Synthesis of collagen by mammalian cell lines of fibroblastic and nonfibroblastic origin

Metabolism in the Tumor Microenvironment

Experiments in culture systems where one cell type is provided with abundant nutrients and oxygen have been used to inform much of our understanding of cancer metabolism. However, many differences have been observed between the metabolism of tumors and the metabolism of cancer cells grown in monoculture. These differences reflect, at least in part, the presence of nonmalignant cells in the tumor microenvironment and the interactions between those cells and cancer cells. However, less is known about how the metabolism of various tumor stromal cell types differs from that of cancer cells, and how this difference might inform therapeutic targeting of metabolic pathways. Emerging data have identified both cooperative and competitive relationships between different cell types in a tumor, and this review examines how four abundant stromal cell types in the tumor microenvironment, fibroblasts, T cells, macrophages, and endothelial cells, contribute to the metabolism of tumors.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

A traffic-activated Golgi-based signalling circuit coordinates the secretory pathway

As with other complex cellular functions, intracellular membrane transport involves the coordinated engagement of a series of organelles and machineries; however, the molecular basis of this coordination is unknown. Here we describe a Golgi-based signalling system that is activated by traffic and is involved in monitoring and balancing trafficking rates into and out of the Golgi complex. We provide evidence that the traffic signal is due to protein chaperones that leave the endoplasmic reticulum and reach the Golgi complex where they bind to the KDEL receptor. This initiates a signalling reaction that includes the activation of a Golgi pool of Src kinases and a phosphorylation cascade that in turn activates intra-Golgi trafficking, thereby maintaining the dynamic equilibrium of the Golgi complex. The concepts emerging from this study should help to understand the control circuits that coordinate high-order cellular functions.

Flexor tendon wound healing in vitro: lactate up-regulation of TGF-beta expression and functional activity

Flexor tendon wound healing in zone II is complicated by adhesions to the surrounding fibro-osseous sheath. These adhesions can significantly alter tendon gliding and ultimately hand function. Lactate and transforming growth factor-beta (TGF-beta) are two important mediators of wound healing that have been demonstrated to independently increase collagen production by cells of the tendon sheath, epitenon, and endotenon. This study examined the effects of lactate on TGF-beta peptide and receptor production by flexor tendon cells. Tendon sheath fibroblasts, epitenon tenocytes, and endotenon tenocytes were isolated from rabbit flexor tendons and cultured separately. Cell cultures were supplemented with 50 mM lactate, and the expression of three TGF-beta peptide isoforms (beta1, beta2, and beta3) and three receptor isoforms (R1, R2, and R3) was quantified with enzyme-linked immunosorbent assays. TGF-beta functional activity was also assessed with the addition of tendon cell conditioned media to mink lung epithelial cells transfected with a luciferase reporter gene expression construct responsive to TGF-beta. Supplementation of the cell culture medium with lactate significantly (p < 0.05) increased the expression of all TGF-beta peptide and receptor isoforms in all three cell lines. Tendon sheath fibroblasts exhibited the greatest increases in beta1 and beta2 peptide isoform expression (30 and 23 percent, respectively), whereas endotenon tenocytes demonstrated the greatest increase in beta3 peptide expression (32 percent). Epitenon tenocytes exhibited the greatest increases in receptor isoform R1 and R2 expression (17 and 19 percent, respectively). All three tendon cell types demonstrated significant (p < 0.05) increases in TGF-beta functional activity when exposed to lactate. Epitenon tenocytes demonstrated the greatest increase in activity (>4 times control values), whereas tendon sheath fibroblasts demonstrated the highest overall levels of total TGF-beta functional activity. Lactate significantly increased TGF-beta peptide (beta1, beta2, and beta3) expression, receptor (R1, R2, and R3) expression, and functional activity, suggesting a common pathway regulating tendon cell collagen production. Modulation of lactate and TGF-beta levels may provide a means of modulating the effects of TGF-beta on adhesion formation in flexor tendon wound healing.

Methylation of the alpha 2(I) collagen gene in chemically transformed rat liver epithelial cells

W8 cells, 2-N-(acetoxyacetyl)aminofluorene-transformed rat liver epithelial-like cells, secrete no alpha 2(I) collagen chains. This paper reports the first demonstration of DNA methylation in the promoter-5' region of an alpha 2(I) collagen gene which occurs in W8 cells. Since inhibition of methylation by azacytidine induces transcription of the alpha 2(I) gene, DNA methylation of W8 alpha 2(I) promoter-5' region could contribute to altered collagen production in these cells.

