Cdc2 phosphorylation of BAD links the cell cycle to the cell death machinery

Methyl jasmonate decreases membrane fluidity and induces apoptosis through tumor necrosis factor receptor 1 in breast cancer cells

In recent years, studies with plant compounds have shown both chemotherapeutic and chemopreventive properties. This study with plant stress hormones (jasmonates) showed growth inhibitory effects in breast cancer cells. cis-Jasmone and methyl jasmonate (MJ) inhibited the long-term proliferation of MDA-MB-435 and MCF-7 cells. Cell cycle analysis showed G0/G1 and S-phase arrest with increasing apoptotic population. Cellular signaling studies with MJ showed decreased membrane fluidity and activation of extrinsic and intrinsic apoptotic pathways. Specifically in extrinsic apoptotic pathway increased expression of TNF receptor 1, activation of mitogen-activated protein kinase and caspase-8 was observed. MJ also decreased the mitochondrial membrane potential and activated caspase-3 in breast cancer cells. In conclusion our results revealed novel-signaling mechanism of MJ in breast cancer cells, indicating that MJ could have potential applications for chemotherapeutic purposes.

Generation of an indestructible cyclin B1 by caspase-6-dependent cleavage during mitotic catastrophe

Overriding the G(2) DNA damage checkpoint permits precocious entry into mitosis that ultimately leads to mitotic catastrophe. Mitotic catastrophe is manifested by an unscheduled activation of CDK1, caspase activation and apoptotic cell death. We found that although cyclin B1 was required for mitotic catastrophe, it was cleaved into a approximately 35 kDa protein by a caspase-dependent mechanism during the process. Cyclin B1 cleavage occurred after Asp123 in the motif ILVD(123) downward arrow, and mutation of this motif attenuated the cleavage. Cleavage was abolished by a pan-caspase inhibitor as well as by specific inhibitors for the effector caspase-6 and the initiator caspase-8. Cleavage created a truncated cyclin B1 lacking part of the NH(2)-terminal regulatory domain that included the destruction box sequence. Although cleavage of cyclin B1 itself was not absolutely required for mitotic catastrophe, expression of the truncated product enhanced cell death. In support of this, ectopic expression of this truncated cyclin B1 was not only sufficient to induce mitotic block and apoptosis but also enhanced mitotic catastrophe induced by ionizing radiation and caffeine. These data underscore a possible linkage between mitotic and apoptotic functions by caspase-dependent processing of mitotic activators.

Cdk5 phosphorylates Cdh1 and modulates cyclin B1 stability in excitotoxicity

Anaphase-promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase that destabilizes cell cycle proteins, is activated by Cdh1 in post-mitotic neurons, where it regulates axonal growth, synaptic plasticity and survival. The APC/C-Cdh1 substrate, cyclin B1, has been found to accumulate in degenerating brain areas in Alzheimer's disease and stroke. This highlights the importance of elucidating cyclin B1 regulation by APC/C-Cdh1 in neurons under stress conditions relevant to neurological disease. Here, we report that stimulation of N-methyl-D-aspartate receptors (NMDARs) that occurs in neurodegenerative diseases promoted the accumulation of cyclin B1 in the nuclei of cortical neurons; this led the neurons to undergo apoptotic death. Moreover, we found that the Ser-40, Thr-121 and Ser-163 triple phosphorylation of Cdh1 by the cyclin-dependent kinase-5 (Cdk5)-p25 complex was necessary and sufficient for cyclin B1 stabilization and apoptotic death after NMDAR stimulation. These results reveal Cdh1 as a novel Cdk5 substrate that mediates cyclin B1 neuronal accumulation in excitotoxicity.

HDAC4 inhibits cell-cycle progression and protects neurons from cell death

HDAC4 is a Class II histone deacetylase (HDAC) that is highly expressed in the brain, but whose functional significance in the brain is not known. We show that forced expression of HDAC4 in cerebellar granule neurons protects them against low potassium-induced apoptosis. HDAC4 also protects HT22 neuroblastoma cells from death induced by oxidative stress. HDAC4-mediated neuroprotection does not require its HDAC catalytic domain and cannot be inhibited by chemical inhibitors of HDACs. Neuroprotection by HDAC4 also does not require the Raf-MEK-ERK or the PI-3 kinase-Akt signaling pathways and occurs despite the activation of c-jun, an event that is generally believed to condemn neurons to die. The protective action of HDAC4 occurs in the nucleus and is mediated by a region that contains the nuclear localization signal. HDAC4 inhibits the activity of cyclin-dependent kinase-1 (CDK1) and the progression of proliferating HEK293T and HT22 cells through the cell cycle. Mice-lacking HDAC4 have elevated CDK1 activity and display cerebellar abnormalities including a progressive loss of Purkinje neurons postnatally in posterior lobes. Surviving Purkinje neurons in these lobes have duplicated soma. Furthermore, large numbers of cells within these affected lobes incorporate BrdU, indicating cell-cycle progression. These abnormalities along with the ability of HDAC4 to inhibit CDK1 and cell-cycle progression in cultured cells suggest that neuroprotection by HDAC4 is mediated by preventing abortive cell-cycle progression.

Premature centromere division of the X chromosome in neurons in Alzheimer's disease

Premature centromere division (PCD) represents a loss of control over the sequential separation and segregation of chromosome centromeres. Although first described in aging women, PCD on the X chromosome (PCD,X) is markedly elevated in peripheral blood lymphocytes of individuals suffering from Alzheimer disease (AD). The present study evaluated PCD,X, using a fluorescent in situ hybridization method, in interphase nuclei of frontal cerebral cortex neurons from sporadic AD patients and age-matched controls. The average frequency of PCD,X in AD patients (8.60 +/- 1.20%) was almost three times higher (p < 0.01) than in the control group (2.96 +/- 1.20). However, consistent with previous studies, no mitotic cells were found in neurons in either AD or control brain, suggesting an intrinsic inability of post-mitotic neurons to divide. In view of the fact that it has been well-documented that neurons in AD can re-enter into the cell division cycle, the findings presented here of increased PCD advance the hypothesis that deregulation of the cell cycle may contribute to neuronal degeneration and subsequent cognitive deficits in AD.

A molecular study of pathways involved in the inhibition of cell proliferation in neuroblastoma B65 cells by the GSK-3 inhibitors lithium and SB-415286

Pharmacological GSK-3 inhibitors are potential drugs for the treatment of neurodegenerative diseases, cancer and diabetes. We examined the antiproliferative effects of two GSK-3 inhibitors, lithium and SB-415286, on B65 neuroblastoma cell line. Treatment of B65 cells with either drug administered separately caused a decrease in cell proliferation that was associated with G₂/M cell cycle arrest. Cell-cycle proteins such as cyclins D, E, A, cdk4 and cdk2 were up-regulated. Since lithium and SB-415286-induced G₂/M arrest we studied changes in the expression of proteins involved in this phase, specifically cyclin B, cdc2 and the phosphorylated form of this protein (tyr15-cdc2). Both drugs increased the expression of tyr15-cdc2, thus inhibiting mitosis. On the other hand, SB-415286 increased the expression of SIRT2, involved in the regulation of proliferation. Moreover, cell-cycle arrest mediated by SB-415286 was accompanied by apoptosis that was not prevented by 100 μM of zVAD-fmk (benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone), a pan-caspase inhibitor. Likewise, GSK-3 inhibitors did not affect the mitochondrial release of apoptosis inducing factor (AIF). We conclude that inhibitors of GSK-3 induced cell-cycle arrest, mediated by the phosphorylation of cdc2 and, in the case of SB-415286, SIRT2 expression, which induced apoptosis in a caspase-independent manner.

