Cell Death & Differentiation

Ryu, S J; An, H J; Oh, Y S; Choi, H R; Ha, M K; Park, S C

doi: 10.1038/cdd.2008.96pmid: 18600231

Major vault protein (MVP), the main component of vault complex, is overexpressed in many multidrug-resistant cancer cell lines, suggesting a possible role for MVP in cell signaling and survival. In this study, we have found that MVP is markedly increased in senescent human diploid fibroblasts (HDFs) as well as in aged organs. We examined whether MVP expression might be affected by apoptotic stress in an aging-dependent manner. We treated young and senescent HDFs with apoptosis-inducing agents such as H2O2, staurosporine and thapsigargin, and monitored MVP expression. We found that MVP expression is markedly reduced in young HDFs but not in senescent HDFs, in response to apoptotic stresses. Downregulation of MVP increased the sensitivity of senescent HDFs to apoptosis. Also, the level of antiapoptotic B-cell lymphoma protein-2 (Bcl-2) was significantly reduced and the accumulation of c-Jun increased in MVP knocked-down senescent HDFs. Moreover, treatment of MVP knocked-down senescent HDFs with SP600125, a specific c-Jun NH(2)-terminal kinase (JNK) inhibitor, restored the level of Bcl-2 protein. Taken together, these results suggest that MVP is important in the resistance of senescent HDFs to apoptosis by modulation of Bcl-2 expression by JNK pathway.

Barisic, S; Strozyk, E; Peters, N; Walczak, H; Kulms, D

doi: 10.1038/cdd.2008.98pmid: 18583989

Although nuclear factor-κB (NF-κB) usually exerts anti-apoptotic activity, upon activation by interleukin-1 (IL-1) it enhances ultraviolet-B radiation (UVB)-induced apoptosis. This paradoxical effect is associated with NF-κB-dependent pronounced secretion of tumour necrosis factor-α (TNF) which activates TNF-R1 in an autocrine fashion to enhance UVB-induced apoptosis. We demonstrate that sustained TNF transcription in UVB+IL-1-treated cells involves complete abrogation of the negative feedback loop of NF-κB preventing IκBα resynthesis, hence allowing uncontrolled NF-κB activity. We show that IκBα is not transcriptionally inhibited but resynthesized protein is immediately marked for degradation due to persistent inhibitor of κB kinaseβ (IKKβ) activity. Continuous IKKβ phosphorylation and activation is caused by UVB-mediated inhibition of the phosphatase PP2A. This study demonstrates that the cellular response to different NF-κB activators may be converted to the opposite reaction when both stimuli act in concert. Our data shed new light on the significance of negative feedback regulation of NF-κB and identifies PP2A as the key regulator of this process.

Rossi, D; Brambilla, L; Valori, C F; Roncoroni, C; Crugnola, A; Yokota, T; Bredesen, D E; Volterra, A

doi: 10.1038/cdd.2008.99pmid: 18617894

Astrocytes emerge as key players in motor neuron degeneration in Amyotrophic Lateral Sclerosis (ALS). Whether astrocytes cause direct damage by releasing toxic factors or contribute indirectly through the loss of physiological functions is unclear. Here we identify in the hSOD1G93A transgenic mouse model of ALS a degenerative process of the astrocytes, restricted to those directly surrounding spinal motor neurons. This phenomenon manifests with an early onset and becomes significant concomitant with the loss of motor cells and the appearance of clinical symptoms. Contrary to wild-type astrocytes, mutant hSOD1-expressing astrocytes are highly vulnerable to glutamate and undergo cell death mediated by the metabotropic type-5 receptor (mGluR5). Blocking mGluR5 in vivo slows down astrocytic degeneration, delays the onset of the disease and slightly extends survival in hSOD1G93A transgenic mice. We propose that excitotoxicity in ALS affects both motor neurons and astrocytes, favouring their local interactive degeneration. This new mechanistic hypothesis has implications for therapeutic interventions.

