Involvement of the MKK6-p38gamma cascade in gamma-radiation-induced cell cycle arrest

Response to hyperosmotic stress

An appropriate response and adaptation to hyperosmolarity, i.e., an external osmolarity that is higher than the physiological range, can be a matter of life or death for all cells. It is especially important for free-living organisms such as the yeast Saccharomyces cerevisiae. When exposed to hyperosmotic stress, the yeast initiates a complex adaptive program that includes temporary arrest of cell-cycle progression, adjustment of transcription and translation patterns, and the synthesis and retention of the compatible osmolyte glycerol. These adaptive responses are mostly governed by the high osmolarity glycerol (HOG) pathway, which is composed of membrane-associated osmosensors, an intracellular signaling pathway whose core is the Hog1 MAP kinase (MAPK) cascade, and cytoplasmic and nuclear effector functions. The entire pathway is conserved in diverse fungal species, while the Hog1 MAPK cascade is conserved even in higher eukaryotes including humans. This conservation is illustrated by the fact that the mammalian stress-responsive p38 MAPK can rescue the osmosensitivity of hog1Δ mutations in response to hyperosmotic challenge. As the HOG pathway is one of the best-understood eukaryotic signal transduction pathways, it is useful not only as a model for analysis of osmostress responses, but also as a model for mathematical analysis of signal transduction pathways. In this review, we have summarized the current understanding of both the upstream signaling mechanism and the downstream adaptive responses to hyperosmotic stress in yeast.

MEK2 regulates ribonucleotide reductase activity through functional interaction with ribonucleotide reductase small subunit p53R2

The p53R2 protein, a newly identified member of the ribonucleotide reductase family that provides nucleotides for DNA damage repair, is directly regulated by p53. We show that p53R2 is also regulated by a MEK2 (ERK kinase 2/MAP kinase kinase 2)-dependent pathway. Increased MEK1/2 phosphorylation by serum stimulation coincided with an increase in the RNR activity in U2OS and H1299 cells. The inhibition of MEK2 activity, either by treatment with a MEK inhibitor or by transfection with MEK2 siRNA, dramatically decreased the serum-stimulated RNR activity. Moreover, p53R2 siRNA, but not R2 siRNA, significantly inhibits serum-stimulated RNR activity, indicating that p53R2 is specifically regulated by a MEK2-dependent pathway. Co-immunoprecipitation analyses revealed that the MEK2 segment comprising amino acids 65-171 is critical for p53R2-MEK2 interaction, and the binding domain of MEK2 is required for MEK2-mediated increased RNR activity. Phosphorylation of MEK1/2 was greatly augmented by ionizing radiation, and RNR activity was concurrently increased. Ionizing radiation-induced RNR activity was markedly attenuated by transfection of MEK2 or p53R2 siRNA, but not R2 siRNA. These data show that MEK2 is an endogenous regulator of p53R2 and suggest that MEK2 may associate with p53R2 and upregulate its activity.

Sir2 plays a key role in cell fate determination upon SAPK activation

Although the benefit of sirtuin activation in age-related diseases is well-characterized, the benefit of sirtuin activation in acute diseases has been elusive. Here we discuss that, at least in yeast, Sir2 activation prevents programmed cell death induced by the sustained activation of the stress activated protein kinase (SAPK) Hog1, the yeast homologue of the p38 SAPK. Sir2 prevents ROS formation and maximize cell survival upon SAPK activation. The conserved function of Sir2 in age-related diseases and the conserved role of SAPKs open the possibility of a novel role for sirtuins in cell fate determination in eukaryotic cells.

TGF-β1 induces endothelial cell apoptosis by shifting VEGF activation of p38(MAPK) from the prosurvival p38β to proapoptotic p38α

TGF-β1 and VEGF, both angiogenesis inducers, have opposing effects on vascular endothelial cells. TGF-β1 induces apoptosis; VEGF induces survival. We have previously shown that TGF-β1 induces endothelial cell expression of VEGF, which mediates TGF-β1 induction of apoptosis through activation of p38 mitogen-activated protein kinase (MAPK). Because VEGF activates p38(MAPK) but protects the cells from apoptosis, this finding suggested that TGF-β1 converts p38(MAPK) signaling from prosurvival to proapoptotic. Four isoforms of p38(MAPK) -α, β, γ, and δ-have been identified. Therefore, we hypothesized that different p38(MAPK) isoforms control endothelial cell apoptosis or survival, and that TGF-β1 directs VEGF activation of p38(MAPK) from a prosurvival to a proapoptotic isoform. Here, we report that cultured endothelial cells express p38α, β, and γ. VEGF activates p38β, whereas TGF-β1 activates p38α. TGF-β1 treatment rapidly induces p38α activation and apoptosis. Subsequently, p38α activation is downregulated, p38β is activated, and the surviving cells become refractory to TGF-β1 induction of apoptosis and proliferate. Gene silencing of p38α blocks TGF-β1 induction of apoptosis, whereas downregulation of p38β or p38γ expression results in massive apoptosis. Thus, in endothelial cells p38α mediates apoptotic signaling, whereas p38β and p38γ transduce survival signaling. TGF-β1 activation of p38α is mediated by VEGF, which in the absence of TGF-β1 activates p38β. Therefore, these results show that TGF-β1 induces endothelial cell apoptosis by shifting VEGF signaling from the prosurvival p38β to the proapoptotic p38α.

RAC1 GTPase plays an important role in γ-irradiation induced G2/M checkpoint activation

Introduction

In response to gamma-irradiation (IR)-induced double-strand DNA breaks, cells undergo cell-cycle arrest, allowing time for DNA repair before reentering the cell cycle. G₂/M checkpoint activation involves activation of ataxia telangiectasia mutated (ATM)/ATM- and rad3-related (ATR) kinases and inhibition of Cdc25 phosphatases, resulting in inhibition of Cdc2 kinase and subsequent G₂/M cell-cycle arrest. Previous studies from our laboratory showed that the G₂/M checkpoint activation after IR exposure of MCF-7 breast cancer cells is dependent on the activation of extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) signaling. In the present studies, we investigated the role of Ras-related C3 botulinum toxin substrate 1 (Rac1) guanosine triphosphatase (GTPase) in IR-induced G₂/M checkpoint response and ERK1/2 activation, as well as in cell survival after IR.

Methods

With Rac1-specific inhibitor, dominant negative mutant Rac1 (N17Rac1) and specific small interfering RNA, the effect of Rac1 on IR-induced G₂/M checkpoint response and ERK1/2 activation was examined in human breast cancer cells. In addition, the effect of Rac1 on cell survival after irradiation was assessed by using Rac1-specific inhibitor.

