Tyrosine kinase 2 (Tyk2) is a nonreceptor tyrosine kinase that belongs to the Janus kinase (Jak) family. Here we identified a homozygous Tyk2 mutation in a patient who had been clinically diagnosed with hyper-IgE syndrome. This patient showed unusual susceptibility to various microorganisms including virus, fungi, and mycobacteria and suffered from atopic dermatitis with elevated serum IgE. The patient's cells displayed defects in multiple cytokine signaling pathways including those for type I interferon (IFN), interleukin (IL)-6, IL-10, IL-12, and IL-23. The cytokine signals were successfully restored by transducing the intact Tyk2 gene. Thus, the Tyk2 deficiency is likely to account for the patient's complex clinical manifestations, including the phenotype of impaired T helper 1 (Th1) differentiation and accelerated Th2 differentiation. This study identifies human Tyk2 deficiency and demonstrates that Tyk2 plays obligatory roles in multiple cytokine signals involved in innate and acquired immunity of humans, which differs substantially from Tyk2 function in mice.

p21 Cip1/WAF1 inhibits cell-cycle progression by binding to G 1 cyclin/CDK complexes and proliferating cell nuclear antigen (PCNA) through its N-and C-terminal domains, respectively. The cell-cycle inhibitory activity of p21 Cip1/WAF1 is correlated with its nuclear localization. Here, we report a novel cytoplasmic localization of p21 Cip1/WAF1 in peripheral blood monocytes (PBMs) and in U937 cells undergoing monocytic differentiation by in vitro treatment with vitamin D3 or ectopic expression of p21 Cip1/WAF1 , and analyze the biological consequences of this cytoplasmic expression. U937 cells which exhibit nuclear p21 Cip1/WAF1 demonstrated G 1 cell-cycle arrest and subsequently differentiated into monocytes. The latter event was associated with a cytoplasmic expression of nuclear p21 Cip1/WAF1 , concomitantly with a resistance to various apoptogenic stimuli. Biochemical analysis showed that cytoplasmic p21 Cip1/WAF1 forms a complex with the apoptosis signalregulating kinase 1 (ASK1) and inhibits stress-activated MAP kinase cascade. Expression of a deletion mutant of p21 Cip1/WAF1 lacking the nuclear localization signal (ΔNLS-p21) did not induce cell cycle arrest nor monocytic differentiation, but led to an apoptosis-resistant phenotype, mediated by binding to and inhibition of the stress-activated ASK1 activity. Thus, cytoplasmic p21 Cip1/WAF1 itself acted as an inhibitor of apoptosis. Our findings highlight the different functional roles of p21 Cip1/WAF1 , which are determined by its intracellular distribution and are dependent on the stage of differentiation.

Mutations of the

The checkpoint kinase Chk2 has a key role in delaying cell cycle progression in response to DNA damage. Upon activation by low-dose ionizing radiation (IR), which occurs in an ataxia telangiectasia mutated (ATM)-dependent manner, Chk2 can phosphorylate the mitosis-inducing phosphatase Cdc25C on an inhibitory site, blocking entry into mitosis, and p53 on a regulatory site, causing G 1 arrest. Here we show that the ATMdependent activation of Chk2 by ␥-radiation requires Nbs1, the gene product involved in the Nijmegen breakage syndrome (NBS), a disorder that shares with AT a variety of phenotypic defects including chromosome fragility, radiosensitivity, and radioresistant DNA synthesis. Thus, whereas in normal cells Chk2 undergoes a time-dependent increased phosphorylation and induction of catalytic activity against Cdc25C, in NBS cells null for Nbs1 protein, Chk2 phosphorylation and activation are both defective. Importantly, these defects in NBS cells can be complemented by reintroduction of wild-type Nbs1, but neither by a carboxyterminal deletion mutant of Nbs1 at amino acid 590, unable to form a complex with and to transport Mre11 and Rad50 in the nucleus, nor by an Nbs1 mutated at Ser343 (S343A), the ATM phosphorylation site. Chk2 nuclear expression is unaffected in NBS cells, hence excluding a mislocalization as the cause of failed Chk2 activation in Nbs1-null cells. Interestingly, the impaired Chk2 function in NBS cells correlates with the inability, unlike normal cells, to stop entry into mitosis immediately after irradiation, a checkpoint abnormality that can be corrected by introduction of the wild-type but not the S343A mutant form of Nbs1. Altogether, these findings underscore the crucial role of a functional Nbs1 complex in Chk2 activation and suggest that checkpoint defects in NBS cells may result from the inability to activate Chk2.The integrity of genetic information is essential for the life and survival of cells. Genomic lesions arising spontaneously during DNA replication or in response to oxidative metabolism or exposure to radiation or chemical mutagens need to be recognized and repaired. Delay of cell cycle progression at specific checkpoints provides the time necessary to prevent replication and segregation of damaged DNA and to process lesions (reviewed in references 52 and 57). A defective or incorrect activation of the surveillance and repair systems can lead to increased mutagenesis, genomic instability, and ultimately cancer (for a review, see reference 13).The Nijmegen breakage syndrome (NBS) and ataxia telangiectasia (AT) are rare human autosomal recessive diseases (22, 51) exhibiting hypersensitivity to ionizing radiation (IR), immunodeficiency, and increased predisposition to develop cancer. NBS patients, however, do not manifest the hallmarks of AT, i.e., cerebellar ataxia and oculocutaneous telangiectasia. At the cellular level, NBS and AT patients show chromosome instability, hypersensitivity to genotoxic agents, and cell cycle checkpoints defects (1,29,30). These similarities su...

