An autoantibody is modified for use as a delivery system to target the cell nucleus: therapeutic implications

A murine monoclonal anti-dsDNA antibody was found to penetrate living cells and localize in the nucleus without pathologic effects. A single mutation in VH markedly enhanced cellular penetration. The mutant antibody was produced as recombinant Fab and single chain antibody fragments to investigate its use as a delivery system to target the cell nucleus. Complexes were made containing Fab fragments and alkaline phosphatase conjugated goat antibodies to mouse |gk chains. Fab fragments transported 305 kDa goat antibody-enzyme complexes into the nucleus in COS-7 and CHO cells. A single chain antibody cDNA was constructed by splice overlap extension PCR and expressed in COS-7 cells. Binding of the single chain antibody to dsDNA was shown by ELISA, and cellular penetration and nuclear localization were demonstrated in COS-7 and CHO cells. The single chain antibody cDNA was ligated into the expression vector, pEGFP, to produce a fusion protein with green fluorescent protein. The fusion protein penetrated COS-7 cells and localized in the cell nucleus. The single chain antibody produced during sustained expression in CHO cells re-entered antibody-producing cells and localized in the nucleus without affecting cell viability. Our results demonstrate the potential use of a modified autoantibody as a delivery system to target the cell nucleus.

The NS3 proteinase domain of hepatitis C virus is a zinc-containing enzyme

NS3 proteinase of hepatitis C virus (HCV), contained within the N-terminal domain of the NS3 protein, is a chymotrypsin-like serine proteinase responsible for processing of the nonstructural region of the HCV polyprotein. In this study, we examined the sensitivity of the NS3 proteinase to divalent metal ions, which is unusual behavior for this proteinase class. By using a cell-free coupled transcription-translation system, we found that HCV polyprotein processing can be activated by Zn2+ (and, to a lesser degree, by Cd2+, Pb2+, and Co2+) and inhibited by Cu2+ and Hg2+ ions. Elemental analysis of the purified NS3 proteinase domain revealed the presence of zinc in an equimolar ratio. The zinc content was unchanged in a mutated NS3 proteinase in which active-site residues His-57 and Ser-139 were replaced with Ala, suggesting that the zinc atom is not directly involved in catalysis but rather may have a structural role. Based on data from site-directed mutagenesis combined with zinc content determination, we propose that Cys-97, Cys-99, Cys-145, and His-149 coordinate the structural zinc in the HCV NS3 proteinase. A similar metal binding motif is found in 2A proteinases of enteroviruses and rhinoviruses, suggesting that these 2A proteinases and HCV NS3 proteinase are structurally related.

Mechanisms of cellular penetration and nuclear localization of an anti-double strand DNA autoantibody

An anti-dsDNA Ab, mAb 3E10, was identified that bound membranes of fixed human renal tubular cells, penetrated live murine renal tubular cells in vivo, and localized in the cell nucleus. mAb 3E10 binds both dsDNA and an extracellular matrix protein, HP8/HEVIN, expressed in high endothelial venules. Previous studies showed both shared and distinct binding determinants of mAb 3E10 VH for DNA and HP8/HEVIN. To independently assess the requirement of DNA and HP8/HEVIN in cellular penetration, site-directed mutants of mAb 3E10 VH and V kappa were studied for penetrating kidney cell lines. The results showed that residues required for binding DNA, but not HP8/HEVIN, were necessary for Ab penetration, indicating that cellular penetration required the presence of DNA or binding of Ab to a membrane determinant precisely resembling DNA. Ab Fab penetrated cells, indicating that neither the Fc nor multivalent Ab binding is necessary for cellular penetration. Ab synthesized in the cytoplasm as a result of deleting heavy and light chain signal peptides was not translocated to the nucleus, indicating a mechanism distinct from the usual protein nuclear localization signals and suggesting the need for a membrane-mediated pathway or for post-translational modification of the Ab.

