Activation of p38 MAP kinase by DNA double-strand breaks in V(D)J recombination induces a G2/M cell cycle checkpoint

Too big not to fail: emerging evidence for size-induced senescence

Cellular senescence refers to a permanent and stable state of cell cycle exit. This process plays an important role in many cellular functions, including tumor suppression. It was first noted that senescence is associated with increased cell size in the early 1960s; however, how this contributes to permanent cell cycle exit was poorly understood until recently. In this review, we discuss new findings that identify increased cell size as not only a consequence but also a cause of permanent cell cycle exit. We highlight recent insights into how increased cell size alters normal cellular physiology and creates homeostatic imbalances that contribute to senescence induction. Finally, we focus on the potential clinical implications of these findings in the context of cell cycle arrest-causing cancer therapeutics and speculate on how tumor cell size changes may impact outcomes in patients treated with these drugs.

Distinct oncogenic phenotypes in hematopoietic specific deletions of Trp53

Loss of function in the tumor suppressor gene TP53 is the most common alteration seen in human cancer. In mice, P53 deletion in all cells leads predominantly to the development of T-cell lymphomas, followed by B-cell lymphomas, sarcomas and teratomas. In order to dissect the role of P53 in the hematopoietic system, we generated and analyzed two different mouse models deficient for P53. A pan-hematopoietic P53 deletion mouse was created using Vav1-Cre based deletion; and a B-cell-specific deletion mouse was created using a CD19-Cre based deletion. The Vav1-P53CKO mice predominantly developed T-cell malignancies in younger mice, and myeloid malignancies in older mice. In T-cell malignancies, there was accelerated thymic cell maturation with overexpression of Notch1 and its downstream effectors. CD19-P53CKO mice developed marginal zone expansion in the spleen, followed by marginal zone lymphoma, some of which progressed to diffuse large B-cell lymphomas. Interestingly, marginal zone and diffuse large B-cell lymphomas had a unique gene expression signature characterized by activation of the PI3K pathway, compared with wild type marginal zone or follicular cells of the spleen. This study demonstrates lineage specific P53 deletion leading to distinct phenotypes secondary to unique gene expression programs set in motion.

Stress Relief Techniques: p38 MAPK Determines the Balance of Cell Cycle and Apoptosis Pathways

Protein signaling networks are formed from diverse and inter-connected cell signaling pathways converging into webs of function and regulation. These signaling pathways both receive and conduct molecular messages, often by a series of post-translation modifications such as phosphorylation or through protein-protein interactions via intrinsic motifs. The mitogen activated protein kinases (MAPKs) are components of kinase cascades that transmit signals through phosphorylation. There are several MAPK subfamilies, and one subfamily is the stress-activated protein kinases, which in mammals is the p38 family. The p38 enzymes mediate a variety of cellular outcomes including DNA repair, cell survival/cell fate decisions, and cell cycle arrest. The cell cycle is itself a signaling system that precisely controls DNA replication, chromosome segregation, and cellular division. Another indispensable cell function influenced by the p38 stress response is programmed cell death (apoptosis). As the regulators of cell survival, the BCL2 family of proteins and their dynamics are exquisitely sensitive to cell stress. The BCL2 family forms a protein-protein interaction network divided into anti-apoptotic and pro-apoptotic members, and the balance of binding between these two sides determines cell survival. Here, we discuss the intersections among the p38 MAPK, cell cycle, and apoptosis signaling pathways.

Timosaponin AIII Induces G2/M Arrest and Apoptosis in Breast Cancer by Activating the ATM/Chk2 and p38 MAPK Signaling Pathways

Timosaponin AIII (TAIII), a steroidal saponin, exerts potent anti-tumor activity in various cancers, especially breast cancer. However, the concrete molecular mechanisms of TAIII against breast cancer are still unclear. Here, we find that TAIII triggers DNA damage, leads to G2/M arrest, and ultimately induces apoptosis in breast cancer both in vitro and in vivo. TAIII induced G2/M phase arrest and apoptosis in MDA-MB-231 and MCF7 cells accompanied with down-regulation of CyclinB1, Cdc2 and Cdc25C. Further data showed that the ATM/Chk2 and p38 pathways were activated representing by up-regulated levels of p-H2A.X and p-p38, which indicated an induction of DNA damage by TAIII, leading to cell cycle arrest and apoptosis. The effects of TAIII were further confirmed by employing inhibitors of ATM and p38 pathways. In vivo, TAIII suppressed the growth of subcutaneous xenograft tumor without obvious toxicity, which indicated by Ki67 and TUNEL analysis. Data also showed that TAIII stimulated the ATM/Chk2 and p38 MAPK pathways in vivo, which in consistent with the effects in vitro. Hence, our data demonstrate that TAIII triggers DNA damage and activates ATM/Chk2 and p38 MAPK pathways, and then induces G2/M phase arrest and apoptosis in breast cancer, which provide theoretical evidence for TAIII utilized as drug against breast cancer.

Donkey milk oligosaccharides influence the growth-related characteristics of intestinal cells and induce G2/M growth arrest via the p38 pathway in HT-29 cells

Donkey milk is considered to be a valuable nutritional source. Deeper knowledge of the constituents of donkey milk is necessary. As multifunctional components of milk, oligosaccharides have been reported to have the potential to support intestine development. We studied the composition and content of donkey milk oligosaccharides (DMOs). Sialylated oligosaccharides were found to be the primary oligosaccharides in DMOs, consisting of 3'-sialyllactose (SL) and 6'-SL. The amount of 3'-SL and 6'-SL in donkey milk was 18.3 ± 0.7 mg L^-1 and 33.1 ± 0.7 mg L^-1, respectively. Moreover, we found that DMOs induced differentiation, promoted apoptosis and inhibited proliferation in HT-29, Caco-2 and HIEC cells in a concentration-dependent manner, suggesting that DMOs promote maturation of intestinal epithelial cells. The mechanism of the DMOs' effects on HT-29 cells was associated with activation of the p38 pathway and cell cycle arrest at the G2/M phase. Our research will help understand the biological functions of DMOs and assess their potential roles in infant nutrition.