Promotion of collagen production by human fibroblasts with gastric cancer cells in vitro

To elucidate the histogenesis of gastric scirrhous cancer, the promotion of collagen production by normal human skin fibroblasts (HSF-1) with human gastric cancer cells (KATO-III, MKN-45 and MKN-28) was investigated by direct coculture and parabiotic culture. Argyrophilic collagenous fibers were demonstrated among fibroblasts on both direct cocultures and parabiotic cultures of the fibroblasts with gastric cancer cells. Microscopic examination showed that these fibers appeared earlier and were more abundant and thicker in direct cocultures and parabiotic cultures than in single cultures of fibroblasts. Gastric cancer cells in single or parabiotic culture did not form argyrophilic fibers. For quantitative proof of the promotion of collagen production by fibroblasts with gastric cancer cells, hydroxyproline produced by fibroblasts was measured. Much higher fibroblast hydroxyproline values were obtained in parabiotic cultures with gastric cancer cell lines than in single cultures of HSF-1. Moreover, the rate of collagen synthesis by HSF-1 was much higher than that of any gastric cancer cell line tested. These results demonstrate that gastric cancer cells enhance collagen production by fibroblasts in vitro. This finding suggests that they may produce a factor promoting fibroblast collagen synthesis and that this may contribute to the formation of stromal collagen in human gastric scirrhous cancer.

Extracellular matrix proteins of human epidermal keratinocytes and feeder 3T3 cells

Cultures of human epidermal keratinocytes obtained from adult epidermis were initiated using irradiated BALB/3T3 cells as feeder layers. At different stages of confluence of the epidermal islands, feeder cells were removed and the extracellular matrix proteins of both pure component cells and cocultures were analyzed biochemically and by immunochemical methods and compared to those of skin fibroblasts of the same donors. The keratinocytes synthesized and secreted fibronectin and small amounts of laminin and type IV collagen. In addition, a nondisulfide-linked collagenous polypeptide (Mr = 120,000) was synthesized by the keratinocytes and was confined to the cell layers. Collagenous polypeptides with Mr = 120,000 were also synthesized by organ cultures of epidermal tissue and were detected in its acid or detergent extracts but again no secretion to culture medium was found. The Mr = 120,000 collagen had biochemical and immunological properties distinct from those of types I-V collagens. In immunofluorescence of keratinocyte cultures, fibronectin staining was prominent in the lining marginal cells of the expanding periphery of the epidermal cell islands but was not detected in the terminally differentiating cells in the upper layers of stratified colonies. Very little type IV collagen was found deposited in pericellular matrix form by the keratinocytes. In contrast, the mouse 3T3 feeder cells were found to produce both type IV collagen and laminin in addition to the previously identified connective tissue glycoproteins of fibroblasts, interstitial procollagens, and fibronectin. Basement membrane collagen of the 3T3 cells was found deposited as apparently unprocessed procollagen alpha 1(IV) and alpha 2(IV) chains. The production in culture conditions of basal lamina glycoproteins by the fibroblastic feeder cells may promote the attachment and growth of the cocultured keratinocytes.

Collagen synthesis in human fibroblasts: effects of ascorbic acid and regulation by hydrocortisone

The effects of hydrocortisone and ascorbic acid on collagen and noncollagen protein synthesis, and on growth were examined in fibroblasts derived from normal human dermis. When the medium was supplemented with 0.28 mM ascorbic acid, the apparent rate of collagen production increased 2-3 fold over the culture cycle. Ascorbic acid also caused a small increase in the apparent rate of synthesis of noncollagen protein and an elevation in growth rate and maximum cell density. Growth was not required for the increase in collagen production since addition of ascorbate to confluent cultures induced a similar increase. Hydrocortisone (1.5 microM) blocked the ascorbate-related increase in collagen production during growth and in confluent cultures. The hormone simultaneously increased the apparent rate of noncollagen protein production and maximum cell density, suggesting that the effect on collagen synthesis was specific. Inhibition of collagen production by hydrocortisone was observed only in the presence of ascorbate, while the increase in growth and noncollagen protein production occurred in the presence and absence of the vitamin.