Mechanisms of cellular penetration and nuclear localization of an anti-double strand DNA autoantibody

An anti-dsDNA Ab, mAb 3E10, was identified that bound membranes of fixed human renal tubular cells, penetrated live murine renal tubular cells in vivo, and localized in the cell nucleus. mAb 3E10 binds both dsDNA and an extracellular matrix protein, HP8/HEVIN, expressed in high endothelial venules. Previous studies showed both shared and distinct binding determinants of mAb 3E10 VH for DNA and HP8/HEVIN. To independently assess the requirement of DNA and HP8/HEVIN in cellular penetration, site-directed mutants of mAb 3E10 VH and V kappa were studied for penetrating kidney cell lines. The results showed that residues required for binding DNA, but not HP8/HEVIN, were necessary for Ab penetration, indicating that cellular penetration required the presence of DNA or binding of Ab to a membrane determinant precisely resembling DNA. Ab Fab penetrated cells, indicating that neither the Fc nor multivalent Ab binding is necessary for cellular penetration. Ab synthesized in the cytoplasm as a result of deleting heavy and light chain signal peptides was not translocated to the nucleus, indicating a mechanism distinct from the usual protein nuclear localization signals and suggesting the need for a membrane-mediated pathway or for post-translational modification of the Ab.

Two kappa immunoglobulin light chains are secreted by an anti-DNA hybridoma: implications for isotypic exclusion

An anti-DNA hybridoma derived from an MRL/lpr mouse secretes two different kappa light chains in combination with a single heavy chain. Multiple single cell clones express and secrete immunoglobulin containing both kappa light chains. The N-terminal protein sequences of the light chains correspond to sequences predicted from functionally rearranged mRNAs subjected to reverse transcription and amplified by polymerase chain reaction (PCR). Karyotype analysis of the hybridoma indicates a clonal line derived from the fusion of two cells. By amino acid sequence comparison and PCR analysis, both functional kappa light chains are derived from the MRL/lpr spleen. The two functional light chain cDNAs were cloned and co-transfected into COS-7 cells with the heavy chain cDNA. Only one of the light chains in combination with mAb 3E10 heavy chain confers anti-DNA reactivity. The presence of two separate kappa light chains and, therefore, two separate antigen receptors on a single B cell may have ramifications for both polyclonal activation and toleration of lupus B cells.

Localization of an Fc-binding reactivity to the constant region of human IgG4. Implications for the pathogenesis of rheumatoid arthritis

The majority of plasma cells in rheumatoid arthritis (RA) synovium produce rheumatoid factors (RF). IgG RF predominate in the immune complexes found in RA synovial fluid and have been implicated in the pathogenesis of RA. IgG4 RF are a major component of IgG RF produced in serum and synovium of RA patients, even though this subclass comprises only 4% of the serum IgG. We produced an IgG4 mAb, hRF-1, with RF reactivity from the synovial tissue of a patient with RA. mAb hRF-1 had binding specificity for mammalian IgG similar to Staphylococcus aureus protein A, which is characteristic of RF from patients with RA. To determine the molecular basis of this particular RF reactivity, the heavy and light chain genes of mAb hRF-1 were amplified by PCR, cloned, and ligated into the pSG5 plasmid for expression in COS-7 cells. Chain recombination experiments localized the Fc-binding reactivity to the hRF-1 heavy chain. Using a series of chimeric Ab sequences, the Fc-binding reactivity was mapped to the constant region of IgG4 rather than the variable region involved in classic RF reactivity. Multiple domains, including Hinge, CH2, and CH3 of the IgG4 constant region were required for Fc binding. Our studies demonstrate an example of RF-like Fc-binding reactivity that is conferred by the gamma-4 constant region rather than the classic Ag binding site and suggest that increased production of IgG4 may contribute to the pathogenesis of RA.

Localization of an Fc-binding reactivity to the constant region of human IgG4. Implications for the pathogenesis of rheumatoid arthritis

The majority of plasma cells in rheumatoid arthritis (RA) synovium produce rheumatoid factors (RF). IgG RF predominate in the immune complexes found in RA synovial fluid and have been implicated in the pathogenesis of RA. IgG4 RF are a major component of IgG RF produced in serum and synovium of RA patients, even though this subclass comprises only 4% of the serum IgG. We produced an IgG4 mAb, hRF-1, with RF reactivity from the synovial tissue of a patient with RA. mAb hRF-1 had binding specificity for mammalian IgG similar to Staphylococcus aureus protein A, which is characteristic of RF from patients with RA. To determine the molecular basis of this particular RF reactivity, the heavy and light chain genes of mAb hRF-1 were amplified by PCR, cloned, and ligated into the pSG5 plasmid for expression in COS-7 cells. Chain recombination experiments localized the Fc-binding reactivity to the hRF-1 heavy chain. Using a series of chimeric Ab sequences, the Fc-binding reactivity was mapped to the constant region of IgG4 rather than the variable region involved in classic RF reactivity. Multiple domains, including Hinge, CH2, and CH3 of the IgG4 constant region were required for Fc binding. Our studies demonstrate an example of RF-like Fc-binding reactivity that is conferred by the gamma-4 constant region rather than the classic Ag binding site and suggest that increased production of IgG4 may contribute to the pathogenesis of RA.