Results

IR exposure of MCF-7 breast cancer cells was associated with a marked activation of Rac1 GTPase. Furthermore, inhibition of Rac1 by using specific inhibitor, dominant-negative Rac1 mutant, or specific siRNA resulted in attenuation of IR-induced G₂/M arrest and concomitant diminution of IR-induced activation of ATM, ATR, Chk1, and Chk2 kinases, as well as phosphorylation of Cdc2-Tyr15. Moreover, Rac1 inhibition or decreased Rac1 expression also abrogated IR-induced phosphorylation of mitogen-activated protein kinase kinase 1 and 2 (MEK1/2) and ERK1/2. Ultimately, inhibition of Rac1 markedly increased cellular sensitivity to IR exposure, which involves induction of apoptosis.

Conclusion

Studies in this report suggest that Rac1 GTPase plays an essential role in the activation of IR-induced ERK1/2 signaling and subsequent G₂/M checkpoint response. Furthermore, results also support a role for Rac1 in promoting cell survival after irradiation treatment.

p38γ activity is required for maintenance of slow skeletal muscle size

INTRODUCTION

p38γ kinase is highly enriched in skeletal muscle and is implicated in myotube formation. However, the activation status of p38γ in muscle is unclear.

METHODS

p38γ activity in slow and fast adult mouse skeletal muscle tissue was examined, as was the impact of p38γ deficiency on muscle development and gene expression.

RESULTS

p38γ is preferentially activated in slow muscle, but it is inactive in fast muscle types. Furthermore, the loss of p38γ in mice led to decreased muscle mass associated with a smaller myofiber diameter in slow muscle, but there was no impact on fast muscle in either mass or myofiber diameter. Finally, p38γ-deficient muscle showed selective changes in genes related to muscle growth in slow muscle fibers.

CONCLUSION

This study provides evidence that p38γ is selectively activated in slow skeletal muscle and is involved in the normal growth and development of a subset of skeletal muscle.

Balance between MKK6 and MKK3 mediates p38 MAPK associated resistance to cisplatin in NSCLC

The p38 MAPK signaling pathway has been proposed as a critical mediator of the therapeutic effect of several antitumor agents, including cisplatin. Here, we found that sensitivity to cisplatin, in a system of 7 non-small cell lung carcinoma derived cell lines, correlated with high levels of MKK6 and marked activation of p38 MAPK. However, knockdown of MKK6 modified neither the response to cisplatin nor the activation of p38 MAPK. Deeper studies showed that resistant cell lines also displayed higher basal levels of MKK3. Interestingly, MKK3 knockdown significantly decreased p38 phosphorylation upon cisplatin exposure and consequently reduced the response to the drug. Indeed, cisplatin poorly activated MKK3 in resistant cells, while in sensitive cell lines MKK3 showed the opposite pattern in response to the drug. Our data also demonstrate that the low levels of MKK6 expressed in resistant cell lines are the consequence of high basal activity of p38 MAPK mediated by the elevated levels of MKK3. This finding supports the existence of a regulatory mechanism between both MAPK kinases through their MAPK. Furthermore, our results were also mirrored in head and neck carcinoma derived cell lines, suggesting our observations boast a potential universal characteristic in cancer resistance of cisplatin. Altogether, our work provides evidence that MKK3 is the major determinant of p38 MAPK activation in response to cisplatin and, hence, the resistance associated with this MAPK. Therefore, these data suggest that the balance between both MKK3 and MKK6 could be a novel mechanism which explains the cellular response to cisplatin.

Fucoidan extract induces apoptosis in MCF-7 cells via a mechanism involving the ROS-dependent JNK activation and mitochondria-mediated pathways

Background

Fucoidan extract (FE), an enzymatically digested compound with a low molecular weight, is extracted from brown seaweed. As a natural compound with various actions, FE is attractive, especially in Asian countries, for improving the therapeutic efficacy and safety of cancer treatment. The present study was carried out to investigate the anti-tumor properties of FE in human carcinoma cells and further examine the underlying mechanisms of its activities.

Methodology/Principal Finding

FE inhibits the growth of MCF-7, MDA-MB-231, HeLa, and HT1080 cells. FE-mediated apoptosis in MCF-7 cancer cells is accompanied by DNA fragmentation, nuclear condensation, and phosphatidylserine exposure. FE induces mitochondrial membrane permeabilization (MMP) through loss of mitochondrial membrane potential (ΔΨm) and regulation of the expression of Bcl-2 family members. Release of apoptosis-inducing factor (AIF) and cytochrome c precedes MMP. AIF release causes DNA fragmentation, the final stage of apoptosis, via a caspase-independent mitochondrial pathway. Additionally, FE was found to induce phosphorylation of c-Jun N-terminal kinase (JNK), p38, and extracellular signal-regulated kinase (ERK) 1/2, and apoptosis was found to be attenuated by inhibition of JNK. Furthermore, FE-mediated apoptosis was found to involve the generation of reactive oxygen species (ROS), which are responsible for the decrease of ΔΨm and phosphorylation of JNK, p38, and ERK1/2 kinases.

Conclusions/Significance

These data suggest that FE activates a caspase-independent apoptotic pathway in MCF-7 cancer cells through activation of ROS-mediated MAP kinases and regulation of the Bcl-2 family protein-mediated mitochondrial pathway. They also provide evidence that FE deserves further investigation as a natural anticancer and cancer preventive agent.

p38γ mitogen-activated protein kinase contributes to oncogenic properties maintenance and resistance to poly (ADP-ribose)-polymerase-1 inhibition in breast cancer

p38γ MAPK, one of the four members of p38 mitogen-activated protein kinases (MAPKs), has previously been shown to harbor oncogenic functions. However, the biologic function of p38γ MAPK in breast cancer has not been well defined. In this study, we have shown that p38γ MAPK is overexpressed in highly metastatic human and mouse breast cancer cell lines and p38γ MAPK expression is preferentially associated with basal-like and metastatic phenotypes of breast tumor samples. Ectopic expression of p38γ MAPK did not lead to an increase in oncogenic properties in vitro in most tested mammary epithelial cells. However, knockdown of p38γ MAPK expression resulted in a dramatic decrease in cell proliferation, colony formation, cell migration, invasion in vitro and significant retardation of tumorigenesis, and long-distance metastasis to the lungs in vivo. Moreover, knockdown of p38γ MAPK triggered the activation of AKT signaling. Inhibition of this feedback loop with various PI3K/AKT signaling inhibitors facilitated the effect of targeting p38γ MAPK. We further found that overexpression of p38γ MAPK did not promote cell resistance to chemotherapeutic agents doxorubicin and paclitaxel but significantly increased cell resistance to PJ-34, a DNA damage agent poly (ADP-ribose)-polymerase-1 (PARP) inhibitor in vitro and in vivo. Finally, we identified that p38γ MAPK overexpression led to marked cell cycle arrest in G(2)/M phase. Our study for the first time clearly demonstrates that p38γ MAPK is a promising target for the design of targeted therapies for basal-like breast cancer with metastatic characteristics and for overcoming potential resistance against the PARP inhibitor.

