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E M Tan

Publications and source records attributed to E M Tan.

At least 37 records · Page 2Linked to original sources
PubMed1998

Immunological characterization of heterochromatin protein p25beta autoantibodies and relationship with centromere autoantibodies and pulmonary fibrosis in systemic scleroderma.

Anticentromere antibodies (ACA) are immunological markers for the subset of systemic scleroderma with the symptoms calcinosis cutis, Raynaud's phenomenon, esophageal dysfunction, sclerodactyly, and telangiectasia (CREST). In Western blotting, some ACA-positive sera also recognize a doublet of 23 kDa (p23) and 25 kDa (p25) in addition to centromere protein antigens A (17 kDa), B (80 kDa), and C (140 kDa). Two forms of p25 have been shown to be human homologues of Drosophila heterochromatin-associated protein HP1. One form of p25 (p25beta) which was recently cloned in this laboratory was used to evaluate anti-p25beta antibody response in scleroderma sera. Of 318 scleroderma sera 42 had ACA (13.2%), and 16 of the 42 sera (38%) had anti-p25beta antibodies. On the other hand, 5 of 276 ACA-negative sera (1.8%) showed anti-p25beta antibody response, demonstrating that anti-p25beta antibody is significantly associated with the ACA response (P < 10[-8]). Clinically the anti-p25beta response was significantly associated with the CREST syndrome. Fourteen (36.8%) of 38 CREST patients compared to seven (2.5%) of 280 patients with other forms of scleroderma were anti-p25beta antibody positive (P < 10[-8]). The 14 CREST patients with anti-p25beta antibodies had significantly more interstitial lung disease than those without anti-p25beta antibodies (P < 0.003). There was also a tendency to increased liver involvement. Two dominant autoepitopes in p25beta were determined by Western blotting using p25beta recombinant fragments. In immunofluorescence C-terminal specific antibodies showed staining of heterochromatin, but N-terminal specific antibodies showed no staining. Interestingly, the majority of sera reacted preferentially with one or the other of the two dominant autoepitopes.

Autoantibodies↗
PubMed1998

Induction of human B2 bradykinin receptor mRNA and membrane receptors by IFNgamma.

A potential mechanism for the increased sensitivity of inflamed tissues to bradykinin is the upregulation of bradykinin receptor expression. We report that recombinant human IFNgamma stimulated a concentration-dependent increase in cell surface bradykinin receptor expression in intact T24 human epithelial-like cells, determined by radioligand binding analysis. Analysis of specific [3H]-bradykinin binding revealed that IFNgamma-treated cells had a two- to threefold increase in bradykinin receptor number compared to the controls with no effect on receptor affinity. The ability of IFNgamma to stimulate increased bradykinin receptor expression was abrogated by treatment with either the transcription inhibitor actinomycin D or the protein synthesis inhibitor cycloheximide. IFNgamma enhanced steady-state human B2 bradykinin receptor mRNA expression in the T24 cells in a dose-dependent manner. B2 bradykinin receptor mRNA expression was increased as early as 1 h following IFNgamma stimulation, and continued to accumulate for 24 h. Bradykinin-stimulated intracellular calcium mobilization was also increased in IFNgamma-treated T24 cells compared to controls. The ability of IFNgamma to upregulate B2 bradykinin receptors in primary epithelial cells was demonstrated using cultured human airway epithelial cells. These observations suggest that increasing IFNgamma levels during inflammation may upregulate the expression of B2 bradykinin receptors, leading to increased sensitivity to bradykinin.

Bradykinin↗
PubMed1998

Distinct cleavage products of nuclear proteins in apoptosis and necrosis revealed by autoantibody probes.

A central mechanism in apoptosis is the activation of proteases of the caspase (cysteine aspartases) family. Protease activation has also been implicated in necrosis, but its role in this cell death process and the identity of the proteases involved and their substrates, are unknown. Using human autoantibodies to well characterized cellular proteins as detecting probes in immunoblotting, we observed that a defined and somewhat similar set of nuclear proteins, including poly (ADP-ribose) polymerase (PARP) and DNA topoisomerase I (Topo I), were selectively cleaved during both apoptosis and necrosis of cultured cells induced by various stimuli. The resulting cleavage products were distinctively different in the two cell death pathways. In contrast to apoptosis, the cleavages of PARP and Topo I during necrosis were not blocked by the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (zVAD-fmk). These findings suggest that different proteases act in apoptosis and necrosis, and that although both cell death processes result in selective cleavage of almost identical cellular proteins, they can be distinguished immunochemically on the basis of their cleavage products.

