p53 inhibitor pifithrin alpha can suppress heat shock and glucocorticoid signaling pathways

Modulation of TCR stimulation and pifithrin-α improve the genomic safety profile of CRISPR-engineered human T cells

CRISPR-engineered chimeric antigen receptor (CAR) T cells are at the forefront of novel cancer treatments. However, several reports describe the occurrence of CRISPR-induced chromosomal aberrations. So far, measures to increase the genomic safety of T cell products focused mainly on the components of the CRISPR-Cas9 system and less on T cell-intrinsic features, such as their massive expansion after T cell receptor (TCR) stimulation. Here, we describe driving forces of indel formation in primary human T cells. Increased T cell activation and proliferation speed correlate with larger deletions. Editing of non-activated T cells reduces the risk of large deletions with the downside of reduced knockout efficiencies. Alternatively, the addition of the small-molecule pifithrin-α limits large deletions, chromosomal translocations, and aneuploidy in a p53-independent manner while maintaining the functionality of CRISPR-engineered T cells, including CAR T cells. Controlling T cell activation and pifithrin-α treatment are easily implementable strategies to improve the genomic integrity of CRISPR-engineered T cells.

Proximal Tubular Lats2 Ablation Exacerbates Ischemia/Reperfusion Injury (IRI)-Induced Renal Maladaptive Repair through the Upregulation of P53

The Hippo pathway mediates renal maladaptive repair after acute kidney injury (AKI), which has been considered a driving force in the progression to chronic kidney disease (CKD). LATS2, a core kinase of the Hippo pathway, exerts non-Hippo-dependent functions in the regulation of the cell cycle and cell fate, providing new insights into AKI and further repair. However, its role remains unknown. Here, we utilized a proximal tubular Lats2 conditional knockout mouse strain (Lats2-CKO) to evaluate the effect of LATS2 deficiency on ischemia/reperfusion-induced AKI-to-CKD transition. Lats2-CKO mice presented with more severe tubular maladaptive repair, inflammatory infiltration, interstitial fibrosis, and apoptosis following AKI. Importantly, we discovered that Lats2 ablation caused the activation of p53, with increased levels of cellular apoptotic molecules (p21, Bax, and cleaved caspase-3), and decreased levels of anti-apoptotic molecules (Bcl-2 and Bcl-xL). Pifithirin-α (p53 inhibitor) effectively attenuated renal fibrosis, inflammation, and apoptosis in Lats2-CKO mice after AKI. Consistently, in vitro Lats2 overexpression decreased p53, p21, Bax and cleaved caspase 3 expression after hypoxia/reoxygenation (H/R) treatment. Of note, the phosphorylation of MDM2, which promotes the ubiquitination degradation of p53, at site Ser186 was decreased in Lats2-CKO kidneys, but increased by Lats2 overexpression in vitro. Therefore, LATS2 deficiency aggravated ischemia/reperfusion injury (IRI)-induced maladaptive repair via regulating the tubular MDM2-p53 axis in AKI-to-CKD transition.

TAF1A and ZBTB41 serve as novel key genes in cervical cancer identified by integrated approaches

Cervical cancer (CC) is the second most common cancer and the leading cause of cancer mortality in women. Numerous studies have found that the development of CC was associated with multiple genes. However, the mechanisms on gene level are enigmatic, hindering the understanding of its functional roles. This study sought to identify prognostic biomarkers of CC, and explore their biological functions. Here we conducted an integrated analysis to screen potential vital genes. Candidate genes were further tested by experiments in clinical specimens and cancer cell line. Then, molecular modeling was used to predict the three-dimensional structure of candidate genes’ proteins, and the interaction pattern was analyzed by docking simulation technique. Among the potential genes identified, we found that TAF1A and ZBTB41 were highly correlated. Furthermore, there was a definite interaction between the proteins of TAF1A and ZBTB41, which was affected by the activity of the p53 signaling pathway. In conclusion, our findings identified TAF1A and ZBTB41 could serve as biomarkers of CC. We confirmed their biological function and deciphered their interaction for the first time, which may be helpful for developing further researches.

Inhibition of p53 DNA binding by a small molecule protects mice from radiation toxicity

Transcription factors are attractive therapeutic targets that are considered non-druggable because they do not have binding sites for small drug-like ligands. We established a cell-free high-throughput screening assay to search for small molecule inhibitors of DNA binding by transcription factors. A screen was performed using p53 as a target, resulting in the identification of NSC194598 that inhibits p53 sequence-specific DNA binding in vitro (IC₅₀ = 180 nM) and in vivo. NSC194598 selectively inhibited DNA binding by p53 and homologs p63/p73, but did not affect E2F1, TCF1, and c-Myc. Treatment of cells with NSC194598 alone paradoxically led to p53 accumulation and modest increase of transcriptional output owing to disruption of the MDM2-negative feedback loop. When p53 was stabilized and activated by irradiation or chemotherapy drug treatment, NSC194598 inhibited p53 DNA binding and induction of target genes. A single dose of NSC194598 increased the survival of mice after irradiation. The results suggest DNA binding by p53 can be targeted using small molecules to reduce acute toxicity to normal tissues by radiation and chemotherapy.

Influence of Tumor Suppressor p53 Functioning on the Expression of Antioxidant System Genes under the Action of Cytotoxic Compounds

The effect of inhibition of the tumor suppressor p53 on the antioxidant system genes expression under the influence of cytotoxic compounds of the platinum group was studied. It was found that the action of platinum(II) and platinum(IV) complexes induced accumulation of p53 protein with a maximum in 12 h, which was confirmed by an increase in the expression of the P21 gene, the target gene of the p53 protein. It was shown that the action of platinum complexes activated the expression of catalase and superoxide dismutase 2 genes. Suppression of p53 protein functions with specific inhibitor α-piphitrin under the action of platinum complexes reduced the expression of catalase and superoxide dismutase 2 genes and the target gene P21, which attested to the p53-dependent regulation of these genes.

SerpinB1 promotes the proliferation of porcine pancreatic stem cells through the STAT3 signaling pathway

Porcine pancreatic stem cells (pPSCs) can be induced to insulin-secreting cells and therefore considered the most promising seeding cells for curing human diabetes in future. However, insufficient pPSCs number is one of the bottleneck problems before its clinical application. SerpinB1 is a serine protease inhibitor in neutrophils and can directly promote the proliferation of β cells. Whether SerpinB1 is involved in pPSC proliferation and differentiation remains unknown. The effects of SerpinB1 on pPSCs proliferation were measured by Cell Counting Kit-8, 5-ethynyl-2'-deoxyuridine, qRT-PCR, western blot, and flow cytometry assays. We found that pPSCs did not efficiently reach the S phase when SerpinB1 expression was knocked down with short hairpin RNA (sh-SerpinB1), the expression of Cyclin D1, CDK-2, and PCNA also decreased. Meanwhile, cell viability and proliferation ability were both declined. Further analyses showed that the expression level of phosphorylated STAT3/STAT3was downregulated, along with an upregulation of p53 and p21. We used a two-step induction method to induce pPSCs to insulin-secreting cells and found that SerpinB1 expression in insulin-secreting cells was higher than in pPSCs. Meanwhile, the protein expression level of phosphorylated STAT3/STAT3 was increased while p53 and p21 was decreased in induced insulin-secreting cells in comparison with control cells. The insulin-secreting cells derived from the sh-SerpinB1 cells secreted less insulin and showed poor sensitivity to high glucose than control group. However, the insulin-secreting cells derived from the ov-SerpinB1 cells has a quite contrary tendency. In conclusion, this study demonstrates that SerpinB1 promotes the proliferation of pPSCs through the STAT3 signaling pathway, and SerpinB1 is a key factor for maintaining the viability of pPSCs during the transition to insulin-secreting cells.

