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PubMed1995

Cortisol downregulates osteoblast alpha 1 (I) procollagen mRNA by transcriptional and posttranscriptional mechanisms.

Glucocorticoids decrease osteoblast proliferation and type I collagen production, and this may play a role in the development of glucocorticoid-induced osteoporosis. Osteoblast-enriched cultures derived from fetal rat calvaria were used to determine the mechanisms by which cortisol decreases alpha 1 (I) procollagen expression in bone cells. A 24 h treatment with cortisol decreased collagen synthesis in these cultures in a dose-dependent manner. Cortisol decreased alpha 1 (I) procollagen transcripts in a dose- and time-dependent manner as well. Repression of alpha 1 (I) procollagen transcripts was evident as early as 2 h of treatment and was maximal after 48 h of treatment. Nuclear run-off assays showed that cortisol downregulated transcription of the alpha 1 (I) procollagen gene. In addition, pretreatment with cortisol decreased the stability of alpha 1 (I) procollagen mRNA in transcription-arrested osteoblast cultures. The ability of cortisol to downregulate alpha 1 (I) procollagen transcripts was sensitive to cycloheximide treatment, suggesting that the gene is under "secondary control" by glucocorticoids. Since cortisol decreases alpha 1 (I) procollagen gene transcription in osteoblasts but does not affect alpha 1 (I) procollagen gene transcription in fibroblasts, we suggest that the mechanisms controlling glucocorticoid repression of collagen expression are cell-type specific.

Animals↗
PubMed1997

Localization of procollagen I in the lysosome/endosome system of human fibroblasts.

A significant amount of newly synthesized collagen is degraded intracellularly rather than secreted, but there is controversy about whether this process occurs in the lysosomes. We addressed this problem using confocal microscopy and immunofluorescence imaging to study the distribution of procollagen I in the Golgi and the lysosome/endosome system of cultured human fibroblasts. Cells were incubated under basal conditions and then permeabilized and exposed to fluorescently tagged probes for procollagen, Golgi markers (Helix pomatia binding protein or beta-coatamer protein), and lysosome/endosome markers (cathepsin B or LAMP-2). Strong signals for procollagen codistributed with the Golgi and lysosome/endosome markers. Of note, many structures were positive for procollagen and lysosome/endosome markers but not for Golgi markers. When cells were incubated with the proline analog cis-hydroxyproline, which inhibits correct triple helix formation and increases intracellular degradation, the amount of procollagen codistributing with the lysosome/endosome markers increased greatly. Similar results were obtained in I-cells, which do not have functioning lysosomal hydrolases. These findings strongly indicate that the lysosome/endosome system participates in the intracellular degradation of newly synthesized procollagen and that trafficking of procollagen to the lysosome/endosome system does not depend on the cells having active lysosomal hydrolases. We present a model that integrates our findings with other work and resolves inconsistencies in the literature. This model postulates the existence of three separate degradation paths for newly synthesized procollagen. In addition to the endosome/lysosome system, degradation also takes place in the proximal region of the secretory pathway such as the endoplasmic reticulum, cis-Golgi network, or cis-Golgi and in a distal region of the secretory pathway such as the trans-Golgi or trans-Golgi network.

Antigens, CD↗
PubMed1985

Modulation of type-IV procollagen and laminin production in A431 human squamous epidermoid carcinoma cells by 12-O-tetradecanoylphorbol-13-acetate (TPA) and epidermal growth factor (EGF).

The effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) and epidermal growth factor (EGF) on type-IV-procollagen (basement-membrane collagen) and laminin synthesis, turnover, and secretion was studied in human A431 squamous epidermoid carcinoma cells. Type-IV procollagen and laminin were biochemically and immunologically identified in the medium and cell extracts using immuno-precipitation followed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. EGF or TPA produced a sixfold increase in type-IV-procollagen and laminin secretion within 2 h; this was accompanied by a three- to fourfold increase in the levels of cell-associated type-IV procollagen and laminin, respectively. The level of type-IV-procollagen and laminin synthesis and secretion remained elevated for at least 16 h after the administration of either EGF or TPA. A combination of EGF and TPA was more effective than either agent alone in promoting the secretion of laminin but not of type-IV procollagen. EGF and/or TPA did not, however, produce a selective increase in the synthesis of collagen and laminin, since total protein synthesis was also increased to the same degree by these agents. As determined by labeling and chase studies, neither EGF nor TPA had any appreciable effect upon type-IV-procollagen or laminin degradation. These results indicate that the synthesis of components associated with the basement membrane in A431 cells (i.e., type-IV procollagen and laminin) can be rapidly modulated by EGF and a tumor promoter, i.e., TPA.(ABSTRACT TRUNCATED AT 250 WORDS)

