UV irradiation-induced apoptosis leads to activation of a 36-kDa myelin basic protein kinase in HL-60 cells

Metabolic Recycling Enhances Proliferation in MYC-Transformed Lymphoma B Cells

Relapses negatively impact cancer patient survival due to the tumorigenesis ability of surviving cancer cells post-therapy. Efforts are needed to better understand and combat this problem. This study hypothesized that dead cell debris post-radiation therapy creates an advantageous microenvironment rich in metabolic materials promoting the growth of remaining live cancer cells. In this study, live cancer cells are co-cultured with dead cancer cells eradicated by UV radiation to mimic a post-therapy environment. Isotopic labeling metabolomics is used to investigate the metabolic behavior of cancer cells grown in a post-radiation-therapy environment. It is found that post-UV-eradicated dead cancer cells serve as nutritional sources of "off-the-shelf" and precursor metabolites for surviving cancer cells. The surviving cancer cells then take up these metabolites, integrate and upregulate multiple vital metabolic processes, thereby significantly increasing growth in vitro and probably in vivo beyond their intrinsic fast-growing characteristics. Importantly, this active metabolite uptake behavior is only observed in oncogenic but not in non-oncogenic cells, presenting opportunities for therapeutic approaches to interrupt the active uptake process of oncogenic cells without affecting normal cells. The process by which living cancer cells re-use vital metabolites released by dead cancer cells post-therapy is coined in this study as "metabolic recycling" of oncogenic cells.

Mst1: Function and Mechanism in Brain and Myocardial Ischemia Reperfusion Injury

Mammalian STE20-like kinase-1 (Mst1) is a generally expressed apoptosis-promoting kinase and a key bridgebuilder of apoptotic signaling in the etiology of tissue injury. Despite the fact that the biological function of Mst1 and its role in the cell's signalling network have yet to be determined, however, there is a lot of evidence that Mst1 plays an important role in cell death which results from tissue injury. Previous studies have shown that Mst1 is not only a target for some apoptosis- related molecules such as caspase 3 and P53, but also act as an activator of these proteinases to magnify apoptosis signal pathways. This article reviews the role of Mst1 in the signaling pathways which is related with the neuronal cell apoptosis or microglia activation following myocardial and brain injury. Therefore, this work contributes to better understanding of the pathological process of myocardial and brain injury.

Whole-genome DNA methylation characteristics in pediatric precursor B cell acute lymphoblastic leukemia (BCP ALL)

In addition to genetic alterations, epigenetic abnormalities have been shown to underlie the pathogenesis of acute lymphoblastic leukemia (ALL)—the most common pediatric cancer. The purpose of this study was to characterize the whole genome DNA methylation profile in children with precursor B-cell ALL (BCP ALL) and to compare this profile with methylation observed in normal bone marrow samples. Additional efforts were made to correlate the observed methylation patterns with selected clinical features. We assessed DNA methylation from bone marrow samples obtained from 38 children with BCP ALL at the time of diagnosis along with 4 samples of normal bone marrow cells as controls using Infinium MethylationEPIC BeadChip Array. Patients were diagnosed and stratified into prognosis groups according to the BFM ALL IC 2009 protocol. The analysis of differentially methylated sites across the genome as well as promoter methylation profiles allowed clear separation of the leukemic and control samples into two clusters. 86.6% of the promoter-associated differentially methylated sites were hypermethylated in BCP ALL. Seven sites were found to correlate with the BFM ALL IC 2009 high risk group. Amongst these, one was located within the gene body of the MBP gene and another was within the promoter region- PSMF1 gene. Differentially methylated sites that were significantly related with subsets of patients with ETV6-RUNX1 fusion and hyperdiploidy. The analyzed translocations and change of genes’ sequence context does not affect methylation and methylation seems not to be a mechanism for the regulation of expression of the resulting fusion genes.

Hydrogen sulfide ameliorates subarachnoid hemorrhage-induced neuronal apoptosis via the ROS-MST1 pathway

Background

Hydrogen sulfide (H₂S) has shown a neuroprotective role in several cerebrovascular diseases. This study aimed to explore the underlying mechanisms of H₂S in early brain injury after subarachnoid hemorrhage (SAH).

Methods

One hundred seventy-seven male Sprague-Dawley rats were employed in this study. Sodium hydrosulfide (NaHS), a donor of H₂S, was injected intraperitoneally at 60 min after SAH was induced by endovascular perforation. Western blot analysis determined the expression of several proteins of interest, and an immunofluorescence assay was used to examine neuronal apoptosis.