Koenig, A; Russell, J Q; Rodgers, W A; Budd, R C

doi: 10.1038/cdd.2008.100pmid: 18617900

Caspase-8, a cysteine-protease, initiates apoptosis when activated by death receptors. Caspase-8 is also essential for initiating T lymphocyte proliferation following T-cell antigen receptor (TCR) signaling. Given these disparate functions of caspase-8, we sought to determine whether this represented only a difference in the magnitude of caspase-8 activation, or different intracellular locations of active caspase-8. We demonstrate by high-resolution multicolor confocal laser scanning microscopy an aggregation of active caspase-8 within membrane lipid rafts in T cells stimulated with anti-CD3. This suggests that following TCR stimulation active caspase-8 physically interacts with lipid raft proteins, possibly to form a signaling platform. In contrast, Fas stimulation of T cells resulted in a much more profound activation of caspase-8 that was exclusively cytosolic. These confocal microscopic findings were confirmed using discontinuous sucrose gradient ultracentrifugation to isolate lipid raft versus cytosolic components. This sequestration model of caspase-8 activation was further supported by the observation that a classic caspase-8 substrate, BID, was not cleaved in CD3-stimulated T cells, but was cleaved after Fas engagement. Our data support a model that the location of active caspase-8 may profoundly influence its functional capacity as a regulator of either cell cycling or cell death.

Kamitsuji, Y; Kuroda, J; Kimura, S; Toyokuni, S; Watanabe, K; Ashihara, E; Tanaka, H; Yui, Y; Watanabe, M; Matsubara, H; Mizushima, Y; Hiraumi, Y; Kawata, E; Yoshikawa, T; Maekawa, T; Nakahata, T; Adachi, S

Lespagnol, A; Duflaut, D; Beekman, C; Blanc, L; Fiucci, G; Marine, J-C; Vidal, M; Amson, R; Telerman, A

doi: 10.1038/cdd.2008.104pmid: 18617898

TSAP6 (tumor suppressor-activated pathway 6), also known as Steap3, is a direct p53 transcriptional target gene. It regulates protein secretion, for example translationally controlled tumor protein (TCTP), which is implicated in tumor reversion. In keeping with the latter, we show herein that TSAP6 is a glycosylated protein present in the trans-Golgi network, endosomal–vesicular compartment and cytoplasmic membrane. To further investigate the physiological function of TSAP6, we have generated TSAP6-deficient mice. These mice exhibit microcytic anemia with abnormal reticulocyte maturation and deficient transferrin receptor downregulation, a process known to be dependent on exosomal secretion. Moreover, we provide direct evidence that exosome production is severely compromised in TSAP6-null cells. Finally, we show that the DNA damage-induced p53-dependent nonclassical exosomal secretory pathway is abrogated in TSAP6-null cells. Given the fact that exosomes are used as cell-free vaccines against cancer and that they could be involved in the biogenesis and spread of human immunodeficiency virus, it is important to understand their regulation. The results presented here provide the first genetic demonstration that exosome formation is a tightly controlled biological process dependent of TSAP6.

Ewing, S J; Zhu, S; Zhu, F; House, J S; Smart, R C

doi: 10.1038/cdd.2008.105pmid: 18636078

CCAAT/enhancer-binding protein-β (C/EBPβ) is a mediator of cell survival and tumorigenesis. When C/EBPβ −/− mice are treated with carcinogens that produce oncogenic Ras mutations in keratinocytes, they respond with abnormally elevated keratinocyte apoptosis and a block in skin tumorigenesis. Although this aberrant carcinogen-induced apoptosis results from abnormal upregulation of p53, it is not known whether upregulated p53 results from oncogenic Ras and its ability to induce p19Arf and/or activate DNA-damage response pathways or from direct carcinogen-induced DNA damage. We report that p19Arf is dramatically elevated in C/EBPβ −/− epidermis and that C/EBPβ represses a p19Arf promoter reporter. To determine whether p19Arf is responsible for the proapoptotic phenotype in C/EBPβ −/− mice, C/EBPβ −/−;p19Arf−/− mice were generated. C/EBPβ −/−;p19Arf−/− mice responded to carcinogen treatment with increased p53 and apoptosis, indicating p19Arf is not essential. To ascertain whether oncogenic Ras activation induces aberrant p53 and apoptosis in C/EBPβ −/− epidermis, we generated K14-ER:Ras;C/EBPβ −/− mice. Oncogenic Ras activation induced by 4-hydroxytamoxifen did not produce increased p53 or apoptosis. Finally, when C/EBPβ −/− mice were treated with differing types of DNA-damaging agents, including alkylating chemotherapeutic agents, they displayed aberrant levels of p53 and apoptosis. These results indicate that C/EBPβ represses p53 to promote cell survival downstream of DNA damage and suggest that inhibition of C/EBPβ may be a target for cancer cotherapy to increase the efficacy of alkylating chemotherapeutic agents.