Apoptosis induced by ardipusilloside III through BAD dephosphorylation and cleavage in human glioblastoma U251MG cells

Ardipusilloside III is a saponin newly isolated from Ardisia pusilla A.DC. Since saponins have exhibited broad anti-cancer and pro-apoptotic activity, we investigated the ability of ardipusilloside III to induce apoptosis in human glioblastoma U251MG cells, as well as the involvement of apoptotic signaling pathways. Ardipusilloside III markedly suppressed proliferation of U251MG cells in a time- and dose-dependent manner (P < 0.05, IC50 = 8.2 microg/ml), but did not affect the growth of primary cultures of human astrocytes. Ardipusilloside III-treated U251MG cells underwent typical apoptotic changes. Exposure to a low dose of ardipusilloside III provoked G2/M-phase cell cycle arrest, which preceded apoptosis characterized by the appearance of cells with sub-G1 DNA content. However, a higher dose of ardipusilloside III induced apoptosis without first causing cell cycle arrest. In addition, ardipusilloside III exposure resulted in time-dependent BAD dephosphorylation and cleavage as well as activation of caspase-8 and caspase-3. Therefore, both the intrinsic pathway of apoptosis, mediated by BAD dephosphorylation and cleavage, and the extrinisic pathway of apoptosis, mediated by caspase-8 and caspase-3 activation, were involved in ardipusilloside III-induced apoptosis. These data suggest that ardipusilloside III is a reliable candidate for chemotherapeutic treatment of human glioblastomas, and should be investigated further.

Expansion and evolution of cell death programmes

Cell death has historically been subdivided into regulated and unregulated mechanisms. Apoptosis, a form of regulated cell death, reflects a cell's decision to die in response to cues and is executed by intrinsic cellular machinery. Unregulated cell death (often called necrosis) is caused by overwhelming stress that is incompatible with cell survival. Emerging evidence, however, suggests that these two processes do not adequately explain the various cell death mechanisms. Recent data point to the existence of multiple non-apoptotic, regulated cell death mechanisms, some of which overlap or are mutually exclusive with apoptosis. Here we examine how and why these different cell death programmes have evolved, with an eye towards new cytoprotective therapeutic opportunities.

Activation of FOXO1 by Cdk1 in cycling cells and postmitotic neurons

Activation of cyclin-dependent kinase 1 (Cdk1) has been linked to cell death of postmitotic neurons in brain development and disease. We found that Cdk1 phosphorylated the transcription factor FOXO1 at Ser249 in vitro and in vivo. The phosphorylation of FOXO1 at Ser249 disrupted FOXO1 binding with 14-3-3 proteins and thereby promoted the nuclear accumulation of FOXO1 and stimulated FOXO1-dependent transcription, leading to cell death in neurons. In proliferating cells, Cdk1 induced FOXO1 Ser249 phosphorylation at the G2/M phase of the cell cycle, resulting in FOXO1-dependent expression of the mitotic regulator Polo-like kinase (Plk). These findings define a conserved signaling link between Cdk1 and FOXO1 that may have a key role in diverse biological processes, including the degeneration of postmitotic neurons.

TGFbeta-Smad2 signaling regulates the Cdh1-APC/SnoN pathway of axonal morphogenesis

Axon growth is critical to the establishment of neuronal connectivity. The E3 ubiquitin ligase Cdh1-anaphase-promoting complex (Cdh1-APC) and its substrate the transcriptional modulator SnoN form a cell-intrinsic pathway that orchestrates axonal morphogenesis in the mammalian brain. How the Cdh1-APC/SnoN pathway is controlled in the nervous system remained unknown. Here, we report that the TGFbeta-regulated signaling protein Smad2 plays a key role in regulating the Cdh1-APC/SnoN pathway in neurons. We find that Smad2 is expressed in primary granule neurons of the developing rat cerebellar cortex. The Smad signaling pathway is basally activated in neurons. Endogenous Smad2 is phosphorylated, localized in the nucleus, and forms a physical complex with endogenous SnoN in granule neurons. Inhibition of Smad signaling by several distinct approaches, including genetic knock-down of Smad2, stimulates axonal growth. Biochemical evidence and genetic epistasis analyses reveal that Smad2 acts upstream of SnoN in a shared pathway with Cdh1-APC in the control of axonal growth. Remarkably, Smad2 knock-down also overrides the ability of adult rat myelin to inhibit axonal growth. Collectively, our findings define a novel function for Smad2 in regulation of the Cdh1-APC/SnoN cell-intrinsic pathway of axonal morphogenesis, and suggest that inhibition of Smad signaling may hold therapeutic potential in stimulating axonal growth after injury in the CNS.

Large scale hippocampal cellular distress may explain the behavioral consequences of repetitive traumatic experiences--a proteomic approach

Early life traumatic experiences are associated with psychopathology in adulthood. This may be due in part to the effects of trauma on hippocampal development and protein expression. The purpose of the study was to investigate the effects of early life trauma and adult re-stress on ventral hippocampal protein expression. Adolescent rats (n = 19) were subjected to a triple stressor on post-natal day 28 followed 7 days later by the first re-stress session and 25 days later (post-natal day 60 = adulthood) by the second re-stress session. Ventral hippocampi were collected on post-natal day 68 for protein expression determinations using protein arrays and 2D-gel electrophoresis with liquid chromatography tandem mass spectrometry. Compared to controls, traumatized animals showed an increase in Ca(2+) homeostatic proteins, dysregulated signaling pathways and energy metabolism enzymes, cytoskeletal protein changes, a decrease in neuroplasticity regulators, energy metabolism enzymes and an increase in apoptotic initiator proteins. These results indicate the extensive impact of trauma on adult brain development and behavior.

Phosphorylation-dependent interaction with 14-3-3 in the regulation of bad trafficking in retinal ganglion cells

PURPOSE

To focus on the proteomic analysis of 14-3-3 proteins and to determine their cellular localization and functional role during glaucomatous neurodegeneration.

METHODS

Complementary proteomic approaches were used to identify phosphorylated proteins in a chronic pressure-induced rat model of glaucoma. To detect interacting proteins, specific protein complexes were eluted using coimmunoprecipitation and recombinant protein-based affinity pull-down for subsequent mass spectrometric analysis. Western blot analysis was performed for validation of the proteomic findings, and immunohistochemical analysis of rat eyes and human donor eyes determined the cellular localization of 14-3-3 proteins. In addition, in vivo treatment experiments were conducted using JNK and protein phosphatase inhibitors.

RESULTS

Findings of mass spectrometry, Western blotting, and tissue immunolabeling revealed the presence of different 14-3-3 isotopes in RGCs and their up-regulation and phosphorylation during glaucomatous neurodegeneration. Consecutive experiments through proteomic analysis identified various proteins interacting with 14-3-3, which included calmodulin and a proapoptotic member of the Bcl-2 family, Bad; 14-3-3 was found to keep phospho-Bad sequestered in the cytoplasm. However, this association was disrupted in ocular hypertensive eyes in correlation with Bad dephosphorylation and 14-3-3 phosphorylation, thereby leading to mitochondrial translocation of Bad for apoptotic function. Inhibition of JNK activity and of protein phosphatase activity complementarily secured the 14-3-3-scaffold of Bad in the cytoplasm and preserved optic nerve axons in ocular hypertensive eyes.

CONCLUSIONS

Findings of this in vivo study identify that an important protein family associated with checkpoint control pathways, 14-3-3, is involved in cellular signaling during glaucomatous neurodegeneration in a phosphorylation-dependent manner.