S5, a Withanolide Isolated from Physalis Pubescens L., Induces G2/M Cell Cycle Arrest via the EGFR/P38 Pathway in Human Melanoma A375 Cells

S5 is a withanolide natural product isolated from Physalis pubescens L. Our previous experimental studies found that it has significant antitumor activity on renal cell carcinoma. In the present study, the anti-melanoma effect of S5 and the related molecular mechanism was first investigated. It was found that S5 induced an obvious growth inhibitory effect on human melanoma A375 cells with low toxicity to human peripheral blood cells. Furthermore, the results demonstrated that the cell death mode of S5 on A375 cells is not due to inducing apoptosis and autophagy. However, there was a significant time-dependent increase in G2/M phase after treatment of A375 with S5. Meanwhile, S5 could also decrease the protein expression of Cdc25c, Cdc2, and CyclinB1, and increased the expression of p-P53 and P21, suggesting that S5 inhibited A375 cell death through G2/M phase arrest. Moreover, the signal pathway factors P38, extracellular regulated protein kinases (ERK), and epidermal growth factor receptor (EGFR) were observed taking part in the S5-induced A375 cells growth inhibitory effect. In addition, suppressing P38 and EGFR reversed the cell proliferation inhibitory effect and G2/M cell cycle arrest induced by S5 and inhibition of EGFR enhanced the downregulation of the expression of P38 and p-P38, indicating that S5 induced A375 G2/M arrest through the EGFR/P38 pathway. Briefly, this study explained for the first time the mechanism of S5-induced A375 cell growth inhibition in order to provide the basis for its clinical application in melanoma.

Human thymopoiesis is influenced by a common genetic variant within the TCRA-TCRD locus

The thymus is the primary lymphoid organ where naïve T cells are generated; however, with the exception of age, the parameters that govern its function in healthy humans remain unknown. We characterized the variability of thymic function among 1000 age- and sex-stratified healthy adults of the Milieu Intérieur cohort, using quantification of T cell receptor excision circles (TRECs) in peripheral blood T cells as a surrogate marker of thymopoiesis. Age and sex were the only nonheritable factors identified that affect thymic function. TREC amounts decreased with age and were higher in women compared to men. In addition, a genome-wide association study revealed a common variant (rs2204985) within the T cell receptor TCRA-TCRD locus, between the DD2 and DD3 gene segments, which associated with TREC amounts. Strikingly, transplantation of human hematopoietic stem cells with the rs2204985 GG genotype into immunodeficient mice led to thymopoiesis with higher TRECs, increased thymocyte counts, and a higher TCR repertoire diversity. Our population immunology approach revealed a genetic locus that influences thymopoiesis in healthy adults, with potentially broad implications in precision medicine.

V(D)J Recombination Exploits DNA Damage Responses to Promote Immunity

It has been recognized for 40 years that the variable (diversity) joining [V(D)J] recombination-mediated assembly of diverse B and T lymphocyte antigen receptor (AgR) genes is not only essential for adaptive immunity, but also a risk for autoimmunity and lymphoid malignancies. Over the past few years, several studies have revealed that recombination-activating gene (RAG) endonuclease-induced DNA double-strand breaks (DSBs) transcend hazardous intermediates during antigen receptor gene assembly. RAG cleavage within the genomes of lymphocyte progenitors and immature lymphocytes regulates the expression of ubiquitous and lymphocyte-specific gene transcripts to control the differentiation and function of both adaptive and innate immune cell lineages. These unexpected discoveries raise important new questions that have broad implications for basic immunology research and the screening, diagnosis, and treatment of human immunological disease.

Cell cycle RNA regulons coordinating early lymphocyte development

Lymphocytes undergo dynamic changes in gene expression as they develop from progenitor cells lacking antigen receptors, to mature cells that are prepared to mount immune responses. While transcription factors have established roles in lymphocyte development, they act in concert with post-transcriptional and post-translational regulators to determine the proteome. Furthermore, the post-transcriptional regulation of RNA regulons consisting of mRNAs whose protein products act cooperatively allows RNA binding proteins to exert their effects at multiple points in a pathway. Here, we review recent evidence demonstrating the importance of RNA binding proteins that control the cell cycle in lymphocyte development and discuss the implications for tumorigenesis. WIREs RNA 2017, 8:e1419. doi: 10.1002/wrna.1419 For further resources related to this article, please visit the WIREs website.

MEDICI: Mining Essentiality Data to Identify Critical Interactions for Cancer Drug Target Discovery and Development

Protein-protein interactions (PPIs) mediate the transmission and regulation of oncogenic signals that are essential to cellular proliferation and survival, and thus represent potential targets for anti-cancer therapeutic discovery. Despite their significance, there is no method to experimentally disrupt and interrogate the essentiality of individual endogenous PPIs. The ability to computationally predict or infer PPI essentiality would help prioritize PPIs for drug discovery and help advance understanding of cancer biology. Here we introduce a computational method (MEDICI) to predict PPI essentiality by combining gene knockdown studies with network models of protein interaction pathways in an analytic framework. Our method uses network topology to model how gene silencing can disrupt PPIs, relating the unknown essentialities of individual PPIs to experimentally observed protein essentialities. This model is then deconvolved to recover the unknown essentialities of individual PPIs. We demonstrate the validity of our approach via prediction of sensitivities to compounds based on PPI essentiality and differences in essentiality based on genetic mutations. We further show that lung cancer patients have improved overall survival when specific PPIs are no longer present, suggesting that these PPIs may be potentially new targets for therapeutic development. Software is freely available at https://github.com/cooperlab/MEDICI. Datasets are available at https://ctd2.nci.nih.gov/dataPortal.

Meta-Analysis of Gene Expression Profiles in Acute Promyelocytic Leukemia Reveals Involved Pathways

Background: Acute promyelocytic leukemia (APL) is a unique subtype of acute leukemia. APL is a curable disease; however, drug resistance, early mortality, disease relapse and treatment-related complications remain challenges in APL patient management. One issue underlying these challenges is that the molecular mechanisms of the disease are not sufficiently understood. Materials and Methods: In this study, we performed a meta-analysis of gene expression profiles derived from microarray experiments and explored the background of disease by functional and pathway analysis. Results: Our analysis revealed a gene signature with 406 genes that are up or down-regulated in APL. The pathway analysis determined that MAPK pathway and its involved elements such as JUN gene and AP-1 play important roles in APL pathogenesis along with insulin-like growth factor-binding protein-7. Conclusion: The results of this meta-analysis could be useful for developing more effective therapy strategies and new targets for diagnosis and drugs.

Pivotal Role of Mitogen-Activated Protein Kinase-Activated Protein Kinase 2 in Inflammatory Pulmonary Diseases

Mitogen-activated protein kinase (MAPK)-activated protein kinase (MK2) is exclusively regulated by p38 MAPK in vivo. Upon activation of p38 MAPK, MK2 binds with p38 MAPK, leading to phosphorylation of TTP, Hsp27, Akt, and Cdc25 that are involved in regulation of various essential cellular functions. In this review, we discuss current knowledge about molecular mechanisms of MK2 in regulation of TNF-α production, NADPH oxidase activation, neutrophil migration, and DNA-damage-induced cell cycle arrest which are involved in the molecular pathogenesis of acute lung injury, pulmonary fibrosis, and non-small-cell lung cancer. Collectively current and emerging new information indicate that developing MK2 inhibitors and blocking MK2-mediated signal pathways are potential therapeutic strategies for treatment of inflammatory and fibrotic lung diseases and lung cancer.

