Changes in cyclin/proliferating cell nuclear antigen distribution during DNA repair synthesis

Exendin-4 Prevents Memory Loss and Neuronal Death in Rats with Sporadic Alzheimer-Like Disease

This study investigated the neuroprotective effects of exendin-4 (EXE-4), an analog of the glucagon-like peptide 1 receptor (GLP-1R) on memory and on the neuronal populations that constitute the hippocampus of rats submitted to a sporadic dementia of Alzheimer's type (SDAT). Male Wistar rats received streptozotocin (STZ icv, 3 mg/kg diluted in aCFS, 5 µl/ventricle) and were treated for 21 days with EXE-4 (10 µg/kg, ip; saline as the vehicle). Four groups were formed: vehicle, EXE-4, STZ, and STZ + EXE-4. The groups were submitted to Y-Maze (YM), object recognition (ORT), and object displacement tasks (ODT) to assess learning and memory. The brains were used for immunohistochemical and immunofluorescent techniques with antibodies to NeuN, cleaved caspase-3 (CC3), PCNA, doublecortin (DCX), synaptophysin (SYP), and insulin receptor (IR). STZ worsened spatial memory in the YMT, as well as short-term (STM) and long-term (LTM) memories in the ORT and ODT, respectively. EXE-4 protected against memory impairment in STZ animals. STZ reduced mature neuron density (NeuN) and increased cell apoptosis (CC3) in the DG, CA1, and CA3. EXE-4 protected against neuronal death in all regions. EXE-4 increased PCNA+ cells in all regions of the hippocampus, and STZ attenuated this effect. STZ reduced neurogenesis in DG per se as well as synaptogenesis induced by EXE-4. EXE-4 increased immunoreactivity to IR in the CA1. From these findings, EXE-4 showed a beneficial effect on hippocampal pyramidal and granular neurons in the SDAT showing anti-apoptotic properties and promoting cell proliferation. In parallel, EXE-4 preserved the memory of SDAT rats. EXE-4 appears to enhance synapses at CA3 and DG. In conclusion, these data indicate that agonists to GLP-1R have a beneficial effect on hippocampal neurons in AD.

Post-Translational Modifications of PCNA: Guiding for the Best DNA Damage Tolerance Choice

The sliding clamp PCNA is a multifunctional homotrimer mainly linked to DNA replication. During this process, cells must ensure an accurate and complete genome replication when constantly challenged by the presence of DNA lesions. Post-translational modifications of PCNA play a crucial role in channeling DNA damage tolerance (DDT) and repair mechanisms to bypass unrepaired lesions and promote optimal fork replication restart. PCNA ubiquitination processes trigger the following two main DDT sub-pathways: Rad6/Rad18-dependent PCNA monoubiquitination and Ubc13-Mms2/Rad5-mediated PCNA polyubiquitination, promoting error-prone translation synthesis (TLS) or error-free template switch (TS) pathways, respectively. However, the fork protection mechanism leading to TS during fork reversal is still poorly understood. In contrast, PCNA sumoylation impedes the homologous recombination (HR)-mediated salvage recombination (SR) repair pathway. Focusing on Saccharomyces cerevisiae budding yeast, we summarized PCNA related-DDT and repair mechanisms that coordinately sustain genome stability and cell survival. In addition, we compared PCNA sequences from various fungal pathogens, considering recent advances in structural features. Importantly, the identification of PCNA epitopes may lead to potential fungal targets for antifungal drug development.

Evading immune surveillance via tyrosine phosphorylation of nuclear PCNA

Increased DNA replication and metastasis are hallmarks of cancer progression, while deregulated proliferation often triggers sustained replication stresses in cancer cells. How cancer cells overcome the growth stress and proceed to metastasis remains largely elusive. Proliferating cell nuclear antigen (PCNA) is an indispensable component of the DNA replication machinery. Here, we show that phosphorylation of PCNA on tyrosine 211 (pY211-PCNA) regulates DNA metabolism and tumor microenvironment. Abrogation of pY211-PCNA blocks fork processivity, resulting in biogenesis of single-stranded DNA (ssDNA) through a MRE11-dependent mechanism. The cytosolic ssDNA subsequently induces inflammatory cytokines through a cyclic GMP-AMP synthetase (cGAS)-dependent cascade, triggering an anti-tumor immunity by natural killer (NK) cells to suppress distant metastasis. Expression of pY211-PCNA is inversely correlated with cytosolic ssDNA and associated with poor survival in patients with cancer. Our results pave the way to biomarkers and therapies exploiting immune responsiveness to target metastatic cancer.

DNA-damage tolerance through PCNA ubiquitination and sumoylation

DNA-damage tolerance (DDT) is employed by eukaryotic cells to bypass replication-blocking lesions induced by DNA-damaging agents. In budding yeast Saccharomyces cerevisiae, DDT is mediated by RAD6 epistatic group genes and the central event for DDT is sequential ubiquitination of proliferating cell nuclear antigen (PCNA), a DNA clamp required for replication and DNA repair. DDT consists of two parallel pathways: error-prone DDT is mediated by PCNA monoubiquitination, which recruits translesion synthesis DNA polymerases to bypass lesions with decreased fidelity; and error-free DDT is mediated by K63-linked polyubiquitination of PCNA at the same residue of monoubiquitination, which facilitates homologous recombination-mediated template switch. Interestingly, the same PCNA residue is also subjected to sumoylation, which leads to inhibition of unwanted recombination at replication forks. All three types of PCNA posttranslational modifications require dedicated conjugating and ligation enzymes, and these enzymes are highly conserved in eukaryotes, from yeast to human.

In Situ Analysis of DNA-Protein Complex Formation upon Radiation-Induced DNA Damage

The importance of determining at the cellular level the formation of DNA–protein complexes after radiation-induced lesions to DNA is outlined by the evidence that such interactions represent one of the first steps of the cellular response to DNA damage. These complexes are formed through recruitment at the sites of the lesion, of proteins deputed to signal the presence of DNA damage, and of DNA repair factors necessary to remove it. Investigating the formation of such complexes has provided, and will probably continue to, relevant information about molecular mechanisms and spatiotemporal dynamics of the processes that constitute the first barrier of cell defense against genome instability and related diseases. In this review, we will summarize and discuss the use of in situ procedures to detect the formation of DNA-protein complexes after radiation-induced DNA damage. This type of analysis provides important information on the spatial localization and temporal resolution of the formation of such complexes, at the single-cell level, allowing the study of heterogeneous cell populations.

