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Stimulation of CD95 leads to oligomerization of this receptor and the recruitment of the Fas-associated death domain (FADD) and procaspase-8 to form the death-inducing signaling complex (DISC). Subsequent proteolytic activation of caspase-8 at the DISC leads to the activation of downstream caspases and execution of apoptosis. The anticancer drug 9-nitrocamptothecin (9NC) inhibits the nuclear enzyme topoisomerase I (Top1), an event followed by apoptosis of cancer cells. We investigated whether other mechanisms downstream of the DNA-Top1-9NC complexing step regulate the apoptotic ability of 9NC in DU145 cells. We demonstrate that induction of apoptosis in DU145 cells, upon exposure to 9NC, is associated with de novo expression of CD95 and CD95L, suggesting that 9NC-induced apoptosis is mediated by the CD95 system. In this line, we observed early activation of procaspase-3, -7, and -8, but not -1, -9, and -10. Moreover, 9NC treatment resulted in the dramatic down-regulation of c-FLIP(short) expression, but not that of c-FLIP(long) or FADD. Furthermore, incubation of DU145 cells with a neutralizing antibody (NOK-1) to CD95L or transient transfection of a c-FLIP(short) expression vector into DU145 cells partially abrogated 9NC-triggered apoptosis. We propose that 9NC triggers apoptosis by driving DU145 cells from a nonapoptotic status (c-FLIP(short)(high), CD95(low), CD95L(low)) toward a proapoptotic status (c-FLIP(short)(low), CD95(high), CD95L(high)). These findings indicate that in addition to a Top1-mediated effect, 9NC can additionally activate a CD95/CD95L-dependent apoptotic pathway.

In this study the mechanism of differential sensitivity of CD3-activated Th1- and Th2-type cells to Fas-mediated apoptosis was explored. We show that the Fas-associated death domain protein (FADD)/caspase-8 pathway is differentially regulated by CD3 activation in the two subsets. The apoptosis resistance of activated Th2-type cells is due to an incomplete processing of caspase-8 at the death-inducing signaling complex (DISC) whereas recruitment of caspase-8 to the DISC of Th1- and Th2-like cells is comparable. Activation of phosphatidylinositol 3'-kinase upon ligation of CD3 in Th2-type cells blocked caspase-8 cleavage to its active fragments at the DISC, thereby preventing induction of apoptosis. This study offers a new pathway for phosphatidylinositol 3'-kinase in mediating protection from Fas-induced apoptosis.

The Caenorhabditis elegans ubiquitin-conjugating enzyme UBC-1 is distinct from other RAD6 homologues in possessing a C-terminal tail 40 amino acid residues long [Leggett, Jones and Candido (1995) DNA Cell Biol. 14, 883-891]. Such extensions from the core catalytic domain have been found in a subset of known conjugating enzymes, where they have been shown to have diverse roles including target recognition, membrane attachment and sporulation. In the present study we used mutagenesis in vitro to examine the role of the tail in specific aspects of UBC-1 structure and activity. Cross-linking experiments with purified recombinant UBC-1 reveal that it forms dimers and probably tetramers. The acidic tail of UBC-1 has an important role in this interaction because deletions of the tail significantly decrease, but do not abolish, this self-association. Ubiquitin conjugation assays show that, in addition to accepting a thiol-bound ubiquitin at its active site, UBC-1 is stably mono-ubiquitinated. Deletion analysis and site-directed mutagenesis localize the site of ubiquitination to Lys-162 in the tail. These findings demonstrate that the C-terminal tail of UBC-1 is important both for its quaternary structure and post-translational modification in vitro.

In recent years apoptosis has attracted more and more attention. In immunology it has become especially popular since it plays an important role in the development and maturation of normal T and B lymphocytes and in lymphoid malignancies. In the normal lymphoid system, apoptosis occurs in primary lymphoid organs such as the bone marrow, liver, and thymus, and is used to eliminate useless precursor cells with nonrearranged or aberrantly rearranged, nonfunctional receptors. Whether lymphocytes die by apoptosis or survive is controlled by various genes and their products. In principle, genes relevant for apoptosis might code for death or survival ligands and their receptors, or a cascade of signaling molecules. Such signaling molecules might be connected to second messengers and bridge membrane events to transcription factors and gene expression. Gene products might then either stimulate or block apoptosis.

The CD95 (APO-1/Fas) receptor has attracted great interest in recent years because it transduces an apoptotic signal in a variety of different tissues. CD95 belongs to the NGF/TNF-receptor superfamily, members of which need to be trimerized by specific protein ligands in order to generate a signal. This review focuses on recent advances in the understanding of the proximal signal transduction mechanism of CD95. The cloning of numerous proteins that interact with CD95 and other members of this receptor family and the in vivo identification of several proteins that associate with CD95 in a ligand-dependent fashion opens the way to delineate the death pathway and to explain crosstalk among these receptors on a molecular basis.

Tuberculous enteritis occurs in about 2 percent of patients with pulmonary tuberculosis. Although it is uncommon in the United States, tuberculous enteritis should be considered in any patient with active pulmonary tuberculosis and abdominal complaints. Eight cases of T. enteritis have been treated at Harbor General Hospital in the last 25 years. Associated pulmonary disease was shown radiologically to be present in seven of eight patients. Findings on contrast studies of the gastrointestinal tract showed disease in six of six patients examined. In five patients, surgical operation was required for diagnosis or complications. Resection of diseased bowel with primary anastomosis was done in five patients. Although medical therapy is the mainstay in the treatment of both pulmonary and intestinal tuberculosis, one staged resection of diseased bowel with primary anastomosis is the procedure of choice for complications such as obstruction, hemorrhage or perforation.