Covalent targeting of non-cysteine residues in PI4KIIIβ

The synthesis and characterisation of fluorosulfate covalent inhibitors of the lipid kinase PI4KIIIβ is described. The conserved lysine residue located within the ATP binding site was targeted, and optimised compounds based upon reversible inhibitors with good activity and physicochemical profile showed strong reversible interactions and slow onset times for the covalent inhibition, resulting in an excellent selectivity profile for the lipid kinase target. X-Ray crystallography demonstrated a distal tyrosine residue could also be targeted using a fluorosulfate strategy. Combination of this knowledge showed that a dual covalent inhibitor could be developed which reveals potential in addressing the challenges associated with drug resistant mutations.

Investigating the effects of the core nitrogen atom configuration on the thermodynamic solubility of 6,5-bicyclic heterocycles

Physicochemical properties, such as solubility, are important when prioritising compounds for progression on a drug discovery project. There is limited literature around the systematic effects of core changes on thermodynamic solubility. This work details the synthesis of nitrogen containing 6,5-bicyclic heterocyclic cores which are common scaffolds in medicinal chemistry and the analysis of their physicochemical properties, particularly, thermodynamic solubility. Crystalline solids were obtained where possible to enable a robust comparison of the thermodynamic solubility. Other parameters such as pK_a, melting point and lipophilicity were also measured to determine the key factors affecting the observed solubility.

Coupling of a Novel TIMP3 Peptide to Carboxypeptidase G2 for Pro-Drug Activation at the Tumour Site

Broad-spectrum cytotoxic drugs have been used in cancer therapy for decades. However, their lack of specificity to cancer cells often results in serious side-effects, limiting efficacy. For this reason, antibodies have been used to attempt to specifically target cytotoxic drugs to tumours. One such approach is antibody-directed enzyme prodrug therapy (ADEPT) which uses a tumour-directed monoclonal antibody, coupled to an enzyme, to convert a systemically administered non-toxic prodrug into a toxic one only at the tumour site. Among the main drawbacks of ADEPT is the immunogenicity of the antibody-enzyme complex, which is exacerbated by slow clearance due to size, hence limiting repeated administration. Additionally, the mono-specificity of the antibody could potentially result in drug resistance with repeated administration. We have identified a novel short peptide sequence, p700, derived from a human tissue inhibitor of metalloproteinases-3 (TIMP-3), which binds to and inhibits a number of tyrosine kinase growth factor receptors (VEGFRs1-3, FGFRs 1-4 and PDGFRα) which are known to be upregulated in many tumours and tumour vasculature. In this report, we fused p700 to His-tagged, codon-optimised, carboxypeptidase G2 (CPG2). CPG2 is a bacterial enzyme used in ADEPT, which activates potent nitrogen-mustard pro-drugs by removal of an inhibitory glutamic acid residue. Recombinant CPG2-p700 was highly expressed in Escherichia coli and successfully purified by nickel affinity chromatography. Biolayer interferometry showed that CPG2-p700 had a 100-fold increase in binding affinity for VEGFR2 compared with CPG2 alone and retained its catalytic activity, as determined by methotrexate cleavage. In the presence of CPG2-p700, the ZD2676P pro-drug showed significant cytotoxicity for 4T1 cells compared with prodrug alone or CPG2 alone. p700 is, therefore, a potentially useful alternative to monoclonal antibodies for enzyme pro-drug therapy and could equally be used for effective delivery of other cytotoxic drugs to tumour tissue.

Discovery of potent and selective Spleen Tyrosine Kinase inhibitors for the topical treatment of inflammatory skin disease

The discovery and lead optimisation of a novel series of SYK inhibitors is described. These were optimised for SYK potency and selectivity against Aurora B. Compounds were profiled in a human skin penetration study to identify a suitable candidate molecule for pre-clinical development. Compound 44 (GSK2646264) was selected for progression and is currently in Phase I clinical trials.

Cell Penetrant Inhibitors of the KDM4 and KDM5 Families of Histone Lysine Demethylases. 1. 3-Amino-4-pyridine Carboxylate Derivatives

Optimization of KDM6B (JMJD3) HTS hit 12 led to the identification of 3-((furan-2-ylmethyl)amino)pyridine-4-carboxylic acid 34 and 3-(((3-methylthiophen-2-yl)methyl)amino)pyridine-4-carboxylic acid 39 that are inhibitors of the KDM4 (JMJD2) family of histone lysine demethylases. Compounds 34 and 39 possess activity, IC50 ≤ 100 nM, in KDM4 family biochemical (RFMS) assays with ≥ 50-fold selectivity against KDM6B and activity in a mechanistic KDM4C cell imaging assay (IC50 = 6-8 μM). Compounds 34 and 39 are also potent inhibitors of KDM5C (JARID1C) (RFMS IC50 = 100-125 nM).

Inhibition of PAD4 activity is sufficient to disrupt mouse and human NET formation

PAD4 has been strongly implicated in the pathogenesis of autoimmune, cardiovascular and oncological diseases, through clinical genetics and gene disruption in mice. Novel, selective PAD4 inhibitors binding to a calcium-deficient form of the PAD4 enzyme have, for the first time, validated the critical enzymatic role of human and mouse PAD4 in both histone citrullination and neutrophil extracellular trap formation. The therapeutic potential of PAD4 inhibitors can now be explored.

