Interaction between the 67 kilodalton metastasis-associated laminin receptor and laminin.

Normal and neoplastic cells interact with laminin via a variety of cell surface proteins. The specific binding sites on laminin for each particular cell surface laminin-binding protein have not yet been identified. In this study, the interaction between laminin and the high affinity metastasis-associated 67 kD laminin receptor (67 LR) was investigated by electron microscopy using the rotary shadowing technique. Laminin receptor that was purified from human colon carcinoma metastases appeared as a globular structure with a diameter of 5.2 +/- 0.8 nm. The 67 LR specifically bound to laminin on its long arm close to the intersection of the long and the short arms. There was no specific interaction of bovine serum albumin with laminin. Biochemical confirmation of the rotary shadowing experiments included slot blot solid phase assays in which [I125]-labeled 67 LR bound in a dose dependent manner to laminin as well as to the chymotrypsin resistant (C1) fragment of laminin that contains a short piece of the long arm. [I125]-labeled 67 LR did not bind to the pepsin resistant (P1) fragment of laminin that did not contain that segment on the long arm. This study therefore identifies the binding site on laminin for the 67 kD metastasis-associated laminin receptor as a region on the long arm of laminin close to the intersection of the four arms.

Urinary type IV collagenase: elevated levels are associated with bladder transitional cell carcinoma.

Accumulating experimental evidence has linked the overproduction of extracellular matrix-degrading metalloproteinases with tumor cell invasion. In the present study one member of the metalloproteinase family, type IV collagenase (M(r) 72,000 gelatinase), is shown to be elevated in the urine of patients with transitional cell carcinoma of the bladder. The form of the enzyme in the urine was studied by three independent methods: enzyme-linked immunosorbent assay, Western immunoblotting; and gelatin zymography. Immunoblotting revealed that the enzyme was present as a series of fragments, each retaining the amino terminus of the mature proenzyme. A prominent M(r) 43,000 fragment was associated with the transitional cell carcinoma cases. Zymography demonstrated that multiple enzyme species with gelatinase activity were present in urine and that high-molecular-weight bands of substrate lysis corresponded to complexes between type IV collagenase and tissue inhibitor of metalloproteinases 2. The total amount of type IV collagenase antigen was significantly elevated in the urine of 37 transitional cell carcinoma patients (range, 0-1081 ng/ml; mean, 318.4 +/- 147.3) compared to 19 normal controls (P < or = 0.004) and 17 inflammatory disease controls (P < or = 0.011). Immunohistochemical staining of bladder tumor biopsies verified that the transitional cell carcinoma cells were producing the M(r) 72,000 enzyme. Thus, M(r) 72,000 type IV collagenase, which is present in the urine in many forms including fragments and complexes with inhibitors, may be a useful marker for bladder cancer diagnosis or prognosis.

Reduced tumor incidence, metastatic potential, and cytokine responsiveness of nm23-transfected melanoma cells.

Reduced expression of the nm23 gene in certain rodent model systems and human breast tumors has been correlated with high tumor metastatic potential. To investigate the functional effects of nm23 expression, we have transfected a constitutive murine nm23-1 expression construct into highly metastatic K-1735 TK murine melanoma cells. TK clones expressing the exogenous nm23-1 construct exhibited a reduced incidence of primary tumor formation, significant reductions in tumor metastatic potential independent of tumor cell growth, and altered responses to the cytokine transforming growth factor beta 1 in soft agar colonization assays, compared with control-transfected TK clones. In contrast, nm23-1-transfected TK clones exhibited no significant differences in intrinsic tumor cell growth, i.e., primary tumor size in vivo, anchorage-dependent growth rate in vitro, and anchorage-independent colony formation in soft agar in vitro. The data demonstrate a suppressive effect of nm23 on several aspects of the cancer process, including tumor metastasis.

Independent expression and cellular processing of Mr 72,000 type IV collagenase and interstitial collagenase in human tumorigenic cell lines.

