Abstract:
The invention is directed to purified and isolated concanavalin A-binding proteins from chondrocytes that are not present in dedifferentiated cells from chondrocytes. The invention is also directed to a purified and isolated chondrocyte membrane protein, (CMP), which is a concanavalin A-binding protein, with a molecular weight of about 76 kD in SDS-PAGE. After treatment with endoglycosidase, CMP has an apparent molecular weight of about 67 kD. The N-terminal amino acid sequence and several internal amino acid sequences are given for CMP. These proteins can be used in assays, methods, or treatments involving differentiation of chondrocytes and the control of cartilaginous osteogenesis.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to a novel glycoprotein which may participate in differentiation of chondrocytes. The new glycoprotein according to this invention may be also applied as a marker for differentiation of chondrocytes. 
     Animal cartilage tissues are composed of chondrocytes and matrices. Cartilage tissues constitute a major portion of skeleton during the embryonic stage and, after birth, they are replaced by bone through cartilaginous osteogenesis. At the onset of cartilaginous osteogenesis, cartilage tissues would be transformed from quiescent cartilage tissues to proliferative cartilage tissues and successively differentiated to hypertrophic cartilage tissues. As discussed above, it has been well-known that chondrocytes are essential cells particularly for osteogenesis during the growth period. However, there remain many aspects not yet elucidated in regard to differentiation of chondrocytes and cartilaginous osteogenesis. 
     On the other hand, Yan et al. [Yan et al.; J. Biol. Chem. vol. 265, pages 10125-10131, 1990)]and Kato et al. [Kato et al., Japanese Journal of Bone Metabolism, vol. 10, No. 2, pages 187-192 (1992)]have studied the effect of lectin on differentiation and proliferation of chondrocytes, and, inter alia, elucidated that concanavalin A, which is a jack bean lectin and has an affinity to α-D-mannose residues and α-D-glucose residues, can strongly increase synthesis of proteoglycan, which is a marker of differentiation of chondrocytes. There remain, however, many unclear points of its mechanism, wherein what receptor molecules concanavalin A may be bound to on the cell membrane of chondrocytes, how its stimulus may be transferred to such target sites as the nucleus in the cells and so on. 
     Moreover, it has been reported that chondrocytes, when excess retinoic acid (identical with Vitamin A) is added, may be modified to the so-called dedifferentiated type of cells, wherein they may be deformed in morphology from the spherical cells peculiar to differentiated chondrocytes to the fibroblast-like flat, expanded cellular form with an increased expansibility and may biochemically lose a synthesis ability of glicosaminoglycan (GAG), which is a differentiation marker for chondrocytes and other [Benya et al., Develop. Biol., vol. 118, pages 296-305 (1986)]. However, there has not yet been reported any relationship between the reactivity of chondrocytes to concanavalin A and the differentiation of chondrocytes. 
     Hence the problem of the present invention was to elucidate the substance capable of controlling the function of chondrocytes and, in the end, the substance capable of controlling enhancement of osteogenesis and to elucidate the substance relating to the differentiation of chondrocytes. This substance leads to a new type of therapy, prophylaxis and diagnosis of cartilaginous metabolic diseases and/or metabolic bone diseases. 
     In order to solve the above-mentioned problem, the present inventors have attempted to obtain a new membrane glycoprotein on the chondrocyte membrane bound to concanavalin A having a potent differentiation-enhancing activity to chondrocytes. And further, the present inventors have also elucidated a relationship between the protein thus obtained and the differentiation of chondrocytes by comparative tests with dedifferentiated cells having no more properties peculiar to chondrocytes with retinoic acid added. 
     Hence the present invention refers to a concanavalin A-binding protein (CMP) existing in chondrocytes, but not in dedifferentiated cells from chondrocytes. In a preferred embodiment CMP has a molecular weight of about 76 KD or of about 67 KD after treatment endoglycosidase as analyzed by SDS-PAGE. In a further particularly preferred embodiment CMP contains at least the N-terminal amino acid sequence ##STR1## wherein Xaa means an unknown amino acid. 