Inactivation of nuclear GSK3β by Ser(389) phosphorylation promotes lymphocyte fitness during DNA double-strand break response

Variable, diversity and joining (V(D)J) recombination and immunoglobulin class switch recombination (CSR) are key processes in adaptive immune responses that naturally generate DNA double-strand breaks (DSBs) and trigger a DNA repair response. It is unclear whether this response is associated with distinct survival signals that protect T and B cells. Glycogen synthase kinase 3β (GSK3β) is a constitutively active kinase known to promote cell death. Here we show that phosphorylation of GSK3β on Ser³⁸⁹ by p38 MAPK (mitogen-activated protein kinase) is induced selectively by DSBs through ATM (ataxia telangiectasia mutated) as a unique mechanism to attenuate the activity of nuclear GSK3β and promote survival of cells undergoing DSBs. Inability to inactivate GSK3β through Ser³⁸⁹ phosphorylation in Ser³⁸⁹Ala knockin mice causes a decrease in the fitness of cells undergoing V(D)J recombination and CSR. Preselection-Tcrβ repertoire is impaired and antigen-specific IgG antibody responses following immunization are blunted in Ser³⁸⁹GSK3β knockin mice. Thus, GSK3β emerges as an important modulator of the adaptive immune response.

Double stranded DNA breaks are generated during rearrangements of lymphocyte antigen receptors. Here the authors show that the DNA breaks induce phosphorylation of nuclear GSK3β at Ser³⁸⁹/Thr³⁹⁰, protecting the activated lymphocytes from necroptosis-mediated cell death.

Inflammation and Oral Cancer: An Update Review on Targeted Therapies

In the recent past, numerous inflammation-mediated molecular pathways have been explored and studied as important events in carcinogenesis with respect to oral squamous cell carcinoma (OSCC). These pathways are engaged in numerous stages during tumorigenesis; which includes processes, like initiation, promotion, malignant conversion, invasion and metastasis. The inflammation-mediated/related carcinogenesis pathways reported in OSCC involves COX-2, epidermal growth factor receptor (EGFR), p38a MAP kinase, NF-kB, STAT, RhoC, PPARy, etc. Many researchers are trying to target these pathways to explore more effective therapeutic interventions in OSCC. The aim of the present paper is to briefly discuss these pathways, with special emphasis on the therapeutic utilities. The therapeutic targets for the aforementioned pathways were searched in databases pubmed and scopus with no restriction to date of publication. Articles published in English medical literature on OSCC were selected for discussion. The recent combinations, modifications in dosage and frequency, or the use of new anti-inflammatory compounds, may exemplify the next generation care for OSCC.

Novel INHAT repressor (NIR) is required for early lymphocyte development

Novel inhibitor of histone acetyltransferase repressor (NIR) is a transcriptional corepressor with inhibitor of histone acetyltransferase activity and is a potent suppressor of p53. Although NIR deficiency in mice leads to early embryonic lethality, lymphoid-restricted deletion resulted in the absence of double-positive CD4(+)CD8(+) thymocytes, whereas bone-marrow-derived B cells were arrested at the B220(+)CD19(-) pro-B-cell stage. V(D)J recombination was preserved in NIR-deficient DN3 double-negative thymocytes, suggesting that NIR does not affect p53 function in response to physiologic DNA breaks. Nevertheless, the combined deficiency of NIR and p53 provided rescue of DN3L double-negative thymocytes and their further differentiation to double- and single-positive thymocytes, whereas B cells in the marrow further developed to the B220(+)CD19(+) pro-B-cell stage. Our results show that NIR cooperate with p53 to impose checkpoint for the generation of mature B and T lymphocytes.

The ataxia telangiectasia mutated and cyclin D3 proteins cooperate to help enforce TCRβ and IgH allelic exclusion

Coordination of V rearrangements between loci on homologous chromosomes is critical for Ig and TCR allelic exclusion. The Ataxia Telangietasia mutated (ATM) protein kinase promotes DNA repair and activates checkpoints to suppress aberrant Ig and TCR rearrangements. In response to RAG cleavage of Igκ loci, ATM inhibits RAG expression and suppresses further Vκ-to-Jκ rearrangements to enforce Igκ allelic exclusion. Because V recombination between alleles is more strictly regulated for TCRβ and IgH loci, we evaluated the ability of ATM to restrict biallelic expression and V-to-DJ recombination of TCRβ and IgH genes. We detected greater frequencies of lymphocytes with biallelic expression or aberrant V-to-DJ rearrangement of TCRβ or IgH loci in mice lacking ATM. A preassembled DJβ complex that decreases the number of TCRβ rearrangements needed for a productive TCRβ gene further increased frequencies of ATM-deficient cells with biallelic TCRβ expression. IgH and TCRβ proteins drive proliferation of prolymphocytes through cyclin D3 (Ccnd3), which also inhibits VH transcription. We show that inactivation of Ccnd3 leads to increased frequencies of lymphocytes with biallelic expression of IgH or TCRβ genes. We also show that Ccnd3 inactivation cooperates with ATM deficiency to increase the frequencies of cells with biallelic TCRβ or IgH expression while decreasing the frequency of ATM-deficient lymphocytes with aberrant V-to-DJ recombination. Our data demonstrate that core components of the DNA damage response and cell cycle machinery cooperate to help enforce IgH and TCRβ allelic exclusion and indicate that control of V-to-DJ rearrangements between alleles is important to maintain genomic stability.

Development of peptide inhibitor as a therapeutic agent against head and neck squamous cell carcinoma (HNSCC) targeting p38alpha MAP kinase

BACKGROUND

The p38alpha MAP kinase pathway is involved in inflammation, cell differentiation, growth, apoptosis and production of pro-inflammatory cytokines TNF-alpha and IL-1beta. The overproduction of these cytokines plays an important role in cancer. The aim of this work was to design a peptide inhibitor on the basis of structural information of the active site of p38alpha.

METHODS

A tetrapeptide, VWCS as p38alpha inhibitor was designed on the basis of structural information of the ATP binding site by molecular modeling. The inhibition study of peptide with p38alpha was performed by ELISA, binding study by Surface Plasmon Resonance and anti-proliferative assays by MTT and flow cytometry.

RESULTS

The percentage inhibition of designed VWCS against pure p38alpha protein and serum of HNSCC patients was 70.30 and 71.5%, respectively. The biochemical assay demonstrated the K(D) and IC50 of the selective peptide as 7.22 x 10(-9) M and 20.08 nM, respectively. The VWCS as inhibitor significantly reduced viability of oral cancer KB cell line with an IC50 value of 10 microM and induced apoptosis by activating Caspase 3 and 7.

