Ced-4 and Apaf-1 belong to a major class of apoptosis regulators that contain caspase-recruitment (CARD) and nucleotide-binding oligomerization domains. Nod1, a protein with an NH 2 -terminal CARD-linked to a nucleotide-binding domain and a COOH-terminal segment with multiple leucine-rich repeats, was identified. Nod-1 was found to bind to multiple caspases with long prodomains, but specifically activated caspase-9 and promoted caspase-9-induced apoptosis. As reported for Apaf-1, Nod1 required both the CARD and P-loop for function. Unlike Apaf-1, Nod1 induced activation of nuclear factor-kappa-B (NF-B) and bound RICK, a CARDcontaining kinase that also induces NF-B activation. Nod1 mutants inhibited NF-B activity induced by RICK, but not that resulting from tumor necrosis factor-␣ stimulation. Thus, Nod1 is a leucine-rich repeatcontaining Apaf-1-like molecule that can regulate both apoptosis and NF-B activation pathways.

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We have identified and characterized Diva, which is a novel regulator of apoptosis. Sequence analysis revealed that Diva is a member of the Bcl-2 family of proteins containing Bcl-2 homology domain 1, 2, 3, and 4 (BH1, BH2, BH3, and BH4) regions and a carboxyl-terminal hydrophobic domain. The expression of Diva mRNA was detected in multiple embryonic tissues but was restricted to the ovary and testis in adult mice. The expression of Diva promoted the death of 293T, Ramsey, and T47D cells as well as that of primary sensory neurons, indicating that Diva is a proapoptotic protein. Significantly, Diva lacks critical residues in the conserved BH3 region that mediate the interaction between BH3-containing proapoptotic Bcl-2 homologues and their prosurvival binding partners. Consistent with this, Diva did not bind to cellular Bcl-2 family members including Bcl-2, Bcl-X L , Bcl-w, Mcl-1, and A1/Bfl-1. Furthermore, mutants of Diva lacking the BH3 region fully retained their proapoptotic activity, confirming that Diva promotes apoptosis in a BH3-independent manner. Significantly, Diva interacted with a viral Bcl-2 homologue (vBcl-2) encoded by the Kaposi's sarcoma-associated herpesvirus. Consistent with these associations, apoptosis induced by Diva was inhibited by vBcl-2 but not by Bcl-X L . Importantly, Diva interacted with Apaf-1, an adapter molecule that activates caspase-9, a central death protease of the apoptotic pathway. The expression of Diva inhibited the binding of Bcl-X L to Apaf-1, as determined by immunoprecipitation assays. Thus, Diva represents a novel type of proapoptotic Bcl-2 homologue that promotes apoptosis independently of the BH3 region through direct binding to Apaf-1, thus preventing Bcl-X L from binding to the caspase-9 regulator Apaf-1.Apoptosis, a morphologically distinguished form of programmed cell death, is critical during development and tissue homeostasis and plays a role in the pathogenesis of a variety of diseases (1). Several regulatory components of the apoptotic pathway have been identified in various living organisms including man (1, 2). A family of proteins that includes Bcl-2, Bcl-X L , Bcl-w, Mcl-1, and A1/Bfl-1 shares conserved regions termed Bcl-2 homology domains 1, 2, 3, and 4 (BH1, BH2, BH3, and BH4) 1 and function by repressing apoptosis (3). The biochemical process by which Bcl-2 family members regulate cell death is poorly understood. Analyses of the nematode cell death regulators CED-3, CED-4, and CED-9 have provided important insight into the biochemical mechanism that regulates apoptosis. CED-9, the nematode homologue of Bcl-2 and Bcl-X L , binds to CED-4 and represses cell death by interacting and inhibiting the killing activity of CED-3 through CED-4 (4 -7). Recently, it was shown that Bcl-X L associates with Apaf-1, a mammalian homologue of CED-4, and inhibits the activation of procaspase-9 (8 -11).Whereas proteins like Bcl-2 and Bcl-X L inhibit cell death, structurally related proteins including Bax, Bak, Bad, Bik/ Nbk, Bid, Hrk, Bim, Bok/Mtd, and BNIP3 promote apo...

We have identified and characterized Mtd, a novel regulator of apoptosis. Sequence analysis revealed that Mtd is a member of the Bcl-2 family of proteins containing conserved BH1, BH2, BH3, and BH4 regions and a carboxyl-terminal hydrophobic domain. In adult tissues, Mtd mRNA was predominantly detected in the brain, liver, and lymphoid tissues, while in the embryo Mtd mRNA was detected in the liver, thymus, lung, and intestinal epithelium. Expression of Mtd promoted the death of primary sensory neurons, 293T cells and HeLa cells, indicating that Mtd is a proapoptotic protein. Unlike all other known death agonists of the Bcl-2 family, Mtd did not bind significantly to the survival-promoting proteins Bcl-2 or Bcl-X L . Furthermore, apoptosis induced by Mtd was not inhibited by Bcl-2 or Bcl-X L . A Mtd mutant with glutamine substitutions of highly conserved amino acids in the BH3 domain retained its ability to promote apoptosis, further indicating that Mtd does not promote apoptosis by heterodimerizing with Bcl-2 or Bcl-X L . Mtd-induced apoptosis was not blocked by broad range synthetic caspase inhibitors z-VAD-fmk or a viral protein CrmA. Mtd is the first example of a naturally occurring Bcl-2 family member that can activate apoptosis independently of heterodimerization with survival-promoting Bcl-2 and Bcl-X L .Apoptosis, a morphologically distinguished form of programmed cell death, is critical not only during development and tissue homeostasis but also in the pathogenesis of a variety of diseases (1). Several regulatory components of the apoptotic pathway have been identified in various living organisms, including man (1, 2). bcl-2, the first member of an evolutionary conserved family of apoptosis regulatory genes, was initially isolated from the t(14;18) chromosomal translocation found in human B-cell follicular lymphomas and was subsequently shown to repress cell death triggered by a diverse array of stimuli (3-6). Several members of the family, including Bcl-2 and Bcl-X L , share conserved regions termed Bcl-2 homology domains 1, 2, 3 and 4 (BH1, BH2, BH3, and BH4) and function by repressing apoptosis (for review, see Ref. 7). The biochemical process by which Bcl-2 family members regulate cell death are poorly understood. The crystal structures of human and rat Bcl-X L have revealed a significant similarity to the pore-forming domains of diphtheria toxin and bacterial colicins, suggesting that Bcl-2 family members could function as channels for ions, proteins, or both (8, 9). Experiments with synthetic membranes have shown that recombinant Bcl-2, Bcl-X L , and Bax exhibit ion channel activity, suggesting that Bcl-2-related proteins could regulate apoptosis by regulating trafficking of molecules through intracellular membranes (10 -12). However, the significance of these latter findings is unclear as there is no evidence that Bcl-2 or related proteins form ion-channels in vivo.Analyses of the nematode cell death regulators CED-3, CED-4, and CED-9 has provided important insight into the biochemical mechanism ...

Orta-Mascaró, Lozano, and collaborators provide the first analysis of CD6-deficient mice, showing that this molecule modulates T cell receptor signaling and the threshold for thymocyte and peripheral T cell subset selection.