Biomedical subjects

A Oehm

Publications and source records attributed to A Oehm.

4 recordsLinked to original sources

PubMed1992

Induction of apoptosis by monoclonal antibody anti-APO-1 class switch variants is dependent on cross-linking of APO-1 cell surface antigens.

Apoptosis, programmed cell death, was previously shown to be induced by the mAb anti-APO-1 (IgG3, kappa) by binding to the APO-1 cell surface Ag, a new member of the nerve growth factor/TNF receptor superfamily. To investigate the role of the Ig H chain Fc regions we compared induction of apoptosis by the original mAb IgG3 anti-APO-1 with anti-APO-1 F(ab')2 fragments and different anti-APO-1 isotypes (IgG1, IgG2b, IgG2a, and IgA) isolated by sequential sublining. We found that IgG3 was the most active isotype; IgG1, IgG2a, and IgA showed intermediate activity, and IgG2b and F(ab')2 were inactive. Cytotoxic activity of the inactive or less active antibody preparations was fully reconstituted by protein A, anti-mouse Ig, or anti-mouse Ig F(ab')2, respectively. Thus, APO-1-mediated induction of apoptosis was dependent on efficient cross-linking of APO-1 cell surface Ag, indirectly augmented by anti-APO-1 Fc-Fc self-aggregation. Because of their different in vitro activity we selected IgG3-, IgG2b-, and IgA anti-APO-1 to test their antitumor activity against solid human B lymphoblastoid tumors in SCID mice. The isotypes showed a different serum half-life (IgG3: 9.2-10.4 days, IgG2b: 1.9-2.6 days, and IgA: 14.1-29.2 h) and a different initial tumor localization 4 h after i.p. injection (IgG3 around the blood vessels, IgG2b homogeneously, and IgA heterogeneously distributed in the tumor). All antibody preparations induced tumor regression by induction of apoptosis, even IgG2b anti-APO-1 inactive in vitro without cross-linking. The activity of IgA anti-APO-1, which did not mediate complement-dependent cytotoxicity or antibody-dependent cellular cytotoxicity indicates that apoptosis may be used as the main if not the only mechanism of induction of tumor regression in vivo. As with in vitro, IgG3 anti-APO-1 was the most effective isotype also in vivo. This result suggests that cross-linking of APO-1 on the tumor cell surface may also be required for tumor regression by apoptosis in vivo. Taken together, our data show that selective targeting of apoptosis to tumors may be an efficient antitumor mechanism.

Animals↗

PubMed1992

Purification and molecular cloning of the APO-1 cell surface antigen, a member of the tumor necrosis factor/nerve growth factor receptor superfamily. Sequence identity with the Fas antigen.

The APO-1 antigen as defined by the mouse monoclonal antibody anti-APO-1 was previously found to be expressed on the cell surface of activated human T and B lymphocytes and a variety of malignant human lymphoid cell lines. Cross-linking of the APO-1 antigen by anti-APO-1 induced programmed cell death, apoptosis, of APO-1 positive cells. To characterize the APO-1 cell surface molecule and to better understand its role in induction of apoptosis, the APO-1 protein was purified to homogeneity from membranes of SKW6.4 B lymphoblastoid cells by solubilization with sodium deoxycholate, affinity chromatography with anti-APO-1 antibody, and reversed phase high performance liquid chromatography. Each purification step was followed by an APO-1-specific solid phase enzyme-linked immunosorbent assay using the monoclonal antibody anti-APO-1. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the APO-1 antigen was found to be a membrane glycoprotein of 48-kDa. Endoproteinase-cleaved peptides of the APO-1 protein were subjected to amino acid sequencing, and corresponding oligonucleotides were used to identify a full-length APO-1 cDNA clone from an SKW6.4 cDNA library. The deduced amino acid sequence of APO-1 showed sequence identity with the Fas antigen, a cysteine-rich transmembrane protein of 335 amino acids with significant similarity to the members of the tumor necrosis factor/nerve growth factor receptor superfamily. The APO-1 antigen was expressed upon transfection of APO-1 cDNA into BL60-P7 Burkitt's lymphoma cells and conferred sensitivity towards anti-APO-1-induced apoptosis to the transfectants.

Amino Acid Sequence↗

PubMed1987

Saccharomyces cerevisiae SSB1 protein and its relationship to nucleolar RNA-binding proteins.

To better define the function of Saccharomyces cerevisiae SSB1, an abundant single-stranded nucleic acid-binding protein, we determined the nucleotide sequence of the SSB1 gene and compared it with those of other proteins of known function. The amino acid sequence contains 293 amino acid residues and has an Mr of 32,853. There are several stretches of sequence characteristic of other eucaryotic single-stranded nucleic acid-binding proteins. At the amino terminus, residues 39 to 54 are highly homologous to a peptide in calf thymus UP1 and UP2 and a human heterogeneous nuclear ribonucleoprotein. Residues 125 to 162 constitute a fivefold tandem repeat of the sequence RGGFRG, the composition of which suggests a nucleic acid-binding site. Near the C terminus, residues 233 to 245 are homologous to several RNA-binding proteins. Of 18 C-terminal residues, 10 are acidic, a characteristic of the procaryotic single-stranded DNA-binding proteins and eucaryotic DNA- and RNA-binding proteins. In addition, examination of the subcellular distribution of SSB1 by immunofluorescence microscopy indicated that SSB1 is a nuclear protein, predominantly located in the nucleolus. Sequence homologies and the nucleolar localization make it likely that SSB1 functions in RNA metabolism in vivo, although an additional role in DNA metabolism cannot be excluded.

Amino Acid Sequence↗

PubMed1986

Yeast DNA replication.

We have explored various strategies for exploiting the yeast genetic and biochemical system for understanding DNA replication. Because of the long time that has intervened between the isolation of random replication mutants of yeast and the identification of the gene products affected, an alternative approach to elucidating the molecular basis of replication has been needed. One such alternative involves purifying replication proteins, isolating the genes encoding them, and constructing the appropriate mutant from the cloned gene. We have applied this "reverse genetics" strategy to three different replication activities: DNA polymerases, single-stranded DNA binding proteins, and proteins that bind to autonomously replicating sequence (ARS) elements.

DNA Polymerase I↗