High production of type VI collagen in multiple fibromatosis with multiple articular dysplasia

Croix B. Selective blockade of tumor angiogenesis

Blocking tumor angiogenesis is an important goal of cancer therapy, but clinically approved anti-angiogenic agents suffer from limited efficacy and adverse side effects, fueling the need to identify alternative angiogenesis regulators. Tumor endothelial marker 8 (TEM8) is a highly conserved cell surface receptor overexpressed on human tumor vasculature. Genetic disruption of Tem8 in mice revealed that TEM8 is important for promoting tumor angiogenesis and tumor growth but dispensable for normal development and wound healing. The induction of TEM8 in cultured endothelial cells by nutrient or growth factor deprivation suggests that TEM8 may be part of a survival response pathway that is activated by tumor microenvironmental stress. In preclinical studies, antibodies targeted against the extracellular domain of TEM8 inhibited tumor angiogenesis and blocked the growth of multiple human tumor xenografts. Anti-TEM8 antibodies augmented the activity of other anti-angiogenic agents, vascular targeting agents and conventional chemotherapeutic agents and displayed no detectable toxicity. Thus, anti-TEM8 antibodies provide a promising new tool for selective blockade of neovascularization associated with cancer and possibly other angiogenesis-dependent diseases.

Fifty years of structural glycoproteins

During decades preceding and following the last war, a favourite subject of biochemists was to study glycoproteins. One class of these substances, found in connective tissues were characterised as polysaccharides, most of them found to be linked to proteins, designated later as glycosaminoglycans and proteoglycans. Another family of glycoconjugates represented epithelial mucins as found in the gastro-intestinal and respiratory tracts and conduits. A third family of glycoconjugates is represented by circulating glycoproteins isolated from the blood plasma, mostly studied by medical biochemists in relation to pathological conditions comprising those increasing during the inflammatory reaction: acute phase glycoproteins. Their study suggested that they might be derived from connective tissues. Although inflammatory glycoproteins derive mostly from the liver, the possibility of connective tissue origin of glycoproteins remained open. Using cornea, an avascular tissue, we could show that connective tissues also synthesize glycoproteins. We proposed to designate them "structural glycoproteins" (SGP-s) to distinguish them from circulating, blood-born glycoproteins coming from the liver. They play locally "structural" roles in connective tissues where they are synthesized. Soon after fibronectin was identified and shown to mediate cell-matrix interactions. A large family of glycoproteins were then isolated from a variety of sources, cells, tissues others than liver, confirming our original hypothesis. The first experiments on these glycoproteins were published from 1961/1962 giving the opportunity to recapitulate this biochemical adventure 50 years later, together with the celebration of the foundation of the first connective tissue society in Europe, as described in the first article in this issue.

The dark sides of capillary morphogenesis gene 2

Capillary morphogenesis gene 2 (CMG2) is a type I membrane protein involved in the homeostasis of the extracellular matrix. While it shares interesting similarities with integrins, its exact molecular role is unknown. The interest and knowledge about CMG2 largely stems from the fact that it is involved in two diseases, one infectious and one genetic. CMG2 is the main receptor of the anthrax toxin, and knocking out this gene in mice renders them insensitive to infection with Bacillus anthracis spores. On the other hand, mutations in CMG2 lead to a rare but severe autosomal recessive disorder in humans called Hyaline Fibromatosis Syndrome (HFS). We will here review what is known about the structure of CMG2 and its ability to mediate anthrax toxin entry into cell. We will then describe the limited knowledge available concerning the physiological role of CMG2. Finally, we will describe HFS and the consequences of HFS-associated mutations in CMG2 at the molecular and cellular level.

Involvement of type VI collagen in interleukin-4-induced mineralization by human osteoblast-like cells in vitro

We recently showed that interleukin-4 (IL-4) enhanced collagen and osteocalcin accumulation and caused mineralization in human periosteal osteoblast-like (SaM-1) cells. At that time, the expression of alpha1(VI) collagen mRNA was induced. In the present study, the possible role of IL-4-induced type VI collagen in the in vitro mineralization in osteoblasts was investigated. Addition of IL-4 in the early stage (for the first 10 days) was essential for the mineralization. The mRNA levels of alpha1(VI) and alpha2(VI) collagen and protein level of type VI collagen were transiently increased by IL-4 treatment up to day 5, whereas the alpha1(I) procollagen mRNA level was greater at day 10 than at day 5. Addition of anti-type VI collagen antibody remarkably reduced the extracellular accumulations of calcium and hydroxyproline induced by IL-4. Furthermore, the transfection of antisense oligonucleotides of alpha1(VI) to SaM-1 cells in the presence of IL-4 partially inhibited IL-4-induced type I collagen accumulation. These results demonstrated that type VI collagen played important roles for IL-4-induced mineralization and hydroxyproline accumulation mostly type I collagen accumulation, in human periosteal osteoblast-like cells.

