Phosphorylation of BAD at Ser-128 during mitosis and paclitaxel-induced apoptosis

Apoptosis as a Barrier against CIN and Aneuploidy

Aneuploidy is the gain or loss of entire chromosomes, chromosome arms or fragments. Over 100 years ago, aneuploidy was described to be a feature of cancer and is now known to be present in 68-90% of malignancies. Aneuploidy promotes cancer growth, reduces therapy response and frequently worsens prognosis. Chromosomal instability (CIN) is recognized as the main cause of aneuploidy. CIN itself is a dynamic but stochastic process consisting of different DNA content-altering events. These can include impaired replication fidelity and insufficient clearance of DNA damage as well as chromosomal mis-segregation, micronuclei formation, chromothripsis or cytokinesis failure. All these events can disembogue in segmental, structural and numerical chromosome alterations. While low levels of CIN can foster malignant disease, high levels frequently trigger cell death, which supports the "aneuploidy paradox" that refers to the intrinsically negative impact of a highly aberrant karyotype on cellular fitness. Here, we review how the cellular response to CIN and aneuploidy can drive the clearance of karyotypically unstable cells through the induction of apoptosis. Furthermore, we discuss the different modes of p53 activation triggered in response to mitotic perturbations that can potentially trigger CIN and/or aneuploidy.

BioID-based proteomic analysis of the Bid interactome identifies novel proteins involved in cell-cycle-dependent apoptotic priming

Apoptotic priming controls the commitment of cells to apoptosis by determining how close they lie to mitochondrial permeabilisation. Variations in priming are important for how both healthy and cancer cells respond to chemotherapeutic agents, but how it is dynamically coordinated by Bcl-2 proteins remains unclear. The Bcl-2 family protein Bid is phosphorylated when cells enter mitosis, increasing apoptotic priming and sensitivity to antimitotic drugs. Here, we report an unbiased proximity biotinylation (BioID) screen to identify regulators of apoptotic priming in mitosis, using Bid as bait. The screen primarily identified proteins outside of the canonical Bid interactome. Specifically, we found that voltage-dependent anion-selective channel protein 2 (VDAC2) was required for Bid phosphorylation-dependent changes in apoptotic priming during mitosis. These results highlight the importance of the wider Bcl-2 family interactome in regulating the temporal control of apoptotic priming.

Comparison between paclitaxel-coated balloon and standard uncoated balloon in the treatment of femoropopliteal long lesions in diabetics

Atherosclerotic diseases may include femoropopliteal artery stenosis or occlusion. Percutaneous transluminal angioplasty (PTA) is an effective and minimally invasive treatment strategy for atherosclerotic femoropopliteal artery stenosis/occlusion disease. Balloon angioplasty is a widely used technique in the management of occlusive disease in almost all arterial segments.We enrolled 111 diabetics with long femoropopliteal lesions, among which 54 received PTA with paclitaxel-coated balloon (the Paclitaxel group), and 57 with standard balloon catheters (the Control group).The primary outcome was set as angiographic late lumen loss (LLL) within 6 months; the secondary angiographic outcome was binary restenosis. Clinical outcomes included Rutherford clarification, ankle-brachial index (ABI) and rate of clinically driven target lesion revascularization (TLR). Two groups had similar basal clinical features, angiographic and procedural characteristics. Compared to controls, the Paclitaxel group had a significantly lower 6-month LLL rate, 12-month binary restenosis rate, 12-month TLR, lower Rutherford grades at 3 and 6 months, and higher ABI at 3 months. For all factors which might influence outcomes, fasting blood glucose was negatively correlated with ABI; the blood urea nitrogen (BUN) was positively related with the Rutherford clarification grades. In addition, the coronary heart disease (CHD) and smoking histories were positively correlated with residual stenosis after treatment.Collectively, the paclitaxel-coated balloon angioplasty can yield more favorable angiographic and clinical outcomes than standard uncoated balloon angioplasty, even in the more challenging lesions (the long and occlusive femoropopliteal lesions) in diabetics, when it had a similar safety profile to the traditional balloon. Blood glucose, BUN, CHD, and smoking imply poor curative effects.

