Enhancement of stress-induced apoptosis in B-lineage cells by caspase-9 inhibitor

KDM6B modulates MAPK pathway mediating multiple myeloma cell growth and survival

Recent studies have delineated cancer-type-specific roles of histone 3 lysine 27 (H3K27) demethylase KDM6B/JMJD3 depending on its H3K27 demethylase activity. Here we show that KDM6B is expressed in multiple myeloma (MM) cells; and that shRNA-mediated knockdown and CRISPR-mediated knockout of KDM6B abrogate MM cell growth and survival. Tumor necrosis factor-α or bone marrow stromal cell culture supernatants induce KDM6B, which is blocked by IKKβ inhibitor MLN120B, suggesting that KDM6B is regulated by NF-κB signaling in MM cells. RNA-seq and subsequent ChIP-qPCR analyses reveal that KDM6B is recruited to the loci of genes encoding components of MAPK signaling pathway including ELK1 and FOS, and upregulates expression of these genes without affecting H3K27 methylation level. Overexpression of catalytically inactive KDM6B activates expression of MAPK pathway-related genes, confirming its function independent of demethylase activity. We further demonstrate that downstream targets of KDM6B, ELK1 and FOS, confer MM cell growth. Our study therefore delineates KDM6B function that links NF-κB and MAPK signaling pathway mediating MM cell growth and survival, and validates KDM6B as a novel therapeutic target in MM.

Inhibition of caspase-9 by oridonin, a diterpenoid isolated from Rabdosia rubescens, augments apoptosis in human laryngeal cancer cells

Rabdosia rubescens, a commonly used traditional Chinese medicine, has increasingly gained attention for its use as an antitumor herb. Oridonin, a bioactive diterpenoid isolated from Rabdosia rubescens, has been reported to induce apoptosis in human laryngeal cancer HEp-2 cells by our group. Here, we made unexpected observations that the caspase-9 inhibitor (C9i) enhanced apoptosis in response to selected stimuli, and HEp-2 cells which were made deficient in caspase-9 using siRNA exhibited no resistance to apoptotic signals and actually demonstrated increased apoptotic sensitivity to oridonin. The results were reversed by the transfection of an exogenous caspase-9 expression vector. Caspase-9 reduced sensitivity to apoptotic stimuli through reactive oxygen species (ROS)-suppressing and autophagy-promoting methods. ROS triggered the progression of apoptosis through activation of both the caspase-9-independent mitochondrial pathway and death receptor pathways, and the autophagy had an anti-apoptotic function in oridonin-treated HEp-2 cells. These collective results suggest that oridonin targets caspase-9 to alter ROS production and autophagy situation to promote HEp-2 cell apoptosis. Therefore, oridonin has the potential to be developed as an anticancer agent, and the combination of oridonin with those agents leading to reduction of caspase-9 expression in tumor cells could represent a novel approach to human laryngeal cancer treatment.

Involvement of caspase-9 in autophagy-mediated cell survival pathway

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been considered for use in the prevention and treatment of cancer malignancy. FR122047 (FR) is known to have an anti-inflammatory effect, but the anticancer activity of the chemical has not yet been identified. In the present study, we could find that treatment of breast cancer MCF-7 cells with FR led to apoptosis accompanying with apparent activation of caspases. Treatment of caspase-specific inhibitors revealed that FR-induced apoptosis was caspase-8-dependent and inhibition of caspase-9 activity resulted in unexpected, marked enhancement of cell death. Knockdown of caspase-9 expression by specific siRNA caused increased susceptibility to FR-induced cell death, consistent with the results obtained with treatment of caspase-9 inhibitor. Inhibition of caspase-9 blocked the autophagic process by modulating lysosomal pH and acid-dependent cathepsin activities and augmented cell death due to blockage of cytoprotective autophagy. MCF-7 cells treated with sulforaphane, an autophagy-inducing drug, also showed marked accumulation of LC3-II, and co-treatment with caspase-9 inhibitor brought about increased susceptibility to sulforaphane-induced cell death. Different from the cases with FR or sulforaphane, etoposide- or doxorubicin-induced cell death was suppressed with co-treatment of caspase-9 inhibitor, and the drugs failed to induce significant autophagy in MCF-7 cells. Taken together, our data originally suggest that inhibition of caspase-9 may block the autophagic flux and enhance cell death due to blockage of cytoprotective autophagy.

