Pharmacological targeting of p53 through RITA is an effective antitumoral strategy for malignant pleural mesothelioma

Malignant mesothelioma, a very aggressive tumor associated to asbestos exposure, is expected to increase in incidence, and unfortunately, no curative modality exists. Reactivation of p53 is a new attractive antitumoral strategy. p53 is rarely mutated in mesothelioma, but it is inactivated in most tumors by the lack of p14^ARF. Here, we evaluated the feasibility of this approach in pleural mesothelioma by testing RITA and nutlin-3, two molecules able to restore p53 function through a different mechanism, on a panel of mesothelioma cell lines representing the epithelioid (NCI-H28, NCI-H2452, IST-MES 2), biphasic (MSTO-211H), and sarcomatoid (NCI-H2052) histotypes compared with the normal mesothelial HMC-hTERT. RITA triggered robust caspase-dependent apoptosis specifically in epithelioid and biphasic mesothelioma cell lines, both through wild-type and mutant p53, concomitant to p21 downregulation. Conversely, nutlin-3 induced a p21-dependent growth arrest, rather than apoptosis, and was slightly toxic on HMC-hTERT.

Interestingly, we identified a previously undetected point mutation of p53 (p.Arg249Ser) in IST-MES 2, and showed that RITA is also able to reactivate this p53 mutant protein and its apoptotic function. RITA reduced tumor growth in a MSTO-211H-derived xenograft model of mesothelioma and synergized with cisplatin, which is the mainstay of treatment for this tumor.

Our data indicate that reactivation of p53 and concomitant p21 downregulation effectively induce cell death in mesothelioma, a tumor characterized by a high intrinsic resistance to apoptosis. Altogether, our findings provide the preclinical framework supporting the use of p53-reactivating agents alone, or in combination regimens, to improve the outcome of patients with mesothelioma.     

Adaptation of cancer cells from different entities to the MDM2 inhibitor nutlin-3 results in the emergence of p53-mutated multi-drug-resistant cancer cells

Six p53 wild-type cancer cell lines from infrequently p53-mutated entities (neuroblastoma, rhabdomyosarcoma, and melanoma) were continuously exposed to increasing concentrations of the murine double minute 2 inhibitor nutlin-3, resulting in the emergence of nutlin-3-resistant, p53-mutated sublines displaying a multi-drug resistance phenotype. Only 2 out of 28 sublines adapted to various cytotoxic drugs harboured p53 mutations. Nutlin-3-adapted UKF-NB-3 cells (UKF-NB-3^rNutlin^10 μM, harbouring a G245C mutation) were also radiation resistant. Analysis of UKF-NB-3 and UKF-NB-3^rNutlin^10 μM cells by RNA interference experiments and lentiviral transduction of wild-type p53 into p53-mutated UKF-NB-3^rNutlin^10 μM cells revealed that the loss of p53 function contributes to the multi-drug resistance of UKF-NB-3^rNutlin^10 μM cells. Bioinformatics PANTHER pathway analysis based on microarray measurements of mRNA abundance indicated a substantial overlap in the signalling pathways differentially regulated between UKF-NB-3^rNutlin^10 μM and UKF-NB-3 and between UKF-NB-3 and its cisplatin-, doxorubicin-, or vincristine-resistant sublines. Repeated nutlin-3 adaptation of neuroblastoma cells resulted in sublines harbouring various p53 mutations with high frequency. A p53 wild-type single cell-derived UKF-NB-3 clone was adapted to nutlin-3 in independent experiments. Eight out of ten resulting sublines were p53-mutated harbouring six different p53 mutations. This indicates that nutlin-3 induces de novo p53 mutations not initially present in the original cell population. Therefore, nutlin-3-treated cancer patients should be carefully monitored for the emergence of p53-mutated, multi-drug-resistant cells.     

