p53 activation in chronic radiation-treated breast cancer cells: regulation of MDM2/p14ARF

KLF11 promotes the proliferation of breast cancer cells by inhibiting p53-MDM2 signaling

Abnormal Krüppel-like factor 11 (KLF11) expression is frequently found in tumor tissues and is associated with cancer prognosis, but its biological functions and corresponding mechanisms remain elusive. Here, we demonstrated that KLF11 functions as an oncoprotein to promote tumor proliferation in breast cancer cells. Mechanistically, at the transcription level, KLF11 decreased TP53 mRNA expression. Notably, KLF11 also interacted with and stabilized MDM2 through inhibiting MDM2 ubiquitination and subsequent degradation. This increase in MDM2 in turn accelerated the ubiquitin-mediated proteolysis of p53, leading to the reduced expression of p53 and its target genes, including CDKN1A, BAX, and NOXA1. Accordingly, data from animals further confirmed that KLF11 significantly upregulated the growth of breast cancer cells and was inversely correlated with p53 expression. Taken together, our findings reveal a novel mechanism for breast cancer progression in which the function of the tumor suppressor p53 is dramatically weakened.

A Novel ERK2 Degrader Z734 Induces Apoptosis of MCF–7 Cells via the HERC3/p53 Signaling Pathway

Breast cancer is one of the leading causes of death worldwide, and synthetic chemicals targeting specific proteins or various molecular pathways for tumor suppression, such as ERK inhibitors and degraders, have been intensively investigated. The targets of ERK participate in the regulation of critical cellular mechanisms and underpin the progression of anticancer therapy. In this study, we identified a novel small molecule, which we named Z734, as a new mitogen–activated protein kinase 1 (ERK2) degrader and demonstrated that Z734 inhibits cell growth by inducing p53–mediated apoptotic pathways in human breast cancer cells. Treatment with Z734 resulted in the inhibition of cancer cell proliferation, colony formation and migration invasion, as well as cancer cell death via apoptosis. In addition, the Co–IP and GST pulldown assays indicated that the HECT and RLD domains containing E3 ubiquitin protein ligase 3 (HERC3) could directly interact with ERK2 through the HECT domain, promoting ERK2 ubiquitination. We also observed a strong link between HERC3 and p53 for the modulation of apoptosis. HERC3 can increase the protein and phosphorylation levels of p53, which further promotes apoptotic activity. In a xenograft mouse model, the effect was obtained in a treatment group that combined Z734 with lapatinib compared with that of the single–treatment groups. In summary, our results indicated that Z734 actively controls the development of breast cancer through apoptosis, and HERC3 may mediate ERK2 and p53 signaling, which offers new potential targets for clinical therapy.

Multiple interactions between melatonin and non-coding RNAs in cancer biology

The melatonin hormone secreted by the pineal gland is involved in physiological functions such as growth and maturation, circadian cycles, and biological activities including antioxidants, anti-tumor, and anti-ischemia. Melatonin not only interacts with proteins but also has functional effects on regulatory RNAs such as long non-coding RNAs (lncRNAs) and microRNAs (miRNAs). In this study, we overview various physiological and pathological conditions affecting melatonin through lncRNA and miRNA. The information compiled herein will serve as a solid foundation to formulate ideas for future mechanistic studies on melatonin. It will also provide a chance to more clarify the emerging functions of the non-coding transcriptome.

Comprehensive transcriptomic and proteomic analyses identify intracellular targets for myriocin to induce Fusarium oxysporum f. sp. niveum cell death

BACKGROUND

Myriocin is a natural product with antifungal activity and is derived from Bacillus amyloliquefaciens LZN01. Our previous work demonstrated that myriocin can inhibit the growth of Fusarium oxysporum f. sp. niveum (Fon) by inducing membrane damage. In this study, the antifungal actions of myriocin against Fon were investigated with a focus on the effects of myriocin on intracellular molecules.

RESULTS

Analysis of DNA binding and fluorescence spectra demonstrated that myriocin can interact with dsDNA from Fon cells. The intracellular-targeted mechanism of action was also supported by transcriptomic and proteomic analyses; a total of 2238 common differentially expressed genes (DEGs) were identified. The DEGs were further verified by RT-qPCR. Most of the DEGs were assigned metabolism and genetic information processing functions and were enriched in ribosome biogenesis in eukaryotes pathway. The expression of some genes and proteins in ribosome biogenesis in eukaryotes pathway was affected by myriocin, primarily the genes controlled by the C6 zinc cluster transcription factor family and the NFYA transcription factor. Myriocin influenced the posttranscriptional processing of gene products by triggering the main RI (retained intron) events of novel alternative splicing; myriocin targeted key genes (FOXG_09470) or proteins (RIOK2) in ribosome biogenesis in eukaryotes pathway, resulting in disordered translation.

