p53 Acetylation: Regulation and Consequences

Exploring the Histone Acylome through Incorporation of γ-Thialysine on Histone Tails

Histone lysine acetyltransferases (KATs) catalyze the transfer of the acetyl group from acetyl Coenzyme A to lysine residues in histones and nonhistone proteins. Here, we report biomolecular studies on epigenetic acetylation and related acylation reactions of lysine and γ-thialysine, a cysteine-derived lysine mimic, which can be site-specifically introduced to histone peptides and histone proteins. Enzyme assays demonstrate that human KATs catalyze an efficient acetylation and propionylation of histone peptides that possess lysine and γ-thialysine. Enzyme kinetics analyses reveal that lysine- and γ-thialysine-containing histone peptides exhibit indistinguishable K_m values, whereas small differences in k_cat values were observed. This work highlights that γ-thialysine may act as a representative and easily accessible lysine mimic for chemical and biochemical examinations of post-translationally modified histones.

Hydroxygenkwanin Inhibits Class I HDAC Expression and Synergistically Enhances the Antitumor Activity of Sorafenib in Liver Cancer Cells

Abnormal histone deacetylase (HDAC) expression is closely related to cancer development and progression. Many HDAC inhibitors have been widely used in cancer treatment; however, severe side effects often limit their clinical application. In this study, we attempted to identify natural compounds with HDAC inhibitory activity and low physiological toxicity and explored their feasibility and mechanisms of action in liver cancer treatment. A yeast screening system was used to identify natural compounds with HDAC inhibitory activity. Further, western blotting was used to verify inhibitory effects on HDAC in human liver cancer cell lines. Cell functional analysis was used to explore the effects and mechanisms and the in vitro results were verified in BALB/c nude mice. We found that hydroxygenkwanin (HGK), an extract from Daphne genkwa, inhibited class I HDAC expression, and thereby induced expression of tumor suppressor p21 and promoted acetylation and activation of p53 and p65. This resulted in the inhibition of growth, migration, and invasion of liver cancer cells and promoted cell apoptosis. Animal models revealed that HGK inhibited tumor growth in a synergistic manner with sorafenib. HGK inhibited class I HDAC expression and had low physiological toxicity. It has great potential as an adjuvant for liver cancer treatment and may be used in combination with anticancer drugs like sorafenib to improve therapeutic efficacy.

Mosaic Small Supernumerary Marker Chromosome Derived from Five Discontinuous Regions of Chromosome 8 in a Patient with Neutropenia and Oral Aphthous Ulcer

Small supernumerary marker chromosomes (sSMCs) are characterized as additional centric chromosome fragments which are too small to be classified by cytogenetic banding alone and smaller than or equal to the size of chromosome 20 of the same metaphase spread. Here, we report a patient who presented with slight neutropenia and oral aphthous ulcers. A mosaic de novo sSMC, which originated from 5 discontinuous regions of chromosome 8, was detected in the patient. Formation of the sSMC(8) can probably be explained by a multi-step process beginning with maternal meiotic nondisjunction, followed by post-zygotic anaphase lag, and resulting in chromothripsis. Chromothripsis is a chromosomal rearrangement which occurs by breakage of one or more chromosomes leading to a fusion of surviving chromosome pieces. This case is a good example for emphasizing the importance of conventional karyotyping from PHA-induced peripheral blood lymphocytes and examining tissues other than bone marrow in patients with inconsistent genotype and phenotype.

Xanthophyll β-Cryptoxanthin Inhibits Highly Refined Carbohydrate Diet-Promoted Hepatocellular Carcinoma Progression in Mice

SCOPE

β-Cryptoxanthin (BCX) can be cleaved by both β-carotene 15,15'-oxygenase (BCO1) and β-carotene 9',10'-oxygenase (BCO2), generating biological active vitamin A and apocarotenoids. We examined whether BCX feeding could inhibit diethylnitrosamine (DEN)-initiated, highly refined carbohydrate diet (HRCD)-promoted hepatocellular carcinoma (HCC) development, dependent or independent of BCO1/BCO2 activity.

METHODS AND RESULTS

Two-week-old male wild-type (WT) and BCO1^-/- /BCO2^-/- double knockout (DKO) mice are given a single intraperitoneal injection of DEN (25 mg kg^-1 body weight) to initiate hepatic carcinogenesis. At 6 weeks of age, all animals are fed HRCD (66.5% of energy from carbohydrate) with or without BCX for 24 weeks. BCX feeding increases hepatic vitamin A levels in WT mice, but not in DKO mice that shows a significant accumulation of hepatic BCX. Compared to their respective HRCD littermates, both WT and DKO fed BCX have significantly lower HCC multiplicity, average tumor size, and total tumor volume, and the steatosis scores. The chemopreventive effects of BCX are associated with increased p53 protein acetylation and decreased protein levels of lactate dehydrogenase and hypoxia-inducible factor-1α in tumors.

CONCLUSION

This study suggests that BCX feeding may alleviate HRCD-promoted HCC progression by modulating the acetylation of p53, hypoxic tumor microenvironment, and glucose metabolism, independent of BCO1/BCO2.

Functions and mechanisms of non-histone protein acetylation

Nε-lysine acetylation was discovered more than half a century ago as a post-translational modification of histones and has been extensively studied in the context of transcription regulation. In the past decade, proteomic analyses have revealed that non-histone proteins are frequently acetylated and constitute a major portion of the acetylome in mammalian cells. Indeed, non-histone protein acetylation is involved in key cellular processes relevant to physiology and disease, such as gene transcription, DNA damage repair, cell division, signal transduction, protein folding, autophagy and metabolism. Acetylation affects protein functions through diverse mechanisms, including by regulating protein stability, enzymatic activity, subcellular localization and crosstalk with other post-translational modifications and by controlling protein-protein and protein-DNA interactions. In this Review, we discuss recent progress in our understanding of the scope, functional diversity and mechanisms of non-histone protein acetylation.

Downregulation of nuclear ING3 expression and translocalization to cytoplasm promotes tumorigenesis and progression in head and neck squamous cell carcinoma (HNSCC)

ING3 (inhibitor of growth gene 3) is a member of the ING gene family, and is considered as a candidate tumor suppressor gene. In order to explore the roles of ING3 in tumorigenesis and cancer progression of head and neck squamous cell carcinoma (HNSCC), ING3 expression was assessed in 173 cases of HNSCC by immunohistochemistry. The expression of ING3 was also compared to clinicopathological variables, and the expression of several tumorigenic markers. Nuclear expression of ING3 in HNSCC was significantly lower than that in dysplasia and normal epithelium, and was negatively correlated with a poor-differentiated status, T staging and TNM staging. In contrast, cytoplasmic expression of ING3 was significantly increased in HNSCC, and was statistically associated with lymph node metastasis and 14-3-3η expression. In addition, nuclear expression of ING3 was positively correlated with the expression of p300, p21 and acetylated p53. In conclusion, decreases in nuclear ING3 may play important roles in tumorigenesis, progression and tumor differentiation in HNSCC. Increases in cytoplasmic ING3 may be due to 14-3-3η binding and may also be involved in malignant progression. Nuclear ING3 may modulate the transactivation of target genes, promoting apoptosis through interactions with p300 and p21. Moreover, ING3 may interact with p300 to upregulate the level of acetylation of p53, and promote p53-mediated cell cycle arrest, senescence and/or apoptosis. Therefore, ING3 may be a potential tumor suppressor and a possible therapeutic target in HNSCC.

p53-Mediated Tumor Suppression: DNA-Damage Response and Alternative Mechanisms

The tumor suppressor p53 regulates different cellular pathways involved in cell survival, DNA repair, apoptosis, and senescence. However, according to an increasing number of studies, the p53-mediated canonical DNA damage response is dispensable for tumor suppression. p53 is involved in mechanisms regulating many other cellular processes, including metabolism, autophagy, and cell migration and invasion, and these pathways might crucially contribute to its tumor suppressor function. In this review we summarize the canonical and non-canonical functions of p53 in an attempt to provide an overview of the potentially crucial aspects related to its tumor suppressor activity.