A peptide derived from TIMP-3 inhibits multiple angiogenic growth factor receptors and tumour growth and inflammatory arthritis in mice

The binding of vascular endothelial growth factor (VEGF) to VEGF receptor-2 (VEGFR-2) on the surface of vascular endothelial cells stimulates many steps in the angiogenic pathway. Inhibition of this interaction is proving of value in moderating the neovascularization accompanying age-related macular degeneration and in the treatment of cancer. Tissue inhibitor of metalloproteinases-3 (TIMP-3) has been shown to be a natural VEGFR-2 specific antagonist-an activity that is independent of its ability to inhibit metalloproteinases. In this investigation we localize this activity to the C-terminal domain of the TIMP-3 molecule and characterize a short peptide, corresponding to part of this domain, that not only inhibits all three VEGF-family receptors, but also fibroblast growth factor and platelet-derived growth factor receptors. This multiple-receptor inhibition may explain why the peptide was also seen to be a powerful inhibitor of tumour growth and also a partial inhibitor of arthritic joint inflammation in vivo.

Discovery of GSK143, a highly potent, selective and orally efficacious spleen tyrosine kinase inhibitor

The lead optimisation of the diaminopyrimidine carboxamide series of spleen tyrosine kinase inhibitors is described. The medicinal chemistry strategy was focused on optimising the human whole blood activity whilst achieving a sufficient margin over liability kinases and hERG activity. GSK143 is a potent and highly selective SYK inhibitor showing good efficacy in the rat Arthus model.

Lentiviral shRNA knock-down of ADAMTS-5 and -9 restores matrix deposition in 3D chondrocyte culture

Aggrecan is one of the two major constituents of articular cartilage, and during diseases such as osteoarthritis (OA) it is subject to degradation by proteolytic enzymes. The primary proteases responsible for aggrecan cleavage are the aggrecanases, identified as members of the ADAMTS family of proteases, which are upregulated in response to inflammatory stimuli. It is uncertain which of the six aggrecanases (ADAMTS-1, -4, -5, -8, -9 and -15) are primarily responsible for the degradation of aggrecan in human cartilage. Here we show that four of the six aggrecanases are expressed in immortalized chondrocyte cell-lines and can be upregulated in response to inflammatory cytokines. Using RNA interference, we demonstrate robust knock-down of ADAMTS-5 and -9 expression in these cells and, by culturing them on three-dimensional (3D) scaffolds, show that reduction in expression of ADAMTS-5 enzyme results in an increase in matrix deposition. These data suggest that the quality of tissue-engineered cartilage matrix might be improved by targeted depletion of aggrecanase expression. Moreover, this work also provides further evidence that ADAMTS-5 may be a therapeutic target in the treatment of arthritic disease.

4-Phenyl-7-azaindoles as potent and selective IKK2 inhibitors

The synthesis and SAR of a novel series of IKK2 inhibitors are described. Modification around the hinge binding region of the 7-azaindole led to a series of potent and selective inhibitors with good cellular activity.

Activity of matrix metalloproteinase-9 against native collagen types I and III

Interstitial collagen types I, II and III are highly resistant to proteolytic attack, due to their triple helical structure, but can be cleaved by matrix metalloproteinase (MMP) collagenases at a specific site, approximately three-quarters of the length from the N-terminus of each chain. MMP-2 and -9 are closely related at the structural level, but MMP-2, and not MMP-9, has been previously described as a collagenase. This report investigates the ability of purified recombinant human MMP-9 produced in insect cells to degrade native collagen types I and III. Purified MMP-9 was able to cleave the soluble, monomeric forms of native collagen types I and III at 37 degrees C and 25 degrees C, respectively. Activity against collagens I and III was abolished by metalloproteinase inhibitors and was not present in the concentrated crude medium of mock-transfected cells, demonstrating that it was MMP-9-derived. Mutated, collagenase-resistant type I collagen was not digested by MMP-9, indicating that the three-quarters/one-quarter locus was the site of initial attack. Digestion of type III collagen generated a three-quarter fragment, as shown by comparison with MMP-1-mediated cleavage. These data demonstrate that MMP-9, like MMP-2, is able to cleave collagens I and III in their native form and in a manner that is characteristic of the unique collagenolytic activity of MMP collagenases.

Cyclical variation of serum neutral endopeptidase lost in asthmatics: A pilot study

Angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP) are two metalloproteases, which have both been isolated from the airways. With the knowledge that young girls experience a worsening of asthma with fluctuations in oestrogen levels, we attempted to establish whether there is a change in ACE or NEP levels throughout the menstrual cycle, accounting for unhydrolysed inflammatory mediators in the airways. Asthmatics and normal controls (n=7) were studied through the follicular and luteal phases of the menstrual cycle. Peak flow rates and serum ACE levels showed no significant difference in either group. There was a four-fold increase in NEP levels in the follicular phase of normal women. Asthmatics had high levels of NEP throughout the cycle, in both the follicular and luteal phases. These results demonstrate an alteration of normal physiology in asthmatics, which might be a natural response to background inflammation.