Role of estrogen receptors, P450 aromatase, PCNA and p53 in high-fat-induced impairment of spermatogenesis in rats

Obesity and overweight are frequently associated with male subfertility. To address new findings on the players involved in the obesity-induced impairment of spermatogenesis, we used a high-fat diet-induced overweight-rat model. Following four weeks of high-fat diet, the organization of seminiferous epithelium was affected, and tubules lumen showed immature/degenerated cells, typical signs of hormonal imbalance and testicular damage. Real-time PCR analysis allowed us to detect increased levels of ERα and decreased levels of aromatase CYP19 transcripts in testis, suggesting an increase in circulating estrogens derived from the accumulating adipose tissue rather than the induction of testicular estrogen synthesis. Moreover, in situ hybridization analysis showed an increased susceptibility towards estrogens in testis from high-fat fed rats, being ERs expressed not only in spermatogonia, as in control testis, but also in spermatids. Western blot and immunohistochemical analyses revealed an increase in the amount of p53 and PCNA, together with a change in their immunodetection, being the proteins localised on germ cells at different stages of maturation. Differences in p53 and PCNA expression may give evidence and be part of a cellular response to stress conditions and damage caused by the excessive intake of saturated fatty acids.

Exocellular extract of Fusarium oxysporum, fungus free, is able to permeate and act selectively in skin

The skin is an important gateway for Fusarium infection in humans. Our hypothesis is that metabolites produced by Fusarium oxysporum should change the barrier structure to permeate the skin. Male Wistar rats received a topical application of a solution (0.05 mg/mL) of Fusarium metabolites. The animals were euthanized 3, 6, 12, 24 h after and the skin was processed for immunostaining by laminin and E-cadherin to investigate whether the Fusarium metabolites can break the barrier of healthy skin. Other techniques were employed: H&E to study the morphology; metalloproteinase-9 (MMP-9), TUNEL, and PCNA immunostaining to evaluate the inflammation, cell death, and proliferation, respectively. There was an inflammatory response mainly centered in the dermis. Qualitatively, the skin of the experimental group showed reduced E-cadherin and laminin immunostaining at 3, 12, and 24 h. Higher intensity staining by TUNEL at 3 h, and PCNA at 6, 12, and 24 h. There was intense MMP-9 activity at 6, 12, and 24 h. None of analyses revealed any changes in the epidermis. It was concluded that the fraction was able to permeate the skin and act selectively in dermis, inducing inflammatory response, increasing MMP-9 immunostaining, inducing apoptosis, and reducing E-cadherin and laminin immunostaining.

Proliferating Cell Nuclear Antigen Immunoreaction in Adrenal Tumors

Aims and background

We studied, retrospectively, 33 cases of adrenal tumors of children at the Pediatric Endocrinology Unit, Children's Institute, São Paulo State University Medical School, from 1975 to 1993. All patients had at least 2 years of follow-up with a few exceptions.

Methods

Clinical follow-up data were correlated with histopathologic review, laboratory data and cell kinetic evaluation (based on detection of proliferating cell nuclear antigens).

Results

With one exception, all the patients had presented signs of androgen production and had high levels of dehydro-epiandrosterone-sulfate. Tumor weight evaluation represented a good parameter of neoplasm evolution: of 19 cases weighing less than 250 g, 17 had no evidence of disease after surgery, and 2 had an unfavorable prognosis. Of 14 cases weighing more than 250 g, only 1 had no evidence of disease and 13 had an unfavorable evolution.

Conclusions

Proliferating cell nuclear antigen (PCNA) was not helpful to evaluate adrenal neoplasm evolution: our study did not show any correlation between PCNA score and prognosis.

PCNA is recruited to irradiated chromatin in late S-phase and is most pronounced in G2 phase of the cell cycle

DNA repair is a complex process that prevents genomic instability. Many proteins play fundamental roles in regulating the optimal repair of DNA lesions. Proliferating cell nuclear antigen (PCNA) is a key factor that initiates recombination-associated DNA synthesis after injury. Here, in very early S-phase, we show that the fluorescence intensity of mCherry-tagged PCNA after local micro-irradiation was less than the fluorescence intensity of non-irradiated mCherry-PCNA-positive replication foci. However, PCNA protein accumulated at locally irradiated chromatin in very late S-phase of the cell cycle, and this effect was more pronounced in the following G2 phase. In comparison to the dispersed form of PCNA, a reduced mobile fraction appeared in PCNA-positive replication foci during S-phase, and we observed similar recovery time after photobleaching at locally induced DNA lesions. This diffusion of mCherry-PCNA in micro-irradiated regions was not affected by cell cycle phases. We also studied the link between function of PCNA and A-type lamins in late S-phase. We found that the accumulation of PCNA at micro-irradiated chromatin is identical in wild-type and A-type lamin-deficient cells. Only micro-irradiation of the nuclear interior, and thus the irradiation of internal A-type lamins, caused the fluorescence intensity of mCherry-tagged PCNA to increase. In summary, we showed that PCNA begins to play a role in DNA repair in late S-phase and that PCNA function in repair is maintained during the G2 phase of the cell cycle. However, PCNA mobility is reduced after local micro-irradiation regardless of the cell cycle phase.

MCM2 and TIP30 are prognostic markers in squamous cell/adenosquamous carcinoma and adenocarcinoma of the gallbladder

The clinicopathological and biological characteristics of squamous cell/adenosquamous carcinoma (SC/ASC) of the gallbladder remain to be fully elucidated, due to the fact that it is a rare gallbladder cancer subtype. In the current study, the expression of minichromosome maintenance complex component 2 (MCM2) and HIV‑1 tat interactive protein 2 (TIP30) was measured in 46 cases of SC/ASC and 80 adenocarcinomas (AC) using immunohistochemistry. Positive MCM2 and negative TIP30 expression were significantly associated with large tumor size, high TNM stage, invasion, lymph node metastasis and lack of surgical curability in SC/ASC and AC. Positive MCM2 and negative TIP30 expression were significantly associated with poor differentiation in AC, whereas only MCM2 was correlated with differentiation in SC/ASC. Univariate Kaplan‑Meier analysis demonstrated that positive MCM2 and negative TIP30 expression, the degree of differentiation, tumor size, TNM stage, invasion, lymph node metastasis and surgical curability were significantly associated with post‑operative survival in patients with SC/ASC and AC. Multivariate Cox regression analysis demonstrated that positive MCM2 and negative TIP30 expression, the degree of differentiation, tumor size, TNM stage, invasion, lymph node metastasis and lack of surgical curability were also independent predictors of poor prognosis in patients with SC/ASC and AC. These data suggest that positive MCM2 and negative TIP30 expression are closely correlated with the clinical, pathological and biological parameters, in addition to poor prognosis in patients with gallbladder cancer.

Proliferation of Perivascular Macrophages Contributes to the Development of Encephalitic Lesions in HIV-Infected Humans and in SIV-Infected Macaques

The aim of the present study was to investigate if macrophage proliferation occurs in the brain during simian immunodeficiency virus (SIV) infection of adult macaques. We examined the expression of the Ki-67 proliferation marker in the brains of uninfected and SIV-infected macaques with or without encephalitis. Double-label immunohistochemistry using antibodies against the pan-macrophage marker CD68 and Ki-67 showed that there was a significant increase in CD68+Ki-67+ cells in macaques with SIV encephalitis (SIVE) compared to uninfected and SIV-infected animals without encephalitis, a trend that was also confirmed in brain samples from patients with HIV encephalitis. Multi-label immunofluorescence for CD163 and Ki-67 confirmed that the vast majority of Ki-67+ nuclei were localized to CD163+ macrophages in perivascular cuffs and lesions. The proliferative capacity of Ki-67+ perivascular macrophages (PVM) was confirmed by their nuclear incorporation of bromodeoxyuridine. Examining SIVE lesions, using double-label immunofluorescence with antibodies against SIV-Gag-p28 and Ki-67, showed that the population of Ki-67+ cells were productively infected and expanded proportionally with lesions. Altogether, this study shows that there are subpopulations of resident PVM that express Ki-67 and are SIV-infected, suggesting a mechanism of macrophage accumulation in the brain via PVM proliferation.