Results

Exogenous NaHS markedly improved neurological scores, attenuated brain edema, and ameliorated neuronal apoptosis at 24 h after SAH induction. The underlying mechanisms of H₂S in ameliorating neuronal apoptosis might be executed through inhibition of the activity of mammalian sterile 20-like kinase 1 (MST1) protein. Western blot analysis demonstrated that exogenous NaHS decreased cleaved MST1 (cl-MST1) while increasing full-length MST1 expression. This anti-apoptotic effect of H₂S could be reversed by chelerythrine, which could activate MST1 via caspase-dependent cleavage.

Conclusions

Exogenous NaHS, as a donor of H₂S, could ameliorate early brain injury after SAH by inhibiting neuronal apoptosis by reducing the activity of the MST1 protein.

Regulation of mammalian Ste20 (Mst) kinases

Initially identified as mammalian homologs to yeast Ste20 kinases, the mammalian sterile twenty-like (Mst) 1/2 kinases have been widely investigated subsequent to their rediscovery as key components of the Hippo tumor suppressor pathway in flies. To date, our understanding of Mst substrates and downstream signaling outstrips our knowledge of how these enzymes are controlled by upstream signals. While much remains to be discovered regarding the mechanisms of Mst regulation, it is clear that Mst1 kinase activity is governed at least in part by its state of dimerization, including self-association and also heterodimerization with various other signaling partners. Here we review the basic architecture of Mst signaling and function and discuss recent advances in our understanding of how these important kinases are regulated.

Protein-L-isoaspartate (D-aspartate) O-methyltransferase protects cardiomyocytes against hypoxia induced apoptosis through inhibiting proapoptotic kinase Mst1

BACKGROUND

Mammalian sterile 20-like kinase 1 (Mst1) is a mammalian homolog of Hippo kinase from Drosophila and it is a critical component of the Hippo signaling pathway, which regulates a variety of biological processes ranging from cell contact inhibition, organ size control, apoptosis and tumor suppression in mammals. Mst1 plays essential roles in heart disease since its activation causes cardiomyocyte apoptosis and dilated cardiomyopathy. However, the mechanism underlying Mst1 activation in the heart is not known.

METHODS AND RESULTS

To identify novel cardiac proteins that may regulate Mst1 activity in the heart under pathophysiological conditions, a yeast two-hybrid screening of a human heart cDNA library with a dominant-negative Mst1 (K59R) mutant used as bait was performed. As a result, protein-L-isoaspartate (D-aspartate) O-methyltransferase (PCMT1) was identified as an Mst1-interacting protein. The interaction of PCMT1 with Mst1 was confirmed by co-immunoprecipitation in both co-transfected HEK293 cells and native cardiomyocytes, in which PCMT1 interacted with the kinase domain of Mst1, but not with its C-terminal regulatory domain. Overexpression of PCMT1 did not affect the Mst1 expression, but significantly attenuated the Mst1 activation and its apoptotic effects in response to the hypoxia/reoxygenation induced injury in cardiomyocytes. Indeed, upregulation of PCMT1 by CGP3466B, a compound related to the anti-Parkinson's drug R-(-)-deprenyl with potent antiapoptotic effects, inhibited the hypoxia/reoxygenation induced Mst1 activation and cardiomyocyte apoptosis.

CONCLUSIONS

These findings implicate PCMT1 as a novel inhibitor of Mst1 activation in cardiomyocytes and suggest that targeting PCMT1 may prevent myocardial apoptosis through inhibition of Mst1.

Cellular signal transduction can be induced by TRAIL conjugated to microcapsules

The extracellular agent tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can induce apoptosis in tumor cells but spare normal cells. Ligation of TRAIL to a nanoparticle would serve to facilitate targeting to an extravascular site. Polymeric ultrasound contrast agents (UCA) (microencapsulated gas bubbles) can be tracked by ultrasound imaging, and fragmented into nanoparticles by focused ultrasound. This tumor-targeted delivery system has been shown to deliver more efficiently than solid nanoparticles. Additionally, small molecule inhibitors such as bortezomib, shown to sensitize TRAIL-resistant cells, could be co-administered within these UCA. In this pilot study, TRAIL was conjugated to UCA while preserving the agent's sensitivity to ultrasound. Human cancer cell lines, OVCAR-3 and A2058, were bathed with the TRAIL-UCA with and without the addition of bortezomib. Apoptosis was quantified using flow cytometry. OVCAR-3 treated with TRAIL-UCA exhibit significant (p < 0.05) apoptotosis compared to unmodified UCA, equal to positive controls, but no synergistic effect when combined with bortezomib. A2058 cells treated with TRAIL-UCA also exhibited significant apoptosis (p < 0.01) compared to unmodified UCA, similar to positive controls and bortezomib significantly increased apoptosis in combination with TRAIL-UCA. We conclude that TRAIL-ligated UCA show exciting potential as a new therapy.

