P53 transcriptional activities: a general overview and some thoughts

Selective Sweeps in Cattle Genomes in Response to the Influence of Urbanization and Environmental Contamination

A genomic study was conducted to identify the effects of urbanization and environmental contaminants with heavy metals on selection footprints in dairy cattle populations reared in the megacity of Bengaluru, South India. Dairy cattle reared along the rural-urban interface of Bengaluru with/without access to roughage from public lakeshores were selected. The genotyped animals were subjected to the cross-population-extended haplotype homozygosity (XP-EHH) methodology to infer selection sweeps caused by urbanization (rural, mixed, and urban) and environmental contamination with cadmium and lead. We postulated that social-ecological challenges contribute to mechanisms of natural selection. A number of selection sweeps were identified when comparing the genomes of cattle located in rural, mixed, or urban regions. The largest effects were identified on BTA21, displaying pronounced peaks for selection sweeps for all three urbanization levels (urban_vs_rural, urban_vs_mixed and rural_vs_mixed). Selection sweeps are located in chromosomal segments in close proximity to the genes lrand rab interactor 3 (RIN3), solute carrier family 24 member 4 (SLC24A4), tetraspanin 3 (TSPAN3), and proline-serine-threonine phosphatase interacting protein 1 (PSTPIP1). Functional enrichment analyses of the selection sweeps for all three comparisons revealed a number of gene ontology (GO) and KEGG terms, which were associated with reproduction, metabolism, and cell signaling-related functional mechanisms. Likewise, a number of the chromosomal segments under selection were observed when creating cattle groups according to cadmium and lead contaminations. Stronger and more intense positive selection sweeps were observed for the cadmium contaminated group, i.e., signals of selection on BTA 16 and BTA19 in close proximity to genes regulating the somatotropic axis (growth factor receptor bound protein 2 (GRB2) and cell ion exchange (chloride voltage-gated channel 6 (CLCN6)). A few novel, so far uncharacterized genes, mostly with effects on immune physiology, were identified. The lead contaminated group revealed sweeps which were annotated with genes involved in carcass traits (TNNC2, SLC12A5, and GABRA4), milk yield (HTR1D, SLCO3A1, TEK, and OPCML), reproduction (GABRA4), hypoxia/stress response (OPRD1 and KDR), cell adhesion (PCDHGC3), inflammatory response (ADORA2A), and immune defense mechanism (ALCAM). Thus, the findings from this study provide a deeper insight into the genomic regions under selection under the effects of urbanization and environmental contamination.

SnRK1 Kinase and the NAC Transcription Factor SOG1 Are Components of a Novel Signaling Pathway Mediating the Low Energy Response Triggered by ATP Depletion

Plant growth is strictly controlled by cell division, elongation, and differentiation for which adequate supplies of intracellular ATP are required. However, it is unclear how changes in the amount of intracellular ATP affect cell division and growth. To reveal the specific pathway dependent on ATP concentration, we performed analyses on the Arabidopsis mitochondria mutation sd3. The mutant is tiny, a result of a low amount of ATP caused by the disruption of Tim21, a subunit of the TIM23 protein complex localized in the inner membrane of the mitochondria. Loss of function of suppressor of gamma response 1 (SOG1) also restored the dwarf phenotype of wild type treated with antimycin A, a blocker of ATP synthesis in mitochondria. The sd3 phenotype is partially restored by the introduction of sog1, suppressor of gamma response 1, and kin10/kin11, subunits of Snf1-related kinase 1 (SnRK1). Additionally, SOG1 interacted with SnRK1, and was modified by phosphorylation in planta only after treatment with antimycin A. Transcripts of several negative regulators of the endocycle were up-regulated in the sd3 mutant, and this high expression was not observed in sd3sog1 and sd3kin11. We suggest that there is a novel regulatory mechanism for the control of plant cell cycle involving SnRK1 and SOG1, which is induced by low amounts of intracellular ATP, and controls plant development.

Expression and clinicopathologic significance of TUFM and p53 for the normal-adenoma-carcinoma sequence in colorectal epithelia

BACKGROUND

Evidence indicates that most cases of colorectal carcinoma (CRC) develop from adenoma. A previous study demonstrated that mitochondrial Tu translation elongation factor (TUFM) might serve as an independent prognostic factor for colorectal cancer. However, the expression and function of TUFM in the normal-adenoma-cancer sequence have not been reported. In this study, we investigated the clinicopathologic significance of TUFM and p53 expression for the normal-adenoma-carcinoma sequence in colorectal epithelia and evaluated the roles of TUFM during the progression of colorectal tumors.