The p53 inactivators pifithrin-μ and pifithrin-α mitigate TBI-induced neuronal damage through regulation of oxidative stress, neuroinflammation, autophagy and mitophagy

Traumatic brain injury (TBI) is one of the most common causes of death and disability worldwide. We investigated whether inhibition of p53 using pifithrin (PFT)-α or PFT-μ provides neuroprotective effects via p53 transcriptional dependent or -independent mechanisms, respectively. Sprague Dawley rats were subjected to controlled cortical impact TBI followed by the administration of PFTα or PFT-μ (2 mg/kg, i.v.) at 5 h after TBI. Brain contusion volume, as well as sensory and motor functions were evaluated at 24 h after TBI. TBI-induced impairments were mitigated by both PFT-α and PFT-μ. Fluoro-Jade C staining was used to label degenerating neurons within the TBI-induced cortical contusion region that, together with Annexin V positive neurons, were reduced by PFT-μ. Double immunofluorescence staining similarly demonstrated that PFT-μ significantly increased HO-1 positive neurons and mRNA expression in the cortical contusion region as well as decreased numbers of 4-hydroxynonenal (4HNE)-positive cells. Levels of mRNA encoding for p53, autophagy, mitophagy, anti-oxidant, anti-inflammatory related genes and proteins were measured by RT-qPCR and immunohistochemical staining, respectively. PFT-α, but not PFT-μ, significantly lowered p53 mRNA expression. Both PFT-α and PFT-μ lowered TBI-induced pro-inflammatory cytokines (IL-1β and IL-6) mRNA levels as well as TBI-induced autophagic marker localization (LC3 and p62). Finally, treatment with PFT-μ mitigated TBI-induced declines in mRNA levels of PINK-1 and SOD2. Our data suggest that both PFT-μ and PFT-α provide neuroprotective actions through regulation of oxidative stress, neuroinflammation, autophagy, and mitophagy mechanisms, and that PFT-μ, in particular, holds promise as a TBI treatment strategy.

Multiplex profiling identifies clinically relevant signalling proteins in an isogenic prostate cancer model of radioresistance

The exact biological mechanism governing the radioresistant phenotype of prostate tumours at a high risk of recurrence despite the delivery of advanced radiotherapy protocols remains unclear. This study analysed the protein expression profiles of a previously generated isogenic 22Rv1 prostate cancer model of radioresistance using DigiWest multiplex protein profiling for a selection of 90 signalling proteins. Comparative analysis of the profiles identified a substantial change in the expression of 43 proteins. Differential PARP-1, AR, p53, Notch-3 and YB-1 protein levels were independently validated using Western Blotting. Pharmacological targeting of these proteins was associated with a mild but significant radiosensitisation effect at 4Gy. This study supports the clinical relevance of isogenic in vitro models of radioresistance and clarifies the molecular radiation response of prostate cancer cells.

Pifithrin-α enhancing anticancer effect of topotecan on p53-expressing cancer cells

p53 is generally known as an effective anti-cancer molecular, but it is lost or mutated in more than 50% of human tumors. It is still a controversial issue whether the activity of p53 really benefits for treating cancers, we wondered what would happen if the endogenous p53 was inhibited before treated with topotecan (TPT) on p53 positive tumor cells. In this study, pifithrin-α (PFTα), a p53 inhibitor, was used 2 h before treated with TPT on three kinds of cancer cell lines including MCF7, BGC823 and HepG2 cells. The IC₅₀s of TPT for MCF7, BGC823 and HepG2 cells after 10 μΜ PFTα pretreated, was 4.8 to 14.4 folds lower than the effect of TPT alone. It was demonstrated that PFTα decreases the p-p53 levels and p-p53 activity, not affects p53 expression in p53 positive tumor cells. PFTα enhanced anticancer effect of TPT on cells was found mainly by two ways. Firstly, it increased the TPT accumulation in cells and nucleus and promoted the inhibition of TPT on activity of Topo I, and induced more DNA damage. Secondly, PFTα decreased formation of p53/mdm2 complex responsible for p53 degradation by inhibiting the protein expression of mdm2, so p53 degradation was decreased in cytoplasm and p53 accumulation was increased in nucleus, which induced more cells undergo apoptosis. So, the crosstalk between p53 and TPT played a pivotal role for enhancing anticancer effects of PFTα and TPT on p53 positive cancer cells. These findings provide a new idea for drug design and combination chemotherapy of cancers.

Intracellular displacement of p53 using transactivation domain (p53 TAD) specific nanobodies

The tumor suppressor p53 is of crucial importance in the prevention of cellular transformation. In the presence of cellular stress signals, the negative feedback loop between p53 and Mdm2, its main negative regulator, is disrupted, which results in the activation and stabilization of p53. Via a complex interplay between both transcription-dependent and - independent functions of p53, the cell will go through transient cell cycle arrest, cellular senescence or apoptosis. However, it remains difficult to completely fathom the mechanisms behind p53 regulation and its responses, considering the presence of multiple layers involved in fine-tuning them. In order to take the next step forward, novel research tools are urgently needed. We have developed single-domain antibodies, also known as nanobodies, that specifically bind with the N-terminal transactivation domain of wild type p53, but that leave the function of p53 as a transcriptional transactivator intact. When the nanobodies are equipped with a mitochondrial-outer-membrane (MOM)-tag, we can capture p53 at the mitochondria. This nanobody-induced mitochondrial delocalization of p53 is, in specific cases, associated with a decrease in cell viability and with morphological changes in the mitochondria. These findings underpin the potential of nanobodies as bona fide research tools to explore protein function and to unravel their biochemical pathways.

Inhibitor of CBP Histone Acetyltransferase Downregulates p53 Activation and Facilitates Methylation at Lysine 27 on Histone H3

Tumor suppressor p53-directed apoptosis triggers loss of normal cells, which contributes to the side-effects from anticancer therapies. Thus, small molecules with potential to downregulate the activation of p53 could minimize pathology emerging from anticancer therapies. Acetylation of p53 by the histone acetyltransferase (HAT) domain is the hallmark of coactivator CREB-binding protein (CBP) epigenetic function. During genotoxic stress, CBP HAT-mediated acetylation is essential for the activation of p53 to transcriptionally govern target genes, which control cellular responses. Here, we present a small molecule, NiCur, which blocks CBP HAT activity and downregulates p53 activation upon genotoxic stress. Computational modeling reveals that NiCur docks into the active site of CBP HAT. On CDKN1A promoter, the recruitment of p53 as well as RNA Polymerase II and levels of acetylation on histone H3 were diminished by NiCur. Specifically, NiCur reduces the levels of acetylation at lysine 27 on histone H3, which concomitantly increases the levels of trimethylation at lysine 27. Finally, NiCur attenuates p53-directed apoptosis by inhibiting the Caspase 3 activity and cleavage of Poly (ADP-ribose) polymerase (PARP) in normal gastrointestinal epithelial cells. Collectively, NiCur demonstrates the potential to reprogram the chromatin landscape and modulate biological outcomes of CBP-mediated acetylation under normal and disease conditions.