CONCLUSIONS

In conclusion, myriocin was determined to exhibit activity against Fon by targeting intracellular molecules. The results of our study may help to elucidate the antifungal actions of myriocin against Fon.

Adaptation to Endoplasmic Reticulum Stress Enhances Resistance of Oral Cancer Cells to Cisplatin by Up-Regulating Polymerase η and Increasing DNA Repair Efficiency

Endoplasmic reticulum (ER) stress response is an adaptive program to cope with cellular stress that disturbs the function and homeostasis of ER, which commonly occurs during cancer progression to late stage. Late-stage cancers, mostly requiring chemotherapy, often develop treatment resistance. Chemoresistance has been linked to ER stress response; however, most of the evidence has come from studies that correlate the expression of stress markers with poor prognosis or demonstrate proapoptosis by the knockdown of stress-responsive genes. Since ER stress in cancers usually persists and is essentially not induced by genetic manipulations, we used low doses of ER stress inducers at levels that allowed cell adaptation to occur in order to investigate the effect of stress response on chemoresistance. We found that prolonged tolerable ER stress promotes mesenchymal-epithelial transition, slows cell-cycle progression, and delays the S-phase exit. Consequently, cisplatin-induced apoptosis was significantly decreased in stress-adapted cells, implying their acquisition of cisplatin resistance. Molecularly, we found that proliferating cell nuclear antigen (PCNA) ubiquitination and the expression of polymerase η, the main polymerase responsible for translesion synthesis across cisplatin-DNA damage, were up-regulated in ER stress-adaptive cells, and their enhanced cisplatin resistance was abrogated by the knockout of polymerase η. We also found that a fraction of p53 in stress-adapted cells was translocated to the nucleus, and that these cells exhibited a significant decline in the level of cisplatin-DNA damage. Consistently, we showed that the nuclear p53 coincided with strong positivity of glucose-related protein 78 (GRP78) on immunostaining of clinical biopsies, and the cisplatin-based chemotherapy was less effective for patients with high levels of ER stress. Taken together, this study uncovers that adaptation to ER stress enhances DNA repair and damage tolerance, with which stressed cells gain resistance to chemotherapeutics.

Discordant gene responses to radiation in humans and mice and the role of hematopoietically humanized mice in the search for radiation biomarkers

The mouse (Mus musculus) is an extensively used model of human disease and responses to stresses such as ionizing radiation. As part of our work developing gene expression biomarkers of radiation exposure, dose, and injury, we have found many genes are either up-regulated (e.g. CDKN1A, MDM2, BBC3, and CCNG1) or down-regulated (e.g. TCF4 and MYC) in both species after irradiation at ~4 and 8 Gy. However, we have also found genes that are consistently up-regulated in humans and down-regulated in mice (e.g. DDB2, PCNA, GADD45A, SESN1, RRM2B, KCNN4, IFI30, and PTPRO). Here we test a hematopoietically humanized mouse as a potential in vivo model for biodosimetry studies, measuring the response of these 14 genes one day after irradiation at 2 and 4 Gy, and comparing it with that of human blood irradiated ex vivo, and blood from whole body irradiated mice. We found that human blood cells in the hematopoietically humanized mouse in vivo environment recapitulated the gene expression pattern expected from human cells, not the pattern seen from in vivo irradiated normal mice. The results of this study support the use of hematopoietically humanized mice as an in vivo model for screening of radiation response genes relevant to humans.

The Benefit of Reactivating p53 under MAPK Inhibition on the Efficacy of Radiotherapy in Melanoma