Proteolysis of CDH1 enhances susceptibility to UV radiation-induced apoptosis

As a critical ubiquitin ligase, the anaphase-promoting complex/cyclosome (APC/C) governs cell cycle progression, signaling modulation and the pathogenesis of some human diseases. Recent studies implicate APC in maintaining genomic integrity, but the mechanism by which it plays such a role remains largely unknown. We report here that acute UV radiation triggers proteolysis of CDH1, an activator of APC, which is involved in regulation of apoptosis induced by UV radiation. Depletion of CDH1 by RNA interference enhances the cellular susceptibility to apoptosis in response to UV radiation, whereas overexpression of non-degradable CDH1 delays UV radiation-induced apoptosis. In addition, UV-induced degradation of CDH1 results in the accumulation of cyclin B1 and therefore to increased CDK1 activity, which is believed to enhance UV-induced apoptosis. The present results unveil a novel role for the APC in UV-induced cell death and demonstrate a new regulatory mechanism for APC/CDH1 through proteolysis.

Class IIA HDACs in the regulation of neurodegeneration

Neurodegenerative diseases affect millions of patients annually and are a significant burden on the health care systems around the world. While there are symptomatic remedies for patients suffering from various neurodegenerative diseases, there are no cures as of today. Cell death by apoptosis is a common hallmark of neurodegeneration. Therefore, deciphering the molecular pathways regulating this process is of significant value to scientists' endeavor to understand neurodegenerative disorders. Efforts along these lines have uncovered a number of molecular pathways that regulate neuronal apoptosis. Recently, a family of proteins known as histone deacetylases (HDACs) has been linked to regulation of cell survival as well as death. The focus of this review is to summarize our current understanding of the role of HDACs and in particular a subgroup of proteins in this family classified as class IIa HDACs in the regulation of neuronal cell death. It is apparent based on the information presented in this review that although very similar in their primary sequence, members of this family of proteins often have distinct roles in orchestrating apoptotic cell death in the brain.

The FLT3 inhibitor PKC412 exerts differential cell cycle effects on leukemic cells depending on the presence of FLT3 mutations

PKC412 is a staurosporine derivative that inhibits several protein kinases including FLT3, and is highly anticipated as a novel therapeutic agent for acute myeloblastic leukemia (AML) carrying FLT3 mutations. In this study, we show that PKC412 exerts differential cell cycle effects on AML cells depending on the presence of FLT3 mutations. PKC412 elicits massive apoptosis without markedly affecting cell cycle patterns in AML cell lines with FLT3 mutations (MV4-11 and MOLM13), whereas it induces G2 arrest but not apoptosis in AML cell lines without FLT3 mutations (THP-1 and U937). In MV4-11 and MOLM13 cells, PKC412 inactivates Myt-1 and activates CDC25c, leading to the activation of CDC2. Activated CDC2 phosphorylates Bad at serine-128 and facilitates its translocation to the mitochondria, where Bad triggers apoptosis. In contrast, PKC412 inactivates CDC2 by inducing serine-216 phosphorylation and subsequent cytoplasmic sequestration of CDC25c in THP-1 and U937 cells. As a result, cells are arrested in the G2 phase of the cell cycle, but do not undergo apoptosis because Bad is not activated. The FLT3 mutation-dependent differential cell cycle effect of PKC412 is considered an important factor when PKC412 is combined with cell cycle-specific anticancer drugs in the treatment of cancer and leukemia.

Structurally related TPR subunits contribute differently to the function of the anaphase-promoting complex in Drosophila melanogaster

The anaphase-promoting complex/cyclosome or APC/C is a key regulator of chromosome segregation and mitotic exit in eukaryotes. It contains at least 11 subunits, most of which are evolutionarily conserved. The most abundant constituents of the vertebrate APC/C are the four structurally related tetratrico-peptide repeat (TPR) subunits, the functions of which are not yet precisely understood. Orthologues of three of the TPR subunits have been identified in Drosophila. We have shown previously that one of the TPR subunits of the Drosophila APC/C, Apc3 (also known as Cdc27 or Mákos), is essential for development, and perturbation of its function results in mitotic cyclin accumulation and metaphase-like arrest. In this study we demonstrate that the Drosophila APC/C associates with a new TPR protein, a genuine orthologue of the vertebrate Apc7 subunit that is not found in yeasts. In addition to this, transgenic flies knocked down for three of the TPR genes Apc6 (Cdc16), Apc7 and Apc8 (Cdc23), by RNA interference were established to investigate their function. Whole-body expression of subunit-specific dsRNA efficiently silences these genes resulting in only residual mRNA concentrations. Apc6/Cdc16 and Apc8/Cdc23 silencing induces developmental delay and causes different pupal lethality. Cytological examination showed that these animals had an elevated level of apoptosis, high mitotic index and delayed or blocked mitosis in a prometaphase-metaphase-like state with overcondensed chromosomes. The arrested neuroblasts contained elevated levels of cyclin B but, surprisingly, cyclin A appeared to be degraded normally. Contrary to the situation for the Apc6/Cdc16 and Apc8/Cdc23 genes, the apparent loss of Apc7 function does not lead to the above abnormalities. Instead, the Apc7 knocked down animals and null mutants are viable and fertile, although they display mild chromosome segregation defects and anaphase delay. Nevertheless, the Apc7 subunit shows synergistic genetic interaction with Apc8/Cdc23 that, together with the phenotypic data, assumes a limited functional role for Apc7. Taken together, these data suggest that the structurally related TPR subunits contribute differently to the function of the anaphase-promoting complex.

PIASx is a MEF2 SUMO E3 ligase that promotes postsynaptic dendritic morphogenesis

Postsynaptic morphogenesis of dendrites is essential for the establishment of neural connectivity in the brain, but the mechanisms that govern postsynaptic dendritic differentiation remain poorly understood. Sumoylation of the transcription factor myocyte enhancer factor 2A (MEF2A) promotes the differentiation of postsynaptic granule neuron dendritic claws in the cerebellar cortex. Here, we identify the protein PIASx as a MEF2 SUMO E3 ligase that represses MEF2-dependent transcription in neurons. Gain-of-function and genetic knockdown experiments in rat cerebellar slices and in the postnatal cerebellum in vivo reveal that PIASx drives the differentiation of granule neuron dendritic claws in the cerebellar cortex. MEF2A knockdown suppresses PIASx-induced dendritic claw differentiation, and expression of sumoylated MEF2A reverses PIASx knockdown-induced loss of dendritic claws. These findings define the PIASx-MEF2 sumoylation signaling link as a key mechanism that orchestrates postsynaptic dendritic claw morphogenesis in the cerebellar cortex and suggest novel functions for SUMO E3 ligases in brain development and plasticity.