The regulation of Mr 72,000 type IV collagenase and interstitial collagenase expression was studied in vitro. Three tumorigenic human cell lines were used, together with human fetal lung fibroblasts as a nontumorigenic control. Mr 72,000 type IV collagenase was expressed constitutively by all four cell lines, whereas only A2058 melanoma cells exhibited constitutive expression of interstitial collagenase. Treatment of cells with transforming growth factor beta 1 (TGF-beta 1) and 12-O-tetradecanoylphorbol-13-acetate (TPA) revealed an opposite pattern of regulation of these two metalloproteinases. Specifically, TPA increased interstitial collagenase mRNA levels in each cell line and decreased type IV collagenase mRNA levels in control fibroblasts and the tumorigenic cell lines, HT-1080 and A2058. TGF-beta 1 treatment increased type IV collagenase mRNA levels in each cell line and decreased interstitial collagenase mRNA levels in A2058 melanoma cells. Interstitial collagenase mRNA induction was accompanied in all cell lines by elevated interstitial procollagenase in the conditioned medium, as detected by zymography. Changes in Mr 72,000 type IV collagenase expression revealed a more complex pattern of regulation. TPA and TGF-beta 1 treatment of HT-1080 cells resulted in the appearance of two bands of gelatinolytic activity with a molecular weight of approximately 62,000 and 59,000. The Mr 62,000 species was also induced by TGF-beta 1 treatment of A2058 cells. Addition of affinity-purified radiolabeled Mr 72,000 type IV procollagenase to TPA-treated HT-1080 cells demonstrated that both species were products of the Mr 72,000 proenzyme and that exogenous proenzyme could be processed by these cells. Western blot analysis with specific antipeptide antibodies revealed that both the Mr 62,000 and 59,000 species were derived from the Mr 72,000 proenzyme by amino-terminal cleavage. There was no evidence for cellular processing of either interstitial procollagenase or the Mr 92,000 type IV procollagenase. These results demonstrate that the Mr 72,000 type IV collagenase is under the control of different regulatory elements from interstitial collagenase, at the level of both mRNA expression and cellular processing, and that this processing appears to be the result of a phorbol ester and TGF-beta 1-inducible cellular activation mechanism. The ratio of active enzyme species to latent Mr 72,000 proenzyme may provide a better correlation with invasive potential than overall levels of this widely expressed metalloproteinase.

Cloning and characterization of human tumor cell interstitial collagenase.

A full-length complementary DNA (cDNA) for interstitial collagenase was isolated from an A2058 melanoma cDNA library using the pCD-X Okayama-Berg vector. The tumor interstitial collagenase cDNA was sequenced and compared to the published sequences for human fibroblast collagenase. The sequence for the tumor collagenase has two DNA base pairs which differ from the sequence of normal fibroblast collagenase. Restriction enzyme digestion of a specific DNA fragment produced by polymerase chain reaction amplification of genomic DNA from human placenta resolves a discrepancy in the previously reported DNA and amino acid sequences for the fibroblast collagenase. A high level of expression of interstitial collagenase message was found in human A2058 melanoma cells by Northern blot analysis, and this level was slightly increased by phorbol ester (phorbol myristate acetate) stimulation. Interstitial collagenase mRNA expression was significantly decreased by treatment with either transforming growth factor-beta 1 or retinoic acid in A2058 melanoma cells. A high level of the collagenase protein secreted into conditioned media was identified by Western blotting. As shown by gelatin zymogram analysis interstitial collagenase was one of at least two metalloproteinases secreted by this same cell line. Thus, human melanoma cells can directly produce interstitial collagenase without a requirement for host cell interaction.

Reduced Nm23/Awd protein in tumour metastasis and aberrant Drosophila development.

Tumour metastasis is the principal cause of death for cancer patients. We have identified the nm23 gene, for which RNA levels are reduced in tumour cells of high metastatic potential. In this report we identify the cytoplasmic and nuclear Nm23 protein, and show that it also is differentially expressed in metastatic tumour cells. We also find that the human Nm23 protein has sequence homology over the entire translated region with a recently described developmentally regulated protein in Drosophila, encoded by the abnormal wing discs (awd) gene. Mutations in awd cause abnormal tissue morphology and necrosis and widespread aberrant differentiation in Drosophila, analogous to changes in malignant progression. The metastatic state may therefore be determined by the loss of genes such as nm23/awd which normally regulate development.

The activation of human type IV collagenase proenzyme. Sequence identification of the major conversion product following organomercurial activation.

Type IV collagenase is a metalloproteinase which cleaves type IV collagen in a pepsin-resistant domain. Organomercurial activation of the latent 70-kDa type IV collagenase (type IV procollagenase) results in the autocatalytic removal of an amino-terminal domain resulting in the conversion to a 62-kDa activated form of the enzyme. Synthetic peptides corresponding to domains from the amino terminus (residues 1-17) and an internal domain near the carboxyl terminus (residues 472-490) were used as antigens to generate affinity-purified polyclonal antibodies which recognized their respective domains on the native type IV procollagenase. Western immunoblotting studies of the time course of the organomercurial activation process demonstrate a direct loss of the amino-terminal domain during the conversion to the lower molecular weight form. The amino-terminal sequence of the purified type IV procollagenase before and after activation reveals cleavage at a single locus with removal of residues 1-80, generating a new amino terminus YNFFPRKPKWDKNQ. This results in the removal of three distal cysteine residues located at positions 31, 36, and 73. The type IV collagenase site of autocatalytic cleavage corresponds exactly to the homologous sites of type I collagenase and stromelysin cleavage during their respective organomercurial activation. This site is adjacent to the carboxyl end of a highly conserved region consisting of the sequence PRCGVPDV, which contains an unpaired cysteine residue.

