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.

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.