Absolute quantitation of specific mRNAs in cell and tissue samples by comparative PCR.

A comparative PCR assay, for the absolute quantitation of specific mRNAs in cell and tissue samples, has been designed to overcome problems with previous techniques. cDNAs made from the RNAs are co-amplified with "competitor" plasmid templates under conditions in which reagents are not limiting at the equivalence point, thereby preventing competition between target and competitor templates and distinguishing the assay from competitive PCR assays. The cDNAs are serially diluted, and competitor templates concentrations are kept constant, rather than vice versa, as occurs in competitive PCR assays. Products from target and competitor templates are resolved by electrophoresis and measured by phosphorescent or fluorescent imagery. Both products are measured to minimize errors in the competitor:target ratio. A synthetic external standard RNA is included in the tissue lysis solution and co-purified with endogenous mRNAs, thereby being subjected to identical losses of yield during subsequent procedures. The determination of the number of copies of external standard cDNA allows inefficiencies of RNA extraction and cDNA synthesis to be taken into account. Standard concentrations of plasmids containing the endogenous target sequences are also measured, so that corrections can be made for discrepancies due to unequal amplification of target and competitor sequences. These corrections, together with the use of an external standard and the PCR conditions chosen, allow for the accurate, specific and sensitive determination of the absolute number of mRNA copies in a sample.

Epithelial cells up-regulate matrix metalloproteinases in cells within the same mammary carcinoma that have undergone an epithelial-mesenchymal transition.

A metastatic rat mammary carcinoma cell line, BC1, contains cells that have retained epithelial differentiation characteristics and metaplastic cells that have undergone an epithelial-mesenchymal transition. These two subpopulations cooperate to degrade collagen. We have used novel PCR assays to quantitate, for the first time, absolute levels of the mRNAs encoding matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in cell and tumor samples. BC1 tumors expressed high levels of the collagenase-3, TIMP-2, stromelysin-1, and gelatinase B genes and low levels of the stromelysin-2 and TIMP-1 genes. This pattern of expression was repeated in cultures of BC1 and cultures containing mixed clones of epithelial cells and metaplastic cells. In both BC1 and the biclonal cultures, metaplastic cells were the main source of collagenase-3, stromelysin-1 and stromelysin-2, whereas TIMPs were equally distributed and epithelial cells were the main source of gelatinase B. High levels of all four MMP mRNAs in metaplastic cells were dependent on coculture with epithelial cells, suggesting the production of an inducing factor by the epithelial cells. In contrast, gelatinase B mRNA was produced at a high level by epithelial cells in the absence of metaplastic cells. TIMP-2 mRNA was abundant in both subpopulations grown alone and did not change substantially upon coculture. Thus, the interclonal cooperativity to degrade collagen in BC1 cells required the induction of MMPs in metaplastic cells by epithelial cells. Interclonal cooperativity may be important to the progression of neoplastic tumors, a feature of which is phenotypic heterogeneity.

Multiple levels of post-transcriptional regulation of collagenase (matrix metalloproteinase 1) in an epithelial cell line.

Multiple levels of regulation of collagenase (matrix metalloproteinase 1; MMP-1), have been demonstrated in a clonal rat epithelial cell line (A5P/B10). Secreted enzyme could not be demonstrated in culture medium from A5P/B10 cells but, using antibodies specific for collagenase, the enzyme was detected within the cytoplasm and on the surface of the cells. A probe for rat collagenase could not detect a signal for mRNA in the cytoplasm while nuclear run-on data demonstrated that the gene for collagenase was being transcribed. Incubating the cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) significantly increased cytoplasmic mRNA levels and slightly increased the intensity of staining in permeabilized cells, but collagenase activity was still not detected in the conditioned medium. This indicated that the protein was being synthesized by the TPA-treated cells but was not being secreted into the medium. These data suggest that the secretion of collagenase may be regulated both following transcription and after the completion of translation and it is suggested that multiple levels of control may be operating to determine the rate of collagenase release and hence, the rate of collagen turnover.