Amino Acid Chloromethyl Ketones↗
PubMed1998

Effects of LTD4 on human airway smooth muscle cell proliferation, matrix expression, and contraction In vitro: differential sensitivity to cysteinyl leukotriene receptor antagonists.

The cysteinyl leukotrienes (CysLTs) mimic many of the features of asthma and are implicated in its pathophysiology. Little, however, is known about the effects of the CysLTs on airways remodeling. In this study the effects of leukotriene D4 (LTD4) on human airway smooth muscle (HASM) cell proliferation and expression of extracellular matrix proteins were investigated. LTD4 (0.1-10 microM) alone had no effect on DNA synthesis in HASM. LTD4, however, markedly augmented proliferation induced by the mitogen, epidermal growth factor (EGF, 1 ng/ml). The potentiating effect of LTD4 (1 microM) on EGF-induced DNA synthesis was abolished by pranlukast (1 microM) or pobilukast (30 microM), but unaffected by zafirlukast (1 microM). In contrast, pranlukast (pKB = 6.9), pobilukast (pKB = 7.0), and zafirlukast (pKB = 6.5) had equivalent potencies for inhibition of LTD4-induced contraction in human bronchus. LTD4 (0.1 or 10 microM) did not increase the total messenger RNA expression of the extracellular matrix proteins (pro-alpha[I] type I or alpha1[IV] type IV collagen), elastin, biglycan, decorin, and fibronectin, and did not influence tumor growth factor-beta (10 ng/ml)-induced effects on the expression of these proteins in HASM cells. These data indicate that LTD4 augments growth factor-induced HASM proliferation but does not alter the expression of various extracellular matrix components. The observed differences in sensitivity to the antagonists suggests that the former phenomenon may be mediated by a CysLT receptor distinct from that which mediates LTD4-induced HASM contraction. Collectively, these results provide preliminary evidence that CysLTs may play a role in airways remodeling in asthma.

Asthma↗
PubMed1997

Regulation of human interstitial collagenase (matrix metalloproteinase-1) promoter activity by fibroblast growth factor.

Basic fibroblast growth factor (bFGF) is a pleiotropic factor that is implicated in tissue remodeling. The growth factor is capable of up-regulating the expression of the interstitial collagenase (matrix metalloproteinase-1 or MMP-1) gene. In this study, the full-length human MMP-1 promoter, spanning 4.3 kb, was sequenced and the regulatory control of its activity by bFGF was examined in NIH3T3 fibroblasts. Several regulatory sequences, including five activator protein-1 (AP-1), five activator protein-2 (AP-2), five glucocorticoid-response elements and multiple ets/polyoma enhancer-binding 3 elements, were identified. Deletion constructs were prepared and transiently transfected into fibroblast cultures incubated with and without bFGF. The results showed that bFGF enhanced the activity of the deletion promoter fragments and the full-length MMP-1 promoter by sixfold or more in the cell cultures. Stimulation of the MMP-1 promoter activity by bFGF was reflected in substantial increase of the collagenase mRNA levels. A bFGF-responsive element appeared to be the AP-1 consensus sequence. Mutation of the first AP-1 site resulted in major reduction of the basal level of the MMP-1 promoter activity, supporting the notion that the AP-1 consensus sequence is essential for the constitutive expression of the MMP-1 gene. Furthermore, bFGF induction of the activity of the promoter constructs containing a mutant AP-1 site was essentially absent, suggesting that the regulatory element is necessary for the induction of the promoter activity by the growth factor. Thus, bFGF up-regulates MMP-1 gene expression in NIH3T3 fibroblasts via induction of its promoter activity that is dependent on an AP-1 consensus sequence.

3T3 Cells↗
PubMed1997

The autoimmunity-inducing xenobiotic mercury interacts with the autoantigen fibrillarin and modifies its molecular and antigenic properties.