Loss of p53 expression in cancer cells alters cell cycle response after inhibition of exportin-1 but does not prevent cell death

The tumor suppressor protein p53 is central to the cellular stress response and may be a predictive biomarker for cancer treatments. Upon stress, wildtype p53 accumulates in the nucleus where it enforces cellular responses, including cell cycle arrest and cell death. p53 is so dominant in its effects, that p53 enforcement – or – restoration therapy is being studied for anti-cancer therapy. Two mechanistically distinct small molecules that act via p53 are the selective inhibitor of nuclear export, selinexor, and MDM2 inhibitor, nutlin-3a. Here, individual cells are studied to define cell cycle response signatures, which captures the variability of responses and includes the impact of loss of p53 expression on cell fates. The individual responses are then used to build the population level response. Matched cell lines with and without p53 expression indicate that while loss-of-function results in altered cell cycle signatures to selinexor treatment, it does not diminish overall cell loss. On the contrary, response to single-agent nutlin-3a shows a strong p53-dependence. Upon treatment with both selinexor and nutlin-3a there are combination effects in at least some cell lines – even when p53 is absent. Collectively, the findings indicate that p53 does act downstream of selinexor and nutlin-3a, and that p53 expression is dispensable for selinexor to cause cell death, but nutlin-3a response is more p53-dependent. Thus, TP53 disruption and lack of expression may not predict poor cell response to selinexor, and selinexor’s mechanism of action potentially provides for strong efficacy regardless of p53 function.     

C-myc通过调控BubR1影响食管鳞癌细胞对紫杉醇的敏感性

探讨C-Myc与有丝分裂期检查点蛋白BubR1的表达关系和对紫杉醇药物作用的可能影响.用免疫组化方法检测23例食管鳞癌组织标本中C-Myc和BubR1的表达水平,并通过免疫印迹的方法比较3株食管鳞癌细胞株ECA-109,KYSE150和KYSE180中C-Myc和BubR1的表达高低,分析相关性;将人BUB1b基因启动子上游约2000bp片段插入pSEAP2分泌型碱性磷酸酶报告质粒中构建为pSEAP2-BubR1-P2000,分别转染至3株鳞癌细胞内,检测启动子激活效果;在ECA-109细胞内过表达C-Myc后再转染pSEAP2-BubR1-P2000后,检测启动子的激活效果;免疫印迹方法检测C-Myc抑制剂10058-F4对BubR1蛋白表达的影响;通过MTT检测10058-F4干扰C-Myc后ECA-109细胞在梯度紫杉醇浓度下的生存率变化;最后通过DAPI染色观察单用C-Myc抑制剂,单用低浓度紫杉醇(100nM)或联用10058-F4和紫杉醇组的凋亡比例.结果发现在临床食管鳞癌标本和食管鳞癌细胞株中C-Myc和BubR1的表达有相关一致性;C-Myc高表达的细胞株中BubR1启动子活性的激活程度更强,并且过表达C-Myc后能进一步上调启动子活性;C-Myc特异性抑制剂10058-F4可以有效下调BubR1表达,并减低细胞在梯度紫杉醇作用下的细胞生存率.DAPI染色结果显示联用10058-F4和低浓度紫杉醇能明显增加细胞处于有丝分裂期的比率.在食管鳞癌细胞中C-Myc能上调有丝分裂期检查点蛋白BuR1的水平,并与食管癌对紫杉醇的敏感性相关,C-Myc可能通过上调BubR1表达而减低食管鳞癌对紫杉醇的反应.     

p53上调凋亡调制物的促凋亡作用

p53上调凋亡调制物(p53up-regulated modulator of apoptosis,PUMA)是Bcl-2家族中BH3-only(Bcl-2 homology 3-only)蛋白质家族成员,通过其BH3结构域与所有的Bcl-2抗凋亡蛋白质结合,引发线粒体功能障碍和胱天蛋白酶(caspase)级联反应,诱导细胞凋亡。PUMA被证实在多种病理性应激介导的细胞凋亡中发挥着至关重要的作用,因而成为近年研究的热点。     