Sequential Alteration of Apoptosis, p53 Expression, and Cell Proliferation in the Rat Pancreas Treated with 4-Hydroxyaminoquinoline 1-Oxide

Changes in p53 expression, apoptosis and cell proliferation after treatment with 4-hydroxyaminoquinoline 1-oxide (4HAQO) were investigated in the rat pancreas and liver, target and nontarget organs for tumorigenesis, respectively. Male rats were given a single intravenous injection of 4HAQO at a dose of 20 mg/kg body weight and control rats received vehicle alone and were euthanized after 2—72 hours. Pancreata and livers were removed for histopathological examination, immunohistochemistry for p53 protein, PCNA and Ki-67, and TUNEL labeling and electron microscopic observation for detecting apoptosis. In the pancreas, p53 expression and apoptosis were significantly increased first at 4 and 6 hours, respectively, while no change was evident in the liver. The rates peaked at 24 hours, consistent with the peak for PCNA-labeling, while Ki-67-labeling rates peaked at 72 hours. Electron microscopically, apoptotic changes in pancreatic acinar cells were observed after 2 hours. No significant apoptosis, p53 expression or cell proliferation were noted in the pancreatic tissues of the control rats nor in liver cells regardless of 4HAQO treatment. Taken together with our previous data, the results suggest that apoptosis, p53 expression, and enhanced cell replication are closely related phenomena involved in the carcinogenesis of 4HAQO following DNA adduct formation.

Proliferating Cell Nuclear Antigen—A Marker for Ovarian Follicle Counts

Enumerating ovarian follicles is an effective way to estimate the extent of ovarian toxicity in female rodents exposed to xenobiotics. Differential follicle counts are useful in safety assessment bioassays and in interspecies extrapolation of ovarian toxicity. Counting the follicles in H&E-stained sections is labor intensive, tedious, and costly. In the present study we demonstrated that in rat formalin-fixed, paraffin-embedded ovary sections follicles of all degrees of maturity can be visualized by the use of antibody directed against proliferating cell nuclear antigen (PCNA). Follicles are easily distinguished from ovarian background with the ability to detect and identify primordial follicles being enhanced. This translates into a significant decrease in variability of follicle counts, labor, and cost. Specifically, variability dropped from 11% to 0.2%, the counting time was reduced by 46%, and the cost by 48%.

Proliferating Cell Nuclear Antigen in Premalignancy and Oral Squamous Cell Carcinoma

INTRODUCTION

Cancer has multifactorial aetiology and is a multistep process involving initiation, promotion and tumour progression. Cellular proliferation is one of the important indicators for the biologic aggressiveness of a malignant lesion. The dysregulated proliferation may be a significant change to determine the potential prognosis of various malignant tumours.

AIM

The aim of this study was to evaluate the expression of proliferating cell nuclear antigen (PCNA) as an indicator for clinical aggressiveness in oral premalignancy and squamous cell carcinoma.

MATERIALS AND METHODS

A total of 50 blocks were taken from the Department of Oral Pathology which was diagnosed previously histopathologically. It comprised of normal oral mucosa (10), dysplasia (10) and grades of oral squamous cell carcinoma (30) of patients between the age group of 40-60 years. From each block, sections of 4 micro metre thicknesses were prepared and placed on poly- L lysine coated slides. These sections were immunohistochemically stained with monoclonal proliferating cell antibody (PC10). The stained slides were evaluated by a single examiner for cell count.

RESULTS

A comparison between study groups and controls showed a probability value (p-value) < 0.05. Significant increase in the proliferative index from the normal to oral squamous cell carcinoma was noticed. Poorly differentiated squamous cell carcinoma showed maximum proliferative index followed by moderately differentiated, well differentiated squamous cell carcinoma, dysplasia and normal mucosa.

CONCLUSION

Present study concluded that PCNA index can be used to assess the proliferation and aggressiveness in dysplasia and different grades oral squamous cell carcinoma.

Subchronic Arsenic Exposure Induces Anxiety-Like Behaviors in Normal Mice and Enhances Depression-Like Behaviors in the Chemically Induced Mouse Model of Depression

Accumulating evidence implicates that subchronic arsenic exposure causes cerebral neurodegeneration leading to behavioral disturbances relevant to psychiatric disorders. However, there is still little information regarding the influence of subchronic exposure to arsenic-contaminated drinking water on mood disorders and its underlying mechanisms in the cerebral prefrontal cortex. The aim of this study is to assess the effects of subchronic arsenic exposure (10 mg/LAs2O3 in drinking water) on the anxiety- and depression-like behaviors in normal mice and in the chemically induced mouse model of depression by reserpine pretreatment. Our findings demonstrated that 4 weeks of arsenic exposure enhance anxiety-like behaviors on elevated plus maze (EPM) and open field test (OFT) in normal mice, and 8 weeks of arsenic exposure augment depression-like behaviors on tail suspension test (TST) and forced swimming test (FST) in the reserpine pretreated mice. In summary, in this present study, we demonstrated that subchronic arsenic exposure induces only the anxiety-like behaviors in normal mice and enhances the depression-like behaviors in the reserpine induced mouse model of depression, in which the cerebral prefrontal cortex BDNF-TrkB signaling pathway is involved. We also found that eight weeks of subchronic arsenic exposure are needed to enhance the depression-like behaviors in the mouse model of depression. These findings imply that arsenic could be an enhancer of depressive symptoms for those patients who already had the attribute of depression.

Minichromosome Maintenance (MCM) Family as potential diagnostic and prognostic tumor markers for human gliomas

Background

Gliomas are the most common type of all central nervous system tumors. Almost all patients diagnosed with these tumors have a poor prognostic outcome. We aimed to identify novel glioma prognosis-associated candidate genes.

Methods

We applied WebArrayDB software to span platform integrate and analyze the microarray datasets. We focused on a subset of the significantly up-regulated genes, the minichromosome maintenance (MCM) family. We used frozen glioma samples to predict the relationship between the expression of MCMs and patients outcome by qPCR and western blot.

Results

We found that MCMs expression was significantly up-regulated in glioma samples. MCM2-7 and MCM10 expressions were associated with WHO tumor grade. High MCM2 mRNA expression appeared to be strongly associated with poor overall survival in patients with high grade glioma. Furthermore, we report that MCM7 is strongly correlated with patient outcome in patients with WHO grade II-IV tumor. MCM3 expression was found to be up-regulated in glioma and correlated with overall survival in patients with WHO grade III tumor. MCM2, MCM3 and MCM7 expression levels were of greater prognostic relevance than histological diagnosis according to the current WHO classification system.

