Michael J. Ausserlechner

The histone deacetylase inhibitor and chemotherapeutic agent suberoylanilide hydroxamic acid (SAHA) induces a cell-death pathway characterized by cleavage of Bid and production of reactive oxygen species.

Many chemotherapeutic agents induce mitochondrial-membrane disruption to initiate apoptosis. However, the upstream events leading to drug-induced mitochondrial perturbation have remained poorly defined. We have used a variety of physiological and pharmacological inhibitors of distinct apoptotic pathways to analyze the manner by which suberoylanilide hydroxamic acid (SAHA), a chemotherapeutic agent and histone deacetylase inhibitor, induces cell death. We demonstrate that SAHA initiates cell death by inducing mitochondria-mediated death pathways characterized by cytochrome c release and the production of reactive oxygen species, and does not require the activation of key caspases such as caspase-8 or -3. We provide evidence that mitochondrial disruption is achieved by means of the cleavage of the BH3-only proapoptotic Bcl-2 family member Bid. SAHA-induced Bid cleavage was not blocked by caspase inhibitors or the overexpression of Bcl-2 but did require the transcriptional regulatory activity of SAHA. These data provide evidence of a mechanism of cell death mediated by transcriptional events that result in the cleavage of Bid, disruption of the mitochondrial membrane, and production of reactive oxygen species to induce cell death.

Resveratrol causes arrest in the S-phase prior to Fas-independent apoptosis in CEM-C7H2 acute leukemia cells

Resveratrol (3,5,4′-trihydroxy-trans-stilbene), in the concentration range of 20 μM and above, induced arrest in the S-phase and apoptosis in the T cell-derived T-ALL lymphocytic leukemia cell line CEM-C7H2 which is deficient in functional p53 and p16. Expression of transgenic p16/INK4A, which causes arrest in G0/G1, markedly reduced the percentage of apoptotic cells. Antagonist antibodies to Fas or FasL, or constitutive expression of crmA did not diminish the extent of resveratrol-induced apoptosis. Furthermore, a caspase-8-negative, Fas-resistant Jurkat cell line was sensitive to resveratrol-induced apoptosis which could be strongly inhibited in the Jurkat as well as in the CEM cell line by z-VAD-fmk and z-IETD-fmk. The almost complete inhibition by z-IETD-fmk and the lack of inhibition by crmA suggested caspase-6 to be the essential initiator caspase. Western blots revealed the massive conversion of procaspase-6 to its active form, while caspase-3 and caspase-2 were proteolytically activated to a much lesser extent. Cell Death and Differentiation (2000) 7, 834–842

Apoptosis induced by the histone deacetylase inhibitor sodium butyrate in human leukemic lymphoblasts

The histone deacetylase inhibitor and potential anti‐cancer drug sodium butyrate is a general inducer of growth arrest, differentiation, and in certain cell types, apoptosis. In human CCRF‐CEM, acute T lymphoblastic leukemia cells, butyrate, and other histone deacetylase inhibitors caused G2/M cell cycle arrest as well as apoptotic cell death. Forced G0/G1 arrest by tetracycline‐regulated expression of transgenic p16/INK4A protected the cells from butyrate‐induced cell death without affecting the extent of histone hyperacetylation, suggesting that the latter may be necessary, but not sufficient, for cell death induction. Nuclear apoptosis, but not G2/M arrest, was delayed but not prevented by the tripeptide broad‐range caspase inhibitor benzyloxycarbonyl‐Val‐Ala‐Asp·fluoromethylketone (zVAD) and, to a lesser extent, by the tetrapeptide ‘effector caspase’ inhibitors benzyloxycarbonyl‐Asp‐Glu‐Val‐Asp·fluoromethylketone (DEVD) and benzyloxycarbonyl‐Val‐Glu‐Ile‐Asp‐fluoromethyl‐ketone (VEID); however, the viral protein inhibitor of ‘inducer caspases’, crmA, had no effect. Bcl‐2 overexpression partially protected stably transfected CCRF‐CEM sublines from butyrate‐induced apoptosis, but showed no effect on butyrate‐induced growth inhibition, further distinguishing these two butyrate effects. c‐myc, constitutively expressed in CCRF‐CEM cells, was down‐regulated by butyrate, but this was not causative for cell death. On the contrary, tetracycline‐induced transgenic c‐myc sensitized stably transfected CCRF‐CEM derivatives to butyrate‐induced cell death.—Bernhard, D., Ausserlechner, M. J., Tonko, M., Löffler, M., Hartmann, B. L., Csordas, A., Kofler, R. Apoptosis induced by the histone deacetylase inhibitor sodium butyrate in human leukemic lymphoblasts. FASEB J. 13, 1991–2001 (1999)

