Possible involvement of caspase-7 in cell cycle progression at mitosis

Apoptosis-Cell Cycle-Autophagy Molecular Mechanisms Network in Heterogeneous Aggressive Phenotype Prostate Hyperplasia Primary Cell Cultures Have a Prognostic Role

Our study highlights the apoptosis, cell cycle, DNA ploidy, and autophagy molecular mechanisms network to identify prostate pathogenesis and its prognostic role. Caspase 3/7 expressions, cell cycle, adhesion glycoproteins, autophagy, nuclear shrinkage, and oxidative stress by flow-cytometry analysis are used to study the BPH microenvironment's heterogeneity. A high late apoptosis expression by caspases 3/7 activity represents an unfavorable prognostic biomarker, a dependent predictor factor for cell adhesion, growth inhibition by arrest in the G2/M phase, and oxidative stress processes network. The heterogeneous aggressive phenotype prostate adenoma primary cell cultures present a high S-phase category (>12%), with an increased risk of death or recurrence due to aneuploid status presence, representing an unfavorable prognostic biomarker, a dependent predictor factor for caspase 3/7 activity (late apoptosis and necrosis), and cell growth inhibition (G2/M arrest)-linked mechanisms. Increased integrin levels in heterogenous BPH cultures suggest epithelial-mesenchymal transition (EMT) that maintains an aggressive phenotype by escaping cell apoptosis, leading to the cell proliferation necessary in prostate cancer (PCa) development. As predictor biomarkers, the biological mechanisms network involved in apoptosis, the cell cycle, and autophagy help to establish patient prognostic survival or target cancer therapy development.

The Extremely-Low-Frequency Electromagnetic Field Affects Apoptosis and Oxidative-Stress-Related Genes and Proteins in the Porcine Endometrium-An In Vitro Study

Nowadays, the extremely-low-frequency electromagnetic field (ELF-EMF) is recognized as environmental pollution. The data indicate that the ELF-EMF may affect factors related to epigenetic regulation and alter important biological processes in the uterus. The impact of the ELF-EMF on apoptosis and oxidative-stress-related genes has not been documented in porcine endometrium. This raises the question of whether the exposure to the ELF-EMF can induce apoptosis and/or oxidative stress in the endometrium of pigs during the peri-implantation period. Porcine endometrial slices (100 ± 5 mg) collected (n = 5) during the peri-implantation period were treated in vitro with ELF-EMF at a frequency of 50 Hz and flux density of 8 × 104 mG for 2 h. To determine the effect of ELF-EMF on apoptosis and oxidative stress in the endometrium, CASP3, CASP7, CIDEB, GADD45G, NOS1, NOS2, NOS3, and TP53I3 mRNA transcript were analyzed using real-time PCR, and protein abundance of CASP3, CASP7 using Western blot, and eNOS using ELISA were determined. Moreover, CASP3/7 and NOS activity was analyzed using flow cytometry and colorimetry, respectively. The decreased CASP7 and increased NOS3 mRNA transcript and protein abundance in ELF-EMF-treated endometrium were observed. Moreover, CIDEB, GADD45G, and TP53I3 mRNA transcript abundance was increased. Only p ≤ 0.05 was considered a statistically significant difference. The documented alterations indicate the potential of the ELF-EMF to affect apoptosis and generate oxidative stress in the endometrium. The insight into observed consequences documents for the first time the fact that the ELF-EMF may influence endometrial cell proliferation, angiogenesis, and/or tissue receptivity during peri-implantation.

Caspase-4 has a role in cell division in epithelial cells through actin depolymerization

In addition to its role in pyroptosis and inflammatory cytokine maturation, caspase-4 (CASP4) also contributes to the fusion of phagosomes with lysosomes and cell migration. However, its role in cell division remains elusive. In this study, we demonstrate that CASP4 is indispensable for proper cell division in epithelial cells. Knockout of CASP4 (CASP4 KO) in HepG2 cells led to delayed cell proliferation, increased cell size, and increased multinucleation. In mitosis, CASP4 KO cells showed multipolar spindles, asymmetric spindle positioning, and chromosome segregation errors, ultimately increasing DNA content and chromosome number. We also found that phalloidin, a marker of filamentous actin, increased in CASP4 KO cells owing to suppressed actin depolymerization. Moreover, the levels of actin polymerization-related proteins, including Rho-associated protein kinase1 (ROCK1), LIM kinase1 (LIMK1), and phosphorylated cofilin, significantly increased in CASP4 KO cells. These results suggest that CASP4 contributes to proper cell division through actin depolymerization.