Some aspects of the modulation and regulation of collagen synthesis in vitro

We reviewed here a number of publications containing data on the quantitative aspects of collagen synthesis in vitro. In one section we discussed the factors which modulate the amount of collagen synthesized in various culture systems and in another section we presented experimental evidence for regulatory mechanisms operating in collagen synthesis on the transcriptional and/or translational levels. We believe that growing knowledge of the mechanisms controlling collagen synthesis will help us to understand and deal with fibrotic processes better.

Glucocorticoid receptors and inhibition of neonatal mouse dermal fibroblast growth in primary culture

Primary cultures of dermal fibroblasts from neonatal mice were used to investigate some of the anti-inflammatory effects of glucocorticoids in vitro as influenced by the genetic background of two different strains of mice (A/J and C47 Bl/6J). Fibroblasts were cultured in the absence or presence of various glucocorticoids for 2-7 days. After 4-7 days in the presence of steroid, DNA synthesis was reduced by 50-85% while protein synthesis was inhibited by 50-60%. Corticosterone produced a dose-dependent inhibition of DNA synthesis in these cells with a 50% reduction occurring at 10 nM. Specific, high affinity, low capacity binding proteins for [3H]dexamethasone or [3H]triamcinolone acetonide were identified in the cytoplasm of neonatal dermal fibroblasts which had an apparent Kd of 9 nM and approximately 5,200-6,400 binding sites/cell. Sedimentation analysis of the [3H]triamcinolone acetonide-receptor complexes on low salt glycerol gradients exhibited binding in the 7 to 8 S region of the gradients. These studies demonstrate that inhibition of growth of primary cultures of mouse neonatal dermal fibroblasts by glucocorticoids is probably mediated by a receptor-mediated pathway, and that this primary culture system might be useful in delineating other anti-inflammatory effects of glucocorticoids in vitro.

Developmental pattern of cAMP, adenyl cyclase, and cAMP phosphodiesterase in the palate, lung, and liver of the fetal mouse: alterations resulting from exposure to methylmercury at levels inhibiting palate closure

Exposure to methylmercury (MeHg: 10 mg Hg/kg maternal body weight) on 12(6) (days hours) of gestation significantly delays palate closure in the Swiss Webster CFW mouse. The cAMP content and activity of adenyl cyclase and phosphodiesterase (PDE) were measured in the tissues of control and MeHg-induced cleft palates between 13(6) and 17(6) of gestation. Lung and liver were investigated similarly to determine if MeHg affected the adenyl cyclase system of the palate in a unique manner. In control palatal tissue, cAMP levels increased sharply from 13(22) (undetectable) to 14(6) (maximum). PDE activity increased similarly up to 14(2), but decreased 50% between 14(2) and 14(6). Since it has been reported that cAMP induces the synthesis of PDE, the difference in cAMP/PDE from 13(22) to 14(2) and from 14(2) to 14(6) suggests the localization of relatively high levels of cAMP in at least two separate compartments. Between 14(6) and 14(10), the adenyl cyclase activity of control palates decreased significantly. This rapid decrease suggests relatively high adenyl cyclase activity in the medial edge epithelial cells which undergo autolysis prior to shelf fusion (centered at 14(15). Maternal MeHg administration at 12(6) delayed the median time of palatal shelf rotation (14(13)) by 5 hours, and significantly altered the developmental pattern of the adenyl cyclase system. Thus, the increase in cAMP between 14(2) and 14(6) was abolished and the decrease in adenyl cyclase activity between 14(6) and 14(10) was delayed by almost 20 hours. These changes may be manifestions of a MeHg-induced delay in medial edge epithelial cell differentiation. In a previous study, we observed that the fetal liver exhibits the highest MeHg concentration of all tissues. Since MeHg only slightly altered the adenyl cyclase system of the fetal liver compared to the lung and palate (in which MeHg uptake is considerably less), it may be that the effects of MeHg on palatal tissue are not due to a direct effect of MeHg on components of the adenyl cyclase system.