Discovering a Reliable Heat-Shock Factor-1 Inhibitor to Treat Human Cancers: Potential Opportunity for Phytochemists

Heat-shock factor-1 (HSF-1) is an important transcription factor that regulates pathogenesis of many human diseases through its extensive transcriptional regulation. Especially, it shows pleiotropic effects in human cancer, and hence it has recently received increased attention of cancer researchers. After myriad investigations on HSF-1, the field has advanced to the phase where there is consensus that finding a potent and selective pharmacological inhibitor for this transcription factor will be a major break-through in the treatment of various human cancers. Presently, all reported inhibitors have their limitations, made evident at different stages of clinical trials. This brief account summarizes the advances with tested natural products as HSF-1 inhibitors and highlights the necessity of phytochemistry in this endeavor of discovering a potent pharmacological HSF-1 inhibitor.

The putative oncotarget CSN5 controls a transcription-uncorrelated p53-mediated autophagy implicated in cancer cell survival under curcumin treatment

Curcumin has shown promise as a safe and specific anticancer agent. The COP9 signalosome (CSN) component CSN5, a known specific target for curcumin, can control p53 stability by increasing its degradation through ubiquitin system. But the correlation of CSN5-controlled p53 to anticancer therapeutic effect of curcumin is currently unknown. Here we showed that CSN5-controlled p53 was transcriptional inactive and responsible for autophagy in human normal BJ cells and cancer HepG2 cells under curcumin treatment. Of note, CSN5-initiated cellular autophagy by curcumin treatment was abolished in p53-null HCT116p^53−/− cancer cells, which could be rescued by reconstitution with wild-type p53 or transcription inactive p53 mutant p53^R273H. Furthermore, CSN5-controlled p53 conferred a pro-survival autophagy in diverse cancer cells response to curcumin. Genetic p53 deletion, as well as autophagy pharmacological inhibition by chloroquine, significantly enhanced the therapeutic effect of curcumin on cancer cells in vitro and in vivo, but not normal cells. This study identifies a novel CSN5-controlled p53 in autophagy of human cells. The p53 expression state is a useful biomarker for predicting the anticancer therapeutic effect of curcumin. Therefore, the pharmacologic autophagy manipulation may benefit the ongoing anticancer clinical trials of curcumin.

Neuroprotective effects of pifithrin-α against traumatic brain injury in the striatum through suppression of neuroinflammation, oxidative stress, autophagy, and apoptosis

Cortical and hippocampal neuronal damages caused by traumatic brain injury (TBI) are associated with motor and cognitive impairments; however, only little attention paid to the striatal damage. It is known that the p53 tumor-suppressor transcription factor participated in TBI-induced secondary brain damage. We investigated how the p53 inactivator pifithrin (PFT)-α affected TBI-induced striatal neuronal damage at 24 h post-injury. Sprague-Dawley rats subjected to a controlled cortical impact were used as TBI models. We observed that p53 mRNA significantly increased, whereas p53 protein expression was distributed predominantly in neurons but not in glia cells in striatum after TBI. PFT-α improved motor deficit following TBI. PFT-α suppressed TBI-induced striatal glial activation and expression of proinflammatory cytokines. PFT-α alleviated TBI-induced oxidative damage TBI induced autophagy was evidenced by increased protein expression of Beclin-1 and shift of microtubule-associated light chain (LC)3-I to LC3-II, and decreased p62. These effects were reduced by PFT-α. Post-injury PFT-α treatment reduced the number of degenerating (FJC-positive) and apoptotic neurons. Our results suggest that PFT-α may provide neuroprotective effects via p53-dependent or -independent mechanisms depending on the cell type and timing after the TBI and can possibly be developed into a novel therapy to ameliorate TBI-induced neuronal damage.

PEPD is a pivotal regulator of p53 tumor suppressor

p53 tumor suppressor responds to various cellular stresses and regulates cell fate. Here, we show that peptidase D (PEPD) binds and suppresses over half of nuclear and cytoplasmic p53 under normal conditions, independent of its enzymatic activity. Eliminating PEPD causes cell death and tumor regression due to p53 activation. PEPD binds to the proline-rich domain in p53, which inhibits phosphorylation of nuclear p53 and MDM2-mediated mitochondrial translocation of nuclear and cytoplasmic p53. However, the PEPD-p53 complex is critical for p53 response to stress, as stress signals doxorubicin and H₂O₂ each must free p53 from PEPD in order to achieve robust p53 activation, which is mediated by reactive oxygen species. Thus, PEPD stores p53 for the stress response, but this also renders cells dependent on PEPD for survival, as it suppresses p53. This finding provides further understanding of p53 regulation and may have significant implications for the treatment of cancer and other diseases.

p53 is a pivotal tumour suppressor that is activated by various cellular stress inducers. Here, the authors show that peptidase D (PEPD) promotes the growth of cancer cells by suppressing p53 and that the complex PEPD-p53 is critical for robust p53 activation in response to stress signals.

MgAl layered double hydroxide/chitosan porous scaffolds loaded with PFTα to promote bone regeneration

Poor bone formation remains a key risk factor associated with acellular scaffolds that occurs in some bone defects, particularly in patients with metabolic bone disorders and local osteoporosis. We herein fabricated for the first time layered double hydroxide-chitosan porous scaffolds loaded with PFTα (LDH-CS-PFTα scaffolds) as therapeutic bone scaffolds for the controlled release of PFTα to enhance stem cell osteogenic differentiation and bone regeneration. The LDH-CS scaffolds had three-dimensional interconnected macropores, and plate-like LDH nanoparticles were uniformly dispersed within or on the CS films. The LDH-CS scaffolds exhibited appropriate PFTα drug delivery due to hydrogen bonding among LDH, CS and PFTα. In vitro functional studies demonstrated that the PFTα molecules exhibited potent ability to induce osteogenesis of hBMSCs via the GSK3β/β-catenin pathway, and the LDH-CS-PFTα scaffolds significantly enhanced the osteogenic differentiation of hBMSCs. In vivo studies revealed significantly increased repair and regeneration of bone tissue in cranial defect model rats compared to control rats at 12 weeks post-implantation. In conclusion, the LDH-CS-PFTα scaffolds exhibited excellent osteogenic differentiation and bone regeneration capability and hold great potential for applications in defined local bone regeneration.

Self-assembly of pifithrin-α-loaded layered double hydroxide/chitosan nanohybrid composites as a drug delivery system for bone repair materials

The self-assembly of pifithrin-α-loaded layered double hydroxide/chitosan nanohybrid composites as a drug delivery system was demonstrated for the first time to improve the cytocompatibility and enhance the osteoinductivity for the treatment of bone defects.

RCAD/Ufl1, a Ufm1 E3 ligase, is essential for hematopoietic stem cell function and murine hematopoiesis

The Ufm1 conjugation system is a novel ubiquitin-like modification system, consisting of Ufm1, Uba5 (E1), Ufc1 (E2) and poorly characterized E3 ligase(s). RCAD/Ufl1 (also known as KIAA0776, NLBP and Maxer) was reported to function as a Ufm1 E3 ligase in ufmylation (Ufm1-mediated conjugation) of DDRGK1 and ASC1 proteins. It has also been implicated in estrogen receptor signaling, unfolded protein response (UPR) and neurodegeneration, yet its physiological function remains completely unknown. In this study, we report that RCAD/Ufl1 is essential for embryonic development, hematopoietic stem cell (HSC) survival and erythroid differentiation. Both germ-line and somatic deletion of RCAD/Ufl1 impaired hematopoietic development, resulting in severe anemia, cytopenia and ultimately animal death. Depletion of RCAD/Ufl1 caused elevated endoplasmic reticulum stress and evoked UPR in bone marrow cells. In addition, loss of RCAD/Ufl1 blocked autophagic degradation, increased mitochondrial mass and reactive oxygen species, and led to DNA damage response, p53 activation and enhanced cell death of HSCs. Collectively, our study provides the first genetic evidence for the indispensable role of RCAD/Ufl1 in murine hematopoiesis and development. The finding of RCAD/Ufl1 as a key regulator of cellular stress response sheds a light into the role of a novel protein network including RCAD/Ufl1 and its associated proteins in regulating cellular homeostasis.

