Alternative splicing of the NC1 domain of the human alpha 3(IV) collagen gene. Differential expression of mRNA transcripts that predict three protein variants with distinct carboxyl regions

Presumed COL4A3/COL4A4 Missense/Synonymous Variants Induce Aberrant Splicing

Background

The incorrect interpretation of missense and synonymous variants can lead to improper molecular diagnosis and subsequent faulty genetic counselling. The aim of this study was to evaluate the pathogenicity of presumed COL4A3/COL4A4 missense and synonymous variants detected by next-generation sequencing to provide evidence for diagnosis and genetic counselling.

Methods

Patients' clinical findings and genetic data were analysed retrospectively. An in vitro minigene assay was conducted to assess the effect of presumed COL4A3/COL4A4 missense and synonymous variants on RNA splicing.

Results

Five unclassified COL4A3/COL4A4 variants, which were detected in five of 343 patients with hereditary kidney diseases, were analysed. All of them were predicted to affect splicing by Human Splicing Finder. The presumed COL4A3 missense variant c.4793T > G [p. (Leu1598Arg)] resulted in a loss of alternative full-length transcript during the splicing process. The COL4A3 transcript carried synonymous variant c.765G > A [p. (Thr255Thr)], led to an in-frame deletion of exon 13. Nevertheless, variants c.3566G > A [p. (Gly1189Glu)] in COL4A3 and c.3990G > A [p. (Pro1330Pro)], c.4766C > T [p. (Pro1589Leu)] in COL4A4 exhibited no deleterious effect on splicing. Among the five patients harbouring the abovementioned COL4A3/COL4A4 variants, three patients were genetically diagnosed with autosomal recessive Alport syndrome, one patient was highly suspected of having thin basement membrane nephropathy, and the other patient was clinically diagnosed with Alport syndrome.

Conclusions

COL4A3 presumed missense variant p. (Leu1598Arg) and synonymous variant p. (Thr255Thr) affect RNA splicing, which highlights the prime importance of transcript analysis of unclassified exonic sequence variants for better molecular diagnosis and genetic counselling. Meanwhile, the reliability of splicing predictions by predictive tools for exonic substitutions needs to be improved.

Mammalian collagen IV

Four decades have passed since the first discovery of collagen IV by Kefalides in 1966. Since then collagen IV has been investigated extensively by a large number of research laboratories around the world. Advances in molecular genetics have resulted in identification of six evolutionary related mammalian genes encoding six different polypeptide chains of collagen IV. The genes are differentially expressed during the embryonic development, providing different tissues with specific collagen IV networks each having unique biochemical properties. Newly translated alpha-chains interact and assemble in the endoplasmic reticulum in a chain-specific fashion and form unique heterotrimers. Unlike most collagens, type IV collagen is an exclusive member of the basement membranes and through a complex inter- and intramolecular interactions form supramolecular networks that influence cell adhesion, migration, and differentiation. Collagen IV is directly involved in a number of genetic and acquired disease such as Alport's and Goodpasture's syndromes. Recent discoveries have also highlighted a new and direct role for collagen IV in the development of rare genetic diseases such as cerebral hemorrhage and porencephaly in infants and hemorrhagic stroke in adults. Years of intensive investigations have resulted in a vast body of information about the structure, function, and biology of collagen IV. In this review article, we will summarize essential findings on the structural and functional relationships of different collagen IV chains and their roles in health and disease.

Molecular Cloning and Functional Characterization of Mouse α3(IV)NC1

Non-collagenous α3 chain of type IV collagen or α3(IV)NC1, a 28 kDa C-terminal domain of collagen type IV is a specific inhibitor of endothelial cell translation and angiogenesis. In the present study we have cloned and expressed mouse α3(IV)NC1 in baculovirus system. The recombinant protein was expressed in soluble form and tested for several of its biological functions. We identified that this recombinant mouse α3(IV)NC1 specifically inhibited proliferation, translation and tube formation of endothelial cells. Also, we show that α3(IV)NC1 treatment results in apoptosis specifically in proliferating endothelial cells. In addition we report for the first time that mouse α3(IV)NC1 inhibits migration and p38 MAPK phosphorylation in addition to inhibition of FAK/Akt/mTOR/4E-BP1 signaling. In mice α3(IV)NC1 treatment reduced tumor growth and CD-31 positive endothelial vasculature in tumors. Collectively, our data demonstrate the expression of biologically active form of mouse α3(IV)NC1 in Sf-9 cells and provide important mechanistic insights on α3(IV)NC1 antiangiogenic actions in endothelial cells.

Characterization of the T-cell epitope that causes anti-GBM glomerulonephritis

BACKGROUND

We have demonstrated that a single T-cell epitope pCol(28-40) (SQTTANPSCPEGT) alone, which is derived from NC1 domain of alpha3 chain of type IV collagen (Col4alpha3 NC1), can induce severe glomerulonephritis in Wistar Kyoto rats. This study further characterized this T-cell epitope.

METHODS

A series of synthetic peptides derived from pCol (28-40) were tested in vivo and in vitro for their T-cell epitope activity and nephritogenicity. Major histocompatability complex (MHC) class II molecules in Wistar Kyoto rats were cloned, and MHC restriction of pCol(28-40) was determined.