The heavy metal mercury elicits a genetically restricted, anti-nucleolar autoantibody response that targets fibrillarin, a 34-kDa protein component of many small nucleolar ribonucleoprotein particles. The mechanisms by which a toxin such as mercury elicits an autoantibody response that predominantly targets a single intracellular protein autoantigen remain uncertain, but may be prefaced by mercury gaining access to the intracellular environment. Mercury-induced cell death was associated with loss of fibrillarin antigenicity and modification of the molecular properties of fibrillarin as revealed by aberrant migration under nonreducing conditions in SDS-PAGE. Addition of mercury to isolated nuclei also resulted in aberrant migration of fibrillarin, but not other nuclear autoantigens. The sensitivity of the HgCl2-induced modification of fibrillarin to 2-ME, iodoacetamide, and hydrogen peroxide suggested interaction of mercury with the two cysteines in the fibrillarin sequence. This was confirmed by mutation of the cysteines to alanines, which abolished the aberrant migration of fibrillarin in the presence of HgCl2. The modification of the molecular structure of fibrillarin by mercury reduced immunoprecipitation by anti-fibrillarin autoantibodies, pointing to unmodified fibrillarin as the B cell Ag and implicating mercury-modified fibrillarin as the source of T cell antigenicity. These observations demonstrate for the first time that an environmental toxin can alter the physicochemical properties of an autoantigen and may help to explain the antigenic specificity of mercury-induced murine autoimmunity.

Antibodies, Monoclonal↗
PubMed1997

High frequency of autoantibodies to insoluble cellular antigens in patients with chronic fatigue syndrome.

OBJECTIVE: To elucidate the humoral immune response in patients with chronic fatigue syndrome (CFS), by identification and characterization of autoantibodies. METHODS: Initial immunofluorescence histochemistry studies of sera using human HEp-2 cell substrate were followed by antibody class subtyping and colocalization studies with reference antibodies. Association of CFS autoantigens with insoluble cellular components was determined by in situ extraction of soluble components and subsequent immunofluorescence histochemistry studies on the extracted cell substrate. RESULTS: Of 60 CFS patients, 41 (68%) were positive for antinuclear antibodies. Localization of nuclear staining was found at the nuclear envelope (52%), in reticulated speckles (25%), in nucleoli (13%), and in dense fine speckles (5%). Twenty-eight CFS sera (47%) also had antibodies to cytoplasmic antigens. The major cytoplasmic staining pattern was of the intermediate filament type (35%). The observed nuclear envelope pattern of staining co-localized with lamina-associated polypeptide 2 (an integral nuclear membrane protein), the reticulated speckle pattern co-localized with non-small nuclear RNP splicing factor SC-35, and the intermediate filament pattern co-localized with vimentin. The intermediate filament antigen was shown to be vimentin in immunoblotting experiments using recombinant human vimentin, and one of the nuclear envelope antigens was shown previously to be lamin B1. Fifty of the 60 CFS patients (83%) had antibodies to one or another of these antigens, all of which are relatively insoluble cellular antigens, whereas a control group of patients without chronic fatigue had a significantly lower frequency of such antibodies (17%). CONCLUSION: The high frequency of autoantibodies to insoluble cellular antigens in CFS represents a unique feature which might help to distinguish CFS from other rheumatic autoimmune diseases.

Antibodies, Monoclonal↗
PubMed1997

Reference sera for antinuclear antibodies. II. Further definition of antibody specificities in international antinuclear antibody reference sera by immunofluorescence and western blotting.

OBJECTIVE: To define the fine specificity of the 10 reference sera used for determination of antinuclear antibodies (ANA) and ANA subsets which are available from the Arthritis Foundation (AF) and from the Centers for Disease Control and Prevention (CDC). METHODS: AF/CDC sera were assessed by experienced laboratory staff, using indirect immunofluorescence and Western blotting. RESULTS: The original assignment of fluorescence patterns to 4 reference sera was confirmed, and the fluorescence intensities were determined using reference fluorescent beads. On Western blots, sera AF/CDC2 (anti-SS-B/La) and AF/CDC7 (anti-SS-A/Ro) did not detect Ro antigens, sera AF/CDC9 and AF/CDC10 appeared to be monospecific anti-Scl-70 and anti-Jo-1 sera, respectively, serum AF/CDC4 (anti-U1 small nuclear RNP) recognized the 70-kd band, and serum AF/CDC5 recognized the Sm antigen with its multiple bands. Semiquantitative analyses revealed that AF/CDC5, AF/CDC2, and AF/CDC10 were strongly reactive sera, whereas AF/CDC4 and AF/CDC9 were much weaker and should be used at lower dilutions on Western blots. CONCLUSION: The AF/CDC ANA reference sera, originally described as reference reagents for indirect immunofluorescence and double immunodiffusion techniques, are also useful for Western blotting. The data presented herein further support the use of these sera for reference purposes.