Induction of DNA damage signaling genes in benzidine-treated HepG2 cells

We examined genotoxicity and DNA damage response in HepG2 cells following exposure to benzidine. Using the Comet assay, we showed that benzidine (50-200 μM) induces DNA damage in HepG2 cells. DNA damage signaling pathway-based PCR arrays were used to investigate expression changes in genes involved in cell-cycle arrest, apoptosis, and DNA repair and showed upregulation of 23 genes and downregulation of one gene in benzidine-treated cells. Induction of G2/M arrest and apoptosis was confirmed at the protein level. Real-time PCR and Western blots were used to demonstrate the expression of select DNA repair-associated genes from the PCR array. Upregulation of the p53 protein in benzidine-treated cells suggests the induction of the p53 DNA damage signaling pathway. Collectively, DNA damage response genes induced by benzidine indicate recruitment complex molecular machinery involved in DNA repair, cell-cycle arrest, and potentially, activation of the apoptosis.

Phosphorylation and stabilization of topoisomerase IIα protein by p38γ mitogen-activated protein kinase sensitize breast cancer cells to its poisons

Cancer drugs suppress tumor cell growth by inhibiting specific cellular targets. However, most drugs also activate several cellular nonspecific stress pathways, and the implications of these off-target effects are mostly unknown. Here, we report that p38γ, but not p38α, MAPK is specifically activated by treatment of breast cancer cells with topoisomerase II (Topo II) drugs, whereas paclitaxel (Taxol) does not have this effect. The activated p38γ in turn phosphorylates and stabilizes Topo IIα protein, and this enhances the growth inhibition by Topo II drugs. Moreover, p38γ activity was shown to be necessary and sufficient for Topo IIα expression, the drug-p38γ-Topo IIα axis is only detected in intrinsically sensitive but not resistant cells, and p38γ is co-overexpressed with Topo IIα protein in primary breast cancers. These results reveal a new paradigm in which p38γ actively regulates the drug-Topo IIα signal transduction, and this may be exploited to increase the therapeutic activity of Topo II drugs.

Coordinated regulation of ATF2 by miR-26b in γ-irradiated lung cancer cells

MicroRNA regulates cellular responses to ionizing radiation (IR) through translational control of target genes. We analyzed time-series changes in microRNA expression following γ-irradiation in H1299 lung cancer cells using microarray analysis. Significantly changed IR-responsive microRNAs were selected based on analysis of variance analysis, and predicted target mRNAs were enriched in mitogen-activated protein kinase (MAPK) signaling. Concurrent analysis of time-series mRNA and microRNA profiles uncovered that expression of miR-26b was down regulated, and its target activating transcription factor 2 (ATF2) mRNA was up regulated in γ-irradiated H1299 cells. IR in miR-26b overexpressed H1299 cells could not induce expression of ATF2. When c-Jun N-terminal kinase activity was inhibited using SP600125, expression of miR-26b was induced following γ-irradiation in H1299 cells. From these results, we concluded that IR-induced up-regulation of ATF2 was coordinately enhanced by suppression of miR-26b in lung cancer cells, which may enhance the effect of IR in the MAPK signaling pathway.

ATM protects against oxidative stress induced by oxidized low-density lipoprotein

Chronic oxidative stress is involved in the pathogenesis of multiple inflammatory diseases, including cardiovascular disease and atherosclerosis. The rare autosomal recessive disorder Ataxia-telangiectasia (A-T) is characterized by progressive cerebellar ataxia secondary to Purkinje cell death, immunodeficiency, and increased cancer incidence. ATM, the protein mutated in A-T, plays a key role in cellular DNA-damage responses. A-T cells show poor cellular anti-oxidant defences and increased oxidant sensitivity compared to normal cells, and ATM functions, in part, as an oxidative stress sensor. The oxidation of low-density lipoprotein (oxLDL) and its uptake by macrophages is an initiating step in the development of atherosclerosis. We demonstrate that oxLDL activates ATM and downstream p21 expression in normal fibroblasts and endothelial cells. In ATM-deficient fibroblasts oxLDL induces DNA double-strand breaks, micronuclei formation and causes chromosome breaks. Furthermore, oxLDL decreases cell viability and inhibits colony formation in A-T fibroblasts more effectively as compared to normal controls. Formation of oxLDL-induced reactive oxygen species is significantly higher in A-T, than normal fibroblasts. Last, pre-treatment of cells with ammonium pyrrolidine dithiocarbamate, a potent antioxidant and inhibitor of transcription factor nuclear factor κB, reduces oxLDL-induced reactive oxygen species formation. Our data indicates that ATM functions in the defence against oxLDL-mediated cytotoxicity.

Evidence of p38γ and p38δ involvement in cell transformation processes

The p38 mitogen-activated protein kinase (p38MAPK) signal transduction pathway is an important regulator of cell processes, whose deregulation leads to the development and progression of cancer. Defining the role of each p38MAPK family member in these processes has been difficult. To date, most studies of the p38MAPK pathways focused on function of the p38α isoform, which is widely considered to negatively regulate malignant transformation; nonetheless, few reports address the p38γ and p38δ isoforms. Here, we used embryonic fibroblasts derived from mice lacking p38γ or p38δ and show evidence that these isoforms participate in several processes involved in malignant transformation. We observed that lack of either p38γ or p38δ increased cell migration and metalloproteinase-2 secretion, whereas only p38δ deficiency impaired cell contact inhibition. In addition, lack of p38γ in K-Ras-transformed fibroblasts led to increased cell proliferation as well as tumorigenesis both in vitro and in vivo. Our results indicate that p38γ and p38δ have a role in the suppression of tumor development.

Beyond ATM: the protein kinase landscape of the DNA damage response

The DNA of all organisms is constantly subjected to damaging agents, both exogenous and endogenous. One extremely harmful lesion is the double-strand break (DSB), which activates a massive signaling network - the DNA damage response (DDR). The chief activator of the DSB response is the ATM protein kinase, which phosphorylates numerous key players in its various branches. Recent phosphoproteomic screens have extended the scope of damage-induced phosphorylations beyond the direct ATM substrates. We review the evidence for the involvement of numerous other protein kinases in the DDR, obtained from documentation of specific pathways as well as high-throughput screens. The emerging picture of the protein phosphorylation landscape in the DDR broadens the current view on the role of this protein modification in the maintenance of genomic stability. Extensive cross-talk between many of these protein kinases forms an interlaced signaling network that spans numerous cellular processes. Versatile protein kinases in this network affect pathways that are different from those they have been identified with to date. The DDR appears to be one of the most extensive signaling responses to cellular stimuli.