CONCLUSIONS

VWCS efficiently interacted at the ATP binding pocket of p38alpha with high potency and can be used as a potent inhibitor in case of HNSCC.

GENERAL SIGNIFICANCE

VWCS can act as an anticancer agent as it potentially inhibits the cell growth and induces apoptosis in oral cancer cell-line in a dose as well as time dependent manner. Hence, p38alpha MAP kinase inhibitor can be a potential therapeutic agent for human oral cancer.

Requirement for dicer in survival of proliferating thymocytes experiencing DNA double-strand breaks

The Dicer nuclease generates small RNAs that regulate diverse biological processes through posttranscriptional gene repression and epigenetic silencing of transcription and recombination. Dicer-deficient cells exhibit impaired differentiation, activity, proliferation, and survival. Dicer inactivation in developing mouse lymphocytes impairs their proliferation and survival and alters Ag receptor gene repertoires for largely undefined reasons. To elucidate functions of Dicer in lymphocyte development and Ag receptor locus transcription and recombination, we analyzed mice with conditional Dicer deletion in thymocytes containing unrearranged or prerearranged TCRβ loci. Expression of either a preassembled functional TCRβ gene (Vβ1(NT)) or the prosurvival BCL2 protein inhibited death and partially rescued proliferative expansion of Dicer-deficient thymocytes. Notably, combined expression of Vβ1(NT) and BCL2 completely rescued proliferative expansion of Dicer-deficient thymocytes and revealed that Dicer promotes survival of cells attempting TCRβ recombination. Finally, inclusion of an endogenous preassembled DJβ complex that enhances Vβ recombination increased death and impaired proliferative expansion of Dicer-deficient thymocytes. These data demonstrate a critical role for Dicer in promoting survival of thymocytes experiencing DNA double-strand breaks (DSBs) during TCRβ recombination. Because DSBs are common and ubiquitous in cells, our findings indicate that impaired cellular survival in response to DSBs should be considered when interpreting Dicer-deficient phenotypes.

Redundant and nonredundant functions of ATM and H2AX in αβ T-lineage lymphocytes

The ataxia telangiectasia mutated (ATM) kinase and H2AX histone tumor suppressor proteins are each critical for maintenance of cellular genomic stability and suppression of lymphomas harboring clonal translocations. ATM is the predominant kinase that phosphorylates H2AX in chromatin around DNA double-strand breaks, including along lymphocyte Ag receptor loci cleaved during V(D)J recombination. However, combined germline inactivation of Atm and H2ax in mice causes early embryonic lethality associated with substantial cellular genomic instability, indicating that ATM and H2AX exhibit nonredundant functions in embryonic cells. To evaluate potential nonredundant roles of ATM and H2AX in somatic cells, we generated and analyzed Atm-deficient mice with conditional deletion of H2ax in αβ T-lineage lymphocytes. Combined Atm/H2ax inactivation starting in early-stage CD4(-)/CD8(-) thymocytes resulted in lower numbers of later-stage CD4(+)/CD8(+) thymocytes, but led to no discernible V(D)J recombination defect in G1 phase cells beyond that observed in Atm-deficient cells. H2ax deletion in Atm-deficient thymocytes also did not affect the incidence or mortality of mice from thymic lymphomas with clonal chromosome 14 (TCRα/δ) translocations. Yet, in vitro-stimulated Atm/H2ax-deficient splenic αβ T cells exhibited a higher frequency of genomic instability, including radial chromosome translocations and TCRβ translocations, compared with cells lacking Atm or H2ax. Collectively, our data demonstrate that both redundant and nonredundant functions of ATM and H2AX are required for normal recombination of TCR loci, proliferative expansion of developing thymocytes, and maintenance of genomic stability in cycling αβ T-lineage cells.

p38β MAP kinase as a therapeutic target for pancreatic cancer

Pancreatic cancer is very difficult to diagnose in its early stage. Molecular marker and imaging have not proven to be accurate modalities for screening of pancreatic cancer. This study aims to develop p38β as a protein marker for pancreatic cancer and to design peptide inhibitor against the same. The serum p38β level of pancreatic cancer (n = 35; 5.06 μg/mL) was twofold higher compared to that of the chronic pancreatitis (n = 10; 2.92 μg/mL) and matched normal control (n = 10; 2.86 μg/ml) (p < 0.0005). Peptide inhibitors were designed to inhibit the activity of p38β and the kinetic assay had shown the dissociation constant, (K(D)) to be 3.16 × 10(-8) M and IC(50), 25 nM by Surface Plasmon Resonance (SPR) and Enzyme-Linked Immunosorbent Assay (ELISA), respectively. The peptide inhibitor also significantly reduced viability and induced cytotoxicity in Human Pancreatic carcinoma epithelial-like cell line (PANC-1) cells.

The p57 CDKi integrates stress signals into cell-cycle progression to promote cell survival upon stress

The stress-activated protein kinase p38 phosphorylates p57/Kip2, resulting in enhanced CDK2 inhibition and a cell-cycle delay that helps cells to survive under stress.

The p57^Kip2 cyclin-dependent kinase inhibitor (CDKi) has been implicated in embryogenesis, stem-cell senescence and pathologies, but little is known of its role in cell cycle control. Here, we show that p57^Kip2 is targeted by the p38 stress-activated protein kinase (SAPK). Phosphorylation of p57^Kip2 at T143 by p38 enhances its association with and inhibition of Cdk2, which results in cell-cycle delay upon stress. Genetic inactivation of the SAPK or the CDKi abolishes cell-cycle delay upon osmostress and results in decreased cell viability. Oxidative stress and ionomycin also induce p38-mediated phosphorylation of p57 and cells lacking p38 or p57 display reduced viability to these stresses. Therefore, cell survival to various stresses depends on p57 phosphorylation by p38 that inhibits CDK activity. Together, these findings provide a novel molecular mechanism by which cells can delay cell cycle progression to maximize cell survival upon stress.