Radiotherapy (RT) in patients with melanoma historically showed suboptimal results, because the disease is often radioresistant due to various mechanisms such as scavenging free radicals by thiols, pigmentary machinery, or enhanced DNA repair. However, radiotherapy has been utilized as adjuvant therapy after the complete excision of primary melanoma and lymph nodes to reduce the rate of nodal recurrences in high-risk patients. The resistance of melanoma cells to radiotherapy may also be in relation with the constitutive activation of the MAPK pathway and/or with the inactivation of p53 observed in about 90% of melanomas. In this study, we aimed to assess the potential benefit of adding RT to BRAF-mutated melanoma cells under a combined p53 reactivation and MAPK inhibition in vitro and in a preclinical animal model. We found that the combination of BRAF inhibition (vemurafenib, which completely shuts down the MAPK pathway), together with p53 reactivation (PRIMA-1Met) significantly enhanced the radiosensitivity of BRAF-mutant melanoma cells. This was accompanied by an increase in both p53 expression and activity. Of note, we found that radiation alone markedly promoted both ERK and AKT phosphorylation, thus contributing to radioresistance. The combination of vemurafenib and PRIMA-1Met caused the inactivation of both MAPK kinase and PI3K/AKT pathways. Furthermore, when combined with radiotherapy, it was able to significantly enhance melanoma cell radiosensitivity. Interestingly, in nude mice bearing melanoma xenografts, the latter triple combination had not only a synergistic effect on tumor growth inhibition, but also a potent control on tumor regrowth in all animals after finishing the triple combination therapy. RT alone had only a weak effect. In conclusion, we provide a basis for a strategy that may overcome the radioresistance of BRAF-mutated melanoma cells to radiotherapy. Whether this will translate into a rational to use radiotherapy in the curative setting in BRAF-mutated melanoma patients deserves consideration.

The oncoprotein HBXIP promotes human breast cancer growth through down-regulating p53 via miR-18b/MDM2 and pAKT/MDM2 pathways

Mammalian hepatitis B X-interacting protein (HBXIP) is an 18-kDa protein that regulates a large number of transcription factors such as TF-IID, E2F1, SP1, STAT3, c-Myc, and LXR by serving as an oncogenic transcription coactivator and plays an important role in the development of breast cancer. We previously showed that HBXIP as an oncoprotein could enhance the promoter activity of MDM2 through coactivating p53, promoting the MDM2 transcription in breast cancer. In this study we investigated the molecular mechanisms underlying the modulation of MDM2/p53 interaction by HBXIP in human breast cancer MCF-7 cells in vitro and in vivo. We showed that HBXIP could up-regulate MDM2 through inducing DNA methylation of miR-18b, thus suppressing the miR-18b expression, leading to the attenuation of p53 in breast cancer cells. In addition, HBXIP could promote the phosphorylation of MDM2 by increasing the level of pAKT and bind to pMDM2, subsequently enhancing the interaction between MDM2 and p53 for the down-regulation of p53 in breast cancer cells. In MCF-7 breast cancer xenograft nude mice, we also observed that overexpression of HBXIP promoted breast cancer growth through the miR-18b/MDM2 and pAKT/MDM2 pathways. In conclusion, oncoprotein HBXIP suppresses miR-18b to elevate MDM2 and activates pAKT to phosphorylate MDM2 for enhancing the interaction between MDM2 and p53, leading to p53 degradation in promotion of breast cancer growth. Our findings shed light on a novel mechanism of p53 down-regulation during the development of breast cancer.

Good Guy or Bad Guy? The Duality of Wild-Type p53 in Hormone-Dependent Breast Cancer Origin, Treatment, and Recurrence

"Lactation is at one point perilously near becoming a cancerous process if it is at all arrested", Beatson, 1896. Most breast cancers arise from the milk-producing cells that are characterized by aberrant cellular, molecular, and epigenetic translation. By understanding the underlying molecular disruptions leading to the origin of cancer, we might be able to design novel strategies for more efficacious treatments or, ambitiously, divert the cancerous process. It is an established reality that full-term pregnancy in a young woman provides a lifetime reduction in breast cancer risk, whereas delay in full-term pregnancy increases short-term breast cancer risk and the probability of latent breast cancer development. Hormonal activation of the p53 protein (encode by the TP53 gene) in the mammary gland at a critical time in pregnancy has been identified as one of the most important determinants of whether the mammary gland develops latent breast cancer. This review discusses what is known about the protective influence of female hormones in young parous women, with a specific focus on the opportune role of wild-type p53 reprogramming in mammary cell differentiation. The importance of p53 as a protector or perpetrator in hormone-dependent breast cancer, resistance to treatment, and recurrence is also explored.

PRL-3 promotes breast cancer progression by downregulating p14ARF-mediated p53 expression

Prior studies have demonstrated that phosphatase of regenerating liver-3 (PRL-3) serves avital function in cell proliferation and metastasis in breast cancer. However, the molecular mechanisms underlying the function of PRL-3 in breast cancer remain unknown. PRL-3 expression was analyzed in 24 pairs of breast cancer and normal tissues using the reverse transcription-quantitative polymerase chain reaction assay. The results of the present study identified that the expression of PLR-3 in breast cancer tissues was increased 4.2-fold, compared with normal tissues. Notably, overexpression of PRL-3 significantly promoted the proliferation of cancer cells and inhibited endogenous p53 expression by downregulating the expression level of p14 alternate reading frame (p14^ARF). In addition, decreased expression levels of PRL-3 resulted in decreased breast cancer cell proliferation and increased expression level of p14^ARF. These results suggested that PRL-3 enhances cell proliferation by downregulating p14^ARF expression, which results in decreased levels ofp53. The results of the present study demonstrated that PRL-3 promotes tumor proliferation by affecting the p14^ARF-p53 axis, and that it may serve as a prognostic marker for patients with breast cancer.