Characterization of collagen synthesized by normal and chemically transformed rat liver epithelial cell lines

A rat liver epithelial cell line (K16) and a 2-[N-(acetoxyacetyl)amino]fluorine-transformed K16 cell line (W8) [Weinstein, I.B., Yamaguchi, R., Gerbert, R., & Kaighn, M.E. (1975) In Vitro 11, 130-141] synthesize and secrete similar quantities of collagenous proteins. The transformed cells produce more total protein so that the percent collagen produced is decreased compared to that of the parent cell line. The type of collagen produced by the transformants differed from that of the parent cell line. After limited pepsin digestion, the pepsin-resistant collagen molecules synthesized by K16 cells precipitated at 2.6 M NaCl and contained both alpha 1 (I) and alpha 2 chains in a 2.5:1 ratio. The collagen synthesized by the W8 cells precipitated at higher salt concentrations, and no pepsin-resistant alpha 2 chains could be demonstrated by CM-cellulose chromatography or gel electrophoresis. The cyanogen bromide peptides of the W8 alpha 1 chains did not cochromatograph with type I rat skin collagen cyanogen bromide peptides on CM-cellulose chromatography, whereas the alpha 1 chains of the K16 cells did cochromatograph. The conversion of procollagen to collagen was also decreased in the transformant cells. Therefore, the chemical transformation of K16 produced transformants with increased protein synthesis and altered collagen metabolism.

Involvement of glucocorticoids in the development of the secondary palate

Genetic differences between various inbred strains of mice in the levels of glucocorticoid receptors embryonic in maxillary mesenchyme cells appear to be reflected in the magnitude of the responses to steroids in these cells. High levels of glucocorticoids cause significant growth inhibition in maxillary mesenchyme cells with subsequent alterations in the production of extracellular matrix components. The presence of higher levels of cytoplasmic glucocorticoid receptor proteins may be one factor which could predispose those strains such as A/J to a greater inhibition of craniofacial growth in vivo by glucocorticoids and therefore increase the frequency of cleft palate production. Furthermore, women with infertility treated with glucocorticoids to support pregnancy give birth to infants with a marked decrease in birth weight [98]. Pharmacologic doses of glucocorticoids can also cause a dramatic reduction in the growth of a number of fetal tissues in mice and humans. In fact, there is evidence that glucocorticoids may be a causative factor in the production of cleft palate in primates [52]. The nature of the molecular elements which determine the biochemical and physiologic responses to glucocorticoids in the palate still remains largely unknown. Although in the mouse there is some evidence to suggest that the major histocompatibility locus (H-2) might be involved, the level(s) at which this control is exerted is unknown. It is possible that this locus may regulate in some manner the level of glucocorticoid receptors and the response to glucocorticoids in the secondary palate. Moreover, there is evidence to suggest that other genes distinct from, but closely linked to the H-2 locus may be important in determining both the strain-dependent differences in susceptibility to glucocorticoid-induced cleft palate and the intracellular levels of cyclic AMP in the secondary palate. It is also apparent that glucocorticoids in conjunction with other hormones or growth factors such as epidermal growth factor and agents which regulate cyclic nucleotide metabolism are essential for the normal development of the secondary palate. Excesses or deficiencies in either the level of these growth regulators and/or in their receptors in specific fetal tissues at defined periods in development are likely to lead to certain fetal malformations. Definition and integration of the genetic, biochemical, and endocrine factors which are involved in the control of cellular growth as influenced by alterations in the composition of cell surface and extracellular matrix components should provide some insights into the events associated with normal palatogenesis.

Expression of collagen biosynthetic activities in lymphocytic cells

Immunoglobulin-producing Merwin plasma cells, MPC-11, have been found to contain proplyl hydroxylase (prolyl-glycyl-peptide,2-oxoglutarate:oxygen oxidoreductase; EC 1.14.11.2) activity and its crossreacting protein, as well as hydroxyproline and a collagenous protein that could not be classified as type I, II, or III collagen. Friend leukemic cells, on the other hand, contained only prolyl hydroxylase. Thymus-derived (T) lymphocytes and bone-marrow-derived (B) lymphocytes freshly isolated from BALB/c mice expressed low but significant prolyl hydroxylase activity. Upon stimulation with phytohemagglutinin, the enzyme activity in T cells increased 22- to 29-fold. Crossreacting protein was also increased and appeared more stable than the prolyl hydroxylase. The effect of lipopolysaccharide stimulation on B cells uas similar but not as pronounced. Thus, even when not accompanied by other collagen biosynthetic activities, prolyl hydroxylase is present in all cells of hematologic origin.