Salicin prevents TNF-α-induced cellular senescence in human umbilical vein endothelial cells (HUVECs)

Cellular senescence is strongly tied to vascular disease. The current study aims to examine ways that endothelial cellular senescence can be prevented and the mechanisms by which prevention of senescence occurs. Human umbilical vein endothelial cells were exposed to TNF-α to induce senescence; then salicin was administered in two doses - 50 and 100 µM - to establish a dose-dependent effect of salicin on SA-β-Gal, G1 cell cycle arrest, expression of p21 and PAI-1, p53 acetylation at K382, NRF2 and oxidative stress. NRF2 was examined as a mediating mechanism of salicin's impact on cellular senescence and was found to account for salicin's impact on SA-β-Gal, p21, PAI-1 and p53. Together, these results provide a compelling case that salicin has a substantial impact on numerous factors tied to cellular senescence in human endothelial cells. Thus, treatment with salicin may hold promise as a means of preventing aging-related vascular disease. Furthermore, salicin appears to operate via a functional pathway that is different from that affected by anti-inflammatory drugs (e.g. aspirin).

Dynamic acetylation profile during mammalian neurulation

BACKGROUND

Neural tube defects (NTDs) result from failure of neural tube closure during embryogenesis. These severe birth defects of the central nervous system include anencephaly and spina bifida, and affect 0.5-2 per 1,000 pregnancies worldwide in humans. It has been demonstrated that acetylation plays a pivotal role during neural tube closure, as animal models for defective histone acetyltransferase proteins display NTDs. Acetylation represents an important component of the complex network of posttranslational regulatory interactions, suggesting a possible fundamental role during primary neurulation events. This study aimed to assess protein acetylation contribution to early patterning of the central nervous system both in human and murine specimens.

METHODS

We used both human and mouse (Cited2 ^-/- ) samples to analyze the dynamic acetylation of proteins during embryo development through immunohistochemistry, western blot analysis and quantitative polymerase chain reaction.

RESULTS

We report the dynamic profile of histone and protein acetylation status during neural tube closure. We also report a rescue effect in an animal model by chemical p53 inhibition.

CONCLUSIONS

Our data suggest that the p53-acetylation equilibrium may play a role in primary neurulation in mammals.

Mass spectrometric analysis of PTM dynamics using stable isotope labeled metabolic precursors in cell culture

Biological organisms represent highly dynamic systems, which are continually exposed to environmental factors and always strive to restore steady-state homeostasis. Posttranslational modifications are key regulators with which biological systems respond to external stimuli. To understand how homeostasis is restored, it is important to study the kinetics of posttranslational modifications. In this review we discuss proteomic approaches using stable isotope labeled metabolic precursors to study dynamics of posttranslational modifications in cell culture.

Epigenetic mechanisms underlying the therapeutic effects of HDAC inhibitors in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a hematological disorder caused by the oncogenic BCR-ABL fusion protein in more than 90% of patients. Despite the striking improvements in the management of CML patients since the introduction of tyrosine kinase inhibitors (TKis), the appearance of TKi resistance and side effects lead to treatment failure, justifying the need of novel therapeutic approaches. Histone deacetylase inhibitors (HDACis), able to modulate gene expression patterns and important cellular signaling pathways through the regulation of the acetylation status of both histone and non-histone protein targets, have been reported to display promising anti-leukemic properties alone or in combination with TKis. This review summarizes pre-clinical and clinical studies that investigated the mechanisms underlying the anticancer potential of HDACis and discusses the rationale for a combination of HDACis with TKis as a therapeutic option in CML.

Augmentation of cellular NAD+ by NQO1 enzymatic action improves age-related hearing impairment

Age-related hearing loss (ARHL) is a major neurodegenerative disorder and the leading cause of communication deficit in the elderly population, which remains largely untreated. The development of ARHL is a multifactorial event that includes both intrinsic and extrinsic factors. Recent studies suggest that NAD⁺ /NADH ratio may play a critical role in cellular senescence by regulating sirtuins, PARP-1, and PGC-1α. Nonetheless, the beneficial effect of direct modulation of cellular NAD⁺ levels on aging and age-related diseases has not been studied, and the underlying mechanisms remain obscure. Herein, we investigated the effect of β-lapachone (β-lap), a known plant-derived metabolite that modulates cellular NAD⁺ by conversion of NADH to NAD⁺ via the enzymatic action of NADH: quinone oxidoreductase 1 (NQO1) on ARHL in C57BL/6 mice. We elucidated that the reduction of cellular NAD⁺ during the aging process was an important contributor for ARHL; it facilitated oxidative stress and pro-inflammatory responses in the cochlear tissue through regulating sirtuins that alter various signaling pathways, such as NF-κB, p53, and IDH2. However, augmentation of NAD⁺ by β-lap effectively prevented ARHL and accompanying deleterious effects through reducing inflammation and oxidative stress, sustaining mitochondrial function, and promoting mitochondrial biogenesis in rodents. These results suggest that direct regulation of cellular NAD⁺ levels by pharmacological agents may be a tangible therapeutic option for treating various age-related diseases, including ARHL.

p53-Dependent pathway and the opening of mPTP mediate the apoptosis of co-cultured Sertoli-germ cells induced by microcystin-LR

Microcystin-LR (MC-LR), a potent endotoxin, can induce reproductive toxicity. In order to investigate the role and mechanisms of apoptosis (p53-dependent and mitochondrial pathways) of germ cells induced by MC-LR, the co-cultured primary Sertoli-germ cells from Sprague-Dawley rats were used for the experiments. Expression levels of proteins, genes, and mitochondrial membrane potential (MMP) were obtained after exposing co-cultured Sertoli-germ cells to MC-LR with or without the addition of the p53 inhibitor, pifithrin-α (PFT-α), and MMP inhibitor, cyclosporin A (CsA). Results indicated that MC-LR could activate p53-dependent pathway-associated proteins in Sertoli-germ cells, leading to a decrease in MMP (indicating the opening of mitochondrial permeability transition pore [mPTP] and the release of Cytochrome-c [Cyt-c]) from the mitochondria into the cytoplasm and eventually the induction of apoptosis. PFT-α inhibited the expression ofp53, ameliorated the MMP of the co-cultured Sertoli-germ cells, and prevented the release of Cyt-c from the mitochondria into the cytoplasm, which reduces the occurrence of apoptosis. Similarly, the decreased release of Cyt-c from the mitochondria into the cytoplasm and the declined level of apoptosis in Sertoli-germ cells induced by MC-LR were observed after the addition of CsA. These results indicated that the apoptosis of the co-cultured Sertoli-germ cells induced by MC-LR was mediated by the p53-dependent pathway, with the involvement of the opening of mPTP.

The Sirt1/P53 Axis in Diabetic Intervertebral Disc Degeneration Pathogenesis and Therapeutics

Intervertebral disc degeneration (IDD) is one of the major causes of low back pain. Diabetes is a risk factor for IDD and may aggravate IDD in rats; however, the mechanism is poorly understood. Previously, we demonstrated that apoptosis and senescence were increased in diabetic nucleus pulposus (NP) tissues; in the current study, we found that hyperglycaemia may promote the incidence of apoptosis and senescence in NP cells in vitro. Meanwhile, the acetylation of P53, a master transcription factor of apoptosis and senescence, was also found increased in diabetic NP tissues in vivo as well as in hyperglycaemic NP cells in vitro. Sirt1 is an NAD⁺-dependent deacetylase, and we showed that the expression of Sirt1 was decreased in NP tissues, while hyperglycaemia could suppress the expression and activity of Sirt1 in NP cells. Furthermore, we demonstrated that butein may inhibit acetylation of P53 and protect NP cells against hyperglycaemia-induced apoptosis and senescence through Sirt1 activation, as the Sirt1 inhibitor Ex527 may counteract the protective effect of butein in hyperglycaemic NP cells. An in vivo study showed that butein could ameliorate the IDD process in diabetic rats, while Sirt1 was increased and acetyl-p53 was decreased in NP tissues in butein-treated rats. These results indicate that the Sirt1/P53 axis is involved in the pathogenesis of diabetic IDD and may serve as a therapeutic target for diabetic IDD.