RESULTS

The T-cell epitope pCol(28-40) was restricted by rat MHC class II RT.1Bl. Ten amino acid residues (29 to 38) were mapped to be the minimum core of the T-cell epitope, which was capable of inducing the T-cell response and severe glomerulonephritis. Only three residues were identified as absolutely critical for the T-cell epitope: position 31 (T) was an anchor residue to the class II molecule, and positions 33 (N) and 34 (P) contributed to the specificity of the T-cell epitope. Thus, only substitution at those positions completely abrogated nephritogenicity of the T-cell epitope. Interestingly, pCol (28-40) also bound to human MHC class II human MHC class II molecule HLA-DRB*1501, which has been linked to human anti-glomerular basement membrane (GBM) disease, suggesting that human homologue of pCol(28-40) could be a potential human T-cell epitope.

CONCLUSION

Our study demonstrated that only few residues in the nephritogenic T-cell epitope pCol(28-40) were critical. Our finding also revealed that pCol(28-40) is a potential nephritogenic T-cell epitope in Goodpasture's syndrome.

Regulation of collagen type IV genes is organ-specific: Evidence from a canine model of Alport syndrome

BACKGROUND

Despite advances in knowledge about collagen type IV at the protein level, little is known about expression of its six alpha chains. X-linked Alport syndrome provides a system to study collagen type IV gene expression within a setting of disturbed protein synthesis. Mutations in the alpha5 chain result in loss of the alpha3/alpha4/alpha5 and alpha1/alpha2/alpha5/alpha6 networks from the kidney, with progressive renal disease.

METHODS

We used a canine model of Alport syndrome to measure expression of the six type IV collagen chains from 11 days to 7(1/2) months of age. We determined to what extent message levels in kidney change over time, and what correlation exists with clinical and pathologic changes in glomeruli, and the primary mutation. The latter was evaluated by examining testis, an organ normally containing the same collagen type IV networks but uninvolved by disease.

RESULTS

The alpha1 to alpha6 mRNAs were expressed at all time points in normal canine kidney. By comparison to normal, in Alport dog kidney, the alpha1 and alpha2 mRNAs were up-regulated after 2 months of age, alpha3 and alpha4 mRNAs were down-regulated by 2 months of age, and the alpha5 mRNA was almost undetectable at any time. In testis, all mRNAs were expressed at comparable levels in normal and affected dogs other than the alpha5 chain, which was not expressed in affected testis.

CONCLUSION

Normal expression of collagen type IV is under control mechanisms specific to each organ and to individual chains. The altered expression in canine Alport syndrome is not the direct result of the mutation, since these changes do not occur in all organs nor are they present from birth. Instead, collagen type IV expression is influenced by disease, with down-regulation of alpha3 and alpha4 chains temporally related to the onset of proteinuria, and up-regulation of alpha1 and alpha2 chains to glomerulosclerosis. This dysregulation of the alpha3 and alpha4 chains is unique to this Alport model, and suggests an unidentified mechanism linking pathology with down-regulation of expression of these two chains.

Genomic profiling of neutrophil transcripts in Asian Qigong practitioners: a pilot study in gene regulation by mind-body interaction

BACKGROUND AND OBJECTIVES

The great similarity of the genomes of humans and other species stimulated us to search for genes regulated by elements associated with human uniqueness, such as the mind-body interaction. DNA microarray technology offers the advantage of analyzing thousands of genes simultaneously, with the potential to determine healthy phenotypic changes in gene expression. The aim of this study was to determine the genomic profile and function of neutrophils in Falun Gong (FLG, an ancient Chinese Qigong) practitioners, with healthy subjects as controls.

SUBJECTS AND DESIGN

Six (6) Asian FLG practitioners and 6 Asian normal healthy controls were recruited for our study. The practitioners have practiced FLG for at least 1 year (range, 1-5 years). The practice includes daily reading of FLG books and daily practice of exercises lasting 1-2 hours. Selected normal healthy controls did not perform Qigong, yoga, t'ai chi, or any other type of mind-body practice, and had not followed any conventional physical exercise program for at least 1 year. Neutrophils were isolated from fresh blood and assayed for gene expression, using microarrays and RNase protection assay (RPA), as well as for function (phagocytosis) and survival (apoptosis).

RESULTS

The changes in gene expression of FLG practitioners in contrast to normal healthy controls were characterized by enhanced immunity, downregulation of cellular metabolism, and alteration of apoptotic genes in favor of a rapid resolution of inflammation. The lifespan of normal neutrophils was prolonged, while the inflammatory neutrophils displayed accelerated cell death in FLG practitioners as determined by enzyme-linked immunosorbent assay. Correlating with enhanced immunity reflected by microarray data, neutrophil phagocytosis was significantly increased in Qigong practitioners. Some of the altered genes observed by microarray were confirmed by RPA.

CONCLUSION

Qigong practice may regulate immunity, metabolic rate, and cell death, possibly at the transcriptional level. Our pilot study provides the first evidence that Qigong practice may exert transcriptional regulation at a genomic level. New approaches are needed to study how genes are regulated by elements associated with human uniqueness, such as consciousness, cognition, and spirituality.