Antibodies, Antinuclear↗
PubMed1997

Range of antinuclear antibodies in "healthy" individuals.

OBJECTIVE: To determine the range of antinuclear antibodies (ANA) in "healthy" individuals compared with that in patients with systemic lupus erythematosus (SLE), systemic sclerosis (SSc; scleroderma), Sjögren's syndrome (SS), rheumatoid arthritis (RA), or soft tissue rheumatism (STR). METHODS: Fifteen international laboratories experienced in performing tests for ANA by indirect immunofluorescence participated in analyzing coded sera from healthy individuals and from patients in the 5 different disease groups described above. Except for the stipulation that HEp-2 cells should be used as substrate, each laboratory used its own in-house methodology so that the data might be expected to reflect the output of a cross-section of worldwide ANA reference laboratories. The sera were analyzed at 4 dilutions: 1:40, 1:80, 1:160, and 1:320. RESULTS: In healthy individuals, the frequency of ANA did not differ significantly across the 4 age subgroups spanning 20-60 years of age. This putatively normal population was ANA positive in 31.7% of individuals at 1:40 serum dilution, 13.3% at 1:80, 5.0% at 1:160, and 3.3% at 1:320. In comparison with the findings among the disease groups, a low cutoff point at 1:40 serum dilution (high sensitivity, low specificity) could have diagnostic value, since it would classify virtually all patients with SLE, SSc, or SS as ANA positive. Conversely, a high positive cutoff at 1:160 serum dilution (high specificity, low sensitivity) would be useful to confirm the presence of disease in only a portion of cases, but would be likely to exclude 95% of normal individuals. CONCLUSION: It is recommended that laboratories performing immunofluorescent ANA tests should report results at both the 1:40 and 1:160 dilutions, and should supply information on the percentage of normal individuals who are positive at these dilutions. A low-titer ANA is not necessarily insignificant and might depend on at least 4 specific factors. ANA assays can be a useful discriminant in recognizing certain disease conditions, but can create misunderstanding when the limitations are not fully appreciated.

Adult↗
PubMed1997

Immune response to cyclin B1 in hepatocellular carcinoma.

Proteins expressed by plasmids encoding human cyclins and cyclin-dependent kinase 2 (CDK2) were used as antigens in immunoblotting. Fifteen of 100 patients with hepatocellular carcinoma (HCC) were found to have autoantibodies reactive with cyclin B1 and with a 40-kd degradation product of cyclin B1-glutathione-S-transferase (GST) fusion protein. Only one serum was found to react with cyclin A and another single serum with CDK2 but no antibodies were detected to cyclin D1 and E. The basis for autoimmune responses to cyclin B1 in HCC are unknown at the present time but the possibilities might include aberrations in cyclin B1 regulation leading to altered product or its expression which resulted in stimulation of immune reactions.

Animals↗
PubMed1997

Heterochromatin protein HP1Hsbeta (p25beta) and its localization with centromeres in mitosis.

Some autoimmune sera containing anticentromere autoantibodies also recognize a doublet of Mr 23 000 (p23) and 25 000 (p25) in addition to CENP (centromere protein)-A (Mr 19 000), -B (Mr 80 000), and -C (Mr 140 000). A p25 antigen (HP1(Hsalpha)) has been shown to be a human homolog of Drosophila HP1 (heterochromatin protein 1). We have isolated a cDNA clone encoding another form of p25 (HP1(Hsbeta ) or p25beta) from a lambdaZap HepG2 library using human autoimmune serum. The deduced amino acid sequence of the clone contained a conserved chromodomain (chromatin modifier domain) in the N-terminal region and a heterochromatin binding domain in the C-terminal region. In immunofluorescence experiments, only affinity purified antibodies reactive with the C-terminal (amino acids 70-185) domain showed nucleoplasmic and heterochromatin staining, whereas N-terminal (amino acids 1-115) specific antibodies were nonreactive. In metaphase chromosome spreads, the C-terminal domain antibody was also localized to the centromeric regions of chromosomes. Association with centromeres was most prominent at anaphase and changed to a more generalized association with whole chromosomes in telophase. The cooccurrence of autoantibodies to centromere proteins and HP1 in certain autoimmune diseases might be a reflection of coordinated immune responses to these closely associated sets of proteins.

3T3 Cells↗
PubMed1997

Diversity of antinuclear antibody responses in hepatocellular carcinoma.