Negative regulation of human U6 snRNA promoter by p38 kinase through Oct-1

Recruitment of Oct-1 protein to the octamer sequence of U6 promoter is critical for optimal transcription by RNA polymerase III. Here we report that p38 kinase inhibitors, SB202190 and SB203580, stimulated U6 promoter activity and this stimulation can be observed only in the presence of octamer sequence. SB202190-treated cell nuclear extract had about 50% increase in Oct-1 binding activity suggesting that the increased U6 promoter activity by p38 kinase inhibitor is mediated through Oct-1. Mutation in octamer sequence significantly reduced the SB202190-stimulated U6 promoter transcription and the distance between octamer and proximal sequence element of U6 promoter is also critical for the p38 kinase inhibitor-stimulated activity. Exogenous Oct-1 expression showed a concentration-dependent activation of U6 promoter that was further stimulated by the p38 kinase inhibitors. When cells were treated with p38 kinase inducer, hydrogen peroxide or phorbol 12-myristate 13-acetate (PMA), U6 promoter activity was down regulated and this inhibition was reversed by p38 kinase inhibitors. Over-expression of p38α kinase down-regulated U6 promoter activity and this inhibition was further enhanced by PMA and p38 kinase inhibitors reversed this inhibition. p38 kinase inhibitor-treated cells had 50% more U6 RNA than the control cells. Taken together, our results show a negative correlation between the p38 kinase levels and Oct-1 binding on U6 promoter, suggesting that U6 promoter is negatively regulated by p38 kinase.

Lymphocyte development: integration of DNA damage response signaling

Lymphocytes traverse functionally discrete stages as they develop into mature B and T cells. This development is directed by cues from a variety of different cell surface receptors. To complete development, all lymphocytes must express a functional nonautoreactive heterodimeric antigen receptor. The genes that encode antigen receptor chains are assembled through the process of V(D)J recombination, a reaction that proceeds through DNA double-stranded break (DSB) intermediates. These DSBs are generated by the RAG endonuclease in G1-phase developing lymphocytes and activate ataxia-telangiectasia mutated (ATM), the kinase that orchestrates cellular DSB responses. The canonical DNA damage response includes cell cycle arrest, DNA break repair, and apoptosis of cells when DSBs are not repaired. However, recent studies have demonstrated that ATM activation in response to RAG DSBs also regulates a transcriptional program including many genes with no known function in canonical DNA damage responses. Rather, these genes have activities that would be important for lymphocyte development. Here, these findings and the broader concept that signals initiated by physiologic DNA DSBs provide cues that regulate cell type-specific processes and functions are discussed.

An emerging role of RNA-binding proteins as multifunctional regulators of lymphocyte development and function

Sequence-specific RNA-binding proteins (RBP) and the regulation of RNA decay have long been recognized as important regulators of the inflammatory response. RBP influence gene expression throughout the lifespan of the mRNA by regulating splicing, polyadenylation, cellular localization, translation, and decay. Increasing evidence now indicates that these proteins, together with the RNA decay machinery that they recruit, also regulate the development and activation of lymphocytes. The activity of RBP is regulated by the same signal transduction pathways that govern lymphocyte development and differentiation in response to antigen and cytokine receptor engagement. Roles for these proteins in regulating the diverse functions of lymphocytes are becoming increasingly apparent.

Antigen receptor allelic exclusion: an update and reappraisal

Most lymphocytes express cell surface Ag receptor chains from single alleles of distinct Ig or TCR loci. Since the identification of Ag receptor allelic exclusion, the importance of this process and the precise molecular mechanisms by which it is achieved have remained enigmatic. This brief review summarizes current knowledge of the extent to which Ig and TCR loci are subject to allelic exclusion. Recent progress in studying and defining mechanistic steps and molecules that may control the monoallelic initiation and subsequent inhibition of V-to-(D)-J recombination is outlined using the mouse TCRβ locus as a model with frequent comparisons to the mouse IgH and Igκ loci. Potential consequences of defects in mechanisms that control Ag receptor allelic exclusion and a reappraisal of the physiologic relevance of this immunologic process also are discussed.

Nuclear proteome analysis of cisplatin-treated HeLa cells

Cisplatin has been widely accepted as one of the most efficient anticancer drugs for decades. However, the mechanisms for the cytotoxic effects of cisplatin are still not fully understood. Cisplatin primarily targets DNA, resulting in the formation of DNA double strand breaks and eventually causing cell death. In this study, we applied two-dimensional electrophoresis coupled with LC-MS/MS to analyze the nuclear proteome of HeLa cells treated with cisplatin, in an effort to uncover new mechanistic clues regarding the cellular response to cisplatin. A total of 19 proteins were successfully identified, and these proteins are involved in a variety of basal metabolic and biological processes in cells, including biosynthesis, cell cycle, glycolysis and apoptosis. Six were related to the regulation of mRNA splicing, and we therefore asked whether the Fas gene might undergo alternative splicing following cisplatin treatment. This proved to be the case, as the splicing forms of Fas were modified in cisplatin-treated HeLa cells. This work provides novel information, from the perspective of the nuclear response, for understanding the cytotoxicity caused by cisplatin-induced DNA damage.

p38 mitogen-activated protein kinase promotes cell survival in response to DNA damage but is not required for the G(2) DNA damage checkpoint in human cancer cells

p38 mitogen-activated protein kinase (MAPK) is rapidly activated by stresses and is believed to play an important role in the stress response. While Chk1 is known to mediate G(2) DNA damage checkpoint control, p38 was also reported to have an essential function in this checkpoint control. Here, we have investigated further the roles of p38 and Chk1 in the G(2) DNA damage checkpoint in cancer cells. We find that although p38 activation is strongly induced by DNA damage, its activity is not required for the G(2) DNA damage checkpoint. In contrast, Chk1 kinase is responsible for the execution of G(2) DNA damage checkpoint control in p53-deficient cells. The inhibition of p38 activity has no effect on Chk1 activation and gamma-H2AX expression. Global gene expression profiling of cancer cells in response to tumor necrosis factor alpha (TNF-alpha) revealed that p38 plays a strong prosurvival role through the coordinated downregulation of proapoptotic genes and upregulation of prosurvival genes. We show that the inhibition of p38 activity during G(2) DNA damage checkpoint arrest triggers apoptosis in a p53-independent manner with a concurrent decrease in the level of Bcl2 family proteins. Our results suggest that although p38 MAPK is not required for the G(2) DNA damage checkpoint function, it plays an important prosurvival role during the G(2) DNA damage checkpoint response through the upregulation of the Bcl2 family proteins.