Conclusions

High expression of MCM 2, MCM3 and MCM7 mRNA correlated with poor outcome and may be clinically useful molecular prognostic markers in glioma.

Alcohol exposure inhibits adult neural stem cell proliferation

Alcohol exposure can reduce adult proliferation and/or neurogenesis, but its impact on the ultimate neurogenic precursors, neural stem cells (NSCs), has been poorly addressed. Accordingly, the impact of voluntary consumption of alcohol on NSCs in the subventricular zone (SVZ) of the lateral ventricle was examined in this study. The NSC population in adult male C57BL/6J mice was measured after voluntary alcohol exposure in a two-bottle choice task using the neurosphere assay, while the number of NSCs that had proliferated 2 weeks prior to tissue collection was indexed using bromodeoxyuridine (BrdU) retention. There was a significant decrease in the number of BrdU-retaining cells in alcohol-consuming mice compared with controls, but no difference in the number of neurosphere-forming cells that could be derived from the SVZ of alcohol-consuming mice compared with controls. Additionally, PCNA-labeled cells in the SVZ tended to be lower, but there was no difference in BrdU labeling in the dentate gyrus following alcohol exposure. To determine alcohol's direct impact on NSCs and their progeny, neurospheres derived from naïve mice were treated with alcohol in vitro. Neurosphere formation was reduced by 100 mM alcohol without reducing cell viability. These findings are the first to assess the impact of moderate voluntary alcohol consumption on selective measures of adult NSCs and indicate that such exposure alters NSC proliferation dynamics in vivo and alcohol has direct but dissociable effects on the expansion and viability on NSCs and their progeny in vitro.

18 F-fluorothymidine uptake in follicular lymphoma and error-prone DNA repair

Background

We observed a disproportional 18 F-fluorothymidine (F-FLT) uptake in follicular lymphoma (FL) relative to its low cell proliferation. We tested the hypothesis that the ‘excess’ uptake of 18 F-FLT in FL is related to error-prone DNA repair and investigated whether this also contributes to 18 F-FLT uptake in diffuse large B cell lymphoma (DLBCL).

Methods

We performed immunohistochemical stainings to assess the pure DNA replication marker MIB-1 as well as markers of both DNA replication and repair like PCNA, TK-1 and RPA1 on lymph node biopsies of 27 FLs and 35 DLBCLs. In 7 FL and 15 DLBCL patients, 18 F-FLT-PET had been performed.

Results

18 F-FLT uptake was lower in FL than in DLBCL (median SUVmax 5.7 vs. 8.9, p = 0,004), but the ratio of 18 F-FLT-SUVmax to percentage of MIB-1 positive cells was significantly higher in FL compared with DLBCL (p = 0.001). The median percentage of MIB-1 positive cells was 10% (range, 10% to 20%) in FL and 70% (40% to 80%) in DLBCL. In contrast, the median percentages of PCNA, TK-1 and RPA1 positive cells were 90% (range, 80 to 100), 90% (80 to 100) and 100% (80 to 100) in FL versus 90% (60 to 100), 90% (60 to 100) and 100% (80 to 100) in DLBCL, respectively.

Conclusions

This is the first demonstration of a striking discordance between 18 F-FLT uptake in FL and tumour cell proliferation. High expression of DNA replication and repair markers compared with the pure proliferation marker MIB-1 in FL suggests that this discordance might be due to error-prone DNA repair. While DNA repair-related 18 F-FLT uptake considerably contributes to 18 F-FLT uptake in FL, its contribution to 18 F-FLT uptake in highly proliferative DLBCL is small. This apparently high contribution of DNA repair to the 18 F-FLT signal in FL may hamper studies where 18 F-FLT is used to assess response to cytostatic therapy or to distinguish between FL and transformed lymphoma.

Replication proteins and human disease

In this article, we discuss the significance of DNA replication proteins in human disease. There is a broad range of mutations in genes encoding replication proteins, which result in several distinct clinical disorders that share common themes. One group of replication proteins, the MCMs, has emerged as effective biomarkers for early detection of a range of common cancers. They offer practical and theoretical advantages over other replication proteins and have been developed for widespread clinical use.

N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) triggers MSH2 and Cdt2 protein-dependent degradation of the cell cycle and mismatch repair (MMR) inhibitor protein p21Waf1/Cip1

p21(Waf1/Cip1) protein levels respond to DNA damage; p21 is induced after ionizing radiation, but degraded after UV. p21 degradation after UV is necessary for optimal DNA repair, presumably because p21 inhibits nucleotide excision repair by blocking proliferating cell nuclear antigen (PCNA). Because p21 also inhibits DNA mismatch repair (MMR), we investigated how p21 levels respond to DNA alkylation by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), which triggers the MMR system. We show that MNNG caused rapid degradation of p21, and this involved the ubiquitin ligase Cdt2 and the proteasome. p21 degradation further required MSH2 but not MLH1. p21 mutants that cannot bind PCNA or cannot be ubiquitinated were resistant to MNNG. MNNG induced the formation of PCNA complexes with MSH6 and Cdt2. Finally, when p21 degradation was blocked, MNNG treatment resulted in reduced recruitment of MMR proteins to chromatin. This study describes a novel pathway that removes p21 to allow cells to efficiently activate the MMR system.

Potential role of minichromosome maintenance protein 2 as a screening biomarker in esophageal cancer high-risk population in China

Minichromosome maintenance proteins are novel proliferative markers that have been proposed as diagnostic markers in many cancers. We evaluated the potential role of minichromosome maintenance protein 2 as a screening biomarker and compared it with proliferating cell nuclear antigen and Ki67 in a population survey of esophageal squamous cell carcinoma. A total of 299 esophageal samples from a high-risk region in China, including 171 from an endoscopy population survey, 30 from brushing cytology, and 98 from surgery and autopsy, underwent immunostaining with minichromosome maintenance protein 2, proliferating cell nuclear antigen, and Ki67 antibodies. Minichromosome maintenance protein 2 expression was confined to the proliferative compartment of normal and abnormal esophageal epithelium and particularly manifested in the surface layer of dysplasia and carcinoma in situ. The expression of proliferating cell nuclear antigen and Ki67 was positively correlated with that of minichromosome maintenance protein 2 (r(s) >0.39, P < .01); but their positive nuclei seldom reached the surface layer, and the labeling indices were significantly lower than those for minichromosome maintenance protein 2 in dysplasia (P < .05) and carcinoma in situ (P < .001). The sensitivity and specificity of minichromosome maintenance protein 2 in diagnosing dysplasia were 91.3% and 61.8%, respectively, higher than those for proliferating cell nuclear antigen (88.4% and 47.1%) and Ki67 (78.3% and 57.8%). Nine of 10 cancer and paracancerous surface-brushing samples expressed minichromosome maintenance protein 2, and the detection was higher than that for proliferating cell nuclear antigen (8/10 and 7/10) and Ki67 (7/10 and 7/10). However, none of 10 normal surface-brushing samples expressed the 3 markers. Minichromosome maintenance protein 2 is more sensitive and specific than proliferating cell nuclear antigen and Ki67 in indicating esophageal dysplasia. Minichromosome maintenance protein 2 immunostaining combined with surface brushing could be valuable in screening patients at high risk of cancer in mass surveys.