Phosphorylation and cytoplasmic localization of MAPK p38 during apoptosis signaling in bone marrow granulocytes of mice irradiated in vivo and the role of amifostine in reducing these effects

We studied p38 phosphorylation and its intracellular localization during p53 and Puma (a p53 upregulated modulator of apoptosis) apoptotic signaling pathway in bone marrow granulocytes in mice irradiated in vivo and the role of the radioprotector amifostine in ameliorating these responses. Sixty-four C57BL mice were randomly assigned in two non-irradiated (Ami-/rad- and Ami+/rad-) and two irradiated (Ami-/rad+ and Ami+/rad+) groups. Animals received 400mg/kg of amifostine i.p. 30 min prior to a single whole body radiation dose of 7Gy. The experiments were performed using immunohistochemistry for caspase-3, cleaved caspase-3, p53, p-p53 (Ser 15), Puma, p38 and p-p38 (Thr 180/Tyr 182) protein expression. In addition transmission electron microscopy was used for ultrastructural characterization of apoptosis. Data showed that: (i) amifostine significantly reduced the number of apoptotic cells, (ii) p-p53 and Puma proteins were strongly immunostained in granulocytes after irradiation (Ami-/rad+), (iii) amifostine decreased the immunostaining of the proteins (Ami+/rad+), (iv) p38 was immunolocalized in physiological conditions in the nucleus and cytoplasm of granulocytes and neither radiation nor amifostine changed the protein immunostaining or its subcellular distribution, but influenced its activation, (v) radiation-induced p38 phosphorylation and its cytoplasmic accumulation during apoptosis signaling in granulocytes after whole body high radiation dose and amifostine markedly reduced these effects.

The P38alpha and P38delta MAP kinases may be gene therapy targets in the future treatment of severe burns

Microvascular barrier damage, induced by thermal injury, imposes life-threatening problems owing to the pathophysiological consequences of plasma loss and impaired perfusion that finally may lead to multiple organ failure. The aim of the present study was to define the signaling role of selected mitogen-activated protein kinases (MAPKs) in general vessel hyperpermeability caused by burns and to look for a potential gene therapy. Rearrangement of cytoskeletons and cell tight junctions were evaluated by phalloidin labeling of actin and immunocytochemical demonstration of the ZO-1 protein, whereas blood vessel permeability was evaluated by a fluorescence ratio technique. The p38 MAPK inhibitor SB203580 largely blocked burn serum-induced stress-fiber formation and tight-junction damage. Using the adenoviral approach to transfect dominant negative forms of p38 MAPKs, we found that p38alpha and p38delta had similar effects. The in vivo part of the study showed that transfection of these two constructs significantly lowered general venular hyperpermeability and enhanced the survival of burned animals. Because the p38 MAPK pathway seems to play a crucial role in burn-induced vascular hyperpermeability, general transfection with p38 MAP dominant negative constructs might become a new therapeutic method to block burn-induced plasma leakage.

Nek10 mediates G2/M cell cycle arrest and MEK autoactivation in response to UV irradiation

Appropriate cell cycle checkpoint control is essential for the maintenance of cell and organismal homeostasis. Members of the Nek (NIMA-related kinase) family of serine/threonine protein kinases have been implicated in the regulation of various aspects of the cell cycle. We explored the cellular functions of Nek10, a novel member of the Nek family, and demonstrate a role for Nek10 in the cellular UV response. Nek10 was required for the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling upon UV irradiation but not in response to mitogens, such as epidermal growth factor stimulation. Nek10 physically associated with Raf-1 and MEK1 in a Raf-1-dependent manner, and the formation of this complex was necessary for Nek10-mediated MEK1 activation. Nek10 did not affect the kinase activity of Raf-1 but instead promoted the autophosphorylation-dependent activation of MEK1. The appropriate maintenance of the G(2)/M checkpoint following UV irradiation required Nek10 expression and ERK1/2 activation. Taken together, our results uncover a role for Nek10 in the cellular response to UV irradiation.

p38γ regulates UV-induced checkpoint signaling and repair of UV-induced DNA damage

In eukaryotic cells, DNA damage triggers activation of checkpoint signaling pathways that coordinate cell cycle arrest and repair of damaged DNA. These DNA damage responses serve to maintain genome stability and prevent accumulation of genetic mutations and development of cancer. The p38 MAPK was previously implicated in cellular responses to several types of DNA damage. However, the role of each of the four p38 isoforms and the mechanism for their involvement in DNA damage responses remained poorly understood. In this study, we demonstrate that p38γ, but not the other p38 isoforms, contributes to the survival of UV-treated cells. Deletion of p38γ sensitizes cells to UV exposure, accompanied by prolonged S phase cell cycle arrest and increased rate of apoptosis. Further investigation reveal that p38γ is essential for the optimal activation of the checkpoint signaling caused by UV, and for the efficient repair of UV-induced DNA damage. These findings have established a novel role of p38γ in UV-induced DNA damage responses, and suggested that p38γ contributes to the ability of cells to cope with UV exposure by regulating the checkpoint signaling pathways and the repair of damaged DNA.

Effects of irradiation on tumor cell survival, invasion and angiogenesis

Ionizing irradiation is a widely applied therapeutic method for the majority of solid malignant neoplasms, including brain tumors where, depending on localization, this might often be the only feasible primary intervention.Without doubt, it has been proved to be a fundamental tool available in the battlefield against cancer, offering a clear survival benefit in most cases. However, numerous studies have associated tumor irradiation with enhanced aggressive phenotype of the remaining cancer cells. A cell population manages to survive after the exposure, either because it receives sublethal doses and/or because it successfully utilizes the repair mechanisms. The biology of irradiated cells is altered leading to up-regulation of genes that favor cell survival, invasion and angiogenesis. In addition, hypoxia within the tumor mass limits the cytotoxicity of irradiation, whereas irradiation itself may worsen hypoxic conditions, which also contribute to the generation of resistant cells. Activation of cell surface receptors, such as the epidermal growth factor receptor, utilization of signaling pathways, and over-expression of cytokines, proteases and growth factors, for example the matrix metalloproteinases and vascular endothelial growth factor, protect tumor and non-tumor cells from apoptosis, increase their ability to invade to adjacent or distant areas, and trigger angiogenesis. This review will try to unfold the various molecular events and interactions that control tumor cell survival, invasion and angiogenesis and which are elicited or influenced by irradiation of the tumor mass, and to emphasize the importance of combining irradiation therapy with molecular targeting.