MST1 promotes apoptosis through phosphorylation of histone H2AX

MST1 (mammalian STE20-like kinase 1) is a serine/threonine kinase that is cleaved and activated by caspases during apoptosis. Overexpression of MST1 induces apoptotic morphological changes such as chromatin condensation, but the mechanism is not clear. Here we show that MST1 induces apoptotic chromatin condensation through its phosphorylation of histone H2AX at Ser-139. During etoposide-induced apoptosis in Jurkat cells, the cleavage of MST1 directly corresponded with strong H2AX phosphorylation. In vitro kinase assay results showed that MST1 strongly phosphorylates histone H2AX. Western blot and kinase assay results with a mutant S139A H2AX confirmed that MST1 phosphorylates H2AX at Ser-139. Direct binding of MST1 and H2AX can be detected when co-expressed in HEK293 cells and was also confirmed by an endogenous immunoprecipitation study. When overexpressed in HeLa cells, both the MST1 full-length protein and the MST1 kinase domain (MST1-NT), but not the kinase-negative mutant (MST1-NT-KN), could induce obvious endogenous histone H2AX phosphorylation. The caspase-3 inhibitor benzyloxycarbonyl-DEVD-fluoromethyl ketone (Z-DEVD-fmk) attenuates phosphorylation of H2AX by MST1 but cannot inhibit MST1-NT-induced histone H2AX phosphorylation, indicating that cleaved MST1 is responsible for H2AX phosphorylation during apoptosis. Histone H2AX phosphorylation and DNA fragmentation were suppressed in MST1 knockdown Jurkat cells after etoposide treatment. Taken together, our data indicated that H2AX is a substrate of MST1, which functions to induce apoptotic chromatin condensation and DNA fragmentation.

Polymorphisms in innate immunity genes and risk of childhood leukemia

The immune system plays an important role in the control of cancer development. To investigate possible genetic contribution to childhood leukemia risk in the innate immune system, we performed an association study for the 1214 SNPs in 146 gene regions related to innate immunity using GoldenGate (Illumina) oligonucleotide pool assay (OPA) in 106 case patients and 123 controls. Childhood leukemia risk was estimated as odds ratios and 95% confidence intervals adjusted for age, gender and birth weight. The minP test was used to identify statistically significant association at gene level. Three SNPs (STAT6 rs703817, C1qG rs17433222, and MBP rs3794845) were significantly associated with childhood leukemia risk (p(trend) < 0.001, minP < 0.01). The most significant association with childhood leukemia risk was for STAT6 rs703817 (GA vs GG: 0.48 (0.26-0.87), AA vs GG: 0.21 (0.07-0.61), p(trend) = 0.0003, minP = 0.002). Subgroup analysis showed that Ly96 rs78380171 and MBP rs3794845 were significantly associated with the risk of acute lymphoblastic leukemia (p(trend) < 0.001). Our results suggest that genetic polymorphisms in innate immunity genes might play a role in the genesis of childhood leukemia with limited biologic evidence. Additional, larger studies are needed to identify the mechanism of these genes in childhood leukemia patients.

Caspases and kinases in a death grip

The complex process of apoptosis is orchestrated by caspases, a family of cysteine proteases with unique substrate specificities. Accumulating evidence suggests that cell death pathways are finely tuned by multiple signaling events, including direct phosphorylation of caspases, whereas kinases are often substrates of active caspases. Importantly, caspase-mediated cleavage of kinases can terminate prosurvival signaling or generate proapoptotic peptide fragments that help to execute the death program and facilitate packaging of the dying cells. Here, we review caspases as kinase substrates and kinases as caspase substrates and discuss how the balance between cell survival and cell death can be shifted through crosstalk between these two enzyme families.

The human WW45 protein enhances MST1-mediated apoptosis in vivo

Mammalian sterile 20-like kinase 1 (MST1) is a serine/threonine protein kinase that is activated in response to a variety of apoptotic stimuli and causes apoptosis when over-expressed in mammalian cells. The physiological regulation and cellular targets of MST1 are not well understood. Using a yeast two-hybrid system, we identified human WW45 (hWW45, also called hSav1) as an MST1-binding protein. The association between the two proteins was confirmed by immunofluorescence and co-immunoprecipitation, and hWW45 was present in both the cytoplasm and nucleus. When hWW45 alone was over-expressed, it weakly induced apoptosis. However, hWW45 augmented MST1-induced apoptosis when the two were co-expressed. Conversely, RNA interference-mediated depletion of endogenous hWW45 suppressed MST1-induced apoptosis. These results indicate that hWW45 is required to enhance MST1-mediated apoptosis in vivo and thus is a critical player in an MST1-driven cell death signaling pathway.