Repeated Rounds of Gonadotropin Stimulation Induce Imbalance in the Antioxidant Machinery and Activation of Pro-Survival Proteins in Mouse Oviducts

Controlled ovarian stimulation (COS) through gonadotropin administration has become a common procedure in assisted reproductive technologies. COS's drawback is the formation of an unbalanced hormonal and molecular environment that could alter several cellular mechanisms. On this basis, we detected the presence of mitochondrial DNA (mtDNA) fragmentation, antioxidant enzymes (catalase; superoxide dismutases 1 and 2, SOD-1 and -2; glutathione peroxidase 1, GPx1) and apoptotic (Bcl-2-associated X protein, Bax; cleaved caspases 3 and 7; phosphorylated (p)-heat shock protein 27, p-HSP27) and cell-cycle-related proteins (p-p38 mitogen-activated protein kinase, p-p38 MAPK; p-MAPK activated protein kinase 2, p-MAPKAPK2; p-stress-activated protein kinase/Jun amino-terminal kinase, p-SAPK/JNK; p-c-Jun) in the oviducts of unstimulated (Ctr) and repeatedly hyperstimulated (eight rounds, 8R) mice. While all the antioxidant enzymes were overexpressed after 8R of stimulation, mtDNA fragmentation decreased in the 8R group, denoting a present yet controlled imbalance in the antioxidant machinery. Apoptotic proteins were not overexpressed, except for a sharp increase in the inflammatory-related cleaved caspase 7, accompanied by a significant decrease in p-HSP27 content. On the other hand, the number of proteins involved in pro-survival mechanisms, such as p-p38 MAPK, p-SAPK/JNK and p-c-Jun, increased almost 50% in the 8R group. Altogether, the present results demonstrate that repeated stimulations cause the activation of the antioxidant machinery in mouse oviducts; however, this is not sufficient to induce apoptosis, and is efficiently counterbalanced by activation of pro-survival proteins.

Cyclin B/CDK1 and Cyclin A/CDK2 phosphorylate DENR to promote mitotic protein translation and faithful cell division

DENR and MCTS1 have been identified as oncogenes in several different tumor entities. The heterodimeric DENR·MCTS1 protein complex promotes translation of mRNAs containing upstream Open Reading Frames (uORFs). We show here that DENR is phosphorylated on Serine 73 by Cyclin B/CDK1 and Cyclin A/CDK2 at the onset of mitosis, and then dephosphorylated as cells exit mitosis. Phosphorylation of Ser73 promotes mitotic stability of DENR protein and prevents its cleavage at Asp26. This leads to enhanced translation of mRNAs involved in mitosis. Indeed, we find that roughly 40% of all mRNAs with elevated translation in mitosis are DENR targets. In the absence of DENR or of Ser73 phosphorylation, cells display elevated levels of aberrant mitoses and cell death. This provides a mechanism how the cell cycle regulates translation of a subset of mitotically relevant mRNAs during mitosis.

Interception Targets of Angelica Gigas Nakai Root Extract versus Pyranocoumarins in Prostate Early Lesions and Neuroendocrine Carcinomas in TRAMP Mice

We reported efficacy of Angelica gigas Nakai (AGN) root ethanol extract and equimolar decursin (D)/decursinol angelate (DA) through daily gavage starting at 8 weeks of age (WOA) to male transgenic adenocarcinoma of mouse prostate (TRAMP) mice such that these modalities suppressed precancerous epithelial lesions in their dorsolateral prostate (DLP) to similar extent, but AGN extract was better than the D/DA mixture at promoting the survival of mice bearing prostate neuroendocrine carcinomas to 28 WOA. Here, we compared by microarray hybridization the mRNA levels in pooled DLP tissues and individual neuroendocrine carcinomas to characterize potential molecular targets of AGN extract and D/DA. Clustering and principal component analyses supported distinct gene expression profiles of TRAMP DLP versus neuroendocrine carcinomas. Pathway Enrichment, Gene Ontology, and Ingenuity Pathway Analyses of differential genes indicated that AGN and D/DA affected chiefly processes of lipid and mitochondrial energy metabolism and oxidation-reduction in TRAMP DLP, while AGN affected neuronal signaling, immune systems and cell cycling in neuroendocrine carcinomas. Protein-Protein Interaction Network analysis predicted and reverse transcription-PCR verified multiple hub genes common in the DLP of AGN- and D/DA-treated TRAMP mice at 28 WOA and select hub genes attributable to the non-D/DA AGN components. The vast majority of hub genes in the AGN-treated neuroendocrine carcinomas differed from those in TRAMP DLP. In summary, the transcriptomic approach illuminated vastly different signaling pathways and networks, cellular processes, and hub genes of two TRAMP prostate malignancy lineages and their associations with the interception efficacy of AGN and D/DA. PREVENTION RELEVANCE: This study explores potential molecular targets associated with in vivo activity of AGN root alcoholic extract and its major pyranocoumarins to intercept precancerous epithelial lesions and early malignancies of the prostate. Without an ethically-acceptable, clearly defined cancer initiation risk reduction strategy available for the prostate, using natural products like AGN to delay formation of malignant tumors could be a plausible approach for prostate cancer prevention.

