p53 Is Cleaved by Caspases Generating Fragments Localizing to Mitochondria

Promising Anticancer Prodrugs Based on Pt(IV) Complexes with Bis-organosilane Ligands in Axial Positions

We report two novel prodrug Pt(IV) complexes with bis-organosilane ligands in axial positions: cis-dichloro(diamine)-trans-[3-(triethoxysilyl)propylcarbamate]platinum(IV) (Pt(IV)-biSi-1) and cis-dichloro(diisopropylamine)-trans-[3-(triethoxysilyl) propyl carbamate]platinum(IV) (Pt(IV)-biSi-2). Pt(IV)-biSi-2 demonstrated enhanced in vitro cytotoxicity against colon cancer cells (HCT 116 and HT-29) compared with cisplatin and Pt(IV)-biSi-1. Notably, Pt(IV)-biSi-2 exhibited higher cytotoxicity toward cancer cells and lower toxicity on nontumorigenic intestinal cells (HIEC6). In preclinical mouse models of colorectal cancer, Pt(IV)-biSi-2 outperformed cisplatin in reducing tumor growth at lower concentrations, with reduced side effects. Mechanistically, Pt(IV)-biSi-2 induced permanent DNA damage independent of p53 levels. DNA damage such as double-strand breaks marked by histone gH2Ax was permanent after treatment with Pt(IV)-biSi-2, in contrast to cisplatin's transient effects. Pt(IV)-biSi-2's faster reduction to Pt(II) species upon exposure to biological reductants supports its superior biological response. These findings unveil a novel strategy for designing Pt(IV) anticancer prodrugs with enhanced activity and specificity, offering therapeutic opportunities beyond conventional Pt drugs.

ERCC1 abundance is an indicator of DNA repair-apoptosis decision upon DNA damage

DNA repair is essential for successful propagation of genetic material and fidelity of transcription. Nucleotide excision repair (NER) is one of the earliest DNA repair mechanisms, functionally conserved from bacteria to human. The fact that number of NER genes vary significantly between prokaryotes and metazoans gives the insight that NER proteins have evolved to acquire additional functions to combat challenges associated with a diploid genome, including being involved in the decision between DNA repair and apoptosis. However, no direct association between apoptosis and NER proteins has been shown to date. In this study, we induced apoptosis with a variety of agents, including oxaliplatin, doxorubicin and TRAIL, and observed changes in the abundance and molecular weight of NER complex proteins. Our results showed that XPA, XPC and ERCC1 protein levels change during DNA damage-induced apoptosis. Among these, ERCC1 decrease was observed as a pre-mitochondria depolarisation event which marks the "point of no return" in apoptosis signalling. ERCC1 decrease was due to proteasomal degradation upon lethal doses of oxaliplatin exposure. When ERCC1 protein was stabilised using proteasome inhibitors, the pro-apoptotic activity of oxaliplatin was attenuated. These results explain why clinical trials using proteasome inhibitors and platinum derivatives showed limited efficacy in carcinoma treatment and also the importance of how deep understanding of DNA repair mechanisms can improve cancer therapy.

PICT-1 regulates p53 splicing and sensitivity of medullary thyroid carcinoma cells to everolimus

Protein interacting with carboxyl terminus 1 (PICT-1) is a nucleolar protein shown to act as a tumor suppressor that interacts with PTEN, or in a contrasting manner to facilitate the accessibility of p53 to ubiquitination and degradation, thus to function as an oncogene. The aim of the study was to examine the potential role of PICT-1 in neuroendocrine neoplasm (NEN) tumorigenesis and response to mTOR inhibitor treatment. PICT-1 was overexpressed in medullary thyroid (TT) and pancreatic (BON1) NEN cell lines using lentiviral vector. Whereas in BON1 cells PICT-1 overexpression exhibited no significant impact, in TT cells it induced the appearance of p53β lacking the C-terminus end. This was accompanied by a robust decrease in p21 expression and elevation of cell viability. Remarkably, PICT-1 overexpression completely reversed the reduction in cell viability of medullary thyroid neoplasm cells induced by everolimus, a therapeutic option for patients with progressive NENs. mTOR pathway investigations revealed that PICT-1 overexpression induced a reduction in PTEN expression and a robust increase in the expression level of phospho-Akt-Ser47 only partially inhibited by everolimus. These findings suggest a possible role of PICT-1 in the spliceosome machinery and provide functional involvement of PICT-1 in the complex network of mTOR.

Emerging methods for and novel insights gained by absolute quantification of mitochondrial DNA copy number and its clinical applications

The past thirty years have seen a surge in interest in pathophysiological roles of mitochondria, and the accurate quantification of mitochondrial DNA copy number (mCN) in cells and tissue samples is a fundamental aspect of assessing changes in mitochondrial health and biogenesis. Quantification of mCN between studies is surprisingly variable due to a combination of physiological variability and diverse protocols being used to measure this endpoint. The advent of novel methods to quantify nucleic acids like digital polymerase chain reaction (dPCR) and high throughput sequencing offer the ability to measure absolute values of mCN. We conducted an in-depth survey of articles published between 1969 -- 2020 to create an overview of mCN values, to assess consensus values of tissue-specific mCN, and to evaluate consistency between methods of assessing mCN. We identify best practices for methods used to assess mCN, and we address the impact of using specific loci on the mitochondrial genome to determine mCN. Current data suggest that clinical measurement of mCN can provide diagnostic and prognostic value in a range of diseases and health conditions, with emphasis on cancer and cardiovascular disease, and the advent of means to measure absolute mCN should improve future clinical applications of mCN measurements.

Microchip-Based Structure Determination of Disease-Relevant p53

The tumor suppressor protein TP53 (p53) plays a multifaceted role in all cells of the human body. Mutations in the TP53 gene are often involved in cancer induction and disease progression. Despite its important role in health and development, structural information for p53 remains incomplete. Here, we present a microchip-based technology to facilitate structural studies of p53 assemblies derived from human cancer cells. These devices do not introduce foreign sequences to the p53 gene and maintain naturally occurring post-translational modifications. Using cryo-electron microscopy, structures for the p53 monomer (∼50 kDa) and tetramer (∼200 kDa) were resolved to ∼4.8 and ∼7 Å, respectively. These structures revealed new insights for flexible regions of p53 along with biologically relevant ubiquitination sites. Collectively, the convergence of nanotechnology tools and structural imaging builds a strong framework to understand the oncogenic impact of p53 in human tissues.

Role of Asparagine Endopeptidase in Mediating Wild-Type p53 Inactivation of Glioblastoma

BACKGROUND

Isocitrate dehydrogenase wild-type (WT) glioblastoma (GBM) accounts for 90% of all GBMs, yet only 27% of isocitrate dehydrogenase WT-GBMs have p53 mutations. However, the tumor surveillance function of WT-p53 in GBM is subverted by mechanisms that are not fully understood.