FKHRL1-mediated expression of Noxa and Bim induces apoptosis via the mitochondria in neuroblastoma cells.

Protein kinase-B (PKB) and its target, the forkhead transcription factor like 1 (FKHRL1)/FoxO3a, have been suggested as regulators of neurotrophin-mediated cell survival in neuronal cells. We analyzed human neuroblastoma cells and found that FKHRL1 was phosphorylated, suggesting its inactivation. To study FKHRL1 function, we infected SH-EP and NB15 cells with a 4OH-tamoxifen-regulated FKHRL1(A3)ERtm transgene. Activation of FKHRL1 promoted cytochrome-c release and caspase-dependent apoptosis. FKHRL1 induced TRAIL and the BH3-only proteins Noxa and Bim, implicating both extrinsic and intrinsic death pathways. However, expression of dnFADD did not inhibit FKHRL1-induced cell death, whereas Bcl2 protected against apoptosis. This excluded the death-receptor pathway and suggested that cell death decision is regulated by Bcl2-rheostat. Importantly, RNAi knockdown of Noxa or Bim decreased apoptosis, indicating that Noxa and Bim cooperate to mediate FKHRL1-induced cell death. We conclude that Noxa and Bim establish a connection between FKHRL1 and mitochondria, and that both BH3-only proteins are critically involved in FKHRL1-induced apoptosis in neuroblastoma.

Gene expression profiles of proliferating vs. G1/G0 arrested human leukemia cells suggest a mechanism for glucocorticoid-induced apoptosis.

Glucocorticoids (GC) have pronounced effects on metabolism, differentiation, proliferation, and cell survival (1). In certain lymphocytes and lymphocyte‐related malignancies, GC inhibit proliferation and induce apoptotic cell death, which has led to their extensive use in the therapy of malignant lymphoproliferative disorders (2). Most of these effects result from regulation of gene expression via the GC receptor (GR), a ligand‐activated transcription factor (3). Although hundreds of genes are regulated by GC (1), how certain biological GC effects relate to individual gene regulation remains enigmatic. To address this question with respect to GC‐induced cell cycle arrest and apoptosis, we applied DNA chip technol¬ogy (4, 5) to determine gene expression profiles in proliferating and G1/G0‐arrested (by conditional expres¬sion of the CDK inhibitor p16/INK4a) acute lymphoblas¬tic Τ cells undergoing GC‐induced apoptosis. Of 7074 genes tested, 163 were found to be regulated by dexamethasone in the first 8 h in proliferating cells and 66 genes in G1/G0‐arrested cells. An almost nonoverlapping set of genes (i.e., only eight genes) was coordinately regulated in proliferating and arrested cells. Analysis of the regulated genes supports the concept that GC‐induced apoptosis results from positive GR autoregulation entail¬ing persistent down‐regulation of metabolic pathways crit¬ical for survival.—Tonko, M., Ausserlechner, M. J., Bernhard, D., Helmberg, A., Kofler, R. Gene expression profiles of proliferating vs. G1/G0 arrested human leu¬kemia cells suggest a mechanism for glucocorticoid‐induced apoptosis. FASEB J. 15, 693‐699 (2001)