Cellular and molecular mechanisms of bromate-induced cytotoxicity in human and rat kidney cells

The mechanisms of bromate (BrO(3)(-))-induced toxicity in Normal Rat Kidney (NRK) and human embryonic kidney 293 (HEK293) cells were investigated. BrO(3)(-) (added as KBrO(3)) induced concentration-dependent decreases in 3-(4, dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) staining after 48 h. BrO(3)(-)-induced necrosis based on tandem increases in annexin V and PI staining. Cell cycle analysis demonstrated that BrO(3)(-) also induced G2/M arrest and nuclear fragmentation, prior to alterations in MTT staining or annexin V and PI staining. Immunoblot analysis demonstrated that the G2/M arrest correlated to induction of phosphorylated (p)-p53, p21, cyclin B1 and p-cdc2. Further, BrO(3)(-) induced time-dependent increases in the activity of the mitogen activated protein kinases p38 and ERK1/2. Treatment of cells with the p38 inhibitor SB202190, but not the ERK1/2 inhibitor PD98059, partially reversed BrO(3)(-)-induced G2/M arrest and decreased BrO(3)(-)-induced p-p53, p21 and cyclin B1 expression. In addition, BrO(3)(-) treatment induced reactive oxygen species (ROS) based on increases in CM-H(2)DCFDA fluorescence. The antioxidant ascorbic acid inhibited BrO(3)(-)-induced p38 activation, G2/M arrest, p-p53, p21 and cyclin B1 expression; however, ascorbic acid had no effect on BrO(3)(-)-induced formation of 8-OHdG, a marker of DNA oxidative damage, whose increases preceded cell death by 24h. These data suggest that ROS mediated MAPK activation is involved in the molecular mechanisms of BrO(3)(-)-induced cell cycle arrest, which occurs independently of 8-OH-dG production. The similar mode of action in both NRK and HEK293 cells suggests that the mechanisms of BrO(3)(-)-induced renal cell death are model-independent.

p38 Mitogen-activated protein kinase and hematologic malignancies

CONTEXT

p38 mitogen-activated protein kinase (MAPK) signaling has been implicated in responses ranging from apoptosis to cell cycle, induction of expression of cytokine genes, and differentiation. This plethora of activators conveys the complexity of the p38 pathway. This complexity is further complicated by the observation that the downstream effects of p38 MAPK activation may be different depending on types of stimuli, cell types, and various p38 MAPK isoforms involved.

OBJECTIVE

This review focuses on the recent advancement of the p38 MAPK isoforms as well as the roles of p38 MAPK in hematologic malignancies.

DATA SOURCES

Review of pertinent published literature and work in our laboratory.

CONCLUSIONS

In some hematologic malignancies, activation of p38 plays a key role in promoting or inhibiting proliferation and also in increasing resistance to chemotherapeutic agents. The importance of different p38 isoforms in various cellular functions has been acknowledged recently. Further understanding of these isoforms will allow the design of more specific inhibitors to target particular isoforms to maximize the treatment effect and minimize the side effects for treating hematopoietic malignancies.

Histone H2AX stabilizes broken DNA strands to suppress chromosome breaks and translocations during V(D)J recombination

The H2AX core histone variant is phosphorylated in chromatin around DNA double strand breaks (DSBs) and functions through unknown mechanisms to suppress antigen receptor locus translocations during V(D)J recombination. Formation of chromosomal coding joins and suppression of translocations involves the ataxia telangiectasia mutated and DNA-dependent protein kinase catalytic subunit serine/threonine kinases, each of which phosphorylates H2AX along cleaved antigen receptor loci. Using Abelson transformed pre–B cell lines, we find that H2AX is not required for coding join formation within chromosomal V(D)J recombination substrates. Yet we show that H2AX is phosphorylated along cleaved Igκ DNA strands and prevents their separation in G1 phase cells and their progression into chromosome breaks and translocations after cellular proliferation. We also show that H2AX prevents chromosome breaks emanating from unrepaired RAG endonuclease-generated TCR-α/δ locus coding ends in primary thymocytes. Our data indicate that histone H2AX suppresses translocations during V(D)J recombination by creating chromatin modifications that stabilize disrupted antigen receptor locus DNA strands to prevent their irreversible dissociation. We propose that such H2AX-dependent mechanisms could function at additional chromosomal locations to facilitate the joining of DNA ends generated by other types of DSBs.

Improved ATM kinase inhibitor KU-60019 radiosensitizes glioma cells, compromises insulin, AKT and ERK prosurvival signaling, and inhibits migration and invasion

Ataxia telangiectasia (A-T) mutated (ATM) is critical for cell cycle checkpoints and DNA repair. Thus, specific small molecule inhibitors targeting ATM could perhaps be developed into efficient radiosensitizers. Recently, a specific inhibitor of the ATM kinase, KU-55933, was shown to radiosensitize human cancer cells. Herein, we report on an improved analogue of KU-55933 (KU-60019) with K(i) and IC(50) values half of those of KU-55933. KU-60019 is 10-fold more effective than KU-55933 at blocking radiation-induced phosphorylation of key ATM targets in human glioma cells. As expected, KU-60019 is a highly effective radiosensitizer of human glioma cells. A-T fibroblasts were not radiosensitized by KU-60019, strongly suggesting that the ATM kinase is specifically targeted. Furthermore, KU-60019 reduced basal S473 AKT phosphorylation, suggesting that the ATM kinase might regulate a protein phosphatase acting on AKT. In line with this finding, the effect of KU-60019 on AKT phosphorylation was countered by low levels of okadaic acid, a phosphatase inhibitor, and A-T cells were impaired in S473 AKT phosphorylation in response to radiation and insulin and unresponsive to KU-60019. We also show that KU-60019 inhibits glioma cell migration and invasion in vitro, suggesting that glioma growth and motility might be controlled by ATM via AKT. Inhibitors of MEK and AKT did not further radiosensitize cells treated with KU-60019, supporting the idea that KU-60019 interferes with prosurvival signaling separate from its radiosensitizing properties. Altogether, KU-60019 inhibits the DNA damage response, reduces AKT phosphorylation and prosurvival signaling, inhibits migration and invasion, and effectively radiosensitizes human glioma cells.

Nuclear localization of p38 MAPK in response to DNA damage

p38 MAP kinase (MAPK) is activated in response to environmental stress, cytokines and DNA damage, and mediates death, cell differentiation and cell cycle checkpoints. The intracellular localization of p38 MAPK upon activation remains unclear, and may depend on the stimulus. We show here that activation of p38 MAPK by stimuli that induce DNA double strand breaks (DSBs), but not other stimuli, leads to its nuclear translocation. In addition, naturally occurring DSBs generated through V(D)J recombination in immature thymocytes also promote nuclear accumulation of p38 MAPK. Nuclear translocation of p38 MAPK does not require its catalytic activity, but is induced by a conformational change of p38 MAPK triggered by phosphorylation within the active site. The selective nuclear accumulation of p38 MAPK in response to DNA damage could be a mechanism to facilitate the phosphorylation of p38 MAPK nuclear targets for the induction of a G2/M cell cycle checkpoint and DNA repair.