METHODS

Paraffin-embedded specimens from 261 colorectal normal mucosa samples, 157 adenomas, and 104 early carcinomas were analyzed for TUFM and p53 expression by immunohistochemistry.

RESULTS

Expression of TUFM and p53 was significantly increased during the colorectal normal-adenoma-carcinoma sequence (all P < 0.05). The expression of TUFM and p53 was associated with histologic type of adenomas (P = 0.028; P = 0.001) and grade of dysplasia (all P = 0.001). Expression of TUFM was positively correlated with that of p53 (r = 0.319, P = 0.001).

CONCLUSIONS

Upregulated TUFM expression may play an important role in the transformation from colorectal normal mucosa to carcinoma through adenoma. Combined immunohistochemical detection of TUFM and p53 may be useful for evaluating the biological behavior of colorectal adenoma.

High-Resolution 4C Reveals Rapid p53-Dependent Chromatin Reorganization of the CDKN1A Locus in Response to Stress

A regulatory program involving hundreds of genes is coordinated by p53 to prevent carcinogenesis in response to stress. Given the importance of chromatin loops in gene regulation, we investigated whether DNA interactions participate in the p53 stress response. To shed light on this issue, we measured the binding dynamics of cohesin in response to stress. We reveal that cohesin is remodeled at specific loci during the stress response and that its binding within genes negatively correlates with transcription. At p53 target genes, stress-induced eviction of cohesin from gene bodies is concomitant to spatial reorganization of loci through the disruption of functional chromatin loops. These findings demonstrate that chromatin loops can be remodeled upon stress and contribute to the p53-driven stress response. Additionally, we also propose a mechanism whereby transcription-coupled eviction of cohesin from CDKN1A might act as a molecular switch to control spatial interactions between regulatory elements.

In Vivo Anti-Cancer Mechanism of Low-Molecular-Weight Fucosylated Chondroitin Sulfate (LFCS) from Sea Cucumber Cucumaria frondosa

The low-molecular-weight fucosylated chondroitin sulfate (LFCS) was prepared from native fucosylated chondroitin sulfate (FCS), which was extracted and isolated from sea cucumber Cucumaria frondosa, and the anti-cancer mechanism of LFCS on mouse Lewis lung carcinoma (LLC) was investigated. The results showed that LFCS remarkably inhibited LLC growth and metastasis in a dose-dependent manner. LFCS induced cell cycle arrest by increasing p53/p21 expression and apoptosis through activation of caspase-3 activity in LLC cells. Meanwhile, LFCS suppressed the expression of vascular endothelial growth factor (VEGF), increased the expression of tissue inhibitor of metalloproteinase-1 (TIMP-1) and downregulated the matrix metalloproteinases (MMPs) level. Furthermore, LFCS significantly suppressed the activation of ERK1/2/p38 MAPK/NF-κB pathway, which played a prime role in expression of MMPs. All of these data indicate LFCS may be used as anti-cancer drug candidates and deserve further study.

Effects of creatine monohydrate supplementation on exercise-induced apoptosis in athletes: A randomized, double-blind, and placebo-controlled study

Background:

Creatine monohydrate (CrM) has been shown to be beneficial to health due to its antioxidant potential. Strenuous exercise is associated with oxidative stress, which could lead to apoptosis. We investigated the ability of CrM in amelioration of apoptosis induced by incremental aerobic exercise (AE) to exhaustion in young athletes.

Materials and Methods:

In a placebo-controlled, double-blind, randomized, parallel study, 31 young athletes (age 19.52 ± 2.75 years, body mass 79.24 ± 16.13 kg, height 1.73 ± 6.49 m, body fat 16.37% ± 5.92%) were randomly assigned to CrM (4 × 5 g/day, n = 15) or placebo (PL: 4 × 5 g/day of maltodextrine powder; n = 16) to investigate the effect of 7 days CrM on serum p53 and insulin-like growth factor-1 (IGF-1) concentration after acute incremental AE test to exhaustion. Subjects performed AE before (test 1) and after 7 days of supplementation (test 2).

Results:

Before supplementation, AE to exhaustion induced a significant increase in serum p53 and IGF-1 concentrations at both CrM and PL groups (P < 0.05). After supplementation, serum p53 concentrations were significantly lower in CrM than PL at post-AE (P < 0.05). There were no differences in IGF-1 concentrations between CrM and PL groups at post-AE (P > 0.05).