MCM-2 and MCM-5 expression in gastric adenocarcinoma: clinical significance and comparison with Ki-67 proliferative marker

BACKGROUND

Minichromosome maintenance (MCM) proteins are essential components of DNA replication, being related to cell proliferation, and serve as useful biomarkers for cancer screening, surveillance and prognosis. The aim of the present study was to evaluate the clinical significance of MCM-2 and MCM-5 expression in gastric adenocarcinoma in comparison with Ki-67 proliferative marker.

METHODS

MCM-2, MCM-5 and Ki-67 expression was assessed immunohistochemically in 66 tumoral samples of gastric adenocarcinoma patients and was statistically analyzed in relation to clinicopathological characteristics and patient survival.

RESULTS

MCM-2 expression did not show significant associations with any clinicopathological parameters, while Ki-67 expression was merely significantly associated with tumor size (P = 0.0150). MCM-2 and Ki-67 expression were more frequently in intestinal (median values: 67.5 and 60%) compared to diffuse-type (median values: 60 and 45%) gastric adenocarcinoma cases without though reaching statistical significance (P > 0.05). MCM-5 expression was significantly associated with tumor size (P = 0.0295), presence of lymph node metastases (P = 0.0216) and tumor histopathological stage (P = 0.0098). Patients presenting high MCM-5 expression had significantly shorter survival times (log-rank test, P = 0.0042), whereas neither MCM-2 nor Ki-67 expression showed significant prognostic value (log-rank test, P = 0.9618 and P = 0.7174, respectively). In multivariate analysis, patient age, histopathological stage and grade of differentiation, but not MCM-5 expression, were identified as independent prognostic factors (Cox regression analysis, P = 0.0097, P = 0.0195, P = 0.0035 and P = 0.3245, respectively).

CONCLUSIONS

The present study showed that MCM-5 expression was associated with clinicopathological parameters in gastric adenocarcinoma. However, further studies highlighting the distinct impact of the two histopathological types, intestinal and diffuse, are warranted to delineate whether MCMs could be used as diagnostic and prognostic markers in gastric neoplasia.

Minichromosome maintenance protein expression according to the grade of atypism in actinic keratosis

The minichromosome maintenance (MCM) family is a group of proteins that are key initiation factors for DNA replication and are expressed only in cycling cells. Recent studies on various cancerous conditions have shown that MCM proteins are better markers for malignant cells compared to other proliferative markers. It has been also proven that MCM proteins are independent prognostic factors. The aim of this study was to characterize the pattern and frequency of MCM 2 protein expression in actinic keratosis (AK) and determine whether the expression is correlated with the degree of histological atypism. Biopsy samples of 34 patients who had been diagnosed as AK were used in this study. Samples were divided into three groups (grade I, grade II, and grade III) according to the degree of atypism. Immunohistochemical staining for MCM 2 protein, Ki-67, and proliferating cell nuclear antigen was performed, and the number of positively staining cells per unit area (10⁻⁴ μm²) was calculated for evaluation of immunoreactivity. MCM 2 protein was expressed in atypical keratinocytes in AK. Mean numbers of immunoreactive cells positive for MCM 2 were 165.1 in grade I, 304.5 in grade II, and 513.3 in grade III. Moreover, the correlation between the immunoreactivity for MCM 2 protein and AK grade was significantly more positive than that for other markers. Thus, we suggest that MCM 2 protein is a reliable marker for diagnosing and grading AK and further could be hypothesized as an important prognostic factor.

Revelation of p53-independent function of MTA1 in DNA damage response via modulation of the p21 WAF1-proliferating cell nuclear antigen pathway

Although metastasis-associated protein 1 (MTA1), a component of the nucleosome remodeling and deacetylase (NuRD) complex, is a DNA-damage response protein and regulates p53-dependent DNA repair, it remains unknown whether MTA1 also participates in p53-independent DNA damage response. Here, we provide evidence that MTA1 is a p53-independent transcriptional corepressor of p21(WAF1), and the underlying mechanism involves recruitment of MTA1-histone deacetylase 2 (HDAC2) complexes onto two selective regions of the p21(WAF1) promoter. Accordingly, MTA1 depletion, despite its effect on p53 down-regulation, superinduces p21(WAF1), increases p21(WAF1) binding to proliferating cell nuclear antigen (PCNA), and decreases the nuclear accumulation of PCNA in response to ionizing radiation. In support of a p53-independent role of MTA1 in DNA damage response, we further demonstrate that induced expression of MTA1 in p53-null cells inhibits p21(WAF1) promoter activity and p21(WAF1) binding to PCNA. Consequently, MTA1 expression in p53-null cells results in increased induction of gamma H2AX foci and DNA double strand break repair, and decreased DNA damage sensitivity following ionizing radiation treatment. These findings uncover a new target of MTA1 and the existence of an additional p53-independent role of MTA1 in DNA damage response, at least in part, by modulating the p21(WAF1)-PCNA pathway, and thus, linking two previously unconnected NuRD complex and DNA-damage response pathways.

Human Timeless and Tipin stabilize replication forks and facilitate sister-chromatid cohesion

The Timeless-Tipin protein complex has been reported to be important for replication checkpoint and normal DNA replication processes. However, the precise mechanisms by which Timeless-Tipin preserves genomic integrity are largely unclear. Here, we describe the roles of Timeless-Tipin in replication fork stabilization and sister chromatid cohesion. We show in human cells that Timeless is recruited to replication origin regions and dissociate from them as replication proceeds. Cdc45, which is known to be required for replication fork progression, shows similar patterns of origin association to those of Timeless. Depletion of Timeless-Tipin causes chromosome fragmentation and defects in damage repair in response to fork collapse, suggesting that it is required for replication fork maintenance under stress. We also demonstrate that depletion of Timeless-Tipin impairs sister chromatid cohesion and causes a defect in mitotic progression. Consistently, Timeless-Tipin co-purifies with cohesin subunits and is required for their stable association with chromatin during S phase. Timeless associates with the cohesion-promoting DNA helicase ChlR1, which, when overexpressed, partially alleviates the cohesion defect of cells depleted of Timeless-Tipin. These results suggest that Timeless-Tipin functions as a replication fork stabilizer that couples DNA replication with sister chromatid cohesion established at replication forks.

PCNA on the crossroad of cancer

Cancer is caused by genetic changes that often arise following failure to accurately replicate the DNA. PCNA (proliferating-cell nuclear antigen) forms a ring around the DNA to facilitate and control DNA replication. Emerging evidence suggests that PCNA is at the very heart of many essential cellular processes, such as DNA replication, repair of DNA damage, chromatin structure maintenance, chromosome segregation and cell-cycle progression. Progression of the DNA replication forks can be blocked by DNA lesions, formed either by endogenous damage or by exogenous agents, for instance anticancer drugs. Cellular response often results in change of PCNA function triggered either by specific post-translational modification of PCNA (i.e. ubiquitylation) or by exchange of its interaction partners. This puts PCNA in a central position in determining the fate of the replication fork. In the present article, we review PCNA modifications and interaction partners, and how those influence the course of events at replication forks, which ultimately determines both tumour progression as well as the outcome of anticancer treatment.

