RNA binding by the Wilms tumor suppressor zinc finger proteins

The Wilms tumor suppressor gene WT1 is implicated in the ontogeny of genito-urinary abnormalities, including Denys-Drash syndrome and Wilms tumor of the kidney. WT1 encodes Kruppel-type zinc finger proteins that can regulate the expression of several growth-related genes, apparently by binding to specific DNA sites located within 5' untranslated leader regions as well as 5' promoter sequences. Both WT1 and a closely related early growth response factor, EGR1, can bind the same DNA sequences from the mouse gene encoding insulin-like growth factor 2 (Igf-2). We report that WT1, but not EGR1, can bind specific Igf-2 exonic RNA sequences, and that the zinc fingers are required for this interaction. WT1 zinc finger 1, which is not represented in EGR1, plays a more significant role in RNA binding than zinc finger 4, which does have a counterpart in EGR1. Furthermore, the normal subnuclear localization of WT1 proteins is shown to be RNase, but not DNase, sensitive. Therefore, WT1 might, like the Kruppel-type zinc finger protein TFIIIA, regulate gene expression by both transcriptional and posttranscriptional mechanisms.

Separation of E. coli expressing functional cell-wall bound antibody fragments by FACS

BACKGROUND

The rapid development of recombinant antibody technology in the last few years has facilitated the generation of antibody libraries in bacteria. Recombinant antibodies against various antigens have been selected from these libraries by presenting each antibody on the surface of a phagemid particle that contains the antibody's gene. An alternative screening system is the display of antibody fragments on bacteria. A major advantage is the possibility to select single cells directly from a large number of bacteria by using fluorescently labeled antigens and fluorescence assisted cell sorting (FACS).

OBJECTIVES

pAP is an expression vector for the bacterial display of antibody fragments. E. coli transformed with pAP express a single chain antibody (scFv) fused to the peptidoglycan-associated-lipoprotein (PAL). This fusion protein binds strongly to the cell wall. To employ this system for screening, we have investigated the possibility of selecting antigen-specific clones by FACS.

STUDY DESIGN AND RESULTS

Several DNA fragments coding for various scFvs were inserted into the pAP expression vector. E. coli were transformed with these plasmids and immunostained with fluorescent antigens under given conditions. We were able to select stained E. coli expressing a specific scFv from unstained E. coli expressing a non-binding scFv by FACS. The specific selection of the bacteria was demonstrated by amplifying their genes by PCR.

CONCLUSIONS

Conditions are described for separating E. coli containing scFv bound to their cell wall by FACS using fluorescently labeled antigens. These studies provide a basis for screening libraries of scFv antibodies.

An RNA recognition motif in Wilms' tumour protein (WT1) revealed by structural modelling

The Wilms' tumour suppressor gene 1 (WT1) (1,2) encodes four C2H2 zinc finger-containing proteins (3) critical for normal mammalian urogenital development (4). Mutations in this gene are observed in the childhood kidney cancer, Wilms' tumour (WT) (5). WT1 can bind specific DNA targets within the promoters of many genes (6-9) and both transcriptional repression and activation domains have been identified (10). On this basis, it has been assumed that regulation of transcription is the basis of WT1 tumour suppressor activity. However, subnuclear localization studies have revealed an association between WT1 proteins and 'speckled bodies' within the nucleus. Degradation of nuclear RNA in cells expressing WT1 abolishes this speckled localization and WT1 co-immunoprecipitates with a number of spliceosomal proteins, suggesting that it may also bind to RNA (11). Using structural rather than sequence comparison, we have now identified an evolutionarily conserved N-terminal RNA recognition motif (RRM) in all known WT1 isoforms similar to that in the constitutive splicing factor U1A. Given the association between WT1 mutations and Wilms' tumours, this study, together with other recent findings, may suggest a novel tumour suppression mechanism.