METHODS

We investigated the proteolytic inactivation of WT-p53 by asparaginyl endopeptidase (AEP) and its effects on GBM progression in cancer cells, murine models, and patients' specimens using biochemical and functional assays. The sera of healthy donors (n = 48) and GBM patients (n = 20) were examined by enzyme-linked immunosorbent assay. Furthermore, effects of AEP inhibitors on GBM progression were evaluated in murine models (n = 6-8 per group). The statistical significance between groups was determined using two-tailed Student t tests.

RESULTS

We demonstrate that AEP binds to and directly cleaves WT-p53, resulting in the inhibition of WT-p53-mediated tumor suppressor function in both tumor cells and stromal cells via extracellular vesicle communication. High expression of uncleavable p53-N311A-mutant rescue AEP-induced tumorigenesis, proliferation, and anti-apoptotic abilities. Knock down or pharmacological inhibition of AEP reduced tumorigenesis and prolonged survival in murine models. However, overexpression of AEP promoted tumorigenesis and shortened the survival time. Moreover, high AEP levels in GBM tissues were associated with a poor prognosis of GBM patients (n = 83; hazard ratio = 3.94, 95% confidence interval = 1.87 to 8.28; P < .001). A correlation was found between high plasma AEP levels and a larger tumor size in GBM patients (r = 0.6, P = .03), which decreased dramatically after surgery.

CONCLUSIONS

Our results indicate that AEP promotes GBM progression via inactivation of WT-p53 and may serve as a prognostic and therapeutic target for GBM.

Curcumin induced apoptosis is mediated through oxidative stress in mutated p53 and wild type p53 colon adenocarcinoma cell lines

Curcumin has anti-oxidant, anti-cancer and anti-carcinogen property. Our laboratory had previously reported that, curcumin treatment induces reactive oxygen species (ROS) generation in HT-29 cell line, an effect contradictory to its anti-oxidant property. This study evaluates the role of p53 in curcumin mediated ROS generation and cell death. Curcumin induced ROS was determined by 2',7'-dichlorofluorescein and apoptosis by Hoechst33342/PI staining in HT-29 and HCT-116 cell lines. ROS generation occurs within 1 hour of 40 µM curcumin treatment and a reduction was observed by third hour in HCT-116 insinuating p53 involvement. N-acetyl cysteine (NAC) pre-treatment effectively quenched ROS and inhibited membrane potential loss in HT-29, but less effective in HCT-116. Mitochondrial membrane potential loss is evident with 10 and 40 µM curcumin in HCT-116 and at 40 µM curcumin in HT-29. Total p53 protein level increase was observed by 24 hours in HCT-116 upon NAC pre-treatment. Our results indicate that curcumin induces ROS mediated cell death in colon adenocarcinoma cell lines and may be mediated via p53.

P53 aggregation, interactions with tau, and impaired DNA damage response in Alzheimer's disease

The transcription factor, p53, is critical for many important cellular functions involved in genome integrity, including cell cycle control, DNA damage response, and apoptosis. Disruption of p53 results in a wide range of disorders including cancer, metabolic diseases, and neurodegenerative diseases. Alzheimer's disease (AD) is a neurodegenerative disorder characterized by protein aggregates that contribute to disease pathology. Although p53 is known to aggregate, its propensity to aggregate in AD has never been assessed. Moreover, AD neuropathology includes lethal cell cycle re-entry, excessive DNA damage, and abnormal cell death which are all controlled by p53. Here, we show p53 forms oligomers and fibrils in human AD brain, but not control brain. p53 oligomers can also be detected in htau and P301L mouse models. Additionally, we demonstrate that p53 interacts with tau, specifically tau oligomers, in AD brain and can be recapitulated by in vitro exogenous tau oligomer treatment in C57BL/6 primary neurons. p53 oligomers also colocalize, potentially seeding, endogenous p53 in primary neurons. Lastly, we demonstrate that in the presence of DNA damage, phosphorylated p53 is mislocalized outside the nucleus and p53-mediated DNA damage responders are significantly decreased in AD brain. Control brain shows a healthy DNA damage response, indicating a loss of nuclear p53 function in AD may be due to p53 aggregation and/or interactions with tau oligomers. Given the critical role of p53 in cellular physiology, the disruption of this crucial transcription factor may set an irreversible course towards neurodegeneration in AD and potentially other tauopathies, warranting further investigation.

Cell-Cycle Cross Talk with Caspases and Their Substrates

Caspases play central roles in mediating both cell death and inflammation. It has more recently become evident that caspases also drive other biological processes. Most prominently, caspases have been shown to be involved in differentiation. Several stem and progenitor cell types rely on caspases to initiate and execute their differentiation processes. These range from neural and glial cells, to skeletal myoblasts and osteoblasts, and several cell types of the hematopoietic system. Beyond differentiation, caspases have also been shown to play roles in other "noncanonical" processes, including cell proliferation, arrest, and senescence, thereby contributing to the mechanisms that regulate tissue homeostasis at multiple levels. Remarkably, caspases directly influence the course of the cell cycle in both a positive and negative manner. Caspases both cleave elements of the cell-cycle machinery and are themselves substrates of cell-cycle kinases. Here we aim to summarize the breadth of interactions between caspases and cell-cycle regulators. We also highlight recent developments in this area.

O-linked N-acetylgalactosamine modification is present on the tumor suppressor p53

BACKGROUND

Mucin-type O-glycosylation (referred to as O-GalNAc glycosylation) is the most abundant O-glycosylation on membrane and secretory proteins. Recently several evidences suggest that nuclear or cytoplasmic proteins might also have O-GalNAc glycosylation. However, what nucleocytoplasmic proteins are O-GalNAc glycosylated and what the biological function of this modification in cells are still poorly understood. Previously, we reported the tumor suppressor p53 could be O-GalNAc glycosylated in vitro. To investigate the existence and function of O-GalNAc glycosylation on nucleocytoplasmic proteins in cell, p53 as a representative nucleocytoplasmic protein was studied.

METHODS

Using lectin blotting with GalNAc specific lectins, enzymatic treatments with O-GlcNAcase, core 1 β1, 3-galactosyltransferase and O-glycosidase, and metabolic labeling with un-O-acetylated GalNAz in UDP-Gal/UDP-GalNAc 4-epimerase (GALE) knockout cells, we validated the O-GalNAc glycosylation on p53. Using mass spectrometry analysis and site-directed mutagenesis, we identified the glycosylated sites and studied the functions of O-GalNAc glycosylation on p53.

RESULTS

The p53 was O-GalNAc glycosylated in cells. Ser121 residue was one of the glycosylated sites on p53. The O-GalNAc glycosylation at Ser121 was associated with the stability and activity of p53.

CONCLUSIONS

These results revealed that the O-GalNAc glycosylation was a novel modification on p53.

GENERAL SIGNIFICANCE

Our study provided a pilot evidence that the O-GalNAc glycosylation existed on nucleocytoplasmic protein.