Stress-induced corneal epithelial apoptosis mediated by K+ channel activation

One of the functional roles of the corneal epithelial layer is to protect the cornea, lens and other underlying ocular structures from damages caused by environmental insults. It is important for corneal epithelial cells to maintain this function by undergoing continuous renewal through a dynamic process of wound healing. Previous studies in corneal epithelial cells have provided substantial evidence showing that environmental insults, such as ultraviolet (UV) irradiation and other biohazards, can induce stress-related cellular responses resulting in apoptosis and thus interrupt the dynamic process of wound healing. We found that UV irradiation-induced apoptotic effects in corneal epithelial cells are started by the hyperactivation of K+ channels in the cell membrane resulting in a fast loss of intracellular K+ ions. Recent studies provide further evidence indicating that these complex responses in corneal epithelial cells are resulted from the activation of stress-related signaling pathways mediated by K+ channel activity. The effect of UV irradiation on corneal epithelial cell fate shares common signaling mechanisms involving the activation of intracellular responses that are often activated by the stimulation of various cytokines. One piece of evidence for making this distinction is that at early times UV irradiation activates a Kv3.4 channel in corneal epithelial cells to elicit activation of c-Jun N-terminal kinase cascades and p53 activation leading to cell cycle arrest and apoptosis. The hypothetic model is that UV-induced potassium channel hyperactivity as an early event initiates fast cell shrinkages due to the loss of intracellular potassium, resulting in the activation of scaffolding protein kinases and cytoskeleton reorganizations. This review article presents important control mechanisms that determine Kv channel activity-mediated cellular responses in corneal epithelial cells, involving activation of stress-induced signaling pathways, arrests of cell cycle progression and/or induction of apoptosis.

Activation of sterile20-like kinase 1 in proteasome inhibitor bortezomib-induced apoptosis in oncogenic K-ras-transformed cells

Bortezomib (PS-341), a specific proteasome inhibitor, exhibits antitumor activity against a wide range of malignancies. However, the molecular mechanisms by which bortezomib causes apoptosis selectively in cancer cells still remain unclear. Ras signaling is involved in multiple cellular processes, including cell cycle progression, differentiation, and apoptosis, and can either promote or inhibit apoptosis depending on the type of apoptotic stimuli and the cell model. Here, we investigated the role of K-ras signaling in bortezomib-induced apoptosis. We found that K-ras-transformed cells were more susceptible to bortezomib-induced apoptosis than were nontransformed cells and that bortezomib-induced apoptosis was mainly caspase dependent in K-ras-transformed cells. We also found that mammalian sterile20-like kinase 1 (MST1) was activated by bortezomib in K-ras-transformed cells and K-ras-mutated cancer cells. Treatment of K-ras-transformed cells with bortezomib resulted in translocation of MST1 from cytoplasm into the nucleus and an increase of phosphorylated histone H2B and histone H2AX. Moreover, pretreatment with leptomycin B, an inhibitor of the nuclear export signal receptor, dramatically enhanced bortezomib-mediated MST1 activation, phosphorylation of histones H2B and H2AX, and apoptosis induction in K-ras-transformed cells. Knockdown of MST1 expression by small interfering RNA diminished bortezomib-induced apoptosis or caspase-3 activation. Our data suggested that bortezomib may be useful for treatment of K-ras-mutated cancer cells, and MST1 is one of the mediators for bortezomib-induced apoptosis in K-ras-transformed cells.

Critical Role of Mst1 in Vascular Remodeling After Injury

Objective— Apoptosis of vascular smooth muscle cells (VSMCs) is observed in chronic vascular lesions such as atherosclerotic plaques and is believed to contribute to the vascular remodeling process. Mst1 is a ubiquitously expressed serine/threonine kinase known to be activated in response to a wide variety of nonphysiological apoptotic stimuli. However, little is known of the physiological function of Mst1, and its role in VSMCs has never been examined.

Methods and Results— Treatment of VSMCs with staurosporine induced apoptosis and cleavage of Mst1, which is a marker of its activation, as well as activation of caspase 3. Adenovirus-mediated overexpression of wild-type Mst1 (AdMst1) in VSMCs increased apoptotic cells with activation of caspase 3. Mst1 was induced and activated in the balloon-injured rat carotid artery. Infection with AdMst1 in balloon-injured rat carotid artery suppressed neointimal formation compared with infection with AdLacZ. Infection with AdMst1 significantly increased the apoptotic cell number in the neointima compared with infection with AdLacZ without affecting BrdU incorporation.

Conclusion— Our results suggest that Mst1 plays an important role in the induction of apoptosis of VSMCs, mediating the vascular remodeling process, and may be a potential therapeutic target for vascular proliferative diseases.