Dysregulation of histone deacetylases in carcinogenesis and tumor progression: a possible link to apoptosis and autophagy

Dysregulation of the epigenome and constitutional epimutation lead to aberrant expression of the genes, which regulate cancer initiation and progression. Histone deacetylases (HDACs), which are highly conserved in yeast to humans, are known to regulate numerous proteins involved in the transcriptional regulation of chromatin structures, apoptosis, autophagy, and mitophagy. In addition, a non-permissive chromatin conformation is created by HDACs, preventing the transcription of the genes encoding the proteins associated with tumorigenesis. Recently, an expanding perspective has been reported from the clinical trials with HDACis (HDAC inhibitors), which has emerged as a determining target for the study of the detailed mechanisms underlying cancer progression. Therefore, the present review focuses on the comprehensive lucubration of post-translational modifications and the molecular mechanisms through which HDACs alter the ambiguities associated with epigenome, with particular insights into the initiation, progression, and regulation of cancer.

Inhibition of sirtuin 1 deacetylase by miR-211-5p provides a mechanism for the induction of cell death in breast cancer cells

Sirtuin 1 is one of the regulators of cell growth and survival and its inhibition is suggested as a suitable mechanism to overcome breast cancer development. In this study we explored the role of miR-211-5p in SIRT1/p53 pathway and its influence on breast cancer cell viability and apoptosis. Cells were transfected with miR-211-5p mimic and inhibitor to modulate cellular miR-211-5p levels in breast cancer cell lines, MDA-MB-231 and MCF-7. Gene expression of miR-211-5p and SIRT1 were measured with real-time PCR. SIRT1 protein level and the acetylation of p53 as well as SIRT1 activity were evaluated by Western blotting and fluorometry, respectively. In order to explore the direct attachment of miR-211-5p to the 3'-UTR of SIRT1 mRNA, luciferase reporter assay was applied. Cell viability in response to miR-211-5p was studied by MTT assay and apoptosis was assessed by annexin V labeling followed by flow cytometry. Results showed that SIRT1 gene and protein expression were inhibited by miR-211-5p and the 3'-UTR of SIRT1 was found to be directly targeted by miR-211-5p. Inhibition of SIRT1 expression resulted in its reduced activity. Up-regulation of miR-211-5p was also followed by a significant decline in the acetylation status of p53 which was associated with remarkable decreased cell viability and induction of apoptosis in breast cancer cells. Antisense oligonucleotide of miR-211-5p acted as its inhibitor and exerted opposite effects both on SIRT1 expression and cell apoptosis. In conclusion, inhibition of SIRT1 by miR-211-5p could effectively reduce breast cancer cell survival and cause cell death and therefore might be considered a seemly mechanism for designing anticancer therapies.

[Structural-functional diversity of p53 proteoforms]

Protein p53 is one of the most studied proteins. This attention is primarily due to its key role in the cellular mechanisms associated with carcinogenesis. Protein p53 is a transcription factor involved in a wide variety of processes: cell cycle regulation and apoptosis, signaling inside the cell, DNA repair, coordination of metabolic processes, regulation of cell interactions, etc. This multifunctionality is apparently determined by the fact that p53 is a vivid example of how the same protein can be represented by numerous proteoforms bearing completely different functional loads. By alternative splicing, using different promoters and translation initiation sites, the TP53 gene gives rise to at least 12 isoforms, which can additionally undergo numerous (>200) post-translational modifications. Proteoforms generated due to numerous point mutations in the TP53 gene are adding more complexity to this picture. The proteoforms produced are involved in various processes, such as the regulation of p53 transcriptional activity in response to various factors. This review is devoted to the description of the currently known p53 proteoforms, as well as their possible functionality.

p53 activation by Cr(VI): a transcriptionally limited response induced by ATR kinase in S-phase

Cellular reduction of carcinogenic chromium(VI) causes several forms of Cr-DNA damage with different genotoxic properties. Chromate-treated cultured cells have shown a strong proapoptotic activity of the DNA damage-sensitive transcription factor p53. However, induction of p53 transcriptional targets by Cr(VI) in rodent lungs was weak or undetectable. We examined Cr(VI) effects on the p53 pathway in human cells with restored levels of ascorbate that acts as a principal reducer of Cr(VI) in vivo but is nearly absent in standard cell cultures. Ascorbate-restored H460 and primary human cells treated with Cr(VI) contained higher levels of p53 and its Ser15 phosphorylation, which were induced by ATR kinase. Cr(VI)-stimulated p53 phosphorylation occurred in S-phase by a diffusible pool of ATR that was separate from the chromatin-bound pool targeting DNA repair substrates at the sites of toxic mismatch repair of Cr-DNA adducts. Even when more abundantly present than after exposure to the radiomimetic bleomycin, Cr(VI)-stabilized p53 showed a much more limited activation of its target genes in two types of primary human cells. No increases in mRNA were found for nucleotide excision repair factors and a majority of proapoptotic genes. A weak transcription activity of Cr(VI)-upregulated p53 was associated with its low lysine acetylation in the regulatory C-terminal domain, resulting from the inability of Cr(VI) to activate ATM in ascorbate-restored cells. Thus, p53 activation by ascorbate-metabolized Cr(VI) represents a limited genome-protective response that is defective in upregulation of DNA repair genes and proapoptotic transcripts for elimination of damaged cells.

p53 modifications: exquisite decorations of the powerful guardian

The last 40 years have witnessed how p53 rose from a viral binding protein to a central factor in both stress responses and tumor suppression. The exquisite regulation of p53 functions is of vital importance for cell fate decisions. Among the multiple layers of mechanisms controlling p53 function, posttranslational modifications (PTMs) represent an efficient and precise way. Major p53 PTMs include phosphorylation, ubiquitination, acetylation, and methylation. Meanwhile, other PTMs like sumoylation, neddylation, O-GlcNAcylation, adenosine diphosphate (ADP)-ribosylation, hydroxylation, and β-hydroxybutyrylation are also shown to play various roles in p53 regulation. By independent action or interaction, PTMs affect p53 stability, conformation, localization, and binding partners. Deregulation of the PTM-related pathway is among the major causes of p53-associated developmental disorders or diseases, especially in cancers. This review focuses on the roles of different p53 modification types and shows how these modifications are orchestrated to produce various outcomes by modulating p53 activities or targeted to treat different diseases caused by p53 dysregulation.

SIRT7 regulates hepatocellular carcinoma response to therapy by altering the p53-dependent cell death pathway

Background

Optimal therapeutic strategies for hepatocellular carcinoma (HCC) patients are still challenging due to the high recurrence rate after surgical resection and chemotherapy resistance. Growing evidence shows that genetic and epigenetic alterations are involved in HCC progression and resistance to therapy, however the molecular mechanisms underlying resistance to therapy have not been fully understood.

Methods

Expression of SIRT7 in 17 paired paraffin-embedded HCC tissues and adjacent nontumoral liver tissues was examined by immunohistochemistry and Western blot. The mRNA expression of SIRT7 in 20 paired frozen HCC tissues and adjacent nontumoral liver tissues was analyzed by quantitative RT-PCR. The biologic consequences of overexpression and knockdown of SIRT7 in HCC therapy sensitivity were studied in vitro and in vivo. Interaction between SIRT7 and p53 were studied in HCC cell lines.

