Collagen-binding growth factors: Production and characterization of functional fusion proteins having a collagen-binding domain

The autocrine/paracrine peptide signaling molecules such as growth factors have many promising biologic activities for clinical applications. However, one cannot expect specific therapeutic effects of the factors administered by ordinary drug delivery systems as they have limited target specificity and short half-lives in vivo. To overcome the difficulties in using growth factors as therapeutic agents, we have produced fusion proteins consisting of growth factor moieties and a collagen-binding domain (CBD) derived from Clostridium histolyticum collagenase. The fusion proteins carrying the epidermal growth factor (EGF) or basic fibroblast growth factor (bFGF) at the N terminal of CBD (CBEGF/CBFGF) tightly bound to insoluble collagen and stimulated the growth of BALB/c 3T3 fibroblasts as much as the unfused counterparts. CBEGF, when injected subcutaneously into nude mice, remained at the sites of injection for up to 10 days, whereas EGF was not detectable 24 h after injection. Although CBEGF did not exert a growth-promoting effect in vivo, CBFGF, but not bFGF, strongly stimulated the DNA synthesis in stromal cells at 5 days and 7 days after injection. These results indicate that CBD may be used as an anchoring unit to produce fusion proteins nondiffusible and long-lasting in vivo.

Synthetic amino acid copolymers that bind to HLA-DR proteins and inhibit type II collagen-reactive T cell clones

Copolymer 1 [poly(Y,E,A,K)] is a random synthetic amino acid copolymer of l-tyrosine, l-glutamic acid, l-alanine, and l-lysine that is effective both in suppression of experimental allergic encephalomyelitis and in the treatment of relapsing forms of multiple sclerosis. Copolymer 1 binds promiscuously and very efficiently to purified HLA-DR molecules within the peptide-binding groove. In the present study, YEAK and YEAK-related copolymers and type II collagen (CII) peptide 261–273, a candidate autoantigen in rheumatoid arthritis (RA), competed for binding to RA-associated HLA-DR molecules encoded by DRB1*0101 and DRB1*0401. Moreover, these copolymers (particularly YEAK, YAK, and YEK) inhibited the response of DR1- and DR4-restricted T cell clones to the CII epitope 261–273 by >50%. This direct evidence both for competitive interactions of these copolymers and CII peptide with RA-associated HLA-DR molecules and for inhibition of CII-specific T cell responses suggests that these compounds should be evaluated in animal models for rheumatoid arthritis.

Primary structure and tissue distribution of two novel proline-rich γ-carboxyglutamic acid proteins

Two human cDNAs that encode novel vitamin K-dependent proteins have been cloned and sequenced. The predicted amino acid sequences suggest that both are single-pass transmembrane proteins with amino-terminal γ-carboxyglutamic acid-containing domains preceded by the typical propeptide sequences required for posttranslational γ-carboxylation of glutamic acid residues. The polypeptides, with deduced molecular masses of 23 and 17 kDa, are proline-rich within their putative cytoplasmic domains and contain several copies of the sequences PPXY and PXXP, motifs found in a variety of signaling and cytoskeletal proteins. Accordingly, these two proteins have been called proline-rich Gla proteins (PRGP1 and PRGP2). Unlike the γ-carboxyglutamic acid domain-containing proteins of the blood coagulation cascade, the two PRGPs are expressed in a variety of extrahepatic tissues, with PRGP1 and PRGP2 most abundantly expressed in the spinal cord and thyroid, respectively, among those tissues tested. Thus, these observations suggest a novel physiological role for these two new members of the vitamin K-dependent family of proteins.