Cell-Cycle Cross Talk with Caspases and Their Substrates

Caspases play central roles in mediating both cell death and inflammation. It has more recently become evident that caspases also drive other biological processes. Most prominently, caspases have been shown to be involved in differentiation. Several stem and progenitor cell types rely on caspases to initiate and execute their differentiation processes. These range from neural and glial cells, to skeletal myoblasts and osteoblasts, and several cell types of the hematopoietic system. Beyond differentiation, caspases have also been shown to play roles in other "noncanonical" processes, including cell proliferation, arrest, and senescence, thereby contributing to the mechanisms that regulate tissue homeostasis at multiple levels. Remarkably, caspases directly influence the course of the cell cycle in both a positive and negative manner. Caspases both cleave elements of the cell-cycle machinery and are themselves substrates of cell-cycle kinases. Here we aim to summarize the breadth of interactions between caspases and cell-cycle regulators. We also highlight recent developments in this area.

The Aurora B specificity switch is required to protect from non-disjunction at the metaphase/anaphase transition

The Aurora B abscission checkpoint delays cytokinesis until resolution of DNA trapped in the cleavage furrow. This process involves PKCε phosphorylation of Aurora B S227. Assessing if this PKCε-Aurora B module provides a more widely exploited genome-protective control for the cell cycle, we show Aurora B phosphorylation at S227 by PKCε also occurs during mitosis. Expression of Aurora B S227A phenocopies inhibition of PKCε in by-passing the delay and resolution at anaphase entry that is associated with non-disjunction and catenation of sister chromatids. Implementation of this anaphase delay is reflected in PKCε activation following cell cycle dependent cleavage by caspase 7; knock-down of caspase 7 phenocopies PKCε loss, in a manner rescued by ectopically expressing/generating a free PKCε catalytic domain. Molecular dynamics indicates that Aurora B S227 phosphorylation induces conformational changes and this manifests in a profound switch in specificity towards S29 TopoIIα phosphorylation, a response necessary for catenation resolution during mitosis.

Mitotic slippage is determined by p31comet and the weakening of the spindle-assembly checkpoint

Mitotic slippage involves cells exiting mitosis without proper chromosome segregation. Although degradation of cyclin B1 during prolonged mitotic arrest is believed to trigger mitotic slippage, its upstream regulation remains obscure. Whether mitotic slippage is caused by APC/C^CDC20 activity that is able to escape spindle-assembly checkpoint (SAC)-mediated inhibition, or is actively promoted by a change in SAC activity remains an outstanding issue. We found that a major culprit for mitotic slippage involves reduction of MAD2 at the kinetochores, resulting in a progressive weakening of SAC during mitotic arrest. A further level of control of the timing of mitotic slippage is through p31^comet-mediated suppression of MAD2 activation. The loss of kinetochore MAD2 was dependent on APC/C^CDC20, indicating a feedback control of APC/C to SAC during prolonged mitotic arrest. The gradual weakening of SAC during mitotic arrest enables APC/C^CDC20 to degrade cyclin B1, cumulating in the cell exiting mitosis by mitotic slippage.

SAHA and EGCG Promote Apoptosis in Triple-negative Breast Cancer Cells, Possibly Through the Modulation of cIAP2

BACKGROUND/AIM

Inhibition of apoptosis is one of the hallmarks of cancer, and anti-apoptotic genes are often targets of genetic and epigenetic alterations. Cellular inhibitor of apoptosis 2 (cIAP2) has a role in degrading caspases by linking them to ubiquitin molecules, and is upregulated in triple-negative breast cancer (TNBC). Previous studies have demonstrated that cIAP2 may play a role in the epithelial-to-mesenchymal transition (EMT).

MATERIALS AND METHODS

Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase (HDAC) inhibitor, was administered to triple-negative breast cancer (TNBC) cells alone or in combination with epigallocatechin-3-gallate (EGCG), a DNA methyltransferase (DNMT) inhibitor isolated from green tea.

RESULTS

The compounds were able to decrease the expression of cIAP2 while increasing the expression of pro-apoptotic caspase 7. There were also changes in histone modifications, suggesting a role of epigenetic mechanisms in these changes in expression of cIAP2. These changes resulted in an increase in apoptosis. SAHA and EGCG were also capable of limiting TNBC cell migration across a fibronectin (FN) matrix.