Basement Membrane↗
PubMed1995

Experimental tissue expansion induces changes in expression of procollagen I and III messenger RNA.

Experimental tissue expansion was performed in nine dogs following placement of subcutaneous silicone balloons. The balloon expander was then filled with 300 ml saline immediately after implantation. Duration of expansion varied from 3 days to 124 days. Unaffected skin and skin over an empty expander served as control tissue. Dermal procollagen I and procollagen III gene expression in response to tissue expansion was investigated by dot-blot analysis using digoxigenin-labeled RNA probes complementary to either human procollagen-alpha 1(I) mRNA or procollagen-alpha 1(III) mRNA. Cross-hybridization of human probes with canine procollagen mRNA was demonstrated by Northern blot analysis. In response to the trauma of surgery, procollagen I and III mRNA transcriptions were found to be decreased significantly within the first few days after implantation. After 9 days of expansion, increased levels of procollagen I mRNA were found, while after 16 days increased levels of procollagen III mRNA were evident. The present study is the first to demonstrate changes in dermal collagen gene expression as a reaction to tissue expansion.

Animals↗
PubMed2004

Active transforming growth factor-beta1 activates the procollagen I promoter in patients with acute lung injury.

OBJECTIVE: Fibroproliferation markers like procollagen I predict mortality in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). We sought to determine whether bronchoalveolar lavage fluid (BALF) from patients with lung injury contained mediators that would activate procollagen I promoter and if this activation predicted important clinical outcomes. DESIGN: Prospective controlled study of ALI/ARDS. SETTING: Intensive care units and laboratory of a university hospital. PATIENTS AND PARTICIPANTS: Acute lung injury/ARDS, cardiogenic edema (negative controls) and pulmonary fibrosis (positive controls) patients. INTERVENTIONS: Bronchoalveolar lavage fluid was collected within 48 h of intubation from ALI/ARDS patients. BALF was also collected from patients with pulmonary fibrosis and cardiogenic pulmonary edema. Human lung fibroblasts were transfected with a procollagen I promoter-luciferase construct and incubated with BALF; procollagen I promoter activity was then measured. BALF active TGF-beta1 levels were measured by ELISA. RESULTS: Twenty-nine ARDS patients, nine negative and six positive controls were enrolled. BALF from ARDS patients induced 41% greater procollagen I promoter activation than that from negative controls (p<0.05) and a TGF-beta1 blocking antibody significantly reduced this activation in ARDS patients. There was a trend toward higher TGF-beta1 levels in the ARDS group compared to negative controls (-1.056 log(10)+/-0.1415 vs -1.505 log(10)+/-0.1425) (p<0.09). Procollagen I promoter activation was not associated with mortality; however, lower TGF-beta1 levels were associated with more ventilator-free and ICU-free days. CONCLUSIONS: Bronchoalveolar lavage fluid from ALI/ARDS patients activates procollagen I promoter, which is due partly to TGF-beta1. Activated TGF-beta1 may impact ARDS outcome independent of its effect on procollagen I activation.

Bronchoalveolar Lavage Fluid↗
PubMed1995

Macrophage colony-stimulating factor 1, a clinically useful tumor marker in endometrial adenocarcinoma: comparison with CA 125 and the aminoterminal propeptide of type III procollagen.

