The homeostasis of animals is regulated not only by the growth and differentiation of cells, but also by cell death through a process known as apoptosis. Apoptosis is mediated by members of the caspase family of proteases, and eventually causes the degradation of chromosomal DNA. A caspase-activated deoxyribonuclease (CAD) and its inhibitor (ICAD) have now been identified in the cytoplasmic fraction of mouse lymphoma cells. CAD is a protein of 343 amino acids which carries a nuclear-localization signal; ICAD exists in a long and a short form. Recombinant ICAD specifically inhibits CAD-induced degradation of nuclear DNA and its DNase activity. When CAD is expressed with ICAD in COS cells or in a cell-free system, CAD is produced as a complex with ICAD: treatment with caspase 3 releases the DNase activity which causes DNA fragmentation in nuclei. ICAD therefore seems to function as a chaperone for CAD during its synthesis, remaining complexed with CAD to inhibit its DNase activity; caspases activated by apoptotic stimuli then cleave ICAD, allowing CAD to enter the nucleus and degrade chromosomal DNA.

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In Xenopus laevis egg extracts, TPX2 is required for the Ran-GTP-dependent assembly of microtubules around chromosomes. Here we show that interfering with the function of the human homologue of TPX2 in HeLa cells causes defects in microtubule organization during mitosis. Suppressing the expression of human TPX2 by RNA interference leads to the formation of two microtubule asters that do not interact and do not form a spindle. Our results suggest that in vivo, even in the presence of duplicated centrosomes, spindle formation requires the function of TPX2 to generate a stable bipolar spindle with overlapping antiparallel microtubule arrays. This indicates that chromosome-induced microtubule production is a general requirement for the formation of functional spindles in animal cells.

We attempted to clarify what factors predominantly influence the survival of patients with non-small-cell lung cancer in each pathologic stage on the basis of information generally obtained by a pathologic examination of completely resected non-small-cell lung cancer. The subjects included 243 patients with stage I, 63 with stage II, and 108 with stage IIIA disease. Pathologic features used in the analysis were as follows: the greatest tumor size (< or = 3.0 cm versus > 3.0 cm), the histologic cell type (squamous versus nonsquamous cell carcinoma), the grade of differentiation, and tumor invasion of pleura and vessels. In stage IIIA, the extent of the metastasis to the lymph nodes was also included in the analysis. The significant prognostic factors (p < 0.05) in stage I demonstrated by a univariate analysis of the survival curves included the tumor size, the grade of differentiation (well differentiated versus moderately and poorly differentiated tumor), pleural involvement, and invasion of the artery and vein. In addition, the histologic cell type and the pleural involvement in stage II and invasion of the vein and the extent of metastasis to the lymph nodes (N0 and N1 versus N2) in stage IIIA were also found to be significant prognostic factors. A multivariate prognostic factor analysis showed that the grade of differentiation, pleural involvement, and venous invasion in stage I; the histologic cell type and pleural involvement in stage II; and venous invasion and mediastinal lymph node metastasis in stage IIIA were all predominant prognostic factors. These observations therefore suggest that a pathologic examination can identify the patients with a poor prognosis, which is different among the stages.

SSX2IP promotes centrosome maturation and maintenance at the onset of vertebrate development, preserving centrosome integrity and mitosis during rapid cleavage divisions and in somatic cells.

Production of Ran–guanosine triphosphate (GTP) around chromosomes induces local nucleation and plus end stabilization of microtubules (MTs). The nuclear protein TPX2 is required for RanGTP-dependent MT nucleation. To find the MT stabilizer, we affinity purify nuclear localization signal (NLS)–containing proteins from Xenopus laevis egg extracts. This NLS protein fraction contains the MT stabilization activity. After further purification, we used mass spectrometry to identify proteins in active fractions, including cyclin-dependent kinase 11 (Cdk11). Cdk11 localizes on spindle poles and MTs in Xenopus culture cells and egg extracts. Recombinant Cdk11 demonstrates RanGTP-dependent MT stabilization activity, whereas a kinase-dead mutant does not. Inactivation of Cdk11 in egg extracts blocks RanGTP-dependent MT stabilization and dramatically decreases the spindle assembly rate. Simultaneous depletion of TPX2 completely inhibits centrosome-dependent spindle assembly. Our results indicate that Cdk11 is responsible for RanGTP-dependent MT stabilization around chromosomes and that this local stabilization is essential for normal rates of spindle assembly and spindle function.

Apoptotic cell death is accompanied by degradation of chromosomal DNA. Here, we established in Drosophila a null mutation in the gene for inhibitor of caspase-activated DNase (ICAD) by P-element insertion. We also identified a loss-of-function mutant in Drosophila for DNase II-like acid DNase. The flies deficient in the ICAD gene did not express CAD, and did not undergo apoptotic DNA fragmentation during embryogenesis and oogenesis. In contrast, the deficiency of DNase II enhanced the apoptotic DNA fragmentation in the embryos and ovary, but paradoxically, the mutant flies accumulated a large amount of DNA, particularly in the ovary. This accumulation of DNA in the DNase II mutants caused the constitutive expression of the antibacterial genes for diptericin and attacin, which are usually activated during bacterial infection. The expression of these genes was further enhanced in flies lacking both dICAD and DNase II. These results indicated that CAD and DNase II work independently to degrade chromosomal DNA during apoptosis, and if the DNA is left undigested, it can activate the innate immunity in Drosophila.[Keywords: apoptosis; DNA fragmentation; mutagenesis; antibacterial peptides; innate immunity] Apoptosis, or programmed cell death, is an evolutionarily conserved process that removes harmful or useless cells during development (Jacobson et al. 1997;Vaux and Korsmeyer 1999). The apoptotic process is accompanied by morphological changes, such as shrinkage and fragmentation of the cells and nuclei, and loss of microvilli from the plasma membranes . Genetic and biochemical studies revealed that caspases, a family of cysteine proteases, are activated during apoptosis (Thornberry and Lazebnik 1998;Earnshaw et al. 1999;Los et al. 1999). More than 100 cellular proteins have been identified in mammalian systems as caspase substrates, the cleavage of which brings about the morphological changes of the cells and nuclei, leading to the cell death (Stroh and Schulze-Osthoff 1998).In addition to the morphological changes of cell and nuclei, the apoptotic process is often accompanied by the degradation of chromosomal DNA (Wyllie 1980; Nagata 2000). We and others have identified a DNase (caspaseactivated DNase, CAD; also called DNA fragmentation factor, DFF40), that is activated in dying cells (Liu et al. 1997;Enari et al. 1998). CAD is complexed with its inhibitor (ICAD, inhibitor of CAD) in proliferating cells. When apoptosis is triggered, caspases-in particular caspase 3-cleave ICAD, and the CAD released from ICAD degrades the chromosomal DNA into nucleosomal units . Accordingly, cells that are deficient in the CAD system do not undergo apoptotic DNA fragmentation in vitro. However, DNA degradation is still observed in vivo in CAD-deficient mice. Because this DNA fragmentation is detected in apoptotic cells inside macrophages, we proposed that the DNA of apoptotic cells can be cleaved by lysosomal acid DNase (DNase II) after the cells are engulfed by macrophages (McIlroy et al. 2000).Programmed cell death plays an import...

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