Cdc20 proteolysis requires p38 MAPK signaling and Cdh1-independent APC/C ubiquitination during spindle assembly checkpoint activation by cadmium

Cdc20, an activator of the anaphase promoting complex/cyclosome (APC/C) ubiquitin ligase, initiates the destruction of key mitotic regulators to facilitate mitosis, while it is negatively regulated by the spindle assembly checkpoint (SAC) to prevent premature anaphase entry. Activation of the p38 mitogen-activated protein kinase could contribute to mitotic arrest, but the underlying mechanism is unknown. Here we report a novel pathway in which the p38 signaling triggers Cdc20 destruction under SAC elicited by cadmium, a human carcinogen. We found that the cadmium-induced prometaphase arrest was linked to decreased Cdc20 and accumulated cyclin A protein levels in human cells, whereas the activity of cyclin B1-Cdk1 was unaffected. The Cdc20 half-life was markedly shortened along with its ubiquitination and degradation via 26S proteasome in cadmium-treated asynchronous or G(2)-enriched cells. Depletion of APC3 markedly suppressed the cadmium-induced Cdc20 ubiquitination and proteolysis, while depletion of Cdh1, another activator of APC/C, did not. Intriguingly, blockage of p38 activity restored the Cdc20 levels for continuing mitosis under cadmium, while inhibition of JNK activity had no effect. The cadmium-induced Cdc20 proteolysis was also suppressed during transient depletion of p38alpha or stable expression a dominant negative form of p38. Inhibition of p38 abolished the induction of Mad2-Cdc20-APC3 complex by cadmium. Moreover, forced expression of MKK6-p38 signaling could promote Cdc20 degradation in a Cdh1-independent APC/C pathway. In summary, accelerated ubiquitination and proteolysis of Cdc20 is essential for prometaphase arrest that is mediated via the p38 signaling during SAC activation.

Human cell toxicogenomic analysis of bromoacetic acid: a regulated drinking water disinfection by-product

The disinfection of drinking water is a major achievement in protecting the public health. However, current disinfection methods also generate disinfection by-products (DBPs). Many DBPs are cytotoxic, genotoxic, teratogenic, and carcinogenic and represent an important class of environmentally hazardous chemicals that may carry long-term human health implications. The objective of this research was to integrate in vitro toxicology with focused toxicogenomic analysis of the regulated DBP, bromoacetic acid (BAA) and to evaluate modulation of gene expression involved in DNA damage/repair and toxic responses, with nontransformed human cells. We generated transcriptome profiles for 168 genes with 30 min and 4 hr exposure times that did not induce acute cytotoxicity. Using qRT-PCR gene arrays, the levels of 25 transcripts were modulated to a statistically significant degree in response to a 30 min treatment with BAA (16 transcripts upregulated and nine downregulated). The largest changes were observed for RAD9A and BRCA1. The majority of the altered transcript profiles are genes involved in DNA repair, especially the repair of double strand DNA breaks, and in cell cycle regulation. With 4 hr of treatment the expression of 28 genes was modulated (12 upregulated and 16 downregulated); the largest fold changes were in HMOX1 and FMO1. This work represents the first nontransformed human cell toxicogenomic study with a regulated drinking water disinfection by-product. These data implicate double strand DNA breaks as a feature of BAA exposure. Future toxicogenomic studies of DBPs will further strengthen our limited knowledge in this growing area of drinking water research.

p38 Mitogen-activated protein kinase signalling regulates vascular inflammation and epithelial barrier dysfunction in an experimental model of radiation-induced colitis

BACKGROUND

: Microvascular injury and epithelial barrier dysfunction are rate-limiting aspects in radiation enteropathy. This study examined the role of p38 mitogen-activated protein kinase (p38 MAPK) signalling in radiation-induced colitis in an experimental model.

METHODS

: The p38 MAPK inhibitor SB239063 was administered to mice immediately before exposure to 20 Gy radiation. Leucocyte- and platelet-endothelium interactions in the colonic microcirculation were assessed by intravital microscopy. Levels of myeloperoxidase (MPO) and CXC chemokines (macrophage inflammatory protein (MIP) 2 and cytokine-induced neutrophil chemoattractant (KC)), and albumin leakage were quantified 16 h after irradiation.

RESULTS

: Irradiation induced an increase in leucocyte and platelet recruitment, MPO activity, CXC chemokine levels and intestinal leakage. Inhibition of p38 MAPK by SB239063 decreased radiation-induced leucocyte and platelet recruitment (leucocyte rolling and adhesion by 70 and 90 per cent, both P < 0.001; that of platelets by 70 and 74 per cent, both P < 0.001). It also reduced radiation-provoked increases in colonic MPO activity by 88 per cent (P < 0.001), formation of MIP-2 and KC by 72 and 74 per cent respectively (P = 0.003 and P < 0.001), and intestinal leakage by 81 per cent (P < 0.001).

CONCLUSION

: p38 MAPK is an important signalling pathway in radiation-induced colitis.

Stepping up melanocytes to the challenge of UV exposure

Exposure to solar ultraviolet radiation (UV) is the main etiological factor for skin cancer, including melanoma. Cutaneous pigmentation, particularly eumelanin, afforded by melanocytes is the main photoprotective mechanism, as it prevents UV-induced DNA damage in the epidermis. Therefore, maintaining genomic stability of melanocytes is crucial for prevention of melanoma, as well as keratinocyte-derived basal and squamous cell carcinoma. A critical independent factor for preventing melanoma is DNA repair capacity. The response of melanocytes to UV is mediated mainly by a network of paracrine factors that not only activate melanogenesis, but also DNA repair, anti-oxidant, and survival pathways that are pivotal for maintenance of genomic stability and prevention of malignant transformation or apoptosis. However, little is known about the stress response of melanocytes to UV and the regulation of DNA repair pathways in melanocytes. Unraveling these mechanisms might lead to strategies to prevent melanoma, as well as non-melanoma skin cancer.

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.

Enzastaurin induces H2AX phosphorylation to regulate apoptosis via MAPK signalling in malignant glioma cells

Enzastaurin is an acyclic bisindolylmaleimide derived from staurosporine that acts as an ATP competitor, and interferes with the activity of protein kinase C (PKC) isoforms. Our previous studies have shown that clinically achievable concentrations of this agent induce apoptosis in many glioma cell lines. Our goal in this study was to expand on the previous results and to determine the signalling mechanisms responsible for enzastaurin-induced inhibition of cell growth and induction of apoptosis. To address these issues, cell cycle progression following enzastaurin treatment was analysed by fluorescence-activated cell sorting (FACS) in parallel with analyses of growth and apoptosis signalling pathways. Enzastaurin treatment activated H2AX and Chk2 phosphorylation, and enhanced phosphorylation of mitogen-activated protein kinase (MAPK) family kinases. Inhibition of MAP kinases by chemical inhibitors reduced H2AX and Chk2 phosphorylation and decreased apoptosis induced by enzastaurin. These data call attention to a novel signalling pathway (MAPK/H2AX) to regulate apoptosis in malignant glioma cells.