Regulation of the immune response by stress-activated protein kinases

Activation of immune cells to mediate an immune response is often triggered by potential 'danger' or 'stress' stimuli that the organism receives. Within the mitogen-activated protein kinases (MAPKs) family, the stress-activated protein kinase (SAPK) group was defined as group of kinases that activated by stimuli that cause cell stress. In the immune cells, SAPKs are activated by antigen receptors (B- or T-cell receptors), Toll-like receptors, cytokine receptors, and physical-chemical changes in the environment among other stimuli. The SAPKs are established to be important mediators of intracellular signaling during adaptive and innate immune responses. Here we summarize what is currently known about the role of two sub-groups of SAPKs - c-Jun NH(2)-terminal kinase and p38 MAPK-in the function of specific components of the immune system and the overall contribution to the immune response.

The selenium analog of the chemopreventive compound S,S'-(1,4-phenylenebis[1,2-ethanediyl])bisisothiourea is a remarkable inducer of apoptosis and inhibitor of cell growth in human non-small cell lung cancer

Lung cancer continues to be the leading cause of cancer deaths throughout the world and conventional therapy remains largely unsuccessful. Although, chemoprevention is a plausible alternative approach to curb the lung cancer epidemic, clinically there are no effective chemopreventive agents. Thus, development of novel compounds that can target cellular and molecular pathways involved in the multistep carcinogenesis process is urgently needed. Previous studies have suggested that substitution of sulfur by selenium in established cancer chemopreventive agents may result in more effective analogs. Thus in the present study we selected the chemopreventive agent S,S'-(1,4-phenylenebis[1,2-ethanediyl])bisisothiourea (PBIT), also known to inhibit inducible nitric oxide synthase (iNOS), synthesized its selenium analog (Se-PBIT) and compared both compounds in preclinical model systems using non-small cell lung cancer (NSCLC) cell lines (NCI-H460 and A549); NSCLC is the most common histologic type of all lung cancer cases. Se-PBIT was found to be superior to PBIT as an inducer of apoptosis and inhibitor of cell growth. Se-PBIT arrested cell cycles at G1 and G2-M stage in both A549 and H460 cell lines. Although both compounds are weakly but equally effective inhibitors of iNOS protein expression and activity, only Se-PBIT significantly enhanced the levels of p53, p38, p27 and p21 protein expression, reduced levels of phospholipase A2 (PLA2) but had no effect on cyclooxygenase-2 (COX-2) protein levels; such molecular targets are involved in cell growth inhibition, induction of apoptosis and cell cycle regulation. The results indicate that Se-PBIT altered molecular targets that are involved in the development of human lung cancer. Although, the mechanisms that can fully account for these effects remain to be determined, the results are encouraging to further evaluate the chemopreventive efficacy of Se-PBIT against the development of NSCLC in a well-defined animal model.

The sticky business of histone H2AX in V(D)J recombination, maintenance of genomic stability, and suppression of lymphoma

DNA double strand breaks (DSBs) induced during cellular metabolism, DNA replication, and genomic rearrangement events lead to phosphorylation of the H2AX core histone variant in surrounding chromatin. H2AX is essential for normal DSB repair, maintenance of genomic stability, and suppression of lymphomas with clonal translocations and intra-chromosomal deletions. One current focus of our lab is to elucidate mechanisms through which H2AX functions in the cellular DNA damage response using V(D)J recombination as a model system. A number of potential H2AX functions can be readily tested using novel experimental approaches developed in our lab. These putative functions include: (1) modulation of chromatin accessibility to facilitate kinetics of DSB repair, (2) stabilization of broken DNA strands to maintain ends in close proximity, and (3) amplification of DNA damage signals. Here, we summarize our recent efforts in elucidating mechanisms by which H2AX functions during V(D)J recombination to coordinate DSB repair with cellular proliferation and survival to prevent translocations and suppress lymphomagenesis.

Kinases that control the cell cycle in response to DNA damage: Chk1, Chk2, and MK2

In response to DNA damage eukaryotic cells activate cell cycle checkpoints -- complex kinase signaling networks that prevent further progression through the cell cycle. Parallel to implementing a cell cycle arrest, checkpoint signaling also mediates the recruitment of DNA repair pathways. If the extent of damage exceeds repair capacity, additional signaling cascades are activated to ensure elimination of these damaged cells. The DNA damage response has traditionally been divided into two major kinase branches. The ATM/Chk2 module is activated after DNA double strand breaks and the ATR/Chk1 pathway responds primarily to DNA single strand breaks or bulky lesions. Both pathways converge on Cdc25, a positive regulator of cell cycle progression, which is inhibited by Chk1-mediated or Chk2-mediated phosphorylation. Recently a third effector kinase complex consisting of p38MAPK and MK2 has emerged. This pathway is activated downstream of ATM and ATR in response to DNA damage. MK2 has been shown to share substrate homology with both Chk1 and Chk2. Here we will discuss recent advances in our understanding of the eukaryotic DNA damage response with emphasis on the Chk1, Chk2, and the newly emerged effector kinases p38MAPK and MK2.

Non-classical p38 map kinase functions: cell cycle checkpoints and survival

The p38 MAPK kinase pathway is activated in response to a wide range of cellular stress stimuli and cytokines. Our understanding of the important functions of p38 MAPK in the process of differentiation and cell death has grown considerably in the recent years and is now relatively established. Here we discuss the role of p38 MAPK in the mediation of cell cycle checkpoints and cell survival, processes that have received less attention. We describe how p38 MAPK regulates both the G2/M as well as a G1/S cell cycle checkpoint in response to cellular stress such as DNA damage. While p38 MAPK has classically been associated with the induction of apoptosis, we discuss that p38 MAPK can also mediate cell survival in specific situations, such as in response to DNA damage. It is important to recognize these less appreciated functions of p38 MAPK when considering the potential use of pharmacological inhibitors of p38 MAPK in therapeutic treatments for disease.

Alteration of Mitogen-Activated Protein Kinase Pathway After Soman Poisoning

The p38 mitogen-activated protein kinase (MAPK) and activated MAPK transcription factors c-jun, c-myc, and elk-1 were investigated in rat enterocytes after sublethal poisoning with soman to study the pathogenetic mechanism of nonspecific long-term effects of nerve agents. Wistar rats were poisoned by intramuscular administration of soman at a dose 60 microg x kg(-1) (70% LD(50)) and sacrificed by cervical dislocation 3 and 5 days after poisoning. Control groups were administered physiologic saline instead of soman. Protein expression in immunohistochemically stained samples from colon transversum of control and poisoned rats was measured using image analysis. In comparison with control groups, activated p38 MAPK from soman-poisoned rats was significantly depressed at both time intervals. c-myc and c-jun expression was significantly increased 3 days after soman poisoning. On the other hand, a decrease in c-myc and c-jun expression was observed 5 days after soman poisoning. No changes in elk-1 expression were found. Long-term depression of MAPK pathway members might allow cells to proliferate in poisoned rats. This mechanism can be linked with apoptosis and carcinogenesis.