Long non-coding RNA and microRNA-675/let-7a mediates the protective effect of melatonin against early brain injury after subarachnoid hemorrhage via targeting TP53 and neural growth factor

The objective of this study was to identify the protective effect of melatonin (MT) against early brain injury (EBI) following subarachnoid hemorrhage (SAH) and explore the underlying molecular mechanism. Real-time polymerase chain reaction (PCR) and luciferase assay were utilized to detect the effect of MT on H19 expression level, computation analysis and luciferase assay were conducted to the underlying mechanism of let-7a and miR-675. Real-time PCR, western blot analysis, immunohistochemistry, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and flow cytometry analysis were performed to detect the effect of MT on H19, miR-675, let-7a, TP53, neural growth factor (NGF) levels, cell viability, and apoptosis status. Melatonin increased H19 expression level by enhancing H19 transcriptional efficiency in a concentration-dependent manner. MiR-675 and let-7a directly targeted P53 and NGF, respectively, and miR-675 reduced luciferase activity of wild-type but not mutant TP53 3′UTR. Meanwhile, let-7a suppressed luciferase activity of wild-type but not mutant NGF 3′UTR. H₂O₂ increased number of SA-b-gal, and while MT administration repressed the premature senescence. H₂O₂ obviously upregulated expressions of H19, miR-675, and NGF, and downregulated let-7a and TP53 levels; however, MT treatment reduced expressions of H19, miR-675, and NGF, and improved let-7a and TP53 levels. Treating with MT attenuated the neurological deficits and reduced the brain swelling. MT treatment repressed apoptosis of neurons caused by SAH. Levels of H19, miR-675, and NGF were much higher in the SAH +  MT group, while there were even higher levels of H19, miR-675, and NGF in the SAH group than in the sham group; levels of let-7a and TP53 were much lower in the SAH + MT group, while they were even lower in the SAH group than in the sham group. Our study revealed that treatment with MT protected against EBI after SAH by modulating the signaling pathways of H19-miR-675-P53-apoptosis and H19-let-7a-NGF-apoptosis.

Annexin/S100A Protein Family Regulation through p14ARF-p53 Activation: A Role in Cell Survival and Predicting Treatment Outcomes in Breast Cancer

The annexin family and S100A associated proteins are important regulators of diverse calcium-dependent cellular processes including cell division, growth regulation and apoptosis. Dysfunction of individual annexin and S100A proteins is associated with cancer progression, metastasis and cancer drug resistance. This manuscript describes the novel finding of differential regulation of the annexin and S100A family of proteins by activation of p53 in breast cancer cells. Additionally, the observed differential regulation is found to be beneficial to the survival of breast cancer cells and to influence treatment efficacy. We have used unbiased, quantitative proteomics to determine the proteomic changes occurring post p14ARF-p53 activation in estrogen receptor (ER) breast cancer cells. In this report we identified differential regulation of the annexin/S100A family, through unique peptide recognition at the N-terminal regions, demonstrating p14ARF-p53 is a central orchestrator of the annexin/S100A family of calcium regulators in favor of pro-survival functions in the breast cancer cell. This regulation was found to be cell-type specific. Retrospective human breast cancer studies have demonstrated that tumors with functional wild type p53 (p53wt) respond poorly to some chemotherapy agents compared to tumors with a non-functional p53. Given that modulation of calcium signaling has been demonstrated to change sensitivity of chemotherapeutic agents to apoptotic signals, in principle, we explored the paradigm of how p53 modulation of calcium regulators in ER+ breast cancer patients impacts and influences therapeutic outcomes.