FOXO3-induced reactive oxygen species are regulated by BCL2L11 (Bim) and SESN3

FOXO transcription factors induce apoptosis and regulate cellular production of reactive oxygen species (ROS). To identify the sequence of molecular events underlying FOXO3 (FKHRL1)-induced apoptosis, we studied the regulation and function of FOXO3 by expressing an ECFP-tagged FOXO3 or a 4OH-tamoxifen (4OHT)-inducible FOXO3–ERtm fusion protein in SH-EP and STA-NB15 neuronal cells. After knockdown of FOXO3 or expression of a dominant-negative FOXO3 mutant we observed that etoposide- and doxorubicin-induced elevation of cellular ROS depends on FOXO3 activation and induction of its transcriptional target BCL2L11 (Bim). Activation of FOXO3 on its own induced two sequential ROS waves as measured by reduced MitoTrackerRed in live cell microscopy. Induction of Bim by FOXO3 is essential for this phenomenon because Bim knockdown or ectopic expression of BCL2L1 (BclxL) prevented FOXO3-mediated overproduction of ROS and apoptosis. Tetracycline-controlled expression of Bim impaired mitochondrial respiration and caused ROS production, suggesting that FOXO3 induces uncoupling of mitochondrial respiration through Bim. FOXO3 also activated a ROS rescue pathway by inducing the peroxiredoxin SESN3 (Sestrin3), which is responsible for the biphasic ROS accumulation. Knockdown of SESN3 caused an increase of FOXO3-induced ROS and accelerated apoptosis. The combined data clearly demonstrate that FOXO3 activates overproduction of ROS as a consequence of Bim-dependent impairment of mitochondrial respiration in neuronal cells, which leads to apoptosis.

X-Linked Inhibitor of Apoptosis Protein – A Critical Death Resistance Regulator and Therapeutic Target for Personalized Cancer Therapy

Defects in apoptosis regulation are one main cause of cancer development and may result from overexpression of anti-apoptotic proteins such as inhibitor of apoptosis proteins (IAPs). IAPs are cell death regulators that, among other functions, bind caspases, and interfere with apoptotic signaling via death receptors or intrinsic cell death pathways. All IAPs share one to three common structures, the so called baculovirus-IAP-repeat (BIR)-domains that allow them to bind caspases and other proteins. X-linked inhibitor of apoptosis protein (XIAP) is the most potent and best-defined anti-apoptotic IAP family member that directly neutralizes caspase-9 via its BIR3 domain and the effector caspases-3 and -7 via its BIR2 domain. A natural inhibitor of XIAP is SMAC/Diablo, which is released from mitochondria in apoptotic cells and displaces bound caspases from the BIR2/BIR3 domains of XIAP thereby reactivating cell death execution. The central apoptosis-inhibitory function of XIAP and its overexpression in many different types of advanced cancers have led to significant efforts to identify therapeutics that neutralize its anti-apoptotic effect. Most of these drugs are chemical derivatives of the N-terminal part of SMAC/Diablo. These “SMAC-mimetics” either specifically induce apoptosis in cancer cells or act as drug-sensitizers. Several “SMAC-mimetics” are currently tested by the pharmaceutical industry in Phase I and Phase II trials. In this review, we will discuss recent advances in understanding the function of IAPs in normal and malignant cells and focus on approaches to specifically neutralize XIAP in cancer cells.

Repression of BIRC5/survivin by FOXO3/FKHRL1 sensitizes human neuroblastoma cells to DNA damage-induced apoptosis.