Conclusion:

Our results suggest that supplementation with CrM prevents apoptosis, as measured by decreases in p53 concentration, induced by AE to exhaustion in young athletes. However, CrM had no effect on IGF-1 concentration after AE to exhaustion in young athletes.

p53 regulates the mevalonate pathway in human glioblastoma multiforme

The mevalonate (MVA) pathway is an important metabolic pathway implicated in multiple aspects of tumorigenesis. In this study, we provided evidence that p53 induces the expression of a group of enzymes of the MVA pathway including 3′-hydroxy-3′-methylglutaryl-coenzyme A reductase, MVA kinase, farnesyl diphosphate synthase and farnesyl diphosphate farnesyl transferase 1, in the human glioblastoma multiforme cell line, U343 cells, and in normal human astrocytes, NHAs. Genetic and pharmacologic perturbation of p53 directly influences the expression of these genes. Furthermore, p53 is recruited to the gene promoters in designated p53-responsive elements, thereby increasing their transcription. Such effect was abolished by site-directed mutagenesis in the p53-responsive element of promoter of the genes. These findings highlight another aspect of p53 functions unrelated to tumor suppression and suggest p53 as a novel regulator of the MVA pathway providing insight into the role of this pathway in cancer progression.

Human bronchial epithelial BEAS-2B cells, an appropriate in vitro model to study heavy metals induced carcinogenesis

Occupational and environmental exposure to arsenic (III) and chromium VI (Cr(VI)) have been confirmed to cause lung cancer. Mechanisms of these metals carcinogenesis are still under investigation. Selection of cell lines to be used is essential for the studies. Human bronchial epithelial BEAS-2B cells are the cells to be utilized by most of scientists. However, due to p53 missense mutation (CCG→TCG) at codon 47 and the codon 72 polymorphism (CGC→CCC) in BEAS-2B cells, its usage has frequently been questioned. The present study has examined activity and expression of 53 and its downstream target protein p21 upon acute or chronic exposure of BEAS-2B cells to arsenic and Cr(VI). The results show that short-term exposure of BEAS-2B cells to arsenic or Cr(VI) was able to activate both p53 and p21. Chronic exposure of BEAS-2B cells to these two metals caused malignant cell transformation and tumorigenesis. In arsenic-transformed BEAS-2B cells reductions in p53 promoter activity, mRNA expression, and phosphorylation of p53 at Ser392 were observed, while the total p53 protein level remained the same compared to those in passage-matched parent ones. p21 promoter activity and expression were decreased in arsenic-transformed cells. Cr(VI)-transformed cells exhibit elevated p53 promoter activity, mRNA expression, and phosphorylation at Ser15, but reduced phosphorylation at Ser392 and total p53 protein level compared to passage-matched parent ones. p21 promoter activity and expression were elevated in Cr(VI)-transformed cells. These results demonstrate that p53 is able to respond to exposure of arsenic or Cr(VI), suggesting that BEAS-2B cells are an appropriate in vitro model to investigate arsenic or Cr(VI) induced lung cancer.

MicroRNA-214 Promotes Apoptosis in Canine Hemangiosarcoma by Targeting the COP1-p53 Axis

MicroRNA-214 regulates both angiogenic function in endothelial cells and apoptosis in various cancers. However, the regulation and function of miR-214 is unclear in canine hemangiosarcoma, which is a spontaneous model of human angiosarcoma. The expression and functional roles of miR-214 in canine hemangiosarcoma were presently explored by performing miRNA TaqMan qRT-PCR and transfecting cells with synthetic microRNA. Here, we report that miR-214 was significantly down-regulated in the cell lines used and in clinical samples of canine hemangiosarcoma. Restoration of miR-214 expression reduced cell growth and induced apoptosis in canine hemangiosarcoma cell lines through transcriptional activation of p53-regulated genes although miR-214 had a slight effect of growth inhibition on normal endothelial cells. We identified COP1, which is a critical negative regulator of p53, as a novel direct target of miR-214. COP1 was overexpressed and the specific COP1 knockdown induced apoptosis through transcriptional activation of p53-regulated genes as well as did miR-214-transfection in HSA cell lines. Furthermore, p53 knockdown abolished the miR-214-COP1-mediated apoptosis; thus, miR-214 and COP1 regulated apoptosis through controlling p53 in HSA. In conclusion, miR-214 functioned as a tumor suppressor in canine hemangiosarcoma by inducing apoptosis through recovering the function of p53. miR-214 down-regulation and COP1 overexpression is likely to contribute to tumorigenesis of HSA. Therefore, targeting miR-214-COP1-p53 axis would possibly be a novel effective strategy for treatment of canine hemangiosarcoma and capable of being applied to the development of novel therapeutics for human angiosarcoma.