Deciphering the intricate regulatory mechanisms for the cellular choice between cell repair, apoptosis or senescence in response to damaging signals

In response to various types of stress, cells can undergo significant phenotypic changes, ranging from an increased DNA repair to senescence and apoptosis. The mechanisms by which p53 manages the choice between three possible cell fates in response to damaging stress remain poorly understood. p53 is not a simple switch that determines cell fate single-handedly; but rather as a component, albeit an important one, of an intricate signal network and molecular interactions. Thus, in addition to p53, fine-tuned interactions between growth- and division-activator molecules such as TGFβ, cMyc and FOXO are important determinants of the cellular fate. The aim of the paper is to resolve the complex interactions between these molecules and to elicit clear and reasonable working mechanisms for these diverse cellular processes.     

IGFBP-3 and apoptosis—a licence to kill?

Insulin-like growth factor binding protein (IGFBP)-3, the major carrier of insulin-like growth factors (IGFs) in the circulation, was first isolated and characterised over a decade ago. More recently, IGFBP-3 has been assigned a role as a putative death-promoting factor, a function that appears, under certain circumstances, to be independent of its IGF-binding ability. This review examines the current evidence for a pro-apoptotic function for IGFBP-3 and speculates on its physiological significance.     

p53 directly suppresses BNIP3 expression to protect against hypoxia-induced cell death

Hypoxia stabilizes the tumour suppressor p53, allowing it to function primarily as a transrepressor; however, the function of p53 during hypoxia remains unclear. In this study, we showed that p53 suppressed BNIP3 expression by directly binding to the p53-response element motif and recruiting corepressor mSin3a to the BNIP3 promoter. The DNA-binding site of p53 must remain intact for the protein to suppress the BNIP3 promoter. In addition, taking advantage of zebrafish as an in vivo model, we confirmed that zebrafish nip3a, a homologous gene of mammalian BNIP3, was indeed induced by hypoxia and p53 mutation/knockdown enhanced nip3a expression under hypoxia resulted in cell death enhancement in p53 mutant embryos. Furthermore, p53 protected against hypoxia-induced cell death mediated by p53 suppression of BNIP3 as illustrated by p53 knockdown/loss assays in both human cell lines and zebrafish model, which is in contrast to the traditional pro-apoptotic role of p53. Our results suggest a novel function of p53 in hypoxia-induced cell death, leading to the development of new treatments for ischaemic heart disease and cerebral stroke.     

Endothelial cells regulate p53-dependent apoptosis of neural progenitors after irradiation

Endothelial cells represent an important component of the neurogenic niche and may regulate self-renewal and differentiation of neural progenitor cells (NPCs). Whether they have a role in determining the apoptotic fate of NPCs after stress or injury is unclear. NPCs are known to undergo p53-dependent apoptosis after ionizing radiation, whereas endothelial cell apoptosis after irradiation is dependent on membrane acid sphingomyelinase (ASMase) and is abrogated in sphingomyelin phosphodiesterase 1 (smpd1)- (gene that encodes ASMase) deficient mice. Here we found that p53-dependent apoptosis of NPCs in vivo after irradiation was inhibited in smpd1-deficient mice. NPCs cultured from mice, wild type (+/+) or knockout (−/−), of the smpd1 gene, however, demonstrated no difference in apoptosis radiosensitivity. NPCs transplanted into the hippocampus of smpd1−/− mice were protected against apoptosis after irradiation compared with those transplanted into smpd1+/+ mice. Intravenous administration of basic fibroblast growth factor, which does not cross the blood–brain barrier, known to protect endothelial cells against apoptosis after irradiation also attenuated the apoptotic response of NPCs. These findings provide evidence that endothelial cells may regulate p53-dependent apoptosis of NPCs after genotoxic stress and add support to an important role of endothelial cells in regulating apoptosis of NPCs after injury or in disease.     