Oncothanin, a peptide from the alpha3 chain of type IV collagen, modifies endothelial cell function and inhibits angiogenesis

Previous studies from our group and the group of the Department of Biochemistry at the University of Rheims, France [corrected] have shown that basement membrane (BM) collagen from anterior lens capsule type IV collagen (ALC-COL IV) and peptides from the noncollagenous domain (NC1) of the alpha3(IV) [corrected] chain, corresponding to residues 185-203 and 179-208, inhibit tumor cell proliferation, specifically through the interaction of the -SNS- tripeptide (residues 189-191) with the CD47/alphavbeta3 integrin receptor complex. Data presented here demonstrate that the alpha3(IV)185-203 and the alpha3(IV)179-208 peptides, from here forward [corrected] designated as oncothanin, regulate endothelial cell (EC) proliferation, adhesion, and motility which [corrected] ultimately influence angiogenesis. The data also indicate that oncothanin, when used as a chemoattractant, greatly enhanced EC chemotaxis. In contrast, pretreatment of EC with oncothanin inhibited chemotaxis toward several different chemoattractants. When oncothanin was used as a substrate, it enhanced EC adhesion that was inhibited when pretreated with same. Analysis of angiogenesis by EC differentiation (tube formation), aortic ring microvessel formation [corrected] and the chorioallantoic membrane assay, [corrected] demonstrate that oncothanin, but not the control medium or peptides, inhibits angiogenesis. In the EC differentiation assay, oncothanin completely inhibited tube formation at 25 microg/ml, whereas peptides with comparable sequences, that lacked [corrected] the -SNS- sequence, from ALC-COL IV NC1 domains alpha1 and alpha2 chains failed to inhibit tube formation. The data support the hypothesis that ALC-COL IV and oncothanin inhibit angiogenesis by modulation of EC function.

A human-mouse chimera of the alpha3alpha4alpha5(IV) collagen protomer rescues the renal phenotype in Col4a3-/- Alport mice

Collagen IV is a major structural component of basement membranes. In the glomerular basement membrane (GBM) of the kidney, the alpha3, alpha4, and alpha5(IV) collagen chains form a distinct network that is essential for the long-term stability of the glomerular filtration barrier, and is absent in most patients affected with Alport syndrome, a progressive inherited nephropathy associated with mutation in COL4A3, COL4A4, or COL4A5 genes. To investigate, in vivo, the regulation of the expression, assembly, and function of the alpha3alpha4alpha5(IV) protomer, we have generated a yeast artificial chromosome transgenic line of mice carrying the human COL4A3-COL4A4 locus. Transgenic mice expressed the human alpha3 and alpha4(IV) chains in a tissue-specific manner. In the kidney, when expressed onto a Col4a3(-/-) background, the human alpha3(IV) chain restored the expression of and co-assembled with the mouse alpha4 and alpha5(IV) chains specifically at sites where the human alpha3(IV) was expressed, demonstrating that the expression of all three chains is required for network assembly. The co-assembly of the human and mouse chains into a hybrid network in the GBM restores a functional GBM and rescues the Alport phenotype, providing further evidence that defective assembly of the alpha3-alpha4-alpha5(IV) protomer, caused by mutations in any of the three chains, is the pathogenic mechanism responsible for the disease. This line of mice, humanized for the alpha3(IV) collagen chain, will also provide a valuable model for studying the pathogenesis of Goodpasture syndrome, an autoimmune disease caused by antibodies against this chain.

T-cell epitope of alpha3 chain of type IV collagen induces severe glomerulonephritis

BACKGROUND

Anti-glomerular basement membrane (GBM) glomerulonephritis is among the earliest recognized human autoimmune diseases. However, the etiology of anti-GBM glomerulonephritis remains unclear. We have previously shown that CD4+ T cells, specific to alpha3 NC1 of type IV collagen (Col4alpha3NC1), were able to induce anti-GBM glomerulonephritis in Wistar-Kyoto (WKY) rats. In the present study, we continued to map the nephritogenic T cell epitope in Col4alpha3NC1.

METHODS

Synthetic peptides, which covered Col4alpha3NC1, were used as immunogens to induce glomerulonephritis in WKY rats. T-cell and B-cell responses to the peptides in the animals were analyzed.

RESULTS

One potent nephritogenic T-cell epitope, pCol(28-40) (SQTTANPSCPEGT), was identified. A single immunization with pCol(28-40) induced extremely severe glomerulonephritis in all 23 rats. Renal pathology revealed nearly 100% of glomeruli with crescentic lesions or tuft necrosis in 21 animals. pCol(28-40) elicited a T-cell response to the peptide; T cells isolated from rats immunized with recombinant Col4alpha3NC1 reacted with pCol(28-40). pCol(28-40) elicited a peptide specific antibody response, which did not react with polypeptide Col4alpha3NC1 or native GBM. An 11-mer peptide, pCol(a30-40) (Ac-TTANPSCPEGT), was further mapped to be the core of the T-cell epitope in pCol(28-40). As expected, immunization with pCol(a30-40) induced severe glomerulonephritis in 10 out of 19 rats.

CONCLUSION

Our study not only demonstrated that a single T-cell epitope of Col4alpha3NC1 is sufficient to induce severe glomerulonephritis, but also provides a unique model for studying T-cell-mediated mechanisms in anti-GBM glomerulonephritis pathogenesis.