The histone deacetylase inhibitor MGCD0103 induces apoptosis in B-cell chronic lymphocytic leukemia cells through a mitochondria-mediated caspase activation cascade

Clinical trials have shown activity of the isotype-selective histone deacetylase (HDAC) inhibitor MGCD0103 in different hematologic malignancies. There are data to support the use of HDAC inhibitors in association with other cancer therapies. To propose a rational combination therapy, it is necessary to depict the molecular basis behind the cytotoxic effect of MGCD0103. In this study, we found that MGCD0103 was substantially more toxic in neoplastic B cells relative to normal cells, and we described the death pathways activated by MGCD0103 in B-cell chronic lymphocytic leukemia (CLL) cells from 32 patients. MGCD0103 decreased the expression of Mcl-1 and induced translocation of Bax to the mitochondria, mitochondrial depolarization, and release of cytochrome c in the cytosol. Caspase processing in the presence of the caspase inhibitor Q-VD-OPh and time course experiments showed that caspase-9 was the apical caspase. Thus, MGCD0103 induced the intrinsic pathway of apoptosis in CLL cells. Moreover, MGCD0103 treatment resulted in the activation of a caspase cascade downstream of caspase-9, caspase-dependent amplification of mitochondrial depolarization, activation of calpain, and Bax cleavage. We propose a model whereby the intrinsic pathway of apoptosis triggered by MGCD0103 in CLL is associated with a mitochondrial death amplification loop.

Novel IL-21 signaling pathway up-regulates c-Myc and induces apoptosis of diffuse large B-cell lymphomas

Interleukin-21 (IL-21), a member of the IL-2 cytokine family, has diverse regulatory effects on natural killer (NK), T, and B cells. In contrast to other cytokines that are usually immunostimulatory, IL-21 can induce apoptosis of murine B cells at specific activation-differentiation stages. This effect may be used for treatment of B-cell malignancies. Herein we report that diffuse large B-cell lymphoma (DLBCL) cell lines exhibit widespread expression of the IL-21 receptor (IL-21R) and that IL-21 stimulation leads to cell-cycle arrest and caspase-dependent apoptosis. IL-21 also induces apoptosis in de novo DLBCL primary tumors but does not affect viability of human healthy B cells. Furthermore, IL-21 promotes tumor regression and prolongs survival of mice harboring xenograft DLBCL tumors. The antilymphoma effects of this cytokine are dependent on a mechanism involving IL-21-activated signal transducer and activator of transcription 3 (STAT3) up-regulating expression of c-Myc. This up-regulation promotes a decrease in expression of antiapoptotic Bcl-2 and Bcl-X(L) proteins triggering cell death. Our results represent one of the first examples in which the STAT3-c-Myc signaling pathway, which can promote survival and oncogenesis, can induce apoptosis in neoplastic cells. Moreover, based on IL-21's potency in vitro and in animal models, our findings indicate that this cytokine should be examined in clinical studies of DLBCL.

Dual mechanisms of sHA 14-1 in inducing cell death through endoplasmic reticulum and mitochondria

HA 14-1 is a small-molecule Bcl-2 antagonist that promotes apoptosis in malignant cells, but its mechanism of action is not well defined. We recently reported that HA 14-1 has a half-life of only 15 min in vitro, which led us to develop a stable analog of HA 14-1 (sHA 14-1). The current study characterizes its mode of action. Because of the antiapoptotic function of Bcl-2 family proteins on the endoplasmic reticulum (ER) and mitochondria, the effect of sHA 14-1 on both organelles was evaluated. sHA 14-1 induced ER calcium release in human leukemic cells within 1 min, followed by induction of the ER stress-inducible transcription factor ATF4. Similar kinetics and stronger intensity of ER calcium release were induced by the sarcoendoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibitor thapsigargin, accompanied by similar kinetics and intensity of ATF4 induction. sHA 14-1 directly inhibited SERCA enzymatic activity but had no effect on the inositol triphosphate receptor. Evaluation of the mitochondrial pathway showed that sHA 14-1 triggered a loss of mitochondrial transmembrane potential (Delta psi m) and weak caspase-9 activation, whereas thapsigargin had no effect. (R)-4-(3-Dimethylamino-1-phenylsulfanylmethyl-propylamino)-N-{4-[4-(4'-chloro-biphenyl-2-ylmethyl)-piperazin-1-yl]-benzoyl}-3-nitrobenzenesulfonamide (ABT-737), a well established small-molecule Bcl-2 antagonist, rapidly induced loss of Delta psi m and caspase-9 activation but had no effect on the ER. The pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone had some protective effect on sHA 14-1-induced cell death. These collective results suggest a unique dual targeting mechanism of sHA 14-1 on the apoptotic resistance machinery of tumor cells that includes antiapoptotic Bcl-2 family proteins and SERCA proteins.