2,4,5-Tris(alkoxyaryl)imidazoline derivatives as potent scaffold for novel p53-MDM2 interaction inhibitors: Design, synthesis, and biological evaluation

Imidazoline-based small molecule inhibitors of p53-MDM2 interaction intended for the treatment of p53 wild-type tumors are the promising structures for design of anticancer drugs. Based on fragment approach we have investigated a key role of substituents in cis-imidazoline core for biological activity of nutlin family compounds. Although the necessity of the substituents in the phenyl rings of cis-imidazoline has been shown, there are no studies in which the replacements of a halogen by other substituents have been investigated. A series of simple cis-imidazoline derivatives containing halogen, hydroxy and alkoxy-substituents were synthesized. The biological activity of the compounds was studied using assays of cytotoxicity (MTT) and p53 level. It was found that the hydroxyl-derivatives were not cytotoxic whereas the alkoxy analogues were the same or more active as halogen-substituted compounds in cell viability test. The synthesized alkoxy derivatives induced an increase of p53 level and did not promote necrotic cell death in the concentration up to 40 µM.

The potential use of bromelain as a natural oral medicine having anticarcinogenic activities

Bromelain (BR), a protease extracted from Ananas comosus, reportedly possesses pharmacological activities including the reduction of thrombogenesis, and antihypertensive, and antimicrobial effects. This study aimed to investigate the potential effects of BR on oral cancer cells. The effect of BR on the viability of Ca9-22 and SCC25 cells was determined using the MTT assay. These cells were also treated with different doses of BR, and Western blotting was conducted to monitor apoptosis. Finally, flow cytometry analysis was performed to identify sub-G1 populations of oral cancer cells. After treatment, the viability of both Ca9-22 and SCC25 cells was markedly reduced, in a dose-dependent manner. BR induced poly (ADP-ribose) polymerase (PARP) and lamin A/C degradation, and generated cleavage products. Flow cytometry analysis showed that BR treatment significantly increased the sub-G1 population. Our findings therefore indicate that BR has potential as a novel, natural anticarcinogenic medicine.

Impact of p53 status on TRAIL-mediated apoptotic and non-apoptotic signaling in cancer cells

Due to their ability to preferentially induce cell death in tumor cells, while sparing healthy cells, TNF-related apoptosis-inducing ligand (TRAIL) and agonistic anti-TRAIL-R1 or anti-TRAIL-R2-specific antibodies are under clinical investigations for cancer-treatment. However, TRAIL-Rs may also induce signaling pathways, which result in malignant progression. TRAIL receptors are transcriptionally upregulated via wild-type p53 following radio- or chemotherapy. Nevertheless, the impact of p53 status on the expression and signaling of TRAIL-Rs is not fully understood. Therefore, we analyzed side by side apoptotic and non-apoptotic signaling induced by TRAIL or the agonistic TRAIL-R-specific antibodies Mapatumumab (anti-TRAIL-R1) and Lexatumumab (anti-TRAIL-R2) in the two isogenic colon carcinoma cell lines HCT116 p53^+/+ and p53^-/-. We found that HCT116 p53^+/+ cells were significantly more sensitive to TRAIL-R-triggering than p53^-/- cells. Similarly, A549 lung cancer cells expressing wild-type p53 were more sensitive to TRAIL-R-mediated cell death than their derivatives with knockdown of p53. Our data demonstrate that the contribution of p53 in regulating TRAIL-R-induced apoptosis does not correlate to the levels of TRAIL-Rs at the plasma membrane, but rather to p53-mediated upregulation of Bax, favouring the mitochondrial amplification loop. Consistently, stronger caspase-9 and caspase-3 activation as well as PARP-cleavage was observed following TRAIL-R-triggering in HCT116 p53^+/+ compared to HCT116 p53^-/- cells. Interestingly, HCT116 p53^+/+ cells showed also a more potent activation of non-canonical TRAIL-R-induced signal transduction pathways like JNK, p38 and ERK1/ERK2 than p53^-/- cells. Likewise, these cells induced IL-8 expression in response to TRAIL, Mapatumumab or Lexatumumab significantly stronger than p53^-/- cells. We obtained similar results in A549 cells with or without p53-knockdown and in the two isogenic colon cancer cell lines RKO p53^+/+ and p53^-/-. In both cellular systems, we could clearly demonstrate the potentiating effects of p53 on TRAIL-R-mediated IL-8 induction. In conclusion, we found that wild-type p53 increases TRAIL-R-mediated apoptosis but simultaneously augments non-apoptotic signaling.

ROR1 Expression and Its Functional Significance in Hepatocellular Carcinoma Cells

Background: Hepatocellular carcinoma (HCC) is a common and deadly cancer; however, very little improvement has been made towards its diagnosis and prognosis. The expression and functional contribution of the receptor tyrosine kinase ROR1 have not been investigated in HCC before. Hence, we investigated the expression of ROR1 in HCC cells and assessed its involvement in hepatocarcinogenesis. Methods: Recombinant bacterial ROR1 protein was used as an immunogen to generate ROR1 monoclonal antibodies. ROR1 transcript levels were detected by RT-qPCR and the protein expression of ROR1 in HCC was assessed by Western blotting by using homemade anti-ROR1 monoclonal antibodies. Apoptosis, cell cycle, trans-well migration, and drug efflux assays were performed in shRNA-ROR1 HCC cell clones to uncover the functional contribution of ROR1 to hepatocarcinogenesis. Results: New ROR1 antibodies specifically detected endogenous ROR1 protein in human and mouse HCC cell lines. ROR1-knockdown resulted in decreased proliferation and migration but enhanced resistance to apoptosis and anoikis. The observed chemotherapy-resistant phenotype of ROR1-knockdown cells was due to enhanced drug efflux and increased expression of multi-drug resistance genes. Conclusions: ROR1 is expressed in HCC and contributes to disease development by interfering with multiple pathways. Acquired ROR1 expression may have diagnostic and prognostic value in HCC.

Cereblon attenuates DNA damage-induced apoptosis by regulating the transcription-independent function of p53

Cereblon (CRBN) is the substrate receptor of the cullin 4-RING E3 ligase complex and has been employed for targeted protein degradation in the treatment of cancers. However, its normal physiological functions and molecular mechanism in the regulation of DNA damage response are largely unknown. Here we find that CRBN plays a protective role against DNA damage-induced apoptosis in cell lines and primary cells. Mechanistic studies demonstrate that although CRBN does not affect the ubiquitination and degradation of the tumor suppressor p53, it directly interacts with p53 and therefore, suppresses the interaction between p53 and anti-apoptotic regulators Bcl-2 and Bcl-X_L. CRBN depletion enhances the interaction between p53 and Bcl-2/Bcl-X_L, reduces mitochondrial membrane potential, increases the cleavage of caspase-3 and poly(ADP-ribose) polymerase 1, and thus promotes DNA damage-induced apoptosis in cell lines and primary cells upon etoposide treatment. Moreover, Crbn knockout mice exhibit increased mortality upon etoposide challenge. Taken together, our data elucidate a novel molecular mechanism by which CRBN inhibits DNA damage response in vitro and in vivo. This work extends our understanding of the broad spectrum of physiological roles for CRBN and may suggest its potential application in the treatment of DNA damage-associated diseases.