p21 induction plays a dual role in anti-cancer activity of ursolic acid

Previous studies have shown that induction of G1 arrest and apoptosis by ursolic acid is associated with up-regulation of cyclin-dependent kinase inhibitor (CDKI) protein p21 in multiple types of cancer cells. However, the functional role of p21 induction in G1 cell cycle arrest and apoptosis, and the mechanisms of p21 induction by ursolic acid have not been critically addressed. In the current study, we demonstrated that p21 played a mediator role in G1 cell cycle arrest by ursolic acid, whereas p21-mediated up-regulation of Mcl-1 compromised apoptotic effect of ursolic acid. These results suggest that p21 induction plays a dual role in the anti-cancer activity of ursolic acid in terms of cell cycle and apoptosis regulation. p21 induction by ursolic acid was attributed to p53 transcriptional activation. Moreover, we found that ursolic acid was able to inhibit murine double minute-2 protein (MDM2) and T-LAK cell-originated protein kinase (TOPK), the two negative regulator of p53, which in turn contributed to ursolic acid-induced p53 activation. Our findings provided novel insights into understanding of the mechanisms involved in cell cycle arrest and apoptosis induction in response to ursolic acid exposure.

Effects of Chronic Low-Dose Radiation on Human Neural Progenitor Cells

The effects of chronic low-dose radiation on human health have not been well established. Recent studies have revealed that neural progenitor cells are present not only in the fetal brain but also in the adult brain. Since immature cells are generally more radiosensitive, here we investigated the effects of chronic low-dose radiation on cultured human neural progenitor cells (hNPCs) derived from embryonic stem cells. Radiation at low doses of 31, 124 and 496 mGy per 72 h was administered to hNPCs. The effects were estimated by gene expression profiling with microarray analysis as well as morphological analysis. Gene expression was dose-dependently changed by radiation. By thirty-one mGy of radiation, inflammatory pathways involving interferon signaling and cell junctions were altered. DNA repair and cell adhesion molecules were affected by 124 mGy of radiation while DNA synthesis, apoptosis, metabolism, and neural differentiation were all affected by 496 mGy of radiation. These in vitro results suggest that 496 mGy radiation affects the development of neuronal progenitor cells while altered gene expression was observed at a radiation dose lower than 100 mGy. This study would contribute to the elucidation of the clinical and subclinical phenotypes of impaired neuronal development induced by chronic low-dose radiation.

miR-15b/16-2 regulates factors that promote p53 phosphorylation and augments the DNA damage response following radiation in the lung

MicroRNAs (miRNAs) are regulatory RNAs frequently dysregulated in disease and following cellular stress. Investigators have described changes in miR-15b expression following exposure to several stress-inducing anticancer agents, including ionizing radiation (IR), etoposide, and hydrogen peroxide. However, the role for miR-15b as a mediator of cellular injury in organs such as the lung has yet to be explored. In this study, we examined miR-15b expression patterns as well as its potential role in DNA damage and repair in the setting of IR exposure. We showed that miR-15b is up-regulated in a dose- and time-dependent manner in human bronchial epithelial cells following IR. miR-15b expression was highest after 2 h of IR and decreased gradually. Survival rates following IR were also higher in miR-15b/16-2-overexpressing cells. Cell cycle arrest in G2/M phase and an increased DNA repair response were observed in IR-exposed miR-15b/16-2 stable cells. We observed an up-regulation of components of the ataxia telangiectasia mutated (ATM)/Chek1/p53 pathway in miR-15b/16-2-overexpressing cells after IR. Moreover, a pathway-based PCR expression array of genes demonstrated that miR-15b/16-2 overexpression significantly induced the expression of genes involved in ATM/ataxia telangiectasia and Rad-3-related (ATR) signaling, apoptosis, the cell cycle, and DNA repair pathways. Here we demonstrated a novel biological link between miR-15b and DNA damage and cellular protection in lung cells. We identified Wip1 (PPM1D) as a functional target for miR-15b and determined that miR-15b induction of the DNA damage response is partially dependent upon suppression of Wip1. Our study suggests that miR-15b/Wip1 could be a potential therapeutic target in radiation-induced lung disease.

Increased hyaluronan levels in HABP1/p32/gC1qR overexpressing HepG2 cells inhibit autophagic vacuolation regulating tumor potency