Pifithrin-α provides neuroprotective effects at the level of mitochondria independently of p53 inhibition

Impaired mitochondrial integrity and function are key features of intrinsic death pathways in neuronal cells. Therefore, key regulators of intrinsic death pathways acting upstream of mitochondria are potential targets for therapeutic approaches of neuroprotection. The tumor suppressor p53 is a well-established regulator of cellular responses towards different kinds of lethal stress, including oxidative stress. Recent reports suggested that p53 may affect mitochondrial integrity and function through both, transcriptional activation of mitochondria-targeted pro-death proteins and direct effects at the mitochondrial membrane. In the present study, we compared the effects of pharmacological inhibition of p53 by pifithrin-α with those of selective p53 gene silencing by RNA interference. Using MTT assay and real-time cell impedance measurements we confirmed the protective effect of both strategies against glutamate-induced oxidative stress in immortalized mouse hippocampal HT-22 neurons. Further, we observed full restoration of mitochondrial membrane potential and inhibition of glutamate-induced mitochondrial fragmentation by pifithrin-α which was, in contrast, not achieved by p53 gene silencing. Downregulation of p53 by siRNA decreased p53 transcriptional activity and reduced expression levels of p21 mRNA, while pifithrin-α did not affect these endpoints. These results suggest a neuroprotective effect of pifithrin-α which occurred at the level of mitochondria and independently of p53 inhibition.

A nanobody modulates the p53 transcriptional program without perturbing its functional architecture

The p53 transcription factor plays an important role in genome integrity. To perform this task, p53 regulates the transcription of genes promoting various cellular outcomes including cell cycle arrest, apoptosis or senescence. The precise regulation of this activity remains elusive as numerous mechanisms, e.g. posttranslational modifications of p53 and (non-)covalent p53 binding partners, influence the p53 transcriptional program. We developed a novel, non-invasive tool to manipulate endogenous p53. Nanobodies (Nb), raised against the DNA-binding domain of p53, allow us to distinctively target both wild type and mutant p53 with great specificity. Nb3 preferentially binds ‘structural’ mutant p53, i.e. R175H and R282W, while a second but distinct nanobody, Nb139, binds both mutant and wild type p53. The co-crystal structure of the p53 DNA-binding domain in complex with Nb139 (1.9 Å resolution) reveals that Nb139 binds opposite the DNA-binding surface. Furthermore, we demonstrate that Nb139 does not disturb the functional architecture of the p53 DNA-binding domain using conformation-specific p53 antibody immunoprecipitations, glutaraldehyde crosslinking assays and chromatin immunoprecipitation. Functionally, the binding of Nb139 to p53 allows us to perturb the transactivation of p53 target genes. We propose that reduced recruitment of transcriptional co-activators or modulation of selected post-transcriptional modifications account for these observations.

Phenethyl isothiocyanate induces DNA damage-associated G2/M arrest and subsequent apoptosis in oral cancer cells with varying p53 mutations

Phenethyl isothiocyanate (PEITC) is a naturally occurring cruciferous vegetable-derived compound that inhibits cell growth and induces apoptosis in oral cancer cells. However, the exact mechanism of PEITC action has not been fully elucidated. This study investigated the molecular mechanism and anticancer potential of PEITC in oral squamous cell carcinoma (OSCC) cells with various p53 statuses. PEITC inhibited the growth of OC2, SCC4, and SCC25 cells (functional p53 mutants) in a dose-dependent manner with low toxicity to normal cells. Treatment with PEITC induced reactive oxygen species production, nitric oxide generation, and GSH depletion and triggered DNA damage response as evidenced by flow cytometry, 8-OHdG formation, and comet assay. Furthermore, the subsequent activation of ATM, Chk2, and p53 as well as the increased expression of downstream proteins p21 and Bax resulted in a G2/M phase arrest by inhibiting Cdc25C, Cdc2, and cyclin B1. The PEITC-induced apoptotic cell death, following a diminished mitochondrial transmembrane potential, reduced the expression of Bcl-2 and Mcl-1, released mitochondrial cytochrome c, and activated caspase 3 and PARP cleavage. The p53 inhibitor pifithrin-α and the antioxidants N-acetylcysteine and glutathione (GSH) protected the cells from PEITC-mediated apoptosis. However, mito-TEMPO, catalase, apocynin, and L-NAME did not prevent PEITC-induced cell death, suggesting that PEITC induced G2/M phase arrest and apoptosis in oral cancer cells via a GSH redox stress and oxidative DNA damage-induced ATM-Chk2-p53-related pathway. These results provide new insights into the critical roles of both GSH redox stress and p53 in the regulation of PEITC-induced G2/M cell cycle arrest and apoptosis in OSCCs.

Mechanisms linked to differences in the mutagenic potential of 1,3-dinitropyrene and 1,8-dinitropyrene

This study explores and characterizes the toxicity of two closely related carcinogenic dinitro-pyrenes (DNPs), 1,3-DNP and 1,8-DNP, in human bronchial epithelial BEAS-2B cells and mouse hepatoma Hepa1c1c7 cells. Neither 1,3-DNP nor 1,8-DNP (3–30 μM) induced cell death in BEAS-2B cells. In Hepa1c1c7 cells only 1,3-DNP (10–30 μM) induced a mixture of apoptotic and necrotic cell death after 24 h. Both compounds increased the level of reactive oxygen species (ROS) in BEAS-2B as measured by CM-H₂DCFDA-fluorescence. A corresponding increase in oxidative damage to DNA was revealed by the formamidopyrimidine-DNA glycosylase (fpg)-modified comet assay. Without fpg, DNP-induced DNA damage detected by the comet assay was only found in Hepa1c1c7 cells. Only 1,8-DNP formed DNA adduct measured by ³²P-postlabelling. In Hepa1c1c cells, 1,8-DNP induced phosphorylation of H2AX (γH2AX) and p53 at a lower concentration than 1,3-DNP and there was no direct correlation between DNA damage/DNA damage response (DR) and induced cytotoxicity. On the other hand, 1,3-DNP-induced apoptosis was inhibited by pifithrin-α, an inhibitor of p53 transcriptional activity. Furthermore, 1,3-DNP triggered an unfolded protein response (UPR), as measured by an increased expression of CHOP, ATF4 and XBP1. Thus, other types of damage possibly linked to endoplasmic reticulum (ER)-stress and/or UPR could be involved in the induced apoptosis. Our results suggest that the stronger carcinogenic potency of 1,8-DNP compared to 1,3-DNP is linked to its higher genotoxic effects. This in combination with its lower potency to induce cell death may increase the probability of causing mutations.