BACKGROUND/AIMS: The development of antinuclear antibodies (ANA) in malignancies has been described but its mechanism is still not understood. The aim of this study was to examine ANA specificities in hepatocellular carcinoma to further understand autoimmunity in cancer. METHODS: Two hundred and four hepatocellular carcinoma patients were compared with 68 chronic hepatitis C, with 126 chronic hepatitis B and with 30 alcoholic liver cirrhosis patients, as well as with 87 healthy donors. Indirect immunofluorescence, immunoblotting, and immunoprecipitation were used to study ANA reactivities. RESULTS: Hepatocellular carcinoma had a significantly higher frequency of ANA using HEp-2 cells as substrate (31%) than chronic hepatitis C (10%), chronic hepatitis B (9.5%), alcoholic liver cirrhosis (10%) or healthy donors (4.5%). A great diversity of ANA specificities was found in hepatocellular carcinoma. Three hepatoma sera had antibodies that co-localized with non-snRNP splicing factor SC35, suggesting that the antigenic targets might be involved in mRNA splicing. We identified antibodies to two known nuclear autoantigens: fibrillarin and p330d/CENP-F. These autoantigens are involved in the 5' processing of precursor ribosomal RNA transcripts and in mitotic functions, respectively. CONCLUSIONS: Diversity was found in the autoantibody specificity, in contrast to the specific subsets of autoantibodies seen in several systemic rheumatic autoimmune diseases. Our data suggest that immune response in hepatocellular carcinoma targets important proteins involved in cellular biosynthetic or proliferative functions.

Adult↗
PubMed1997

Major suppression of pro-alpha1(I) type I collagen gene expression in the dermis after keloid excision and immediate intrawound injection of triamcinolone acetonide.

BACKGROUND: A keloid is a benign tumor that contains excess collagen, primarily type I collagen. A common therapy is intralesional injection of a glucocorticosteroid, such as triamcinolone acetonide (TA). Surgical excision is also common; often a glucocorticosteroid is injected weeks after excision when wound repair has already begun. OBJECTIVE: Our purpose was to determine the efficacy of TA in reducing the pro-alpha1(I) type I collagen mRNA in the dermis, when TA is injected into the wound bed immediately after surgical excision of the keloid. METHODS: Six patients with previously untreated keloids were studied. Three were treated with 10 mg/ml of TA immediately after excision of the keloid (experimental group); the other three patients were not treated with TA until 2 weeks after excision (control). Punch biopsy specimens were obtained from the TA-treated sites 2 weeks after removal of the keloid and from the wounds of the control group of patients before they were treated with TA. Sections were prepared for in situ hybridization analysis of the pro-alpha1(I) collagen mRNA, as well as for histochemical analysis of collagen fibers. RESULTS: All keloids showed greatly elevated levels of pro-alpha1(I) type I collagen mRNA in the dermis. Postsurgical wounds injected with TA after removal of the keloid expressed decreased pro-alpha1(I) collagen transcripts, compared with skin not treated with TA. The collagen bundles were also thinner and less dense in the TA-treated skin. CONCLUSION: Downregulation of the type I collagen gene expression is elicited by immediate TA injection after keloid excision. This suggests that prevention of recurrent keloid growth is possible if surgical excision is accompanied by immediate TA injection into the wound bed and that healing of the wound is not apparently compromised by inhibition of type I collagen gene expression.

Administration, Topical↗
PubMed1997

Basic FGF regulates interstitial collagenase gene expression in human smooth muscle cells.

Basic fibroblast growth factor (bFGF) is a mitogenic factor that is implicated in smooth muscle cell growth in atherosclerosis and vascular restenosis. In this study, we examined the effect of bFGF on the expression of the interstitial collagenase gene in human vascular smooth muscle cells. Results from Northern transfer analysis showed that bFGF increased collagenase mRNA levels greater than threefold as early as 24 h. Collagenase pre-mRNA levels were elevated approximately threefold by bFGF, according to RT-PCR analysis. Transient transfections of the smooth muscle cells with a 4.4-kb human collagenase promoter-CAT reporter gene, however, failed to show upregulation of the promoter activity by bFGF. Interestingly, transfections with deleted fragments containing promoter sequences from -1047 to -2271 resulted in modest stimulation of the collagenase-CAT promoter activity by bFGF, bFGF did not alter the stability of the collagenase mRNA, as demonstrated by degradation studies. The enhanced collagenase mRNA levels elicited by bFGF were reflected in increased amounts of collagenase protein that were detected by Western blot analysis. In summary, bFGF upregulates the interstitial collagenase expression, resulting in turnover of the extracellular matrix, an event that could facilitate smooth muscle cell migration and proliferation during the early stages of atherosclerosis and restenosis.