K(+) channel activity and redox status are differentially required for JNK activation by UV and reactive oxygen species

Upon exposure to ultraviolet (UV) radiation, osmotic changes or the presence of reactive oxygen species (ROS) c-Jun N-terminal kinases (JNKs) are rapidly activated. Extensive studies have elucidated molecular components that mediate the activation of JNKs. However, it remains unclear whether activation of JNKs by various stress signals involves different pathways. Here we show that K(+) channel activity is involved in mediating apoptosis induced by UV but not by H(2)O(2) in myelocytic leukemic ML-1 cells. Specifically, JNKs were rapidly phosphorylated upon treatment of ML-1 cells with UV and H(2)O(2). UV-induced, but not H(2)O(2)-induced, JNK-1 phosphorylation was inhibited by pretreatment with 4-aminopyridine (4-AP), a K(+) channel blocker. 4-AP also blocked UV-induced increase in JNK activity as well as p38 phosphorylation. Immunofluorescent microscopy revealed that phosphorylated JNKs were concentrated at centrosomes in ML-1 cells and that these proteins underwent rapid subcellular translocation upon UV treatment. Consistently, the subcellular translocation of JNKs induced by UV was largely blocked by 4-AP. Furthermore, UV-induced JNK activation was blocked by NEM, a sulfhydryl alkylating agent also affecting K(+) current. Both UV- and H(2)O(2)-induced JNK activities were inhibited by glutathione, suggesting that the redox status does play an important role in the activation of JNKs. Taken together, our findings suggest that JNK activation by UV and H(2)O(2) is mediated by distinct yet overlapping pathways and that K(+) channel activity and redox status are differentially required for UV- and H(2)O(2)-induced activation of JNKs.

Caspase cleavage of MST1 promotes nuclear translocation and chromatin condensation

MST1, mammalian STE20-like kinase 1, is a serine/threonine kinase that is cleaved and activated by caspases during apoptosis. MST1 is capable of inducing apoptotic morphological changes such as chromatin condensation upon overexpression. In this study, we show that MST1 contains two functional nuclear export signals (NESs) in the C-terminal domain, which is released from the N-terminal kinase domain upon caspase-mediated cleavage. Full-length MST1 is excluded from the nucleus and localized to the cytoplasm. However, either truncation of the C-terminal domain, point mutation of the two putative NESs, or treatment with leptomycin B, an inhibitor of the NES receptor, results in nuclear localization of MST1. Staurosporine treatment induces chromatin condensation, MST1 cleavage, and nuclear translocation. Staurosporine-induced chromatin condensation is partially inhibited by expressing a kinase-negative mutant of MST1, suggesting an important role of MST1 in this process. Significantly, MST1 is more efficient at inducing chromatin condensation when it is constitutively localized to the nucleus by mutation of its NESs. Moreover, inhibition of MST1 nuclear translocation by mutation of its cleavage sites reduces its ability to induce chromatin condensation. Taken together, these results suggest that truncation of the C-terminal domain of MST1 by caspases may result in translocation of MST1 into the nucleus, where it promotes chromatin condensation.

Human cultured skin fibroblasts survive profound inherited ubiquinone depletion

Beside its role in electron transfer in the mitochondrial respiratory chain, ubiquinone is known to prevent lipid peroxidation and DNA damage by trapping cellular free radicals. Thanks to its antioxidant properties, ubiquinone may represent an important factor controlling both necrotic and apoptotic processes. We have investigated the consequences of a profound inherited ubiquinone depletion on cultured skin fibroblasts of a patient presenting with encephalomyopathy. Interestingly, cell respiration, mitochondrial oxidation of various substrates, and cell growth of ubiquinone-deficient fibroblasts were only partially decreased. Moreover, these cells did not apparently overproduce superoxide anions or lipoperoxides. Finally, apoptosis did not increase as compared to control, even after serum deprivation. These observations suggest that ubiquinone may not play a major role in the antioxidant defenses of cultured fibroblasts and that its role in controlling oxidative stress and apoptosis may greatly vary across cell types, especially as not all tissues were equally affected in the patient despite the widespread ubiquinone depletion in vivo.

MST1-JNK promotes apoptosis via caspase-dependent and independent pathways

BACKGROUND

MST1 is an upstream kinase of the JNK and p38 MAPK pathways whose expression induces apoptotic morphological changes such as nuclear condensation. During apoptosis, caspase cleavage of MST1 removes a C-terminal regulatory domain, increasing the kinase activity of the MST1 N-terminal domain. Downstream pathways of MST1 in the induction of apoptosis remain to be clarified.

RESULTS

In this study, we found that the expression of MST1 resulted in caspase-3 activation. Therefore, MST1 is not only a target of caspases but also an activator of caspases. This caspase activation and apoptotic changes occur through JNK, since the co-expression of a dominant-negative mutant of JNK inhibited MST1-induced morphological changes as well as caspase activation. In contrast, neither a dominant-negative p38 nor the p38 inhibitor SB203580 inhibited them. MST1 induced nucleosomal DNA fragmentation, which was suppressed by caspase inhibitors or ICAD (Inhibitor of Caspase-Activated DNase). Surprisingly, however, other changes such as membrane blebbing and chromatin condensation were not inhibited by caspase inhibitors.