Dependence of the differentiated state on the cellular environment: modulation of collagen synthesis in tendon cells

In an adequate environment, primary avian tendon cells are capable of retaining both the full expression of differentiated function and a correct morphological orientation for 1 week in culture. At high density and in the presence of ascorbate, they are fully stabilized in that they devote 25-30% of their total protein synthesis to collagen, a level comparable to that in tendon cells in ovo. However, either at low density or in medium without ascorbate, they synthesize collagen at only a third of this level. If plated on a collagen matrix, these cells will orient themselves in a manner similar to that of tendon cells in vivo. Furthermore, they are capable of fully modulating the percentage of collagen synthesis upon addition or removal of ascorbate and serum. The variation in the percentage of collagen produced is a result of alterations in collagen synthesis rather than of changes in total protein synthesis or hydroxylation of proline in collagen. Primary avian tendon cells, therefore, provide a suitable model for understanding the stability of the differentiated state, the mechanism of action of ascorbate, and the regulation of collagen biosynthesis.

Establishment and characterization of 5 human cell lines derived from a series of 50 primary intracranial tumors

A series of 50 human primary intracranial tumors were cultivated in vitro in an attempt to establish cell lines with the trypsinization technique. During the in vitro adaptation period, cultures were maintained at high cell density to avoid rapid over-growth by connective tissue. Five lines were established from 5 tumors including 4 malignant gliomas (SA4, SA44, SA45, SA101) and 1 meningeal sarcoma (SA39). These 5 lines were compared for the following investigations and criteria: light and electron microscopy, chromosomal patterns, saturation density, plating efficiency, doubling time, synthesis of collagen, S-100 and GFA proteins, response to d b-c AMP and tumorigenicity into nude mice. For one or more of the characteristics mentioned above each line was distinct from the others. None of the growth parameters that serve to define the abnormal state in vitro correlated consistently with cellular tumorigenicity in athymic nude mice. The nature of lines derived from gliomas remain uncertain and the collagen synthesis in vitro is not sufficient to affirm that these lines are mesenchymal rather than glial.

A murine tumor producing a matrix of basement membrane

We have studied a murine tumor previously classified as a poorly differentiated chondrosarcoma. Although the cells in this tumor are surrounded by large quantities of extracellular matrix material, the matrix fails to react with stains specific for the sulfated glycosaminoglycans present in normal cartilage. Here we show at the ultrastructural level that the tumor matrix is a homogeneous, nonfibrillar material, resembling basement membrane. Neither the proteoglycan matrix granules nor collagen fibrils characteristic of cartilage are present in the tumor matrix. Amino acid analyses of whole tumor tissue, enzyme-solubilized tumor components, and the protein extracted from lathyritic tumors confirmed that the tumor matrix is a basement membrane collagen. The collagenous protein extracted from the tumor by nonenzymatic means contains three unique polypeptides larger than the alpha-chain components of the other types of collagen. These studies indicate that the tumor is not a type of chondrosarcoma but a basement membrane producing tumor.

Pleomorphic adenoma of the salivary gland. With special reference to histochemical and electron microscopic studies and biochemical analysis of glycosaminoglycans in vivo and in vitro

Pleomorphic adenoma of the salivary gland is classified into two types based on the morphology of the cells and biochemical analysis of glycosaminoglycans. Type 1: the tumors consisted mainly of spindle cells, producing a large amount of mucinous material, and contained not only chondroitin 4- and 6-sulfate and hyaluronic acid but also heparan sulfate. When the tumors of this type were dissociated and cultivated, spindle cells proliferated vigorously as mulitlayer and secreted mucinous substance into the intercellular space. The cells looked like non-epithelial cells in a conventional culture bottle, but showed an epithelial-like arrangement when they were cultivated in sponge matrix or inoculated subcutaneously into mice. Fine fibres stained with orceine or resorcin-fuchsin were observed in the intercellular material both in resected tissue and in culture. Type 2: the tumors consisted mainly of ductal cells, having no mucinous area, and contained little heparan sulfate. When the tumors were cultivated, the growth of epithelial-like polygonal cells was observed in monotonous pattern, producing scanty intercellular substance, and proliferating, as monolayer, much less rapidly than the cells of Type 1.