Tumor growth and development is influenced by its microenvironment. A major extracellular matrix molecule involved in cancer progression is hyaluronan (HA). Hyaluronan and expression of a number of hyaladherin family proteins are dramatically increased in many cancer malignancies. One such hyaladherin, hyaluronan-binding protein 1 (HABP1/p32/gC1qR) has been considered to be a biomarker for tumor progression. Interestingly, overexpression of HABP1 in fibroblast has been shown to increase autophagy via generation of excess reactive oxygen species (ROS) and depletion of HA leading to apoptosis. Cancerous cells are often found to exhibit decreased rate of proteolysis/autophagy in comparison to their normal counterparts. To determine if HABP1 levels alter tumorigenicity of cancerous cells, HepR21, the stable transfectant overexpressing HABP1 in HepG2 cell line was derived. HepR21 has been shown to have increased proliferation rate than HepG2, intracellular HA cable formation and enhanced tumor potency without any significant alteration of intracellular ROS. In this paper we have observed that HepR21 cells containing higher endogenous HA levels, have downregulated expression of the autophagic marker, MAP-LC3, consistent with unaltered levels of endogenous ROS. In fact, HepR21 cells seem to have significant resistance to exogenous ROS stimuli and glutathione depletion. HepR21 cells were also found to be more resilient to nutrient starvation in comparison to its parent cell line. Decline in intracellular HA levels and HA cables in HepR21 cells upon treatment with HAS inhibitor (4-MU), induced a surge in ROS levels leading to increased expression of MAP-LC3 and tumor suppressors Beclin 1 and PTEN. This suggests the importance of HABP1 induced HA cable formation in enhancing tumor potency by maintaining the oxidant levels and subsequent autophagic vacuolation.

Genetic variants in p53-related genes confer susceptibility to second primary malignancy in patients with index squamous cell carcinoma of head and neck

Because of their important roles in mediating the stabilization and expression of p53, we hypothesized that high-risk genotypes of polymorphisms in p53-related genes, including p53, p73, p14(ARF), MDM2 and MDM4, may be associated with an increased risk of second primary malignancy (SPM) after index squamous cell carcinoma of the head and neck (SCCHN). We analyzed data from a cohort of 1283 patients with index SCCHN who were recruited between 1995 and 2007 at MD Anderson Cancer Center and followed for SPM development. Patients were genotyped for nine polymorphisms of p53-related genes. A log-rank test and Cox models were used to compare SPM-free survival and risk. Our results demonstrated that each p53-related polymorphism had a moderate effect on increased SPM risk, but when we combined risk genotypes of these nine polymorphisms together, we found that SPM-free survival was significantly shorter among risk groups with a greater number of combined risk genotypes. SPM risk increased with increasing number of risk genotypes (P < 0.0001 for trend). Compared with the low-risk group (0-3 combined risk genotypes), both the medium-risk (4-5 combined risk genotypes) and high-risk (6-9 combined risk genotypes) groups had significantly increased SPM risk [hazard ratio (HR): 1.6; 95% confidence interval (CI): 1.0-2.6 and HR: 3.0; 95% CI: 1.8-5.0, respectively]. Moreover, such significant associations were even higher in several subgroups. Our findings suggest that combined risk genotypes of p53-related genes may jointly modify SPM risk, especially in patients who are smokers and those with index non-oropharyngeal cancers. However, larger studies are needed to validate our findings.

Cyclin B1/Cdk1 phosphorylation of mitochondrial p53 induces anti-apoptotic response

The pro-apoptotic function of p53 has been well defined in preventing genomic instability and cell transformation. However, the intriguing fact that p53 contributes to a pro-survival advantage of tumor cells under DNA damage conditions raises a critical question in radiation therapy for the 50% human cancers with intact p53 function. Herein, we reveal an anti-apoptotic role of mitochondrial p53 regulated by the cell cycle complex cyclin B1/Cdk1 in irradiated human colon cancer HCT116 cells with p53^+/+ status. Steady-state levels of p53 and cyclin B1/Cdk1 were identified in the mitochondria of many human and mouse cells, and their mitochondrial influx was significantly enhanced by radiation. The mitochondrial kinase activity of cyclin B1/Cdk1 was found to specifically phosphorylate p53 at Ser-315 residue, leading to enhanced mitochondrial ATP production and reduced mitochondrial apoptosis. The improved mitochondrial function can be blocked by transfection of mutant p53 Ser-315-Ala, or by siRNA knockdown of cyclin B1 and Cdk1 genes. Enforced translocation of cyclin B1 and Cdk1 into mitochondria with a mitochondrial-targeting-peptide increased levels of Ser-315 phosphorylation on mitochondrial p53, improved ATP production and decreased apoptosis by sequestering p53 from binding to Bcl-2 and Bcl-xL. Furthermore, reconstitution of wild-type p53 in p53-deficient HCT116 p53^−/− cells resulted in an increased mitochondrial ATP production and suppression of apoptosis. Such phenomena were absent in the p53-deficient HCT116 p53^−/− cells reconstituted with the mutant p53. These results demonstrate a unique anti-apoptotic function of mitochondrial p53 regulated by cyclin B1/Cdk1-mediated Ser-315 phosphorylation in p53-wild-type tumor cells, which may provide insights for improving the efficacy of anti-cancer therapy, especially for tumors that retain p53.