Analysis of full length ADAMTS6 transcript reveals alternative splicing and a role for the 5' untranslated region in translational control

The ADAMTS (A Disintegrin and metalloproteinase with thrombospondin-1 type repeats) family of enzymes have been implicated in turnover of extracellular matrix. We previously showed that levels of ADAMTS6 mRNA in ARPE-19 cells were markedly increased following treatment with tumour necrosis factor alpha (TNFalpha). This study shows that the ADAMTS6 transcript contains unusually large untranslated regions (UTRs) at both the 5' and 3'end. The 5'UTR contains 11 AUG codons upstream of the predicted ADAMTS6 start codon and potently inhibits translation of a downstream reporter gene. However some translation can be restored by truncating the 5'UTR from the 5'end. The 5'UTR was tested for internal ribosome entry site activity using a bicistronic luciferase reporter plasmid, but none was detected. Using the 5' and 3'UTR sequences to screen the GenBank database we identified a full length ADAMTS6 cDNA of 7262 bp. This transcript is alternatively spliced at the 3'end of the open reading frame (ORF), resulting in an extended ORF containing 3 additional tsp-1 type repeats. Quantitative RT-PCR showed that the long and short form of the ADAMTS6 ORF are co-expressed in ARPE-19 cells, but the relative levels of the two forms is modulated by TNFalpha. The region of the transcript encoding the catalytic domain also contains several notable differences compared to the previously published ADAMTS6 cDNA sequence, including a redefinition of the predicted active site motif.

TIMP3 mutation in Sorsby's fundus dystrophy: molecular insights

Sorsby's fundus dystrophy (SFD) is a rare autosomal dominant disorder that results in degeneration of the macular region of the retina, with onset usually in the fourth to fifth decade of life. It leads to the rapid loss of central vision, often followed by further loss of peripheral vision. SFD shares several pathological features commonly found in the 'wet' or exudative form of age-related macular degeneration (AMD), the most common cause of blindness in the elderly in developed countries. These phenotypic similarities have led to SFD being proposed as an acceptable genetic model for AMD. Whereas AMD appears to have a complex aetiology, with both genetic and environmental factors playing a role, SFD has been shown to be a single-gene disorder, linked to mutations in exon 5 of the tissue inhibitor of metalloproteinases 3 (TIMP3) gene on chromosome 22q12-q13. This review confines itself to a discussion of the known biochemical properties of the wild-type and SFD TIMP3 proteins and attempts to relate these to the pathology encountered in SFD patients. We also discuss briefly how, despite the lack of inherited mutations in the structural gene, the TIMP3 protein might play a role in the onset and progression of AMD.

Sorsby's fundus dystrophy mutations impair turnover of TIMP-3 by retinal pigment epithelial cells

Sorsby's fundus dystrophy (SFD) is an autosomal dominant degenerative disease of the retina, caused by mutations in exon 5 of the gene for tissue inhibitor of metalloproteinases-3 (TIMP-3). The mechanism by which these mutations give rise to the disease phenotype is unknown. In an attempt to identify common properties of these molecules that might underlie the disease phenotype, a range of SFD mutants were expressed from human retinal pigment epithelial (RPE) cells. This showed that resistance to turnover, resulting from intermolecular disulfide bond formation, was a common property of all the SFD mutants examined, providing a possible explanation for the increased deposition of the protein observed in eyes from SFD patients. In contrast, SFD mutants varied in their ability to inhibit cell-surface activation of matrix metalloproteinase-2 (MMP-2), a potent mediator of angiogenesis, ranging from being fully active to totally inactive. These data show that increased deposition of active TIMP-3, rather than dysregulation of metalloproteinase inhibition, is likely to be the primary, initiating event in SFD.

The use of membrane translocating peptides to identify sites of interaction between the C5a receptor and downstream effector proteins

The complement fragment C5a is a potent leucocyte chemoattractant and activator, mediating its effects through a G-protein-coupled receptor. Whilst the C-terminal domain of this receptor has been shown to be essential for receptor desensitization and internalization, it is not known which domains couple to the receptor's heterotrimeric G proteins. In this report we have used a membrane translocating sequence (MTS) to examine the effects of the four intracellular domains of the human C5a receptor (C5aR) on the receptor's signalling via G(alphai) family heterotrimeric G proteins in intact RBL-2H3 cells. The results indicate that all of the intracellular domains couple to downstream signalling, with the proximal region of the C terminus being a major binding site and intracellular loop 3 playing a role in G protein activation or receptor desensitization.

Expression of mutant and wild-type TIMP3 in primary gingival fibroblasts from Sorsby's fundus dystrophy patients

Gingival fibroblast cell lines were derived from Sorsby's fundus dystrophy (SFD) patients carrying the S181C TIMP3 and the E139X TIMP3 mutations. These cell lines were grown in culture to study expression of the wild-type and mutant tissue inhibitor of metalloproteinase 3 (TIMP3) alleles from a normal diploid cell type. Firstly, patient cells were found to co-express the wild-type and mutant TIMP3 alleles, S181C TIMP3 or E139X TIMP3, at the mRNA level using restriction fragment length polymorphism (RFLP) analysis. A SpeI RFLP for E139X TIMP3 is described. Low levels of endogenous TIMP3 protein expression were elevated using the natural polysaccharide calcium pentosan polysulfate (CaPPs) in combination with the cytokine IL-1alpha. Immunoblotting detected protein expression from both wild-type and mutant alleles, S181C TIMP3 or E139X TIMP3. S181C TIMP3 from these cells was found to dimerise and retain MMP2 inhibitory activity. To facilitate studies of the E139X TIMP3 protein, the allele was expressed using HighFive insect cells. In this cell type, the E139X TIMP3 was synthesised as a mixture of monomer and dimer. Both monomeric and dimeric E139X TIMP3 protein retained MMP2 inhibitory activity in gelatin zymography. Expression of mutant E139X or S181C TIMP3 protein from a normal diploid patient-derived fibroblast cell had no effect on either MMP2 or MMP9 expression or activation whilst transcribed from their normal promoter context.