Mapping Mitotic Death: Functional Integration of Mitochondria, Spindle Assembly Checkpoint and Apoptosis

Targeting the mitotic pathways of rapidly proliferating tumor cells has been an effective strategy in traditional cancer therapy. Chemotherapeutics such as taxanes and vinca alkaloids, which disrupt microtubule function, have enjoyed clinical success; however, the accompanying side effects, toxicity and multi drug resistance remain as serious concerns. The emerging classes of inhibitors targeting mitotic kinases and proteasome face their own set of challenges. It is hoped that elucidation of the regulatory interface between mitotic checkpoints, mitochondria and mitotic death will aid the development of more efficacious anti-mitotic agents and improved treatment protocols. The links between the spindle assembly checkpoint (SAC) and mitochondrial dynamics that control the progression of anti-mitotic agent-induced apoptosis have been under investigation for several years and the functional integration of these various signaling networks is now beginning to emerge. In this review, we highlight current research on the regulation of SAC, the death pathway and mitochondria with particular focus on their regulatory interconnections.

Antitubulin sulfonamides: The successful combination of an established drug class and a multifaceted target

Tubulin, the microtubules and their dynamic behavior are amongst the most successful antitumor, antifungal, antiparasitic, and herbicidal drug targets. Sulfonamides are exemplary drugs with applications in the clinic, in veterinary and in the agrochemical industry. This review summarizes the actual state and recent progress of both fields looking from the double point of view of the target and its drugs, with special focus onto the structural aspects. The article starts with a brief description of tubulin structure and its dynamic assembly and disassembly into microtubules and other polymers. Posttranslational modifications and the many cellular means of regulating and modulating tubulin's biology are briefly presented in the tubulin code. Next, the structurally characterized drug binding sites, their occupying drugs and the effects they induce are described, emphasizing on the structural requirements for high potency, selectivity, and low toxicity. The second part starts with a summary of the favorable and highly tunable combination of physical-chemical and biological properties that render sulfonamides a prototypical example of privileged scaffolds with representatives in many therapeutic areas. A complete description of tubulin-binding sulfonamides is provided, covering the different species and drug sites. Some of the antimitotic sulfonamides have met with very successful applications and others less so, thus illustrating the advances, limitations, and future perspectives of the field. All of them combine in a mechanism of action and a clinical outcome that conform efficient drugs.

Perturbing mitosis for anti-cancer therapy: is cell death the only answer?

Interfering with mitosis for cancer treatment is an old concept that has proven highly successful in the clinics. Microtubule poisons are used to treat patients with different types of blood or solid cancer since more than 20 years, but how these drugs achieve clinical response is still unclear. Arresting cells in mitosis can promote their demise, at least in a petri dish. Yet, at the molecular level, this type of cell death is poorly defined and cancer cells often find ways to escape. The signaling pathways activated can lead to mitotic slippage, cell death, or senescence. Therefore, any attempt to unravel the mechanistic action of microtubule poisons will have to investigate aspects of cell cycle control, cell death initiation in mitosis and after slippage, at single-cell resolution. Here, we discuss possible mechanisms and signaling pathways controlling cell death in mitosis or after escape from mitotic arrest, as well as secondary consequences of mitotic errors, particularly sterile inflammation, and finally address the question how clinical efficacy of anti-mitotic drugs may come about and could be improved.

Targeting Apoptotic Activity Against Prostate Cancer Stem Cells

Numerous data suggest that an increase of cancer stem cells (CSCs) in tumor mass can be the reason for failure of conventional therapies because of their resistance. CD44+/CD24- cells are a putative cancer stem cells subpopulation in prostate cancer. TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) is an activator of apoptosis in tumor cells. However, some tumors are TRAIL-resistant. Cancer cells can be re-sensitized to TRAIL induced apoptosis by a combination of TRAIL and taxanes. The aim of this work was to analyze the enhancement of the anticancer effect of TRAIL by paclitaxel, cabazitaxel and docetaxel in the whole population of PC3 and DU145 prostate cancer cells, but also in CD44+/CD24- prostate cancer stem cells. We examined the apoptotic effect of TRAIL and taxanes using flow cytometry and Annexin-V-PE staining. The co-treatment with taxanes and TRAIL enhanced significantly the apoptosis in CD44+/CD24- cells only in PC3 cell line but not in DU145 cells. We discovered also that taxanes can increase the expression of death receptor TRAIL-R2 in PC3 prostate cancer cells. The results of our study show that treatment with paclitaxel, cabazitaxel and docetaxel is able to enhance the apoptosis induced by TRAIL even in prostate cancer stem cells.

Mitosis and mitochondrial priming for apoptosis

Cell division is a period of danger for cells, as inaccurate segregation of chromosomes can lead to loss of cell viability or aneuploidy. In order to protect against these dangers, cells ultimately initiate mitochondrial apoptosis if they are unable to correctly exit mitosis. A number of important chemotherapeutics exploit this response to delayed mitotic exit, but despite this, the molecular mechanism of the apoptotic timer in mitosis has proved elusive. Some recent studies have now shed light on this, showing how passage through the cell cycle fine-tunes a cell's apoptotic sensitivity such that it can respond appropriately when errors arise.