FANCI protein binds to DNA and interacts with FANCD2 to recognize branched structures

In this study, we report that the purified wild-type FANCI (Fanconi anemia complementation group I) protein directly binds to a variety of DNA substrates. The DNA binding domain roughly encompasses residues 200–1000, as suggested by the truncation study. When co-expressed in insect cells, a small fraction of FANCI forms a stable complex with FANCD2 (Fanconi anemia complementation group D2). Intriguingly, the purified FANCI-FANCD2 complex preferentially binds to the branched DNA structures when compared with either FANCI or FANCD2 alone. Co-immunoprecipitation with purified proteins indicates that FANCI interacts with FANCD2 through its C-terminal amino acid 1001–1328 fragment. Although the C terminus of FANCI is dispensable for direct DNA binding, it seems to be involved in the regulation of DNA binding activity. This notion is further enhanced by two C-terminal point mutations, R1285Q and D1301A, which showed differentiated DNA binding activity. We also demonstrate that FANCI forms discrete nuclear foci in HeLa cells in the absence or presence of exogenous DNA damage. The FANCI foci are colocalized perfectly with FANCD2 and partially with proliferating cell nuclear antigen irrespective of mitomycin C treatment. An increased number of FANCI foci form and become resistant to Triton X extraction in response to mitomycin C treatment. Our data suggest that the FANCI-FANCD2 complex may participate in repair of damaged replication forks through its preferential recognition of branched structures.

Histone deacetylase inhibitor sodium butyrate enhances the cell killing effect of psoralen plus UVA by attenuating nucleotide excision repair

The use of histone deacetylase inhibitors (HDACI), a promising new class of antineoplastic agents, in combination with cytotoxic agents, such as ionizing radiation and anticancer drugs, has been attracting attention. In this study, we found that sodium butyrate (SB), a widely studied HDACI, remarkably enhanced the cell killing effect of psoralen plus UVA (PUVA) in several cancer cell lines, including skin melanoma. Although a single treatment with PUVA or SB did not greatly affect cell survival, combined treatment with SB and PUVA induced marked apoptosis within 24 hours. The SB-induced augmentation of the cell killing effect was more dramatic in combination with PUVA than with anticancer drugs. The number of double-strand breaks that formed during the repair of PUVA-induced interstrand cross-links (ICL) in chromosomal DNA was significantly reduced in SB-pretreated cells, suggesting that the ability to repair ICL was attenuated by SB. In addition, the incorporation of bromodeoxyuridine and the formation of repair foci of proliferating cell nuclear antigen after PUVA treatment, associated with nucleotide excision repair (NER) in the removal of ICL, were not observed in SB-pretreated cells. Furthermore, the repair kinetics of UV-induced cyclobutane pyrimidine dimers (well-known photolesions repaired by NER) were much slower in SB-pretreated cells than in untreated cells. These results indicated that the enhanced cell killing effect of PUVA by SB was attributable to an attenuated ability to repair DNA and, especially, dysfunctional NER.

Clinical significance of MCM-2 and MCM-5 expression in colon cancer: association with clinicopathological parameters and tumor proliferative capacity

Minichromosome maintenance (MCM) proteins are essential components of DNA replication, being related to cell proliferation, and serve as useful markers for cancer screening, surveillance, and prognosis. Our aim was to examine the clinical significance of MCM-2 and MCM-5 protein expression in colon cancer and to evaluate the association with various clinicopathological characteristics and tumor proliferative capacity. Immunohistochemical expression of MCM-2 and MCM-5 was performed on paraffin-embedded malignant tissue sections obtained from 96 patients with colon cancer. MCM-2 and MCM-5 expression was correlated with different clinicopathological characteristics, proliferative capacity (Ki-67 labeling index), and p53 cell-cycle regulator expression. MCM-2 and Ki-67 expression was significantly associated with the tumors' histological grade (P = 0.003), existence of nodular metastases (N) (P = 0.003 and P = 0.030, respectively), malignancy on adenoma (P = 0.029 and P = 0.024, respectively), and vascular invasion (P = 0.010 and P = 0.011, respectively). MCM-2 expression was additionally associated with Dukes' stage (P = 0.005). Significant positive relationships were found between the expression of MCM-2 or MCM-5 proteins and that of Ki-67 protein (r = 0.963, P-value < 0.001, and r = 0.738, P-value < 0.001, respectively), as well as between MCM-2 and MCM-5 proteins (r = 0.745, P-value < 0.001). Significant positive relationships were also observed between the expression of MCM-2 or MCM-5 proteins and that of p53 protein; however, they were consistently lower than the corresponding with Ki-67 protein. No significant association was observed between MCM-5 protein expression and the clinicopathological characteristics examined. The current data suggest that MCM-2 protein expression is significantly associated with important clinicopathological characteristics for patients' management, being correlated with the cell proliferation state in colon cancer.

The highly conserved nuclear lamin Ig-fold binds to PCNA: its role in DNA replication

This study provides insights into the role of nuclear lamins in DNA replication. Our data demonstrate that the Ig-fold motif located in the lamin C terminus binds directly to proliferating cell nuclear antigen (PCNA), the processivity factor necessary for the chain elongation phase of DNA replication. We find that the introduction of a mutation in the Ig-fold, which alters its structure and causes human muscular dystrophy, inhibits PCNA binding. Studies of nuclear assembly and DNA replication show that lamins, PCNA, and chromatin are closely associated in situ. Exposure of replicating nuclei to an excess of the lamin domain containing the Ig-fold inhibits DNA replication in a concentration-dependent fashion. This inhibitory effect is significantly diminished in nuclei exposed to the same domain bearing the Ig-fold mutation. Using the crystal structures of the lamin Ig-fold and PCNA, molecular docking simulations suggest probable interaction sites. These findings also provide insights into the mechanisms underlying the numerous disease-causing mutations located within the lamin Ig-fold.

Characterization of plant XRCC1 and its interaction with proliferating cell nuclear antigen

In plants, there are no DNA polymerase beta (Pol beta) and DNA ligase III (Lig3) genes. Thus, the plant short-patch base excision repair (short-patch BER) pathway must differ considerably from that in mammals. We characterized the rice (Oryza Sativa L. cv. Nipponbare) homologue of the mammalian X-ray repair cross complementing 1 (XRCC1), a well-known BER protein. The plant XRCC1 lacks the N-terminal domain (NTD) which is required for Pol beta binding and is essential for mammalian cell survival. The recombinant rice XRCC1 (OsXRCC1) protein binds single-stranded DNA (ssDNA) as well as double-stranded DNA (dsDNA) and also interacts with rice proliferating cell nuclear antigen (OsPCNA) in a pull-down assay. Through immunoprecipitation, we demonstrated that OsXRCC1 forms a complex with PCNA in vivo. OsXRCC1 mRNA was expressed in all rice organs and was induced by application of bleomycin, but not of MMS, H(2)O(2) or UV-B. Bleomycin also increased the fraction of OsXRCC1 associated with chromatin. These results suggest that OsXRCC1 contributes to DNA repair pathways that differ from the mammalian BER system.