IL-18 translational inhibition restricts IFN-gamma expression in crescentic glomerulonephritis

BACKGROUND

Interleukin-18 (IL-18), a potent inducer of interferon gamma (IFN-gamma) production, is a cytokine involved in the cell-mediated immune response that is expressed during inflammatory and pathologic conditions. IFN-gamma plays a role in the development of some models of glomerulonephritis (GN); however, the role of IL-18 in the production of IFN-gamma during these pathologies has not been studied.

METHODS

Rat IL-18 cDNA was isolated and the regulation of IL-18 gene expression was studied. IFN-gamma and IL-18 expression were determined in anti-glomerular basement membrane (GBM) antibody (Ab)-induced GN. Recombinant active IL-18 (rIL-18) was used to further identify its effect on IFN-gamma production during this GN. Glomerular injury and levels of IFN-gamma were assayed in Wistar Kyoto (WKY) rats with anti-GBM GN in the presence or absence of rIL-18.

RESULTS

Rat IL-18, similar to the mouse clone, requires processing by the IL-1beta converting enzyme to become activated. A rat IL-18 5'-untranslated region (UTR) translational inhibitor was identified that strongly inhibited the synthesis of IL-18. This translational inhibitor with different lengths (180 and 130 bp) was highly expressed during GN and correlated with minimal IFN-gamma mRNA expression. Injection of recombinant active IL-18 in WKY rats with anti-GBM GN was associated with an increase of glomerular IFN-gamma levels, proliferating cell nuclear antigen (PCNA)-ED1+ cells, and PCNA-CD8+ cells, with worsening of glomerular injury.

CONCLUSION

These data suggest that the translational control of IL-18 expression by its 5'-UTR limits the production of IL-18, resulting in restricted expression of mRNA and protein IFN-gamma in this model of GN. Furthermore, it was suggested that possible IL-18/IFN-gamma induction of local proliferation of macrophages and CD8+ cells might be an important mechanism for amplifying CD8+-mediated macrophage-dependent GN.

Designing new metal affinity peptides by random mutagenesis of a natural metal-binding site

The metal-binding site of a Helicobacter pylori ATPase 439 (heli(WT)-tag) was successfully used as a new fusion peptide for immobilized metal ion affinity chromatography (IMAC). It produced higher yields than the frequently used his6-tag. Due to stronger binding of the peptide to metal ions, harsher elution conditions were, however, necessary. This undesired side-effect was overcome by modifying the heli(WT)-tag by polymerase chain reaction-directed mutagenesis. The modified tags were screened by an automated high-throughput IMAC system, leading to a heliM14-tag peptide that could be eluted under conditions similar to those of the his6-tag but at the same time produced 20% higher yields of the desired protein.

Inhibition of tumor cell proliferation by type IV collagen requires increased levels of cAMP

Previous studies from our laboratories demonstrated that a peptide from the noncollagenous domain of the alpha3 chain of basement membrane collagen (COL IV), comprising residues 185-203, inhibits polymorphonuclear leukocyte activation and melanoma cell proliferation; this property requires the presence of the triplet -SNS- in residues 189-191 (Monboisse et al., J. Biol. Chem., 269, 25475, 1994; Han et al., J. Biol. Chem., 272, 20395, 1997). In the present study, we demonstrate that whole native COL IV and -SNS- containing synthetic peptides (10 microg/ml) added to culture medium inhibit the proliferation of not only melanoma cells, but also breast-, pancreas- and stomach-tumor cells up to 67%, and prostate tumor cells by 15%. ALC-COL IV at 5 microg/ml was shown to inhibit melanoma cell proliferation maximally at 69% and the alpha3(IV)185-203 peptide inhibited proliferation (62%) maximally at 10 microg/ml. Treatment of the alpha3(IV)185-203 peptide with either a specific mAb or a polyclonal antibody, prepared against the sequence alpha3(IV)179-208, decreased the ability of the peptide to inhibit cell proliferation by 97%, while treatment of ALC-COL IV with the same antibodies inhibited proliferation by 44%. Exposure of the above tumor cells to COL IV or the peptides resulted in an increase of intracellular cAMP that was inhibited by prior treatment of the protein with the above antibodies. To investigate the role of cAMP in the inhibition of cell proliferation, cAMP analogs and inhibitors were used. cAMP analogs mimicked the inhibitory effect of the peptide. Rp-cAMPS, a cAMP competitive inhibitor, suppressed the inhibitory effect of ALC-COL IV and of the cAMP analogs. The protein kinase-A inhibitor H-89 blocked the ability of ALC-COL IV and of the alpha3(IV)185-203 peptide to inhibit tumor cell proliferation. These data suggest that ALC-COL IV, through its alpha3(IV) chain, inhibits tumor cell proliferation utilizing a signal transduction pathway which includes cAMP and cAMP-dependent protein kinase(s).