Dexamethasone regulation of terminal differentiation in 3T3-F442A preadipocyte cell line

The 3T3-F442A preadipocyte cell line was previously shown to possess specific glucocorticoid receptors whose number increased in the time course of differentiation. We have examined the effects of a three day dexamethasone treatment, added at confluence, on cells differentiated in the presence or absence of insulin. Triglyceride accumulation, polyamine content as well as glycerophosphate dehydrogenase and fatty acid synthetase activities were measured during the adipose conversion. We have also determined 2-deoxyglucose uptake in non-differentiated and differentiated cells. Dexamethasone was shown to decrease the adipose conversion by 3T3-F442A cells in the presence or absence of insulin. Intracellular spermidine content in differentiating cells was sensitive to dexamethasone and insulin in the same way as an enzymatic marker of terminal differentiation, glycerophosphate dehydrogenase. Dexamethasone decreases the 2 deoxyglucose uptake in non-differentiated and differentiated cells while insulin increases this uptake only in differentiated cells. This work shows that glucocorticoids inhibit adipocyte metabolism at distinct levels and suggests that these hormones might play an important role in the regulation of adipose tissue mass.Abbreviations DEX dexamethasone - FAS fatty acid synthetase - GPDH glycerophosphate dehydrogenase - MIX 1-methyl-3-isobutylxanthine     

Characterization of the cell death induced by cadmium in HaCaT and C6 cell lines

Cell death resulting from cadmium (Cd) intoxication has been confirmed to induce both necrosis and apoptosis. The ratio between both types of cell death is dose- and cell-type-dependent. This study used the human keratinocytes HaCaT expressing a mutated p53 and the rat glial cells C6 expressing a wild p53 as models to characterize Cd-induced apoptosis, using sub-lethal and lethal doses. At these concentrations, features of apoptosis were observed 24 h after C6 cell treatment: apoptotic DNA fragmentation and caspase-9 activation, whereas Cd did not induce caspase-3. In HaCaT, Cd did not induce apoptotic DNA fragmentation or caspase-9 and -3 activation. The results also showed that the inhibition of p53 led to a resistance of the C6 cells to 20 µm Cd, decreased the apoptosis and increased the metallothioneins in these cells. p53 restoration increased the sensitivity of HaCaT cells to Cd but did not affect the MT expression. The results suggest that Cd induced apoptosis in C6 cells but a non-apoptotic cellular death in HaCaT cells.     

Immune responses to p53 in patients with cancer:enrichment in tetramer+ p53 peptide-specific T cells and regulatory T cells at tumor sites

Objective: A majority of human cancers, including head and neck cancer (HNC), overexpress p53. Although T cells specific for wild-type (wt) sequence p53 peptides are detectable in the peripheral blood of patients with HNC, it is unknown whether such T cells accumulate in tumor-involved tissues. Also, the localization of regulatory T cells (Treg) to tumor sites in HNC has not been investigated to date. Methods: Tumor infiltrating lymphocytes (TIL), tumor-involved or non-involved lymph node lymphocytes (LNL) and peripheral blood mononuclear cells (PBMC) were obtained from 24 HLA-A2.1+ patients with HNC. Using tetramers and four-color flow cytometry, the frequency of Treg and CD3+CD8+ T cells specific for wt p53 epitopes as well as their functional attributes were determined. Results: The CD3+CD8+ tetramer+ cell frequency was significantly higher (P<0.001) in TIL than autologous PBMC as was the percentage of CD4+CD25+ T cells (P<0.003). TIL were enriched in FOXp3+, GITR+ and CTLA-4+ Treg. CD8+ TIL had low expression and produced little IFN- after ex vivo stimulation relative to autologous PBMC or PBMC from NC. Conclusions: Anti-wt p53 epitope-specific T cells and Treg preferentially localize to tumor sites in patients with HNC. However, despite enrichment in tumor peptide-specific T cells, the effector cell population (CD3+CD8+) in TIL or PBMC was unresponsive to activation in the tumor microenvironment enriched in Treg.