1,721,091 research outputs found
Pramanicin analog induces apoptosis in human colon cancer cells: critical roles for Bcl-2, Bim, and p38 MAPK signaling
Full text linkPramanicin (PMC) is an antifungal agent that was previously demonstrated to exhibit antiangiogenic and anticancer properties in a few in vitro studies. We initially screened a number of PMC analogs for their cytotoxic effects on HCT116 human colon cancer cells. PMC-A, the analog with the most potent antiproliferative effect was chosen to further interrogate the underlying mechanism of action. PMC-A led to apoptosis through activation of caspase-9 and -3. The apoptotic nature of cell death was confirmed by abrogation of cell death with pretreatment with specific caspase inhibitors. Stress-related MAPKs JNK and p38 were both activated concomittantly with the intrinsic apoptotic pathway. Moreover, pharmacological inhibition of p38 proved to attenuate the cell death induction while pretreatment with JNK inhibitor did not exhibit a protective effect. Resistance of Bax -/- cells and the protective nature of caspase-9 inhibition indicate that mitochondria play a central role in PMC-A induced apoptosis. Early post-exposure elevation of cellular Bim and Bax was followed by a marginal Bcl-2 depletion and Bid cleavage. Further analysis revealed that Bcl-2 downregulation occurs at the mRNA level and is critical to mediate PMC-A induced apoptosis, as ectopic Bcl-2 expression substantially spared the cells from death. Conversely, forced expression of Bim proved to significantly increase cell death. In addition, analyses of p53-/- cells demonstrated that Bcl-2/Bim/Bax modulation and MAPK activations take place independently of p53 expression. Taken together, p53-independent transcriptional Bcl-2 downregulation and p38 signaling appear to be the key modulatory events in PMC-A induced apoptosis
p73 induces apoptosis via PUMA transactivation and Bax mitochondrial translocation
No full textp73, an important developmental gene, shares a high sequence homology with p53 and induces both G(1) cell cycle arrest and apoptosis. However, the molecular mechanisms through which p73 induces apoptosis are unclear. We found that p73-induced apoptosis is mediated by PUMA (p53 up-regulated modulator of apoptosis) induction, which, in turn, causes Bax mitochondrial translocation and cytochrome c release. Overexpression of p73 isoforms promotes cell death and bax promoter transactivation in a time-dependent manner. However, the kinetics of apoptosis do not correlate with the increase of Bax protein levels. Instead, p73-induced mitochondrial translocation of Bax is kinetically compatible with the induction of cell death. p73 is localized in the nucleus and remains nuclear during the induction of cell death, indicating that the effect of p73 on Bax translocation is indirect. The ability of p73 to directly trans-activate PUMA and the direct effect of PUMA on Bax conformation and mitochondrial relocalization suggest a molecular link between p73 and the mitochondrial apoptotic pathway. Our data therefore indicate that PUMA-mediated Bax mitochondrial translocation, rather than its direct transactivation, correlates with cell death. Finally, human DeltaNp73, an isoform lacking the amino-terminal transactivation domain, inhibits TAp73-induced as well as p53-induced apoptosis. The DeltaNp73 isoforms seem therefore to act as dominant negatives, repressing the PUMA/Bax system and, thus, finely tuning p73-induced apoptosis. Our findings demonstrate that p73 elicits apoptosis via the mitochondrial pathway using PUMA and Bax as mediators
p73-alpha is capable of inducing scotin and ER stress
No full textp73, like its family member p53, can induce programmed cell death following DNA damage. Here, we report that this mechanism also involves endoplasmic reticulum (ER) stress and the transactivation of scotin, a protein identified recently as a p53 target able to induce ER stress. By using Tet-On inducible cell lines (Saos 2 osteosarcoma cells that lack p53), we observed that TAp73alpha elicits significant alterations in the morphology of the ER system, namely in the. ne subcellular localization of calnexin. We found that both TAp73alpha and p53 are strong inducers of scotin. On the other hand, the transcriptionally deficient short isoforms DeltaNp73alpha did not upregulate the steady-state mRNA level of scotin, as evaluated by real-time RT-PCR. Following the induction of scotin, ER staining with calnexin showed evidence of morphological alteration, with variations in the intracellular concentration of free calcium, visualized by fluo-3 staining. The induction of ER stress by p73 was further supported by the transcriptional induction of Gadd 153, a transcription factor induced under ER stress conditions. In conclusion, the data reported indicate the ability of TAp73alpha and p53 (not DeltaNp73alpha) to elicit scotin transactivation and ER stress. This molecular mechanism might contribute to the effector events inducing apoptosis downstream of p73
Hdm2 recruits a hypoxia-sensitive corepressor to negatively regulate p53-dependent transcription
No full textThe transcription factor p53 lies at the center of a protein network that controls cell cycle progression and commitment to apoptosis. p53 is inactive in proliferating cells, largely because of negative regulation by the Hdm2/Mdm2 oncoprotein, with which it physically associates. Release from this negative regulation is sufficient to activate p53 and can be triggered in cells by multiple stimuli through diverse pathways. This diversity is achieved in part because Hdm2 uses multiple mechanisms to inactivate p53; it targets p53 for ubiquitination and degradation by the proteosome, shuttles it out of the nucleus and into the cytoplasm, prevents its interaction with transcriptional coactivators, and contains an intrinsic transcriptional repressor activity. Here we show that Hdm2 can also repress p53 activity through the recruitment of a known transcriptional corepressor, hCtBP2. This interaction, and consequent repression of p53-dependent transcription, is relieved under hypoxia or hypoxia-mimicking conditions that are known to increase levels of intracellular NADH. CtBP proteins can undergo an NADH-induced conformational change, which we show here results in a loss of their Hdm2 binding ability. This pathway represents a novel mechanism whereby p53 activity can be induced by cellular stress.<br/
Diacylglycerol kinase α controls RCP-dependent integrin trafficking to promote invasive migration
No full textDiacylglycerol kinase α controls RCP-dependent integrin trafficking to promote invasive migration
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Equine sarcoids: Bovine Papillomavirus type 1 transformed fibroblasts are sensitive to cisplatin and UVB induced apoptosis and show aberrant expression of p53
Full text linkBovine papillomavirus type 1 infects not only cattle but also equids and is a causative factor in the pathogenesis of
commonly occurring equine sarcoid tumours. Whilst treatment of sarcoids is notoriously difficult, cisplatin has been
shown to be one of the most effective treatment strategies for sarcoids. In this study we show that in equine
fibroblasts, BPV-1 sensitises cells to cisplatin-induced and UVB-induced apoptosis, a known cofactor for
papillomavirus associated disease, however BPV-1 transformed fibroblasts show increased clonogenic survival, which
may potentially limit the therapeutic effects of repeated cisplatin treatment. Furthermore we show that BPV-1
increases p53 expression in sarcoid cell lines and p53 expression can be either nuclear or cytoplasmic. The
mechanism and clinical significance of increase/abnormal p53 expression remains to be established
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