Identification of trichlormethiazide as a Mdr1a/b gene expression enhancer via a dual secretion-based promoter assay

Transporters of the ATP-binding cassette (ABC) family such as MDR1 play a pivotal role in persistence of brain homeostasis by contributing to the strict permeability properties of the blood–brain barrier. This barrier on one hand compromises treatment of central nervous system diseases by restricting access of drugs; on the other hand, an impaired or altered function of barrier building cells has been described in neurological disorders. The latter might contribute to increased vulnerability of the brain under pathological conditions or even enforce pathogenesis. Here, we present a novel approach for a systematic examination of drug impact on Mdr1 gene expression by establishing a dual reporter gene assay for the murine upstream core promoters of Mdr1a and b. We validated the time-resolved assay in comparison with single reporter gene constructs and applied it to analyze effects of a Food and Drug Administration (FDA)-approved drug library consisting of 627 substances. The chemo-preventive synthetic dithiolethione oltipraz was reidentified with our assay as an already known inducer of Mdr1 gene expression. Together with two newly characterized modifiers – gemcitabine and trichlormethiazide – we prove our findings in a blood–brain barrier culture model as well as in wild-type and Mdr1 knockout mice. In sum, we could demonstrate that our dual reporter gene assay delivers results, which also persist in the living animal and consequently is applicable for further analysis and prediction of Mdr1 regulation in vivo.

Distinct Rayleigh scattering from hot spot mutant p53 proteins reveals cancer cells

The scattering of light redirects and resonances when an electromagnetic wave interacts with electrons orbits in the hot spot core protein and oscillated electron of the gold nanoparticles (AuNP). This report demonstrates convincingly that resonant Rayleigh scattering generated from hot spot mutant p53 proteins is correspondence to cancer cells. Hot spot mutants have unique local electron density changes that affect specificity of DNA binding affinity compared with wild types. Rayleigh scattering changes introduced by hot-spot mutations were monitored by localized surface plasmon resonance (LSPR) shift changes. The LSPR λmax shift for hot-spot mutants ranged from 1.7 to 4.2 nm for mouse samples and from 0.64 nm to 2.66 nm for human samples, compared to 9.6 nm and 15 nm for wild type and mouse and human proteins, respectively with a detection sensitivity of p53 concentration at 17.9 nM. It is interesting that hot-spot mutants, which affect only interaction with DNA, launches affinitive changes as considerable as wild types. These changes propose that hot-spot mutants p53 proteins can be easily detected by local electron density alterations that disturbs the specificity of DNA binding of p53 core domain on the surface of the DNA probed-nanoplasmonic sensor.

Bacterial programmed cell death: making sense of a paradox

Although the concept of programmed cell death (PCD) in bacteria has been met with scepticism, a growing body of evidence suggests that it can no longer be ignored. Several recent studies indicate that the phenotypic manifestations of apoptosis, which are processes that are associated with ordered cellular disassembly in eukaryotes, are conserved in bacteria. In this Opinion article, I propose a model for the coordinated control of potential bacterial PCD effectors and argue that the processes involved are functionally analogous to eukaryotic PCD systems.

Combined modality doxorubicin-based chemotherapy and chitosan-mediated p53 gene therapy using double-walled microspheres for treatment of human hepatocellular carcinoma

The therapeutic efficiency of combined chemotherapy and gene therapy on human hepatocellular carcinoma HepG2 cells was investigated using double-walled microspheres that consisted of a poly(D,L-lactic-co-glycolic acid) (PLGA) core surrounded by a poly(L-lactic acid) (PLLA) shell layer and fabricated via the precision particle fabrication (PPF) technique. Here, double-walled microspheres were used to deliver doxorubicin (Dox) and/or chitosan-DNA nanoparticles containing the gene encoding the p53 tumor suppressor protein (chi-p53), loaded in the core and shell phases, respectively. Preliminary studies on chi-DNA nanoparticles were performed to optimize gene transfer to HepG2 cells. The transfection efficiency of chi-DNA nanoparticles was optimal at an N/P ratio of 7. In comparison to the 25-kDa branched polyethylenimine (PEI), chitosan showed no inherent toxicity towards the cells. Next, the therapeutic efficiencies of Dox and/or chi-p53 in microsphere formulations were compared to free drug(s) and evaluated in terms of growth inhibition, and cellular expression of tumor suppressor p53 and apoptotic caspase 3 proteins. Overall, the combined Dox and chi-p53 treatment exhibited enhanced cytotoxicity as compared to either Dox or chi-p53 treatments alone. Moreover, the antiproliferative effect was more substantial when cells were treated with microspheres than those treated with free drugs. High p53 expression was maintained during a five-day period, and was largely due to the controlled and sustained release of the microspheres. Moreover, increased activation of caspase 3 was observed, and was likely to have been facilitated by high levels of p53 expression. Overall, double-walled microspheres present a promising dual anticancer delivery system for combined chemotherapy and gene therapy.