Opposing roles for caspase and calpain death proteases in L-glutamate-induced oxidative neurotoxicity

Oxidative glutamate toxicity in HT22 murine hippocampal cells is a model for neuronal death by oxidative stress. We have investigated the role of proteases in HT22 cell oxidative glutamate toxicity. L-glutamate-induced toxicity was characterized by cell and nuclear shrinkage and chromatin condensation, yet occurred in the absence of either DNA fragmentation or mitochondrial cytochrome c release. Pretreatment with the selective caspase inhibitors either benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (pan-caspase), N-acetyl-Leu-Glu-His-Asp-aldehyde (caspase 9) or N-acetyl-Ile-Glu-Thr-Asp-aldehyde (caspase 8), significantly increased L-glutamate-induced cell death with a corresponding increase in observed nuclear shrinkage and chromatin condensation. This enhancement of glutamate toxicity correlated with an increase in L-glutamate-dependent production of reactive oxygen species (ROS) as a result of caspase inhibition. Pretreating the cells with N-acetyl-L-cysteine prevented ROS production, cell shrinkage and cell death from L-glutamate as well as that associated with the presence of the pan-caspase inhibitor. In contrast, the caspase-3/-7 inhibitor N-acetyl-Asp-Glu-Val-Asp aldehyde was without significant effect. However, pretreating the cells with the calpain inhibitor N-acetyl-Leu-Leu-Nle-CHO, but not the cathepsin B inhibitor CA-074, prevented cell death. The cytotoxic role of calpains was confirmed further by: 1) cytotoxic dependency on intracellular Ca(2+) increase, 2) increased cleavage of the calpain substrate Suc-Leu-Leu-Val-Tyr-AMC and 3) immunoblot detection of the calpain-selective 145 kDa alpha-fodrin cleavage fragment. We conclude that oxidative L-glutamate toxicity in HT22 cells is mediated via calpain activation, whereas inhibition of caspases-8 and -9 may exacerbate L-glutamate-induced oxidative neuronal damage through increased oxidative stress.

The novel Akt inhibitor, perifosine, induces caspase-dependent apoptosis and downregulates P-glycoprotein expression in multidrug-resistant human T-acute leukemia cells by a JNK-dependent mechanism

A significant impediment to the success of cancer chemotherapy is the occurrence of multidrug resistance, which, in many cases, is attributable to overexpression of membrane transport proteins, such as the 170-kDa P-glycoprotein (P-gp). Also, upregulation of the phosphatidylinositol 3-kinase (PI3K)/Akt-signaling pathway is known to play an important role in drug resistance, and has been implicated in the aggressiveness of a number of different cancers, including T-acute lymphoblastic leukemia (T-ALL). We have investigated the therapeutic potential of the novel Akt inhibitor, perifosine (a synthetic alkylphospholipid), on human T-ALL CEM cells (CEM-R), characterized by both overexpression of P-gp and constitutive upregulation of the PI3K/Akt network. Perifosine treatment induced death by apoptosis in CEM-R cells. Apoptosis was characterized by caspase activation, Bid cleavage and cytochrome c release from mitochondria. The proapoptotic effect of perifosine was in part dependent on the Fas/FasL interactions and c-Jun NH(2)-terminal kinase (JNK) activation, as well as on the integrity of lipid rafts. Perifosine downregulated the expression of P-gp mRNA and protein and this effect required JNK activity. Our findings indicate that perifosine is a promising therapeutic agent for treatment of T-ALL cases characterized by both upregulation of the PI3K/Akt survival pathway and overexpression of P-gp.