OBJECTIVE: We investigated the clinical utility of macrophage colony-stimulating factor 1 versus CA 125 and the aminoterminal propeptide of type III procollagen in endometrial carcinoma. STUDY DESIGN: Serum levels of the three substances were measured in 159 patients with untreated endometrial adenocarcinoma and in 24 patients treated with cytotoxic chemotherapy for recurrent endometrial adenocarcinoma. RESULTS: Initial concentrations of colony-stimulating factor 1, CA 125, and the aminoterminal peptide of type III procollagen were above the normal range in 73%, 11%, and 27%, respectively, of the patients. Colony-stimulating factor 1 levels correlated with those of the aminoterminal peptide of type III procollagen (r = 0.3, p = 0.002) and CA 125 (r = 0.20, p = 0.036) in the total group and with those of the aminoterminal peptide of type III procollagen in stage I and II patients (r = 0.3, p = 0.0023). Colony-stimulating factor 1 levels correlated significantly with tumor grade, whereas those of CA 125 and the aminoterminal peptide of type III procollagen correlated more closely with clinical stage. Mean colony-stimulating factor 1 levels (9.6 vs 7.7 ng/ml, p = 0.04) and the frequency of elevated CA 125 levels (31% vs 8%, p = 0.048) were higher in patients with poor prognosis than in those with good prognosis. Colony-stimulating factor 1, the aminoterminal peptide of type III procollagen, and CA 125 levels were useful in monitoring clinical behavior of the disease in 88%, 79%, and 63% of the cases, respectively. Levels of all three markers rose with disease progression, whereas colony-stimulating factor 1 and the aminoterminal peptide of type III procollagen fell with clinical responses to therapy. CONCLUSION: Elevated serum colony-stimulating factor 1 levels were the most accurate indicator of the presence and activity (progression, stabilization, or regression) of primary or recurrent disease. Accuracy was not further enhanced by measurement of CA 125 or the aminoterminal peptide of type III procollagen levels.

Adenocarcinoma↗
PubMed1994

Differential processing of type I and type III procollagens in the tumour cysts and peritoneal ascitic fluid of patients with benign and malignant ovarian tumours.

Progressive ovarian carcinoma induces the synthesis of type I and type III procollagens both in the tumour tissue and in the peritoneal cavity. We studied the processing of these proteins by determining the different antigen forms related to their propeptide parts by gel filtration and subsequent immunological assays. Samples of ovarian cyst fluid and peritoneal ascitic fluid were obtained from patients with benign and malignant ovarian tumours. In both benign and malignant ovarian cysts, the predominant procollagen antigens were the free propeptides, with few or no larger components, indicating efficient processing of types I and III procollagens in the tumour tissue. In ascitic fluid the processing was more variable. The aminoterminus of type III procollagen was partially unprocessed in all samples studied, whereas that of type I procollagen was nearly always completely processed. There was a clear difference between malignant and benign tumours in the processing of the carboxyterminus of type I procollagen: a significant part of the carboxyterminal propeptide antigen was invariably associated with a collagenous domain in malignant tumours, whereas in benign tumours the free propeptide predominanted. The results indicate that interstitial procollagens are effectively processed in the tumour tissue during the fibroproliferative reaction typical of malignant ovarian tumours, whereas the processing of the procollagens released into peritoneal ascitic fluid is incomplete.

Ascitic Fluid↗
PubMed1991

Serum aminoterminal propeptide of type III procollagen in psoriasis and psoriatic arthritis: relation to liver fibrosis and arthritis.

Levels of serum aminoterminal propeptide of type III procollagen were measured in 170 patients with psoriasis (49% with coexistent psoriatic arthritis) who had liver biopsies performed during or before treatment with methotrexate or, in some cases, with retinoids. Psoriasis patients with fibrosis or cirrhosis in their liver biopsy specimens had a significantly higher mean serum aminoterminal propeptide of type III procollagen than did patients without fibrosis and without arthritis. Only 4% of patients without cirrhosis or fibrosis and no arthritis had an elevated serum aminoterminal propeptide of type III procollagen. In contrast, 38% of patients with psoriatic arthritis had an increased aminoterminal propeptide of type III procollagen in the absence of detectable liver fibrosis. It is concluded that the number of liver biopsies performed on methotrexate-treated psoriasis patients with or without arthritis may be reduced to a minimum as long as serum aminoterminal propeptide of type III procollagen is normal. Increased serum aminoterminal propeptide of type III procollagen in the absence of arthritis is a strong indicator of liver fibrogenesis and suggests the need for liver biopsy to monitor possible methotrexate-induced toxicity. In patients with psoriatic arthritis an increased aminoterminal propeptide of type III procollagen may be related to the joint disease. Patients with psoriatic arthritis and increased levels of aminoterminal propeptide of type III procollagen should therefore follow the established guidelines for the use of methotrexate in psoriasis.