Affinity enhancement of a recombinant antibody: formation of complexes with multiple valency by a single-chain Fv fragment-core streptavidin fusion

In antigen-antibody interactions, the high avidity of antibodies depends on the affinity and number of the individual binding sites. To develop artificial antibodies with multiple valency, we have fused the single-chain antibody Fv fragments to core streptavidin. The resulting fusion protein, termed scFv::strep, was found after expression in Escherichia coli in periplasmic inclusion bodies. After purification of the recombinant product by immobilized metal affinity chromatography, refolding and size-exclusion FPLC, tetrameric complexes resembling those of mature streptavidin were formed. The purified tetrameric scFv::strep complexes demonstrated both antigen- and biotin-binding activity, were stable over a wide range of pH and did not dissociate at high temperatures (up to 70 degrees C). Surface plasmon resonance measurements in a BIAlite system showed that the pure scFv::strep tetramers bound immobilized antigen very tightly and no dissociation was measurable. The association rate constant for scFv::strep tetramers was higher than those for scFv monomers and dimers. This was also reflected in the apparent constants, which was found to be 35 times higher for pure scFv::strep tetramers than monomeric single-chain antibodies. We could also show that most of biotin binding sites were accessible and not blocked by biotinylated E.coli proteins or free biotin from the medium. These sites should therefore facilitate the construction of bispecific multivalent antibodies by the addition of biotinylated ligands.

Health, education, and the virtues of efficiency

Managerialism has been seen in recent times as an answer to problems which fall well outside the boundaries of commercial enterprise. This trend can be seen in both education at university level and health. But there are major risks in transporting the techniques and values of the market into domains which serve non-commercial ends. Many of the most desired achievement of both health and education cannot be costed in monetary terms, and many of the activities that can be costed cannot produce profits. Education and health both have aims that are essentially moral, and the intrusion of managerialism undermines the morality and excuses departures from the central functions of both disciplines. This is not to say that efficiency and cost-cutting may not serve the good of education and health, but they cannot replace functions such as teaching, learning, and healing. There is a cogent argument for redefining the functions and structures of management in order to serve the knowledge workers whose role in health and education is indispensable, rather than to devolve increasing responsibility for management to them. The freedom of knowledge workers to practise their professions, to teach, to do research, and to reflect should be increased, rather than diminished progressively by institutional demands for more and more commitment the minutiae of management.

Placement outcomes of 206 severely maltreated children in the Boston Juvenile Court system: a 7.5-year follow-up study

This study examines placement outcomes of 206 severely maltreated children 7.5 years after arraignment in Boston Juvenile Court (BJC) on Care and Protection Petitions. Sixty-seven percent (n = 138) of the sample had been permanently removed from their parents and 33% (n = 68) had their cases dismissed in the BJC. At time of this follow-up, 21% of the full sample (n = 44) were still in temporary custody awaiting permanent placement. In addition, 4% (n = 8) of children had "drifted" back to their abusive/neglectful parents despite prior permanent removal. The average time children in this sample spent in probate proceedings (awaiting permanent placement) had increased substantially to 2.1 years since the last overview study of this sample 4 years ago. The rate of court referral for incidences of reabuse (a C&P filing), or delinquency was significantly lower among children who had been permanently placed (p < .003). Rates of court-referral for reabuse charges were the same (16%) for children who were in temporary custody at the time of follow-up and children who had been dismissed back to the parent for whom the original C&P had been filed. Results are discussed in light of the urgent need to restructure time limits in juvenile court proceedings, integrate adequate tracking of child abuse and neglect cases through and across court and agency boundaries, and the use standardized assessments of abused and neglected children as a tool in the adjudication process.

Human antibody libraries in Escherichia coli

A potentially vast pool of human antibodies with novel specificities for diagnostic and therapeutic purposes can be generated in Escherichia coli. Antibodies to infectious agents have already been isolated by amplifying the heavy and light chain repertoires of donor lymphocytes and they have even been rescued many years after the initial infection from memory cells cultivated in SCID mice. Eventually, however, the creation of extremely large and diverse libraries from the naive antibody repertoire of unactivated B lymphocytes or by gene synthesis using random oligonucleotides for the hypervariable regions could provide a rapid means of obtaining human antibodies to any particular antigen. An important breakthrough for exploiting the potential size and diversity of these libraries has been the development of systems for the surface display of antibodies that are physically linked to their own genes. This allows large numbers of clones to be screened simultaneously and antibodies with affinities of up to 10(8) M-1 have already been obtained using these vectors. It seems quite feasible, therefore, that antibodies with affinities approaching those obtained in the secondary immune response can be obtained by systematically optimizing the strategies for making antibody libraries. Furthermore, it might be possible to establish extremely large antibody repertoires in E. coli by the in vivo recombination of phage and plasmid antibody libraries. The affinity of the selected antibodies could be increased by chain shuffling or random mutagenesis followed by several rounds of selection under increasingly stringent conditions.