Expression of ADAMTS metalloproteinases in the retinal pigment epithelium derived cell line ARPE-19: transcriptional regulation by TNFalpha

ADAMTS (A Disintegrin-like And Metalloprotease domain with ThromboSpondin type I motifs) are multidomain proteins with demonstrated metalloproteinase functionality and have potential roles in embryonic development, angiogenesis and cartilage degradation. We present here investigations of ADAMTS expression in an ocular cell type, ARPE-19, with a view to implicating them in retinal matrix turnover. Expression analysis was undertaken using a combination of reverse transcription polymerase chain reaction (RT-PCR) and Northern blotting experiments, which together detected the expression of mRNAs for several ADAMTS proteins, all of which have active site motifs characteristic of matrix metalloproteases (MMPs). These included ADAMTS1, ADAMTS2, ADAMTS3, ADAMTS5, ADAMTS6, ADAMTS7 and ADAMTS9. The expression of mRNA isoforms for ADAMTS7 and ADAMTS9 were also detected. Following stimulation with TNFalpha, ADAMTS1, ADAMTS6 and both ADAMTS9 transcripts expressed in ARPE-19 cells showed a potent upregulation. The expression of ADAMTS genes in ARPE-19 cells and the transcriptional stimulation of some family members by TNFalpha may implicate them in inflammatory eye disease and the compromise of retinal matrix structure, which is evident in age-related macular degeneration (ARMD) and other retinal pathologies.

Inhibition of cartilage degradation: a combined tissue engineering and gene therapy approach

OBJECTIVE

To determine if tissue-engineered cartilage can be protected from cytokine-induced degradation using a gene therapy approach.

METHODS

Chemical and pantropic retroviral gene transfer methodologies were compared for their ability to introduce a luciferase reporter gene into adult bovine cartilage chondrocytes grown in monolayer. Pantropic retrovirus was then used to transduce these cells with human tissue inhibitor of metalloproteinases 1 (TIMP-1), and the stability of expression in monolayer or pellet culture was monitored for 6 weeks. Untransduced and TIMP-1-transduced cells were also used to tissue engineer 3-dimensional cartilage constructs that were then challenged with interleukin-1 (IL-1) for 4 weeks. Conditioned media and residual cartilage were collected for analysis of matrix components, including type II collagen and proteoglycans, and for TIMP-1 production and matrix metalloproteinase (MMP) activity.

RESULTS

Chemical transfection of adult bovine chondrocytes gave rise to short-lived reporter expression that was virtually undetectable after 4 weeks of culture. In contrast, pantropic retroviral transduction gave rise to stable expression that persisted at a high level for at least 6 weeks. Pantropic transduction of the cells with TIMP-1 gave rise to similar long-term expression, both in monolayer and pellet cultures. TIMP-1-transduced tissue-engineered cartilage also retained TIMP-1 expression for an additional 4 weeks of culture in the presence of IL-1. Compared with control samples, TIMP-1-transgenic cartilage resisted the catabolic effects of IL-1, with MMP activity reduced to basal levels and a decreased loss of type II collagen.

CONCLUSION

Pantropic retroviral transduction permits long-term expression of potentially therapeutic transgenes in adult tissue-engineered cartilage. While TIMP-1 transduction could be used to prevent collagen breakdown, alternative transgenes may be necessary to protect cartilage proteoglycans.

Three-dimensional tissue engineering of hyaline cartilage: comparison of adult nasal and articular chondrocytes

Adult chondrocytes are less chondrogenic than immature cells, yet it is likely that autologous cells from adult patients will be used clinically for cartilage engineering. The aim of this study was to compare the postexpansion chondrogenic potential of adult nasal and articular chondrocytes. Bovine or human chondrocytes were expanded in monolayer culture, seeded onto polyglycolic acid (PGA) scaffolds, and cultured for 40 days. Engineered cartilage constructs were processed for histological and quantitative analysis of the extracellular matrix and mRNA. Some engineered constructs were implanted in athymic mice for up to six additional weeks before analysis. Using adult bovine tissues as a cell source, nasal chondrocytes generated a matrix with significantly higher fractions of collagen type II and glycosaminoglycans as compared with articular chondrocytes. Human adult nasal chondrocytes proliferated approximately four times faster than human articular chondrocytes in monolayer culture, and had a markedly higher chondrogenic capacity, as assessed by the mRNA and protein analysis of in vitro-engineered constructs. Cartilage engineered from human nasal cells survived and grew during 6 weeks of implantation in vivo whereas articular cartilage constructs failed to survive. In conclusion, for adult patients nasal septum chondrocytes are a better cell source than articular chondrocytes for the in vitro engineering of autologous cartilage grafts. It remains to be established whether cartilage engineered from nasal cells can function effectively when implanted at an articular site.