Cells, Cultured↗
PubMed1997

High frequency of neoplasia in patients with autoantibodies to centromere protein CENP-F.

OBJECTIVE: To study the clinical features of patients with autoantibodies to centromere protein CENP-F and the frequency of CENP-F autoantibodies in patients with various diseases. DESIGN: Retrospective clinical and serologic study. METHODS: Thirty-six patients with anti-CENP-F were identified by a characteristic pattern of indirect immunofluorescence (IIF) on HEp-2 cells. Fifty patients with melanoma, 50 with breast cancer, 10 with lung cancer, 354 with systemic sclerosis, 120 with systemic lupus erythematosus and 50 with rheumatoid arthritis were also studied. Recombinant proteins were produced from 5 CENP-F cDNA clones representing amino acids 2192-3317 (p-F1), 5561-7126 (p-F2), 5892-6883 (p-F3), 7538-10,116 (p-F4) and 9242-10,096 (p-F5). The presence of CENP-F antigen was studied in a breast carcinoma cell line, cryosections of breast carcinoma, normal breast tissue and tonsils. RESULTS: Twenty-two of 36 patients with CENP-F antibodies had neoplasms; breast (9/22) and lung (5/22) cancer were the most common diagnoses. Thirty-three sera were available for further study; when tested for reactivity to the recombinant peptides, the sera of 21 of 21 patients with neoplasms and 5 of 12 patients with other diseases bound the C-terminal p-F4 peptide. When the terminal third of the p-F4 peptide (p-F5) was studied, a significant difference in pattern of reactivity was not detected. By comparison, the frequency of reactivity with peptides representing other domains of CENP-F was less than that with p-F4 (p-F2 > p-F3 > p-F1). CENP-F autoantibodies were not found in any of the control sera from patients with systemic lupus erythematosus, rheumatoid arthritis or systemic sclerosis or in unselected sera from various malignancies. CENP-F antigens were identified in breast carcinoma tissue but were rarely observed in normal tissues. CONCLUSIONS: A high proportion of individuals with CENP-F antibodies have neoplasia, and there is a bias among their sera for reactivity with determinants in the carboxy terminal domain of CENP-F. CENP-F antigens appear to be highly expressed in malignant tissues.

Adult↗
PubMed1996

Biosynthesis and processing of type XVI collagen in human fibroblasts and smooth muscle cells.

The alpha 1(XVI) collagen chain, recently identified by cDNA cloning, exhibits structural similarity to a subgroup of collagens that associate with collagen fibrils. Recombinant alpha 1(XVI) collagen chains produced in embryonic kidney cells are able to form stable homotrimers, which are rapidly converted into smaller polypeptides after secretion into the culture medium. In this study, we investigated the biosynthesis of native type XVI collagen by immunoprecipitation of metabolically labeled human cells. Dermal fibroblasts and arterial smooth muscle cells were precipitated with three antibodies raised against distinct regions in the N- and C-terminal part of the human alpha 1(XVI) collagen chain. A disulfide-bonded polypeptide of 220 kDa was obtained from the culture medium, cells and extracellular matrix with all three antibodies. This polypeptide is sensitive to bacterial collagenase digestion and partially resistant to pepsin digestion, suggesting that it is the endogenous alpha 1(XVI) collagen chain. Pulse/chase experiments showed that the newly synthesized alpha 1(XVI) chains are secreted into the medium and deposited in the extracellular matrix in a time-dependent manner. Unlike the recombinant chain, the native type XVI collagen does not undergo extensive proteolytic processing upon secretion. Both cell types deposit a substantial amount of the newly synthesized alpha 1(XVI) chain into the extracellular matrix, in which the 220-kDa polypeptide is the only product immunoprecipitated. There is little evidence for the presence of another constituent chain. The data are consistent with a nomotrimeric chain composition for type XVI collagen. No apparent difference exists in the rate of synthesis and secretion between fibroblasts and smooth muscle cells. Indirect immunofluorescence microscopy showed an extracellular distribution of type XVI collagen, which is located close to cells but not associated with fibrillar structures.

Cells, Cultured↗