Eosinophilia: secondary, clonal and idiopathic

Blood eosinophilia signifies either a cytokine-mediated reactive phenomenon (secondary) or an integral phenotype of an underlying haematological neoplasm (primary). Secondary eosinophilia is usually associated with parasitosis in Third World countries and allergic conditions in the West. Primary eosinophilia is operationally classified as being clonal or idiopathic, depending on the respective presence or absence of a molecular, cytogenetic or histological evidence for a myeloid malignancy. The current communication features a comprehensive clinical summary of both secondary and primary eosinophilic disorders with emphasis on recent developments in molecular pathogenesis and treatment.

Suppression of alveolar macrophage apoptosis prolongs survival of rats and mice with pneumocystis pneumonia

The number of alveolar macrophages is decreased in patients or animals with Pneumocystis pneumonia (Pcp). This loss of alveolar macrophages is in part due to apoptosis caused by Pneumocystis infection. The mechanism of apoptosis induction is unknown. Cell-free bronchoalveolar lavage fluids from Pneumocystis-infected rats or mice have the ability to induce apoptosis in normal alveolar macrophages. To characterize the mechanisms by which apoptosis proceeds in alveolar macrophages during Pcp, specific caspase inhibitors are tested for their ability to suppress the apoptosis. In vitro induction of apoptosis can be inhibited by the caspase-9 inhibitor (Z-LEHD-FMK) but not by the inhibitor to caspase-8 or -10. The caspase-9 inhibitor can also inhibit apoptosis of alveolar macrophages in vivo when it is intranasally instilled into dexamethasone-immunosuppressed, Pneumocystis-infected rats or L3T4 cell-depleted, Pneumocystis-infected mice. The number of alveolar macrophages rebounds in caspase-9 inhibitor-treated Pcp animals. Phagocytic activity of alveolar macrophages in treated animals is also recovered, and organism burden in these animals is reduced. Administration of caspase-9 inhibitor also clears the exudate that normally fills the alveoli during Pcp and decreases lung inflammation. Furthermore, caspase-9-treated Pcp animals survive for the entire 70-day period of the study, whereas nontreated Pcp animals die 40-60 days after initiation of infection. Depletion of recovered alveolar macrophages by intranasal administration of clodronate-containing liposomes in caspase-9 inhibitor-treated animals abrogates the effects of the inhibitor. Together, these results indicate that immunomodulation of the host response may be an alternative to current treatments for Pcp.

Caspase-dependent cleavage of 170-kDa P-glycoprotein during apoptosis of human T-lymphoblastoid CEM cells

Multidrug resistance (MDR) mediated by the drug efflux protein, 170-kDa P-glycoprotein (P-gp), is one mechanism that tumor cells use to escape cell death induced by chemotherapeutic drugs. Moreover, evidence suggests that cell lines expressing high levels of 170-kDa P-gp are less sensitive to caspase-mediated apoptosis induced by a wide range of death stimuli, including Fas ligand, tumor necrosis factor, and ultraviolet irradiation. However, the fate of 170-kDa P-gp during apoptosis is unknown. In this study, we demonstrate for the first time that 170-kDa P-gp is cleaved during apoptosis of VBL100 human T-lymphoblastoid CEM cells. Apoptotic cell death was induced by LY294002 (a pharmacological inhibitor of the phosphoinositide 3-kinase/Akt survival pathway), H2O2, and Z-LEHD-FMK (a caspase-9 inhibitor which has been recently reported to induce apoptosis in CEM cells). Using an antibody to a common epitope present in both the third and the sixth extracellular loop of P-gp, two cleavage products were detected, with an apparent molecular weight of 80 and 85 kDa. DEVD-FMK (a caspase-3 inhibitor), but not VEID-CHO (a caspase-6 inhibitor), blocked 170-kDa P-gp cleavage. Recombinant caspase-3 was able to cleave in vitro 170-kDa P-gp yielding two fragments of equal size to those generated in vivo. Considering the size of the cleaved fragments and their reactivity with antibodies, which recognize either the N-half or the C-half region of the protein, it is conceivable that the cleavage occurs intracytoplasmically. Since 170-kDa P-gp has been reported to counteract apoptosis, its cleavage may be a mechanism aimed at blocking an important cell survival component.