Cytoplasmic pro-apoptotic function of the tumor suppressor p73 is mediated through a modified mode of recognition of the anti-apoptotic regulator Bcl-XL

In response to genotoxic stress, the tumor suppressor protein p73 induces apoptosis and cell cycle arrest. Despite extensive studies on p73-mediated apoptosis, little is known about the cytoplasmic apoptotic function of p73. Here, using H1299 lung cancer cells and diverse biochemical approaches, including colony formation, DNA fragmentation, GST pulldown, and apoptosis assays along with NMR spectroscopy, we show that p73 induces transcription-independent apoptosis via its transactivation domain (TAD) through a mitochondrial pathway and that this apoptosis is mediated by the interaction between p73-TAD and the anti-apoptotic protein B-cell lymphoma-extra large (Bcl-X_L or BCL2L1). This binding disrupted an interaction between Bcl-X_L and the pro-apoptotic protein BH3-interacting domain death agonist (Bid). In particular, we found that a 16-mer p73-TAD peptide motif (p73-TAD16) mediates transcription-independent apoptosis, accompanied by cytochrome c release from the mitochondria, by interacting with Bcl-X_L Interestingly, the structure of the Bcl-X_L-p73-TAD16 peptide complex revealed a novel mechanism of Bcl-X_L recognition by p73-TAD. We observed that the α-helical p73-TAD16 peptide binds to a noncanonical site in Bcl-X_L, comprising the BH1, BH2, and BH3 domains in an orientation opposite to those of pro-apoptotic BH3 peptides. Taken together, our results indicate that the cytoplasmic apoptotic function of p73 is mediated through a noncanonical mode of Bcl-X_L recognition. This finding sheds light on a critical transcription-independent, p73-mediated mechanism for apoptosis induction, which has potential implications for anticancer therapy.

Pir2/Rnf144b is a potential endometrial cancer biomarker that promotes cell proliferation

Endometrial cancer is one of the most common gynaecological cancers in developed countries. Its incidence has increased 20% over the last decade and the death rate has increased >100% over the past two decades. Current models for prediction of prognosis and treatment response are suboptimal, and as such biomarkers to support clinical decision-making and contribute to individualised treatment are needed. In this study, we show that the E3-ubiquitin ligase PIR2/RNF144B is a potential targetable biomarker in endometrial cancer. At transcript level, it is expressed both in normal endometrium and tumour samples, but at protein level, it is expressed in tumours only. By using endometrial cancer cell lines, we demonstrated that PIR2/RNF144B is stabilised via phosphorylation downstream of GSK3β and this is necessary for the proliferation of endometrial cancer cells, in the absence of oestrogenic growth stimuli. Here, inactivation of GSK3β activity is associated with loss of PIR2/RNF144B protein and consequent inhibition of cell proliferation. Our results, therefore, substantiate PIR2/RNF144B as a novel candidate for targeted therapy in endometrial cancer.

Mitochondrial determinants of cancer health disparities

Mitochondria, which are multi-functional, have been implicated in cancer initiation, progression, and metastasis due to metabolic alterations in transformed cells. Mitochondria are involved in the generation of energy, cell growth and differentiation, cellular signaling, cell cycle control, and cell death. To date, the mitochondrial basis of cancer disparities is unknown. The goal of this review is to provide an understanding and a framework of mitochondrial determinants that may contribute to cancer disparities in racially different populations. Due to maternal inheritance and ethnic-based diversity, the mitochondrial genome (mtDNA) contributes to inherited racial disparities. In people of African ancestry, several germline, population-specific haplotype variants in mtDNA as well as depletion of mtDNA have been linked to cancer predisposition and cancer disparities. Indeed, depletion of mtDNA and mutations in mtDNA or nuclear genome (nDNA)-encoded mitochondrial proteins lead to mitochondrial dysfunction and promote resistance to apoptosis, the epithelial-to-mesenchymal transition, and metastatic disease, all of which can contribute to cancer disparity and tumor aggressiveness related to racial disparities. Ethnic differences at the level of expression or genetic variations in nDNA encoding the mitochondrial proteome, including mitochondria-localized mtDNA replication and repair proteins, miRNA, transcription factors, kinases and phosphatases, and tumor suppressors and oncogenes may underlie susceptibility to high-risk and aggressive cancers found in African population and other ethnicities. The mitochondrial retrograde signaling that alters the expression profile of nuclear genes in response to dysfunctional mitochondria is a mechanism for tumorigenesis. In ethnic populations, differences in mitochondrial function may alter the cross talk between mitochondria and the nucleus at epigenetic and genetic levels, which can also contribute to cancer health disparities. Targeting mitochondrial determinants and mitochondrial retrograde signaling could provide a promising strategy for the development of selective anticancer therapy for dealing with cancer disparities. Further, agents that restore mitochondrial function to optimal levels should permit sensitivity to anticancer agents for the treatment of aggressive tumors that occur in racially diverse populations and hence help in reducing racial disparities.

Hematoporphyrin monomethyl ether combined with He-Ne laser irradiation-induced apoptosis in canine breast cancer cells through the mitochondrial pathway

Hematoporphyrin monomethyl ether (HMME) combined with He-Ne laser irradiation is a novel and promising photodynamic therapy (PDT)-induced apoptosis that can be applied in vitro on canine breast cancer cells. However, the exact pathway responsible for HMME-PDT in canine breast cancer cells remains unknown. CHMm cells morphology and apoptosis were analyzed using optical microscope, terminal deoxynucleotidyl transferase dUTP nick end labeling fluorescein staining and DNA ladder assays. Apoptotic pathway was further confirmed by Real-time-polymerase chain reaction and Western blotting assays. Our results showed that HMME-PDT induced significant changes in cell morphology, such as formation of cytoplasmic vacuoles and the gradual rounding of cells coupled with decreased size and detachment. DNA fragmentation and cell death was shown to occur in a time-dependent manner. Furthermore, HMME-PDT increased the activities of caspase-9 and caspase-3, and released cytochrome c from mitochondria into the cytoplasm. HMME-PDT also significantly increased both mRNA and protein levels of Bax and decreased P53 gene expression in a time-dependent manner, while the mRNA and protein expression of Bcl-2 were repressed. These alterations suggest that HMME-PDT induced CHMm cell apoptosis via the mitochondrial apoptosis pathway and had anti-canine breast cancer effects in vitro.