A single expression system for the display, purification and conjugation of single-chain antibodies

To facilitate the purification and conjugation of single-chain antibodies (scFv) selected from a phage display library, we have incorporated His6, an amber stop codon and a C-terminal Cys into a surface expression vector. The vector also contains a lacIq gene for improving the efficiency of regulation and a sequence coding for a marker peptide.

The Pediatric Symptom Checklist. Support for a role in a managed care environment

OBJECTIVES

To gather data based on studies of the Pediatric Symptom Checklist, identify risk factors associated with high levels of dysfunction in primary care pediatric settings, and explore the relationship between common risk factors and psychosocial problems identified by pediatricians.

DESIGN

Retrospective review and cross-sectional, case-referent survey.

SETTING

Subjects were selected from three primary care pediatric clinics in Massachusetts: a private practice in a predominantly white, middle-class suburb, an urban health maintenance organization clinic, and an inner-city clinic.

PARTICIPANTS

Of 423 outpatients aged 6 to 12 years screened for psychosocial problems, 72 children and their families were seen for in-depth structured and clinical interviews (24 from each site).

INTERVENTIONS

None.

MEASUREMENTS/MAIN RESULTS

Children with a single parent and/or those who were economically disadvantaged were significantly more likely to show psychosocial impairment. The specificity of the Pediatric Symptom Checklist was 100% in samples with a lower socioeconomic status compared with 68% in middle-class samples, and sensitivity was 95% in middle-class samples compared with 80% in lower-class samples. Pediatricians identified psychosocial problems in eight of 15 children with a history of familial mental illness or substance abuse and seven of eight children with a history of physical or sexual abuse, but only six of 17 cases from single-parent families and four of 11 cases from poor families.

CONCLUSIONS

Pediatricians should be sensitive to psychosocial dysfunction especially in single-parent and low-income families. Use of the Pediatric Symptom Checklist for psychosocial screening in a managed health care delivery system could target capitated resources efficiently by providing early identification and secondary prevention of psychosocial morbidity.

Bacterial expression and refolding of single-chain Fv fragments with C-terminal cysteines

Two antibody single-chain Fv (scFv) fragments carrying five C-terminal histidine residues were expressed in Escherichia coli as periplasmic inclusion bodies. Their variable heavy (VH) and light (VL) domains are derived from the mouse monoclonal antibody 215 (MAb215), specific for the largest subunit of RNA polymerase II of Drosophila melanogaster and rat MAb Yol1/34, specific for pig brain alpha-tubulin. ScFv-215 contains an additional cysteine residue near to its C-terminus. After solubilization of inclusion bodies followed by immobilized metal affinity chromatography (IMAC) in 6M urea and a renaturation procedure, scFv monomers, noncovalent dimers, and aggregated antibody fragments were separated by size exclusion chromatography. In addition, a fraction of disulfide-bonded scFv-215 homodimers (scFv')2 was also isolated. The various antibody forms appear to be in equilibrium after renaturation since first peak composed mainly of aggregates could be resolved into a similar pattern of aggregates, dimers, and monomers after repeating the denaturation/renaturation procedure. All fractions of the recombinant scFv-215 demonstrated high antigen-binding activity and specificity as shown by enzyme-linked immunosorbent assay (ELISA) and Western blot analysis. Affinity measurements carried out by competitive immunoassays showed that covalently linked (scFv')2 have binding constants quite close to those of the parental MAbs and fourfold higher than scFv' monomers. ScFv derivatives, specifically biotinylated through the free sulfhydryl group, recognize the corresponding antigen in ELISA and Western blot analysis, thus demonstrating the possibility of using chemically modified scFv antibodies for immunodetection.