Alkaline Phosphatase↗
PubMed1996

Elevated serum aminoterminal procollagen type-III-peptide parallels collagen accumulation in rats with secondary biliary fibrosis.

BACKGROUND/AIMS: The aminoterminal procollagen type-III-peptide, which can be released during collagen type III deposition, has been suggested as a serum marker of fibrogenesis in patients with chronic liver disease. However, longitudinal studies correlating procollagen type-III-peptide concentrations in serum with the evolution of liver fibrosis are still needed. The purpose of the present study was to prove the significance of procollagen type-III-peptide concentrations in serum as a non-invasive marker of liver fibrogenesis in an animal model that best resembles progressive human liver fibrosis. METHODS: In 88 female Wistar rats the biliary system was occluded by double ligation of the choledochal duct followed by retrograde injection of a mixture of prolamine/ethanole (Ethibloc). Sixteen rats served as controls. Groups of 8-10 rats were sacrificed at days 2, 7, 14, 21, 30, 32, 35, 60 and 90 after bile duct occlusion. In the groups histological staging (fibrosis score), determination of total liver hydroxyproline, measurement of serum procollagen type-III-peptide and routine liver function tests were performed. RESULTS: First histological signs of liver fibrosis were seen as early as 7 days after bile duct occlusion. Progressive fibrosis was paralleled by an increase of serum procollagen type-III-peptide. There was a significant correlation between serum procollagen type-III-peptide and histological stages of fibrosis (r = 0.80; p < 0.0001) as well as between serum procollagen type-III-peptide and hydroxyproline in total liver tissue (r = 0.85; p < 0.0001) CONCLUSIONS: These results indicate that: (1) complete bile duct occlusion in rats produces progressive hepatic fibrosis resembling human secondary biliary fibrosis, and (2) procollagen type-III-peptide concentrations in serum reflect ongoing collagen formation in the liver unrelated to serum markers of cholestasis and inflammation.

Animals↗
PubMed1990

Detection of procollagen biosynthesis using peptide-specific antibodies.

Peptides corresponding to selected sequences of the alpha 1 chain of the COOH propeptide of type I and type III human procollagen were synthesized and used as antigens to develop polyclonal and monoclonal antibodies. The antibodies were shown to be epitope specific using a peptide-based solid phase enzyme-linked immunoadsorbent assay. The antibodies were specific for the appropriate procollagens and the COOH propeptides isolated from serum-free culture supernatants of human skin fibroblasts. The rabbit antisera directed to the type I synthetic peptide bound the intact procollagen molecule and both the procollagen alpha 1(I) and alpha 2(I) chains after the reduction of the disulfide bonds. In addition, the antisera bound intact type I COOH propeptide, generated by bacterial collagenase treatment of procollagen, and the individual chains of the propeptide after reduction. In contrast, a monoclonal antibody to the type I peptide was able to bind only to the reduced form of the COOH propeptide. Both rabbit polyclonal and murine monoclonal antibodies directed to the type III synthetic peptide bound the intact and the individual chains of type III procollagen as well as the intact and reduced forms of the type III COOH propeptide. The antibodies have been used to detect procollagen synthesis in two human osteosarcoma cell lines and the differential expression of procollagen in the culture medium of rat lung fibroblasts grown in the presence or absence of glucocorticoids.

Amino Acid Sequence↗
PubMed1977

The disulphide-bonded nature of procollagen and the role of the extension peptides in the assembly of the molecule.