The chondroprotective drugs, Arteparon and sodium pentosan polysulphate, increase collagenase activity and inhibit stromelysin activity in vitro.

The effects of the chondroprotective drugs, sodium pentosan polysulphate (SP54) and Arteparon (glycosaminoglycan polysulphate), on the in vitro activities of the purified matrix metalloproteinases interstitial collagenase (matrix metalloproteinase 1, MMP1) and stromelysin (MMP3) were examined. Both drugs produced concentration-dependent enhancement of the degradation of type I collagen fibrils by purified human fibroblast collagenase and rat tumour collagenase. Rat collagenase activity was increased by drug concentrations above 0.5 microgram/mL, whereas human collagenase activity was only increased by higher drug concentrations, above 5 micrograms/mL. The concentration dependence of the increase in rat collagenase activity was similar for both drugs, with a maximal 3-fold increase at 50 micrograms/mL. In contrast, human collagenase activity was increased to a greater extent by SP 54 compared to Arteparon, with maximal increases at 5000 micrograms/mL of 6-fold and 2-4-fold, respectively. Both drugs produced concentration-dependent inhibition of the proteoglycan-degrading activity of both human fibroblast stromelysin and rat tumour stromelysin. Rat and human stromelysin activities were inhibited at drug concentrations above 0.005 microgram/mL, with a similar concentration dependence for both drugs. Fifty percent inhibition of rat stromelysin was produced by concentrations of each drug in the 0.5-5 microgram/mL range. The pattern of inhibition of human stromelysin was similar, except that drug concentrations in the 500-5000 micrograms/mL range produced 50% inhibition. The possible modes of action for these drug effects and their possible pharmacological significance are discussed.

Characteristics of a 95-kDa matrix metalloproteinase produced by mammary carcinoma cells.

A Mr 95,000 matrix metalloproteinase (MMP) produced by rat mammary carcinoma cells has been isolated and characterized. The MMP was secreted in a proteolytically inactive form that was free from bound tissue inhibitor of metalloproteinases. The enzyme was highly glycosylated as evident from an apparent drop of Mr from 95,000 to 83,000 after treatment with N-glycanase. Rotary shadowing electron micrographs of purified proenzyme preparations revealed a uniform set of ellipsoidal molecules. Treatment of the proenzyme with 1% SDS resulted in generation of catalytic activity and exposed a cryptic unpaired Cys residue. The latent proenzyme may be activated in at least three additional ways: either spontaneously upon storage, by treatment with organomercurials, or by limited proteolysis by trypsin. Each mode of activation yielded a distinct pattern of cleavage of the enzyme. The activated enzyme cleaved gelatin (denatured type I collagen) and native type IV and V collagen at 30-37 degrees C. Noncollagenous proteins including alpha 1-proteinase inhibitor, casein, and fibrinogen also were cleaved. The rat mammary carcinoma cell line that produces the Mr 95,000 MMP is composed of two distinct (epithelial- and myoepithelial-like) cell types. The enzyme is expressed constitutively by the epithelial cells. This suggests that expression of the Mr 95,000 MMP is regulated differently from that of interstitial collagenase, which is produced by the epithelial cells only in response to specific inductive factor(s) from the myoepithelial-like cells. Monoclonal antibodies raised against the purified latent Mr 95,000 form of the enzyme bind specifically to the Mr 95,000 MMP and have been used to localize the enzyme to the Golgi region and cytoplasmic granules of the epithelial cells.

The identification, purification and characterisation of an inhibitor of collagenase (20K) produced by neoplastic epithelial cells.

A rat carcinoma cell line (T2/H7) constitutively synthesised interstitial collagenase. When these cells were incubated with 12-O-tetradecanoylphorbol 13-acetate (TPA) they secreted an inhibitor of collagenase, which resulted in a net decrease of collagenolytic activity being detected in conditioned medium. Using reverse zymography, the Mr of the inhibitor was found to be 20,000 which suggests that it may be the rat homologue of inhibitor of metalloproteinase 2 (IMP2; TIMP-2), as it inhibited both the gelatinolytic and collagenolytic activities of rat collagenase. The inhibitor was separated from collagenase by filtration through a YM30 membrane. The inhibitor was purified further by sequential chromatography on heparin-Sepharose and Con A-Sepharose. It bound to heparin-Sepharose in 75 mM NaCl and was eluted with 300 mM NaCl. It did not bind to Con A-Sepharose, suggesting that it was a non-glycosylated molecule. The inhibitor was resistant to treatment with either trypsin, APMA or heat.