Ionizing radiation induces cellular senescence of articular chondrocytes via negative regulation of SIRT1 by p38 kinase

Radiotherapy is increasingly used in the treatment of joint diseases, but limited information is available on the effects of radiation on cartilage. Here, we characterize the molecular mechanisms leading to cellular senescence in irradiated primary cultured articular chondrocytes. Ionizing radiation (IR) causes activation of ERK, in turn generating intracellular reactive oxygen species (ROS) with induction of senescence-associated beta-galactosidase (SA-beta-gal) activity. ROS activate p38 kinase, which further promotes ROS generation, forming a positive feedback loop to sustain ROS-p38 kinase signaling. The ROS inhibitors, nordihydroguaiaretic acid and GSH, suppress phosphorylation of p38 and cell numbers positive for SA-beta-gal following irradiation. Moreover, inhibition of the ERK and p38 kinase pathways leads to blockage of IR-induced SA-beta-gal activity via reduction of ROS generation. Although JNK is activated by ROS, this pathway is not associated with cellular senescence of chondrocytes. Interestingly, IR triggers down-regulation of SIRT1 protein expression but not the transcript level, indicative of post-transcriptional cleavage of the protein. SIRT1 degradation is markedly blocked by SB203589 or MG132 after IR treatment, suggesting that cleavage occurs as a result of binding with p38 kinase, followed by processing via the 26 S proteasomal degradation pathway. Overexpression or activation of SIRT1 significantly reduces the IR-induced senescence phenotype, whereas inhibition of SIRT1 activity induces senescence. Based on these findings, we propose that IR induces cellular senescence of articular chondrocytes by negative post-translational regulation of SIRT1 via ROS-dependent p38 kinase activation.

Signal integration by JNK and p38 MAPK pathways in cancer development

Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) family members function in a cell context-specific and cell type-specific manner to integrate signals that affect proliferation, differentiation, survival and migration. Consistent with the importance of these events in tumorigenesis, JNK and p38 MAPK signalling is associated with cancers in humans and mice. Studies in mouse models have been essential to better understand how these MAPKs control cancer development, and these models are expected to provide new strategies for the design of improved therapeutic approaches. In this Review we highlight the recent progress made in defining the functions of the JNK and p38 MAPK pathways in different cancers.

Signal integration by JNK and p38 MAPK pathways in cancer development

Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) family members function in a cell context-specific and cell type-specific manner to integrate signals that affect proliferation, differentiation, survival and migration. Consistent with the importance of these events in tumorigenesis, JNK and p38 MAPK signalling is associated with cancers in humans and mice. Studies in mouse models have been essential to better understand how these MAPKs control cancer development, and these models are expected to provide new strategies for the design of improved therapeutic approaches. In this Review we highlight the recent progress made in defining the functions of the JNK and p38 MAPK pathways in different cancers.

Platelet-derived growth factor-receptor alpha strongly inhibits melanoma growth in vitro and in vivo

Cutaneous melanoma is the most aggressive skin cancer; it is highly metastatic and responds poorly to current therapies. The expression of platelet-derived growth factor receptors (PDGF-Rs) is reported to be reduced in metastatic melanoma compared with benign nevi or normal skin; we then hypothesized that PDGF-Ralpha may control growth of melanoma cells. We show here that melanoma cells overexpressing PDGF-Ralpha respond to serum with a significantly lower proliferation compared with that of controls. Apoptosis, cell cycle arrest, pRb dephosphorylation, and DNA synthesis inhibition were also observed in cells overexpressing PDGF-Ralpha. Proliferation was rescued by PDGF-Ralpha inhibitors, allowing to exclude nonspecific toxic effects and indicating that PDGF-Ralpha mediates autocrine antiproliferation signals in melanoma cells. Accordingly, PDGF-Ralpha was found to mediate staurosporine cytotoxicity. A protein array-based analysis of the mitogen-activated protein kinase pathway revealed that melanoma cells overexpressing PDGF-Ralpha show a strong reduction of c-Jun phosphorylated in serine 63 and of protein phosphatase 2A/Balpha and a marked increase of p38gamma, mitogen-activated protein kinase kinase 3, and signal regulatory protein alpha1 protein expression. In a mouse model of primary melanoma growth, infection with the Ad-vector overexpressing PDGF-Ralpha reached a significant 70% inhibition of primary melanoma growth (P < .001) and a similar inhibition of tumor angiogenesis. All together, these data demonstrate that PDGF-Ralpha strongly impairs melanoma growth likely through autocrine mechanisms and indicate a novel endogenous mechanism involved in melanoma control.

p38 Mitogen-activated protein kinase- and HuR-dependent stabilization of p21(Cip1) mRNA mediates the G(1)/S checkpoint

Activation of p38 mitogen-activated protein kinase (MAPK) plays an important role in the G(2)/M cell cycle arrest induced by DNA damage, but little is known about the role of this signaling pathway in the G(1)/S transition. Upregulation of the cyclin-dependent kinase inhibitor p21(Cip1) is thought to make a major contribution to the G(1)/S cell cycle arrest induced by gamma radiation. We show here that inhibition of p38 MAPK impairs p21(Cip1) accumulation and, as a result, the ability of cells to arrest in G(1) in response to gamma radiation. We found that p38 MAPK induces p21(Cip1) mRNA stabilization, without affecting its transcription or the stability of the protein. In particular, p38 MAPK phosphorylates the mRNA binding protein HuR on Thr118, which results in cytoplasmic accumulation of HuR and its enhanced binding to the p21(Cip1) mRNA. Our findings help to understand the emerging role of p38 MAPK in the cellular responses to DNA damage and reveal the existence of p53-independent networks that cooperate in modulating p21(Cip1) levels at the G(1)/S checkpoint.

ERM protein moesin is phosphorylated by advanced glycation end products and modulates endothelial permeability

Advanced glycation end products (AGEs) accumulated in different pathological conditions have the potent capacity to alter cellular properties that include endothelial structural and functional regulations. The disruption of endothelial barrier integrity may contribute to AGE-induced microangiopathy and macrovasculopathy. Previous studies have shown that AGEs induced the rearrangement of actin and subsequent hyperpermeability in endothelial cells (ECs). However, the mechanisms involved in this AGE-evoked EC malfunction are not well understood. This study directly evaluated the involvement of moesin phosphorylation in AGE-induced alterations and the effects of the RhoA and p38 MAPK pathways on this process. Using immortalized human dermal microvascular ECs (HMVECs), we first confirmed that the ezrin/radixin/moesin (ERM) protein moesin is required in AGE-induced F-actin rearrangement and hyperpermeability responses in ECs by knockdown of moesin protein expression with small interfering RNA. We then detected AGE-induced moesin phosphorylation by Western blot analysis. The mechanisms involved in moesin phosphorylation were analyzed by blocking AGE receptor binding and inhibiting Rho and MAPK pathways. AGE-treated HMVECs exhibited time- and dose-dependent increases in the Thr(558) phosphorylation of moesin. The increased moesin phosphorylation was attenuated by preadministrations of AGE receptor antibody, Rho kinase (ROCK), or p38 inhibitor. Suppression of p38 activation via the expression of dominant negative mutants with Ad.MKK6b or Ad.p38alpha also decreased moesin phosphorylation. The activation of the p38 pathway by transfection of HMVECs with an adenoviral construct of dominant active MKK6b resulted in moesin phosphorylation. These results suggest a critical role of moesin phosphorylation in AGE-induced EC functional and morphological regulations. Activation of the ROCK and p38 pathways is required in moesin phosphorylation.