Biosynthesis of glycosaminoglycans by mammalian corneal epithelium and fibroblasts in vitro. I. Isolation and fractionation-differences of GAG from the two cell types

Labeled glycosaminoglycans (GAG) were isolated and fractionated from cultured rabbit corneal epithelium, rabbit or bovine corneal fibroblasts and rabbit bone fibroblasts that had been previously incubated with either Na235SO4 or D-glucosamine-6-3H precursors. Thus it was demonstrated that the epithelium produces GAG. The fractionations indicated that the epithelial cells predominantly synthesize GAG with a lower degree of sulfation than those produced by corneal fibroblasts. The GAG-fractionation-patterns of the corneal epithelium and bone fibroblasts were similar.

Cyclic nucleotides and growth control in cultured mouse cells: correlation of changes in intracellular 3':5' cGMP concentration with a specific phase of the cell cycle

The commencement of cell growth following serum addition to quiescent cultures of mouse fibroblasts is preceded by transient changes in intracellular concentrations of cAMP and cGMP. By artificial depletion of the culture medium for different nutrients, cell growth can be reversibly arrested in various phases of the cell cycle. Here it is shown that the major cGMP increases are only observed when cultures which are arrested in the G(0) phase are stimulated to grow or when synchronized growing cells pass through the G(1) phase. In addition to its concomitant decrease, cAMP exhibits rhythmic changes during the cell cycle. This suggests that the increase in cGMP could act as a specific signal for movement of cells out of the G(0) or G(1) phase of the cell cycle by activating the pleiotypic and mitogenic program of the cell.

Collagen biosynthesis in nonfibroblastic cell lines

Prolyl hydroxylase and other enzymes of collagen synthesis have been found in cloned cells, including epithelium, melanoma, liver, HeLa, pituitary, kidney, and neuroblastoma. The significance of collagen biosynthesis in nonfibroblastic cells lines is discussed.

Secretion of collagen by corneal epithelium. I. Morphology of the collagenous products produced by isolated epithelia grown on frozen-killed lens

Corneal epithelium from 5-7-day old chick embryos was isolated with EDTA and grown in culture on frozen-killed lens as a substratum. Autoradiographs showed that in the presence of [(3)H]proline, the corneal epithelium synthesized and secreted onto the lens substratum, radioactive materials resistant to extraction by sodium hydroxide. The radioactive label was associated with newly formed striated collagen fibrils, large "sheets" of collagen, and basal lamina. The repeat period and interband pattern of the abundant new collagen sheets and fibrils was typical of "native" or so-called "mesenchymal" collagen. Collagen-like materials were observed in secretory (Golgi) vacuoles within the corneal cells and collagen fibrils within the intercellular canals (lateral interfaces) of the epithelium, as well as at the base of the cells. Both the granular endoplasmic reticulum and Golgi complexes were highly developed in the corneal epithelium. In the discussion, the role of cytoplasmic organelles in collagen secretion, the origin and structure of the basal lamina, and variations in collagen polymerization patterns in vitro are reviewed and evaluated. The morphogenetic significance of the synthesis and secretion of collagen by embryonic epithelium is appraised and the production of true native-striated collagen by epithelium is stressed.

Connective tissue synthesis by scleroderma skin fibroblasts in cell culture

Skin fibroblasts from subjects with scleroderma and control subjects were grown in tissue culture to compare the characteristics of connective tissue metabolism. A striking increase in soluble collagen (media hydroxyproline) was observed in eight of nine scleroderma cultures when they were compared with identically handled control cultures matched for the age and sex of the donor and the anatomic site of the donor skin. Glycoprotein content as estimated by hexosamine and sialic acid was also significantly increased in the scleroderma cultures. Estimations of protein-polysaccharide content by uronic acid determinations were low in all cultures and not significantly increased in scleroderma cultures. This report demonstrates the feasibility of using fibroblast cell cultures to study chronic rheumatic and connective tissue disorders. The initial results suggest a net increase in collagen and glycoprotein synthesis in scleroderma fibroblast cultures. The implications of an abnormality of connective tissue metabolism by skin fibroblasts propagated in vitro in the acquired disorder scleroderma are discussed.