Alanine scanning mutagenesis of CCR3 reveals that the three intracellular loops are essential for functional receptor expression

Intracellular signaling mediated by the eotaxin receptor, CCR3, has been implicated in allergic diseases involving the recruitment and activation of eosinophils. To investigate the structural requirements of the three intracellular loops (ICL) of CCR3, a panel of 15 alanine triplet mutants were generated and their effects on function assessed by assays of cell surface expression and chemotactic responsiveness. While the majority of constructs were efficiently expressed when compared with their wild-type counterpart, their abilities to migrate in response to eotaxin were relatively poor, suggesting that all three intracellular loops of CCR3 are involved to some degree in coupling to G proteins. - Another panel of 7 point mutants were then constructed to examine the DRY motif which resides in ICL2 and is highly conserved throughout the chemokine receptors identified to date. The conservative mutants D130E and R131K were well tolerated and gave chemotactic responses approaching 35 % of wild-type CCR3, but the less conserved substitutions D130A, D130N and R131L were non-functioning. Tyrosine 131 was particularly sensitive to mutation as both Y131F and Y131S mutants were poorly expressed and were chemotactically inactive. Together, this data suggest that the acidic / basic / polar nature of the DRY motif is a prerequisite for CCR3 function.

Clinical features of a novel TIMP-3 mutation causing Sorsby's fundus dystrophy: implications for disease mechanism

AIMS

To describe the phenotype in three family members affected by a novel mutation in the gene coding for the enzyme tissue inhibitor of metalloproteinase-3 (TIMP-3).

METHODS

Three members of the same family were seen with a history of nyctalopia and visual loss due to maculopathy. Clinical features were consistent with Sorsby's fundus dystrophy. Exon 5 of the gene coding for TIMP-3 was amplified by the polymerase chain reaction, single strand conformation polymorphism analysis undertaken and exon 5 amplicons were directly sequenced.

RESULTS

Onset of symptoms was in the third to fourth decade. Five of six eyes had geographic macular atrophy rather than neovascularisation as a cause for central visual loss. Peripheral retinal pigmentary disturbances were present. Scotopic ERGs were abnormal in all three. Mutation analysis showed a G-->T transversion in all three resulting in a premature termination codon, E139X, deleting most of the carboxy terminal domain of TIMP-3.

CONCLUSIONS

The patients described had a form of Sorsby's fundus dystrophy which fell at the severe end of the spectrum of this disease. Postulated disease mechanisms include deposition of dimerised TIMP-3 protein.

A novel tissue inhibitor of metalloproteinases-3 mutation reveals a common molecular phenotype in Sorsby's fundus dystrophy

Sorsby's fundus dystrophy (SFD) is a dominantly inherited degenerative disease of the retina that leads to loss of vision in middle age. It has been shown to be caused by mutations in the gene for tissue inhibitor of metalloproteinases-3 (TIMP-3). Five different mutations have previously been identified, all introducing an extra cysteine residue into exon 5 (which forms part of the C-terminal domain) of the TIMP-3 molecule; however, the significance of these mutations to the disease phenotype was unknown. In this report, we describe the expression of several of these mutated genes, together with a previously unreported novel TIMP-3 mutation from a family with SFD that results in truncation of most of the C-terminal domain of the molecule. Despite these differences, all of these molecules are expressed and exhibit characteristics of the normal protein, including inhibition of metalloproteinases and binding to the extracellular matrix. However, unlike wild-type TIMP-3, they all form dimers. These observations, together with the recent finding that expression of TIMP-3 is increased, rather than decreased, in eyes from patients with SFD, provides compelling evidence that dimerized TIMP-3 plays an active role in the disease process by accumulating in the eye. Increased expression of TIMP-3 is also observed in other degenerative retinal diseases, including the more severe forms of age-related macular degeneration, the most common cause of blindness in the elderly in developed countries. We hypothesize that overexpression of TIMP-3 may prove to be a critical step in the progression of a variety of degenerative retinopathies.

The solid phase synthesis of a series of tri-substituted hydantoin ligands for the somatostatin SST5 receptor

A series of trisubstituted hydantoins has been prepared by a versatile solid phase route employing primary alcohols, amines and amino acids as the monomeric building blocks. Several compounds showed submicromolar affinity in binding assays at recombinant human somatostatin receptors.

Localization of the functional domains of human tissue inhibitor of metalloproteinases-3 and the effects of a Sorsby's fundus dystrophy mutation

A transient COS-7 cell expression system was used to investigate the functional domain arrangement of tissue inhibitor of metalloproteinases-3 (TIMP-3), specifically to assess the contribution of the amino- and carboxyl-terminal domains of the molecule to its matrix metalloproteinase (MMP) inhibitory and extracellular matrix (ECM) binding properties. Wild type TIMP-3 was entirely localized to the ECM in both its glycosylated (27 kDa) and unglycosylated (24 kDa) forms. A COOH-terminally truncated TIMP-3 molecule was found to be a non-ECM bound MMP inhibitor, whereas a chimeric TIMP molecule, consisting of the NH2-terminal domain of TIMP-2 fused to the COOH-terminal domain of TIMP-3, displayed ECM binding, albeit with a lower affinity than the wild type TIMP-3 molecule. Thus the functional domain arrangement of TIMP-3 is analogous to that seen in TIMP-1 and -2, namely that the NH2-terminal domain is responsible for MMP inhibition whereas the COOH-terminal domain is most important in mediating the specific functions of the molecule. A mutant TIMP-3 in which serine 181 was changed to a cysteine, found in Sorsby's fundus dystrophy, a hereditary macular degenerative disease, was also expressed in COS-7 cells. This gave rise to an additional 48-kDa species (possibly a TIMP-3 dimer) that retained its ability to inhibit MMPs and localize to the ECM. These data favor the hypothesis that the TIMP-3 mutations seen in Sorsby's fundus dystrophy contribute to disease progression by accumulation of mutant protein rather than by the loss of functional TIMP-3.