p38alpha and p38gamma mediate oncogenic ras-induced senescence through differential mechanisms

Oncogene-induced senescence is a tumor-suppressive defense mechanism triggered upon activation of certain oncogenes in normal cells. Recently, the senescence response to oncogene activation has been shown to act as a bona fide barrier to cancer development in vivo. Multiple previous studies have implicated the importance of the p38 MAPK pathway in oncogene-induced senescence. However, the contribution of each of the four p38 isoforms (encoded by different genes) to senescence induction is unclear. In the current study, we demonstrated that p38alpha and p38gamma, but not p38beta, play an essential role in oncogenic ras-induced senescence. Both p38alpha and p38gamma are expressed in primary human fibroblasts and are activated upon transduction of oncogenic ras. Small hairpin RNA-mediated silencing of p38alpha or p38gamma expression abrogated ras-induced senescence, whereas constitutive activation of p38alpha and p38gamma caused premature senescence. Furthermore, upon activation by oncogenic ras, p38gamma stimulated the transcriptional activity of p53 by phosphorylating p53 at Ser(33), suggesting that the ability of p38gamma to mediate senescence is at least partly achieved through p53. However, p38alpha contributed to ras-inducted senescence via a p53-indepdendent mechanism in cells by mediating ras-induced expression of p16(INK4A), another key senescence effector. These findings have identified p38alpha and p38gamma as essential components of the signaling pathway that regulates the tumor-suppressing senescence response, providing insights into the molecular mechanisms underlying the differential involvement of the p38 isoforms in senescence induction.

c-Src-p38 mitogen-activated protein kinase signaling is required for Akt activation in response to ionizing radiation

The Akt and mitogen-activated protein kinase (MAPK) pathways have been implicated in tumor cell survival and contribute to radiation resistance. However, the molecular basis for link between MAPK and Akt in cell survival response to radiation is unclear. Here, we show that c-Src-Rac1-p38 MAPK pathway signals Akt activation and cell survival in response to radiation. Ionizing radiation triggered Thr(308) and Ser(473) phosphorylation of Akt. Exposure of cells to radiation also induced p38 MAPK and c-Jun NH(2)-terminal kinase activations. Inhibition of c-Jun NH(2)-terminal kinase suppressed radiation-induced cell death, whereas inhibition of p38 MAPK effectively increased sensitivity to radiation. Interestingly, inhibition of p38 MAPK completely attenuated radiation-induced Ser(473) phosphorylation of Akt but did not affect Thr(308) phosphorylation. Conversely, overexpression of p38 MAPK enhanced Ser(473) phosphorylation of Akt in response to radiation. In addition, inhibition of p38 MAPK failed to alter phosphoinositide 3-kinase and phosphoinositide-dependent protein kinase activities. Ectopic expression of RacN17, dominant-negative form of Rac1, inhibited p38 MAPK activation and Ser(473) phosphorylation of Akt. Following exposure to radiation, c-Src was selectively activated among Src family tyrosine kinases. Inhibition of c-Src attenuated Rac1 and p38 MAPK activations and Ser(473) phosphorylation of Akt. Our results support the notion that the c-Src-Rac1-p38 MAPK pathway is required for activation of Akt in response to radiation and plays a cytoprotective role against radiation in human cancer cells.

Differential activation of mitogen-activated protein kinases following high and low LET radiation in murine macrophage cell line

Mitogen-activated protein kinases have been shown to respond to various stimuli including cytokines, mitogens and gamma irradiation, leading to cell proliferation, differentiation, or death. The duration of their activation determines the specificity of response to each stimulus in various cells. In this study, the crucial intracellular kinases, ERK, JNK, and p38 kinase involved in cell survival, death, or damage and repair were examined for their activity in RAW 264.7 cells at various time points after irradiation with 2 Gy doses of proton ions or X-rays. This is the first report that shows that the MAPK signaling induced after heavy ion or X-ray exposure is not the same. Unlike gamma irradiation, there was prolonged but marginal activation of prosurvival ERK pathway and significant activation of proapoptotic p38 pathway in response to high LET radiation.

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.

All-trans-retinoic acid ameliorates carbon tetrachloride-induced liver fibrosis in mice through modulating cytokine production

BACKGROUND/AIMS

Liver fibrosis with any aetiology, induced by the transdifferentiation and proliferation of hepatic stellate cells (HSCs) to produce collagen, is characterized by progressive worsening in liver function, leading to a high incidence of death. We have recently reported that all-trans-retinoic acid (ATRA) suppresses the transdifferentiation and proliferation of lung fibroblasts and prevents radiation- or bleomycin-induced lung fibrosis.

METHODS

We examined the impact of ATRA on carbon tetrachloride (CCl(4))-induced liver fibrosis. We performed histological examinations and quantitative measurements of transforming growth factor (TGF)-beta1 and interleukin (IL)-6 in CCl(4)-treated mouse liver tissues with or without the administration of ATRA, and investigated the effect of ATRA on the production of the cytokines in quiescent and activated HSCs.

RESULTS

CCl(4)-induced liver fibrosis was attenuated in histology by intraperitoneal administration of ATRA, and the overall survival rate at 12 weeks was 26.5% without ATRA (n=25), whereas it was 75.0% (n=24) in the treatment group (P=0.0187). In vitro studies disclosed that the administration of ATRA reduced (i) the production of TGF-beta1, IL-6 and collagen from HSCs, (ii) TGF-beta-dependent transdifferentiation of the cells and IL-6-dependent cell proliferation and (iii) the activities of nuclear factor-kappaB p65 and p38mitogen-activated protein kinase, which stimulate the production of TGF-beta1 and IL-6, which could be the mechanism underlying the preventive effect of ATRA on liver fibrosis.

CONCLUSIONS

Our findings indicate that ATRA ameliorates liver fibrosis. As the oral administration of the drug results in good compliance, ATRA could be a novel approach in the treatment of liver fibrosis.