Results

SIRT7 expression was frequently upregulated in clinical HCC samples, and its expression was highly associated with TACE-resistance and poor survival (P = 0.008.) Depletion of SIRT7 from multiple liver cancer cell lines significantly increased doxorubicin toxicity while overexpression of SIRT7 largely abolished doxorubicin induced apoptosis. At the molecular level, we observed that SIRT7 interacts with and induces deacetylation of p53 at lysines 320 and 373. Deacetylated p53 showed significantly less affinity for the NOXA promoter and its transcription. In mouse xenografts, SIRT7 suppression increased doxorubicin induced p53 activation, inhibited tumor growth and induced apoptosis.

Conclusion

The newly identified SIRT7-p53-NOXA axis partially illustrates the molecular mechanism of HCC resistance to therapy and represents a novel potential therapeutic target for HCC treatment.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1246-4) contains supplementary material, which is available to authorized users.

Systems Biology Approaches to Investigate Genetic and Epigenetic Molecular Progression Mechanisms for Identifying Gene Expression Signatures in Papillary Thyroid Cancer

Thyroid cancer is the most common endocrine cancer. Particularly, papillary thyroid cancer (PTC) accounts for the highest proportion of thyroid cancer. Up to now, there are few researches discussing the pathogenesis and progression mechanisms of PTC from the viewpoint of systems biology approaches. In this study, first we constructed the candidate genetic and epigenetic network (GEN) consisting of candidate protein–protein interaction network (PPIN) and candidate gene regulatory network (GRN) by big database mining. Secondly, system identification and system order detection methods were applied to prune candidate GEN via next-generation sequencing (NGS) and DNA methylation profiles to obtain the real GEN. After that, we extracted core GENs from real GENs by the principal network projection (PNP) method. To investigate the pathogenic and progression mechanisms in each stage of PTC, core GEN was denoted in respect of KEGG pathways. Finally, by comparing two successive core signaling pathways of PTC, we not only shed light on the causes of PTC progression, but also identified essential biomarkers with specific gene expression signature. Moreover, based on the identified gene expression signature, we suggested potential candidate drugs to prevent the progression of PTC with querying Connectivity Map (CMap).

Nicotinamide N-methyltransferase enhances chemoresistance in breast cancer through SIRT1 protein stabilization

Background

Nicotinamide N-methyltransferase (NNMT) is overexpressed in various human tumors and involved in the development and progression of several carcinomas. In breast cancer, NNMT was found to be overexpressed in several cell lines. However, the clinical relevance of NNMT in breast cancer is not yet clear.

Methods

NNMT expression in breast carcinoma was examined by immunohistochemistry, and then, its relationship with patient clinicopathological characteristics was analyzed. The effects of NNMT on chemoresistance in breast cancer cells were assessed by cell viability, colony formation, and apoptosis assay. The NNMT, SIRT1, p53, and acetyl-p53 proteins, which are involved in NNMT-related chemoresistance, were examined by Western blotting. The SIRT1 mRNA was examined by real-time PCR, and its activity was measured by using the SIRT1 deacetylase fluorometric reagent kit.

Results

NNMT expression was significantly higher (53.9%) in breast carcinoma than in paracancerous tissues (10.0%) and breast hyperplasia (13.3%). A high level of NNMT expression correlated with poor survival and chemotherapy response in breast cancer patients who received chemotherapy. Ectopic overexpression of NNMT significantly inhibited the apoptotic cell death and suppression of colony formation induced by adriamycin and paclitaxel. Mechanistic studies revealed that NNMT overexpression increased SIRT1 expression and promoted its activity. Either inhibition of SIRT1 by EX527 or knockdown of SIRT1 by siRNA could reverse NNMT-mediated resistance to adriamycin and paclitaxel, which suggests that SIRT1 plays a critical role in NNMT-related chemoresistance in breast cancer.

Conclusions

The results of this study demonstrate a novel correlation between the NNMT expression level and patient survival, suggesting that NNMT has the potential to become a new prognostic biomarker to predict the treatment outcomes of the clinical chemotherapy in breast cancer. Moreover, targeting NNMT or downstream SIRT1 may represent a new therapeutic approach to improve the efficacy of breast cancer chemotherapy.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1150-z) contains supplementary material, which is available to authorized users.

Low-dose aspirin protective effects are correlated with deregulation of HNF factor expression in the preeclamptic placentas from mice and humans

Aspirin (acetyl-salicylic acid) is one of the most ancient drugs of the human pharmacopeia. Nonetheless, its action at low doses is not well understood at the molecular level. One of the applications of low-dose aspirin treatment is the prevention of preeclampsia (PE) in patients at risk. Foeto-placental overexpression of the STOX1A transcription factor in mice triggers PE symptoms. Transcriptomic analysis of the placentas, showed that aspirin massively down-regulates genes of the coagulation and complement cascade, as well as genes involved in lipid transport. The genes modified by aspirin treatment are not the ones that are modified by STOX1 overexpression, suggesting that aspirin could act downstream, symptomatically on the preeclamptic disease. Bioinformatics analysis of the promoters of the deregulated genes showed that they are strongly enriched in HNF transcription factors-binding sites, in accordance with existing literature showing their roles as regulators of coagulation. Two of these transcription factors, Hnf1β and Hnf4α are found down-regulated by aspirin treatment. In parallel, we show that in human patient placentas, aspirin-induced deregulations of genes of the coagulation cascade are also observed. Finally, the expression of Hnf1β target sequences (Kif12, F2, Hnf4α promoters and a synthetic concatemer of the Hnf1β-binding site) were investigated by transfection in trophoblast cell models, with or without aspirin treatment and with or without STOX1A overexpression. In this model we observed that STOX1A and aspirin tended to synergize in the down-regulation of Hnf1β target genes in trophoblasts.

Calpain-mediated cleavage of p53 in human cytomegalovirus-infected lung fibroblasts

Endogenous fragments of p53 protein were identified in human cytomegalovirus (HCMV)-infected human lung fibroblasts, particularly a 44-kDa N-terminal fragment [hereafter referred to as p53(ΔCp44)], generated via calpain cleavage. The fragment abundance increased in a biphasic manner, peaking at 6-9 hours and 48 hours post infection. Treatment of LU cells with calpain inhibitors eliminated most detectable p53 fragments. In cell-free experiments, exogenous m-calpain cleavage generated p53(ΔCp44). Attempts to preserve p53 proteins by treating cells with the calpain inhibitor E64d for 6 hours before harvesting increased the sensitivity of p53 to calpain cleavage. p53 in mock-infected cell lysates was much more sensitive to cleavage and degradation by exogenous calpain than that in HCMV-infected cells. The proteasome inhibitor MG132 stabilized p53(ΔCp44), particularly in mock-infected cells. p53(ΔCp44) appeared to be tightly associated with a chromatin-rich fraction. The abundance of p53β was unchanged over a 96-h time course and very similar in mock- and HCMV-infected cells, making it unlikely that p53(ΔCp44) was p53β. The biological activities of this and other fragments lacking C-terminal sequences are unknown, but deserve further investigation, given the association of p53(ΔCp44) with the chromatin-rich (or buffer C insoluble) fraction in HCMV-infected cells.

The tumor suppressor protein p53 and the ferroptosis network

Ferroptosis is a form of lipid peroxidation-induced cell death that can be regulated in many ways, from altering the activity of antioxidant enzymes to the level of transcription factors. The p53 tumor suppressor is 'the guardian of the genome' that participates in the control of cell survival and division under various stresses. Beyond its effects on apoptosis, autophagy, and cell cycle, p53 also regulates ferroptosis either through a transcriptional or posttranslational mechanism. On one hand, p53 can enhance ferroptosis by inhibiting the expression of SLC7A11 (solute carrier family 7 member 11) or by enhancing that of SAT1 (spermidine/spermine N1-acetyltransferase 1) and GLS2 (glutaminase 2). On the other hand, p53 suppresses ferroptosis through the direct inhibition of DPP4 (dipeptidyl peptidase 4) activity or by the induction of CDKN1A/p21 (cyclin dependent kinase inhibitor 1 A) expression. Here, we review recent discoveries and emerging trends in the study of the ferroptosis network and highlight the context-dependent impact of p53 on ferroptosis and oxidative stress.