Regulation of tumor cell chemotaxis by type IV collagen is mediated by a Ca(2+)-dependent mechanism requiring CD47 and the integrin alpha(V)beta(3)

Studies from our laboratories demonstrated that synthetic peptides from the non-collagenous (NC-1) domain of the alpha3 (IV) chain of type IV collagen (COL IV) enhanced tumor cell adhesion (Han, J., Ohno, N., Monboisse, J. C., Pasco, S., Borel, J. P., and Kefalides, N. A. (1997) J. Biol. Chem. 272, 20395-20401). We have isolated the receptors for the alpha3(IV)185-203 peptide from melanoma and prostate tumor cells and identified them as CD47/integrin-associated protein and the integrin alpha(V)beta(3) (Shahan, T. A., Ziaie, Z., Pasco, S., Fawzi, A., Bellon, G., Monboisse, J. C., and Kefalides, N. A. (1999) Cancer Res. 59, 4584-4590). In the present study we have examined the effect of CD47 and the integrin alpha(V)beta(3) on in vitro tumor cell chemotaxis and Ca(2+)(i) modulation in response to COL IV, from the anterior lens capsule (ALC-COL IV) and peptides from its NC-1 domain. COL IV as well as the alpha3(IV) peptide promoted tumor cell chemotaxis with an immediate increase in intracellular [Ca(2+)]. Treating tumor cells with CD47 and integrin alpha(V)beta(3)-reactive antibodies reduced chemotaxis as well as the rise in [Ca(2+)](i) in response to ALC-COL IV or the alpha3(IV)185-203 peptide but not to Engelbreth-Holm-Swarm-COL IV or fibronectin. The alpha3(IV)185-203 synthetic peptide stimulated an increase in calcium from intracellular stores exclusively, whereas ALC-COL IV, Engelbreth-Holm-Swarm-COL IV, and fibronectin stimulated Ca(2+) flux from both internal and external stores. Furthermore, treatment of the cells with Ca(2+) chelator bis-(O-aminophenoxyl)ethane-N,N,N',N'-tetraaceticacid- acetomethoxy ester inhibited chemotaxis toward both ALC-COL IV and the alpha3(IV)185-203 peptide. These data indicate that CD47 and integrin alpha(V)beta(3) regulate tumor cell chemotaxis in response to COL IV and the alpha3(IV)185-203 peptide through a Ca(2+)-dependent mechanism.

Heparin-binding EGF-like growth factor contributes to reduced glomerular filtration rate during glomerulonephritis in rats

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the epidermal growth factor (EGF) family, is expressed during inflammatory and pathological conditions. We have cloned the rat HB-EGF and followed the expression of HB-EGF in rat kidneys treated with anti- glomerular basement membrane (anti-GBM) antibody (Ab) to induce glomerulonephritis (GN). We observed glomerular HB-EGF mRNA and protein within 30 minutes of Ab administration and showed by in situ hybridization that glomerular HB-EGF mRNA expression was predominantly in mesangial and epithelial cells. Expression of HB-EGF correlated with the onset of decreased renal function in this model. To test the direct effect of HB-EGF on renal function, we infused the renal cortex with active rHB-EGF, prepared from transfected Drosophila melanogaster cells. This treatment induced a significant decrease in single nephron GFR (SNGFR), single nephron plasma flow, and glomerular ultrafiltration coefficient and an increase in the glomerular capillary hydrostatic pressure gradient. In addition, anti-HB-EGF Ab administered just before anti-GBM Ab blocked the fall in SNGFR and GFR at 90 minutes without any change in the glomerular histologic response. These studies suggest that HB-EGF expressed early in the anti-GBM Ab GN model contributes to the observed acute glomerular hemodynamic alterations.

Characterization of Fractalkine in Rat Brain Cells: Migratory and Activation Signals for CX3CR-1-Expressing Microglia

Molecular analyses of the chemokine fractalkine and its receptor CX3C-R1 in the rat brain have revealed a striking polarization: fractalkine is expressed constitutively in neurons and is up-regulated by TNF-α and IL-1β in astrocytes. Expression of its specific receptor, CX3C-R1, is restricted to astrocytes and microglia. We have analyzed the functional correlates of this expression and demonstrate that fractalkine induces microglial cell migration and activation. However, the activity of this chemokine on astrocytes may also be highly relevant in inducing astrocyte-microglia cell interactions through cytokine/mediator release leading to microglial activation.

Prevention of crescentic glomerulonephritis by immunoneutralization of the fractalkine receptor CX3CR1 rapid communication

BACKGROUND

Fractalkine is a newly identified T-cell and monocyte/macrophage (Mphi) chemokine with a transmembrane domain and is a cell-surface protein on activated endothelium. It can mediate adhesion of cells expressing the fractalkine receptor CX3CR1. These unique features make fractalkine well suited for leukocyte recruitment in tissues with high blood flow as in the renal glomerulus.

METHODS

Fractalkine expression in glomeruli and response of isolated glomerular inflammatory cells to fractalkine were studied in the Wistar-Kyoto (WKY) crescentic glomerulonephritis model. Antibody was used to confirm the proinflammatory role of fractalkine.

RESULTS

Fractalkine was markedly induced in the endothelium of nephritic rat glomeruli, and inflammatory leukocytes infiltrating the glomeruli expressed increased levels of CX3CR1. Anti-CX3CR1 antibody treatment dramatically blocked leukocyte infiltration in the glomeruli, prevented crescent formation, and improved renal function.

CONCLUSIONS

Fractalkine plays a central role in leukocyte trafficking at the endothelium in the high-flow glomerular circuit and, in turn, implicates CX3CR1 as a prime drug target for therapeutic intervention of endothelium-related inflammatory diseases.