Expression of minichromosome maintenance 5 protein in proliferative and malignant skin diseases

BACKGROUND

The entire minichromosome maintenance (MCM) family (MCM2-7) play roles in the initiation and elongation of DNA replication. Many studies have demonstrated that MCM proteins may be better indicators of a wide variety of proliferative or cancer cells in malignant tissues.

OBJECTIVES

To characterize the pattern and frequency of MCM5 expression in proliferative and malignant skin diseases in comparison with those of proliferating cell nuclear antigen (PCNA).

METHODS

Twelve normal skin specimens, 12 specimens of psoriasis, 21 specimens of bowenoid papulosis (BP), 16 specimens of Bowen's disease (BD), 38 specimens of skin squamous cell carcinoma (SCC), and 11 specimens of basal cell carcinoma (BCC) were subjected to immunohistochemical staining for MCM5 and PCNA. Results MCM5 protein was expressed in the lower layers of epidermis in psoriasis, while MCM5 protein were present throughout the tumor cells in BP, BD, and moderately/poorly differentiated SCC. MCM5 protein was preferentially expressed in the periphery of well-differentiated SCC or bigger nests of BCC, although some small nests of BCC seemingly showed diffuse staining patterns. The percentages of MCM5-positive cells were 15.7% in normal skin, 21.8% in psoriasis, 75.9% in BP, 83.8% in BD, 63.5% in well-differentiated SCC, 77.5% in moderately differentiated SCC, 79.8% in poorly differentiated SCC, and 21.2% in BCC in average. Well-differentiated SCC showed a significantly lower percentage of positive cells than did moderately differentiated SCC or poorly differentiated SCC. MCM5 staining basically show a similar staining pattern to that of PCNA, but more cells tended to be stained with MCM5 than with PCNA.

CONCLUSIONS

Our results demonstrate pattern and frequency of MCM5 expression in various skin diseases and suggest that MCM5 may be a useful marker to detect cell proliferation in skin tissue sections.

TGF-beta1-induced cardiac myofibroblasts are nonproliferating functional cells carrying DNA damages

TGF-beta1 induces differentiation and total inhibition of cardiac MyoFb cell division and DNA synthesis. These effects of TGF-beta1 are irreversible. Inhibition of MyoFb proliferation is accompanied with the expression of Smad1, Mad1, p15Ink4B and total inhibition of telomerase activity. Surprisingly, TGF-beta1-activated MyoFbs are growth-arrested not only at G1-phase but also at S-phase of the cell cycle. Staining with TUNEL indicates that these cells carry DNA damages. However, the absolute majority of MyoFbs are non-apoptotic cells as established with two apoptosis-specific methods, flow cytometry and caspase-dependent cleavage of cytokeratin 18. Expression in MyoFbs of proliferative cell nuclear antigen even in the absence of serum confirms that these MyoFbs perform repair of DNA damages. These results suggest that TGF-beta1-activated MyoFbs can be growth-arrested by two checkpoints, the G1/S checkpoint, which prevents cells from entering S-phase and the intra-S checkpoint, which is activated by encountering DNA damage during the S phase or by unrepaired damage that escapes the G1/S checkpoint. Despite carrying of the DNA damages TGF-beta1-activated MyoFbs are highly functional cells producing lysyl oxidase and contracting the collagen matrix.

Expression of proliferation markers and cell cycle regulators in T cell lymphoproliferative skin disorders

BACKGROUND

Abnormal cell proliferation, which results from deregulation of the cell cycle, is fundamental in tumorigenesis.

OBJECTIVES

To investigate the expression of proliferation markers and cell cycle regulators in a range of T cell lymphoproliferative skin diseases.

METHODS

We studied skin specimens of 51 patients with parapsoriasis (PP), mycosis fungiodes (MF), or lymphomatoid papulosis (LyP). Immunohistochemistry was performed for Ki-67, proliferating cell nuclear antigen (PCNA), minichromosome maintenance protein 7 (MCM7), and p21.

RESULTS

MF with stage IIB-IV and LyP showed a significantly greater number of Ki-67-positive cells than PP (P=0.02 and 0.001) and MF I-IIA (P=0.019 and 0.003), respectively. MCM7 staining revealed significantly higher labeling indices for MF IIB-IV and LyP when compared to PP (P=0.002 and 0.04) and MF I-IIA (P=0.0005 and 0.01), respectively. Compared to PP and MF I-IIA, MF IIB-IV was associated with significantly higher labeling indices for PCNA (P=0.006 and 0.0004). p21 staining was significantly increased in MF IIB-IV and LyP when compared to PP (P=0.006 and 0.003) and MF I-IIA (P=0.003). However, p21 staining was all in all very weak.

CONCLUSIONS

Ki-67 and PCNA seem to be useful immunohistological parameters for the correlation with the clinical stage of MF. In the differentiation and prognostication of T cell lymphoproliferative skin disorders, MCM7 may serve as a novel biomarker which is, in contrast to Ki-67 and PCNA, stable throughout the cell cycle.

Electroconvulsive seizures stimulate glial proliferation and reduce expression of Sprouty2 within the prefrontal cortex of rats

BACKGROUND

Reductions in cell number are found within the medial prefrontal cortex (PFC) in major depression and bipolar disorder, conditions for which electroconvulsive therapy (ECT) is a highly effective treatment. We investigated whether electroconvulsive seizure (ECS) in rats stimulates cellular proliferation in the PFC immediately and four weeks after the treatments. In parallel, we examined if ECS also alters the expression of Sprouty2 (SPRY2), an inhibitor of cell proliferation.

METHODS

Sprague-Dawley rats received 10 days of ECS treatments and bromodeoxyuridine (BrdU) injections. After a four week survival period, we estimated the density and number of BrdU-, proliferating cell nuclear antigen (PCNA)-, and SPRY2-immunoreactive cells in the medial (infralimbic) PFC (ILPFC). We also determined the percentage of BrdU-labeled cells that were immunoreactive for markers specific to oligodendrocytes, astrocytes, endothelial cells and neurons.

RESULTS

ECS dramatically enhanced the proliferation of new cells in the infralimbic PFC, and this effect persisted four weeks following the treatments. The percentage of new cells expressing oligodendrocyte precursor cell markers increased slightly following ECS. In contrast, ECS dramatically reduced the number of cells expressing SPRY2.

CONCLUSIONS

ECS stimulates long-lasting increases in glial proliferation within the ILPFC. ECS also decreases SPRY2 expression in the same region, an effect that might contribute to increased glial proliferation.