1. The molecular weights of chick tendon and cartilage procollagens, and their constituent polypeptides, were determined by gel filtration and gel electrophoresis. The values obtained are in good agreement and indicate that the mol.wts. of the secreted procollagens (types I and II) and their individual pro-alpha-chains are of the order of 405 000-445 000 and 137 000-145 000 respectively.2. Digestion of tendon procollagen with human rheumatoid synovial collagenase gave products consistent with the presence of large non-helical peptide extensions at both N-and C-termini. Electrophoretic analysis gave apparent mol.wts. of 17 500 and 36 000 for the respective N- and C-terminal extensions of pro-alpha1(I)-and pro-alpha2-chains, and inter-chain disulphide bonds were restricted to the C-terminal location. 3. During the biosynthesis of procollagen by tendon and cartilage cells a close correlation was observed between the extent of inter-chain disulphide bonding and the proportion of procollagen polypeptides having a triple-helical conformation. These processes appeared to commence in the rough endoplasmic reticulum and be completed in the smooth endoplasmic reticulum, but the rate at which they occur in cartilage cells is markedly slower than that found in tendon cells. 4. When the intracellular [14C]procollagen polypeptides present in the rough-endoplasmic-reticulum fractions of tendon and cartilage cells were analysed under non-reducing conditions on agarose/polyacrylamide composite gels, no significant pools of dimeric intermediates were detected. 5. In both cell types, inter-chain disulphide-bond formation occurred even when hydroxylation, and hence triple-helix formation, was inhibited. The presence of pro-alpha1- and pro-alpha2-components in a ratio of 2:1 in the disulphide-linked unhydroxylated procollagen isolated from tendon cells demonstrated that correct chain association occurs in the absence of hydroxylation. This observation is consistent with a model for the assembly of pro-gamma112-chains in which the recognition and selection of pro-alpha1-and pro-alpha2-chains in a 2:1 ratio are directed by the non-helical C-terminal extension peptides of tendon procollagen.

Anaerobiosis↗
PubMed1994

Interaction of procollagen I and other collagens with colligin.

Colligin is a collagen-binding glycoprotein of molecular mass 46000 Da localized to the endoplasmic reticulum (ER) of diverse kinds of cells that produce collagen I. In order to help define its role in collagen biosynthesis and to study the interaction of colligin with procollagen I in detail, the binding characteristics of colligin purified from L6 myoblasts have been studied. A total of 3 mol were found to bind/mol of procollagen I, with a Kd of about 25 nM. Both pure and separated pro alpha 1(I) and procollagen alpha 2 (I) chains were able to compete with procollagen I for binding to colligin. However, colligin binds to pro alpha 2 (I) with higher affinity than to pro alpha 1 (I). To find if the binding activity of colligin was altered during purification, an assay to measure colligin binding to procollagen in crude myoblast cell extracts was developed. This procedure gave the same binding parameters as did the highly purified colligin. Among different collagen types, colligin was found to bind to collagen I and collagen IV, but not to collagen III. In order to examine whether glycosylation or phosphorylation of colligin were required for the binding of colligin to procollagen I and to obtain enough colligin for further studies, recombinant protein was produced in Escherichia coli. An immunoaffinity purification scheme was used to get virtually pure protein in milligram yields. Comparison of the recombinant colligin with that isolated from L6 myoblasts showed that both types existed in solution as monomers and dimers. In addition, both types of colligins showed identical properties with regard to their binding to procollagen I and the isolated pro alpha 1(I) and pro alpha 2(I) chains. Post-translational modifications of colligin were thus not essential for binding to procollagen I.

Animals↗
PubMed1978

Codistribution of pericellular matrix proteins in cultured fibroblasts and loss in transformation: fibronectin and procollagen.