CONCLUSION

SAHA and EGCG reduce the metastatic potential of TNBC by inducing the apoptotic pathway.

When dying is not the end: Apoptotic caspases as drivers of proliferation

Caspases are well known for their role as executioners of apoptosis. However, recent studies have revealed that these lethal enzymes also have important mitogenic functions. Caspases can promote proliferation through autonomous regulation of the cell cycle, as well as by induction of secreted signals, which have a profound impact in neighboring tissues. Here, I review the proliferative role of caspases during development and homeostasis, in addition to their key regenerative function during tissue repair upon injury. Furthermore, the emerging properties of apoptotic caspases as drivers of carcinogenesis are discussed, as well as their involvement in other diseases. Finally, I examine further effects of caspases regulating death and survival in a non-autonomous manner.

Overexpression of caspase 7 is ERα dependent to affect proliferation and cell growth in breast cancer cells by targeting p21(Cip)

Caspase 7 (CASP7) expression has important function during cell cycle progression and cell growth in certain cancer cells and is also involved in the development and differentiation of dental tissues. However, the function of CASP7 in breast cancer cells is unclear. The aim of this study was to analyze the expression of CASP7 in breast carcinoma patients and determine the role of CASP7 in regulating tumorigenicity in breast cancer cells. In this study, we show that the CASP7 expression is high in breast carcinoma tissues compared with normal counterpart. The ectopic expression of CASP7 is significantly associated with ERα expression status and persistently elevated in different stages of the breast tumor grades. High level of CASP7 expression showed better prognosis in breast cancer patients with systemic endocrine therapy as observed from Kaplan–Meier analysis. S3 and S4, estrogen responsive element (ERE) in the CASP7 promoter, is important for estrogen-ERα-mediated CASP7 overexpression. Increased recruitment of p300, acetylated H3 and pol II in the ERE region of CASP7 promoter is observed after hormone stimulation. Ectopic expression of CASP7 in breast cancer cells results in cell growth and proliferation inhibition via p21^Cip reduction, whereas small interfering RNA (siRNA) mediated reduction of CASP7 rescued p21^Cip levels. We also show that pro- and active forms of CASP7 is located in the nucleus apart from cytoplasmic region of breast cancer cells. The proliferation and growth of breast cancer cells is significantly reduced by broad-spectrum peptide inhibitors and siRNA of CASP7. Taken together, our findings show that CASP7 is aberrantly expressed in breast cancer and contributes to cell growth and proliferation by downregulating p21^Cip protein, suggesting that targeting CASP7-positive breast cancer could be one of the potential therapeutic strategies.

RNA disruption is associated with response to multiple classes of chemotherapy drugs in tumor cell lines

BACKGROUND

Cellular stressors and apoptosis-inducing agents have been shown to induce ribosomal RNA (rRNA) degradation in eukaryotic cells. Recently, RNA degradation in vivo was observed in patients with locally advanced breast cancer, where mid-treatment tumor RNA degradation was associated with complete tumor destruction and enhanced patient survival. However, it is not clear how widespread chemotherapy induced "RNA disruption" is, the extent to which it is associated with drug response or what the underlying mechanisms are.

METHODS

Ovarian (A2780, CaOV3) and breast (MDA-MB-231, MCF-7, BT474, SKBR3) cancer cell lines were treated with several cytotoxic chemotherapy drugs and total RNA was isolated. RNA was also prepared from docetaxel resistant A2780DXL and carboplatin resistant A2780CBN cells following drug exposure. Disruption of RNA was analyzed by capillary electrophoresis. Northern blotting was performed using probes complementary to the 28S and 18S rRNA to determine the origins of degradation bands. Apoptosis activation was assessed by flow cytometric monitoring of annexin-V and propidium iodide (PI) binding to cells and by measuring caspase-3 activation. The link between apoptosis and RNA degradation (disruption) was investigated using a caspase-3 inhibitor.

RESULTS

All chemotherapy drugs tested were capable of inducing similar RNA disruption patterns. Docetaxel treatment of the resistant A2780DXL cells and carboplatin treatment of the A2780CBN cells did not result in RNA disruption. Northern blotting indicated that two RNA disruption bands were derived from the 3'-end of the 28S rRNA. Annexin-V and PI staining of docetaxel treated cells, along with assessment of caspase-3 activation, showed concurrent initiation of apoptosis and RNA disruption, while inhibition of caspase-3 activity significantly reduced RNA disruption.

CONCLUSIONS

Supporting the in vivo evidence, our results demonstrate that RNA disruption is induced by multiple chemotherapy agents in cell lines from different tissues and is associated with drug response. Although present, the link between apoptosis and RNA disruption is not completely understood. Evaluation of RNA disruption is thus proposed as a novel and effective biomarker to assess response to chemotherapy drugs in vitro and in vivo.