Characterization of a second proliferating cell nuclear antigen (PCNA2) from Drosophila melanogaster

The eukaryotic DNA polymerase processivity factor, proliferating cell nuclear antigen, is an essential component in the DNA replication and repair machinery. In Drosophila melanogaster, we cloned a second PCNA cDNA that differs from that encoded by the gene mus209 (for convenience called DmPCNA1 in this article). The second PCNA cDNA (DmPCNA2) encoded a 255 amino acid protein with 51.7% identity to DmPCNA1, and was ubiquitously expressed during Drosophila development. DmPCNA2 was localized in nuclei as a homotrimeric complex and associated with Drosophila DNA polymerase delta and epsilonin vivo. Treatment of cells with methyl methanesulfonate or hydrogen peroxide increased the amount of both DmPCNA2 and DmPCNA1 associating with chromatin, whereas exposure to UV light increased the level of association of only DmPCNA1. Our observations suggest that DmPCNA2 may function as an independent sliding clamp of DmPCNA1 when DNA repair occurs.

Expression analysis of PCNA gene in chronic myelogenous leukemia--combined application of siRNA silencing and expression arrays

Imatinib metylase is the first choice treatment for BCR/ABL positive chronic myelogenous leukemia (CML). However, as some CML patients develop resistance to imatinib therapy, there is a significant interest in development of alternative treatment strategies, such as identifying targets other than BCR/ABL that may participate in CML. Previously, we demonstrated strong PCNA up-regulation in CML patients. To further study its role in CML pathogenesis, we performed silencing of PCNA expression followed by array experiments. PCNA inhibition led to down-regulation of CDK1, CDK4, PLK1, ERK3, JNK1, STAT5, and several inhibitors of apoptosis (DAXX, Mdm2, survivin). The following genes were up-regulated: CDK inhibitors p21 and p19-INK4D, pro-apoptotic FAST kinase, fibronectin, etc. However, as PCNA affects cell growth in naturally proliferating cells as well as in cancerous cells, it seems to act a secondary role relating to proliferation activity of leukemic cells.

Spatiotemporal dynamics of p21CDKN1A protein recruitment to DNA-damage sites and interaction with proliferating cell nuclear antigen

The cyclin-dependent kinase inhibitor p21CDKN1A plays a fundamental role in the DNA-damage response by inducing cell-cycle arrest, and by inhibiting DNA replication through association with the proliferating cell nuclear antigen (PCNA). However, the role of such an interaction in DNA repair is poorly understood and controversial. Here, we provide evidence that a pool of p21 protein is rapidly recruited to UV-induced DNA-damage sites, where it colocalises with PCNA and PCNA-interacting proteins involved in nucleotide excision repair (NER), such as DNA polymerase δ, XPG and CAF-1. In vivo imaging and confocal fluorescence microscopy analysis of cells coexpressing p21 and PCNA fused to green or red fluorescent protein (p21-GFP, RFP-PCNA), showed a rapid relocation of both proteins at microirradiated nuclear spots, although dynamic measurements suggested that p21-GFP was recruited with slower kinetics. An exogenously expressed p21 mutant protein unable to bind PCNA neither colocalised, nor coimmunoprecipitated with PCNA after UV irradiation. In NER-deficient XP-A fibroblasts, p21 relocation was greatly delayed, concomitantly with that of PCNA. These results indicate that early recruitment of p21 protein to DNA-damage sites is a NER-related process dependent on interaction with PCNA, thus suggesting a direct involvement of p21 in DNA repair.

Expression of minichromosome maintenance protein 2 as a marker for proliferation and prognosis in diffuse large B-cell lymphoma: a tissue microarray and clinico-pathological analysis

Background

Minichromosome maintenance (MCM) proteins are essential for the initiation of DNA replication and have been found to be relevant markers for prognosis in a variety of tumours. The aim of this study was to assess the proliferative activity of diffuse large B-cell lymphoma (DLBCL) in tissue microarray (TMA) using one of the minichromosome maintenance proteins (Mcm2) and to explore its potential value to predict prognosis.

Methods

Immunohistochemistry for Mcm2 was performed on TMAs constructed from 302 cases of DLBCL. A monoclonal mouse antibody was used after heat induced antigen retrieval. Mcm2 expression was scored quantitatively. Positivity for Mcm2 was defined as presence of nuclear expression of Mcm2 in greater than or equal to 40 % of tumour cells. A statistical analysis was carried out of the association of Mcm2 and the clinico-pathological characteristics.

Results

Mcm2 expression was clearly evident in the nuclei of proliferating non-neoplastic cells and tumour cells. Positivity for Mcm2 was found in 46% (98/211) of analysable cases. A significant correlation existed between Mcm2 expression and presence of bulky disease (p = 0.003). Poor disease specific survival was observed in patients with DLBCL positive for Mcm2 expression in the univariate analysis (p = 0.0424).

Conclusion

Mcm2 expression can be used to assess tumour proliferation and may be useful as an additional prognostic marker to refine the prediction of outcome in DLBCL.

How does a cell repair damaged DNA?

DNA in living cells is constantly subjected to different chemical and physical factors of the environment and to cell metabolites. Some changes altering DNA structure occur spontaneously. This raises the potential danger of harmful mutations that could be transmitted to offspring. To avoid the danger of mutations and changing genetic information, a cell is capable to switch on multiple mechanisms of DNA repair that remove damage and restore native structure. In many cases, removal of the same damage may involve several alternative pathways; this is very important for DNA repair under the most unfavorable conditions. This review summarizes data about all known mechanisms of eukaryotic DNA repair including excision repair (base excision repair and nucleotide excision repair), mismatch repair, repair of double-strand breaks, and cross-link repair. Special attention is given to the regulation of excision repair by different proteins--proliferating cell nuclear antigen (PCNA), p53, and proteasome. The review also highlights problem of bypassing irremovable lesions in DNA.

Expression of Ki67, PCNA and the chromosome replication licensing protein Mcm2 in glial cells of the ageing human hippocampus increases with the burden of Alzheimer-type pathology

Cell-cycle mechanisms may be aberrantly reactivated in the ageing brain and associated with the development of pathology, including Alzheimer's disease. Activation of cell-cycle mechanisms in glia has, however, been little studied. Our aim was to determine whether expression of a marker for chromosomal replication licensing, Mcm2, occurs in glia of the ageing hippocampus, and to compare its expression to that of Ki67 and PCNA. Blocks of hippocampus were obtained from 19 elderly brains derived from the MRC-CFAS neuropathology cohort, which included a spectrum of Alzheimer-type pathology, semi-quantified using the Braak scoring system for neurofibrillary tangles. Mcm2, PCNA and Ki67 were detected immunohistochemically. Expression of Mcm2, Ki67 and PCNA was observed in glial cells and neurons, with a trend to increased expression in association with higher burdens of Alzheimer-type pathology. Mcm2 expression in glial cells showed a significant linear trend across Braak stages (P = 0.043). This study demonstrates that grey and white matter glial cells show expression of cell-cycle markers in the ageing brain and that re-licensing for chromosomal replication is a component of the mechanisms activated. A quantitative relationship to the burden of Alzheimer-type pathology suggests that cell-cycle re-entry in glial cells may be important in the pathogenesis of age-related neurodegeneration.