Antibodies to ribosomal P proteins of Trypanosoma cruzi in Chagas disease possess functional autoreactivity with heart tissue and differ from anti-P autoantibodies in lupus

Anti-P antibodies present in sera from patients with chronic Chagas heart disease (cChHD) recognize peptide R13, EEEDDDMGFGLFD, which encompasses the C-terminal region of the Trypanosoma cruzi ribosomal P1 and P2 proteins. This peptide shares homology with the C-terminal region (peptide H13 EESDDDMGFGLFD) of the human ribosomal P proteins, which is in turn the target of anti-P autoantibodies in systemic lupus erythematosus (SLE), and with the acidic epitope, AESDE, of the second extracellular loop of the β1-adrenergic receptor. Anti-P antibodies from chagasic patients showed a marked preference for recombinant parasite ribosomal P proteins and peptides, whereas anti-P autoantibodies from SLE reacted with human and parasite ribosomal P proteins and peptides to the same extent. A semi-quantitative estimation of the binding of cChHD anti-P antibodies to R13 and H13 using biosensor technology indicated that the average affinity constant was about 5 times higher for R13 than for H13. Competitive enzyme immunoassays demonstrated that cChHD anti-P antibodies bind to the acidic portions of peptide H13, as well as to peptide H26R, encompassing the second extracellular loop of the β1 adrenoreceptor. Anti-P antibodies isolated from cChHD patients exert a positive chronotropic effect in vitro on cardiomyocytes from neonatal rats, which resembles closely that of anti-β1 receptor antibodies isolated from the same patient. In contrast, SLE anti-P autoantibodies have no functional effect. Our results suggest that the adrenergic-stimulating activity of anti-P antibodies may be implicated in the induction of functional myocardial impairments observed in cChHD.

Tissue-specific knockout of the mouse Pig-a gene reveals important roles for GPI-anchored proteins in skin development

Glycosylphosphatidylinositol (GPI)-anchored proteins are widely distributed on plasma membranes of eukaryotes. More than 50 GPI-anchored proteins have been shown to be spatiotemporally expressed in mice with a deficiency of GPI-anchor biosynthesis that causes embryonic lethality. Here, we examine the functional roles of GPI-anchored proteins in mouse skin using the Cre-loxP recombination system. We disrupted the Pig-a gene, an X-linked gene essential for GPI-anchor biosynthesis, in skin. The Cre-mediated Pig-a disruption occurred in skin at almost 100% efficiency in male mice bearing two identically orientated loxP sites within the Pig-a gene. Expression of GPI-anchored proteins was completely absent in the skin of these mice. The skin of such mutants looked wrinkled and more scaly than that of wild-type mice. Furthermore, histological examination of mutant mice showed that the epidermal horny layer was tightly packed and thickened. Electron microscopy showed that the intercellular space was narrow and there were many small vesicles embedded in the intercellular space that were not observed in equivalent wild-type mouse skin preparations. Mutant mice died within a few days after birth, suggesting that Pig-a function is essential for proper skin differentiation and maintenance.

Identification of a family of low-affinity insulin-like growth factor binding proteins (IGFBPs): Characterization of connective tissue growth factor as a member of the IGFBP superfamily

The insulin-like growth factor (IGF) binding proteins (IGFBPs) modulate the actions of the insulin-like growth factors in endocrine, paracrine, and autocrine settings. Additionally, some IGFBPs appear to exhibit biological effects that are IGF independent. The six high-affinity IGFBPs that have been characterized to date exhibit 40–60% amino acid sequence identity overall, with the most conserved sequences in their NH2 and COOH termini. We have recently demonstrated that the product of the mac25/IGFBP-7 gene, which shows significant conservation in the NH2 terminus, including an “IGFBP motif” (GCGCCXXC), exhibits low-affinity IGF binding. The closely related mammalian genes connective tissue growth factor (CTGF) gene, nov, and cyr61 encode secreted proteins that also contain the conserved sequences and IGFBP motifs in their NH2 termini. To ascertain if these genes, along with mac25/IGFBP-7, encode a family of low-affinity IGFBPs, we assessed the IGF binding characteristics of recombinant human CTGF (rhCTGF). The ability of baculovirus-synthesized rhCTGF to bind IGFs was demonstrated by Western ligand blotting, affinity cross-linking, and competitive affinity binding assays using 125I-labeled IGF-I or IGF-II and unlabeled IGFs. CTGF, like mac25/IGFBP-7, specifically binds IGFs, although with relatively low affinity. On the basis of these data, we propose that CTGF represents another member of the IGFBP family (IGFBP-8) and that the CTGF gene, mac25/IGFBP-7, nov, and cyr61 are members of a family of low-affinity IGFBP genes. These genes, along with those encoding the high-affinity IGFBPs 1–6, together constitute an IGFBP superfamily whose products function in IGF-dependent or IGF-independent modes to regulate normal and neoplastic cell growth.