Decrease of mitochondrial p53 during late apoptosis is linked to its dephosphorylation on serine 20

Following a genotoxic stress, the tumor suppressor p53 translocates to mitochondria to take part in direct induction of apoptosis, via interaction with BCL-2 family members such as BAK and BAX. We determined the kinetics of the mitochondrial translocation of p53 in HCT-116 and PA-1 cells exposed to different genotoxic stresses (doxorubicin, camptothecin, UVB). This analysis revealed an early escalation in the amount of mitochondrial p53, followed by a peak amount and a decrease of mitochondrial p53 at later time points. We show that the serine 20 phosphorylated form of p53 is present at the mitochondria and that the decrease of p53 mitochondrial level during late apoptosis correlates with a decrease of Ser-20 phosphorylation. Moreover, the S20A p53 mutant translocates well to mitochondria after a genotoxic stress but its mitochondrial localization is very low during late apoptosis when compared to wt p53. The S20A mutant also appears to be compromised for interaction with BAK. We propose here that the level of serine 20 phosphorylation is influential on p53 mitochondrial localization during late apoptosis. Additionally, we report the presence of a new ≃45 kDa caspase-cleaved fragment of p53 in the cytosolic and mitochondrial fractions of apoptotic cells.

Nuclear localization of the caspase-3-cleaved form of p73 in anoikis

The transcription factor p73 is a homologue of p53 that can be expressed as pro- or anti-apoptotic isoforms. Unlike p53, p73 is rarely mutated or lost in cancers and it is found to replace defective p53 inducing apoptosis. Here, we investigated the p73 involvement in anoikis, a type of apoptosis caused by inadequate cell-matrix interactions. Breast cancer cell lines with different p53 status were treated with doxorubicin (DOX) or docetaxel (DOC) and cells detached from the extracellular matrix were analyzed. We demonstrate for the first time that DOX-induced cell detachment is associated with p73 cleavage and caspase activation, independently of the p53 status. However, we did not detect p73 cleavage or caspase activation in detached cells under DOC treatment. Overexpressing the apoptotic isoform of p73 led to cell detachment associated with p73 cleavage and caspase activation. Interestingly, p73 cleaved forms localize to the nucleus during the late phase of cell death indicating an increase in the transcriptional activity. Our study suggests that the cleavage of p73 on specific sites may release its pro-apoptotic function and contribute to cell death.

Alterations in Mitochondrial and Endoplasmic Reticulum Signaling by p53 Mutants

The p53 protein is probably the most important tumor suppressor, acting as a nuclear transcription factor primarily through the modulation of cell death. However, currently, it is well accepted that p53 can also exert important transcription-independent pro-cell death actions. Indeed, cytosolic localization of endogenous wild-type or transactivation-deficient p53 is necessary and sufficient for the induction of apoptosis and autophagy. Here, we present the extra-nuclear activities of p53 associated with the mitochondria and the endoplasmic reticulum, highlighting the activities of the p53 mutants on these compartments. These two intracellular organelles play crucial roles in the regulation of cell death, and it is now well established that they also represent sites where p53 can accumulate.

p63 threonine phosphorylation signals the interaction with the WW domain of the E3 ligase Itch

Both in epithelial development as well as in epithelial cancers, the p53 family member p63 plays a crucial role acting as a master transcriptional regulator. P63 steady state protein levels are regulated by the E3 ubiquitin ligase Itch, via a physical interaction between the PPxY consensus sequence (PY motif) of p63 and one of the 4 WW domains of Itch; this substrate recognition process leads to protein-ubiquitylation and p63 proteasomal degradation. The interaction of the WW domains, a highly compact protein-protein binding module, with the short proline-rich sequences is therefore a crucial regulatory event that may offer innovative potential therapeutic opportunity. Previous molecular studies on the Itch-p63 recognition have been performed in vitro using the Itch-WW2 domain and the peptide interacting fragment of p63 (pep63), which includes the PY motif. Itch-WW2-pep63 interaction is also stabilized in vitro by the conformational constriction of the S-S cyclization in the p63 peptide. The PY motif of p63, as also for other proteins, is characterized by the nearby presence of a (T/S)P motif, which is a potential recognition site of the WW domain of the IV group present in the prolyl-isomerase Pin1. In this study, we demonstrate, by in silico and spectroscopical studies using both the linear pep63 and its cyclic form, that the threonine phosphorylation of the (T/S)PPPxY motif may represent a crucial regulatory event of the Itch-mediated p63 ubiquitylation, increasing the Itch-WW domains-p63 recognition event and stabilizing in vivo the Itch-WW-p63 complex. Moreover, our studies confirm that the subsequently trans/cis proline isomerization of (T/S)P motif by the Pin1 prolyl-isomerase, could modulate the E3-ligase interaction, and that the (T/S)pPtransPPxY motif represent the best conformer for the ItchWW-(T/S)PPPxY motif recognition.

Structural insights into the transcription-independent apoptotic pathway of p53

Reactivating the p53 pathway in tumors is an important strategy for anticancer therapy. In response to diverse cellular stresses, the tumor suppressor p53 mediates apoptosis in a transcriptionindependent and transcription-dependent manner. Although extensive studies have focused on the transcription-dependent apoptotic pathway of p53, the transcription-independent apoptotic pathway of p53 has only recently been discovered. Molecular interactions between p53 and Bcl-2 family proteins in the mitochondria play an essential role in the transcriptionindependent apoptosis of p53. This review describes the structural basis for the transcription-independent apoptotic pathway of p53 and discusses its potential application to anticancer therapy. [BMB Reports 2014; 47(3): 167-172]

Tumor suppressor p53 and estrogen receptors in nuclear-mitochondrial communication

Several gene transcription regulators considered solely localized within the nuclear compartment are being reported to be present in the mitochondria as well. There is growing interest in the role of mitochondria in regulating cellular metabolism in normal and disease states. Various findings demonstrate the importance of crosstalk between nuclear and mitochondrial genomes, transcriptomes, and proteomes in regulating cellular functions. Both tumor suppressor p53 and estrogen receptor (ER) were originally characterized as nuclear transcription factors. In addition to their individual roles as regulators of various genes, these two proteins interact resulting in major cellular consequences. In addition to its nuclear role, p53 has been localized to the mitochondria where it executes various transcription-independent functions. Likewise, ERs are reported to be present in mitochondria; however their functional roles remain to be clearly defined. In this review, we provide an integrated view of the current knowledge of nuclear and mitochondrial p53 and ERs and how it relates to normal and pathological physiology.

Comprehensive genomic profiling in diabetic nephropathy reveals the predominance of proinflammatory pathways

Despite advances in the treatment of diabetic nephropathy (DN), currently available therapies have not prevented the epidemic of progressive chronic kidney disease (CKD). The morbidity of CKD, and the inexorable increase in the prevalence of end-stage renal disease, demands more effective approaches to prevent and treat progressive CKD. We undertook next-generation sequencing in a rat model of diabetic nephropathy to study in depth the pathogenic alterations involved in DN with progressive CKD. We employed the obese, diabetic ZS rat, a model that develops diabetic nephropathy, characterized by progressive CKD, inflammation, and fibrosis, the hallmarks of human disease. We then used RNA-seq to examine the combined effects of renal cells and infiltrating inflammatory cells acting as a pathophysiological unit. The comprehensive systems biology analysis of progressive CKD revealed multiple interactions of altered genes that were integrated into morbid networks. These pathological gene assemblies lead to renal inflammation and promote apoptosis and cell cycle arrest in progressive CKD. Moreover, in what is clearly a major therapeutic challenge, multiple and redundant pathways were found to be linked to renal fibrosis, a major cause of kidney loss. We conclude that systems biology applied to progressive CKD in DN can be used to develop novel therapeutic strategies directed to restore critical anomalies in affected gene networks.