12-o-Tetradecanoylphorbol 13-acetate prevents baicalein-induced apoptosis via activation of protein kinase C and JNKs in human leukemia cells

In the present study, we found that baicalein (BE), but not its glycoside baicalin (BI), induced apoptosis in human leukemia HL-60 and Jurkat cells, but not in primary murine peritoneal macrophages (PMs) or human polymorphonuclear (PMN) cells, by the MTT assay, LDH release assay, and flow cytometric analysis. Activation of the caspase 3, but not caspase 1, enzyme via inducing protein processing was detected in BE-induced apoptosis. The ROS-scavenging activity of BE was identified by the anti-DPPH radical, DCHF-DA, and in vitro plasmid digestion assay, and none of chemical antioxidants including allpurinol (ALL), N-acetyl-cystein (NAC), and diphenylene iodonium (DPI) affected BE-induced apoptosis in HL-60 cells. This suggests that apoptosis induced by BE is independent of the production of ROS in HL-60 cells. Interestingly, the apoptotic events such as DNA ladders formation and activation of the caspase 3 cascade were significantly blocked by TPA addition in the presence of membrane translocation of PKCalpha, and TPA-induced protection was reduced by adding the PKC inhibitors, GF-109203X and staurosporin. TPA addition induces the phosphorylation of JNKs and ERKs, but not p38, protein in HL-60 cells, and incubation of HL-60 cells with JNKs inhibitor SP600125, but not ERKs inhibitor, PD98059 or the p38 inhibitor SB203580, suppressed the protective effect of TPA against BE-induced apoptotic events including DNA ladders, apoptotic bodies, caspase 3 and D4-GDI protein cleavage in according with blocking JNKs protein phosphorylation. In addition, PKC inhibitor GF-109203X treatment blocks TPA-induced ERKs and JNKs protein phosphorylation, which indicates that activation of PKC locates at upstream of MAPKs activation in TPA-treated HL-60 cells. Additionally, a loss in mitochondrial membrane potential with a reduction in Bcl-2 protein expression, the induction of Bad protein phosphorylation, and translocation of cytochrome c from mitochondria to the cytosol were observed in BE-treated HL-60 cells, and these events were prevented by the addition of TPA. GF-109203X and SP600125 suppression of TPA against cytochrome c release induced by BE was identified. This suggests that activation of PKC and JNKs participate in TPA's prevention of BE-induced apoptosis via suppressing mitochondrial dysfunction in HL-60 cells.

Increased expression of cyclin B1 sensitizes prostate cancer cells to apoptosis induced by chemotherapy

Chemotherapeutic drugs ideally should take advantage of the differences between transformed and normal cells and induce apoptosis only in cancer cells. One such difference may be the overexpression of cyclin B1 protein in cancer cells, which is required for the proper progression through mitosis. Previously, we showed that treatment of human prostate cancer cells with 2-methoxyestradiol (2-ME) or docetaxel results in an accumulation of cyclin B1 protein and an increase in cyclin B1 kinase activity, followed by induction of apoptotic cell death. Inhibition of cyclin B1 kinase lowers apoptosis induced by 2-ME and docetaxel. In this study, we established a positive correlation between cyclin B1 protein and apoptosis induced by chemotherapy in prostate cancer cells. There is minimal cyclin B1 and induction of apoptosis by chemotherapy in nontransformed cells. LNCaP and PC-3 prostate cancer cells stably overexpressing cyclin B1 are more sensitive to apoptosis induced by chemotherapy. LNCaP cells expressing cyclin B1 small interfering RNA to lower cyclin B1 protein or dominant negative cyclin-dependent kinase 1 to inhibit cyclin B1 kinase show a decrease in apoptosis. Increased sensitivity to apoptosis by overexpression of cyclin B1 may be due to lower Bcl-2, higher p53, and decreased neuroendocrine differentiation. We suggest that a cancer-specific mechanism whereby 2-ME and docetaxel may exert anti-prostate cancer activity is the deregulated activation of cyclin B1 kinase, leading to the induction of apoptotic cell death. Our results also suggest that higher levels of cyclin B1 in prostate cancer cells may be a good prognostic marker for chemotherapy.

The nuclear localization of SET mediated by impalpha3/impbeta attenuates its cytosolic toxicity in neurons

SET is a multi-functional protein in proliferating cells. Some of the proposed functions of SET suggest an important nuclear role. However, the nuclear import pathway of SET is also unknown and the function of SET in neurons is unclear. Presently, using cortical neurons, we report that the nuclear import of SET is mediated by an impalpha/impbeta-dependent pathway. Nuclear localization signal, (168)KRSSQTQNKASRKR(181), in SET interacts with impalpha3, which recruits impbeta to form a ternary complex, resulting in efficient transportation of SET into nucleus. By in vitro nuclear import assay based on digitonin-permeabilized neurons, we further demonstrated that the nuclear import of SET relies on Ran GTPase. We provide evidence that this nuclear localization of SET is important in neuronal survival. Under basal conditions, SET is predominately nuclear. However, upon death induced by genotoxic stress, endogenous SET decreases in the nucleus and increases in the cytoplasm. Consistent with a toxic role of SET in the cytoplasm, targeted expression of SET to the cytoplasm exacerbates death compared to wild type SET expression which is protective following DNA damage. Taken together, our results indicate that SET is imported into the nucleus through its association with impalpha3/impbeta, and that localization of SET is important in regulation of neuronal death.

CaMKII and CaMKIV mediate distinct prosurvival signaling pathways in response to depolarization in neurons

By fusing the CaMKII-inhibitory peptide AIP to GFP, we constructed a specific and effective CaMKII inhibitor, GFP-AIP. Expression of GFP-AIP and/or dominant-inhibitory CaMKIV in cultured neonatal rat spiral ganglion neurons (SGNs) shows that CaMKII and CaMKIV act additively and in parallel to mediate the prosurvival effect of depolarization. Depolarization or expression of constitutively active CaMKII functionally inactivates Bad, indicating that this is one means by which CaMKII promotes neuronal survival. CaMKIV, but not CaMKII, requires CREB to promote SGN survival, consistent with the exclusively nuclear localization of CaMKIV and indicating that the principal prosurvival function of CaMKIV is activation of CREB. Consistent with this, a constitutively active CREB construct that provides a high level of CREB activity promotes SGN survival, although low levels of CREB activity did not do so. Also, in apoptotic SGNs, activation of CREB by depolarization is disabled, presumably as part of a cellular commitment to apoptosis.

Cell cycle regulation in the postmitotic neuron: oxymoron or new biology?

Adult CNS neurons are typically described as permanently postmitotic but there is probably nothing permanent about the neuronal cell cycle arrest. Rather, it appears that these highly differentiated cells must constantly keep their cell cycle in check. Relaxation of this vigilance leads to the initiation of a cell cycle and entrance into an altered and vulnerable state, often leading to death. There is evidence that neurons which are at risk of neurodegeneration are also at risk of re-initiating a cell cycle process that involves the expression of cell cycle proteins and DNA replication. Failure of cell cycle regulation might be a root cause of several neurodegenerative disorders and a final common pathway for others.

Pin1 in neuronal apoptosis

While the role of the prolyl isomerase Pin1 in dividing cells has long been recognized, Pin1's function in postmitotic neurons is poorly understood. We have identified a novel mechanism by which Pin1 mediates activation of the mitochondrial cell death machinery specifically in neurons. This perspective presents a sophisticated signaling pathway that triggers neuronal apoptosis upon JNK-mediated phosphorylation of the BH3-only protein BIM(EL) at serine 65. Pin1 is enriched at the mitochondria in neurons together with BIM(EL) and components of a neuron-specific JNK signaling complex and functions as a molecular switch that couples the phosphorylation of BIM(EL) by JNK to apoptosis specifically in neurons. We discuss how these findings relate to our understanding of the development of the nervous system and the pathogenesis of neurologic disorders.