Attachment-regulated signaling networks in the fibroblast-populated 3D collagen matrix

Fibroblasts in the attached collagen matrix are in a pro-survival, pro-proliferative state relative to fibroblasts in the released collagen matrix, such that matrix cell number increases in the former over time. Gene array data from attached vs. released matrices were analyzed for putative networks that regulated matrix cell number. Select networks then underwent augmentation and/or inhibition in order to determine their biologic relevance. Matrix stress-release was associated with modulation of signaling networks that involved IL6, IL8, NF-κB, TGF-β1, p53, interferon-γ, and other entities as central participants. Perturbation of select networks in multiple fibroblast strains suggested that IL6 and IL8 secretion may have been involved in preservation of matrix cell population in the released matrix, though there was variability in testing results among the strains. NF-κB activation may have contributed to the induction of population regression after matrix release.

p53 and mitochondrial function in neurons

The p53 tumor suppressor plays a central role in dictating cell survival and death as a cellular sensor for a myriad of stresses including DNA damage, oxidative and nutritional stress, ischemia and disruption of nucleolar function. Activation of p53-dependent apoptosis leads to mitochondrial apoptotic changes via the intrinsic and extrinsic pathways triggering cell death execution most notably by release of cytochrome c and activation of the caspase cascade. Although it was previously believed that p53 induces apoptotic mitochondrial changes exclusively through transcription-dependent mechanisms, recent studies suggest that p53 also regulates apoptosis via a transcription-independent action at the mitochondria. Recent evidence further suggests that p53 can regulate necrotic cell death and autophagic activity including mitophagy. An increasing number of cytosolic and mitochondrial proteins involved in mitochondrial metabolism and respiration are regulated by p53, which influences mitochondrial ROS production as well. Cellular redox homeostasis is also directly regulated by p53 through modified expression of pro- and anti-oxidant proteins. Proper regulation of mitochondrial size and shape through fission and fusion assures optimal mitochondrial bioenergetic function while enabling adequate mitochondrial transport to accommodate local energy demands unique to neuronal architecture. Abnormal regulation of mitochondrial dynamics has been increasingly implicated in neurodegeneration, where elevated levels of p53 may have a direct contribution as the expression of some fission/fusion proteins are directly regulated by p53. Thus, p53 may have a much wider influence on mitochondrial integrity and function than one would expect from its well-established ability to transcriptionally induce mitochondrial apoptosis. However, much of the evidence demonstrating that p53 can influence mitochondria through nuclear, cytosolic or intra-mitochondrial sites of action has yet to be confirmed in neurons. Nonetheless, as mitochondria are essential for supporting normal neuronal functions and in initiating/propagating cell death signaling, it appears certain that the mitochondria-related functions of p53 will have broader implications than previously thought in acute and progressive neurological conditions, providing new therapeutic targets for treatment.

Cell cycle regulation and regeneration

Regeneration of ear punch holes in the MRL mouse and amputated limbs of the axolotl show a number of similarities. A large proportion of the fibroblasts of the uninjured MRL mouse ear are arrested in G2 of the cell cycle, and enter nerve-dependent mitosis after injury to form a ring-shaped blastema that regenerates the ear tissue. Multiple cell types contribute to the establishment of the regeneration blastema of the urodele limb by dedifferentiation, and there is substantial reason to believe that the cells of this early blastema are also arrested in G2, and enter mitosis under the influence of nerve-dependent factors supplied by the apical epidermal cap. Molecular analysis reveals other parallels, such as; (1) the upregulation of Evi5, a centrosomal protein that prevents mitosis by stabilizing Emi1, a protein that inhibits the degradation of cyclins by the anaphase promoting complex and (2) the expression of sodium channels by the epidermis. A central feature in the entry into the cell cycle by MRL ear fibroblasts is a natural downregulation of p21, and knockout of p21 in wild-type mice confers regenerative capacity on non-regenerating ear tissue. Whether the same is true for entry into the cell cycle in regenerating urodele limbs is presently unknown.

p53 orchestrates the PGC-1α-mediated antioxidant response upon mild redox and metabolic imbalance

AIMS

The transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator-1 α (PPARGC1A or PGC-1α) is a powerful controller of cell metabolism and assures the balance between the production and the scavenging of pro-oxidant molecules by coordinating mitochondrial biogenesis and the expression of antioxidants. However, even though a huge amount of data referring to the role of PGC-1α is available, the molecular mechanisms of its regulation at the transcriptional level are not completely understood. In the present report, we aim at characterizing whether the decrease of antioxidant glutathione (GSH) modulates PGC-1α expression and its downstream metabolic pathways.

RESULTS

We found that upon GSH shortage, induced either by its chemical depletion or by metabolic stress (i.e., fasting), p53 binds to the PPARGC1A promoter of both human and mouse genes, and this event is positively related to increased PGC-1α expression. This effect was abrogated by inhibiting nitric oxide (NO) synthase or guanylate cyclase, implicating NO/cGMP signaling in such a process. We show that p53-mediated PGC-1α upregulation is directed to potentiate the antioxidant defense through nuclear factor (erythroid-derived 2)-like2 (NFE2L2)-mediated expression of manganese superoxide dismutase (SOD2) and γ-glutamylcysteine ligase without modulating mitochondrial biogenesis.

INNOVATION AND CONCLUSIONS

We outlined a new NO-dependent signaling axis responsible for survival antioxidant response upon mild metabolic stress (fasting) and/or oxidative imbalance (GSH depletion). Such signaling axis could become the cornerstone for new pharmacological or dietary approaches for improving antioxidant response during ageing and human pathologies associated with oxidative stress.

Pro-apoptotic Effect of Pifithrin-α on Preimplantation Porcine In vitro Fertilized Embryo Development

The aim of this study was to investigate the impact of a reported p53 inhibitor, pifithrin-α (PFT-α), on preimplantation porcine in vitro fertilized (IVF) embryo development in culture. Treatment of PFT-α was administered at both early (0 to 48 hpi), and later stages (48 to 168 hpi) of preimplantation development, and its impact upon the expression of five genes related to apoptosis (p53, bak, bcl-xL, p66Shc and caspase3), was assessed in resulting d 7 blastocysts, using real-time quantitative PCR. Total cell numbers, along with the number of apoptotic nuclei, as detected by the in situ cell death detection assay, were also calculated on d 7 in treated and non-treated control embryos. The results indicate that PFT-α, when administered at both early and later stages of porcine IVF embryo development, increases the incidence of apoptosis in resulting blastocysts. When administered at early cleavage stages, PFT-α treatment was shown to reduce the developmental competence of porcine IVF embryos, as well as reducing the quality of resulting blastocysts in terms of overall cell numbers. In contrast, at later stages, PFT-α administration resulted in marginally increased blastocyst development rates amongst treated embryos, but did not affect cell numbers. However, PFT-α treatment induced apoptosis and apoptotic related gene expression, in all treated embryos, irrespective of the timing of treatment. Our results indicate that PFT-α may severely compromise the developmental potential of porcine IVF embryos, and is a potent apoptotic agent when placed into porcine embryo culture media. Thus, caution should be exercised when using PFT-α as a specific inhibitor of p53 mediated apoptosis, in the context of porcine IVF embryo culture systems.

Forkhead box M1 is regulated by heat shock factor 1 and promotes glioma cells survival under heat shock stress

The forkhead box M1 (FoxM1) is a key transcription factor regulating multiple aspects of cell biology. Prior studies have shown that FoxM1 is overexpressed in a variety of human tumors, including brain tumor, and plays a critical role in cancer development and progression. In this study we found that FoxM1 was up-regulated by heat shock factor 1 (HSF1) under heat shock stress condition in multiple cell lines. Knockdown of HSF1 with HSF1 siRNA or inhibition of HSF1 with a HSF1 inhibitor abrogated heat shock-induced expression of FoxM1. Genetic deletion of HSF1 in mouse embryo fibroblast cells also abolished heat shock stress-induced FoxM1 expression. Moreover, we showed that HSF1 directly bound to FoxM1 promoter and increased FoxM1 promoter activity. Furthermore, we demonstrated that FoxM1 was required for the G(2)-M phase progression through regulating Cdc2, Cdc20, and Cdc25B under a mild heat shock stress but enhanced cell survival under lethal heat shock stress condition. Finally, in human glioblastoma specimens, FoxM1 overexpression correlated with elevated HSF1 expression. Our results indicate that FoxM1 is regulated by HSF1 and is critical for HSF1-mediated heat shock response. We demonstrated a novel mechanism of stress resistance controlled by HSF1 and a new HSF-FoxM1 connection that mediates cellular thermotolerance.