Interstitial collagenase (matrix metalloproteinase 1) associated with the plasma membrane of both neoplastic and nonneoplastic cells.

Epithelial cell lines (BC1, BC3, BC4, and BC5), derived from 4 separate invasive and metastatic rat mammary carcinomas, all secreted interstitial collagenase (matrix metalloproteinase 1, MMP 1) in culture. Neither a cloned cell line (A5P/B10), derived from a noninvasive rat epithelial tumor, nor nonneoplastic rat fibroblasts secreted the enzyme. Western blot analyses of proteins extracted from the plasma membranes indicated the presence of interstitial collagenase (MMP 1) on the surface of all of the 6 cell lines. These data suggest that the control of collagenolysis may involve the association of collagenase molecules with the plasma membrane. The aggressiveness of malignant tumors may be due in part to the breakdown of such a control.

Interstitial collagenase from rat mammary carcinoma cells: interaction with substrates and inhibitors.

Functional characteristics of the interstitial collagenase purified from the BCl rat mammary carcinoma cell line were examined and compared with literature reports of the corresponding characteristics of collagenase from non-neoplastic cells. BCl collagenase degraded soluble collagen types I, II and III at the same rate and degraded fibrillar tendon collagen with an activation energy of 75 kcal/mol; these characteristics were identical to collagenase from normal rat uterine smooth muscle cells. Degradation of fibrillar collagen by BCl collagenase was completely inhibited by rat alpha 2-macroglobulin which was concomitantly cleaved into half-fragments. BCl collagenase was also inhibited by native and recombinant tissue inhibitor of metalloproteinases, a synthetic peptide collagenase inhibitor (Z-pro-leugly-NHOH), and Zn2+. In all functional characteristics examined, BCl collagenase was the same as interstitial collagenases from non-neoplastic sources.

Immunolocalization of collagenase in neoplastic epithelial cells.

The distribution of interstitial collagenase in a rat mammary carcinoma model system has been studied by immunocytochemistry. Rabbit antibodies were raised against collagenase from neoplastic epithelial cells which were derived from an anaplastic, invasive, rat mammary carcinoma (BC1). Specificity of the antibodies was determined by Western blot analysis which showed reactivity with the inactive procollagenase from conditioned culture medium of BC1 cells as well as with purified, active BC1 collagenase. Anti-BC1 collagenase antibodies did not recognize BC1 collagenase entrapped by the inhibitor, rat alpha-2-macroglobulin (alpha 2M), or collagenase derived from TPA-stimulated human fibroblasts. Anti-human fibroblast collagenase antibodies did not recognize BC1 collagenase, suggesting that the human-mesenchymal and rat-epithelial enzymes are immunologically distinct molecules. Collagenase was immunolocalized intracellularly in BC1 cells cultured in the presence of monensin. Neither BC1 collagenase, alpha 2M nor enzyme-inhibitor complexes were demonstrated in or around invading tumours by immunostaining of tissue sections of rat mammary carcinomas.

Identification, partial purification and characterization of high-molecular-weight gelatin-degrading metalloproteinases produced by a rat mammary carcinoma cell line.

BC1 rat mammary carcinoma cells were found to secrete a unique profile of metalloproteinases, distinguished by two gelatin-degrading metalloproteinases of Mr greater than 220.10(3) and Mr much greater than 220.10(3). These enzymes were each partially purified by gel-filtration chromatography, and inhibitor studies showed them to be metalloproteinases. Under conditions where denatured collagen types I, II, and V were completely degraded, native collagen types I, II, IV and V, fibronectin, fibrinogen, C1q, casein, and denatured transferrin were not degraded significantly by these enzymes. The relationship of these enzymes to other extracellular matrix-degrading metalloproteinases and their possible significance in tumour invasion and metastasis is discussed.