The CDC2 I-G-T haplotype associated with the APOE ɛ4 allele increases the risk of sporadic Alzheimer's disease in Sicily

The cell division cycle 2 (CDC2) gene is a candidate susceptibility gene for Alzheimer's disease (AD). We investigated the CDC2 genotype, and allele and haplotype frequencies in AD patients and matched controls, distinguishing between apolipoprotein E (APOE) epsilon4 allele carriers and non-carriers. APOE epsilon4 is an established predictor of AD risk. APOE and CDC2 genotypes were examined in 109 sporadic AD patients and in 110 healthy age- and sex-matched controls from Sicily. The epsilon4 allele of APOE was predictive of AD risk in our study group (odds ratio: 5.37, 95% CI 2.77-10.41; P<0.0001). Genotype and allele frequencies of the three tested CDC2 polymorphisms (Ex6+7I/D, Ex7-15 G>A, Ex7-14 T>A) were not significantly different between AD patients and controls. However, a significant different distribution of a specific CDC2 haplotype (I-G-T) was found between AD patients and controls when analyzing APOE epsilon4-positive subjects (P=0.0288). Moreover, the combined presence of the I-G-T haplotype and the epsilon4 allele almost doubled the risk of AD (odds ratio: 10.09, 95% CI 3.88-26.25; P<0.0001) compared to carriers of epsilon4 alone. This study suggests that the I-G-T haplotype of the CDC2 gene increases the risk of AD in APOE epsilon4 carriers.

Transcription factor Sp4 regulates dendritic patterning during cerebellar maturation

Integration of inputs by a neuron depends on dendritic arborization patterns. In mammals, the genetic programs that regulate dynamic remodeling of dendrites during development and in response to activity are incompletely understood. Here we report that knockdown of the transcription factor Sp4 led to an increased number of highly branched dendrites during maturation of cerebellar granule neurons in dissociated cultures and in cerebellar cortex. Time-course analysis revealed that depletion of Sp4 led to persistent generation of dendritic branches and a failure in resorption of transient dendrites. Depolarization induced a reduction in the number of dendrites, and knockdown of Sp4 blocked depolarization-induced remodeling. Furthermore, overexpression of Sp4 wild type, but not a mutant lacking the DNA-binding domain, was sufficient to promote dendritic pruning in nondepolarizing conditions. These findings indicate that the transcription factor Sp4 controls dendritic patterning during cerebellar development by limiting branch formation and promoting activity-dependent pruning.

Opposing effects of Bad phosphorylation at two distinct sites by Akt1 and JNK1/2 on ischemic brain injury

Increasing evidence suggests that the Bcl-2 family proteins play pivotal roles in regulation of the mitochondria cell-death pathway on transient cerebral ischemia. Bad, a BH3-only proapoptotic Bcl-2 family protein, has been shown to be phosphorylated extensively on serine by kinds of kinases. However, the exact mechanisms of the upstream kinases in regulation of Bad signaling pathway remain unknown. Here, we reported that Bad could be phosphorylated not only by Akt1 but also by JNK1/2 after transient global ischemia in rat hippocampal CA1 region. Our data demonstrated that Akt1 mediated the phosphorylation of Bad at serine 136, which increased the interaction of serine 136-phosphorylated Bad with 14-3-3 proteins and prevented the dimerization of Bad with Bcl-Xl, inhibited the release of cytochrome c to the cytosol and the death effector caspase-3 activation, leading to the survival of neuron. In contrast, JNK1/2 induced the phosphorylation of Bad at a novel site of serine 128 after brain ischemia/reperfusion, which inhibited the interaction of PI3K/Akt-induced serine 136-phosphorylated Bad with 14-3-3 proteins, thereby promoted the apoptotic effect of Bad. In addition, activated Akt1 inhibited the activation of Bad(S128) through downregulating JNK1/2 activation, thus inhibiting JNK-mediated Bad apoptosis pathway. Furthermore, the fate of cell to survive or to die was determined by a balance between prosurvival and proapoptotic signals. Taken together, our studies reveal that Bad phosphorylation at two distinct sites induced by Akt1 and JNK1/2 have opposing effects on ischemic brain injury, and present the possibility of Bad as a potential therapeutic target for stroke treatment.

Connecting cell-cycle activation to neurodegeneration in Drosophila

Studies in cell-culture systems and in postmortem tissue from human disease have suggested a connection between cell-cycle activation and neurodegeneration. The fruit fly Drosophila melanogaster has recently emerged as a powerful model system in which to model neurodegenerative diseases. Here we review work in the fly that has begun to address some of the important questions regarding the relationship between cell-cycle activation and neurodegeneration in vivo, including recent data implicating cell-cycle activation as a downstream effector of tau-induced neurodegeneration. We suggest how powerful research tools in Drosophila might be utilized to approach fundamental questions that remain.

The X-linked mental retardation gene SMCX/JARID1C defines a family of histone H3 lysine 4 demethylases

Histone methylation regulates chromatin structure and transcription. The recently identified histone demethylase lysine-specific demethylase 1 (LSD1) is chemically restricted to demethylation of only mono- and di- but not trimethylated histone H3 lysine 4 (H3K4me3). We show that the X-linked mental retardation (XLMR) gene SMCX (JARID1C), which encodes a JmjC-domain protein, reversed H3K4me3 to di- and mono- but not unmethylated products. Other SMCX family members, including SMCY, RBP2, and PLU-1, also demethylated H3K4me3. SMCX bound H3K9me3 via its N-terminal PHD (plant homeodomain) finger, which may help coordinate H3K4 demethylation and H3K9 methylation in transcriptional repression. Significantly, several XLMR-patient point mutations reduced SMCX demethylase activity and binding to H3K9me3 peptides, respectively. Importantly, studies in zebrafish and primary mammalian neurons demonstrated a role for SMCX in neuronal survival and dendritic development and a link to the demethylase activity. Our findings thus identify a family of H3K4me3 demethylases and uncover a critical link between histone modifications and XLMR.

Paclitaxel induced apoptosis in breast cancer cells requires cell cycle transit but not Cdc2 activity

PURPOSE

Paclitaxel (PTX) is a widely used chemotherapy agent and may cause cell death by apoptosis subsequent to microtubule (MT) disruption. In this paper, we have investigated whether cell cycle transit and or Cdc2 (Cdk1) activity is required for the apoptosis induced by PTX.

METHODS

Cell cycle was analyzed by flow cytometry, Cdc2 was assayed bio chemically. Cdc2 activity was decreased by siRNA and dominant negative (dn) Cdc2 expression. Cells were arrested by chemical or biological inhibitors in a G1 or S phase. Apoptosis was measured by DNA fragmentation and examination of nuclei by microscopy. JNK and AKT activations were assessed as well.

RESULTS

Cell cycle inhibition was highly effective in decreasing PTX induced apoptosis. MT morphology was not altered by these inhibitors. PTX induced JNK activity or AKT mediated BAD phosphorylation was unaffected by cell cycle inhibitors. Abrogation of Cdc 2 activity was without effect on PTX induced apoptosis.

CONCLUSIONS

While cell cycle transit is required for PTX induced apoptosis; Cdc2 activity is not required.

Cdc2-mediated Schwann cell migration during peripheral nerve regeneration

Schwann cell migration facilitates peripheral nerve regeneration after injury. We have recently found increased activation of Cdc2 kinase in regenerating sciatic nerves. Here we show that Cdc2 phosphorylation of caldesmon regulates Schwann cell migration and nerve regeneration. A robust but transient increase in Cdc2 expression was found in cultured Schwann cells prepared from the sciatic nerve in rats that had undergone crush injury for 7 days. These `injury-preconditioned' Schwann cells exhibited enhanced migration compared with non-preconditioned control cells and treatment with the cdk inhibitor roscovitine prevented cell migration. After transduction with recombinant Cdc2 DNA adenoviral vectors, Schwann cells were implanted into sciatic nerves; those expressing wild-type Cdc2 migrated further in the distal direction than those expressing dominant-negative Cdc2. We identified caldesmon as a downstream substrate of Cdc2 in Schwann cells and its phosphorylation by Cdc2 changed its subcellular localization. Overexpression of dominant-negative caldesmon significantly counteracted the migration effect caused by Cdc2. Finally, neurite outgrowth of cultured DRG sensory neurons, facilitated by co-culture with injury-preconditioned Schwann cells, was suppressed by roscovitine treatment. The results indicate that activation of the Cdc2-caldesmon pathway is necessary for Schwann cell migration and suggest a role for this pathway in peripheral axonal growth.