Apoptotic Caspases in Promoting Cancer: Implications from Their Roles in Development and Tissue Homeostasis

Apoptosis, a major form of programmed cell death, is an important mechanism to remove extra or unwanted cells during development. In tissue homeostasis apoptosis also acts as a monitoring machinery to eliminate damaged cells in response to environmental stresses. During these processes, caspases, a group of proteases, have been well defined as key drivers of cell death. However, a wealth of evidence is emerging which supports the existence of many other non-apoptotic functions of these caspases, which are essential not only in proper organism development but also in tissue homeostasis and post-injury recovery. In particular, apoptotic caspases in stress-induced dying cells can activate mitogenic signals leading to proliferation of neighbouring cells, a phenomenon termed apoptosis-induced proliferation. Apparently, such non-apoptotic functions of caspases need to be controlled and restrained in a context-dependent manner during development to prevent their detrimental effects. Intriguingly, accumulating studies suggest that cancer cells are able to utilise these functions of caspases to their advantage to enable their survival, proliferation and metastasis in order to grow and progress. This book chapter will review non-apoptotic functions of the caspases in development and tissue homeostasis with focus on how these cellular processes can be hijacked by cancer cells and contribute to tumourigenesis.

Immunoreactivity of Ki-67/β-tubulin and immunocolocalization with active caspase-3 in rat dentate gyrus during postnatal development

This study was based on our previous report that the expression of active caspase-3 kept at a high level in dentate gyrus during postnatal development, which is not related to an apoptotic event. We addressed the hypothesis that the active caspase-3 expression may be related to a nonapoptotic role in the regulation of the cell cycle and differentiation or other physiological functions. To confirm this hypothesis, through a temporal investigation from postnatal day (P) 0, 4, 7, 10, 14, 21, 28, to 56, based on immunofluorescent method, we dual labeled active caspase-3 with Ki-67 or β-tubulin in the dentate gyrus. Our results showed a minority of active caspase-3 positive cells were colabeled with the proliferation marker Ki-67 in stratum moleculare (MOL), granular cell layer (GCL), subgranular zone (SGZ) and polymorphic stratum (POLY) from P0 to P14, and the colabeled cells decreased gradually with age. From P21 to P56, the colocalization of the two proteins was mainly focused on SGZ. There was a positive correlation between the positive cells of active caspase-3 with that of Ki-67. In addition, an extensive colocalization between active caspase-3 and β-tubulin was observed at all the age groups. There was a strong positive correlation between the intensity of active caspase-3 in GCL with that of β-tubulin in MOL, GCL and POLY of dentate gyrus and the stratum lucidum of CA3. Our data raised the possibility of a nonapoptotic role of active caspase-3 in dentate gyrus, which may be partly associated with cellular proliferation and differentiation, and also may be related to neurite outgrowth, axonal transport, or dendrite elongation of granular cells during postnatal development.

Development of high content imaging methods for cell death detection in human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CM) are being investigated as a new source of cardiac cells for drug safety assessment. We developed a novel scalable high content microscopy-based method for the detection of cell death in hPSC-CM that can serve for future predictive in vitro cardio-toxicological screens. Using rat neonatal ventricular cardiomyocytes (RVNC) or hPSC-CM, assays for nuclear remodelling, mitochondrial status, apoptosis and necrosis were designed using a combination of fluorescent dyes and antibodies on an automated microscopy platform. This allowed the observation of a chelerythrine-induced concentration-dependent apoptosis to necrosis switch and time-dependent progression of early apoptotic cells towards a necrotic-like phenotype. Susceptibility of hPSC-CM to chelerythrine-stimulated apoptosis varied with time after differentiation, but at most time points, hPSC-CM were more resistant than RVNC. This simple and scalable humanized high-content assay generates accurate cardiotoxicity profiles that can serve as a base for further assessment of cardioprotective strategies and drug safety.

Preferential Fas-mediated apoptotic execution at G1 phase: the resistance of mitotic cells to the cell death

Apoptosis is induced by various stresses generated from the extracellular and intracellular environments. The fidelity of the cell cycle is monitored by surveillance mechanisms that arrest its further progression if any crucial process has not been completed or damages are sustained, and then the cells with problems undergo apoptosis. Although the molecular mechanisms involved in the regulation of the cell cycle and that of apoptosis have been elucidated, the links between them are not clear, especially that between cell cycle and death receptor-mediated apoptosis. By using the HeLa.S-Fucci (fluorescent ubiquitination-based cell cycle indicator) cells, we investigated the relationship between the cell cycle progression and apoptotic execution. To monitor apoptotic execution during cell cycle progression, we observed the cells after induction of apoptosis with time-lapse fluorescent microscopy. About 70% of Fas-mediated apoptotic cells were present at G₁ phase and about 20% of cells died immediately after cytokinesis, whereas more than 60% of etoposide-induced apoptotic cells were at S/G₂ phases in random culture of the cells. These results were confirmed by using synchronized culture of the cells. Furthermore, mitotic cells showed the resistance to Fas-mediated apoptosis. In conclusion, these findings suggest that apoptotic execution is dependent on cell cycle phase and Fas-mediated apoptosis preferentially occurs at G₁ phase.