The phosphatidylinositol 3-kinase (PI3K)-protein kinase B (PKB) pathway regulates survival and chemotherapy resistance of neuronal cells, and its deregulation in neuroblastoma (NB) tumors predicts an adverse clinical outcome. Here, we show that inhibition of PI3K-PKB signaling in human NB cells induces nuclear translocation of FOXO3/FKHRL1, represses the prosurvival protein BIRC5/Survivin, and sensitizes to DNA-damaging agents. To specifically address whether FKHRL1 contributes to Survivin regulation, we introduced a 4-hydroxy-tamoxifen-regulated FKHRL1(A3)ERtm allele into NB cells. Conditional FKHRL1 activation repressed Survivin transcription and protein expression. Transgenic Survivin exerted a significant antiapoptotic effect and prevented the accumulation of Bim and Bax at mitochondria, the loss of mitochondrial membrane potential as well as the release of cytochrome c during FKHRL1-induced apoptosis. In concordance, Survivin knockdown by retroviral short hairpin RNA technology accelerated FKHRL1-induced apoptosis. Low-dose activation of FKHRL1 sensitized to the DNA-damaging agents doxorubicin and etoposide, whereas the overexpression of Survivin diminished FKHRL1 sensitization to these drugs. These results suggest that repression of Survivin by FKHRL1 facilitates FKHRL1-induced apoptosis and sensitizes to cell death induced by DNA-damaging agents, which supports the central role of PI3K-PKB-FKHRL1 signaling in drug resistance of human NB.

BIRC5/Survivin enhances aerobic glycolysis and drug resistance by altered regulation of the mitochondrial fusion/fission machinery

Gain of chromosome 17q correlates with high-stage disease, an adverse clinical outcome and leads to the overexpression of the antiapoptotic protein BIRC5/Survivin in neuroblastoma (NB). We have shown before that Survivin defines a threshold for the sensitivity of NB cells to DNA-damaging chemotherapeutic agents that require FOXO3 activation for apoptosis induction. To investigate the molecular basis of apoptosis inhibition we analyzed the function of Survivin at mitochondria and uncovered that Survivin induces mitochondrial fragmentation, reduces mitochondrial respiration and represses BCL2L11/Bim. Mitochondrial fission depends on Survivin-induced recruitment of the fission regulator DNM1L/Drp1 to mitochondria. In parallel, Survivin expression inhibits the respiratory complex-I, thereby preventing reactive oxygen species accumulation and, as a consequence, FOXO3-induced apoptosis. The loss of energy production via oxidative phosphorylation is compensated by increased glycolysis in Survivin-overexpressing NB tumor cells. Glycolysis inhibitors neutralize the antiapoptotic effect of Survivin and sensitize high-stage NB to DNA-damaging drugs. This suggests that glycolysis inhibitors target an ‘archilles heel’ of Survivin-overexpressing NB and may be highly useful as chemosensitizers in the treatment of high-stage NB.

Premature aging of the immune system in children with juvenile idiopathic arthritis

OBJECTIVE Juvenile idiopathic arthritis (JIA) is an autoimmune disease of the young. The pathogenesis is not completely understood. Premature aging, associated thymic involution, and compensatory autoproliferation could play important roles in the pathogenesis of autoimmunity. We undertook this study to determine whether patients with JIA demonstrate premature immunosenescence. METHODS To test this hypothesis, we measured 3 indicators of aging: the percentages and total counts of peripheral blood naive T cells, the frequency of T cell receptor excision circles (TRECs) in naive T cells, and telomeric erosion and Ki-67 expression as estimates of the replicative history of homeostatic proliferation. RESULTS JIA patients showed an accelerated loss of CD4+,CD45RA+,CD62L+ naive T cells with advancing age and a compensatory increase in the number of CD4+,CD45RO+ memory T cells. JIA patients demonstrated a significantly decreased frequency of TRECs in CD4+,CD45RA+ naive T cells compared with age-matched healthy donors (P = 0.002). TREC numbers correlated with age only in healthy donors (P = 0.0001). Telomeric erosion in CD4+,CD45RA+ naive T cells was increased in JIA patients (P = 0.01). The percentages of Ki-67-positive CD4+,CD45RA+ naive T cells were increased in JIA patients (P = 0.001) and correlated with disease duration (P = 0.003), which was also an independent factor contributing to telomeric erosion (P = 0.04). CONCLUSION Our findings suggest that age-inappropriate T cell senescence and disturbed T cell homeostasis may contribute to the development of JIA. In patients with JIA, dysfunction in the ability to reconstitute the T cell compartment should be considered when exploring new therapeutic strategies.