CONCLUSION

These results suggest that MST1 most likely promotes two events through JNK activation; first, MST1 induces the activation of caspases, resulting in CAD-mediated DNA fragmentation, and second, MST1 induces chromatin condensation and membrane blebbing without utilizing downstream caspases.

p53 is dispensable for UV-induced cell cycle arrest at late G(1) in mammalian cells

Genotoxic agents, including gamma-rays and UV light, induce transient arrest at different phases of the cell cycle. These arrests are required for efficient repair of DNA lesions, and employ several factors, including the product of the tumor suppressor gene p53 that plays a central role in the cellular response to DNA damage. p53 protein has a major function in the gamma-ray-induced cell cycle delay in G(1) phase. However, it remains uncertain as to whether p53 is also involved in the UV-mediated G(1) delay. This report provides evidence that p53 is not involved in UV-induced cellular growth arrest in late G(1) phase. This has been demonstrated in HeLa cells synchronized at the G(1)/S border by aphidicolin, followed by UV exposure. Interestingly, the length of this p53-independent G(1) arrest has been shown to be UV dose-dependent. Similar results were also obtained with other p53-deficient cell lines, including human promyelocytic leukemia HL-60 and mouse p53 knock-out cells. As expected, all of these cell lines were defective in gamma-ray-induced cell growth arrest at late G(1). Moreover, it is shown that in addition to cell cycle arrest, HL-60 cells undergo apoptosis in G(1) phase in response to UV light but not to gamma-rays. Together, these findings indicate that p53- compromised cells have a differential response following exposure to ionizing radiation or UV light.

Morphological patterns of death by myocytes in arrhythmogenic right ventricular dysplasia

There are two forms of nuclear loss from eukaryotic cells: biochemical DNA degradation in apoptosis and nuclear extrusion from the cell body as seen in mammalian erythroblasts. In biopsies of right ventricular myocardium from 8 patients with arrhythmogenic right ventricular dysplasia (ARVD), we found not only a terminal deoxynucleotidyl transferase-mediated digoxigenin-deoxyuridine triphosphate nick-end labeling (TUNEL)-positive nucleus in mononuclear myocytes, but also 1 or 2 TUNEL-positive nuclei in multinuclear myocytes. With electron microscopy, we found a nuclear dislocation to the cell periphery, followed by its extrusion into the extracellular space. Both the migration and extrusion of the nuclei of myocytes resemble the morphogenesis of human erythroblasts. Nuclear extrusion from myocytes may be another form of programmed cell death. In support of this possibility, we also found evidence of cytoplasmic degradation in right ventricular myocytes from our ARVD cases, a process similar to one often seen in developmental programmed cell death and differing from typical nuclear apoptosis. In our ARVD cases, we thus found several different patterns of cell death, all associated with initial preservation of the plasmalemma and avoidance of local inflammation. All these features may be different responses to common signals for selective non-necrotic (apoptotic) death of right ventricular myocytes.

Detection of a novel quiescence-dependent protein kinase

We have identified a cell quiescence-specific 33-kDa cytoplasmic protein kinase (p33(QIK), Quiescence-Induced Kinase) based on induction of p33(QIK)-specific kinase activity of cells growth-arrested in the quiescent phase and deactivation upon entry into the cell cycle. Blockage of macromolecular synthesis prevents p33(QIK) from deactivation, indicating a requirement of newly synthesized regulators for deactivation of p33(QIK) during G(0)/G(1) transition. Stress shock induces additional increases of p33(QIK) activity in a quiescence-dependent manner that correlates with induction of apoptosis. Using a specific antibody to Krs1/Mst2 protein, we found that p33(QIK) is related to p63(Krs1) and is distinguishable from a 36-kDa protein kinase, which is induced through proteolytic modification of activated p63(Krs1) in proliferating cells undergoing apoptosis. p33(QIK) is constantly expressed in quiescent, proliferating, and apoptotic quiescent cells. Regulation of p33(QIK) activity involves protein phosphorylation/dephosphorylation in a proteolysis-independent manner. Regulation of p33(QIK) and related p63(Krs1) and p36 appears to involve distinct pathways in quiescent and proliferating cells, respectively. Our results illustrate the relevance of p33(QIK) activity for cell quiescence that may provide a new insight into signaling pathways regulated in cells during quiescence and quiescence-related apoptosis.