Proliferating γδ T cells manifest high and spatially confined caspase-3 activity

Caspase-8 serves two paradoxical roles in T lymphocytes: it initiates apoptosis following death receptor engagement, and is also indispensible for proliferation following T-cell antigen receptor (TCR) signalling. These opposing processes appear to be controlled by both spatial and quantitative differences in caspase-8 activation. Given differences in the turnover of T-cell subsets, we compared caspase activity and susceptibility to cell death following TCR restimulation in murine CD4(+) and CD8(+) αβ T cells and γδ T cells. We observed a spectrum of caspase activity in non-dying effector T cells in which CD4(+) T cells manifested the lowest levels of active caspases whereas γδ T cells manifested the highest levels. Further analysis revealed that most of the difference in T-cell subsets was the result of high levels of active caspase-3 in non-dying effector γδ T cells. Despite this, γδ T cells manifested little spontaneous or CD3 restimulation-induced cell death as the result of confinement of active caspases to the cell membrane. By contrast, CD4(+) T cells were highly sensitive to CD3-induced cell death, associated with the appearance of active caspases in the cytoplasm and cleavage of the caspase substrates Bid and ICAD. Hence, the location and amount of active caspases distinguishes effector T-cell subsets and profoundly influences the fate of the T-cell response.

Non-apoptotic function of apoptotic proteins in the development of Malpighian tubules of Drosophila melanogaster

Drosophila metamorphosis is characterized by the histolysis of larval structures by programmed cell death, which paves the way for the establishment of adult-specific structures under the influence of the steroid hormone ecdysone. Malpighian tubules function as an excretory system and are one of the larval structures that are not destroyed during metamorphosis and are carried over to adulthood. The pupal Malpighian tubules evade destruction in spite of expressing apoptotic proteins, Reaper, Hid, Grim, Dronc and Drice. Here we show that in the Malpighian tubules expression of apoptotic proteins commences right from embryonic development and continues throughout the larval stages. Overexpression of these proteins in the Malpighian tubules causes larval lethality resulting in malformed tubules. The number and regular organization of principal and stellate cells of Malpighian tubules is disturbed, in turn disrupting the physiological functioning of the tubules as well. Strikingly, the localization of beta-tubulin, F-actin and Disclarge (Dlg) is also disrupted. These results suggest that the apoptotic proteins could be having non-apoptotic function in the development of Malpighian tubules.

Regulation of caspase pathways by protein kinase CK2: identification of proteins with overlapping CK2 and caspase consensus motifs

Apoptosis, or programmed cell death, is a vital cellular process often impaired in diseases such as cancer. Aspartic acid-directed proteases known as caspases cleave a broad spectrum of cellular proteins and are central constituents of the apoptotic machinery. Caspases are regulated by a variety of mechanisms including protein phosphorylation. One intriguing mechanism by which protein kinases can modulate caspase pathways is by blocking substrate cleavage through phosphorylation of residues adjacent to caspase cleavage sites. To explore this mechanism in detail, we recently undertook a systematic investigation using a combination of bioinformatics, peptide arrays, and peptide cleavage assays to identify proteins with overlapping protein kinase and caspase recognition motifs (Duncan et al., Sci Signal 4:ra30, 2011). These studies implicated protein kinase CK2 as a global regulator of apoptotic pathways. In this article, we extend the analysis of proteins with overlapping CK2 and caspase consensus motifs to examine the convergence of CK2 with specific caspases and to identify CK2/caspase substrates known to be phosphorylated or cleaved in cells. Given its constitutive activity and elevated expression in cancer, these observations suggest that the ability of CK2 to modulate caspase pathways may contribute to a role in promoting cancer cell survival and raise interesting prospects for therapeutic targeting of CK2.