Characterization of a novel type of serine/threonine kinase that specifically phosphorylates the human goodpasture antigen

Goodpasture disease is an autoimmune disorder that occurs naturally only in humans. Also exclusive to humans is the phosphorylation process that targets the unique N-terminal region of the Goodpasture antigen. Here we report the molecular cloning of GPBP (Goodpasture antigen-binding protein), a previously unknown 624-residue polypeptide. Although the predicted sequence does not meet the conventional structural requirements for a protein kinase, its recombinant counterpart specifically binds to and phosphorylates the exclusive N-terminal region of the human Goodpasture antigen in vitro. This novel kinase is widely expressed in human tissues but shows preferential expression in the histological structures that are targets of common autoimmune responses. The work presented in this report highlights a novel gene to be explored in human autoimmunity.

Role for neuronally derived fractalkine in mediating interactions between neurons and CX3CR1-expressing microglia

A recently identified chemokine, fractalkine, is a member of the chemokine gene family, which consists principally of secreted, proinflammatory molecules. Fractalkine is distinguished structurally by the presence of a CX3C motif as well as transmembrane spanning and mucin-like domains and shows atypical constitutive expression in a number of nonhematopoietic tissues, including brain. We undertook an extensive characterization of this chemokine and its receptor CX3CR1 in the brain to gain insights into use of chemokine-dependent systems in the central nervous system. Expression of fractalkine in rat brain was found to be widespread and localized principally to neurons. Recombinant rat CX3CR1, as expressed in Chinese hamster ovary cells, specifically bound fractalkine and signaled in the presence of either membrane-anchored or soluble forms of fractalkine protein. Fractalkine stimulated chemotaxis and elevated intracellular calcium levels of microglia; these responses were blocked by anti-CX3CR1 antibodies. After facial motor nerve axotomy, dramatic changes in the levels of CX3CR1 and fractalkine in the facial nucleus were evident. These included increases in the number and perineuronal location of CX3CR1-expressing microglia, decreased levels of motor neuron-expressed fractalkine mRNA, and an alteration in the forms of fractalkine protein expressed. These data describe mechanisms of cellular communication between neurons and microglia, involving fractalkine and CX3CR1, which occur in both normal and pathological states of the central nervous system.

In vivo inhibition of CC and CX3C chemokine-induced leukocyte infiltration and attenuation of glomerulonephritis in Wistar-Kyoto (WKY) rats by vMIP-II

Chemokines play a central role in immune and inflammatory responses. It has been observed recently that certain viruses have evolved molecular piracy and mimicry mechanisms by encoding and synthesizing proteins that interfere with the normal host defense response. One such viral protein, vMIP-II, encoded by human herpesvirus 8, has been identified with in vitro antagonistic activities against CC and CXC chemokine receptors. We report here that vMIP-II has additional antagonistic activity against CX3CR1, the receptor for fractalkine. To investigate the potential therapeutic effect of this broad-spectrum chemokine antagonist, we studied the antiinflammatory activity of vMIP-II in a rat model of experimental glomerulonephritis induced by an antiglomerular basement membrane antibody. vMIP-II potently inhibited monocyte chemoattractant protein 1-, macrophage inflammatory protein 1beta-, RANTES (regulated on activation, normal T cell expressed and secreted)-, and fractalkine-induced chemotaxis of activated leukocytes isolated from nephritic glomeruli, significantly reduced leukocyte infiltration to the glomeruli, and markedly attenuated proteinuria. These results suggest that molecules encoded by some viruses may serve as useful templates for the development of antiinflammatory compounds.

LIM protein KyoT2 negatively regulates transcription by association with the RBP-J DNA-binding protein

The RBP-J/Su(H) DNA-binding protein plays a key role in transcriptional regulation by targeting Epstein-Barr virus nuclear antigen 2 (EBNA2) and the intracellular portions of Notch receptors to specific promoters. Using the yeast two-hybrid system, we isolated a LIM-only protein, KyoT, which physically interacts with RBP-J. Differential splicing gave rise to two transcripts of the KyoT gene, KyoT1 and KyoT2, that encoded proteins with four and two LIM domains, respectively. With differential splicing resulting in deletion of an exon, KyoT2 lacked two LIM domains from the C terminus and had a frameshift in the last exon, creating the RBP-J-binding region in the C terminus. KyoT1 had a negligible level of interaction with RBP-J. Strong expression of KyoT mRNAs was detected in skeletal muscle and lung, with a predominance of KyoT1 mRNA. When expressed in F9 embryonal carcinoma cells, KyoT1 and KyoT2 were localized in the cytoplasm and the nucleus, respectively. The binding site of KyoT2 on RBP-J overlaps those of EBNA2 and Notchl but is distinct from that of Hairless, the negative regulator of RBP-J-mediated transcription in Drosophila. KyoT2 but not KyoT1 repressed the RBP-J-mediated transcriptional activation by EBNA2 and Notch1 by competing with them for binding to RBP-J and by dislocating RBP-J from DNA. KyoT2 is a novel negative regulatory molecule for RBP-J-mediated transcription in mammalian systems.