Suppression of heat shock protein-70 by ceramide in heat shock-induced HL-60 cell apoptosis

Ceramide has emerged as a mediator of cell growth, differentiation, and apoptosis in many biological systems. Many kinds of stresses are reported to induce apoptosis with an increase of ceramide generation. Here we showed that the intracellular ceramide levels increased in parallel with heat shock (HS)-induced apoptosis in an intensity- and time-dependent manner, and synthetic N-acetylsphingosine (C(2)-ceramide) synergistically enhanced HS-induced apoptosis in HL-60 cells. In order to know the role of ceramide generation in HS-induced apoptosis, we examined the effects of C(2)-ceramide on the levels of mRNA and protein of heat shock proteins (HSPs). The increase of HSP-70 mRNA levels 1-2 h after HS at 42 degrees C for 30 min was suppressed by C(2)-ceramide in a dose-dependent manner. In comparison with HSP-70, the levels of HSP-60 and -90 mRNAs were faintly suppressed by C(2)-ceramide. Similarly, the increase in the protein levels of HSP-70 was significantly suppressed 4-8 h after HS by C(2)-ceramide in a dose-dependent manner. Additionally, in 293 cells, which are constitutively overexpressing HSP-70 gene, the levels of HSP-70 mRNA were suppressed by C(2)-ceramide in parallel with the increase of apoptotic cells. We next examined the mechanisms by which C(2)-ceramide suppressed HS-increased HSP-70 expression. The treatment with C(2)-ceramide did not affect both an activation of a nuclear transcription factor for HSP-70, heat shock factor-1, and an increased transcriptional rate of HSP-70 by HS, but increased the rates of HSP-70 mRNA degradation. In summary, ceramide may efficiently induce HS-induced apoptosis by suppressing anti-apoptotic HSP-70 through a post-transcriptional regulation.

On the nature of cell death during remodeling of hypertrophied human myocardium

Cardiocyte loss during myocardial hypertrophy leads to progressive dysfunction in human hearts with chronic hemodynamic overload. The mechanism for such cell elimination is unknown. We examined lysosomal participation in cardiocytic degradation present in human cardiac biopsies, utilizing electron microscopic cytochemistry (acid phosphatase). Lysosomes were significantly increased in number (t-test, P<0.001) in 50 hemodynamically overloaded hearts (375+/-69, mean+/-s.e.m., per 5,000 microm(2) cardiocytic area; eight controls, 38+/-11). Secondary lysosomes were prominent near degenerative intracellular organelles in both hypertrophic and atrophic cardiocytes. Increased lysosomal and phagocytic activity in the cytoplasm without typical nuclear apoptosis resembled cytoplasmic degradation in developmental programmed cell death described in different tissues. We also demonstrated cardiocytic DNA degradation (in situ nick-end labeling) in autopsy hearts, including 299 nuclei normalized per 10(6) observed nuclei from five concentrically hypertrophied hearts, 1961 nuclei from five eccentrically hypertrophied hearts, and no positive nuclei in five controls. We postulate a chronic self-controlled cytoplasmic proteolysis in cardiocytes, not initially associated with either nuclear degradation or intercellular dehiscence but later possibly accompanied by apoptotic nuclear elimination, and leading to apoptotic cell death.

Requirement of protein kinase (Krs/MST) activation for MT-21-induced apoptosis

Fas is a well characterized apoptosis-inducing factor. One of our synthetic compounds, MT-21, induced apoptosis in human leukemia HL-60 cells similar to Fas. MT-21 activated caspase-3, an important cysteine aspartic protease for apoptosis induction. MT-21 also activated c-Jun-NH2-terminal kinase (JNK), a member of mitogen activated protein kinase (MAPK) superfamily that is involved in the regulation of cell growth, differentiation and cell death. Moreover, MT-21 treatment resulted in the activation of a 36 kDa kinase which uses myelin basic protein (MBP) as a substrate. However, MAPK and p38 were not activated by treatment with MT-21. The 36 kDa MBP kinase was shown to be a proteolytic product derived from the Krs protein with a molecular weight of 60 kDa. The Krs protein is a Ser/Thr protein kinase whose activity is enhanced by digestion of its C-terminal regulatory domain by caspase-3. When a kinase-inactive mutant form of Krs protein was overexpressed in HL-60 cells, JNK activation and apoptosis induction by MT-21 were suppressed. Furthermore, overexpression of dominant negative c-Jun also suppressed apoptosis induction by MT-21. These findings indicate that MT-21 induces apoptosis by the activation of JNK via the Krs protein, which is activated by caspase cleavage.