Identification of a metalloproteinase co-purifying with rat tumour collagenase and the characteristics of fragments of both enzymes.

A metalloproteinase similar or identical to stromelysin was shown to co-purify with interstitial collagenase from the rat mammary carcinoma cell line, BC1. The mixture of BC1 metalloproteinase and collagenase degraded casein, gelatin, fibronectin, fibrinogen, laminin, proteoglycan and type IV collagen, in addition to types I and II collagen. Using SDS-PAGE and zymography, the Mr of both enzymes was 51.10(3). During storage, the 51.10(3) protein converted to fragments of Mr 34.10(3) and 24.10(3), and isoelectric points of 4.6-5.3 and 5.7-6.0, respectively. The fragments were separated from the intact (Mr 51.10(3) enzymes by DEAE-Sepharose chromatography, but intact metalloproteinase and collagenase activities resisted separation by a range of chromatographic methods. The Mr 34.10(3) fragment retained the proteinolytic activities of the intact enzymes, excepting collagenase cleavage of collagen types I and II. The Mr 24.10(3) fragment had no proteinolytic activity, showed an increase in Mr of 6.10(3) upon reduction, in common with the intact enzymes, and also had similar chromatographic properties to the intact enzymes. The data presented are consistent with a pattern of breakdown which is common to both collagenase and the metalloproteinase, and suggest that both enzymes are comprised of two protein domains.

The collagenase produced by neoplastic rat epithelial cells: modulation of secretion, molecular weight characteristics, and purification.

The modulation of the production of collagenase by an epithelial cell line derived from a spontaneously arising rat mammary carcinoma has been studied. The cell line, BC1, was grown permanently under defined serum-free conditions, thus avoiding the poorly characterized and variable effects of serum on collagenase production. Piperazine-N,N'-bis-(2-ethanesulfonic acid) (Pipes), retinoic acid and cytochalasin B all stimulated collagenase secretion, while dexamethasone inhibited it and progesterone, prolactin, prostaglandin E2, and estrogen had no effect. This profile of response to exogenous compounds was distinct from that of cells of mesenchymal origin and from human keratinocytes. For the production of large quantities of collagenase, culture medium was supplemented with Pipes (30 mM, pH 6.8), and retinoic acid (1 microM, on alternate feeds). The collagenase secreted by BC1 cells grown under these conditions was latent and had a molecular mass of 59 kDa. Treatment of the 59 kDa form with trypsin or APMA caused a progressive decrease in molecular mass via 54 kDa and 52 kDa intermediates, to a 48 kDa form. This form was purified to electrophoretic homogeneity by heparin-Sepharose, zinc-chelate-Sepharose, and Sephacryl S-200 chromatography. Five milligrams of purified collagenase were recovered per litre of culture medium.

Cellular interactions determining the production of collagenase by a rat mammary carcinoma cell line.

The cellular interactions regulating the production of collagenase by a cell line derived from a spontaneously arising rat mammary carcinoma have been studied. The cell line, BC1, was grown permanently under defined serum-free conditions, so that the poorly characterized and variable effects of serum on collagenase expression were avoided. Two stable subpopulations of cells present in BC1 cultures were defined as epithelioid cells ("E-cells") and myoepithelioid cells ("M-cells"). These subpopulations differed in their morphology, pattern of growth and susceptibility to detachment from culture vessels by trypsin. Seven clones of M-cells and 7 clones of E-cells, obtained by the limiting dilution technique, were used to determine the cellular source of collagenase and the interactions which led to its expression. M-cells displayed an absolute dependence on a soluble factor produced by E-cells for their survival in vitro. The presence of both cellular types in culture was necessary for collagenase secretion to occur, E-cells being the major source of enzyme in mixed cultures. A soluble factor produced by M-cells was largely, if not completely, responsible for the induction of collagenase secretion by E-cells. Clones representative of both subpopulations were tumorigenic in syngeneic host animals. These results suggest that the phenotypic diversity which occurs within populations of neoplastic cells may give rise to subpopulations of cells which display a more aggressive phenotype in coexistence than in isolation.