Cytotoxic effects of bromelain in human gastrointestinal carcinoma cell lines (MKN45, KATO-III, HT29-5F12, and HT29-5M21)

Background

Bromelain is a pineapple stem extract with a variety of therapeutic benefits arising from interaction with a number of different biological processes. Several preclinical studies and anecdotal clinical observations have reported the anticancer properties of bromelain. In the present study, we investigated the cytotoxic effects of bromelain in four human cancer cell lines of gastrointestinal origin and the mechanisms involved.

Methods

The gastric carcinoma cell lines (KATO-III and MKN45) and two chemoresistant subpopulations of the HT29 colon adenocarcinoma cell line (HT29-5M21 and HT29-5F12) were treated with a range of concentrations of bromelain, as well as with cisplatin as a positive control. The effect of bromelain on the growth and proliferation of cancer cells was determined using a sulforhodamine B assay after 72 hours of treatment. Expression of apoptosis-associated proteins in MKN45 cells treated with bromelain was analyzed by Western blotting.

Results

Data from our sulforhodamine B assay showed that bromelain inhibited proliferation of HT29-5F12, HT29-5M21, MKN45, and KATO-III cells, with respective half maximal inhibitory concentration values of 29, 34, 94, and 142 μg/mL. Analyzing the expression of proapoptotic and antiapoptotic proteins in bromelain-treated MKN45 cells, we observed activation of the caspase system, cleavage of PARP and p53, overexpression of cytochrome C, attenuation of phospho-Akt and Bcl2, and removal of MUC1. Apart from the caspase-dependent apoptosis observed, emergence of cleaved p53 supports a direct, extranuclear apoptotic function of p53. Moreover, interrupted Akt signaling and attenuation of Bcl2 and MUC1 oncoproteins suggest impaired survival of cancer cells.

Conclusion

Our findings collectively indicate that bromelain exerts cytotoxic effects in a panel of human gastric and colon carcinoma cells. Our study of MKN45 cells implicated different mechanisms in bromelain-induced cell death. While promoting apoptosis with involvement of the caspase system and extranuclear p53, bromelain also appears to impair cancer cell survival by blocking the Akt pathway and attenuating Bcl2 and MUC1 oncoproteins.

Caspase-3 mediated release of SAC domain containing fragment from Par-4 is necessary for the sphingosine-induced apoptosis in Jurkat cells

Background

Prostate apoptosis response-4 (Par-4) is a tumor-suppressor protein that selectively activates and induces apoptosis in cancer cells, but not in normal cells. The cancer specific pro-apoptotic function of Par-4 is encoded in its centrally located SAC (Selective for Apoptosis induction in Cancer cells) domain (amino acids 137–195). The SAC domain itself is capable of nuclear entry, caspase activation, inhibition of NF-κB activity, and induction of apoptosis in cancer cells. However, the precise mechanism(s) of how the SAC domain is released from Par-4, in response to apoptotic stimulation, is not well explored.

Results

In this study, we demonstrate for the first time that sphingosine (SPH), a member of the sphingolipid family, induces caspase-dependant cleavage of Par-4, leading to the release of SAC domain containing fragment from it. Par-4 is cleaved at the EEPD131G site on incubation with caspase-3 in vitro, and by treating cells with several anti-cancer agents. The caspase-3 mediated cleavage of Par-4 is blocked by addition of the pan-caspase inhibitor z-VAD-fmk, caspase-3 specific inhibitor Ac-DEVD-CHO, and by introduction of alanine substitution for D131 residue. Moreover, suppression of SPH-induced Akt dephosphorylation also abrogated the caspase dependant cleavage of Par-4.

Conclusion

Evidence provided here shows that Par-4 is cleaved by caspase-3 during SPH-induced apoptosis. Cleavage of Par-4 leads to the generation of SAC domain containing fragment which may possibly be essential and sufficient to induce or augment apoptosis in cancer cells.

In vitro radiosensitization by pentoxifylline does not depend on p53 status

PURPOSE

The mode by which the xanthine derivative, pentoxifylline, induces a radiosensitizing effect in cell cultures is a key and controversial radiobiological issue and requires further elucidation.

MATERIALS AND METHODS

Six human glioblastoma cell lines were tested for the effect of pentoxifylline treatment at maximum G2/M block on the basis of cell survival, mitotic activity, and micronucleus formation after exposure to gamma radiation. Cell survival was measured by the colony-forming assay. Micronucleus formation (an indicator of DNA damage) and the proportion of binucleated cells (a representation of mitotic activity) were determined using the cytokinesis-block assay.

RESULTS

Remarkably, exposure to a single dose of 4 Gy produced strong G2/M blocks in both p53 mutant and wild-type cells. Addition of pentoxifylline at the peak of radiation-induced G2/M blocks resulted in a p53-independent reduction in cell survival in all cell lines. This radiosensitization was strongly correlated with the magnitude of the radiation-induced G2/M block. The changes observed in mitotic activity and micronucleus yield were also p53-independent.

CONCLUSIONS

These results are at variance with the view that pentoxifylline preferentially sensitizes p53 mutant cells, and that sensitization occurs only when cells are irradiated in the presence of the drug. The data suggest that the effectiveness of pentoxifylline as radiosensitizer depends on the proportion of cells that are arrested in the G2/M phase transition following exposure to ionizing radiation. These findings can assist in the identification of cancers that may benefit from therapies using G2/M checkpoint abrogators.

Phosphorylation of eIF2α attenuates statin-induced apoptosis by inhibiting the stabilization and translocation of p53 to the mitochondria

Statins are effective cholesterol-lowering drugs that exert pleiotropic effects, including cytotoxicity to cancer cells. We previously reported that simvastatin triggered the mitochondrial apoptotic pathway in MethA fibrosarcoma cells, which was accompanied by the translocation of stabilized p53 to the mitochondria. In this study, we investigated whether statins induce the endoplasmic reticulum (ER) stress response and the mechanisms by which this response is linked to the stabilization of p53 and its translocation to the mitochondria. Statins induced typical ER stress-related proteins, such as BiP/78 kDa glucose-regulated protein (Grp78) and CCAAT/ enhancer-binding protein homologous protein (CHOP), as well as the phosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (PERK), eIF2α and JNK. The statin-induced phosphorylation of eIF2α and JNK was inhibited by supplementation with components of the mevalonate pathway, such as mevalonate, farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). Salubrinal, an inhibitor of the dephosphorylation of eIF2α, suppressed the loss of mitochondrial membrane potential and the translocation of stabilized p53 and Bax to the mitochondria; however, SP600125, a JNK kinase inhibitor, did not exert this effect. Furthermore, the eIF2α knockdown sensitized cells to simvastatin-induced apoptosis and the overexpression of a non-phosphorylatable eIF2α-mutant [serine 51(Ser51)/alanine] enhanced the stabilization of p53 and its translocation to the mitochondria in response to simvastatin treatment. Taken together, these data indicate that eIF2α phosphorylation in the context of the ER stress response plays a role in cell survival by counteracting the p53-mediated mitochondrial apoptosis in response to statins.