     CMP can be obtained by a method containing the following steps: 
     (a) isolating chondrocytes; 
     (b) separating membrane proteins from the chondrocytes of step (a); 
     (c) isolating concanavalin A-binding glycoproteins through a concanavalin A-affinity column; and 
     (d) isolating CMP, 
     preferably by a method wherein prior to step (c) other membrane proteins than concanavalin A-binding glycoproteins were separated. 
     Most preferred, CMP can be isolated by the following method: 
     As to the materials for chondrocytes, one may use cartilaginous tissues of various animals and one may obtain chondrocytes, for example, by treatment of the material of costal cartilage growth plates of rabbits with protease and collagenase according to the method by Kato et al. [Kato et al., J. Cell Biol., vol. 100, pages 477-485 (1985,)]. The chondrocytes thus separated can be incubated in a medium containing fetal calf serum (FCS) in petri plates at 37° C. under environment of 5% CO 2  and 95% air. The chondrocytes thus incubated can be recovered, fractioned by means of a homogenizer and subjected e.g. to precipitation equilibrium centrifugation with sucrose equilibrium density-gradients of 17%/40% in order to recover membrane proteins. The membrane proteins thus recovered can be developed directly with a concanavalin A-affinity column or in a preferred embodiment previously developed with an affinity column using, for example, a representative lectin, a wheat germ lectin for removing other membrane proteins bound to lectins than concanavalin A and thereafter developed with a concanavalin A-affinity column, or using other methods to further fractionate concanavalin A-binding protein fractions. Dedifferentiated cartilage cells are derived and formed with various concentrations of retinoic acids and concanavalin A-binding protein fractions are also fractionated. The specificity of the concanavalin A-binding proteins thus obtained to cartilage cells can be investigated by comparing these fractions by way of SDS-polyacrylamide gel electrophoresis (SDS-PAGE). SDS-Page analysis of the deglycosilated forms of CMP was also carried out. The glycoprotein specific to the aimed cartilage cells was characterized by amino acid sequencing of the N-terminus. 
     CMP provided according to this invention is the substance that relates to differentiation of chondrocytes and also to control of functions by chondrocytes and control of cartilaginous osteogenesis. Therefore, CMP or antibodis against CMP can be utilized as a new type of therapy, prophylaxis and diagnosis against cartilaginous metabolic diseases and/or metabolic bone diseases. Therefore, the present invention refers also to a pharmaceutical or a diagnostic aid containing CMP or antibodis against CMP. 
     The present invention will be explained in detail by way of the following examples, which are not to be construed to limit the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the electrophoresis pattern of concanavalin A-binding glycoproteins, 
     FIG. 2 shows endoglycosidase digestion of purified CMP, 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Example 1 
     (1) Purification of CMP 
     (1) Isolation and culture of chondrocytes 
     Rabbit chondrocytes were used as the chondrocytes. Rib cartilage growth plates of 4 weeks old New Zealand rabbits were surgically dissected out and then rib cartilage growth plates were treated with trypsin and collagenase according to the method by Kato et al. (op cit.) to isolate chondrocytes. According to this procedure, there were obtained chondrocytes of about 4×10 6  cells per rabbit. These chondrocytes were sprayed onto culture dishes, each having a culture area of 500 cm 2 , at about 8×10 5  cells per dish, 100 ml of DEME medium containing 10% fetal calf serum was added and incubation was carried out at 37° C. under atmosphere of 5% CO 2  and 95% air. 
     (2) Isolation of membrane proteins from chondrocytes 
     The chondrocytes obtained as described in the above (1) were incubated until they became confluent, the cultured chondrocytes were washed twice with physiological saline as they adhered onto the culture dishes and then the chondrocytes were recovered by means of a scraper. The cells thus recovered were suspended in a four times volume of a cell-disruption buffer (0.25M sucrose, 5mM MOPS/KOH pH 7.4, 1 mM EDTA, 1 mM PMSF, 10μM pepstatin) and the cells were disrupted on ice by means of a homogenizer (available from Polytron Inc.). 