Diversity and phylogeny of gephyrin: Tissue-specific splice variants, gene structure, and sequence similarities to molybdenum cofactor-synthesizing and cytoskeleton-associated proteins

Gephyrin is essential for both the postsynaptic localization of inhibitory neurotransmitter receptors in the central nervous system and the biosynthesis of the molybdenum cofactor (Moco) in different peripheral organs. Several alternatively spliced gephyrin transcripts have been identified in rat brain that differ in their 5′ coding regions. Here, we describe gephyrin splice variants that are differentially expressed in non-neuronal tissues and different regions of the adult mouse brain. Analysis of the murine gephyrin gene indicates a highly mosaic organization, with eight of its 29 exons corresponding to the alternatively spliced regions identified by cDNA sequencing. The N- and C-terminal domains of gephyrin encoded by exons 3–7 and 16–29, respectively, display sequence similarities to bacterial, invertebrate, and plant proteins involved in Moco biosynthesis, whereas the central exons 8, 13, and 14 encode motifs that may mediate oligomerization and tubulin binding. Our data are consistent with gephyrin having evolved from a Moco biosynthetic protein by insertion of protein interaction sequences.

Tissue-engineered cells producing complex recombinant proteins inhibit ovarian cancer in vivo

Techniques of tissue engineering and cell and molecular biology were used to create a biodegradable scaffold for transfected cells to produce complex proteins. Mullerian Inhibiting Substance (MIS) causes regression of Mullerian ducts in the mammalian embryo. MIS also causes regression in vitro of ovarian tumor cell lines and primary cells from ovarian carcinomas, which derive from Mullerian structures. In a strategy to circumvent the complicated purification protocols for MIS, Chinese hamster ovary cells transfected with the human MIS gene were seeded onto biodegradable polymers of polyglycolic acid fibers and secretion of MIS confirmed. The polymer-cell graft was implanted into the right ovarian pedicle of severe combined immunodeficient mice. Serum MIS in the mice rose to supraphysiologic levels over time. One week after implantation of the polymer-cell graft, IGROV-1 human tumors were implanted under the renal capsule of the left kidney. Growth of the IGROV-1 tumors was significantly inhibited in the animals with a polymer-cell graft of MIS-producing cells, compared with controls. This novel MIS delivery system could have broader applications for other inhibitory agents not amenable to efficient purification and provides in vivo evidence for a role of MIS in the treatment of ovarian cancer.

Corneal collagen fibril structure in three dimensions: Structural insights into fibril assembly, mechanical properties, and tissue organization

The ability of the cornea to transmit light while being mechanically resilient is directly attributable to the formation of an extracellular matrix containing orthogonal sheets of collagen fibrils. The detailed structure of the fibrils and how this structure underpins the mechanical properties and organization of the cornea is understood poorly. In this study, we used automated electron tomography to study the three-dimensional organization of molecules in corneal collagen fibrils. The reconstructions show that the collagen molecules in the 36-nm diameter collagen fibrils are organized into microfibrils (≈4-nm diameter) that are tilted by ≈15° to the fibril long axis in a right-handed helix. An unexpected finding was that the microfibrils exhibit a constant-tilt angle independent of radial position within the fibril. This feature suggests that microfibrils in concentric layers are not always parallel to each other and cannot retain the same neighbors between layers. Analysis of the lateral structure shows that the microfibrils exhibit regions of order and disorder within the 67-nm axial repeat of collagen fibrils. Furthermore, the microfibrils are ordered at three specific regions of the axial repeat of collagen fibrils that correspond to the N- and C-telopeptides and the d-band of the gap zone. The reconstructions also show macromolecules binding to the fibril surface at sites that correspond precisely to where the microfibrils are most orderly.