Dual-site interactions of p53 protein transactivation domain with anti-apoptotic Bcl-2 family proteins reveal a highly convergent mechanism of divergent p53 pathways

Molecular interactions between the tumor suppressor p53 and the anti-apoptotic Bcl-2 family proteins play an important role in the transcription-independent apoptosis of p53. The p53 transactivation domain (p53TAD) contains two conserved ΦXXΦΦ motifs (Φ indicates a bulky hydrophobic residue and X is any other residue) referred to as p53TAD1 (residues 15-29) and p53TAD2 (residues 39-57). We previously showed that p53TAD1 can act as a binding motif for anti-apoptotic Bcl-2 family proteins. In this study, we have identified p53TAD2 as a binding motif for anti-apoptotic Bcl-2 family proteins by using NMR spectroscopy, and we calculated the structures of Bcl-X(L)/Bcl-2 in complex with the p53TAD2 peptide. NMR chemical shift perturbation data showed that p53TAD2 peptide binds to diverse members of the anti-apoptotic Bcl-2 family independently of p53TAD1, and the binding between p53TAD2 and p53TAD1 to Bcl-X(L) is competitive. Refined structural models of the Bcl-X(L)·p53TAD2 and Bcl-2·p53TAD2 complexes showed that the binding sites occupied by p53TAD2 in Bcl-X(L) and Bcl-2 overlap well with those occupied by pro-apoptotic BH3 peptides. Taken together with the mutagenesis, isothermal titration calorimetry, and paramagnetic relaxation enhancement data, our structural comparisons provided the structural basis of p53TAD2-mediated interaction with the anti-apoptotic proteins, revealing that Bcl-X(L)/Bcl-2, MDM2, and cAMP-response element-binding protein-binding protein/p300 share highly similar modes of binding to the dual p53TAD motifs, p53TAD1 and p53TAD2. In conclusion, our results suggest that the dual-site interaction of p53TAD is a highly conserved mechanism underlying target protein binding in the transcription-dependent and transcription-independent apoptotic pathways of p53.

Inhibition of platelet-derived growth factor receptor tyrosine kinase and downstream signaling pathways by Compound C

AMP-activated protein kinase (AMPK) has been implicated in anti-proliferative actions in a range of cell systems. Recently, it was observed that Compound C, an inhibitor of AMPK, also reduced the cell viability in human diploid fibroblasts (HDFs). Compound C-induced growth arrest was associated with a decrease in the cell cycle regulatory proteins, such as proliferating cell nuclear antigen, phosphorylated pRB, cyclin-dependent protein kinases (Cdk 2 and 4), cyclins (D and E), and the Cdk inhibitors (p21, p16, and p27). Therefore, the present study examined the molecular mechanism of the antiproliferative effects of Compound C. Although Compound C inhibited serum-induced phosphorylation of Akt and its substrate, glycogen synthase kinase-3β, it did not affect the Akt activity in vitro. Compound C significantly inhibited the receptor tyrosine phosphorylation and the activity of downstream signaling molecules, such as p85 phosphoinositide 3-kinase, phospholipase C-γ1, and extracellular signal-regulated kinase 1/2, induced by platelet-derived growth factor (PDGF) but not by epidermal growth factor- and insulin-like growth factor. In vitro growth factor receptor tyrosine kinase activity profiling revealed the IC50 for PDGF receptor-β (PDGFRβ) to be 5.07μM, whereas the IC50 for the epidermal growth factor receptor and insulin-like growth factor receptor was ≥100μM. The inhibitory effect of Compound C on PDGFRβ and Akt was also observed in AMPKα1/α2-knockout mouse embryonic fibroblasts, indicating that its inhibitory effect is independent of the AMPK activity. The inhibitory effect of Compound C on cell proliferation and PDGFRβ tyrosine phosphorylation was also demonstrated in various PDGFR-expressing cells, including MRC-5, BEAS-2B, rat aortic vascular smooth muscle cells, and A172 glioblastoma cells. These results indicate that Compound C can be used as a potential antiproliferative agent for PDGF- or PDGFR-associated diseases, such as cancer, atherosclerosis, and fibrosis.

Fludarabine nucleoside induces accumulations of p53, p63 and p73 in the nuclei of human B-lymphoid cell lines, with cytosolic and mitochondrial increases in p53

PURPOSE

Human Raji cells treated with fludarabine nucleoside (2-FaraA, 3 μM) undergo apoptosis with accumulation of p53 in the nuclei as multiple phosphorylated isoforms and C-terminal truncated derivatives. Changes induced by 2-FaraA in the levels of p53, p63 and p73 in the nuclear, cytosolic and mitochondrial fractions have been determined in four human B-lymphoid cell lines that are TP53-functional (Raji and IM9) and TP53-mutated (MEC1 and U266).

EXPERIMENTAL DESIGN

The B-lymphoid cell lines were treated with 2-FaraA (3 μM, 24 h, 48 h) and viability determined. Protein extracts of subcellular fractions from 2-FaraA-treated cells were analysed by 1D and 2D electrophoresis; multiple phosphorylated isoforms and truncated derivatives were identified by Western blots for p53, p63 and p73.

RESULTS

p53 and p63 were present in all three fractions, while p73 was only detected in nuclei. After treatment with 2-FaraA, nuclear p53, p63 and p73 accumulated as multiple phosphorylated isoforms and truncated derivatives. The association of p63 with mitochondria in human cells is novel.

CONCLUSIONS AND CLINICAL RELEVANCE

Comprehensive information on the subcellular distributions and responses of p53, p63 and p73 to 2-FaraA provides additional insight into mechanisms for induction of apoptosis in the treatment of B-lymphoproliferative disorders with fludarabine.