p53 Stabilization induces cell growth inhibition and affects IGF2 pathway in response to radiotherapy in adrenocortical cancer cells

Adrenocortical carcinoma (ACC) is a very rare endocrine tumour, with variable prognosis, depending on tumour stage and time of diagnosis. However, it is generally fatal, with an overall survival of 5 years from detection. Radiotherapy usefulness for ACC treatment has been widely debated and seems to be dependent on molecular alterations, which in turn lead to increased radio-resistance. Many studies have shown that p53 loss is an important risk factor for malignant adrenocortical tumour onset and it has been reported that somatic mutations in TP53 gene occur in 27 to 70% of adult sporadic ACCs. In this study, we investigated the role of somatic mutations of the TP53 gene in response to ionizing radiation (IR). We studied the status of p53 in two adrenocortical cell lines, H295R and SW-13, harbouring non-functioning forms of this protein, owing to the lack of exons 8 and 9 and a point mutation in exon 6, respectively. Moreover, these cell lines show high levels of p-Akt and IGF2, especially H295R. We noticed that restoration of p53 activity led to inhibition of growth after transient transfection of cells with wild type p53. Evaluation of their response to IR in terms of cell proliferation and viability was determined by means of cell count and TUNEL assay.(wt)p53 over-expression also increased cell death by apoptosis following radiation in both cell lines. Moreover, RT-PCR and Western blotting analysis of some p53 target genes, such as BCL2, IGF2 and Akt demonstrated that p53 activation following IR led to a decrease in IGF2 expression. This was associated with a reduction in the active form of Akt. Taken together, these results highlight the role of p53 in response to radiation of ACC cell lines, suggesting its importance as a predictive factor for radiotherapy in malignant adrenocortical tumours cases.

Monodisperse double-walled microspheres loaded with chitosan-p53 nanoparticles and doxorubicin for combined gene therapy and chemotherapy

We have designed and evaluated a dual anticancer delivery system to provide combined gene therapy and chemotherapy. Double-walled microspheres consisting of a poly(d,l-lactic-co-glycolic acid) (PLGA) core surrounded by a poly(lactic acid) (PLA) shell were fabricated via the precision particle fabrication (PPF) technique. We make use of the advantages of double-walled microspheres to deliver chitosan-DNA nanoparticles containing the gene encoding the p53 tumor suppressor protein (chi-p53) and/or doxorubicin (Dox), loaded in the shell and core phases, respectively. Different molecular weights of PLA were used to form the shell layer for each formulation. The microspheres were monodisperse with a mean diameter of 65 to 75 μm and uniform shell thickness of 8 to 17 μm. Blank and Dox-loaded microspheres typically exhibited a smooth surface with relatively few small pores, while chi-microspheres containing p53 nanoparticles, with and without Dox, presented rough and porous surfaces. The encapsulation efficiency of Dox was significantly higher when it was encapsulated alone compared to co-encapsulation with chi-p53 nanoparticles. The encapsulation efficiency of chi-p53 nanoparticles, on the other hand, was not affected by the presence of Dox. As desired, chi-p53 nanoparticles were released first, followed by simultaneous release of chi-p53 nanoparticles and Dox at a near zero-order rate. Thus, we have demonstrated that the PPF method is capable of producing double-walled microspheres and encapsulating dual agents for combined modality treatment, such as gene therapy and chemotherapy.

Meta-analysis of the association between P53 codon 72 polymorphisms and gastric cancer

PURPOSE

This meta-analysis aims to examine whether the P53 codon 72 polymorphisms is associated with gastric cancer risk.

METHODS

Pooled odds ratios (ORs) were appropriately derived from random-effects models. Separate analyses were conducted on Asian and Caucasian populations. And a total of 21 studies were eligible (5,867 cases and 7,001 controls); 15 of them were conducted on Asians, others on Caucasians.