Inhibitors of apoptosis in testicular germ cells: synthesis and biological evaluation of some novel IBTs bearing sulfonamide moiety

Pifithrin-α, a known p53 inactivator, inhibits p53-dependant mitochondrial cell death induced by toxins or γ-radiation. It has been found that aromatic IBT analogues of PFT-α are more cytoprotective and nonpeptide-based, isatin sulfonamides selectively inhibit caspases 3 and 7, responsible for mitochondrial mediated apoptosis. Therefore, we envisioned the synthesis of novel IBTs 4 and 5 bearing sulfonamide moiety and observed the mitigating effects of these IBTs in rescue of malathion induced apoptosis in testicular germ cells of goat. Two IBTs (4b; R = CH(3), 5b; R(1) = Cl) showed very high survival rate of cells whereas IBT 4f (R = NO(2)) showed some exceptional behaviour by increasing the apoptosis. These IBTs nullify the cytotoxic effect of malathion on mitochondria, following p53-independent pathway.

Pifithrin-μ increases mitochondrial COX biogenesis and MnSOD activity in skeletal muscle of middle-aged mice

We investigated the biogenesis and mitochondrial antioxidant capacity of cytochrome c oxidase (COX) within the skeletal muscle under the treatments of p53 inhibitors (pifithrin, PFTα and PFTμ). Significantly, PFTμ increased mtDNA content and COX biogenesis. These changes coincided with increases in the activity and expression of manganese superoxide dismutase (MnSOD), the key antioxidant enzyme in mitochondria. Conversely, PFTα caused muscle loss, increased oxidative damage and decreased MnSOD activity in intermyofibrillar (IMF) mitochondria. Mechanically, PFTμ inhibited p53 translocation to mitochondria and thus increased its transcriptional activity for expression of synthesis of cytochrome c oxidase 2 (SCO2), an important assembly protein for COX. This study provides in vivo evidence that PFTμ, superior to PFTα, preserves muscle mass and increases mitochondrial antioxidant activity.

Heat shock factor-1 knockout induces multidrug resistance gene, MDR1b, and enhances P-glycoprotein (ABCB1)-based drug extrusion in the heart

Heat-shock factor 1 (HSF-1), a transcription factor for heat-shock proteins (HSPs), is known to interfere with the transcriptional activity of many oncogenic factors. In the present work, we have discovered that HSF-1 ablation induced the multidrug resistance gene, MDR1b, in the heart and increased the expression of P-glycoprotein (P-gp, ABCB1), an ATP binding cassette that is usually associated with multidrug-resistant cancer cells. The increase in P-gp enhanced the extrusion of doxorubicin (Dox) to alleviate Dox-induced heart failure and reduce mortality in mice. Dox-induced left ventricular (LV) dysfunction was significantly reduced in HSF-1(-/-) mice. DNA-binding activity of NF-κB was higher in HSF-1(-/-) mice. IκB, the NF-κB inhibitor, was depleted due to enhanced IκB kinase (IKK)-α activity. In parallel, MDR1b gene expression and a large increase in P-gp and lowering Dox loading were observed in HSF-1(-/-) mouse hearts. Moreover, application of the P-gp antagonist, verapamil, increased Dox loading in HSF-1(-/-) cardiomyocytes, deteriorated cardiac function in HSF-1(-/-) mice, and decreased survival. MDR1 promoter activity was higher in HSF-1(-/-) cardiomyocytes, whereas a mutant MDR1 promoter with heat-shock element (HSE) mutation showed increased activity only in HSF-1(+/+) cardiomyocytes. However, deletion of HSE and NF-κB binding sites diminished luminescence in both HSF-1(+/+) and HSF-1(-/-) cardiomyocytes, suggesting that HSF-1 inhibits MDR1 activity in the heart. Thus, because high levels of HSF-1 are attributed to poor prognosis of cancer, systemic down-regulation of HSF-1 before chemotherapy is a potential therapeutic approach to ameliorate the chemotherapy-induced cardiotoxicity and enhance cancer prognosis.

p53 mediates autophagy activation and mitochondria dysfunction in kainic acid-induced excitotoxicity in primary striatal neurons

The present study sought to investigate if p53 mediates autophagy activation and mitochondria dysfunction in primary striatal neurons in kainic acid (KA)-induced excitotoxicity. The excitotoxic model of primary striatal neurons was established with KA. The levels of p53, microtubule-associated protein 1 light chain 3 (LC3), Beclin1, and p62 were examined by Western blot and immunostaining. Autophagy activation was also determined with electron microscope. To evaluate the contribution of p53 to autophagy activation and mitochondria dysfunction in KA-induced excitotoxicity, the protein levels of LC3, Beclin1, and p62, the mitochondrial transmembrane potential and the mitochondrial Reactive oxygen species (ROS) after pretreatment with the p53 inhibitor pifithrin-alpha (PFT-α) and the autophagy inhibitor 3-methyladenine (3-MA) were analyzed. Excitotoxic neuronal injury was induced after KA treatment as demonstrated by increases in lactate dehydrogenase (LDH) leakage and was significantly inhibited by PFT-α. Western blot and immunostaining showed that the induction of p53 protein occurred in the cytosol and the nucleus. Increases in autophagic proteins LC3 and Beclin1 were observed, whereas the protein levels of p62 decreased after KA treatment. Electron microscope analysis showed increased autophagosomes in the cytoplasm. The changes in LC3, Beclin1, and p62 levels were blocked by PFT-α, PFT-μ, 3-MA, and E64d but not Z-DEVD-FMK. JC-1 staining showed the depolarization of mitochondrial membrane potential after excitotoxic insult. Mito-tracker and RedoxSensor Red CC-1 staining showed an increased production of mitochondrial ROS after excitotoxic insult. These effects were significantly suppressed after pretreatment with PFT-α and 3-MA. This study suggests that p53 mediates KA-induced autophagy activation and mitochondrial dysfunction in striatal neurons.

The p53 inhibitor pifithrin-α can stimulate fibrosis in a rat model of ischemic acute kidney injury

Inhibition of the tumor suppressor p53 diminishes tubular cell apoptosis and protects renal function in animal models of acute kidney injury (AKI). Therefore, targeting p53 has become an attractive therapeutic strategy in the approach to AKI. Although the acute protective effects of p53 inhibition in AKI have been examined, there is still relatively little known regarding the impact of acute p53 inhibition on the chronic sequelae of AKI. Consequently, we utilized the p53 inhibitor pifithrin-α to examine the long-term effects of p53 inhibition in a rodent model of ischemic AKI. Male Sprague-Dawley rats were subjected to bilateral renal artery clamping for 30 min followed by reperfusion for up to 8 wk. Pifithrin-α or vehicle control was administered at the time of surgery and then daily for 2 days [brief acute administration (BA)] or 7 days [prolonged acute administration (PA)]. Despite the acute protective effect of pifithrin-α in models of ischemic AKI, we found no protection in the microvascular rarefaction at 4 wk or development fibrosis at 8 wk with pifithrin-α administered on the BA schedule compared with vehicle control-treated animals. Furthermore, pifithrin-α administered on a PA schedule actually produced worse fibrosis compared with vehicle control animals after ischemic injury [21%/area (SD4.4) vs.16%/area (SD3.6)] as well as under sham conditions [2.6%/area (SD1.8) vs. 4.7%/area (SD1.3)]. The development of fibrosis with PA administration was independent of microvascular rarefaction. We identified enhanced extracellular matrix production, epithelial-to-mesenchymal transition, and amplified inflammatory responses as potential contributors to the augmented fibrosis observed with PA administration of pifithrin-α.