Differential gene expression in primary human skin keratinocytes and fibroblasts in response to ionizing radiation

Although skin is usually exposed during human exposures to ionizing radiation, there have been no thorough examinations of the transcriptional response of skin fibroblasts and keratinocytes to radiation. The transcriptional response of quiescent primary fibroblasts and keratinocytes exposed to from 10 cGy to 5 Gy and collected 4 h after treatment was examined. RNA was isolated and examined by microarray analysis for changes in the levels of gene expression. Exposure to ionizing radiation altered the expression of 279 genes across both cell types. Changes in RNA expression could be arranged into three main categories: (1) changes in keratinocytes but not in fibroblasts, (2) changes in fibroblasts but not in keratinocytes, and (3) changes in both. All of these changes were primarily of p53 target genes. Similar radiation-induced changes were induced in immortalized fibroblasts or keratinocytes. In separate experiments, protein was collected and analyzed by Western blotting for expression of proteins observed in microarray experiments to be overexpressed at the mRNA level. Both Q-PCR and Western blot analysis experiments validated these transcription changes. Our results are consistent with changes in the expression of p53 target genes as indicating the magnitude of cell responses to ionizing radiation.

Concurrent hormone and radiation therapy in patients with breast cancer: what is the rationale?

Endocrine therapy is often given together with postoperative radiotherapy in patients with breast cancer and positive hormone-receptor status. However, few experimental or clinical studies address the combined effects of hormone and radiation therapy. Preclinical models have shown changes in tumour cell kinetics with the addition of tamoxifen, and some show reduced tumour cell death with concurrent anti-oestrogen treatment and radiotherapy. Although data from in-vitro studies support the notion of antagonistic effects of concurrent tamoxifen and radiotherapy on tumour cells, in-vivo research suggests a synergistic effect that could be attributable to micro-environmental changes in tumour responsiveness to ionising radiation and hormone therapy. Retrospective studies suggest that in practical application, concurrent administration of tamoxifen with radiotherapy does not compromise local control but might increase toxicity. Preliminary results from simultaneous treatment with aromatase inhibitors and radiation indicate that this combination of endocrine and radiation therapy could enhance cytotoxicity and improve tumour response. Further studies are needed to clarify the physiological mechanisms activated by oestrogens, which will allow a more thorough understanding of the complex interactions between 17beta-oestradiol and P53/P21(WAF1/CIP1)/Rb pathways and of the interaction between endocrine therapy and radiotherapy.

Latent membrane protein 1 of Epstein-Barr virus regulates p53 phosphorylation through MAP kinases

The Epstein-Barr virus (EBV) encoded latent membrane protein 1 (LMP1), an oncogenic protein, plays an important role in the carcinogenesis of nasopharyngeal carcinoma (NPC). Phosphorylation of p53 protein is likely to play the key role in regulating its activity. p53 protein accumulates but mutation of p53 gene is not common in NPC. The molecular mechanisms of p53 augmentation have not been completely elucidated. Here, the role of MAP kinases in the phosphorylation of p53 modulated by LMP1 was determined. p53 could be activated and phosphorylated clearly at Ser15, Ser20, Ser392, and Thr81 modulated by LMP1. Furthermore, LMP1-induced phosphorylation of p53 at Ser15 was directly by ERKs; at Ser20 and Thr81 by JNK, at Ser 15 and Ser392 by p38 kinase. The phosphorylation of p53 was associated with its transcriptional activity and stability modulated by LMP1. These results strongly suggest that MAP kinases have a direct role in LMP1-induced phosphorylation of p53 at multiple sites, which provide a novel view for us to understand the mechanism of the activation of p53 in the carcinogenesis of nasopharyngeal carcinoma.

Low-dose irradiation alters the transcript profiles of human lymphoblastoid cells including genes associated with cytogenetic radioadaptive response