Thinking within the D box: initial identification of Cdh1-APC substrates in the nervous system

The anaphase-promoting complex (APC) has a well-established role in cell cycle control, but recent exciting evidence has uncovered unexpected neurobiological functions for this complex E3 ubiquitin ligase. With its co-activator Cdh1, APC's effects upon the nervous system range from regulation of axon growth and patterning to development of synapses to neuronal survival. The Cdh1-APC substrates that control these biological processes in neurons are just beginning to be identified. These findings may offer a glimpse of the wide spectrum of neural activities that are orchestrated by Cdh1-APC.

p21 blocks irradiation-induced apoptosis downstream of mitochondria by inhibition of cyclin-dependent kinase-mediated caspase-9 activation

The role of the cyclin-dependent kinase (CDK) inhibitor p21 as a mediator of p53-induced growth arrest is well established. In addition, recent data provide strong evidence for new emerging functions of p21, including a role as a modulator of apoptosis. The mechanisms, however, by which p21 interferes with the death machinery, especially following ionizing radiation (IR), are largely unknown. Here, we report that IR induced caspase-9 and caspase-3 activation and subsequent apoptosis only in p21-deficient colon carcinoma cells, whereas similar treated wild-type cells were permanently arrested in the G(2)-M phase, correlating with the induction of cellular senescence. Interestingly, activation of the mitochondrial pathway, including caspase-2 processing, depolarization of the outer mitochondrial membrane, and cytochrome c release, was achieved by IR in both cell lines, indicating that p21 inhibits an event downstream of mitochondria but preceding caspase-9 activation. IR-induced p21 protein expression was restricted to the nucleus, and no evidence for a mitochondrial or cytoplasmic association was found. In addition, p21 did neither interact with caspase-3 or caspase-9, suggesting that these events are not required for the observed protection. Consistent with this assumption, we found that CDK inhibitors potently abrogated IR-induced caspase processing and activation without affecting mitochondrial events. In addition, in vitro caspase activation assays yielded higher caspase-3 activities in extracts of irradiated p21-deficient cells compared with extracts of similar treated wild-type cells. Thus, our results strongly indicate that p21 protects cells from IR-induced apoptosis by suppression of CDK activity that seems to be required for activation of the caspase cascade downstream of the mitochondria.

Necdin downregulates CDC2 expression to attenuate neuronal apoptosis

The cell cycle-regulatory transcription factor E2F1 induces apoptosis of postmitotic neurons in developmental and pathological situations. E2F1 transcriptionally activates many proapoptotic genes including the cyclin-dependent protein kinase cell division cycle 2 (Cdc2). Necdin is a potent mitotic suppressor expressed predominantly in postmitotic neurons and interacts with E2F1 to suppress E2F1-mediated gene transcription. The necdin gene NDN is maternally imprinted and expressed only from the paternal allele. Deletion of the paternal NDN is implicated in the pathogenesis of Prader-Willi syndrome, a genomic imprinting-associated neurodevelopmental disorder. Here, we show that paternally expressed necdin represses E2F1-dependent cdc2 gene transcription and attenuates apoptosis of postmitotic neurons. Necdin was abundantly expressed in differentiated cerebellar granule neurons (CGNs). Neuronal activity deprivation elevated the expression of both E2F1 and Cdc2 in primary CGNs prepared from mice at postnatal day 6, whereas the necdin levels remained unchanged. In chromatin immunoprecipitation analysis, endogenous necdin was associated with the cdc2 promoter containing an E2F-binding site in activity-deprived CGNs. After activity deprivation, CGNs underwent apoptosis, which was augmented in those prepared from mice defective in the paternal Ndn allele (Ndn(+m/-p)). The levels of cdc2 mRNA, protein, and kinase activity were significantly higher in Ndn(+m/-p) CGNs than in wild-type CGNs under activity-deprived conditions. Furthermore, the populations of Cdc2-immunoreactive and apoptotic cells were increased in the cerebellum in vivo of Ndn(+m/-p) mice. These results suggest that endogenous necdin attenuates neuronal apoptosis by suppressing the E2F1-Cdc2 system.

Cell cycle inhibition attenuates microglia induced inflammatory response and alleviates neuronal cell death after spinal cord injury in rats

The spinal cord is well known to undergo inflammatory reactions in response to traumatic injury. Activation and proliferation of microglial cells, with associated proinflammatory cytokines expression, plays an important role in the secondary damage following spinal cord injury. It is likely that microglial cells are at the center of injury cascade and are targets for treatments of CNS traumatic diseases. Recently, we have demonstrated that the cell cycle inhibitor olomoucine attenuates astroglial proliferation and glial scar formation, decreases lesion cavity and mitigates functional deficits after spinal cord injury (SCI) in rats [Tian, D.S., Yu, Z.Y., Xie, M.J., Bu, B.T., Witte, O.W., Wang, W., 2006. Suppression of astroglial scar formation and enhanced axonal regeneration associated with functional recovery in a spinal cord injury rat model by the cell cycle inhibitor olomoucine. J. Neurosci. Res. 84, 1053-1063]. Whether neuroprotective effects of cell cycle inhibition are involved in attenuation of microglial induced inflammation awaits to be elucidated. In the present study, we sought to determine the influence of olomoucine on microglial proliferation with associated inflammatory response after spinal cord injury. Tissue edema formation, microglial response and neuronal cell death were quantified in rats subjected to spinal cord hemisection. Microglial proliferation and neuronal apoptosis were observed by immunofluorescence. Level of the proinflammatory cytokine interleukin-1beta (IL-1beta) expression in the injured cord was determined by Western blot analysis. Our results showed that the cell cycle inhibitor olomoucine, administered at 1 h post injury, significantly suppressed microglial proliferation and produced a remarkable reduction of tissue edema formation. In the olomoucine-treated group, a significant reduction of activated and/or proliferated microglial induced IL-1beta expression was observed 24 h after SCI. Moreover, olomoucine evidently attenuated the number of apoptotic neurons after SCI. Our findings suggest that modulation of microglial proliferation with associated proinflammatory cytokine expression may be a mechanism of cell cycle inhibition-mediated neuroprotections in the CNS trauma.

Chromosomal instability by beta-catenin/TCF transcription in APC or beta-catenin mutant cells

Adenomatous polyposis coli (APC/Apc) gene encodes a key tumor suppressor whose mutations activate beta-catenin/T-cell factor (TCF)-mediated transcription (canonical Wnt signaling). Here, we show that Wnt signaling can cause chromosomal instability (CIN). As an indicator of CIN, we scored anaphase bridge index (ABI) in mouse polyps and ES cells where Wnt signaling was activated by Apc or beta-catenin mutations. We found three to nine times higher ABI than in wild-type controls. Furthermore, karyotype analysis confirmed that the Wnt signal-activated ES cells produced new chromosomal aberrations at higher rates; hence CIN. Consistently, expression of dominant-negative TCFs in these cells reduced their ABI. We also found that Wnt signal activation increased phosphorylation of Cdc2 (Cdk1) that inhibited its activity, and suppressed apoptosis upon exposure of the cells to nocodazole or colcemid. The data suggest that Wnt signaling stimulates the cells to escape from mitotic arrest and apoptosis, resulting in CIN. In human gastric cancer tissues with nuclear beta-catenin, ABI was significantly higher than in those without. These results collectively indicate that beta-catenin/TCF-mediated transcription itself increases CIN through dysregulation of G2/M progression.