SIRT1 suppresses p53-dependent apoptosis by modulation of p21 in osteoblast-like MC3T3-E1 cells exposed to fluoride

Fluoride is very crucial for development of teeth and bones. Excessive fluoride, however, causes damage to teeth and bones resulting in serious public health problem. SIRT1 regulates physiological and pathological processes such as apoptosis and cell cycle. Although SIRT1 inhibits p53-mediated transactivation, how SIRT1 regulates p53 in fluorosis remains unclear. This study aims to investigate the involvement of SIRT1 in fluoride-induced cell cycle arrest and apoptosis in MC3T3-E1 cells and the underlying mechanism. Cell apoptosis was determined using Annexin V-FITC/PI dual staining, cell cycle detected with PI staining, intracellular ROS levels measured with DCFH-DA probe, and apoptosis-related protein expressions determined using Western blotting. Results showed that there was a promotion in apoptosis rate, intracellular ROS levels, the ratio of Bax/Bcl-2, protein expression (Cyt c, Caspase-3, p53, Ac-p53 and p21) and blockage of S phase after cells were exposed to NaF. Afterwards, the influence of SIRT1 on apoptosis was explored after SRT1720 (SIRT1 activator) and Ex-527 (SIRT1 inhibitor) was introduced. Results indicated that SRT1720 in combination with fluoride significantly decreased the intracellular ROS levels, the protein expression of Caspase-3, Ac-p53 and p21 and alleviated apoptosis, while it was reversed by Ex-527. Collectively, SIRT1 plays an essential role in protection against fluoride-induced oxidative stress and mitochondria-dependent apoptosis in MC3T3-E1 cells. The SIRT1/p53/p21 pathway may be a potential therapeutic target for fluorosis.

Suppression of SIRT1 in Diabetic Conditions Induces Osteogenic Differentiation of Human Vascular Smooth Muscle Cells via RUNX2 Signalling

Vascular calcification is associated with significant morbidity and mortality within diabetes, involving activation of osteogenic regulators and transcription factors. Recent evidence demonstrates the beneficial role of Sirtuin 1 (SIRT1), an NAD⁺ dependant deacetylase, in improved insulin sensitivity and glucose homeostasis, linking hyperglycaemia and SIRT1 downregulation. This study aimed to determine the role of SIRT1 in vascular smooth muscle cell (vSMC) calcification within the diabetic environment. An 80% reduction in SIRT1 levels was observed in patients with diabetes, both in serum and the arterial smooth muscle layer, whilst both RUNX2 and Osteocalcin levels were elevated. Human vSMCs exposed to hyperglycaemic conditions in vitro demonstrated enhanced calcification, which was positively associated with the induction of cellular senescence, verified by senescence-associated β-galactosidase activity and cell cycle markers p16 and p21. Activation of SIRT1 by SRT1720 reduced Alizarin red staining by a third, via inhibition of the RUNX2 pathway and prevention of senescence. Conversely, inhibition of SIRT1 via Sirtinol and siRNA increased RUNX2 by over 50%. These findings demonstrate the key role that SIRT1 plays in preventing calcification in a diabetic environment, through the inhibition of RUNX2 and senescence pathways, suggesting a downregulation of SIRT1 may be responsible for perpetuating vascular calcification in diabetes.

Modulating Effect of Diet on Alzheimer's Disease

As life expectancy is growing, neurodegenerative disorders, such as Alzheimer's disease, are increasing. This disease is characterised by the accumulation of intracellular neurofibrillary tangles formed by hyperphosphorylated tau protein, senile plaques composed of an extracellular deposit of β-amyloid peptide (Aβ), and neuronal loss. This is accompanied by deficient mitochondrial function, increased oxidative stress, altered inflammatory response, and autophagy process impairment. The present study gathers scientific evidence that demonstrates that specific nutrients exert a direct effect on both Aβ production and Tau processing and their elimination by autophagy activation. Likewise, certain nutrients can modulate the inflammatory response and the oxidative stress related to the disease. However, the extent to which these effects come with beneficial clinical outcomes remains unclear. Even so, several studies have shown the benefits of the Mediterranean diet on Alzheimer's disease, due to its richness in many of these compounds, to which can be attributed their neuroprotective properties due to the pleiotropic effect they show on the aforementioned processes. These indications highlight the potential role of adequate dietary recommendations for clinical management of both Alzheimer's diagnosed patients and those in risk of developing it, emphasising once again the importance of diet on health.

Inflammatory and oxidative stress biomarkers at protein and molecular levels in workers occupationally exposed to crystalline silica

Workers chronically exposed to respirable crystalline silica (CS) are susceptible to adverse health effects like silicosis and lung cancer. This study aimed to investigate potential early peripheral biomarkers of inflammation and oxidative stress in miners. The subjects enrolled in this study were occupationally unexposed workers (OUW, n = 29) and workers exposed to crystalline silica (WECS), composed by miners, which were divided into two subgroups: workers without silicosis (WECS I, n = 39) and workers diagnosed with silicosis, retired from work (WECS II, n = 42). The following biomarkers were evaluated: gene expression of L-selectin, CXCL2, CXCL8 (IL-8), HO-1, and p53; malondialdehyde (MDA) plasma levels and non-protein thiol levels in erythrocytes. Additionally, protein expression of L-selectin was evaluated to confirm our previous findings. The results demonstrated that gene expression of L-selectin was decreased in the WECS I group when compared to the OUW group (p < 0.05). Regarding gene expression of CXCL2, CXCL8 (IL-8), HO-1, and p53, significant fold change decreases were observed in workers exposed to CS in relation to unexposed workers (p < 0.05). The results of L-selectin protein expression in lymphocyte surface corroborated with our previous findings; thus, significant downregulation in the WECS groups was observed compared to OUW group (p < 0.05). The MDA was negatively associated with the gene expression of CXCL-2, CXCL8 (IL-8), and p53 (p < 0.05). The participants with silicosis (WECS II) presented significant increased non-protein thiol levels in relation to other groups (p < 0.05). Taken together, our findings may contribute to help the knowledge about the complex mechanisms involved in the silicosis pathogenesis and in the risk of lung cancer development in workers chronically exposed to respirable CS.

Progesterone up-regulates p27 through an increased binding of the progesterone receptor-A-p53 protein complex onto the non-canonical p53 binding motif in HUVEC

We previously demonstrated that progesterone (P4) up-regulated p53 expression, which in turn increased p21 and p27 expression, and finally resulted in proliferation inhibition in human umbilical vein endothelial cells (HUVEC). While a direct transcriptional activation of p21 by p53 protein has been clearly elucidated, the mechanism by which p53 induces p27 expression has not been documented. In this study, we identified three putative p53 protein binding domains at the p27 promoter. Luciferase assay showed that the activity of ectopically introduced p27 promoter constructs containing the potential p53 protein binding region was significantly increased by P4. Immunoblotting analysis indicated that P4 increased the level of p53 protein. Treatment with pifithrin-α-HBr (PFTα), a specific blocker of p53-responsive gene transactivation, reduced the P4-increased p27 promoter activity and p27 protein expression. Transfection with dominant-negative mutants of p53 (C135Y, R175H and R248 W) abolished the P4-increased p27 promoter activity. Moreover, deletion or TCCT nucleotide sequence fill-in at the core site of any of p53 protein binding domains led to the irresponsiveness of the p27 promoter to P4 treatment. Interestingly, immunoprecipitation and chromatin-immunoprecipitation analyses demonstrated that P4 increased the complex of p53-P4 receptor (PR) protein in the nucleus and the assembly of PR protein to the p53 protein binding region of the p27 promoter. Ectopic co-overexpression of p53 and PR-A constructs further augmented the P4-increased p27 promoter activity. Taken together, the results from the present study suggest that P4-increased p53 expression might directly up-regulate p27 transactivation, and PR-A protein might promote this effect by forming complex with p53 protein.