G2/M Cell Cycle Arrest and Tumor Selective Apoptosis of Acute Leukemia Cells by a Promising Benzophenone Thiosemicarbazone Compound

Anti-mitotic therapies have been considered a hallmark in strategies against abnormally proliferating cells. Focusing on the extensively studied family of thiosemicarbazone (TSC) compounds, we have previously identified 4,4'-dimethoxybenzophenone thiosemicarbazone (T44Bf) as a promising pharmacological compound in a panel of human leukemia cell lines (HL60, U937, KG1a and Jurkat). Present findings indicate that T44Bf-mediated antiproliferative effects are associated with a reversible chronic mitotic arrest caused by defects in chromosome alignment, followed by induced programmed cell death. Furthermore, T44Bf selectively induces apoptosis in leukemia cell lines when compared to normal peripheral blood mononuclear cells. The underlying mechanism of action involves the activation of the mitochondria signaling pathway, with loss of mitochondrial membrane potential and sustained phosphorylation of anti-apoptotic protein Bcl-xL as well as increased Bcl-2 (enhanced phosphorylated fraction) and pro-apoptotic protein Bad levels. In addition, ERK signaling pathway activation was found to be a requisite for T44Bf apoptotic activity. Our findings further describe a novel activity for a benzophenone thiosemicarbazone and propose T44Bf as a promising anti-mitotic prototype to develop chemotherapeutic agents to treat acute leukemia malignancies.

ABT-737, a small molecule Bcl-2/Bcl-xL antagonist, increases antimitotic-mediated apoptosis in human prostate cancer cells

Castration-resistant prostate cancer (CRPC) expresses high levels of the anti-apoptotic proteins Bcl-2, Bcl-xL and Mcl-1, resulting in resistance to apoptosis and association with poor prognosis. Docetaxel, an antimitotic drug that is the first-line treatment strategy for CRPC, is known to provide a small survival benefit. However, docetaxel chemotherapy alone is not enough to counteract the high levels of Bcl-2/Bcl-xL/Mcl-1 present in CRPC. ABT-737 is a small molecule that binds to Bcl-2/Bcl-xL (but not Mcl-1) with high affinity and disrupts their interaction with pro-apoptotic Bax/Bak, thus enhancing apoptosis. Our results indicate that ABT-737 can sensitize androgen-dependent LNCaP and CRPC PC3 cells to docetaxel- and to the novel antimitotic ENMD-1198-mediated caspase-dependent apoptosis. CRPC DU145 cells, however, are more resistant to ABT-737 because they are Bax null and not because they express the highest levels of anti-apoptotic Mcl-1 (associated with ABT-737 resistance). Knockdown of Bax or Bak in LNCaP indicates that ABT-737-induced antimitotic enhancement of apoptosis is more dependent on the levels of Bax than Bak. Furthermore, we find that the ability of docetaxel to increase cyclin B1/Cdk1-mediated phosphorylation of Bcl-2/Bcl-xL and decrease Mcl-1 is required for ABT-737 to enhance apoptosis in PC3 cells, as determined by addition of Cdk1 inhibitor purvalanol A and expression of shRNA specific for cyclin B1. Overall, our data suggests that the high levels of anti-apoptotic proteins in Bax-expressing CRPC cells can be overcome by targeting Bcl-2/Bcl-xL with ABT-737 and Mcl-1 with antimitotics.

Pro-apoptotic role of Cdc25A: activation of cyclin B1/Cdc2 by the Cdc25A C-terminal domain

Cdc25A is a dual specificity protein phosphatase that activates cyclin/cyclin-dependent protein kinase (Cdk) complexes by removing inhibitory phosphates from conserved threonine and tyrosine in Cdks. To address how Cdc25A promotes apoptosis, Jurkat cells were treated with staurosporine, an apoptosis inducer. Upon staurosporine treatment, a Cdc25A C-terminal 37-kDa fragment, designated C37, was generated by caspase cleavage at Asp-223. Thr-507 in C37 became dephosphorylated, which prevented 14-3-3 binding, as shown previously. C37 exhibited higher phosphatase activity than full-length Cdc25A. C37 with alanine substitution for Thr-507 (C37/T507A) that imitated the cleavage product during staurosporine treatment interacted with Cdc2, Cdk2, cyclin A, and cyclin B1 and markedly activated cyclin B1/Cdc2. The dephosphorylation of Thr-507 might expose the Cdc2/Cdk2-docking site in C37. C37/T507A also induced apoptosis in Jurkat and K562 cells, resulting from activating cyclin B1/Cdc2 but not Cdk2. Thus, this study reveals that Cdc25A is a pro-apoptotic protein that amplifies staurosporine-induced apoptosis through the activation of cyclin B1/Cdc2 by its C-terminal domain.