The C terminus of the human C5a receptor (CD88) is required for normal ligand-dependent receptor internalization

The biological effects of the potent inflammatory mediator C5a, a complement split product, on human neutrophils and monocytes are limited by the rapid internalization of its specific receptor (C5aR, CD88). The C terminus of the C5aR is phosphorylated after stimulation with C5a of phorbol ester, and this phosphorylation might lead to receptor internalization. In this context, we have studied the effects on C5aR internalization of C5a, phorbol 12-myristate 13-acetate (PMA), the protein kinase inhibitor staurosporine, and pertussis toxin on rat basophilic RBL.2H3 cells stably transfected with the human wild-type or mutant C5aR. C5aR mutants lacked either part of the cytosolic C terminus, including suggested major phosphorylation sites, or a putative phosphorylation motif for protein kinase C in the third cytosolic loop. Additionally, agonist-induced internalization was analyzed on HEK293 cells co-transfected with C5aR and the pertussis toxin-resistant G protein alpha subunit, G alpha 16. Staurosporine-sensitive agonist-dependent C5aR internalization could be detected, suggesting that C5aR phosphorylation, most likely of the C terminus, participates in this type of internalization. In contrast, PMA-induced C5aR internalization seems to be independent of putative phosphorylation sites in either the truncated section of the C terminus or the third cytosolic loop. The phorbol ester-induced C5aR internalization may, therefore, be caused by an indirect and less specific effect of protein kinase C on the internalization machinery. Manipulation of the pertussis toxin-sensitive or -resistant G protein-dependent signal transduction had no effect on ligand-induced internalization.

Mutation of glutamate 199 of the human C5a receptor defines a binding site for ligand distinct from the receptor N terminus

C5a, a potent chemoattractant for monocytes, neutrophils, and other leukocytes, binds to a cell surface receptor of the seven-transmembrane superfamily. Here we report the effects of substituting Gln for Glu199 of the human C5a receptor (hC5aR) expressed in a model cell system for chemoattractant receptor signaling, the rat basophilic leukemia cell line RBL-2H3. Both the binding affinity for hC5a and the EC50 for subsequent cellular signals are reduced 5-10-fold by this substitution. A peptide mimic of the C terminus of C5a also binds to, and activates, hC5aR. The response to this peptide is reduced in cells bearing mutated hC5aR, indicating that the mutation affects interactions with the C terminus of hC5a. The C-terminal peptide contains only two basic residues, a Lys and an Arg (assumed to be analogous to Lys68 and Arg74 of hC5a), which could act as counter-ions for Glu199 of the receptor. If the counter-ion on hC5a was Arg74, then it would be expected that intact hC5a and hC5a des-Arg74 would have identical affinities and potencies when interacting with mutant hC5aR. It was found, however, that the binding affinity and potency (for receptor signaling events) of hC5a des-Arg74 was always lower than for intact hC5a. Furthermore, the equivalent C-terminal peptide to hC5a des-Arg74 (i.e. lacking the C-terminal Arg) could partially activate the wild type but not the mutant receptor, whereas the converse peptide, containing Arg but containing Met instead of Lys, had equal potencies for both wild type and mutant receptors. Taken together these data indicate that Glu199 of hC5aR is not involved in an interaction with Arg74 of hC5a, but may interact with Lys68 of hC5a. Mutation of Glu199 defines a second ligand binding site on hC5aR, distinct from the previously characterized site on the receptor N terminus. Unlike the N-terminal binding site, this second site is associated not just with the interaction with hC5a, but also with receptor activation.

Mutation of aspartate 82 of the human C5a receptor abolishes the secretory response to human C5a in transfected rat basophilic leukemia cells

C5a is a potent chemoattractant for monocytes, neutrophils and other leukocytes. The receptor for human C5a is a member of the rhodopsin superfamily of G protein-coupled receptors and contains an aspartate residue (Asp82) within the putative second transmembrane domain conserved in all other G protein-linked receptors. We investigated the role of this residue and also the carboxy-terminal 23 residues of the C5a receptor in ligand binding and signal transduction by expressing wild-type and mutant receptors in the rat basophilic leukemia cell line RBL-2H3. Wild-type and truncated receptors coupled efficiently to effector systems, resulting in the C5a-dependent discharge of granule contents. In contrast RBL cells transfected with receptors in which Asp82 had been mutated to asparagine did not respond to human C5a by secretion despite binding human C5a with high affinity. We conclude therefore that Asp82 is not involved in the interaction with ligand but is essential for the proper transduction of the ligand binding signal.