Requirement for p38 mitogen-activated protein kinase activity in neointima formation after vascular injury

BACKGROUND

Angioplasty and stent delivery are performed to treat atherosclerotic vascular disease but often cause deleterious neointimal lesion formation. Previously, growth factor receptor-bound protein 2 (Grb2), an intracellular linker protein, was shown to be essential for neointima formation and for p38 mitogen-activated protein kinase (MAPK) activation in vascular smooth muscle cells (SMCs). In this study, the role of vascular SMC p38alpha MAPK in neointimal development was examined.

METHODS AND RESULTS

Compound transgenic mice were generated with doxycycline-inducible SMC-specific expression of dominant-negative p38alpha MAPK (DN-p38alpha). Doxycycline treatment resulted in the expression of DN-p38alpha mRNA and protein in transgenic arteries. Doxycycline-treated compound transgenic mice were resistant to neointima formation 21 days after carotid injury and showed reduced arterial p38 MAPK activation. To explore the mechanism by which p38alpha MAPK promotes neointima formation, an in vitro SMC culture system was used. Inhibition of p38alpha MAPK in cultured SMCs by treatment with SB202190 or small interfering RNA blocked platelet-derived growth factor-induced SMC proliferation, DNA replication, phosphorylation of the retinoblastoma protein, and induction of minichromosome maintenance protein 6.

CONCLUSIONS

SMC p38alpha MAPK activation is required for neointima formation, perhaps because of its ability to promote retinoblastoma protein phosphorylation and minichromosome maintenance protein 6 expression.

Phosphorylation by p38 MAPK as an alternative pathway for GSK3beta inactivation

Glycogen synthase kinase 3beta (GSK3beta) is involved in metabolism, neurodegeneration, and cancer. Inhibition of GSK3beta activity is the primary mechanism that regulates this widely expressed active kinase. Although the protein kinase Akt inhibits GSK3beta by phosphorylation at the N terminus, preventing Akt-mediated phosphorylation does not affect the cell-survival pathway activated through the GSK3beta substrate beta-catenin. Here, we show that p38 mitogen-activated protein kinase (MAPK) also inactivates GSK3beta by direct phosphorylation at its C terminus, and this inactivation can lead to an accumulation of beta-catenin. p38 MAPK-mediated phosphorylation of GSK3beta occurs primarily in the brain and thymocytes. Activation of beta-catenin-mediated signaling through GSK3beta inhibition provides a potential mechanism for p38 MAPK-mediated survival in specific tissues.

Bendamustine induces G2 cell cycle arrest and apoptosis in myeloma cells: the role of ATM-Chk2-Cdc25A and ATM-p53-p21-pathways

PURPOSE

Multiple myeloma is a fatal hematological disease caused by malignant transformation of plasma cells. Bendamustine has been proven to be a potent alternative to melphalan in phase 3 studies, yet its molecular mode of action is still poorly understood.

METHODS

The four-myeloma cell lines NCI-H929, OPM-2, RPMI-8226, and U266 were cultured in vitro. Apoptosis was measured by flow cytometry after annexin V FITC and propidium iodide staining. Cell cycle distribution of cells was determined by DNA staining with propidium iodide. Intracellular levels of (phosphorylated) proteins were determined by western blot.

RESULTS

We show that bendamustine induces apoptosis with an IC50 of 35-65 mug/ml and with cleavage of caspase 3. Incubation with 10-30 mug/ml results in G2 cell cycle arrest in all four-cell lines. The primary DNA-damage signaling kinases ATM and Chk2, but not ATR and Chk1, are activated. The Chk2 substrate Cdc25A phosphatase is degraded and Cdc2 is inhibited by inhibitory phosphorylation of Tyr15 accompanied by increased cyclin B levels. Additionally, p53 activation occurs as phosphorylation of Ser15, the phosphorylation site for ATM. p53 promotes Cdc2 inhibition by upregulation of p21. Targeting of p38 MAPK by the selective inhibitor SB202190 significantly increases bendamustine induced apoptosis. Additionally, SB202190 completely abrogates G2 cell cycle arrest.

CONCLUSION

Bendamustine induces ATM-Chk2-Cdc2-mediated G2 arrest and p53 mediated apoptosis. Inhibition of p38 MAPK augments apoptosis and abrogates G2 arrest and can be considered as a new therapeutic strategy in combination with bendamustine.

Choreography of MAGUKs during T cell activation

T cell receptor activation requires the membrane-associated guanylate kinase CARMA1. A new study finds that a second such kinase, Dlgh1, is also required specifically for activation of the alternative p38 kinase pathway.

TAO kinases mediate activation of p38 in response to DNA damage

Thousand and one amino acid (TAO) kinases are Ste20p-related MAP kinase kinase kinases (MAP3Ks) that activate p38 MAPK. Here we show that the TAO kinases mediate the activation of p38 in response to various genotoxic stimuli. TAO kinases are activated acutely by ionizing radiation, ultraviolet radiation, and hydroxyurea. Full-length and truncated fragments of dominant negative TAOs inhibit the activation of p38 by DNA damage. Inhibition of TAO expression by siRNA also decreases p38 activation by these agents. Cells in which TAO kinases have been knocked down are less capable of engaging the DNA damage-induced G2/M checkpoint and display increased sensitivity to IR. The DNA damage kinase ataxia telangiectasia mutated (ATM) phosphorylates TAOs in vitro; radiation induces phosphorylation of TAO on a consensus site for phosphorylation by the ATM protein kinase in cells; and TAO and p38 activation is compromised in cells from a patient with ataxia telangiectasia that lack ATM. These findings indicate that TAO kinases are regulators of p38-mediated responses to DNA damage and are intermediates in the activation of p38 by ATM.

Methylation-controlled J protein promotes c-Jun degradation to prevent ABCB1 transporter expression

Methylation-controlled J protein (MCJ) is a newly identified member of the DnaJ family of cochaperones. Hypermethylation-mediated transcriptional silencing of the MCJ gene has been associated with increased chemotherapeutic resistance in ovarian cancer. However, the biology and function of MCJ remain unknown. Here we show that MCJ is a type II transmembrane cochaperone localized in the Golgi network and present only in vertebrates. MCJ is expressed in drug-sensitive breast cancer cells but not in multidrug-resistant cells. The inhibition of MCJ expression increases resistance to specific drugs by inducing expression of the ABCB1 drug transporter that prevents intracellular drug accumulation. The induction of ABCB1 gene expression is mediated by increased levels of c-Jun due to an impaired degradation of this transcription factor in the absence of MCJ. Thus, MCJ is required in these cells to prevent c-Jun-mediated expression of ABCB1 and maintain drug response.