     The disrupted cell suspension was treated by means of a glass homogenizer using a Teflon rod to disrupt the cell more finely, centrifugation was performed at 4° C. and 105,000× g for one hour and the supernatant was discarded. The precipitate was resuspended in 24 ml of the same cell-disruption buffer and then cell-disruption was again performed using the glass homogenizer and a Teflon pestle. The cell-disrupted suspension was overlapped on the solutions of sucrose equilibrium density-gradients of 17%/40% previously placed into a centrifuge tube and sedimentation equilibrium centrifugation was performed at 4° C. and 200,000× g for 1.5 hours. Thereafter, the membrane proteins separated at the interface between 17% sucrose and 40% sucrose were isolated. 
     (3) Isolation of concanavalin A-binding glycoproteins The above-mentioned membrane fraction was subjected to the following procedure in order to remove the sucrose remaining in the fraction. 
     The above-mentioned membrane fraction was diluted with a buffer (5 mM MOPS, pH 7.4) and then centrifuged at 4° C. and 100,500× g for one hour to remove the supernatant. The precipitate was dissolved in a buffer for solubilization (10 mM tris-HCl (pH 7.4), 10 μM APMSF, 10 μM pepstatin) containing 1% deoxycholic acid. 
     Then, for obtaining the glycoprotein specifically binding concanavalin A, the fractions binding to a wheat germ lectin, was removed from the resultant solution. More specifically, the solution was developed using the wheat germ lectin-WGA-Sepharose 6 MB column (4 cm×2.5 cm, available from Pharmacia AB) previously equilibrated with the buffer for solubilization to recover the non-binding fractions. Thereafter, the fraction not bound to the wheat germ lectin-Sepharose column was developed with the concanavalin A Sepharose column (5 cm×1.5 cm, available from Pharmacia AB) previously equilibrated with the buffer for solubilization, the column was washed with the same buffer as above and the bound glycoproteins were eluted with the same buffer containing 0.5M methyl-α-mannopyranoside. 
     The eluted fraction was enclosed into a dialysis tube, dialyzed against a dialysis buffer (10mM Tris-HCl, pH 7.4) and then concentrated with an ultrafiltration membrane (available from Centricon-Aminon Inc.). 
     The concentrated sample was subjected to electrophoresis using 4%/20% gradient gels under a reduced condition according to the method by Lammli. Identification of the proteins were performed with Coomassie Brilliant Blue(CBB) or silver staining. As a result, there was confirmed the presence of 20 or more types of the glycoproteins having different molecular weights. 
     (4) Extraction of CMP isolated with the gradient gels from the said gels Of the proteins isolated by means of the said electrophoresis, the band having a molecular weight of about 76 kDa was cut out together with the gel thereof in the state of non-CBB staining or silver staining and then the aimed protein was extracted from the gel using an electroeluter (available from Bio-Rad Laboratories, Inc. U.S.A.). 
     According to the aforesaid procedure, there were obtained the homogeneous glycoproteins having a molecular weight of about 76 kDa, which was named &#34;chondrocyte membrane protein&#34; abbreviated as CMP. 
     (5) Enzymatic deglycosilation of CMP For endoglycosidase reactions (C. Maillard et al.; Bone vol. 13, pages 257-264, 1992), purified CMP was incubated with endoglycosidase H (Endo H), endoglycosidase F (Endo F) or N-glycosidase F (NGF) (Boehringer Mannheim Biochemica, Germany). Purified CMP 0.5 μg was incubated with 20 μl of Endo H assay buffer (8 mU Endo H, 50 mM sodium phosphate, pH 5.6, 50 mM EDTA, 0.5 mM PMSF), Endo F assay buffer (40 mU Endo F, 50 mM sodium phosphate, pH 5.6, 50 mM EDTA, 0.5% nonident P40, 0.2% SDS, 1% mercaptoethanol) or NGF assay buffer (5 mU NGF, 45 mM potassium phosphate, pH 7.4, 50 mM EDTA, 0.5% nonident P40, 2% SDS, 1% 2-mercaptoethanol) for 5 hr. or overnight at 37° C. Control incubations were carried out in the absence of enzymes. Samples were boiled for 30 min. Digested protein was analyzed on SDS-PAGE with silver stain to determine molecular weight changes. The results are shown in FIG. 2. 