Site directed mutagenesis of the complement C5a receptor--examination of a model for its interaction with the ligand C5a

C5a is a 74 amino acid peptide cleaved from the fifth component of the complement system after activation of either the alternative or classical pathways. It is a potent chemoattractant for neutrophils and monocytes binding to identical receptors on the cell surface. Following the cloning of the cDNA encoding for the human complement C5a receptor, revealing it to be a member of the rhodopsin superfamily of G-protein coupled receptors, a model for the interaction of the C5a receptor with its ligand was proposed, the structure for the receptor being modelled on that of the well defined receptor bacteriorhodopsin. In this model two key residues of the receptor, aspartate82 and either glutamate179 or glutamate 180 were proposed to make up part of the binding site for C5a, acting as counter ions for arginine74 and arginine40, respectively of the C5a molecule. Replacement of aspartate82, glutamate179 and glutamate180 of the C5a receptor with asparagine and glutamine, respectively was shown to have little effect on the dissociation constant of the receptor as detected by Scatchard analysis and competitive binding assays. Hence this modus operandi for the interaction of C5a with its receptor can be rejected.

Multiple signalling pathways in the C5a-induced expression of adhesion receptor Mac-1

The CD11/CD18 family of leukocyte glycoproteins is essential in the process of adherence to endothelial and other cells that occurs during the acute inflammatory response. The cell surface expression of one member of this family, CD11b/CD18, or Mac-1, is increased on monocytes, neutrophils and other cell types by a number of agents, including chemotactic peptides and lipid mediators. The intracellular signalling mechanisms which control Mac-1 expression are not fully understood. In this report we have investigated the role of G proteins and extracellular Ca2+ in the stimulation of Mac-1 upregulation by the chemoattractant C5a in the human monocyte-like cell line, U937. Two signal transduction pathways are apparently involved and can be distinguished by their sensitivity to pertussis toxin, which inhibits activation of the Gi class of G proteins. The results indicate that a pertussis toxin-insensitive influx of extracellular Ca2+ may be one part of a network of signals leading to Mac-1 upregulation on U937 cells. This is in contrast to the stimulation of this process in neutrophils by chemotactic peptide, which is reported to be entirely dependent on pertussis toxin sensitive G proteins and independent of extracellular Ca2+.

Generation of chimeric C5a/formyl peptide receptors: towards the identification of the human C5a receptor binding site

We employed the polymerase chain reaction to produce a series of chimeric C5a/formyl peptide receptors. Chinese hamster ovary cells transfected with these constructs were tested for their ability to bind C5a. Substitution of three of the extracellular domains of the C5a receptor with the corresponding domains of the formyl peptide receptor abolished C5a binding, whilst replacement of the first extracellular loop of the C5a receptor with that of the formyl peptide receptor had little effect on the affinity of the receptor for C5a. We therefore conclude that this first outer loop of the C5a receptor does not participate in ligand binding, whilst involvement of the other extracellular domains of the receptor cannot be ruled out.

C5a stimulus-secretion coupling in rat basophilic leukaemia (RBL-2H3) cells transfected with the human C5a receptor is mediated by pertussis and cholera toxin-sensitive G proteins

Rat basophilic leukaemia cells (RBL-2H3) were transfected with either the wild type human C5a receptor or a truncated form lacking the last 23 C-terminal residues. Transfected cells bound human C5a specifically, with affinities in the range 3-20nM, and 12-166,000 receptors per cell, similar values to those obtained on human neutrophils and monocytic cells. The stimulation of secretion by human C5a was completely inhibited by pertussis toxin and partially sensitive to cholera toxin, indicating that both wild-type and mutated receptors are coupled to G proteins. Cells transfected with the mutated receptor were equally sensitive to hC5a, suggesting that this portion of the C terminus is not an absolute requirement for signal transduction.

N-linked glycosylation of the C5a receptor

The recent cloning of the cDNA encoding the human C5a receptor reveals a single potential site for N-linked glycosylation. Previous studies have suggested the presence of at least one carbohydrate moiety in the C5a receptor. Enzymatic digestion with Endoglycosidase F confirmed this presence and a point mutation at the predicted site of glycosylation was sufficient to lower the apparent molecular weight of the receptor as determined by SDS-PAGE. Removal of the carbohydrate moiety failed to abolish expression of the receptor and brought about only a slight reduction in the dissociation constant of the C5a receptor suggesting that the role of glycosylation in the binding of C5a by its receptor is limited.

Recombinant human antibodies: linkage of an Fab fragment from a combinatorial library to an Fc fragment for expression in mammalian cell culture

The combinatorial phage library approach to immunoglobulin repertoire cloning recently made it possible to isolate gene fragments encoding human immunoglobulin G1 Fabs binding with high affinity to specific antigens. Here we describe the construction of genes encoding whole human anti-tetanus toxoid antibodies based on one of these gene fragments and the efficient expression of these constructs by co-transfection of separate heavy and light chain vectors into a Chinese hamster ovary cell line constitutively expressing a viral transactivator protein. This system will be generally useful for the rapid analysis of recombinant antibodies derived from combinatorial libraries.