Selection of optimum affinity tags from a phage-displayed peptide library. Application to immobilized copper(II) affinity chromatography

Immobilized metal affinity chromatography (IMAC) is a versatile tool for the purification of proteins with affinity for immobilized metals. Moreover, this technique has also been used for the separation of proteins that do not exhibit significant metal affinity in the native form, by their fusion to a short metal-binding peptide (a tail), most commonly, a sequence consisting of six adjacent histidine residues (His6). A phage-displayed random hexamer library is used to select for peptides with affinity for immobilized copper. The study follows our previous investigation in which a stringent selection protocol led to the selection of only one copper-binding peptide containing two histidines. The less stringent conditions employed in this work resulted in the selection of a more diverse population of peptides, but again, dominated by peptides containing two histidines (13 out of 19). The prevalence of peptides with two histidines, in contrast to peptides with a higher number of histidines (e.g. His6 or HHHMVH), is explained based on the differences in the pH dependence of their affinity for copper. As discussed, the selected peptides with two histidines will be superior affinity tails than peptides with a higher histidine content (e.g. His6). Moreover, a peptide with a single histidine but with a very high copper affinity, is also identified. Its high copper affinity is related to the presence of several hydrophobic residues in the neighborhood of histidine. Chromatography of human interleukin-1 beta (hIL-1 beta) and several other proteins containing a single surface-exposed histidine surrounded by several hydrophobic residues confirmed that such a sequence could also serve as a very effective metal binding domain for protein purification using immobilized copper(II) columns.

A cell binding domain from the alpha3 chain of type IV collagen inhibits proliferation of melanoma cells

Our previous studies have shown that a peptide corresponding to the residue sequence 185-203 of the NC1 domain of the alpha3 chain of basement membrane collagen (type IV) inhibits the activation of polymorphonuclear leukocytes. Peptides from the same region of the alpha1, alpha2, alpha4, and alpha5(IV) chains did not exhibit this property. Because of the intimate relationship between metastasizing neoplastic cells and vascular as well as epithelial basement membranes, we measured the cell adhesion-promoting activity of peptides from the NC1 domain of type IV collagen and their effect on proliferation of human melanoma cells. We found that peptide alpha3(IV)185-203 (CNYYSNSYSFWLASLNPER) not only promotes adhesion of human melanoma cells but also inhibits their proliferation. Adhesion increased by 50-60% over control. Melanoma cell proliferation was inhibited by 40% when cells were grown in a medium containing 5 microg/ml peptide for 5 days. Studies showed that replacement of serine in position 189 or 191 by alanine resulted in significantly reduced adhesion. Similarly, serine replacement resulted in reduced ability to inhibit proliferation. Our data suggest that a region of the NC1 domain of the alpha3(IV) chain, contained within the sequence 185-203, not only specifically promotes adhesion but also inhibits proliferation of melanoma cells. These properties appear to be dependent on the presence of the triplet sequence -SNS- (residues 189-191), which is unique to the alpha3 chain and may represent an important functional epitope.

Corticotropin-releasing factor and adrenocorticotrophic hormone as potential central mediators of OB effects

OB (leptin) has been identified as a factor that suppresses appetite and stimulates metabolism. Attention has focused on the hypothalamus as its potential site of action, but OB could also act on other brain regions. In addition, the paradox of high OB levels in obese humans remains unresolved. Here we show in mice that both the long and short form of the OB receptor are expressed not only in the hypothalamus but also in the amygdala and pituitary. Recombinant murine OB elicited the release of corticotropin-releasing factor from superfused brain slice preparations containing hypothalamus or amygdala. Because corticotropin-releasing factor inhibits appetite and stimulates metabolism, it may be a key mediator of central OB effects. Recombinant OB also induced pituitary release of adrenocorticotrophic hormone. Because adrenocorticotrophic hormone-induced elevation of plasma glucocorticoid levels can inhibit corticotropin-releasing factor release via negative feedback, the OB effects on pituitary adrenocorticotrophic hormone release may be pertinent to human obesity, which combines increased plasma glucocorticoid levels with elevated levels of OB. An imbalance between the effects of OB on corticotropin-releasing factor release from the hypothalamus and on adrenocorticotrophic hormone release from the pituitary could contribute to obesity.

Basement-membrane stromal relationships: interactions between collagen fibrils and the lamina densa

Collagens, the most abundant molecules in the extracellular space, predominantly form either fibrillar or sheet-like structures-the two major supramolecular conformations that maintain tissue integrity. In connective tissues, other than cartilage, collagen fibrils are mainly composed of collagens I, III, and V at different molecular ratios, exhibiting a D-periodic banding pattern, with diameters ranging from 30 to 150 nm, that can form a coarse network in the extracellular matrix in comparison with a fine meshwork of lamina densa. The lamina densa represents a stable sheet-like meshwork composed of collagen IV, laminin, nidogen, and perlecan compartmentalizing tissue from one another. We hypothesize that the interactions between collagen fibrils and the lamina densa are crucial for maintaining tissue-tissue interactions. A detailed analysis of these interactions forms the basis of this review article. Here, we demonstrate that there is a direct connection between collagen fibrils and the lamina densa and propose that collagen V may play a crucial role in this connection. Collagen V might also be involved in regulation of collagen fibril diameter and anchoring of epithelia to underlying connective tissues.