Radiation-induced intercellular signaling mediated by cytochrome-c via a p53-dependent pathway in hepatoma cells

The tumor suppressor p53 has a crucial role in cellular response to DNA damage caused by ionizing radiation, but it is still unclear whether p53 can modulate radiation-induced bystander effects (RIBE). In the present work, three different hepatoma cell lines, namely HepG2 (wild p53), PLC/PRF/5 (mutation p53) and Hep3B (p53 null), were irradiated with γ-rays and then co-cultured with normal Chang liver cell (wild p53) in order to elucidate the mechanisms of RIBE. Results showed that the radiosensitivity of HepG2 cells was higher than that of PLC/PRF/5 and Hep3B cells. Only irradiated HepG2 cells, rather than irradiated PLC/PRF/5 or Hep3B cells, could induce bystander effect of micronuclei (MN) formation in the neighboring Chang liver cells. When HepG2 cells were treated with 20 μM pifithrin-α, an inhibitor of p53 function, or 5 μM cyclosporin A (CsA), an inhibitor of cytochrome-c release from mitochondria, the MN induction in bystander Chang liver cells was diminished. In fact, it was found that after irradiation, cytochrome-c was released from mitochondria into the cytoplasm only in HepG2 cells in a p53-dependent manner, but not in PLC/PRF/5 and Hep3B cells. Interestingly, when 50 μg/ml exogenous cytochrome-c was added into cell co-culture medium, RIBE was significantly triggered by irradiated PLC/PRF/5 and Hep3B cells, which previously failed to provoke a bystander effect. In addition, this exogenous cytochrome-c also partly recovered the RIBE induced by irradiated HepG2 cells even with CsA treatment. Our results provide new evidence that the RIBE can be modulated by the p53 status of irradiated hepatoma cells and that a p53-dependent release of cytochrome-c may be involved in the RIBE.

Haploinsufficiency for ribosomal protein genes causes selective activation of p53 in human erythroid progenitor cells

Haploinsufficiency for ribosomal protein genes has been implicated in the pathophysiology of Diamond-Blackfan anemia (DBA) and the 5q-syndrome, a subtype of myelodysplastic syndrome. The p53 pathway is activated by ribosome dysfunction, but the molecular basis for selective impairment of the erythroid lineage in disorders of ribosome function has not been determined. We found that p53 accumulates selectively in the erythroid lineage in primary human hematopoietic progenitor cells after expression of shRNAs targeting RPS14, the ribosomal protein gene deleted in the 5q-syndrome, or RPS19, the most commonly mutated gene in DBA. Induction of p53 led to lineage-specific accumulation of p21 and consequent cell cycle arrest in erythroid progenitor cells. Pharmacologic inhibition of p53 rescued the erythroid defect, whereas nutlin-3, a compound that activates p53 through inhibition of HDM2, selectively impaired erythropoiesis. In bone marrow biopsies from patients with DBA or del(5q) myelodysplastic syndrome, we found an accumulation of nuclear p53 staining in erythroid progenitor cells that was not present in control samples. Our findings indicate that the erythroid lineage has a low threshold for the induction of p53, providing a basis for the failure of erythropoiesis in the 5q-syndrome, DBA, and perhaps other bone marrow failure syndromes.

Hypoxia downregulates p53 but induces apoptosis and enhances expression of BAD in cultures of human syncytiotrophoblasts

Hypoxia is commonly assigned a role in the placental dysfunction characteristic of preeclampsia and intrauterine growth restriction. We previously showed that hypoxia upregulates p53 and enhances apoptosis in primary cultures of human cytotrophoblasts. Here we tested the hypothesis that hypoxia also induces apoptosis in syncytiotrophoblasts by upregulation of p53. Primary cultures of human cytotrophoblasts that had differentiated into syncytiotrophoblasts by 52 h were exposed for ≤24 h to 20% or <1% oxygen in the presence or absence of staurosporine or the p53 modulators nutlin-3, pifithrin-α, and pifithrin-μ. Proteins were detected by Western blot analysis or immunofluorescence. Compared with 20% oxygen, exposure of syncytiotrophoblasts to <1% oxygen upregulated hypoxia-inducible factor (HIF)-1α and rapidly downregulated p53. Activity of p53 in hypoxic syncytiotrophoblasts was reduced by the higher expression of the negative p53 regulator MDMX and by the reduction of phosphorylation of p53 at Ser(392), which reduces p53 activity. Conversely, staurosporine, a kinase inhibitor, and nutlin-3, a drug that enhances p53 expression, both raised p53 levels and increased the rate of apoptosis in syncytiotrophoblasts compared with vehicle controls. Immunofluorescence staining showed p53 immunolocalized to both cytoplasm and nuclei of nutlin-3-exposed syncytiotrophoblasts. The hypoxia-induced apoptosis in syncytiotrophoblasts correlated with enhanced expression of the proapoptotic BAD and a reduced level of antiapoptotic BAD phosphorylated on Ser(112). We surmise that cell death induced by extreme hypoxia in syncytiotrophoblasts follows a non-p53-dependent pathway, unlike that of a nonhypoxic stimulus and unlike hypoxic cytotrophoblasts. We speculate that downregulation of p53 activity in response to hypoxia reduces or eliminates the apoptosis transduced by the p53 pathway in syncytiotrophoblasts, thereby limiting cell death and maintaining the integrity of this critical villous component.

p53 mediates cigarette smoke-induced apoptosis of pulmonary endothelial cells: inhibitory effects of macrophage migration inhibitor factor

Exposure to cigarette smoke (CS) is the most common cause of emphysema, a debilitating pulmonary disease histopathologically characterized by the irreversible destruction of lung architecture. Mounting evidence links enhanced endothelial apoptosis causally to the development of emphysema. However, the molecular determinants of human endothelial cell apoptosis and survival in response to CS are not fully defined. Such determinants could represent clinically relevant targets for intervention. We show here that CS extract (CSE) triggers the death of human pulmonary macrovascular endothelial cells (HPAECs) through a caspase 9-dependent apoptotic pathway. Exposure to CSE results in the increased expression of p53 in HPAECs. Using the p53 inhibitor, pifithrin-α (PFT-α), and RNA interference (RNAi) directed at p53, we demonstrate that p53 function and expression are required for CSE-mediated apoptosis. The expression of macrophage migration inhibitory factor (MIF), an antiapoptotic cytokine produced by HPAECs, also increases in response to CSE exposure. The addition of recombinant human MIF prevents cell death from exposure to CSE. Further, the suppression of MIF or its receptor/binding partner, Jun activation domain-binding protein 1 (Jab-1), with RNAi enhances the sensitivity of human pulmonary endothelial cells to CSE via a p53-dependent (PFT-α-inhibitable) pathway. Finally, we demonstrate that MIF is a negative regulator of p53 expression in response to CSE, placing MIF upstream of p53 as an antagonist of CSE-induced apoptosis. We conclude that MIF can protect human vascular endothelium from the toxic effects of CSE via the antagonism of p53-mediated apoptosis.