     FIG. 2 shows endoglycosidase digestion of purified CMP. Lanes 1 and 12 show high and low molecular markers, respectively. Lane 2 shows the purified CMP. Lanes 3, 6 and 9 show endoglycosidase without CMP. Lanes 4, 7, 10 and 5, 8, 11 show the electrophoresis patterns when CMP was incubated with Endo H, NGF and Endo F for 5 hr. and overnight at 37° C., respectively. 
     Incubation of CMP with Endo H or NGF resulted in a reduction of the molecular weight of the protein from 76 kDa to 67 kDa, indicating removal of carbohydrate. However, Endo F did not result in molecular weight change of the glycoprotein. 
     Example 2 
     (1) Determination of the N-terminal amino acid sequence of CMP The amino acid sequence of N-terminus of CMP was determined according to the following procedure. More specifically, the proteins in the SDS-PAGE gel obtained according to the procedure as described in Example 1 (3) were electrically transcripted onto a PVDE membrane and stained with 1% acetic acid and 0.2% Ponceau S to confirm the band of individual protein and then marked on the membrane. Then, the stained membrane was decolorized with a 0.5 mM sodium hydroxide solution, the CMP-transcripted part of the PVDE membrane was cut out and the N-terminal amino acid sequence was determined by means of an amino acid analyzer (available from Applied Biosystems, Inc., U.S.A.). SEQ ID No. 1 shows the amino acid sequence of N-terminus as determined. In the Sequence, &#34;Xaa&#34; does mean that the amino acid residues were not determined. 
     (2) Determination of the internal amino acid sequence of CMP The peptide mapping of CMP was performed according to &#34;A Practical Guide To Protein And Peptide Purification For Microsequencing&#34; (Academic Press Inc., 1989). Homogenous CMP (20 μg) was reduced in 50 μl of 8M urea and 0.4M ammonium bicarbonate pH 8.0, containing 45 mM dithiothreitol for 15 rain at 50° C. Carboxymethylation was performed by adding 5 μl of 100 mM iodoacetamide for 15 min at room temperature. 140 μl of water and trypsin (3 mU/mg protein) was added to the reaction mixture. The digestion was allowed to proceed for 24 hr. at 37° C. Peptide mapping was performed on C2/C18 reverse phase column linked to Smart system chromatography (Pharmacia Inc., Sweden). Peptides were eluted with a gradient of 0% -100% solvent B (100% acetonitrile in 0.12% trifluoroacetic acid) over 110 min at a flow rate of 0.1 ml/min. Elution of the peptides from the column was monitored by measuring absorbance at 215 nm. 4 peptide fragments were isolated and named T1, T2, T3 and T4, respectively. Their amino acid sequences were determined by 476A Protein Sequencer (Applied Biosystems, Inc., U.S.A.) and shown in the Sequence listing. 
     T1 is shown in SEQ ID NO:2; T2 is shown in SEQ ID NO:3; T3 is shown in SEQ ID NO:4; and T4 is shown in SEQ ID NO:5. 
     Example 3 
     Comparison of CMP found in chondrocytes and fibroblast-like cells derived by dedifferentiation with a retinoic acid The chondrocytes isolated as described in Example 1 (1) was treated with a retinoic acid to dedifferentiate to fibroblast-like cells. More specifically, to the cultured broth of chondrocytes obtained as described in Example 1(1) was added a retinoic acid in the form of its ethanolic solutions so as to be final concentrations of 0, 0.01 μM, 0.1 μM and 1 μM, respectively, and then the incubation was performed for 96 hours. 