A spectrophotometric collagenase assay.

A quantitative collagenase assay using Coomassie blue staining and microtiter spectrophotometry is described. Collagen is gelled and dried onto the bottom of microwells as substrate, washed, incubated with samples, washed again, and then stained. Absorbance at 590 nm increases linearly with increasing amounts of collagen in the range 5-40 micrograms. Bacterial and mammalian collagenases can be detected within 2 h, and 10 ng of bacterial collagenase may be detected in 16 h. For simple screening applications, activity may be detected by eye. The assay is safe, simple, fast, economical, and sensitive.

Rat carcinoma cells in long-term, serum-free culture provide a continuing supply of collagenase.

Neoplastic, epithelial cells derived from a spontaneously-arising rat mammary carcinoma have been cultured in a defined medium, in the absence of serum, continuously, for over 2 years. The medium is a mixture of Ham's F12 and Dulbecco's Modified Eagle's media supplemented with insulin, transferrin and bovine serum albumin. The cells have retained their potential to produce tumours and, in culture, a true vertebrate collagenase. This system provides a continuing supply of vertebrate collagenase through the application of recently developed methods.

Osteoclasts and the resorption of bone by transplanted mammary carcinoma in rats.

Rat mammary tumour cells were grafted to parietal bones as an experimental model to study the nature of bone resorption around metastatic carcinomas in the skeleton. After periods of growth of from 6 to 56 days bones and tumours were removed and embedded in epoxy resin. The appearances were compared with those found when whole parathyroid glands were grafted in similar positions. Tumours were evident in all animals at the time of death and some were palpable five days after grafting. In 15 of the 21 animals with tumour, osteoclasts and resorption were found, and in only two of these were the tumour cells not separated from the bone surfaces. In 6 animals killed between 6 and 12 days after grafting there was new bone formation without resorption. There were osteoclasts and resorption under the grafted parathyroid glands which were always separated from the resorbing cells by fibrous tissue. The appearances of the bone surfaces under the tumours and the parathyroid glands suggested that the resorption in both situations was similar, was brought about by the secretion of a locally active agent and mediated by osteoclasts. This is further support for the role of osteoclasts in bone resorption around metastatic carcinomas.

A fluorescent screening assay for collagenase using collagen labeled with 2-methoxy-2,4-diphenyl-3(2H)-furanone.

This report describes the use of the compound 2-methoxy-2,4-diphenyl-3(2H)-furanone to label collagen as a substrate for the detection of mammalian collagenase in a fluorescent assay which is suitable for screening large numbers of samples. The compound 2-methoxy-2,4-diphenyl-3(2H)-furanone presents distinct advantages over other fluorophores, since both the unbound reagent and its hydrolysis products are nonfluorescent. The labeling procedure uses commercially available collagen, is fast and simple, and gives a 90% yield of labeled substrate. The fluorescent collagen substrate is stable and retains fluorescence over a wide range of pH. The assay detects, reproducibly, metal-dependent collagenase activity in microliter volumes of conditioned media from cultured neoplastic cells or in chromatographic fractions from such media.

Collagenolytic activity by malignant tumours.

Five carcinomas and 5 sarcomas were investigated in relation to their production of neutral proteases capable of digesting polymeric collagen. The carcinomas were far more active than the sarcomas but all the malignant tumours produced enzymes which were capable of causing collagenolysis in vitro. collagenolytic enzymes were recovered from extracts of neoplastic cells from long-term culture, from the media in which these cells were cultured, from the media of mixed cell cultures (neoplastic, stromal and inflammatory cells from minced tumours), and from normal fibroblasts cultures. In contrast to the cultures of non-neoplastic fibroblasts, the tumour cells produced active enzymes, since limited proteolysis with trypsin or treatment with p-aminophenyl-mercuric acetate (APMA) caused no increase in enzyme activity. These tumours possess collagenolytic ability in vitro which may be partly responsible for their invasive nature in vivo.