DCUN1D3, a novel UVC-responsive gene that is involved in cell cycle progression and cell growth

DCUN1D3 (DCN1, defective in cullin neddylation 1, domain containing 3) was found during the process of high throughput screening of novel human genes associated with serum response element (SRE) pathway activation. The DCUN1D3 gene is highly conserved among vertebrates. Human DCUN1D3 complementary DNA (cDNA) encodes 304 amino acids with an apparent molecular mass of 34 kDa. However, there has been no report about the function of DCUN1D3. This study detected that DCUN1D3 was broadly expressed in several tumor tissues and cultured cell lines; however, UVC irradiation of different doses significantly increased DCUN1D3 expression level in these cancer cell lines. Over-expression of the DCUN1D3 inhibits cell growth in HeLa. When the DCUN1D3 gene was silenced by siRNA in UVC-treated HeLa, the cell cycle in S phase was remarkably blocked; furthermore, the UVC-induced cell death was inhibited. In addition, DCUN1D3 localized mainly in the cytoplasm and perinuclear, but after UVC treatment, the DCUN1D3 gradually entered the nucleus. All the results above indicate that DCUN1D3 is a novel UVC-response gene involved in cell cycle regulation and cell survival.

Novel synthetic triterpenoid methyl 25-hydroxy-3-oxoolean-12-en-28-oate induces apoptosis through JNK and p38 MAPK pathways in human breast adenocarcinoma MCF-7 cells

Breast cancer is the most common neoplasm in women and is the leading cause of cancer-related death for women. Therefore, new agents targeting prevention and treatment of breast cancer are urgently needed. The present study first investigates that a novel triterpenoid Methyl 25-Hydroxy-3-oxoolean-12-en-28-oate (AMR-Me) derived from 25-Hydroxy-3-oxoolean-12-en-28-oic acid (AMR) is a potent inhibitor of cell growth by inducing human breast cancer MCF-7 cells to undergo apoptosis. AMR-Me induced DNA fragmentation and PARP degradation which were preceded by changing Bax/Bcl-2 ratios, cytochrome c release, and subsequent induction of pro-caspase-9 and -7 processing in breast carcinoma MCF-7 cells, but it did not act on Fas/Fas ligand pathways and the activation of caspase-8, suggesting AMR-Me triggered the mitochondrial apoptotic pathway. The general caspase blocking peptide VAD partially blocked AMR-Me induced apoptosis. AMR-Me stimulated p38 mitogen-activated protein kinase and c-Jun NH2-terminal kinase (JNK), but not extracellular signal-regulated kinase activation during apoptosis. SP600125, a specific inhibitor for JNK and SB203580, a p38 MAPK-specific inhibitor suppressed AMR-Me induced apoptosis indicating that activation of JNK and p38 MAPKs involved in the mitochondrial activation-mediated cell death pathway. Our results suggest that AMR-Me can utilize two different MAPK signaling pathways for amplifying the apoptosis cascade, is critical for both our understanding of cell death events and development of cancer preventive/therapeutic agents.

Gamma-irradiation-induced DNA damage checkpoint activation involves feedback regulation between extracellular signal-regulated kinase 1/2 and BRCA1

Previous studies from our laboratory have shown that the activation of G(2)-M checkpoint after exposure of MCF-7 breast cancer cells to gamma-irradiation (IR) is dependent on the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. Studies presented in this report indicate that IR exposure of MCF-7 cells is associated with a marked increase in expression of breast cancer 1 (BRCA1) tumor suppressor, an effect that requires ERK1/2 activation and involves posttranscriptional control mechanisms. Furthermore, reciprocal coimmunoprecipitation, as well as colocalization studies, indicate an interaction between BRCA1 and ERK1/2 in both nonirradiated and irradiated cells. Studies using short hairpin RNA targeting BRCA1 show that BRCA1 expression is necessary for IR-induced G(2)-M cell cycle arrest, as well as ERK1/2 activation in MCF-7 cells. Although BRCA1 expression is not required for IR-induced phosphorylation of ataxia telangiectasia mutated (ATM)-Ser1981, it is required for ATM-mediated downstream signaling events, including IR-induced phosphorylation of Chk2-Thr68 and p53-Ser20. Moreover, BRCA1 expression is also required for IR-induced ATM and rad3 related activation and Chk1 phosphorylation in MCF-7 cells. These results implicate an important interaction between BRCA1 and ERK1/2 in the regulation of cellular response after IR-induced DNA damage in MCF-7 cells.

Anti-tumor effect of beta-elemene in glioblastoma cells depends on p38 MAPK activation

beta-Elemene, a natural plant drug extracted from Curcuma wenyujin, has been used as an antitumor drug for different tumors, including glioblastoma. However, the mechanism of its anti-tumor effect is largely unknown. Here we report that anti-proliferation of glioblastoma cells induced by beta-elemene was dependent on p38 MAPK activation. Treatment of glioblastoma cell lines with beta-elemene, led to phosphorylation of p38 MAPK, cell-cycle arrest in G0/G1 phase and inhibition of proliferation of these cells. Inhibition of p38 MAPK reversed beta-elemene-mediated anti-proliferation effect. Furthermore, the growth of glioblastoma cell-transplanted tumors in nude mice was inhibited by intraperitoneal injection of beta-elemene. Taken together, our findings indicate that activation of p38 MAPK is critical for the anti-proliferation effect of beta-elemene and that p38 MAPK might be a putative pharmacological target for glioblastoma therapy.

Critical involvement of the ATM-dependent DNA damage response in the apoptotic demise of HIV-1-elicited syncytia

DNA damage can activate the oncosuppressor protein ataxia telangiectasia mutated (ATM), which phosphorylates the histone H2AX within characteristic DNA damage foci. Here, we show that ATM undergoes an activating phosphorylation in syncytia elicited by the envelope glycoprotein complex (Env) of human immunodeficiency virus-1 (HIV-1) in vitro. This was accompanied by aggregation of ATM in discrete nuclear foci that also contained phospho-histone H2AX. DNA damage foci containing phosphorylated ATM and H2AX were detectable in syncytia present in the brain or lymph nodes from patients with HIV-1 infection, as well as in a fraction of blood leukocytes, correlating with viral status. Knockdown of ATM or of its obligate activating factor NBS1 (Nijmegen breakage syndrome 1 protein), as well as pharmacological inhibition of ATM with KU-55933, inhibited H2AX phosphorylation and prevented Env-elicited syncytia from undergoing apoptosis. ATM was found indispensable for the activation of MAP kinase p38, which catalyzes the activating phosphorylation of p53 on serine 46, thereby causing p53 dependent apoptosis. Both wild type HIV-1 and an HIV-1 mutant lacking integrase activity induced syncytial apoptosis, which could be suppressed by inhibiting ATM. HIV-1-infected T lymphoblasts from patients with inactivating ATM or NBS1 mutations also exhibited reduced syncytial apoptosis. Altogether these results indicate that apoptosis induced by a fusogenic HIV-1 Env follows a pro-apoptotic pathway involving the sequential activation of ATM, p38MAPK and p53.