Bcl-2 protein family: implications in vascular apoptosis and atherosclerosis

Apoptosis has been recognized as a central component in the pathogenesis of atherosclerosis, in addition to the other human pathologies such as cancer and diabetes. The pathophysiology of atherosclerosis is complex, involving both apoptosis and proliferation at different phases of its progression. Oxidative modification of lipids and inflammation differentially regulate the apoptotic and proliferative responses of vascular cells during progression of the atherosclerotic lesion. Bcl-2 proteins act as the major regulators of extrinsic and intrinsic apoptosis signalling pathways and more recently it has become evident that they mediate the apoptotic response of vascular cells in response to oxidation and inflammation either in a provocative or an inhibitory mode of action. Here we address Bcl-2 proteins as major therapeutic targets for the treatment of atherosclerosis and underscore the need for the novel preventive and therapeutic interventions against atherosclerosis, which should be designed in the light of molecular mechanisms regulating apoptosis of vascular cells in atherosclerotic lesions.

TOR-mediated cell-cycle activation causes neurodegeneration in a Drosophila tauopathy model

BACKGROUND

Previous studies have demonstrated reexpression of cell-cycle markers within postmitotic neurons in neurodegenerative tauopathies, including Alzheimer's disease (AD). However, the critical questions of whether cell-cycle activation is causal or epiphenomenal to tau-induced neurodegeneration and which signaling pathways mediate cell-cycle activation in tauopathy remain unresolved.

RESULTS

Cell-cycle activation accompanies wild-type and mutant tau-induced neurodegeneration in Drosophila, and genetically interfering with cell-cycle progression substantially reduces neurodegeneration. Our data support a role for cell-cycle activation downstream of tau phosphorylation, directly preceding apoptosis. We accordingly show that ectopic cell-cycle activation leads to apoptosis of postmitotic neurons in vivo. As in AD, TOR (target of rapamycin kinase) activity is increased in our model and is required for neurodegeneration. TOR activation enhances tau-induced neurodegeneration in a cell cycle-dependent manner and, when ectopically activated, drives cell-cycle activation and apoptosis in postmitotic neurons.

CONCLUSIONS

TOR-mediated cell-cycle activation causes neurodegeneration in a Drosophila tauopathy model, identifying TOR and the cell cycle as potential therapeutic targets in tauopathies and AD.

Dissecting the roles of checkpoint kinase 1/CDC2 and mitogen-activated protein kinase kinase 1/2/extracellular signal-regulated kinase 1/2 in relation to 7-hydroxystaurosporine-induced apoptosis in human multiple myeloma cells

The functional roles of Cdc2 and checkpoint kinase 1 (Chk1) in synergistic interactions between 7-hydroxystaurosporine (UCN-01) and mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitors [e.g., 2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide (PD184352)] were examined in human multiple myeloma cells in relation to MEK1/2/ERK1/2 activation and lethality. Time course studies revealed that MEK1/2/extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation preceded Cdc2 dephosphorylation (Tyr15) after UCN-01 exposure. Furthermore, enforced expression of Cdc2 or small inducible RNA (siRNA)-mediated Cdc2 knockdown failed to modify ERK1/2 activation status in either the presence or absence of UCN-01, arguing against a causal relationship between these events. However, ectopic expression of Cdc2 sensitized cells to the lethality of UCN-01/MEK inhibitor regimen, whereas Cdc2 knockdown by siRNA significantly diminished the lethal effects of this combination. Conversely, Chk1 knockdown by siRNA enhanced lethality mediated by UCN-01/PD184352. It is interesting that Chk1 knockdown reduced basal ERK1/2 activation and antagonized the ability of UCN-01 to activate ERK1/2. Finally, ectopic expression of constitutively active MEK1 significantly protected cells from the UCN-01/MEK1/2 inhibitor regimen without modifying Cdc2 activation status. Together, these findings indicate that although UCN-01-mediated Chk1 inhibition and Cdc2 activation are unlikely to be responsible for MEK1/2/ERK1/2 activation, both of these events contribute functionally to enhanced lethality in cells coexposed to MEK inhibitors. They also suggest a role for Chk1 in UCN-01-induced ERK1/2 activation, implying the existence of a heretofore unrecognized link between Chk1 and ERK1/2 signaling.

Investigation of anti-tumor mechanisms of K2154: characterization of tubulin isotypes, mitotic arrest and apoptotic machinery

Microtubules are crucial targets for cancer chemotherapeutic drugs, and new microtubule-directed agents are of continued interest in drug development. A novel microtubule-directed agent, ethyl-2-[N-rho-chlorobenzyl-(2'-methoxy)]-anilino-4-oxo -4, 5-dihydro-furan-3-carboxylate, was identified. The compound, designated K2154, inhibited cell proliferation, with IC(50) values of 10.3, 15.3, 9.6, 11.2, 12.8 and 12.1 muM in prostate cancer PC-3, hepatocellular carcinoma Hep3B, non-small cell lung cancer A549, colorectal cancer HT29 and HCT116, and P-glycoprotein-rich breast cancer NCI/ADR-RES cells, respectively. Because NCI/ADR-RES cells were susceptible to inhibition by K2154, it indicated that this compound is a poor substrate for P-glycoprotein. In this study, PC-3 cells were used to identify the anticancer mechanisms of K2154. K2154 induced an arrest of the cell cycle at G2/M phase and a subsequent increase of hypodiploid phase in PC-3 cells, whereas it only induced a moderate level of G2/M arrest with little increase of hypodiploid phase in normal prostate cells. K2154 inhibited microtubule assembly in both in vitro turbidity assay and in vivo microtubule spin-down experiment. Immunochemical examination showed that K2154 caused formation of abnormal mitotic characteristics with bipolar spindles, particularly, in beta(II)- and beta(III)-tubulin staining. It also induced several pathways, including cyclin B1 up-regulation, dephosphorylation on Tyr(15) and phosphorylation on Thr(161) of Cdk1 and Cdc25C phosphorylation, and roscovitine (a Cdk1 inhibitor) significantly inhibited K2154-induced apoptosis, suggesting a pro-apoptotic role of Cdk1. Phosphorylation of Bcl-2 and Bcl-xL and cleavage of Mcl-1, together with activation of caspase-9 and -3, indicated that mitochondrial pathway played a central role in K2154-mediated apoptotic cell death. Additionally, AIF contributed to a late phase of K2154-induced apoptotic pathway. In conclusion, it is suggested that K2154 displays an anticancer activity through a target on microtubules and a subsequent signaling cascade on cell cycle regulation and apoptotic machinery.