Regulators of Oncogenic Mutant TP53 Gain of Function

The tumor suppressor p53 (TP53) is the most frequently mutated human gene. Mutations in TP53 not only disrupt its tumor suppressor function, but also endow oncogenic gain-of-function (GOF) activities in a manner independent of wild-type TP53 (wtp53). Mutant TP53 (mutp53) GOF is mainly mediated by its binding with other tumor suppressive or oncogenic proteins. Increasing evidence indicates that stabilization of mutp53 is crucial for its GOF activity. However, little is known about factors that alter mutp53 stability and its oncogenic GOF activities. In this review article, we primarily summarize key regulators of mutp53 stability/activities, including genotoxic stress, post-translational modifications, ubiquitin ligases, and molecular chaperones, as well as a single nucleotide polymorphism (SNP) and dimer-forming mutations in mutp53.

S-Adenosylmethionine regulates apoptosis and autophagy in MCF-7 breast cancer cells through the modulation of specific microRNAs

Background

To get insight into the molecular mechanisms underlying the anti-tumor activity of S-adenosyl-l-methionine (AdoMet), we analyzed AdoMet-induced modulation of microRNAs (miRNAs) expression profile in MCF-7 breast cell line and its correlation with cancer-related biological pathways.

Methods

MiRNA expression profiling was performed using a TaqMan MiRNA Array, following 500 µM AdoMet-treatment. The results were confirmed by Quantitative real-time PCR analysis. MCF-7 were transfected with miR-34a, miR-34c and miR-486-5p, mimics and inhibitors in presence or not of 500 µM AdoMet for 72 h. Apoptosis and autophagy were analyzed by flow cytometry and the modulation of the main antiproliferative signaling pathways were evaluated by Western blotting. The potential mRNA targets for each miRNA were identified by the TargetScan miRNA target prediction software.

Results

Twenty-eight microRNAs resulted differentially expressed in AdoMet-treated MCF-7 cells compared to control cells. Among them, miRNA-34a and miRNA-34c were up-regulated while miRNA-486-5p was down-regulated. Moreover, we confirmed the ability of AdoMet to regulate these miRNAs in MDA-MB 231 breast cancer cell line. We demonstrate that, in MCF7 cells, the combination of either miR-34a or miR-34c mimic with AdoMet greatly potentiated the pro-apoptotic effect of AdoMet, by a caspase-dependent mechanism and activates p53 acetylation by inhibiting SIRT1 and HDAC1 expression. We also showed that miR-486-5p inhibitor induces autophagy and enhances AdoMet-induced autophagic process by increasing PTEN expression and by inhibiting AKT signaling.

Conclusions

Our findings provide the first evidence that AdoMet can regulate miRNA expression in MCF-7 increasing our knowledge on the molecular basis of the antitumor effect of the sulfonium compound and suggest the use of AdoMet as an attractive miRNA-mediated chemopreventive and therapeutic strategy in breast cancer.

Forcing ATGL expression in hepatocarcinoma cells imposes glycolytic rewiring through PPAR-α/p300-mediated acetylation of p53

Metabolic reprogramming is a typical feature of cancer cells aimed at sustaining high-energetic demand and proliferation rate. Here, we report clear-cut evidence for decreased expression of the adipose triglyceride lipase (ATGL), the first and rate-limiting enzyme of triglyceride hydrolysis, in both human and mouse-induced hepatocellular carcinoma (HCC). We identified metabolic rewiring as major outcome of ATGL overexpression in HCC-derived cell lines. Indeed, ATGL slackened both glucose uptake/utilization and cell proliferation in parallel with increased oxidative metabolism of fatty acids and enhanced mitochondria capacity. We ascribed these ATGL—downstream events to the activity of the tumor-suppressor p53, whose protein levels—but not transcript—were upregulated upon ATGL overexpression. The role of p53 was further assessed by abrogation of the ATGL-mediated effects upon p53 silencing or in p53-null hepatocarcinoma Hep3B cells. Furthermore, we provided insights on the molecular mechanisms governed by ATGL in HCC cells, identifying a new PPAR-α/p300 axis responsible for p53 acetylation/accumulation. Finally, we highlighted that ATGL levels confer different susceptibility of HCC cells to common therapeutic drugs, with ATGL overexpressing cells being more resistant to glycolysis inhibitors (e.g., 2-deoxyglucose and 3-bromopyruvate), compared to genotoxic compounds. Collectively, our data provide evidence for a previously uncovered tumor-suppressor function of ATGL in HCC, with the outlined molecular mechanisms shedding light on new potential targets for anticancer therapy.

Chromatin-remodeling factor, RSF1, controls p53-mediated transcription in apoptosis upon DNA strand breaks

Remodeling and spacing factor 1 (RSF1), which is one of chromatin-remodeling factors, has been linked to the DNA damage response (DDR) and DNA repair. However, the biological consequence of RSF1 deficiency in DDR in vivo and its molecular mechanisms remain unknown. Because defective DDR is related to neuropathological phenotypes, we developed neural-specific Rsf1 knockout mice. Rsf1 deficiency did not result in any neuropathological abnormalities, but prevented neural apoptosis triggered by excessive DNA strand breaks during neurogenesis. Likewise, cell death was significantly reduced in RSF1 deficient human cell lines after DNA damage, and the global transcriptome of these cells revealed that the expressions of p53 downstream genes were significantly reduced upon DNA strand breaks. Inactivation of these genes resulted from decreased binding of p53/p300 complex and subsequent reduction of H3 acetylation at their promoters. Our data show that RSF1 is necessary for p53-dependent gene expression in response to DNA strand breaks via controlling the accessibility of p53/p300 complex to its target genes and contributes to the maintenance of cellular integrity.

TdIF1: a putative oncogene in NSCLC tumor progression

TdT-interacting factor 1 (TdIF1) is a ubiquitously expressed DNA- and protein-binding protein that directly binds to terminal deoxynucleotidyl transferase (TdT) polymerase. Little is known about the functional role of TdIF1 in cancer cellular signaling, nor has it previously been identified as aberrant in any type of cancer. We report here for the first time that TdIF1 is abundantly expressed in clinical lung cancer patients and that high expression of TdIF1 is associated with poor patient prognosis. We further established that TdIF1 is highly expressed in human non-small cell lung cancer (NSCLC) cell lines compared to a normal lung cell line. shRNA-mediated gene silencing of TdIF1 resulted in the suppression of proliferation and anchorage-independent colony formation of the A549 adenocarcinoma cell line. Moreover, when these TdIF1-silenced cells were used to establish a mouse xenograft model of human NSCLC, tumor size was greatly reduced. These data suggest that TdIF1 is a potent regulator of lung tumor development. Several cell cycle-related and tumor growth signaling pathways, including the p53 and HDAC1/2 pathways, were identified as participating in the TdIF1 signaling network by in silico analysis. Microarray, transcriptome and protein-level analyses validated p53 and HDAC1/2 modulation upon TdIF1 downregulation in an NSCLC cellular model. Moreover, several other cell cycle regulators were affected at the transcript level by TdIF1 silencing, including an increase in CDKN1A/p21 transcripts. Taken together, these results indicate that TdIF1 is a bona fide tumor-promoting factor in NSCLC and a potential target for therapy.

A protein involved in the immune system also plays a role in the most common type of lung cancer. Weiping Min, of the University of Western Ontario in Canada, and international colleagues found, for the first time, that the protein TdIF1 is significantly upregulated in non-small cell lung cancer (NSCLC) tissues in patients. High expression levels of this protein were correlated with poor prognosis. NSCLC tumor tissues grown in mice where TdIF1 expression was ‘knocked down’ were significantly smaller than in those without TdIF1 knockdown. Further analyses showed the protein was involved in known cell signaling pathways with roles in NSCLC progression. The findings indicate TdIF1 should be further investigated as a biomarker of NSCLC or as a molecular target for its treatment.