Antibodies to fibronectin and to distinct types of procollagens and collagens were used in immunofluorescent staining to localize these proteins in cell cultures. Normal human skin or lung fibroblasts produced a fibrillar pericellular matrix in which fibronectin and procollagen (types I and III) showed extensive codistribution. Fibronectin and procollagen were synthesized by the same cells as judged by double-stain immunofluorescence. Pericellular procollagen was specifically digested with collagenase without an effect on the fibrillar distribution of matrix fibronectin. Brief treatment with trypsin removed both matrix proteins. The human tumor cell lines HT-1080 (fibrosarcoma) and RD (rhabdomyosarcoma) produced little or no matrix fibronectin or procollagen. At sites of cell contact, simian virus 40-transformed lung fibroblasts (VA13) produced small amounts of pericellular fibrillar matrix fibronectin that codistributed with procollagen type I. Intracellular fibronectin and procollagen were visualized in all of these human sarcoma cell lines. When chicken embryo fibroblasts infected with a T class mutant (NY68) of Rous sarcoma virus temperature-sensitive for transformation were maintained at the nonpermissive temperature (41 degrees ) the cells had normal phenotype and a fibrillar matrix containing fibronectin and procollagen was present. At the permissive temperature (35 degrees ), the cells showed transformed phenotype and the matrix was lost. The failure to produce a pericellular fibronectin/collagen matrix may account for several phenotypic characteristics of transformed cultured fibroblasts.

Cell Line↗
PubMed1980

Thermal stability of type I and type III procollagens from normal human fibroblasts and from a patient with osteogenesis imperfecta.

Type I and type III procollagens were isolated from the medium of human fibroblast cultures in amounts adequate for examination by circular dichroism. Type I procollagen had a spectrum similar to that of type I procollagen and collagen from chicken embryos. The human type III procollagen showed a red shift not seen in type III collagen from calf skin. The midpoint (tm) for the helix-to-coil transition for both human procollagens was 40 degrees C. the same tm values were obtained with type I and type III procollagens synthesized by fibroblasts from a patient with osteogenesis imperfecta. Type I procollagen synthesized by the patient's fibroblasts, however, tended to aggregate more readily than type I procollagen from normal human fibroblasts, apparently because of a structural alteration of the protein.

Cells, Cultured↗
PubMed1980

A defect in the structure of type I procollagen in a patient who had osteogenesis imperfecta: excess mannose in the COOH-terminal propeptide.

Fibroblasts from normal human subjects and from a patient who had osteogenesis imperfecta were incubated with [3H]mannose, and types I and III procollagens were isolated from the culture medium. The type I procollagen from the patient's fibroblasts contained 2-3 time more [3H]mannose than the type I procollagen from the normal fibroblasts. In contrast, there was no difference in the [3H]mannose content of the type III procollagen simultaneously synthesized and secreted by the same cells. Isolation of a collagenase-resistant peptide fragment from the type I procollagen showed that the excess mannose was located in the COOH-terminal propeptide of the protein. Radioimmunoassays of the medium and the cell layer showed that the type I procollagen synthesized by the patient's fibroblasts was secreted into the medium more slowly than the type I procollagen synthesized by normal fibroblasts. These results appear to provide evidence for an alteration in the structure of procollagen in osteogenesis imperfecta.

Cells, Cultured↗
PubMed2004

Single amino acid substitutions in procollagen VII affect early stages of assembly of anchoring fibrils.

Procollagen VII is a homotrimer of 350-kDa pro-alpha1(VII) chains, each consisting of a central collagenous domain flanked by the noncollagenous N-terminal NC1 domain and the C-terminal NC2 domain. After secretion from cells, procollagen VII molecules form anti-parallel dimers with a C-terminal 60-nm overlap. Characteristic alignment of procollagen VII monomers forming a dimer depends on site-specific binding between the NC2 domain and the triple-helical region adjacent to Cys-2634 of the interacting procollagen VII molecules. Formation of the intermolecular disulfide bonds between Cys-2634 and either Cys-2802 or Cys-2804 is promoted by the cleavage of the NC2 domain by procollagen C-proteinase. By employing recombinant procollagen VII variants harboring G2575R, R2622Q, or G2623C substitutions previously disclosed in patients with dystrophic epidermolysis bullosa, we studied how these amino acid substitutions affect intermolecular interactions. Binding assays utilizing an optical biosensor demonstrated that the G2575R substitution increased affinity between mutant molecules. In contrast, homotypic binding between the R2622Q or G2623C molecules was not detected. In addition, kinetics of heterotypic binding of all analyzed mutants to wild type collagen VII were different from those for binding between wild type molecules. Moreover, solid-state binding assays demonstrated that R2622Q and G2623C substitutions prevent formation of stable assemblies of procollagen C-proteinase-processed mutants. These results indicate that single amino acid substitutions in procollagen VII alter its self-assembly and provide a basis for understanding the pathomechanisms leading from mutations in the COL7A1 gene to fragility of the dermal-epidermal junction seen in patients with dystrophic forms of epidermolysis bullosa.