Role of the transcription factor E2F1 in CXCR4-mediated neurotoxicity and HIV neuropathology

This study sought to determine the role of the transcription factor E2F1 in CXCR4-mediated neurotoxicity and HIV neuropathology. We studied the effect of the HIV envelope protein gp120 on the expression of E2F1-dependent apoptotic proteins in human and rodent neurons and examined the expression pattern of E2F1 in the brain of HIV-infected individuals. Our findings suggest that in cultured neurons gp120 increased E2F1 levels in the nucleus, stimulated its transcriptional activity and enhanced the expression of the E2F1 target proteins Cdc2 and Puma. Studies with neuronal cultures from E2F1 deficient mice demonstrated that the transcription factor is required for gp120-induced neurotoxicity and up-regulation of Cdc2 and Puma. Levels of E2F1 protein were greater in the nucleus of neurons in brains of HIV-infected patients exhibiting dementia when compared to HIV-negative subjects or HIV-positive neurologically normal patients. Overall, these studies indicate that E2F1 is primarily involved in CXCR4-mediated neurotoxicity and HIV neuropathogenesis.

Sensitizing hormone-refractory prostate cancer cells to drug treatment by targeting 14-3-3sigma

Advanced and hormone-refractory prostate cancer has long been considered as a chemoresistant disease. Recently, it was found that 14-3-3sigma expression increases as prostate tumor progresses, and that 14-3-3sigma contributes significantly to drug resistance in breast cancers. We, thus, hypothesized that advanced and hormone-refractory prostate cancers may have an increased level of 14-3-3sigma, which in turn may contribute to drug resistance in advanced and hormone-refractory prostate cancers. In this study, we tested this hypothesis and found that, indeed, the expression level of 14-3-3sigma in androgen-independent prostate cancer cell lines DU145, PC3, and CWR22RV are much higher than that in the androgen-dependent cell line LNCaP, and that the androgen-independent cells are more resistant to mitoxantrone and Adriamycin than the androgen-dependent cells. Depleting 14-3-3sigma expression in DU145 and CWR22RV by RNA interference significantly sensitized these cells to mitoxantrone and Adriamycin by abrogating G2-M checkpoint and increasing apoptosis, whereas restoring 14-3-3sigma expression in LNCaP cells enhanced drug resistance. We also showed that 14-3-3sigma deficiency caused nuclear localization of Cdc2 and dephosphorylation of the Tyr15 residue upon DNA damage. Based on these studies, we propose that therapeutic intervention targeting 14-3-3sigma may be useful for sensitizing hormone-refractory prostate cancers to chemotherapy by both G2-M checkpoint abrogation and apoptosis enhancement.

Six1 and Six4 promote survival of sensory neurons during early trigeminal gangliogenesis

Survival of sensory neurons is tightly regulated in cell-type and developmental-stage-specific manners. The transcriptional regulatory mechanisms underlying this regulation remain to be elucidated. In the present study, we investigated the role of Six1 and Six4 in the development of trigeminal ganglia. Abundant expression of Six1 and Six4 was noted in sensory neurons during early trigeminal gangliogenesis. Loss of both Six1 and Six4 in mice caused severe defects in the trigeminal ganglia, wherein massive apoptosis accompanied by activation of caspase-3 was observed at early but not late stages of gangliogenesis. In Six1(-/-)Six4(-/-) mice, trigeminal sensory neurons were generated, but showed reduced expression of Bcl-x compared with the wild-type mice. Accordingly, neurons from the deficient mice could not survive in culture even in the presence of neurotrophins. Our results suggest a cell-intrinsic role of Six1 and Six4 in the survival of early-generated trigeminal sensory neurons.

Divergence from a dedicated cellular suicide mechanism: exploring the evolution of cell death

The developmental cell death in the nematode C. elegans is controlled by a simple and dedicated genetic program. This genetic program is evolutionarily conserved in higher organisms, including mammals. However, although mammalian homologs of C. elegans cell death gene products continue to regulate apoptosis, they are no longer dedicated regulators of cell death. On the other hand, multiple cellular noncell death-related mechanisms have been recruited to regulate cell death under different conditions. Such evidence suggests that evolution has led to an extensive integration of mammalian apoptosis machinery with multiple cellular physiological processes.

Quiescence induced by iron challenge protects neuroblastoma cells from oxidative stress

The brain uses massive amounts of oxygen, generating large quantities of reactive oxygen species (ROS). Because of its lipid composition, rich in unsaturated fatty acids, the brain is especially vulnerable to ROS. Furthermore, oxidative damage in the brain is often associated with iron, which has pro-oxidative properties. Iron-mediated oxidative damage in the brain is compounded by the fact that brain iron distribution is non-uniform, being particularly high in areas sensitive to neurodegeneration. This work was aimed to further our understanding of the cellular mechanisms by which SHSY5Y neuroblastoma cells adapt to, and survive increasing iron loads. Using an iron accumulation protocol that kills about 50% of the cell population, we found by cell sorting analysis that the SHSY5Y sub-population that survived the iron loading arrested in the G(0) phase of the cell cycle. These cells expressed neuronal markers, while their electrical properties remained largely unaltered. These results suggest that upon iron challenge, neuroblastoma cells respond by entering the G(0) phase, somehow rendering them resistant to oxidative stress. A similar physiological condition might be involved in neuronal survival in tissues known to accumulate iron with age, such as the hippocampus and the substantia nigra pars compacta.

The analysis of doxorubicin resistance in human breast cancer cells using antibody microarrays

Doxorubicin is considered to be the most effective agent in the treatment of breast cancer patients. Unfortunately, resistance to this agent is common, representing a major obstacle to successful treatment. The identification of novel biomarkers that are able to predict treatment response may allow therapy to be tailored to individual patients. Antibody microarrays provide a powerful new technique, enabling the global comparative analysis of many proteins simultaneously. This technology may identify a panel of proteins to discriminate between drug-resistant and drug-sensitive samples. The Panorama Cell Signaling Antibody Microarray was exploited to analyze the MDA-MB-231 breast cancer cell line and a novel derivative, which displays significant resistance to doxorubicin at clinically relevant concentrations. The microarray comprised 224 antibodies selected from a variety of pathways, including apoptotic and cell signaling pathways. A standard >/=2.0-fold cutoff value was used to determine differentially expressed proteins. A decrease in the expression of mitogen-activated protein kinase-activated monophosphotyrosine (phosphorylated extracellular signal-regulated kinase; 2.8-fold decrease), cyclin D2 (2.5-fold decrease), cytokeratin 18 (2.5-fold decrease), cyclin B1 (2.4-fold decrease), and heterogeneous nuclear ribonucleoprotein m3-m4 (2.0-fold decrease) was associated with doxorubicin resistance. Western blotting was exploited to confirm results from the antibody microarray experiment. These results suggest that antibody microarrays can be used to identify novel biomarkers and further validation may reveal mechanisms of chemotherapy resistance and identify potential therapeutic targets. [Mol Cancer Ther 2006;5(8):2115-20].

A conserved MST-FOXO signaling pathway mediates oxidative-stress responses and extends life span

Oxidative stress influences cell survival and homeostasis, but the mechanisms underlying the biological effects of oxidative stress remain to be elucidated. Here, we demonstrate that the protein kinase MST1 mediates oxidative-stress-induced cell death in primary mammalian neurons by directly activating the FOXO transcription factors. MST1 phosphorylates FOXO proteins at a conserved site within the forkhead domain that disrupts their interaction with 14-3-3 proteins, promotes FOXO nuclear translocation, and thereby induces cell death in neurons. We also extend the MST-FOXO signaling link to nematodes. Knockdown of the C. elegans MST1 ortholog CST-1 shortens life span and accelerates tissue aging, while overexpression of cst-1 promotes life span and delays aging. The cst-1-induced life-span extension occurs in a daf-16-dependent manner. The identification of the FOXO transcription factors as major and evolutionarily conserved targets of MST1 suggests that MST kinases play important roles in diverse biological processes including cellular responses to oxidative stress and longevity.