Manipulation of the membrane binding site of vitamin K-dependent proteins: Enhanced biological function of human factor VII

Recent studies suggested that modification of the membrane contact site of vitamin K-dependent proteins may enhance the membrane affinity and function of members of this protein family. The properties of a factor VII mutant, factor VII-Q10E32, relative to wild-type factor VII (VII, containing P10K32), have been compared. Membrane affinity of VII-Q10E32 was about 20-fold higher than that of wild-type factor VII. The rate of autoactivation VII-Q10E32 with soluble tissue factor was 100-fold faster than wild-type VII and its rate of activation by factor Xa was 30 times greater than that of wild-type factor VII. When combined with soluble tissue factor and phospholipid, activated factor VII-Q10E32 displayed increased activation of factor X. Its coagulant activity was enhanced in all types of plasma and with all sources of tissue factor tested. This difference in activity (maximum 50-fold) was greatest when coagulation conditions were minimal, such as limiting levels of tissue factor and/or phospholipid. Because of its enhanced activity, factor VII-Q10E32 and its derivatives may provide important reagents for research and may be more effective in treatment of bleeding and/or clotting disorders.

Breakers of advanced glycation end products restore large artery properties in experimental diabetes

Glucose and other reducing sugars react with proteins by a nonenzymatic, posttranslational modification process called nonenzymatic glycation. The formation of advanced glycation end products (AGEs) on connective tissue and matrix components accounts largely for the increase in collagen crosslinking that accompanies normal aging and which occurs at an accelerated rate in diabetes, leading to an increase in arterial stiffness. A new class of AGE crosslink “breakers” reacts with and cleaves these covalent, AGE-derived protein crosslinks. Treatment of rats with streptozotocin-induced diabetes with the AGE-breaker ALT-711 for 1–3 weeks reversed the diabetes-induced increase of large artery stiffness as measured by systemic arterial compliance, aortic impedance, and carotid artery compliance and distensibility. These findings will have considerable implications for the treatment of patients with diabetes-related complications and aging.

Measurement of cytosolic, mitochondrial, and Golgi pH in single living cells with green fluorescent proteins

Many cellular events depend on a tightly compartmentalized distribution of H+ ions across membrane-bound organelles. However, measurements of organelle pH in living cells have been scarce. Several mutants of the Aequorea victoria green fluorescent protein (GFP) displayed a pH-dependent absorbance and fluorescent emission, with apparent pKa values ranging from 6.15 (mutations F64L/S65T/H231L) and 6.4 (K26R/F64L/S65T/Y66W/N146I/M153T/V163A/N164H/H231L) to a remarkable 7.1 (S65G/S72A/T203Y/H231L). We have targeted these GFPs to the cytosol plus nucleus, the medial/trans-Golgi by fusion with galactosyltransferase, and the mitochondrial matrix by using the targeting signal from subunit IV of cytochrome c oxidase. Cells in culture transfected with these cDNAs displayed the expected subcellular localization by light and electron microscopy and reported local pH that was calibrated in situ with ionophores. We monitored cytosolic and nuclear pH of HeLa cells, and mitochondrial matrix pH in HeLa cells and in rat neonatal cardiomyocytes. The pH of the medial/trans-Golgi was measured at steady-state (calibrated to be 6.58 in HeLa cells) and after various manipulations. These demonstrated that the Golgi membrane in intact cells is relatively permeable to H+, and that Cl− serves as a counter-ion for H+ transport and likely helps to maintain electroneutrality. The amenability to engineer GFPs to specific subcellular locations or tissue targets using gene fusion and transfer techniques should allow us to examine pH at sites previously inaccessible.