RESULTS

The combined results based on all studies showed that there was significant difference in genotype distribution between gastric cancer and non-cancer patients in the allele contrast (Pro vs. Arg); the codominant model (Pro/Pro vs. Arg/Arg) and the recessive model (Pro/Pro vs. Pro/Arg + Arg/Arg). When stratifying for race, patients with gastric cancer had a significantly higher frequency of Pro (OR = 1.136, 95% CI = 1.051-1.229), Pro/Pro (OR = 1.314, 95% CI = 1.110-1.555), Pro/Arg (OR = 1.099, 95% CI = 1.009-1.197), (Pro/Pro + Pro/Arg (OR = 1.153, 95% CI = 1.059-1.255) than non-cancer patients among Asians. There was statistically significant heterogeneity across all included studies with the Q statistic and study population may be the most important factor contributed to the heterogeneity.

CONCLUSIONS

In conclusion, the P53 codon 72 polymorphisms seems to be associated with gastric cancer risk and the analyses suggested that P53 codon 72 polymorphisms may be an important biomarker of gastric cancer susceptibility for Asians.

Mutations and polymorphisms in TP53 gene--an overview on the role in colorectal cancer

A functionally normal TP53 is essential to protect organisms from developing cancer. Somatic mutations in the gene represent one of the highest recurring perturbations in human tumours, including colorectal cancer (CRC). However, the variegated phenotype of wide spectrum of somatic mutations in TP53 and the complexity of the disease prevent a straight interpretation of the mutational analysis in tumours. In addition to the presence of somatic mutations, polymorphic features of the gene may also contribute to alteration of the normal TP53 functioning and variants, mainly in the form of single nucleotide polymorphisms, can be expected to impact susceptibility to sporadic CRC. In the present study, we reviewed the potential role of alterations in the TP53 gene, both somatic mutations and inherited sequence variations, in predisposition to CRC and in the prognosis and response to therapy. The available data from association studies have mostly shown contradictory outcomes. The majority of the studies were based on limited sample sizes and focussed on a limited number of polymorphisms, with main being the rs1042522 (Arg72Pro). Thus far, there is no possible generalisation of the role of TP53 as also a predictor of therapeutic response and prognosis. The effects of TP53, and its abnormalities, on the response of tumours to cytotoxic drugs, radiation and chemoradiation are complex. However, from studies it is emerging that the inherited genetics of TP53 pathway components could be utilised to further define patient populations in their abilities to induce p53 activity in response to either DNA damaging or p53-targeted therapies.

Canine tumors: a spontaneous animal model of human carcinogenesis

The enormous biologic complexity of human cancer has stimulated the development of more appropriate experimental models that could resemble in a natural and spontaneous manner the physiopathologic aspects of cancer biology. Companion animals have many desired characteristics that fill the gap between in vitro and in vivo studies, and these characteristics have proven to be important in understanding many complex molecular aspects of human cancer. Spontaneous tumors in dogs share a wide variety of epidemiologic, biologic, and clinical features with human cancer, which makes this animal model both attractive and underused in oncology research. In this review, we summarize the importance of naturally occurring canine tumors as valuable tools for studying numerous aspects of human cancer as well as the potential use of this animal model for the development of new cancer treatments. We address specifically the use of canine mammary tumors as an increasingly powerful model to study human breast cancer.

Genetic variants of the p53 and p73 genes jointly increase risk of second primary malignancies in patients after index squamous cell carcinoma of the head and neck

BACKGROUND

Because of the structural and biochemical similarities between the antitumor p53 and p73 proteins, the authors hypothesized that individuals who carry high-risk genotypes of p53 codon 72 and p73 G4C14-to-A4T14 polymorphisms have a higher risk of developing second primary malignancy (SPM) after index squamous cell carcinoma of the head and neck (SCCHN).

METHODS

A cohort of 1269 patients with index cases of SCCHN was recruited between May 1995 and January 2007 at The University of Texas MD Anderson Cancer Center and followed for SPM development. Patients were genotyped for p53 codon 72 and p73 G4C14-to-A4T14 polymorphisms. A log-rank test and Cox proportional hazard models were used to compare SPM-free survival and SPM risk among different risk groups with the combined risk genotypes of the 2 polymorphisms.