Shenqi Fuzheng Injection Reverses Cisplatin Resistance through Mitofusin-2-Mediated Cell Cycle Arrest and Apoptosis in A549/DDP Cells

The goal of this evaluation was to examine the mechanisms of Shenqi Fuzheng injection (SFI), an extract made from the plants Radix Astragali and Radix Codonopsis, in the process of chemotherapy sensitivity in non-small-cell lung cancer (NSCLC) cells. We investigated the expression of mitofusin-2 (Mfn2), a mitochondrial GTPase that may be related to chemoresistance, and found that Mfn2 expression was lower in human cisplatin-resistant lung carcinoma A549/DDP cells than in cisplatin-susceptible A549 cells. Chemosensitivity to cisplatin was restored in A549/DDP cells following supplementation in conjunction with SFI treatment, the effect of which we evaluated via cell cycle, apoptosis, and cell signaling analysis. We found that the combined use of A549/DDP cells with SFI and cisplatin enhanced cell cycle arrested in the G₂/M phase, which was accompanied by upregulation of p53 and p21 protein expression and induced mitochondrial apoptosis in conjunction with the upregulation of Bax and the downregulation of Bcl-2 protein expression. Moreover, cell cycle arrest and mitochondrial apoptosis coincided with the upregulation of Mfn2 expression, which, in turn, was related to the increased mitochondrial membrane permeabilization and elevated reactive oxygen species. In summary, our findings suggest that the effect of SFI in increasing chemotherapy sensitivity in cisplatin resistance of NSCLCs occurs through cell cycle arrest and the initiation of mitochondrial apoptosis involved in the upregulation of Mfn2 expression.

AIMP3 depletion causes genome instability and loss of stemness in mouse embryonic stem cells

Aminoacyl-tRNA synthetase-interacting multifunctional protein-3 (AIMP3) is a component of the multi-aminoacyl-tRNA synthetase complex and is involved in diverse cellular processes. Given that AIMP3 deficiency causes early embryonic lethality in mice, AIMP3 is expected to play a critical role in early mouse development. To elucidate a functional role of AIMP3 in early mouse development, we induced AIMP3 depletion in mouse embryonic stem cells (mESCs) derived from blastocysts of AIMP3^f/f; Cre^ERT2 mice. In the present study, AIMP3 depletion resulted in loss of self-renewal and ability to differentiate to three germ layers in mESCs. AIMP3 depletion led to accumulation of DNA damage by blocking double-strand break repair, in particular homologous recombination. Through microarray analysis, the p53 signaling pathway was identified as being activated in AIMP3-depleted mESCs. Knockdown of p53 rescued loss of stem cell characteristics by AIMP3 depletion in mESCs. These results imply that AIMP3 depletion in mESCs leads to accumulation of DNA damage and p53 transactivation, resulting in loss of stemness. We propose that AIMP3 is involved in maintenance of genome stability and stemness in mESCs.

KLLN-mediated DNA damage-induced apoptosis is associated with regulation of p53 phosphorylation and acetylation in breast cancer cells

KLLN is a target of p53 involved in S-phase cell cycle regulation deemed necessary and sufficient for p53-mediated apoptosis. Germline promoter hypermethylation of KLLN is associated with a cancer-predisposition syndrome, Cowden syndrome. KLLN’s DNA-binding ability is associated with transcription regulation and maintenance of genomic stability. Here, we report on KLLN’s role in DNA damage response (DDR) mediated through apoptosis in breast cells with and without a cancer phenotype. KLLN expression was upregulated after doxorubicin-induced DNA damage and this upregulation can be abrogated using RNAi-mediated gene silencing. Silencing KLLN after doxorubicin treatment effected DDR shown by decreased γ-H2AX foci and expression, and apoptosis assessed by decreased frequency of apoptotic nuclei and decreased expression of definitive markers of apoptosis. Contrary to expectations, there was no change in cell cycle regulation after KLLN silencing. These results were observed in breast cells with wildtype and mutant p53. At early timepoints after doxorubicin treatment, knocking down KLLN resulted in decreased Ser15-phosphorylation of p53 but not Thr68-phosphorylation of CHK2 or the phosphorylation of upstream regulators such as ATM and ATR. Interestingly, a second pathway for p53 activation was also affected by knockdown of KLLN. After doxorubicin treatment, Thr454-phosphorylation of DBC1, required to inhibit deacetylation of p53 by SIRT1, was decreased and therefore acetylation of p53 was also decreased with KLLN knockdown. Therefore, our observations suggest that KLLN’s role in DNA damage-induced apoptosis is likely independent of p53 and is associated with a two-pronged regulation of p53 activation.

Ectopic expression of aPKC-mediated phosphorylation in p300 modulates hippocampal neurogenesis, CREB binding and fear memory differently with age

Epigenetic modifications have become an emerging interface that links extrinsic signals to alterations of gene expression that determine cell identity and function. However, direct signaling that regulates epigenetic modifications is unknown. Our previous work demonstrated that phosphorylation of CBP at Ser 436 by atypical protein kinase C (aPKC) regulates age-dependent hippocampal neurogenesis and memory. p300, a close family member of CBP, lacks the aPKC-mediated phosphorylation found in CBP. Here, we use a phosphorylation-competent p300 (G442S) knock-in (KI) mouse model that ectopically expresses p300 phosphorylation in a homologous site to CBP Ser436, and assess its roles in modulating hippocampal neurogenesis, CREB binding ability, and fear memory. Young adult (3 months) p300G422S-KI mice exhibit enhanced hippocampal neurogenesis due to increased cell survival of newly-generated neurons, without alterations in CREB binding and contextual fear memory. On the other hand, mature adult (6 months) p300G422S-KI mice display reduced CREB binding, associated with impaired contextual fear memory without alterations in hippocampal neurogenesis. Additionally, we show that repulsive interaction between pS133-CREB and pS422-p300G422S may contribute to the reduced CREB binding to p300G422S. Together, these data suggest that a single phosphorylation change in p300 has the capability to modulate hippocampal neurogenesis, CREB binding, and associative fear memory.

Role of p53 circuitry in tumorigenesis: A brief review

Maintenance of genome integrity under the stressed condition is paramount for normal functioning of cells in the multicellular organisms. Cells are programmed to protect their genome through specialized adaptive mechanisms which will help decide their fate under stressed conditions. These mechanisms are the outcome of activation of the intricate circuitries that are regulated by the p53 master protein. In this paper, we provided a comprehensive review on p53, p53 homologues and their isoforms, including a description about the ubiquitin-proteasome system emphasizing its role in p53 regulation. p53 induced E3(Ub)-ligases are an integral part of the ubiquitin-proteasome system. This review outlines the roles of important E3(Ub)-ligases and their splice variants in maintaining cellular p53 protein homeostasis. It also covers up-to-date and relevant information on small molecule Mdm2 inhibitors originated from different organizations. The review ends with a discussion on future prospects and investigation directives for the development of next-generation modulators as p53 therapeutics.