Combined modality immunotherapy and chemotherapy: a new perspective

The results of recent clinical trials have demonstrated that cancer vaccines continue to struggle to achieve tangible clinical benefits as monotherapy. Tumor-induced abnormalities in the immune system hamper anti-tumor T cell responses limiting the effectiveness of cancer immunotherapy. Recently, evidence has been mounting to suggest that immunotherapy has the possibility of achieving better success when used in combination with conventional chemotherapy. In clinical trials, immune responses elicited by cancer vaccines appear to augment the effectiveness of subsequent conventional cancer therapies.

Growth arrest and apoptosis induced by quercetin is not linked to adipogenic conversion of human preadipocytes

Quercetin is involved in several biological activities including inhibition of cell growth and induction of apoptosis in cancer cells. However, it is unclear and unknown whether quercetin influences cell maturation. We examined the effect of quercetin on the growth and differentiation of human preadipocyte cells AML-I. Induced growth arrest of AML-I by quercetin was accompanied by the appearance of characteristics of apoptosis under the adipogenic stimulation by annexin V-fluorescein isothiocyanate staining method. A decrease of nuclear factor-kappaB and the antiapoptotic protein Mcl-1 and an increase of the proapoptotic protein Bad were observed in time-dependent fashion in the quercetin-treated cells compared with the vehicle-treated cells by Western blot analysis. Structure-related flavonoids, including rutin (quercetin-3-O-rutinoside) and quercitrin (quercetin-3-O-rhamnoside), did not have any cytotoxic effect on AML-I. Interestingly, exposure of AML-I to quercetin for 6 days increased the amount of cytoplasmic lipid droplets as well as the expression of fatty acid synthase and peroxisome proliferator-activated receptor gamma proteins. These results suggested that apoptosis induced by quercetin was not linked to adipogenic conversion of preadipocytes.

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.

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 sulindac derivatives OSI-461, OSIP486823, and OSIP487703 arrest colon cancer cells in mitosis by causing microtubule depolymerization

Exisulind (sulindac sulfone) and three highly potent derivatives, OSI-461 (CP461), OSIP486823 (CP248), and OSIP487703, inhibit growth and induce apoptosis in SW480 human colon cancer cells, with IC(50)s of 200, 2, 0.1, and 0.003 micromol/L, respectively. The latter three compounds, but not exisulind, induce marked M-phase cell cycle arrest in these cells. This effect seems to be independent of the known ability of these compounds to cause activation of protein kinase G. When tested at twice their IC(50) concentration for growth inhibition, OSI-461, OSIP486823, and OSIP487703 cause depolymerization of microtubules in interphase cells, inhibit spindle formation in mitotic cells, and induce multinucleated cells. In vitro tubulin polymerization assays indicate that all three compounds interact with tubulin directly to cause microtubule depolymerization and/or inhibit de novo tubulin polymerization. These results suggest that the dual effects of OSI-461, OSIP486823, and OSIP487703 on impairment of microtubule functions and protein kinase G activation may explain the potent antiproliferative and apoptotic effects of these compounds in cancer cells.

BAD Ser128 is not phosphorylated by c-Jun NH2-terminal kinase for promoting apoptosis

The phosphorylation and regulation of the proapoptotic Bcl-2 family protein BAD by c-Jun NH2-terminal kinase (JNK) is controversial. JNK can suppress interleukin-3 withdrawal-induced apoptosis via phosphorylation of BAD at Thr201. However, it has also been reported that JNK promotes apoptosis through phosphorylation of BAD at Ser128. Here, we report that JNK is not a BAD Ser128 kinase. JNK phosphorylates murine BAD (mBAD), but not human BAD (hBAD), in which Ser91 is equivalent to Ser128 in mBAD. In contrast, Cdc2, which phosphorylates Ser128, phosphorylates both mBAD and hBAD. Replacement of Ser128 by alanine has no effects on BAD phosphorylation by JNK in vitro and in vivo. Two-dimensional phosphopeptide mapping in combination with phosphoamino acid analysis reveals that JNK does not phosphorylate BAD at Ser128. Elimination of Ser128 phosphorylation has no effects on the proapoptotic activity of BAD in apoptosis induced by UV via JNK or growth factor withdrawal. Thus, our results show that Ser128 is not phosphorylated by JNK for promoting cell death.