RESULTS

The data demonstrated that patients with p53 WP + PP and p73 GC/GC genotypes had a worse SPM-free survival and an increased SPM risk compared with the corresponding p53 WW and p73 GC/AT + AT/AT genotypes. After combining the 2 polymorphisms, a borderline significantly or significantly reduced SPM-free survival and increased SPM risk were observed in the medium-risk group (p53 WW and p73 GC/GC or p53 P carriers and p73 AT carriers) and high-risk group (p53 P carriers and p73 GC/GC) compared with low-risk group (p53 WW and p73 AT carriers), respectively.

CONCLUSIONS

The results suggest an increased risk of SPM after index SCCHN with both p53 and p73 polymorphisms individually and in combination.

Formation of stress-specific p53 binding patterns is influenced by chromatin but not by modulation of p53 binding affinity to response elements

The p53 protein is crucial for adapting programs of gene expression in response to stress. Recently, we revealed that this occurs partly through the formation of stress-specific p53 binding patterns. However, the mechanisms that generate these binding patterns remain largely unknown. It is not established whether the selective binding of p53 is achieved through modulation of its binding affinity to certain response elements (REs) or via a chromatin-dependent mechanism. To shed light on this issue, we used a microsphere assay for protein-DNA binding to measure p53 binding patterns on naked DNA. In parallel, we measured p53 binding patterns within chromatin using chromatin immunoprecipitation and DNase I coupled to ligation-mediated polymerase chain reaction footprinting. Through this experimental approach, we revealed that UVB and Nutlin-3 doses, which lead to different cellular outcomes, induce similar p53 binding patterns on naked DNA. Conversely, the same treatments lead to stress-specific p53 binding patterns on chromatin. We show further that altering chromatin remodeling using an histone acetyltransferase inhibitor reduces p53 binding to REs. Altogether, our results reveal that the formation of p53 binding patterns is not due to the modulation of sequence-specific p53 binding affinity. Rather, we propose that chromatin and chromatin remodeling are required in this process.

DNA damage, DNA repair rates and mRNA expression levels of cell cycle genes (TP53, p21(CDKN1A), BCL2 and BAX) with respect to occupational exposure to styrene

We studied the relationship between DNA damage, DNA repair rates and messenger RNA (mRNA) expression levels of cell cycle genes TP53, p21(CDKN1A), BCL2 and BAX in a group of 71 styrene-exposed workers and 51 control individuals. The exposure was assessed by measuring the concentration of styrene at workplace and in blood. Parameters of DNA damage [measured as single-strand breaks (SSBs) and endonuclease III-sensitive sites], γ-irradiation-specific DNA repair rates and mRNA levels of studied genes were analyzed in peripheral blood lymphocytes. The workers were divided into low (<50 mg/m³) and high (>50 mg/m³) styrene exposure groups. We found negative correlations between mRNA expression of TP53, BCL2, BAX and styrene exposure (P < 0.001 for all parameters). In contrast, p21(CDKN1A) mRNA expression significantly increased with increasing styrene exposure (P = 0.001). SSBs and endonuclease III-sensitive sites increased with increasing mRNA levels of TP53 (P < 0.001 for both) and BCL2 (P = 0.038, P = 0.002, respectively), whereas the same parameters decreased with increasing mRNA levels of p21(CDKN1A) (P < 0.001, P = 0.007, respectively). γ-Irradiation-specific DNA repair rates increased with p21(CDKN1A) mRNA levels up to the low exposure level (P = 0.044). Our study suggests a possible relationship between styrene exposure, DNA damage and transcript levels of key cell cycle genes.

p53 functions and cell lines: have we learned the lessons from the past?

p53 has a determinant role in cancer prevention and is among the most studied proteins in the world. The majority of studies devoted to this protein are carried out in cell lines because they are easy to use and have naturally emerged as the main research tool in laboratories. However, the p53 pathway is commonly deregulated in cancer cells, from which the experimental cell lines are generally derived. The fact that the pathway is deregulated challenges the relevance of using cancer-derived cell lines to study wild-type p53 activities, or, in a broader sense, to study any normal cellular process. In the present article, we identify and discuss a number of limitations of cell lines using examples related to p53. Finally, we point out the general limitations of cell lines and propose solutions as alternatives to these cells.