PAK2 is cleaved and activated during hyperosmotic shock-induced apoptosis via a caspase-dependent mechanism: evidence for the involvement of oxidative stress

Hyperosmotic shock elicits a stress response in mammalian cells and can lead to apoptotic cell death. In the present study, we report that hyperosmotic shock can induce activation of a 36 kDa kinase detected by an in-gel kinase assay in several cell types, including mouse Balb/c 3T3 fibroblasts, and human Hep 3B and A431 cells. This 36 kDa kinase can be recognized by an antibody against the C-terminal region of a family of p21Cdc42/Rac-activated kinases (PAKs) on immunoblot. Further studies with this antibody and a PAK2-specific antibody against the N-terminal region of PAK2 demonstrate that hyperosmotic shock can induce cleavage of PAK2 to generate a 36 kDa C-terminal catalytic fragment in cells. The cleavage and activation of PAK2 was found to be closely associated with both DNA fragmentation and activation of an ICE/CED-3 family cysteine protease termed caspase-3 in hyperosmotically shocked cells. Furthermore, pretreating the cells with two caspase inhibitors (Ac-DEVD-cho and Ac-YVAD-cmk) could inhibit both cleavage/activation of PAK2 and DNA fragmentation induced by hyperosmotic shock. Moreover, all these hyperosmotic shock-induced changes (i.e., activation of caspase-3, cleavage/activation of PAK2, and DNA fragmentation) in cells could be blocked by antioxidants such as ascorbic acid (vitamine C), alpha-tocopherol (vitamine E), dithiothreitol, beta-mercaptoethanol, and glutathione. Taken together, our results show that PAK2 is cleaved and activated via a caspase-dependent mechanism during hyperosmotic shock-induced apoptosis and suggest the involvement of antioxidant-preventable oxidative stress in inducing this process.

Effects of a novel antitumor depsipeptide, FR901228, on human breast cancer cells

Human breast cancer MCF7 and MDA-MB231 cells were used to investigate the biological and molecular activities of a novel naturally occurring agent, FR901228 (FR), that possesses a potent antitumor activity against human and murine tumor cells. Investigation of the cytotoxicity of FR and induction of internucleosomal DNA degradation in FR-treated cultures revealed that FR induced apoptotic-like cell death of MCF7 and MDA-MB231 cells. In FR-treated apoptotic cultures, flow cytometry revealed that there was a significant decrease of cells in S phase of the cell cycle. In FR-treated cells there was an increased expression of p21Cip1 and phosphorylation of Bcl-2 as determined by Western immunoblotting, and a novel cytoplasmic kinase of 33 kDa, p33 kinase, as determined by the in-gel kinase assay using myelin basic protein (MBP) as a substrate. Increased expression of p21CiP1, phosphorylation of Bcl-2, and activation of p33 MBP kinase may play part of the key mechanism for FR-induced apoptosis.

Activation of bcl-2 suppressible 40 and 44 kDa p38-like kinases during apoptosis of early and late B lymphocytic cell lines

Activation of several different kinases characterizes the induction of apoptosis. Abelson virus transformed pre-B lymphocytes undergo apoptosis within 24 h of serum deprivation, PKA activation or gamma-irradiation, and the activity of two kinases of ca. 40 and 44 kDa is specifically induced during this apoptotic process. Bcl-2 expression prevents both apoptosis and the induction of these kinases. Immunologic and substrate similarities indicate that these kinases are related to the p38 family of MAP kinases. More mature cells of the B lymphocytic lineage, plasmacytomas, also exhibit induction of these kinases when apoptosis is induced by withdrawal of serum or IL-6. Treatment of the pre-B cells with ICE protease inhibitors when apoptotic stimuli are delivered prevents induction of the kinase activity, and partially inhibits apoptosis. These findings indicate that the induction of these 40 and 44 kDa p38 related kinases is a common feature of apoptosis in mouse B lymphocytic cells and may represent a step downstream of ICE proteases in the signal cascade that leads to programmed cell death.

Activation of hPAK65 by caspase cleavage induces some of the morphological and biochemical changes of apoptosis

Apoptosis is a highly regulated form of cell death, characterized by distinctive features such as cellular shrinkage and nuclear condensation. We demonstrate here that proteolytic activation of hPAK65, a p21-activated kinase, induces morphological changes and elicits apoptosis. hPAK65 is cleaved both in vitro and in vivo by caspases at a single site between the N-terminal regulatory p21-binding domain and the C-terminal kinase domain. The C-terminal cleavage product becomes activated, with a kinetic profile that parallels caspase activation during apoptosis. This C-terminal hPAK65 fragment also activates the c-Jun N-terminal kinase pathway in vivo. Microinjection or transfection of this truncated hPAK65 causes striking alterations in cellular and nuclear morphology, which subsequently promotes apoptosis in both CHO and Hela cells. Conversely, apoptosis is delayed in cells expressing a dominant-negative form of hPAK65. These findings provide a direct evidence that the activated form of hPAK65 generated by caspase cleavage is a proapoptotic effector that mediates morphological and biochemical changes seen in apoptosis.