DNA binding capacity of the WT1 protein is abolished by Denys-Drash syndrome WT1 point mutations

Constitutional point mutations in the zinc finger (ZF) region of the Wilms' tumour suppressor gene 1 (WT1) lead to Denys-Drash syndrome (DDS). Patients with this syndrome display renal failure, Wilms' tumour (WT) and pseudohermaphroditism. DDS WT1 mutations fall into three major categories: (a) missense mutations altering amino acids which directly interact with the DNA target; (b) substitution of amino acids involved in zinc complexing; and (c) nonsense mutations leading to the removal of at least two zinc fingers. We have expressed the WT1 zinc fingers as glutathione-S-transferase fusion proteins, with the lysine-threonine-serine (KTS) alternate splice between ZF3 and ZF4 either present or absent. WT1 fusion constructs with all three classes of DDS mutation were also created. Wild-type and mutant fusion proteins were assayed for their DNA-binding affinity using four previously identified WT1 DNA targets: an EGR1 consensus site; murine insulin-like growth factor 2 promoter 2 (IGF2P2); a (TCC)n motif from the PDGFA-chain promoter; and +P5, a genomic fragment isolated by its affinity for WT1 + KTS. WT1-KTS bound all four targets, but WT1 + KTS only bound +P5. All three classes of DDS mutation investigated, with or without KTS, abolished binding to all four targets. This provides evidence that DDS mutations act either as dominant-negative antimorphs, or elicit their effect through disturbed isoform dosage balance.

A single-chain TNF receptor antagonist is an effective inhibitor of TNF mediated cytotoxicity

Tumour necrosis factor (TNF) is an important mediator of immune and inflammatory responses and has been recognized as a major pathogenic factor in several autoimmune and inflammatory diseases. TNF receptor TR60 plays a critical role in signalling the pathogenic activities of TNF. We here describe molecular cloning and bacterial production of a single-chain antibody (scFv H398) directed against TR60 which possesses antagonistic activity. VH and VL encoding sequences were isolated by PCR from the murine hybridoma cell line H398, cloned into a scFv expression vector and expressed in Escherichia coli. The recombinant antibody (Ab) fragment was found as an active soluble protein in the periplasm but also formed inclusion bodies. Re-folded scFv H398 purified from inclusion bodies was shown to be functional and stable at 37 degrees C with a half-life of 50 h. Comparison of the antigen binding characteristics of scFv with the parental enzymatically produced Fab H398 revealed that both Ab fragments have the same epitope specificity and an identical antigen binding affinity of 1.5 nM. In an in vitro assay it was demonstrated that scFv H398 is an efficient inhibitor of TNF mediated cytotoxicity with an IC50 of 22 nM, which is comparable to the antagonistic activity of natural Fab H398 with an IC50 of 12 nM. As scFv H398 possesses the high affinity TR60 binding and receptor antagonistic activity of the parental Ab H398 but is expected to be less antigenic in man, it provides a valuable tool for the development of novel therapeutic reagents against TNF mediated diseases.

Bifunctional and multimeric complexes of streptavidin fused to single chain antibodies (scFv)

Multivalent and multispecific antibodies with defined stoichiometry could provide valuable tools for biological and medical research and for the diagnosis and therapy of cancer. We have therefore fused single chain antibodies (scFv) with core-streptavidin. This chimeric protein, expressed by the vector pSTE-215 (plasmid for streptavidin-tagged expression), can form tetrameric complexes, binds antigen and contains the biotin binding site which may be used for further complex formation. An additional cysteine was inserted near the carboxy terminus to facilitate the construction of covalently linked bifunctional molecules. The scFv fusion protein could be purified by affinity chromatography using biotin analogues. We have also shown that the scFv fusion protein could be used for direct detection of its antigen in ELISA and Western blots when stained with biotinylated horseradish peroxidase.

Screening for psychosocial dysfunction in pediatric inpatients

Screening pediatric inpatients for psychosocial dysfunction offers physicians an opportunity to identify emotional and behavioral problems that might otherwise go unrecognized. In this study, the Pediatric Symptom Checklist (PSC), a brief, parent-completed questionnaire, which has been validated in a variety of outpatient settings, was used to screen 98 pediatric inpatients. Results indicated that the PSC can be easily administered in a busy inpatient setting and is well-tolerated by both house staff and patients' parents as a routine part of the admissions process. The percentage of children who screened positive with the PSC in this inpatient setting was similar to the percentages generated by using the PSC in outpatient settings. Routine use of the PSC in inpatient settings serves to heighten house staff awareness of psychosocial concerns and facilitate parent-physician discussion of pediatric mental health issues.