Caspase activity is not required for the mitotic checkpoint or mitotic slippage in human cells

Biochemical studies suggest that caspase activity is required for a functional mitotic checkpoint (MC) and mitotic slippage. To test this directly, we followed nontransformed human telomerase immortalized human retinal pigment epithelia (RPE-1) cells through mitosis after inhibiting or depleting selected caspases. We found that inhibiting caspases individually, in combination, or in toto did not affect the duration or fidelity of mitosis in otherwise untreated cells. When satisfaction of the MC was prevented with 500 nM nocodazole or 2.5 μM dimethylenastron (an Eg5 inhibitor), 92-100% of RPE-1 cells slipped from mitosis in the presence of pan-caspase inhibitors or after simultaneously depleting caspase-3 and -9, and they did so with the same kinetics (~21-22 h) as after treatment with nocodazole or Eg5 inhibitors alone. Surprisingly, inhibiting or depleting caspase-9 alone doubled the number of nocodazole-treated, but not Eg5-inhibited, cells that died in mitosis. In addition, inhibiting or depleting caspase-9 and -3 together accelerated the rate of slippage ~40% (to ~13-15 h). Finally, nocodazole-treated cells that recently slipped through mitosis in the presence or absence of pan-caspase inhibitors contained numerous BubR1 foci in their nuclei. From these data, we conclude that caspase activity is not required for a functional MC or for mitotic slippage.

Contribution of caspase(s) to the cell cycle regulation at mitotic phase

Caspases have been suggested to contribute to not only apoptosis regulation but also non-apoptotic cellular phenomena. Recently, we have reported the involvement of caspase-7 to the cell cycle progression at mitotic phase by knockdown of caspase-7 using small interfering RNAs and short hairpin RNA. Here we showed that chemically synthesized broad-spectrum caspase inhibitors, which have been used to suppress apoptosis, prevented the cell proliferation in a dose-dependent manner, and that the subtype-specific peptide-based caspase inhibitor for caspase-3 and -7, but not for caspase-9, inhibited cell proliferation. It was also indicated that the BIR2 domain of X-linked inhibitor of apoptosis protein, functioning as an inhibitor for caspase-3 and -7, but not the BIR3 domain which plays as a caspase-9 inhibitor, induced cell cycle arrest. Furthermore, flow cytometry revealed that the cells treated with caspase inhibitors arrested at G₂/M phase. By using HeLa.S-Fucci (fluorescent ubiquitination-based cell cycle indicator) cells, the prevention of the cell proliferation by caspase inhibitors induced cell cycle arrest at mitotic phase accompanying the accumulation of the substrates for APC/C, suggesting the impairment of the APC/C activity at the transition from M to G₁ phases. These results indicate that caspase(s) contribute to the cell cycle regulation at mitotic phase.

Caspase-3-dependent mitotic checkpoint inactivation by the small-molecule inducers of mitotic slippage SU6656 and geraldol

Microtubule-targeting cancer drugs such as paclitaxel block cell-cycle progression at mitosis by prolonged activation of the mitotic checkpoint. Cells can spontaneously escape mitotic arrest and enter interphase without chromosome segregation by a process termed mitotic slippage that involves the degradation of cyclin B1 without mitotic checkpoint inactivation. Inducing mitotic slippage with chemicals causes cells to die after multiple rounds of DNA replication without cell division, which may enhance the antitumor activity of microtubule-targeting drugs. Here, we explore pathways leading to mitotic slippage by using SU6656 and geraldol, two recently identified chemical inducers of mitotic slippage. Mitotic slippage induced by SU6656 or geraldol was blocked by the proteasome inhibitor MG-132 and involved proteasome-dependent degradation of cyclin B1 and the mitotic checkpoint proteins budding uninhibited by benzimidazole related 1 (BubR1) and cell division cycle 20 (Cdc20) in T98G cells. Mitotic slippage and the degradation of BubR1 and Cdc20 were also inhibited by the caspase-3 and -7 inhibitor DEVD-CHO. MCF-7 cells lacking caspase-3 expression could not degrade BubR1 or undergo mitotic slippage in response to SU6656 or geraldol. Introduction of caspase-3 completely restored the ability of MCF-7 cells to degrade BubR1 and undergo mitotic slippage. However, lack of expression of caspase-3 did not affect cell death after exposure to paclitaxel, with or without mitotic slippage induction. The requirement for caspase-3 for chemically induced mitotic slippage reveals a new mechanism for mitotic exit and a link between mitosis and apoptosis that has implications for the outcome of cancer chemotherapy.