The generation of stable CHO cell lines expressing very high levels of complement C5A receptors and subsequent modulation of binding affinity for C5A

A single gene fragment encoding for the C5a receptor was produced by reverse transcription of mRNA isolated from differentiated U937 cells and subsequently amplified by means of the polymerase chain reaction. This fragment was introduced into the mammalian expression vector pEE6hCMV.neo and used to transfect a CHO cell line constitutively expressing a viral transactivator protein. Binding characteristics identical to the native neutrophil receptor were observed. A combination of antibiotic selection and cell sorting using anti-C5a receptor antiserum were then used to generate stable cell lines expressing up to 1.2 x 10(7) functional C5a receptors/cell with a lower affinity for C5a. It is postulated that this modulation of receptor affinity is dependent on coupling to native G-proteins in the host cells.

Recruitment of actin to the cytoskeletons of human monocyte-like cells activated by complement fragment C5a. Is protein kinase C involved?

U-937 cells differentiated by exposure to dibutyryl cyclic AMP respond to complement fragment C5a with a marked increase in cytoskeletal F-actin, which can be detected by fluorescence-activated cell sorting (f.a.c.s.) analysis of their rhodamine phalloidin-stained cytoskeletons. The C5a-induced increase in F-actin content can be prevented by prior exposure of the cells to cytochalasin B and pertussis toxin. It is insensitive to removal of extra cellular Ca2+, to cholera toxin or to neomycin. Phorbol myristate acetate (PMA), an activator of protein kinase C, does not induce actin polymerization in the differentiated cells. Both C5a and PMA stimulate superoxide production. The action of C5a on superoxide formation is also inhibited by neomycin, a phospholipase inhibitor. These results suggest that the cytoskeletal response to C5a requires activation of a G protein, but probably does not involve phospholipase C and protein kinase C, and is not highly dependent on the availability of Ca2+. Phospholipase C and kinase C may, however, be components of the pathway leading from C5a binding to superoxide production.

The chemoattractant des-Arg74-C5a regulates the expression of its own receptor on a monocyte-like cell line

The interaction of the chemoattractant des-Arg74-C5a (C5a des Arg) with its receptor on a human monocyte-like cell line, U-937, was examined. The data obtained suggest that C5a des Arg receptor expression is regulated by the extracellular concentration of C5a des Arg itself.

Kinestatic charge detection

A new technique for detecting ionizing radiation in two dimensions, called "kinestatic charge detection," is proposed and analyzed. This technique is useful when the signal photons must be integrated, as in computed tomography and digital radiography, rather than counted, as in nuclear medicine imaging. A generic treatment of the technique with gas-, liquid-, or solid-state radiation detectors is presented. A theoretical analysis is given of the fundamental physical parameters required for kinestatic charge detection to be successful.

The use of monoclonal antibodies to study the proteins specified by the transforming region of human adenoviruses

Monoclonal antibodies against two of the proteins specified by one of the transforming genes (early region 1B) of human adenovirus type 2 have been produced and characterized. Two clones (RA1 and PA6), generated by fusion of mouse myeloma NSO cells with splenocytes from rats immunized with whole-cell lysates of an adenovirus-transformed rat cell line (F19), secreted antibodies against a 58 kDa protein. Another clone (DC1) produced antibodies against the same protein, and resulted from fusion of immune rat splenocytes with the rat myeloma Y3.Ag.1.2.3. Immunoprecipitation studies showed that all three antibodies recognized [35S]-methionine-labelled 58 kDa protein, and phosphorylated derivatives of the 58 kDa protein labelled with [32P]orthophosphate present in infected human cells. One clone (EC3) produced antibody against a 19 kDa protein also encoded by early region 1B, but not sharing sequence homology with 58 kDa. The identity of the 19 kDa protein recognized by the EC3 antibody was established by immunoprecipitation from lysates of labelled-infected cells and from products of cell-free translation directed by mRNA isolated from adenovirus 2-infected cells. Indirect immunofluorescent-antibody staining of infected human cells using the RA1 and EC3 antibodies revealed a nuclear location of the 58 kDa protein and a mainly cytoplasmic location of the 19 kDa protein.

Specificity and locale of the L-3-glycerophosphate-flavoprotein oxidoreductase of mitochondria isolated from the flight muscle of Sarcophaga barbata thoms

1. The oxidation of l-3-glycerophosphate by flight-muscle mitochondria isolated from the flesh fly Sarcophaga barbata has been studied. Use of substrate analogues indicates that the catalytic and effector l-3-glycerophosphate binding sites on the allosteric l-3-glycerophosphate-flavoprotein oxidoreductase differ markedly in specificity. 2. The l-3-glycerophosphate-cyanoferrate oxidoreductase system in these mitochondria is antimycin-insensitive whereas the corresponding NADH-cyanoferrate oxidoreductase is extremely sensitive to this respiratory-chain inhibitor. Also no swelling is observed when these mitochondria are suspended in iso-osmotic solutions of ammonium glycerophosphate in contrast with the extensive swelling seen in similar solutions of ammonium pyruvate. These observations indicate that l-3-glycerophosphate does not penetrate the mitochondrial matrix whereas pyruvate does. 3. Submitochondrial particles catalyse the ATP-driven reduction of NAD(+) by l-3-glycerophosphate but at a far lower rate than that seen when succinate is the electron donor. These particles do not have an energy-linked pyridine nucleotide transhydrogenase activity. 4. We conclude that the l-3-glycerophosphate-flavoprotein oxidoreductase is located on the outer surface of the inner membrane of the flight-muscle mitochondria.