Tissue factor gene expression in the adipose tissues of obese mice

Altered expression of proteins of the fibrinolytic and coagulation cascades in obesity may contribute to the cardiovascular risk associated with this condition. We previously reported that plasminogen activator inhibitor 1 (PAI-1) is dramatically up-regulated in the plasma and adipose tissues of genetically obese mice. This change may disturb normal hemostatic balance and create a severe hypofibrinolytic state. Here we show that tissue factor (TF) gene expression also is significantly elevated in the epididymal and subcutaneous fat pads from ob/ob mice compared with their lean counterparts, and that its level of expression in obese mice increases with age and the degree of obesity. Cell fractionation and in situ hybridization analysis of adipose tissues indicate that TF mRNA is increased in adipocytes and in unidentified stromal vascular cells. Transforming growth factor β (TGF-β) is known to be elevated in the adipose tissue of obese mice, and administration of TGF-β increased TF mRNA expression in adipocytes in vivo and in vitro. These observations raise the possibility that TF and TGF-β may contribute to the increased cardiovascular disease that accompanies obesity and related non-insulin-dependent diabetes mellitus, and that the adipocyte plays a key role in this process. The recent demonstration that TF also influences angiogenesis, cell adhesion, and signaling suggests that its exact role in adipose tissue physiology/pathology, may be complex.

Neuregulin-3 (NRG3): A novel neural tissue-enriched protein that binds and activates ErbB4

We describe the identification of Neuregulin-3 (NRG3), a novel protein that is structurally related to the neuregulins (NRG1). The NRG1/neuregulins are a diverse family of proteins that arise by alternative splicing from a single gene. These proteins play an important role in controlling the growth and differentiation of glial, epithelial, and muscle cells. The biological effects of NRG1 are mediated by receptor tyrosine kinases ErbB2, ErbB3, and ErbB4. However, genetic studies have suggested that the activity of ErbB4 may also be regulated in the central nervous system by a ligand distinct from NRG1. NRG3 is predicted to contain an extracellular domain with an epidermal growth factor (EGF) motif, a transmembrane domain, and a large cytoplasmic domain. We show that the EGF-like domain of NRG3 binds to the extracellular domain of ErbB4 in vitro. Moreover, NRG3 binds to ErbB4 expressed on cells and stimulates tyrosine phosphorylation of this receptor. The expression of NRG3 is highly restricted to the developing and adult nervous system. These data suggest that NRG3 is a novel, neural-enriched ligand for ErbB4.

Identification and classification of 16 new kinesin superfamily (KIF) proteins in mouse genome

KIF (kinesin superfamily) proteins are microtubule-dependent molecular motors that play important roles in intracellular transport and cell division. The extent to which KIFs are involved in various transporting phenomena, as well as their regulation mechanism, are unknown. The identification of 16 new KIFs in this report doubles the existing number of KIFs known in the mouse. Conserved nucleotide sequences in the motor domain were amplified by PCR using cDNAs of mouse nervous tissue, kidney, and small intestine as templates. The new KIFs were studied with respect to their expression patterns in different tissues, chromosomal location, and molecular evolution. Our results suggest that (i) there is no apparent tendency among related subclasses of KIFs of cosegregation in chromosomal mapping, and (ii) according to their tissue distribution patterns, KIFs can be divided into two classes–i.e., ubiquitous and specific tissue-dominant. Further characterization of KIFs may elucidate unknown fundamental phenomena underlying intracellular transport. Finally, we propose a straightforward nomenclature system for the members of the mouse kinesin superfamily.