The promyelocytic leukemia zinc finger (PLZF) protein exerts neuroprotective effects in neuronal cells and is dysregulated in experimental stroke

Stroke is one of the major medical burdens in industrialized countries. Animal experiments indicate that blockade of the angiotensin AT1 receptor (AT1R) improves neurological outcome after cerebral ischemia. These protective effects are partially mediated by the angiotensin AT2 receptor (AT2R). The transcription factor promyelocytic leukemia zinc finger (PLZF) was identified as a direct adapter protein of the AT2R. Furthermore, our group was able to demonstrate that PLZF also directly binds and mediates the effects of the human (pro)renin receptor [(P)RR] which is involved in brain development. Therefore, we hypothesized that PLZF is involved in neuroprotection. Here we show that PLZF and its receptors (P)RR and AT2R exhibited an ubiquitous expression pattern in different brain regions. Furthermore, stable PLZF overexpression in human neuronal cells was able to mediate neuroprotection in a glutamate toxicity model in vitro. Consistently, PLZF mRNA and protein were downregulated on the ipsilateral side in a stroke model in vivo, whereas the neurodetrimental PLZF target genes cyclin A2 and BID were upregulated under this condition. Further analyses indicated that the neuroprotective AT2R is upregulated upon stable PLZF overexpression in cultured neuronal cells. Finally, reporter gene assays demonstrated the functionality of (P)RR promoter polymorphisms regarding basal and PLZF-induced activity.

The enigmatic roles of caspases in tumor development

One function ascribed to apoptosis is the suicidal destruction of potentially harmful cells, such as cancerous cells. Hence, their growth depends on evasion of apoptosis, which is considered as one of the hallmarks of cancer. Apoptosis is ultimately carried out by the sequential activation of initiator and executioner caspases, which constitute a family of intracellular proteases involved in dismantling the cell in an ordered fashion. In cancer, therefore, one would anticipate caspases to be frequently rendered inactive, either by gene silencing or by somatic mutations. From clinical data, however, there is little evidence that caspase genes are impaired in cancer. Executioner caspases have only rarely been found mutated or silenced, and also initiator caspases are only affected in particular types of cancer. There is experimental evidence from transgenic mice that certain initiator caspases, such as caspase-8 and -2, might act as tumor suppressors. Loss of the initiator caspase of the intrinsic apoptotic pathway, caspase-9, however, did not promote cellular transformation. These data seem to question a general tumor-suppressive role of caspases. We discuss several possible ways how tumor cells might evade the need for alterations of caspase genes. First, alternative splicing in tumor cells might generate caspase variants that counteract apoptosis. Second, in tumor cells caspases might be kept in check by cellular caspase inhibitors such as c-FLIP or XIAP. Third, pathways upstream of caspase activation might be disrupted in tumor cells. Finally, caspase-independent cell death mechanisms might abrogate the selection pressure for caspase inactivation during tumor development. These scenarios, however, are hardly compatible with the considerable frequency of spontaneous apoptosis occurring in several cancer types. Therefore, alternative concepts might come into play, such as compensatory proliferation. Herein, apoptosis and/or non-apoptotic functions of caspases may even promote tumor development. Moreover, experimental evidence suggests that caspases might play non-apoptotic roles in processes that are crucial for tumorigenesis, such as cell proliferation, migration, or invasion. We thus propose a model wherein caspases are preserved in tumor cells due to their functional contributions to development and progression of tumors.

Targeting polo-like kinase 1 enhances radiation efficacy for head-and-neck squamous cell carcinoma

PURPOSE

To investigate the efficacy of targeting polo-like kinase 1 (Plk1) combined with ionizing radiotherapy (RT) for head-and-neck squamous cell carcinoma (HNSCC).

METHODS AND MATERIALS

Polo-like kinase 1 messenger ribonucleic acid (mRNA) was targeted by small interfering RNA (siRNA) transfection into the FaDu HNSCC cell line; reduction was confirmed using quantitative real-time polymerase chain reaction. The cellular effects were assessed using [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium], clonogenic, flow cytometric, and caspase assays. In vivo efficacy of siPlk1 was evaluated using mouse xenograft models.

RESULTS

Small interfering Plk1 significantly decreased Plk1 mRNA expression, while also increasing cyclin B1 and p21(Waf1/CIP1) mRNA levels after 24 h. This depletion resulted in a time-dependent increase in FaDu cytotoxicity, which was enhanced by the addition of RT. Flow cytometric and caspase assays demonstrated progressive apoptosis, DNA double-strand breaks (gamma-H2AX), G2/M arrest, and activation of caspases 3 and 7. Implantation of siPlk1-treated FaDu cells in severe combined immunodeficient mice delayed tumor formation, and systemic administration of siPlk1 inhibited tumor growth enhanced by RT.

CONCLUSIONS

These data demonstrate the suitability of Plk1 as a potential therapeutic target for HNSCC, because Plk1 depletion resulted in significant cytotoxicity in vitro and abrogated tumor-forming potential in vivo. The effects of Plk1 depletion were enhanced with the addition of RT, indicating that Plk1 represents an important potential radiation sensitizer for HNSCC.