminogen degradation exhibited by SV3T3 cells was approximately two time greater than that of 3T3 cells, which presumably reflects differences in endocytosis or lysosomal hydrolysis, or both. The rates were unaffected by addition of pancreatic or soybean trypsin inhibitor sufficient to inhibit PDMC. In the incubation medium, plasminogen was activated to plasmin by SV3T3, but not by 3T3 cells. However, 95-100% of plasmin covalently bound to a 47,000-dalton canine serum component, which could be dissociated from plasmin by hydroxylamine: 95-100% of the plasmin was inactive to reaction with DF32P. Thus the serum component is a plasmin inhibitor. The plasmin-containing complex in the medium had an apparent molecular weight of 212,000. Under denaturing conditions, the complex dissociated into two covalently modified plasmin-containing species of 153,000 and 127,000 daltons. In addition to forming a complex with a serum component, the plasmin is cleaved into two small fragments (approximately 10,000 and 12,000 daltons) by as-yet uncharacterized serum factors.

Enhanced neutral protease activity in proliferating rheumatoid synovial cells

Proteolytic enzymes associated with rheumatoid synovial cells (RSC) have been implicated in the degradation of articular cartilage. Proteases have been measured in proliferating rheumatoid synovial cells (P-RSC), proliferating nonrheumatoid synovial cells (P-NSC), and their nonproliferating counterparts (NP-RSC and NP-NSC). The P-RSC and P-NSC exhibit enhanced total surface-associated plus secreted neutral protease activity, as compared with NP-RSC and NP-NSC. The P-RSC exhibited significantly higher protease activity in this category compared to P-NSC. The RSC also secreted higher levels of secreted proteases alone compared to NSC. The secreted protease activity alone was not related to the proliferative state of the cells. Extractable protease activity was measured in early-passaged and serially-passaged P-RSC, NP-RSC, P-NSC, and NP-NSC. Extractable cellular protease activity measured at pH ranges from 5.0 through 8.0 was not significantly different between P-RSC and NP-RSC or between P-NSC and NP-NSC. The RSC contained elevated extractable cellular protease activity measured at pH ranges from 5.0 through 8.0 compared to extracts from later-passaged cells. The neutral protease activity in the early-passaged RSC was also higher than that measured at pH 6.0 or 8.0. In synovial cells cellular protease activity was related to the proliferative state and the origin of the cells. The P-RSC exhibited the highest levels of surface associated plus secreted neutral protease activity. The RSC also possessed the highest levels of extractable protease activity compared to NSC.

Undifferentiated (embryonal) sarcoma of the liver with alpha-1-antitrypsin deposits: immunohistochemical and ultrastructural studies

Periodic acid-Schiff-positive diastase-resistant globules are described in an undifferentiated (embryonal) sarcoma of the liver in a 14-year-old boy. These globules were shown to contain alpha-1-antitrypsin (A-1-AT) protein by immunofluorescence techniques. Further immunohistochemical studied revealed albumin and gamma globulins, but no alpha-feto protein (AFP). Electron microscopic studies showed large, electron-dense bodies consistent with phagolysosomal structures, and distinct from that described in alpha-1-antitrypsin deficiency (A-1-ATD). These findings suggested that the globules in this tumor may represent trapping of serum proteins by the malignant cell. These observations are discussed in connection with recent studies linking the deficiency disease and epithelial hepatic tumors.

Inhibition of cell proliferation and protease activity by cartilage factors and heparin

Proliferating rat smooth muscle cells and fibroblasts have membrane-associated protease activity. High concentrations of heparin inhibited membrane-associated protease activity and cell proliferation, while low concentration of heparin promoted smooth muscle cell proliferation. The inhibition of protease activity and proliferation was abolished when heparin was treated with protamine sulfate or when acid treated fetal calf serum was used. Heparin required the presence of an acid labile factor(s) in serum for the inhibition of protease activity and proliferation. Heparin and antithrombin III in the presence of acid-treated fetal calf serum did not inhibit cell proliferation or protease activity. Cartilage factors isolated from bovine nasal cartilage containing trypsin inhibitory activity, but not papain inhibitory activity, inhibited rat smooth muscle and fibroblast proliferation and surface associated protease activity. The cartilage factors did not require acid-labile components in the fetal calf serum for the inhibitory activity. The inhibitory activity due to heparin and cartilage factors was not permanent under our experimental condition. Protein synthesis was not inhibited by heparin or the cartilage factors. In rat smooth muscle cells and fibroblasts, the expression of surface-associated protease activity was related to the proliferative state of the cells. Surface protease activity was only present on proliferating cells. When surface protease activity was inhibited by high concentrations of heparin in the presence of an acid-labile serum component(s) or cartilage factors, cell proliferation was also inhibited.

Proteolytic enzymes and plasminogen activator in melanoma

Proteolytic activities were measured in extracts of human skin melanoma, lymphatic metastasis and in nonmalignant naevi by using various proteinase substrates as well as plasminogen activator assay. pH-optima for hydrolysis of various proteinase substrates by these tumors were found to be essentially the same as in healthy human skin. Melanoma extracts were found to especially readily hydrolyze N-alpha-benzoyl-DL-arginine beta-naphthylamine (BANA) at pH 5.8 in the presence of 1 mmol/l dithiothreitol and EDTA (cathepsin B1-like enzyme) as well as histones and p-tosyl-L-arginine methyl ester (TAME) at pH 7.5, and showed increased capacity to activate plasminogen when compared to nonmalignant naevus. The possible role of proteinases in malignant melanoma is discussed.

Binding of bovine parathyroid hormone to surface receptors of cultured B-lymphocytes

Binding of parathyroid hormone onto B-lymphocytes is detected by the utilization of the labelled antibody membrane assay. The amount of parathyroid hormone bound to the receptor sites was depending on the quantity of cells in the incubation milieu. Each cell line showed typical characteristics in time course of parathyroid hormone binding and maximal receptor capacity. Fragmentation of intact parathyroid hormone, also varying with the cell line tested, was very rapid, even at 24 degrees C. Within 20 min most of the cell lines destroyed 20% of the native hormone in the incubation mixture, indicating a fragmentation rate of up to 2.25 ng/min at 37 degrees C. Bmax and KD for the different lymphocytes was 5.3--19 . 10(11) M and 1.8--18,5 . 10(11) M, respectively. These values are in the range of reported plasma concentrations and may therefore represent more physiological values for the capacity and affinity of membrane receptors.