Single-chain antibody streptavidin fusions: tetrameric bifunctional scFv-complexes with biotin binding activity and enhanced affinity to antigen

To increase the avidity of single-chain antibodies (scFv) for their antigen, we have fused them to core-streptavidin. The chimeric protein, expressed by the vector pSTE (plasmid for streptavidin-tagged expression) from Escherichia coli, can form tetrameric complexes, binds its antigen and contains four biotin binding sites per tetrameric complex. An additional cysteine inserted near the carboxy terminus further stabilised the complex. The scFv fusion protein tetramers could be enriched by affinity chromatography using the biotin analog 2-iminobiotin from periplasmic inclusion bodies after refolding. We have also shown that the scFv fusion protein could be used for direct detection of its antigen in ELISA when stained with biotinylated horseradish peroxidase. The affinity of the scFv-antibody complex was substantially increased by avidity effects due to the tetrameric structure. The biotin binding sites may be used for coupling other antibodies and molecules to form bispecific and bifunctional reagents.

Recombinant single-chain Fv fragments carrying C-terminal cysteine residues: production of bivalent and biotinylated miniantibodies

A murine antibody single-chain Fv (scFv) fragment carrying five C-terminal histidine residues preceded by a cysteine residue and a marker peptide was expressed in Escherichia coli. Its variable heavy (VH) and light (VL) domains are derived from the mouse monoclonal antibody mAb215, which is specific for the largest subunit of RNA polymerase II of Drosophila melanogaster. ScFv' monomers, covalently linked (scFv')2 and non-covalent dimers, as well as aggregated antibody fragments, were isolated from an E. coli cell paste by immobilized metal affinity chromatography in 6 M urea followed by a renaturation procedure that does not use any sulfhydryl agents. In a final step, the components were separated by size exclusion chromatography. All the recombinant antibody fractions demonstrated high antigen-binding activity and specificity as shown by ELISA and Western blot analysis. Affinity measurements carried out by competitive immunoassays showed that covalently linked (scFv')2 have binding constants quite close to those of the parental monoclonal antibodies and four-fold higher than scFv' monomers. ScFv derivatives, specifically biotinylated through the free sulfhydryl group, recognize the corresponding antigen in ELISA and Western blot analysis, thus demonstrating the possibility of using chemically modified scFv antibodies for immunodetection.

Isolation of IgG antibody Fv-DNA from various mouse and rat hybridoma cell lines using the polymerase chain reaction with a simple set of primers

To facilitate the isolation of IgG antibody Fv-DNA sequences from hybridoma cell lines, we have established a polymerase chain reaction (PCR) procedure requiring only a small number of primers. The sense primers homologous to DNA coding for the first framework sequences were designed to hybridize to all the known antibody sequences under conditions that permit a high number of mismatches. The antisense primers were homologous to DNA coding for the beginning of the constant regions of the gamma and kappa chains. Restriction sites introduced by the primers enable the DNA to be cloned into bacterial expression vectors. Only three sense VH primers and two sense VL primers paired with one backward primer for the heavy and light chains, respectively, were necessary for the amplification of Fv-DNA from a total of 17 rodent cell lines that we have so far worked with. These consisted of 12 mouse cell lines and five rat cell lines. This procedure will therefore probably be sufficient to isolate the Fv-DNA from most mouse cell lines and possibly also from most rat cell lines.

Simultaneous mutagenesis of antibody CDR regions by overlap extension and PCR

A method for the facile simultaneous mutagenesis of complementary-determining regions (CDRs) in a single chain antibody (scFv) is described. Overlapping sets of oligonucleotides containing random sequences within the CDRs corresponding to the heavy chain variable region (VH) jointed to a linker peptide (J) and the light chain variable region (VL) were extended under PCR conditions to full-length genes. These gene products were then further amplified using short PCR primers containing complementary overlaps between the 3' and 5' ends of the VH-J and VL genes respectively. In a final step, the VH-J and VL gene products were mixed and assembled into scFv DNA products by overlap extension under standard PCR conditions. Sequence analyses indicated that the method is basically successful. However, some deletions were observed, which probably reflects difficulties in the automatic synthesis of long degenerate oligonucleotides.

Production of monoclonal antibodies against epitopes of the main coat protein of filamentous fd phages

Three monoclonal antibodies (MAbs) were produced which react with epitopes of the main structural coat protein (pVIII) of filamentous fd phages as demonstrated by solid-phase fluorometric enzyme immunoassays and by immunoelectron microscopy. The antibodies are of the IgG1, IgG2a and IgG2b immunoglobulin subclasses. Since they also react with recombinant phages expressing antigen fragments in their pIII region they may be suitable reagents for the demonstration and isolation of filamentous phages used in recombinant protein technology.