DNA mimics a self-protein that may be a target for some anti-DNA antibodies in systemic lupus erythematosus

Recent studies suggest that some anti-DNA Abs in systemic lupus erythematosus may actually be Abs to specific proteins and that binding to dsDNA is a nonspecific cross-reactive event. To identify such proteins that bind to anti-DNA Abs, a cDNA expression library from human placenta was screened with mAb 3E10, a pathogenic anti-dsDNA Ab. MAb 3E10 was shown to bind to a 44-amino-acid fragment of HP8, a newly identified protein with amino acid sequence homology to the family of SPARC extracellular matrix proteins. To determine if Ab binding to both dsDNA and HP8 protein occurs through a common binding site, and therefore represents molecular mimicry, the Ab binding domains for protein and DNA were mapped. Chain recombinations between mAb 3E10 and a non-anti-DNA mAb showed that both the heavy and the light chains of mAb 3E10 were essential for anti-dsDNA and anti-HP8 reactivity. Mutagenesis experiments demonstrated that dsDNA and HP8 shared several critical binding residues located in all three complementarity-determining regions of mAb 3E10 VH. Moreover, Abs to HP8 were demonstrated in the sera of a subset of lupus patients. These results indicate that DNA mimics the HP8 protein in binding a lupus Ab, and that this protein may be a target for a subpopulation of anti-dsDNA Abs in systemic lupus erythematosus.

DNA mimics a self-protein that may be a target for some anti-DNA antibodies in systemic lupus erythematosus

Recent studies suggest that some anti-DNA Abs in systemic lupus erythematosus may actually be Abs to specific proteins and that binding to dsDNA is a nonspecific cross-reactive event. To identify such proteins that bind to anti-DNA Abs, a cDNA expression library from human placenta was screened with mAb 3E10, a pathogenic anti-dsDNA Ab. MAb 3E10 was shown to bind to a 44-amino-acid fragment of HP8, a newly identified protein with amino acid sequence homology to the family of SPARC extracellular matrix proteins. To determine if Ab binding to both dsDNA and HP8 protein occurs through a common binding site, and therefore represents molecular mimicry, the Ab binding domains for protein and DNA were mapped. Chain recombinations between mAb 3E10 and a non-anti-DNA mAb showed that both the heavy and the light chains of mAb 3E10 were essential for anti-dsDNA and anti-HP8 reactivity. Mutagenesis experiments demonstrated that dsDNA and HP8 shared several critical binding residues located in all three complementarity-determining regions of mAb 3E10 VH. Moreover, Abs to HP8 were demonstrated in the sera of a subset of lupus patients. These results indicate that DNA mimics the HP8 protein in binding a lupus Ab, and that this protein may be a target for a subpopulation of anti-dsDNA Abs in systemic lupus erythematosus.

[The most frequent complications during long-term corticotherapy]

In 274 outpatients with chronic spastic bronchitis long-term treatment with corticosteroids was used due to their clinical condition. In patients treated for 6 years with daily doses of 1-2 mg of prednisolone no corticosteroid-induced complications were observed. Transient ecchymoses occurred in patients treated for longer time periods with prednisolone 4 mg daily. In 12.5% of patients pityriasis versicolor developed, and muscle weakness was the complaint in 3.1% of cases. In patients treated with 6 mg daily of prednisolone petechiae were noted in 35% of cases, in 10% subcutaneous tissue atrophy, in 2.5% osteoporosis was observed, and menstruation disturbances were reported in 25% of the treated women. In patients receiving prednisolone 8 mg daily subcutaneous extravasations developed in 80% of cases, skin atrophy in 50%, myopathy in 25%, crural thrombophlebitis in 5%, cushingoid features in 7.5%. In patients receiving prednisolone 12 mg daily, besides the above complications, fractures occurred in 14.2% of cases, and psychotic symptoms in 7%.