Hyperthermia-associated carboplatin resistance: differential role of p53, HSF1 and Hsp70 in hepatoma cells

Due to substantial technical improvements, clinical application of heat as a co-adjuvant in cancer treatment is acquiring new interest. The effect of hyperthermia on hepatoma cell lines Hep3B (p53 defective) and HepG2 (p53 wild type) when investigated led to an interesting observation that Hep3B cells are more susceptible to heat stress than HepG2 cells. In addition, heat-induced carboplatin resistance was observed in HepG2 cells only. To investigate the reasons, heat shock response was explored and it was observed that heat stress augmented heat shock protein 70 (Hsp70) expression levels in HepG2 and not in Hep3B cells. Furthermore, in HepG2 cells, induced Hsp70 is regulated by both p53 and heat shock transcription factor 1 (HSF1) wherein HSF1 levels are modulated by p53. The data implies that Hep3B are more susceptible to death upon heat stress than HepG2 cells because of non-induction of Hsp70. In addition, it was observed that inhibition of heat-induced p53/HSF1 diminishes Hsp70 levels, thereby restoring the sensitivity of heat-stressed HepG2 cells to carboplatin-triggered cell death. Collectively, the present study establishes interplay of p53, HSF1, and Hsp70 upon heat stress in HepG2 cells and also defines novel strategies to overcome constraints of utility of hyperthermia in cancer therapy through p53/HSF1-targeted therapeutic intervention.

Pathologies associated with the p53 response

Although p53 is a major cancer preventive factor, under certain extreme stress conditions it may induce severe pathologies. Analyses of animal models indicate that p53 is largely responsible for the toxicity of ionizing radiation or DNA damaging drugs contributing to hematopoietic component of acute radiation syndrome and largely determining severe adverse effects of cancer treatment. p53-mediated damage is strictly tissue specific and occurs in tissues prone to p53-dependent apoptosis (e.g., hematopoietic system and hair follicles); on the contrary, p53 can serve as a survival factor in tissues that respond to p53 activation by cell cycle arrest (e.g., endothelium of small intestine). There are multiple experimental indications that p53 contributes to pathogenicity of acute ischemic diseases. Temporary reversible suppression of p53 by small molecules can be an effective and safe approach to reduce severity of p53-associated pathologies.

p53 induction contributes to excitotoxic neuronal death in rat striatum through apoptotic and autophagic mechanisms

The present study sought to investigate mechanisms by which p53 induction contributes to excitotoxic neuronal injury. Rats were intrastriatally administered the N-methyl-D-aspartate (NMDA) receptor agonist quinolinic acid (QA), the changes in the expression of p53 and its target genes involved in apoptosis and autophagy, including p53-upregulated modulator of apoptosis (PUMA), Bax, Bcl-2, damage-regulated autophagy modulator (DRAM) and other autophagic proteins including microtubule-associated protein 1 light chain 3 (LC3) and beclin 1 were assessed. The contribution of p53-mediated autophagy activation to apoptotic death of striatal neurons was assessed with co-administration of the nuclear factor-kappaB (NF-kappaB) inhibitor SN50, the p53 inhibitor Pifithrin-alpha (PFT-alpha) or the autophagy inhibitor 3-methyladenine (3-MA). The increased formation of autophagosomes and secondary lysosomes were observed with transmission electron microscope after excitotoxin exposure. QA induced increases in the expression of p53, PUMA, Bax and a decrease in Bcl-2. These changes were significantly attenuated by pre-treatment with SN50, PFT-alpha or 3-MA. SN50, PFT-alpha or 3-MA also reversed QA-induced upregulation of DRAM, the ratio of LC3-II/LC3-I and beclin 1 protein levels in the striatum. QA-induced internucleosomal DNA fragmentation and loss of striatal neurons were robustly inhibited by SN50, PFT-alpha or 3-MA. These results suggest that overstimulation of NMDA receptors can induce NF-kappaB-dependent expression of p53. p53 participates in excitotoxic neuronal death probably through both apoptotic and autophagic mechanisms.

Pifithrin-alpha decreases the radioprotective efficacy of a Podophyllum hexandrum Himalayan mayapple fraction REC-2006 in HepG2 cells

Inhibition of the tumour suppressor p53 by PFT (pifithrin-alpha) promotes p53-mediated apoptosis and protects against doxorubicin-induced apoptosis. The present study was carried out to evaluate the effect of PFT on the radioprotective potential of Podophyllum hexandrum fraction (REC-2006) in HepG2 (p53++) cell line. REC-2006 (10-5 microg/ml) treatment at 2 h before irradiation (10 Gy) rendered 80+/-3% protection in HepG2 cells, whereas PFT debilitated the radioprotective potential of REC-2006. REC-2006 increased the expression of Hsp70 (heat-shock protein 70), HSF1 (heat-shock factor 1) and Bcl-2 in irradiated HepG2 cells, whereas PFT when treated with REC-2006 decreased the expression of Hsp70, HSF1 and Bcl-2 in HepG2 cells. REC-2006 facilitated post-irradiation DNA repair by pausing cell-cycle progression at G1- and G2-phase, whereas no such cell-cycle arrest was observed in irradiated HepG2 cells pretreated with PFT in irradiated HepG2 cells. No change was observed in Mdm2 (murine double minute 2) and Ras-GAP (Ras-GTPase-activating protein) expression with or without PFT treatment. Decrease in the expression of caspase 3 and Bax was observed in HepG2 cells when REC-2006 treatment was given 2 h before irradiation; however, PFT treatment increased the expression of Bax leading to apoptosis. It can be concluded that p53 expression plays a major role in the REC-2006-mediated protection against acute irradiation in HepG2 cells. PFT treatment reduced the radioprotective efficacy of REC-2006 by inhibiting the expression of HSF1 and Hsp70 and thereby the expression of Bcl-2, by up-regulating the cell-cycle-regulatory proteins and therefore reducing the span of time for DNA repair and also by inducing Bax-mediated apoptosis. PFT did not, however, show any effect on p53 regulating protein (Mdm2) and pro-survival protein (Ras-GAP).

Nuclear accumulation and activation of p53 in embryonic stem cells after DNA damage

BACKGROUND

P53 is a key tumor suppressor protein. In response to DNA damage, p53 accumulates to high levels in differentiated cells and activates target genes that initiate cell cycle arrest and apoptosis. Since stem cells provide the proliferative cell pool within organisms, an efficient DNA damage response is crucial.

RESULTS

In proliferating embryonic stem cells, p53 is localized predominantly in the cytoplasm. DNA damage-induced nuclear accumulation of p53 in embryonic stem cells activates transcription of the target genes mdm2, p21, puma and noxa. We observed bi-phasic kinetics for nuclear accumulation of p53 after ionizing radiation. During the first wave of nuclear accumulation, p53 levels were increased and the p53 target genes mdm2, p21 and puma were transcribed. Transcription of noxa correlated with the second wave of nuclear accumulation. Transcriptional activation of p53 target genes resulted in an increased amount of proteins with the exception of p21. While p21 transcripts were efficiently translated in 3T3 cells, we failed to see an increase in p21 protein levels after IR in embryonal stem cells.

CONCLUSION

In embryonic stem cells where (anti-proliferative) p53 activity is not necessary, or even unfavorable, p53 is retained in the cytoplasm and prevented from activating its target genes. However, if its activity is beneficial or required, p53 is allowed to accumulate in the nucleus and activates its target genes, even in embryonic stem cells.