Binding domain for laminin on type IV collagen.

Binding of type IV collagen to laminin was studied by attaching one member of the ligand pair to a solid phase. When laminin was bound to a solid phase, type IV collagen exhibited saturable binding. Digestion of type IV collagen with high concentrations of pepsin destroyed the laminin binding activity. Type IV collagen was also found to bind to fibronectin but the binding activity was not destroyed by pepsin treatment. Rotary shadowing electron microscopy of the pepsin digested type IV collagen indicated that the carboxy terminal end region of about 100 nm is cleaved. Rotary shadowing electron microscopy studies demonstrate that the carboxy terminal end of type IV collagen has a major laminin binding site.

Laminin receptor on human breast carcinoma cells.

Human MCF-7 breast carcinoma cells possess a receptor-like moiety on their surface that has a high binding affinity (Kd = 2 nM) for laminin, a glycoprotein localized in basement membranes. Laminin preferentially stimulates (8-fold) MCF-7 cells to attach to type IV (basement membrane) collagen, whereas fibronectin stimulates attachment only 2-fold for these cells on type I collagen. The attachment properties of two other human breast carcinoma cell lines to type IV collagen were also studied. The attachment of ZR-75-1 cells was stimulated 4-fold by laminin and 5-fold by fibronectin, whereas T47-D cell attachment was stimulated 2-fold by laminin and 7-fold by fibronectin. By employing protease-derived fragments of laminin, the major domains of the laminin molecule that participate in MCF-7 cell attachment to type IV collagen were identified. The whole laminin molecule has the configuration of a four-armed cross with three short arms and one long arm. A major cell-binding domain was found to reside near the intersection point of the short arms, and the type IV collagen-binding domain was associated with the globular end regions of the short arms. The receptor for laminin on the surface of these tumor cells may be involved in the initial interaction of tumor cells via laminin with the vascular basement membrane to facilitate invasion and subsequent promotion of metastasis.

Effect of natural protease inhibitors and a chemoattractant on tumor cell invasion in vitro.

The effect of natural protease inhibitors and a chemoattractant on tumor cell invasion were studied with the use of a new in vitro quantitative assay of tumor cell penetration of native connective tissue. Human amnion membrane denuded of its epithelium is composed of a continuous basement membrane (BM) attached to a dense avascular collagenous stroma. M5076 reticulum sarcoma cells, known to be highly invasive in vivo, were placed on the BM side of the amnion connective tissue. Tumor cells penetrating the full thickness of the connective tissue barrier were collected on the stromal side with a Millipore filter. N-Formylmethionyl-leucyl-phenylalanine (FMLP) at an optimal concentration of 10(-7) M stimulated the penetration of up to 600% more tumor cells into the connective tissue after 20 hours in comparison to the number of tumor cells spontaneously penetrating in serum-free media. Natural protease inhibitors blocked both FMLP-stimulated and spontaneous invasion. A bovine cartilage extract containing inhibitors of both serine proteinases and metalloproteinases caused a 500% decrease in invasion. Furthermore, a 500% inhibition of invasion was produced by a purified collagenase (metalloproteinase) inhibitor. In contrast, soybean trypsin inhibitor and bovine serum albumin did not significantly alter the invasion rate. The protease inhibitors were nontoxic and did not reduce tumor cell proliferation, attachment to the amnion, and the rate of tumor cell migration through Nuclepore filters. These data support the hypothesis that collagenolytic metalloproteinases play a necessary role in tumor cell invasion of native connective tissue.

Isolation of a subunit of laminin and its role in molecular structure and tumor cell attachment.

Laminin, the glycoprotein of basement membranes, migrates as two components of 200 kilodaltons (kDa) (alpha subunit) and 400 kDa (beta subunit) after reduction on polyacrylamide gel electrophoresis. We have isolated the alpha subunit and studied its structure by electron microscopy and its function as an attachment factor for tumor cells. Using selective proteolysis of laminin by alpha-thrombin, the beta subunit was removed without any change in the quantity or size of the alpha subunit. Removal of the beta subunit caused a 35-40% decrease in the total mass of the laminin molecule. The alpha and beta subunits differed by 50-fold in the amount of reducing agent required for complete migration on polyacrylamide gels. By electron microscopy, the whole laminin molecule appeared as a "cross" with three identical short arms (37 nm) and one long arm (75 nm). The alpha subunit examined by electron microscopy was missing the long arm and had no change in the length of the three short arms. This subunit of laminin mediated the attachment of human squamous carcinoma cells to type IV collagen. Such attachment properties were lost after pepsin treatment which is known to remove the globular end regions of the short arms. We conclude that the beta subunit of laminin is embodied in the long arm of the molecule and that the alpha subunit consists of three similar chains of 200 kDa. The globular end regions of the laminin short arms are required for the attachment of tumor cells to type IV collagen.