Arsenite induced poly(ADP-ribosyl)ation of tumor suppressor P53 in human skin keratinocytes as a possible mechanism for carcinogenesis associated with arsenic exposure

Arsenite is an environmental pollutant. Exposure to inorganic arsenic in drinking water is associated with elevated cancer risk, especially in skin. Arsenite alone does not cause skin cancer in animals, but arsenite can enhance the carcinogenicity of solar UV. Arsenite is not a significant mutagen at non-toxic concentrations, but it enhances the mutagenicity of other carcinogens. The tumor suppressor protein P53 and nuclear enzyme PARP-1 are both key players in DNA damage response. This laboratory demonstrated earlier that in cells treated with arsenite, the P53-dependent increase in p21(WAF1/CIP1) expression, normally a block to cell cycle progression after DNA damage, is deficient. Here we show that although long-term exposure of human keratinocytes (HaCaT) to a nontoxic concentration (0.1 microM) of arsenite decreases the level of global protein poly(ADP-ribosyl)ation, it increases poly(ADP-ribosyl)ation of P53 protein and PARP-1 protein abundance. We also demonstrate that exposure to 0.1 microM arsenite depresses the constitutive expression of p21 mRNA and P21 protein in HaCaT cells. Poly(ADP-ribosyl)ation of P53 is reported to block its activation, DNA binding and its functioning as a transcription factor. Our results suggest that arsenite's interference with activation of P53 via poly(ADP-ribosyl)ation may play a role in the comutagenic and cocarcinogenic effects of arsenite.

Apoptotic and necrotic action mechanisms of trimethyltin in human hepatoma G2 (HepG2) cells

In evaluating the cytotoxic effects and the mechanisms of the apoptotic and necrotic actions of trimethyltin chloride (TMT) on human hepatoma G2 (HepG2) cells, the present study focused on the involvement of antiproliferation, DNA damage, cell death, apoptosis-related proteins, and p53-dependent transcriptional activity. Twenty-four hour TMT treatments (4-64 microM) induced apoptosis and necrosis in HepG2 cells. Thirty-two micromolar and higher concentration significantly increases cell death. DNA damage was observed at 8 microM. Additionally, TMT increased the activity of cellular caspase-3 and the release of mitochondrial cytochrome c in a concentration-dependent manner. Our data demonstrated that the Bcl-2 family of proteins was involved in the apoptotic process but that p53 expression level was not affected. The results of luciferase reporter assay indicated that TMT-induced apoptosis seemed to adopt a transcription-dependent route, by activating p53 target genes such as PUMA and p21.

Biologic variability of human foreskin fibroblasts in 2D and 3D culture: implications for a wound healing model

Background

The fibroblast-populated 3D collagen matrix is a model of tissue and healing which has been used since the 1980's. It was hypothesized that anchorage disruption of the collagen matrix would produce p53-dependent apoptosis in the embedded fibroblasts, but results of hypothesis testing were variant.

Findings

The response of p53 to anchorage disruption in 3D culture or to UV irradiation in 2D culture was influenced both by fibroblast strain and culture conditions. It also was determined that data scatter in a collagen matrix contraction assay was related to fibroblast strain and possibly to technical factors, such as cell culture technician and/or number of matrices utilized. Subsequent analysis suggested that phenotypic drift and/or inter-strain genetic variability may have been responsible for the data scatter. In addition, several technical factors were identified that may have contributed to the scatter.

Conclusion

Experimentation with human foreskin fibroblasts in both 2D and 3D culture can produce variant data. The underlying cause of the data scatter appears to be partially due to the biologic variability of the fibroblast.

p53 Pre- and post-binding event theories revisited: stresses reveal specific and dynamic p53-binding patterns on the p21 gene promoter

p53 is a master transcription factor that prevents neoplasia and genomic instability. It is an important target for anticancer drug design. Understanding the molecular mechanisms behind its transcriptional activities in normal cells is a prerequisite to further understand the deregulation effected by mutant p53 in cancerous cells. Currently, how p53 coordinates transcription programs in response to stress remains unclear. One theory proposes that stresses induce pre-binding events that direct p53 to bind to specific response elements, whereas a second posits that, in response to stress, p53 binds most response elements and post-binding events then regulate transcription initiation. It is critical to establish the relevance of both theories and investigate whether stresses induce specific p53-binding patterns correlated with effector gene induction. Using unique in cellulo genomic footprinting experiments, we studied p53 binding to the five response elements of p21 in response to stresses and monitored p21 mRNA variant transcription. We show clear footprints of p53 bound to response elements in living cells and reveal that the binding of p53 to response elements is transient, subject to dynamic changes during stress responses, and influenced by response element pentamer orientations. We show further that stresses lead to specific p53-binding patterns correlated with particular p21 mRNA variant transcription profiles and that p53 binding is necessary but not sufficient to induce p21 transcription. Our results indicate that pre- and post-binding events act together to regulate adapted stress responses; this paves the way to the unification of pre- and post-binding event theories.