Contact-inhibited revertant cell lines isolated from simian virus 40-transformed cells. 3. Concanavalin A-selected revertant cells

Contact-inhibited variants have been isolated by treatment of simian virus 40 (SV40)-transformed Balb/c 3T3 cells (SVT2) with the plant lectin concanavalin A. These con A revertant cells exhibit the following properties: (i) they resemble 3T3 cells morphologically and grow to saturation densities which are similar to that of 3T3 cells; (ii) they synthesize the SV40-specific T antigen and yield infectious virus after fusion with permissive monkey cells; (iii) they contain a high sialic acid content similar to that of 3T3 cells and not to that of SVT2 cells; sialic acid composition was found to be independent of serum concentration; (iv) they contain more chromosomes with the average number in the tetraploid range than the SVT2 cells from which they were derived; and (v) SVT2 and revertant cells, confluent or subconfluent, produce more collagen than Balb/3T3 cells. The relationship of surface membrane properties to contact inhibition of growth and the mechanisms for generating revertant cells are discussed.

Contact-inhibited revertant cell lines isolated from SV40-transformed cells. I. Biologic, virologic, and chemical properties

Two contact-inhibited "revertant" cell lines were isolated from an SV40-transformed mouse 3T3 cell line (SV-3T3) after exposure to 5-fluoro-2'-deoxyuridine. Revertant cells resembled 3T3 cells morphologically and grew to saturation densities which were similar to those of 3T3 cells; however, revertant cells readily formed both single and multinucleated giant cells in confluent cultures. SV40 virus was rescued from revertant cells by fusion with permissive monkey cells. The rescued virus transformed 3T3 cells with the same efficiency as wild type virus, and produced transformed colonies which were phenotypically similar to those produced by wild type virus. The revertant cells also resembled normal 3T3 cells in that they contained higher quantities of sialic acid than SV-3T3 cells. An inverse correlation was found between the saturation density of cells and their sialic acid content. Collagen content, however, of revertant cells was similar to that of SV-3T3 cells. The data presented suggest that the property of contact inhibition in revertant cells is related to the sialic acid content of the plasma membrane and that changes in sialic acid content of transformed cells are not directly specified by the viral genome.

The nature of the collagen synthesized by cultured human fibroblasts

The hydroxyproline-containing proteins (hyproproteins) synthesized by cultured human fibroblasts have been partially characterized. The hyproprotein extracted from the cell layer was found to be similar to the collagen extracted from skin in the ratio of hydroxyproline to proline, chain composition, solubility, and resistance to proteolytic digestion.The hyproproteins isolated from the medium were different. About 20% of the peptide-bound hydroxyproline was found in randomly coiled chains. The alpha2 chains were present in considerable excess over the alpha1 chains, suggesting that the alpha2 chain may be synthesized in quantities greater than required to form a collagen molecule with a chain composition (alpha1)(2)alpha2. The remaining medium hyproprotein appeared to be an unusual form of native collagen which, unlike typical native collagen, was soluble under physiological conditions. This hyproprotein did not yield alpha chains when denatured and contained material that had a molecular weight greater than alpha chains. A similar size distribution was observed in the protein synthesized in the presence of beta-aminopropionitrile, a specific inhibitor of collagen cross-linking. After treatment with pepsin, typical alpha1 and alpha2 chains were obtained from the protein in a 2:1 ratio. Since the medium protein is soluble and has properties different from the typical collagen molecule, it may represent a modified form that functions in the transport of collagen from the cell to the fiber.

Oxygen-collagen priority and the early metazoan fossil record

The thesis is developed that a low oxygen level Precambrian atmosphere presented early-evolving metazoan organisms with physiological connective tissue priorities resulting from the important molecular oxygen requirements in the biosynthesis of collagen hydroxyproline. Shells, cuticles, and carapaces which are not mandatory metazoan prerequisites but which directly or indirectly demand substantial connective tissue collagen are oxygen expensive, low priority features. A marked increase in atmospheric oxygen level near the beginning of the Paleozoic would eliminate oxygen-collagen priorities simultaneously and on a world-wide basis in all metazoan stocks providing evolutionary pressure for enlarged musculatures and associated "hard parts." This could explain the sudden presence in the fossil record of the early Cambrian of advanced and diversified metazoans, the earlier forms of which were essentially unpreservable.