     The chondrocytes have a weak cell-expanding ability and a spherical shape and, where a retinoic acid is added, they were dedifferentiated to fibroblast-like cells so that they can have an increased expanding ability to take a cellular morphology of being flat and expanded. It may be established upon such morphological changes whether or not dedifferentiation might be performed, and the dedifferentiation was also confirmed by this experiment. Also, it was confirmed that the dedifferentiation level may depend upon the concentration of a retinoic acid and the period of time for treatment. 
     On each of the chondrocytes incubated with the various concentrations of a retinoic acid added as described above, cells were recovered according to the procedure as described in Example 1 (2) to obtain membrane proteins. Then, the concanavalin A-binding glycoprotein fraction was obtained according to the procedure as described in Example 1 (3) and its electrophoresis pattern was compared using SDS-PAGE. The results are shown in FIG. 1. 
     FIG. 1 shows a comparison of CMP&#39;s found in chondrocytes and fibroblast-like cells derived by dedifferentiation. Lane 1shows the electrophoresis pattern when no retinoic acid was added, and Lanes 2, 3 and 4 show the electrophoresis patterns when a retinoic acid was added to the medium at final concentrations of 0.01 μM, 0.1 μM and 1 μM, respectively. Molecular weights are shown on the left side of Lanes, while the location of CMP is shown on the right side of Lanes together with its molecular weight. 
     Thus, it was confirmed that CMP disappeared depending upon the concentrations of a retinoic acid added. CMP disappeared together with dedifferentiation, namely, dedifferentiation to fibroblast-like cells. 
     Example 4 
     Preparation of anti-CMP antiserum 
     The gel band containing CMP obtained as described in Example 1 (4) was cut out together with its gel portion, homogenized and subcutaneously administered to mice. At 3 weeks after the administration, partial blood samples were collected to confirm a sufficiently high level of the antibody valence to CMP and then the serum was collected to obtain anti-CMP antiserum. 
     Example 5 
     Confirmation test for the presence of CMP in various organs 
     The specific expression of CMP in chondrocytes was further investigated using various organs or cells according to Western blot technique with the anti-CMP antiserum obtained as described in Example 4. 
     More specifically, the membrane proteins were obtained from 6 types of rabbit organs; kidney, liver, brain, testis, intestine and spleen, and rabbit cultured fibroblasts, respectively according to the procedure as described in Example 1 (2). The membrane proteins above were individually investigated for the presence or absence of CMP according to Western blot technique to confirm that CMP is not found in all fractions, which proved that CMP is a protein specifically expressed in chondrocytes. 
     
         __________________________________________________________________________SEQUENCE LISTING(1) GENERAL INFORMATION:(iii) NUMBER OF SEQUENCES: 5(2) INFORMATION FOR SEQ ID NO:1:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 15 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(ix) FEATURE:(A) NAME/KEY: Peptide(B) LOCATION: 6..7(D) OTHER INFORMATION: /note=&#34;Xaa is an unknown aminoacid.&#34;(xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:SerValGluValArgXaaXaaThrAlaSerGluProProGlnGln151015(2) INFORMATION FOR SEQ ID NO:2:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 18 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(ix) FEATURE:(A) NAME/KEY: Peptide(B) LOCATION: 16(D) OTHER INFORMATION: /note=&#34;Xaa is an unknown aminoacid.&#34;(xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:HisThrThrTyrPheAspAsnThrAsnGlyHisAsnProGluProXaa151015AlaAla(2) INFORMATION FOR SEQ ID NO:3:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 16 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:ThrValGlyTrpAsnValProValGlyTyrLeuValAspSerGlyArg151015(2) INFORMATION FOR SEQ ID NO:4:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 20 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(ix) FEATURE:(A) NAME/KEY: Peptide(B) LOCATION: 18(D) OTHER INFORMATION: /note=&#34;Xaa is an unknown aminoacid.&#34;(xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:ThrThrTyrGlnAspThrLeuGlyProAspTyrValAlaAlaLeuGlu151015GlyXaaGlnSer20(2) INFORMATION FOR SEQ ID NO:5:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 9 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: peptide(xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:TyrTyrAspTyrSerGlyAlaPheArg15__________________________________________________________________________