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p21Cip1/WAF1 has cell cycle inhibitory activity by binding to and inhibiting both cyclin/Cdk kinases and proliferating cell nuclear antigen. Here we show that p21Cip1/WAF1 is induced in the cytoplasm during the course of differentiation of chick retinal precursor cells and N1E-115 cells. Ectopic expression of p21Cip1/WAF1 lacking the nuclear localization signal in N1E-115 cells and NIH3T3 cells affects the formation of actin structures, characteristic of inactivation of Rho. p21Cip1/WAF1 forms a complex with Rho-kinase and inhibits its activity in vitro and in vivo. Neurite outgrowth and branching from the hippocampal neurons are promoted if p21Cip1/WAF1 is expressed abundantly in the cytoplasm. These results suggest that cytoplasmic p21Cip1/WAF1 may contribute to the developmental process of the newborn neurons that extend axons and dendrites into target regions.

We evaluated the efficacy of a treatment strategy in which infants with acute lymphoblastic leukemia (ALL) were stratified by their MLL gene status and then assigned to different riskbased therapies. A total of 102 patients were registered on two consecutive multicenter trials, designated MLL96 and MLL98, between 1995 and2001. Those with a rearranged MLL gene (MLL-R, n ¼ 80) were assigned to receive intensive chemotherapy followed by hematopoietic stem cell transplantation (HSCT), while those with germline MLL (MLL-G, n ¼ 22) were treated with chemotherapy alone. The 5-year event-free survival (EFS) rate for all 102 infants was 50.9% (95% confidence interval, 41.0-60.8%). The most prominent late effect was growth impairment, observed in 58.9% of all evaluable patients in the MLL-R group. This plan of risk-based therapy appears to have improved the overall prognosis for infants with ALL, compared with previously reported results. However, over half the events in patients with MLL rearrangement occurred before the instigation of HSCT, and that HSCT-related toxic events comprised 36.3% (8/22) of post-transplantation events, suggesting that further stratification within the MLL-R group and the development of more effective early-phase intensification chemotherapy will be needed before the full potential of this strategy is realized.

Most patients with acute myeloid leukemia (AML) enter complete remission (CR) after treatment with chemotherapy, but a large number of them experience relapse with resistant disease. To identify genes that are associated with their prognoses, we analyzed gene expression in 54 pediatric patients with AML using an oligonucleotide microarray that contained 12 566 probe sets. A supervised approach using the Student t test selected a prognostic set of 35 genes, some of which are associated with the regulation of cell cycle and apoptosis. Most of these genes had not previously been reported to be associated with prognosis and were not correlated with morphologically classified French-American-British (FAB) subtypes or with karyotypes. These results indicate the existence of prognosis-associated genes that are independent of cell lineage and cytogenetic abnormalities, and they can provide therapeutic direction for individual risk-adapted therapy for pediatric AML patients.