Low-dose ionizing radiation alters the gene expression profiles of mammalian cells, yet there is little understanding of the underlying cellular mechanisms responsible for these changes or of their consequences for genomic stability. We investigated the cytogenetic adaptive response of human lymphoblastoid cell lines exposed to 5 cGy (priming dose) followed by 2 Gy (challenge dose) compared to cells that received a single 2-Gy dose to (a) determine how the priming dose influences subsequent gene transcript expression in reproducibly adapting and non-adapting cell lines, and (b) identify gene transcripts that are associated with reductions in the magnitude of chromosomal damage after the challenge dose. The transcript profiles were evaluated using oligonucleotide arrays and RNA obtained 4 h after the challenge dose. A set of 145 genes (false discovery rate = 5%) with transcripts that were affected by the 5-cGy priming dose fell into two categories: (a) a set of common genes that were similarly modulated by the 5-cGy priming dose irrespective of whether the cells subsequently adapted or not and (b) genes with differential transcription in accordance with the cell lines that showed either adaptive or non-adaptive outcomes. The common priming-dose response genes showed up-regulation for protein synthesis genes and down-regulation of metabolic and signal transduction genes (>10-fold differences). The genes associated with subsequent adaptive and non-adaptive outcomes involved DNA repair, stress response, cell cycle control and apoptosis. Our findings support the importance of TP53-related functions in the control of the low-dose cytogenetic radioadaptive response and suggest that certain low-dose-induced alterations in cellular functions are predictive for the risk of subsequent genomic damage.

Microarray and real-time RT-PCR analyses of a novel set of differentially expressed human genes in ECV304 endothelial-like cells infected with dengue virus type 2

The cellular and molecular pathways of dengue infection have not been as intensively studied compared to the host immunological responses. Changes in mRNA expression levels of ECV304 human endothelial-like cells following infection with the virulent New Guinea C strain of dengue virus type 2 were analyzed by a microarray system comprising 7600 oligonucleotide cDNAs. After normalization against the uninfected control using two independent software programs, 111 genes exhibited at least a 1.5-fold difference in expression level. Out of these, 21 mRNAs were upregulated while 90mRNAs were downregulated. Quantitative real-time RT-PCR was then performed to determine the expression patterns of 15 selected genes of interest involved in the cell cycle (MAD3), apoptosis (RIPK3, PDCD8), cellular receptors (H963, CCR7, KLRC3), transcriptional regulation (RUNX3, HNF4G, MIZ1), signal transduction (HSP27, TRIP, MAP4K4), enzymes (angiotensinogen), protein transport (AP4M1), and cytoskeleton (ACTA2). Dengue virus infection resulted in the downregulation of the C-terminal alternatively spliced p53 variant, the pro-apoptotic IG20 and IG20-SV2 isoforms, and the Fas apoptosis inhibitory molecule (FAIM). Most of the real-time RT-PCR data showed concordance with the normalized microarray data. Hence, real-time RT-PCR validation of high-throughput gene microarray screening is important and necessary before further conclusions on gene expression can be drawn. This study elucidated novel information on the complex responses at the transcriptional level in susceptible human endothelial-like cells induced by a virulent dengue virus strain implicated in the pathogenesis of dengue and/or its complications.

Co-activation of ERK, NF-kappaB, and GADD45beta in response to ionizing radiation

NF-kappaB has been well documented to play a critical role in signaling cell stress reactions. The extracellular signal-regulated kinase (ERK) regulates cell proliferation and survival. GADD45beta is a primary cell cycle element responsive to NF-kappaB activation in anti-apoptotic responses. The present study provides evidence demonstrating that NK-kappaB, ERK and GADD45beta are co-activated by ionizing radiation (IR) in a pattern of mutually dependence to increase cell survival. Stress conditions generated in human breast cancer MCF-7 cells by the administration of a single exposure of 5 Gy IR resulted in the activation of ERK but not p38 or JNK, along with an enhancement of the NF-kappaB transactivation and GADD45beta expression. Overexpression of dominant negative Erk (DN-Erk) or pre-exposure to ERK inhibitor PD98059 inhibited NF-kappaB. Transfection of dominant negative mutant IkappaB that blocks NF-kappaB nuclear translocation, inhibited ERK activity and GADD45beta expression and increased cell radiosensitivity. Interaction of p65 and ERK was visualized in living MCF-7 cells by bimolecular fluorescence complementation analysis. Antisense inhibition of GADD45beta strikingly blocked IR-induced NF-kappaB and ERK but not p38 and JNK. Overall, these results demonstrate a possibility that NF-kappaB, ERK, and GADD45beta are able to coordinate in a loop-like signaling network to defend cells against the cytotoxicity induced by ionizing radiation.

Post-translational modification of p53 in tumorigenesis

Interest in the tumour suppressor p53 has generated much information regarding the complexity of its function and regulation in carcinogenesis. However, gaps still exist in our knowledge regarding the role of p53 post-translational modifications in carcinogenesis and cancer prevention. A thorough understanding of p53 will be extremely useful in the development of new strategies for treating and preventing cancer, including restoration of p53 function and selective killing of tumours with mutant TP53.