Makhov, P; Golovine, K; Uzzo, R G; Rothman, J; Crispen, P L; Shaw, T; Scoll, B J; Kolenko, V M

doi: 10.1038/cdd.2008.106pmid: 18617897

The X-linked inhibitor of apoptosis (XIAP), the most potent member of the inhibitor of apoptosis protein (IAP) family of endogenous caspase inhibitors, blocks the initiation and execution phases of the apoptotic cascade. As such, XIAP represents an attractive target for treating apoptosis-resistant forms of cancer. Here, we demonstrate that treatment with the membrane-permeable zinc chelator, N,N,N′,N′,-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN) induces a rapid depletion of XIAP at the post-translational level in human PC-3 prostate cancer cells and several non-prostate cell lines. The depletion of XIAP is selective, as TPEN has no effect on the expression of other zinc-binding members of the IAP family, including cIAP1, cIAP2 and survivin. The downregulation of XIAP in TPEN-treated cells occurs via proteasome- and caspase-independent mechanisms and is completely prevented by the serine protease inhibitor, Pefabloc. Finally, our studies demonstrate that TPEN promotes activation of caspases-3 and -9 and sensitizes PC-3 prostate cancer cells to TRAIL-mediated apoptosis. Taken together, our findings indicate that zinc-chelating agents may be used to sensitize malignant cells to established cytotoxic agents via downregulation of XIAP.

Yuan, M; Tomlinson, V; Lara, R; Holliday, D; Chelala, C; Harada, T; Gangeswaran, R; Manson-Bishop, C; Smith, P; Danovi, S A; Pardo, O; Crook, T; Mein, C A; Lemoine, N R; Jones, L J; Basu, S

Zhang, Y; Kong, L; Carlson, C S; Liu, C-j

doi: 10.1038/cdd.2008.112pmid: 18636074

We reported earlier that an interferon-inducible p204 protein serves as a cofactor of Cbfa1 and promotes osteogenesis. Here we establish that p204 demonstrates prominent expression in growth plate chondrocytes. It is differentially expressed in the course of bone morphogenetic protein-2-triggered chondrocyte differentiation of pluripotent C3H10T1/2 cells. This expression is probably due to the activation of p204 gene by Cbfa1 and repression by Sox5 transcription factor. Cbfa1 and Sox5 bind to the 5′-flanking regulatory region of p204 gene at their consensus binding elements. Overexpression of p204 accelerates chondrocyte hypertrophy, as revealed by enhanced expression of type X Collagen and matrix metalloproteinase-13; however, knockdown of p204 via an siRNA approach abolishes hypertrophic chondrocyte differentiation. p204 acts as a cofactor of Cbfa1 in chondrocyte hypertrophy: (1) overexpression of p204 augments, whereas suppression of p204 decreases, the Cbfa1-dependent transactivation of a Collagen X-specific reporter gene; (2) p204 enhances Cbfa1-mediated chondrocyte hypertrophy; and (3) p204 associates with Cbfa1 in chondrocyte differentiation. In addition, altered expression of p204 in chondrocyte hypertrophy was accompanied by altered levels of Indian hedgehog (IHH) and parathyroid hormone/parathyroid hormone-related peptide receptor-1 (PTHR1). Collectively, p204 is a novel regulator of chondrocyte differentiation by (1) acting as a coactivator of Cbfa1 and (2) affecting IHH/PTPrP signaling.