Phosphorylation of the Goodpasture antigen by type A protein kinases

Collagen IV is the major component of basement membranes. The human alpha 3 chain of collagen IV contains an antigenic domain called the Goodpasture antigen that is the target for the circulating immunopathogenic antibodies present in patients with Goodpasture syndrome. Characteristically, the gene region encoding the Goodpasture antigen generates multiple alternative products that retain the antigen amino-terminal region with a five-residue motif (KRGDS). The serine therein appears to be the major in vitro cAMP-dependent protein kinase phosphorylation site in the isolated antigen and can be phosphorylated in vitro by two protein kinases of approximately 50 and 41 kDa associated with human kidney plasma membrane, suggesting that it can also be phosphorylated in vivo. Consistent with this, the Goodpasture antigen is isolated from human kidney in phosphorylated and non-phosphorylated forms and only the non-phosphorylated form is susceptible to phosphorylation in vitro. Since this motif is exclusive to the human alpha 3(IV) chain and includes the RGD cell adhesion motif, its phosphorylation might play a role in pathogenesis and influence cell attachment to basement membrane.

Characterization and expression of multiple alternatively spliced transcripts of the Goodpasture antigen gene region. Goodpasture antibodies recognize recombinant proteins representing the autoantigen and one of its alternative forms

Collagen IV, the major component of basement membranes, is composed of six distinct alpha chains (alpha 1-alpha 6). Atypically among the collagen IV genes, the exons encoding the carboxyl-terminal region of the human alpha 3(IV) chain undergo alternative splicing. This region has been designated as the Goodpasture antigen because of its reactivity in the kidney and lung with the pathogenic autoantibodies causing Goodpasture syndrome. The data presented in this report demonstrate that, in human kidney, the gene region encompassing the Goodpasture antigen generates at least six alternatively spliced transcripts predicting five distinct proteins that differ in their carboxyl-terminus and retain, except in one case, the exon that harbors the characteristic amino-terminus of the antigen. Goodpasture antibodies specifically recognize recombinant proteins representing the antigen and the alternative form that retains the amino-half of the antigen, suggesting that this moiety could be involved in the in vivo binding of the pathogenic antibodies. Furthermore, the sera of control individuals contain autoantibodies against the antigen that can be differentiated from those causing the syndrome based on their specific reactivities, suggesting that the binding of the pathogenic autoantibodies to a specific determinant likely trigger a distinct and unique cascade of events causing the disease.

Identification of three N-terminal ends of type XVIII collagen chains and tissue-specific differences in the expression of the corresponding transcripts. The longest form contains a novel motif homologous to rat and Drosophila frizzled proteins

Transcripts for the alpha 1 chain of mouse type XVIII collagen were found to be heterogeneous at their 5'-ends and to encode three variant N-terminal sequences of the ensuing 1315-, 1527-, or 1774-residue collagen chains. The variant mRNAs appeared to originate from the use of two alternate promoters of the alpha 1(XVIII) chain gene, resulting in the synthesis of either short or long N-terminal non-collagenous NC1 domains, the latter being further subject to modification due to alternative splicing of the transcripts. As a result, the 1527- and 1774-residue polypeptides share the same signal peptide, and the lengths of their NC1 domains are 517 or 764 amino acid residues, respectively, while the 1315-residue polypeptide has a different signal peptide and a 301-residue NC1 domain. The longest NC1 domain was strikingly characterized by a 110-residue sequence with 10 cysteines, which was found to be homologous with the previously identified frizzled proteins belonging to the family of G-protein-coupled membrane receptors. Thus, it is proposed that the cysteine-rich motif, termed fz, represents a new sequence motif that can be found in otherwise unrelated proteins. Tissues containing mainly one or two NC1 domain mRNA variants or all three NC1 domains were identified, indicating that there is tissue-specific utilization of two alternate promoters and alternative splicing of alpha 1(XVIII) transcripts.

Differential expression of an acidic domain in the amino-terminal propeptide of mouse pro-alpha 2(XI) collagen by complex alternative splicing

We isolated and sequenced genomic and cDNA clones encoding the complete amino-terminal portion and the 5'-untranslated region of mouse pro-alpha 2(XI) collagen mRNA. Fourteen exons encoded the amino-terminal propeptide, which was divided into three consecutive domains (a long globular domain, an amino-terminal triple helical domain, and a telopeptide domain). The long globular domain was further divided into an upstream basic subdomain and a downstream highly acidic subdomain, as is the case for the amino-terminal propeptides of pro-alpha 1(V) and pro alpha 1(XI) collagens. We also demonstrated that the primary transcript undergoes complex alternative splicing. Three consecutive exons (exons 6, 7, and 8) encoding most of the acidic subdomain showed alternative splicing which dramatically affected the structure of the amino-terminal propeptide of pro-alpha 2(XI) collagen. Using the reverse transcription-polymerase chain reaction, we analyzed the expression of these exons in various tissues and in developing limb buds of mice. The pro-alpha 2(XI) transcripts were abundant in cartilage, but most of them lacked the 3-exon sequences encoding the acidic domain. Most of other tissues also contained mRNAs that corresponded to longer splice variants, including exons 6-8. The differential expression of specific domains of pro-alpha 2(XI) collagen may be important in modulating interactions between various components of the extracellular matrix and/or may influence heterotypic collagen assembly.