Purification and structural analysis of extracellular matrix of a skin tumor from a patient with juvenile hyaline fibromatosis

Juvenile hyaline fibromatosis is a rare mesenchymal dysplasia that is inherited in an autosomal recessive fashion. The histological features of the tumor-like lesions are characterized by the deposition of amorphous hyaline material in the extracellular spaces of the dermis and soft tissues. We have analyzed the hyaline substance in a specimen of a skin tumor obtained from a 4-year-old Japanese girl with juvenile hyaline fibromatosis. It was found to consist mainly of type VI collagen; a small amount of type I collagen was also present. These components were separated by DEAE-cellulose ion-exchange chromatography under reducing conditions. The ratio of the dry weights of type I and type VI collagen was 1:4. Of the three chains of type VI collagen (alpha 1(VI), alpha 2(VI) and alpha 3(VI)), alpha 3(VI) was the most abundant. Glycosaminoglycans in the tumor tissue comprised dermatan sulfate, chondroitin sulfate and hyaluronan, with dermatan sulfate predominating. In contrast, hyaluronan is the most abundant in normal skin.

Increased expression of type VI collagen genes in drug-induced gingival enlargement

Fibrotic gingival enlargements induced by phenytoin or nifedipine were examined with special reference to type VI collagen expression. Immunolocalization studies showed abnormal accumulation of type VI collagen around the collagen fiber bundles in the fibrotic gingival enlargements. Examination of total RNA extracted from fibroblasts and tissues of enlarged gingivae demonstrated increased type VI collagen steady-state mRNA levels. These results suggest that excessive deposition of type VI collagen in drug-induced gingival enlargement is attributed to increased expression of the collagen genes.

Effect of transforming growth factor-beta on collagen type VI expression in human dermal fibroblasts

Steady-state mRNA levels and protein synthesis of collagen type VI were determined after stimulation of human dermal fibroblasts with transforming growth factor-beta (TGF beta). While there was a 227% increase in the alpha 3(VI) subunit mRNA at maximal TGF-beta concentration, alpha 1(VI) and alpha 2(VI) subunit mRNA levels remained unchanged. Concomitantly collagen type VI immuno-reactive material increased up to 172% of controls in cell culture medium and cell layer extracts. Regulation of alpha 3(VI) gene expression is therefore critical for the control of collagen type VI synthesis and determines the deposition of collagen type VI heterotrimeric molecules.

Collagens in human atherosclerosis. Immunohistochemical analysis using collagen type-specific antibodies

This study represents a systematic analysis of the distribution of collagen types in human atherosclerotic lesions. Formalin-fixed, paraffin-embedded aortic tissues of 40 lesions from 16 different individuals ranging in age from 1 month to 84 years were examined immunohistochemically using antibodies to type I, III, IV, V, and VI collagens. Preembedding immunoelectron microscopy was used to simultaneously localize type V and VI collagens within the lesions. Localization of type III collagen was very similar to that of type I, and type VI collagen appeared together with these two types of collagen in the thickened intimas of all stages of the lesion. Type V collagen was not detected in either fatty streaks or the mild intimal thickening of the aortas of children. With advancing age and lesion progression, the immunoreactivity with anti-type V collagen antibody became more intense. Type IV collagen was detected in the basement membrane region of intimal cells. In advanced lesions thick deposits of type IV collagen were found around the elongated smooth muscle cells. Using immunoelectron microscopy, type V collagen was found to be localized to cross-banded collagen fibers, and type VI collagen was found to be localized to beaded filaments present throughout the interstitium of the thickened intima. These findings suggest that collagens preserve the pathophysiological and functional integrity of the vascular wall by providing mechanical support as well as assuring the proper interaction of cells during the formation of atherosclerotic lesions.

Distribution of type VI collagen expression in synovial tissue and cultured synoviocytes: relation to fibronectin expression

Type VI collagen has recently been shown to be an important component of connective tissue. Double label immunofluorescence procedures were used to immunolocalize type VI collagen in normal and rheumatoid synovium and its distribution was compared with that of fibronectin. In normal synovium type VI collagen is expressed in the synovial membrane but not in the interstitium of the villus. In rheumatoid synovium, however, type VI collagen is extensively deposited in both the interstitial connective tissue and along the lining of the synovial membrane. Cultured rheumatoid and normal synoviocytes produce type VI collagen and fibronectin and incorporate them into their extracellular matrix. These data suggest that type VI collagen may play a part in matrix remodelling of the inflamed joint.

Collagen gene expression by cultured human skin fibroblasts. Abundant steady-state levels of type VI procollagen messenger RNAs

Previous studies have suggested that procollagen types I and III are the major collagenous gene products of cultured human skin fibroblasts. In this study the expression of 10 different genes, encoding the subunit polypeptides for collagen types I-VI, by human skin fibroblasts in culture was analyzed by molecular hybridizations. Northern transfer analysis demonstrated the presence of specific mRNA transcripts for collagen types I, III, IV, V, and VI, but not for type II collagen. Quantitation of the abundance of these mRNAs by slot blot hybridizations revealed that type I, III, and VI procollagens were the major collagenous gene products of skin fibroblasts in culture. The mRNAs for type IV and V collagens represented only a small percentage of the total collagenous mRNA transcripts. Further analysis by in situ hybridization demonstrated that the majority of the cultured cells coexpressed the genes for type I, III, and VI procollagen pro-alpha chains. Further in situ hybridization analyses revealed the expression of type VI collagen genes in normal human skin. These data demonstrate that human skin fibroblast cultures can be used to study the transcriptional regulation of at least nine genetically distinct procollagen genes. The data further suggest that type VI collagen, in addition to types I and III, may be a major collagenous component of human skin.