Amino Acid Substitution↗
PubMed1982

Loss of type I procollagen gene expression in SV40-transformed human fibroblasts is accompanied by hypermethylation of these genes.

Transformation of human lung fibroblasts (WI-38) by Simian Virus 40 (SV40) resulted in a decline of 25-30% in the amount of secreted collagen. The collagen produced by the transformed fibroblasts contained no type I collagen (i.e. alpha 1(I) and alpha 2 chains), which was the major collagen component produced by untransformed fibroblasts. Measurement of the procollagen mRNA levels by dot hybridization with nick-translated procollagen-cDNA clones showed that the absence of type I collagen was due to the absence of alpha 1(I) and alpha 2 procollagen mRNAs. This result was confirmed by hybridization of cDNA to total RNA with southern blots of the procollagen clones. To clarify the mechanism by which type I procollagen gene transcription is abolished in transformed cells, the methylation patterns of the alpha 1(I) and alpha 2 procollagen genes in normal and SV40-transformed fibroblasts were compared, using the chicken alpha 1(I) and alpha 2 procollagen-cDNA clones as probes. Methylated sites were detected by means of the restriction endonuclease isoschizomers HpaII and MspI. Methylation of the procollagen alpha 1(I) and alpha 2 genes was increased in the SV40-transformed fibroblasts, concurrently with the loss of type I collagen synthesis. DNA methylation may thus contribute to altered regulation of gene expression upon cell transformation.

Cell Line↗
PubMed1998

HSP47, a collagen-specific molecular chaperone, delays the secretion of type III procollagen transfected in human embryonic kidney cell line 293: a possible role for HSP47 in collagen modification.

HSP47 is a stress protein (heat shock protein) which resides in the endoplasmic reticulum, and is postulated to function as a collagen-specific molecular chaperone. To elucidate the role of HSP47 in procollagen biosynthesis, we have established human embryonic kidney 293 cell lines, which were stably transfected with alpha1(III) procollagen chains with or without HSP47. 293 cells do not produce any extracellular matrix proteins including collagens, and the level of HSP47 expression is almost undetectable in this cell line. Recombinant type III procollagens in 293 cells form trypsin-resistant homotrimers, which are secreted into the medium as trimers in the presence or absence of recombinant mouse HSP47. The secretion of procollagen III was delayed in 293 cells stably transfected with proalpha1(III) collagen chains [293+proalpha1(III) cells] in comparison with human rhabdomyosarcoma cell line RD, which normally produces type III procollagens. In this study, we examined the rate of type III procollagen secretion in detail. In cells cotransfected with mouse HSP47 [293+proalpha1(III)+HSP47 cells], the rate of type III procollagen secretion was slower than in 293+proalpha1(III) cells. The binding of HSP47 with proalpha1(III) collagen chains was confirmed by immunoprecipitation using the chemical cross-linker, DSP. The electrophoretic mobility of proalpha1(III) collagen chains in 293+proalpha1(III) cells was slightly slower than that in RD cells, whereas the recombinant proalpha1(III) chains of 293+proalpha1(III)+HSP47 cells showed almost the same electrophoretic mobility as those of RD cells. The melting temperature (Tm) of type III procollagen in 293+proalpha1(III)+HSP47 cells was almost the same as that in RD cells, and the Tm in 293+proalpha1(III) cells was slightly higher than that in RD cells. These data suggest that the recombinant proalpha1(III) collagen chain is overmodified in 293+proalpha1(III) cells, but not in 293+proalpha1(III)+HSP47 cells.

Animals↗