TSPYL2 is a novel regulator of SIRT1 and p300 activity in response to DNA damage

Protein acetylation and deacetylation events are finely regulated by lysine-acetyl-transferases and lysine-deacetylases and constitute an important tool for the activation or inhibition of specific cellular pathways. One of the most important lysine-acetyl-transferases is p300, which is involved in the regulation of gene expression, cell growth, DNA repair, differentiation, apoptosis, and tumorigenesis. A well-known target of p300 is constituted by the tumor suppressor protein p53, which plays a critical role in the maintenance of genomic stability and whose activity is known to be controlled by post-translational modifications, among which acetylation. p300 activity toward p53 is negatively regulated by the NAD-dependent deacetylase SIRT1, which deacetylates p53 preventing its transcriptional activation and the induction of p53-dependent apoptosis. However, the mechanisms responsible for p53 regulation by p300 and SIRT1 are still poorly understood. Here we identify the nucleosome assembly protein TSPY-Like 2 (TSPYL2, also known as TSPX, DENTT, and CDA1) as a novel regulator of SIRT1 and p300 function. We demonstrate that, upon DNA damage, TSPYL2 inhibits SIRT1, disrupting its association with target proteins, and promotes p300 acetylation and activation, finally stimulating p53 acetylation and p53-dependent cell death. Indeed, in response to DNA damage, cells silenced for TSPYL2 were found to be defective in p53 activation and apoptosis induction and these events were shown to be dependent on SIRT1 and p300 function. Collectively, our results shed new light on the regulation of p53 acetylation and activation and reveal a novel TSPYL2 function with important implications in cancerogenesis.

Biological processes and signal transduction pathways regulated by the protein methyltransferase SETD7 and their significance in cancer

Protein methyltransferases have been shown to methylate histone and non-histone proteins, leading to regulation of several biological processes that control cell homeostasis. Over the past few years, the histone-lysine N-methyltransferase SETD7 (SETD7; also known as SET7/9, KIAA1717, KMT7, SET7, SET9) has emerged as an important regulator of at least 30 non-histone proteins and a potential target for the treatment of several human diseases. This review discusses current knowledge of the structure and subcellular localization of SETD7, as well as its function as a histone and non-histone methyltransferase. This work also underlines the putative contribution of SETD7 to the regulation of gene expression, control of cell proliferation, differentiation and endoplasmic reticulum stress, which indicate that SETD7 is a candidate for novel targeted therapies with the aim of either stimulating or inhibiting its activity, depending on the cell signaling context.

Iron overloaded polarizes macrophage to proinflammation phenotype through ROS/acetyl-p53 pathway

Purpose

Macrophages play critical roles in inflammation and wound healing and can be divided into two subtypes: classically activated (M1) and alternatively activated (M2) macrophages. Macrophages also play important roles in regulating iron homeostasis, and intracellular iron accumulation induces M1‐type macrophage polarization which provides a potential approach to tumor immunotherapy through M2 tumor‐associated macrophage repolarization. However, the mechanisms underlying iron‐induced M1 polarization remain unclear.

Methods

Western blotting, qRT‐PCR, and flow cytometry were used to detect the polarization indexes in RAW 264.7 murine macrophages treated with iron, and Western bloting and qRT‐PCR were used to detect p21 expression. The compound 2,7‐dichlorofluorescein diacetate was used to measure reactive oxygen species (ROS) levels in macrophages after iron or N‐acetyl‐l‐cysteine (NAC) treatment. The p300/CREB‐binding protein (CBP) inhibitor C646 was used to inhibit p53 acetylation, and Western bloting, qRT‐PCR, and immunofluorescence were used to detect p53 expression and acetylation. BALB/c mice were subcutaneously injected with H22 hepatoma cells, and macrophage polarization status was investigated after tail intravenous injection of iron. Immunohistochemical staining was used to evaluate the protein expression of cluster of differentiation 86 (CD86) and EGF‐like module‐containing mucin‐like hormone receptor‐like 1 (F4/80) in the subcutaneous tumors.

Results

Iron overload induced M1 polarization by increasing ROS production and inducing p53 acetylation in RAW cells, and reduction in ROS levels by NAC repressed M1 polarization and p53 acetylation. Inhibition of acetyl‐p53 by a p300/CBP inhibitor prevented M1 polarization and inhibited p21 expression. These results showed that high ROS levels induced by iron overload polarized macrophages to the M1 subtype by enhancing p300/CBP acetyltransferase activity and promoting p53 acetylation.

Human Oncoviruses and p53 Tumor Suppressor Pathway Deregulation at the Origin of Human Cancers

Viral oncogenesis is a multistep process largely depending on the complex interplay between viruses and host factors. The oncoviruses are capable of subverting the cell signaling machinery and metabolic pathways and exploit them for infection, replication, and persistence. Several viral oncoproteins are able to functionally inactivate the tumor suppressor p53, causing deregulated expression of many genes orchestrated by p53, such as those involved in apoptosis, DNA stability, and cell proliferation. The Epstein–Barr virus (EBV) BZLF1, the high-risk human papillomavirus (HPV) E6, and the hepatitis C virus (HCV) NS5 proteins have shown to directly bind to and degrade p53. The hepatitis B virus (HBV) HBx and the human T cell lymphotropic virus-1 (HTLV-1) Tax proteins inhibit p53 activity through the modulation of p300/CBP nuclear factors, while the Kaposi’s sarcoma herpesvirus (HHV8) LANA, vIRF-1 and vIRF-3 proteins have been shown to destabilize the oncosuppressor, causing a decrease in its levels in the infected cells. The large T antigen of the Merkel cell polyomavirus (MCPyV) does not bind to p53 but significantly reduces p53-dependent transcription. This review describes the main molecular mechanisms involved in the interaction between viral oncoproteins and p53-related pathways as well as in the development of therapeutic strategies targeting such interactions.

Resveratrol Ameliorates Microcystin-LR-Induced Testis Germ Cell Apoptosis in Rats via SIRT1 Signaling Pathway Activation

Microcystin-leucine arginine (MC-LR), a cyclic heptapeptide produced by cyanobacteria, is a strong reproductive toxin. Studies performed in rat Sertoli cells and Chinese hamster ovary cells have demonstrated typical apoptosis after MC-LR exposure. However, little is known on how to protect against the reproductive toxicity induced by MC-LR. The present study aimed to explore the possible molecular mechanism underlying the anti-apoptosis and protective effects of resveratrol (RES) on the co-culture of Sertoli–germ cells and rat testes. The results demonstrated that MC-LR treatment inhibited the proliferation of Sertoli–germ cells and induced apoptosis. Furthermore, sirtuin 1 (SIRT1) and Bcl-2 were inhibited, while p53 and Ku70 acetylation, Bax expression, and cleaved caspase-3 were upregulated by MC-LR. However, RES pretreatment ameliorated MC-LR-induced apoptosis and SIRT1 inhibition, and downregulated the MC-LR-induced increase in p53 and Ku70 acetylation, Bax expression, and caspase-3 activation. In addition, RES reversed the MC-LR-mediated reduction in Ku70 binding to Bax. The present study indicated that the administration of RES could ameliorate MC-LR-induced Sertoli–germ cell apoptosis and protect against reproductive toxicity in rats by stimulating the SIRT1/p53 pathway, suppressing p53 and Ku70 acetylation and enhancing the binding of Ku70 to Bax.

Mutant and Wild-Type Tumor Suppressor p53 Induces p300 Autoacetylation

The transcriptional co-activator p300 is essential for p53 transactivation, although its precise role remains unclear. We report that p53 activates the acetyltransferase activity of p300 through the enhancement of p300 autoacetylation. Autoacetylated p300 accumulates near the transcription start sites accompanied by a similar enrichment of activating histone marks near those sites. Abrogation of p53-p300 interaction by a site-directed peptide inhibitor abolished p300-mediated histone acetylation, suggesting a crucial role played by the activation in p53-mediated gene regulation. Gain-of-function mutant p53, known to impart aggressive proliferative properties in tumor cells, also activates p300 autoacetylation. The same peptide abolished many of the gain-of-function properties of mutant p53 as well. Reversal of gain-of-function properties of mutant p53 suggests that molecules targeting the p53-p300 interface may be good candidates for anti-tumor drugs.

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Wild-type and mutant p53 are potent inducers of p300 autoacetylation

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p53 activates p300 catalytic activity by altering its structural conformation

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Induction of p300 autoacetylation possibly enhances p53-targeted gene expression

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Mutant-p53-induced p300 autoacetylation could be critical for tumorigenicity