Resistance to butyrate impairs bile acid-induced apoptosis in human colon adenocarcinoma cells via up-regulation of Bcl-2 and inactivation of Bax

A critical risk factor in colorectal carcinogenesis and tumor therapy is the resistance to the apoptotic effects of different compounds from the intestinal lumen, among them butyrate (main regulator of colonic epithelium homeostasis). Insensitivity to butyrate-induced apoptosis yields resistance to other agents, as bile acids or chemotherapy drugs, allowing the selective growth of malignant cell subpopulations. Here we analyze bile acid-induced apoptosis in a butyrate-resistant human colon adenocarcinoma cell line (BCS-TC2.BR2) to determine the mechanisms that underlay the resistance to these agents in comparison with their parental butyrate-sensitive BCS-TC2 cells. This study demonstrates that DCA and CDCA still induce apoptosis in butyrate-resistant cells through increased ROS production by activation of membrane-associated enzymes and subsequent triggering of the intrinsic mitochondrial apoptotic pathway. Although this mechanism is similar to that described in butyrate-sensitive cells, cell viability is significantly higher in resistant cells. Moreover, butyrate-resistant cells show higher Bcl-2 levels that confer resistance to bile acid-induced apoptosis sequestering Bax and avoiding Bax-dependent pore formation in the mitochondria. We have confirmed that this resistance is reverted using the Bcl-2 inhibitor ABT-263, thus demonstrating that the lower sensitivity of butyrate-resistant cells to the apoptotic effects of bile acids is mainly due to increased Bcl-2 levels.

Mitochondrial dysfunction in Pten haplo-insufficient mice with social deficits and repetitive behavior: interplay between Pten and p53

Etiology of aberrant social behavior consistently points to a strong polygenetic component involved in fundamental developmental pathways, with the potential of being enhanced by defects in bioenergetics. To this end, the occurrence of social deficits and mitochondrial outcomes were evaluated in conditional Pten (Phosphatase and tensin homolog) haplo-insufficient mice, in which only one allele was selectively knocked-out in neural tissues. Pten mutations have been linked to Alzheimer's disease and syndromic autism spectrum disorders, among others. By 4–6 weeks of age, Pten insufficiency resulted in the increase of several mitochondrial Complex activities (II–III, IV and V) not accompanied by increases in mitochondrial mass, consistent with an activation of the PI3K/Akt pathway, of which Pten is a negative modulator. At 8–13 weeks of age, Pten haplo-insufficient mice did not show significant behavioral abnormalities or changes in mitochondrial outcomes, but by 20–29 weeks, they displayed aberrant social behavior (social avoidance, failure to recognize familiar mouse, and repetitive self-grooming), macrocephaly, increased oxidative stress, decreased cytochrome c oxidase (CCO) activity (50%) and increased mtDNA deletions in cerebellum and hippocampus. Mitochondrial dysfunction was the result of a downregulation of p53-signaling pathway evaluated by lower protein expression of p21 (65% of controls) and the CCO chaperone SCO2 (47% of controls), two p53-downstream targets. This mechanism was confirmed in Pten-deficient striatal neurons and, HCT 116 cells with different p53 gene dosage. These results suggest a unique pathogenic mechanism of the Pten-p53 axis in mice with aberrant social behavior: loss of Pten (via p53) impairs mitochondrial function elicited by an early defective assembly of CCO and later enhanced by the accumulation of mtDNA deletions. Consistent with our results, (i) SCO2 deficiency and/or CCO activity defects have been reported in patients with learning disabilities including autism and (ii) mutated proteins in ASD have been found associated with p53-signaling pathways.

Ubiquitin C-terminal hydrolase l1 in tumorigenesis

Ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1, aka PGP9.5) is an abundant, neuronal deubiquitinating enzyme that has also been suggested to possess E3 ubiquitin-protein ligase activity and/or stabilize ubiquitin monomers in vivo. Recent evidence implicates dysregulation of UCH-L1 in the pathogenesis and progression of human cancers. Although typically only expressed in neurons, high levels of UCH-L1 have been found in many nonneuronal tumors, including breast, colorectal, and pancreatic carcinomas. UCH-L1 has also been implicated in the regulation of metastasis and cell growth during the progression of nonsmall cell lung carcinoma, colorectal cancer, and lymphoma. Together these studies suggest UCH-L1 has a potent oncogenic role and drives tumor development. Conversely, others have observed promoter methylation-mediated silencing of UCH-L1 in certain tumor subtypes, suggesting a potential tumor suppressor role for UCH-L1. In this paper, we provide an overview of the evidence supporting the involvement of UCH-L1 in tumor development and discuss the potential mechanisms of action of UCH-L1 in oncogenesis.

Immune complex-mediated co-ligation of the BCR with FcγRIIB results in homeostatic apoptosis of B cells involving Fas signalling that is defective in the MRL/Lpr model of systemic lupus erythematosus

Negative regulation of B cell activation by cognate immune complexes plays an important homeostatic role in suppressing B cell hyperactivity and preventing consequent autoimmunity. Immune complexes co-ligate the BCR and FcγRIIB resulting in both growth arrest and apoptosis. We now show that such apoptotic signalling involves induction and activation of p53 and its target genes, the pro-apoptotic Bcl-2 family members, Bad and Bid, as well as nuclear export of p53. Collectively, these events result in destabilisation of the mitochondrial and lysosomal compartments with consequent activation and interplay of executioner caspases and endosomal-derived proteases. In addition, the upregulation of Fas and FasL with consequent activation of caspase 8-dependent death receptor signalling is required to facilitate efficient apoptosis of B cells. Consistent with this role for Fas death receptor signalling, apoptosis resulting from co-ligation of the BCR and FcγRIIB is defective in B cells from Fas-deficient MRL/MpJ-Fas(lpr) mice. As these mice develop spontaneous, immune complex-driven lupus-like glomerulonephritis, targeting this FcγRIIB-mediated apoptotic pathway may therefore have novel therapeutic implications for systemic autoimmune disease.

Regulation of p73 activity by post-translational modifications

The transcription factor p73 is a member of the p53 family that can be expressed as at least 24 different isoforms with pro- or anti-apoptotic attributes. The TAp73 isoforms are expressed from an upstream promoter and are regarded as bona fide tumor suppressors; they can induce cell cycle arrest/apoptosis and protect against genomic instability. On the other hand, ΔNp73 isoforms lack the N-terminus transactivation domain; hence, cannot induce the expression of pro-apoptotic genes, but still can oligomerize with TAp73 or p53 to block their transcriptional activities. Therefore, the ratio of TAp73 isoforms to ΔNp73 isoforms is critical for the quality of the response to a genomic insult and needs to be delicately regulated at both transcriptional and post-translational level. In this review, we will summarize the current knowledge on the post-translational regulatory pathways involved to keep p73 protein under control. A comprehensive understanding of p73 post-translational modifications will be extremely useful for the development of new strategies for treating and preventing cancer.

Deoxycholic and chenodeoxycholic bile acids induce apoptosis via oxidative stress in human colon adenocarcinoma cells

The continuous exposure of the colonic epithelium to high concentrations of bile acids may exert cytotoxic effects and has been related to pathogenesis of colon cancer. A better knowledge of the mechanisms by which bile acids induce toxicity is still required and may be useful for the development of new therapeutic strategies. We have studied the effect of deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA) treatments in BCS-TC2 human colon adenocarcinoma cells. Both bile acids promote cell death, being this effect higher for CDCA. Apoptosis is detected after 30 min-2 h of treatment, as observed by cell detachment, loss of membrane asymmetry, internucleosomal DNA degradation, appearance of mitochondrial transition permeability (MPT), and caspase and Bax activation. At longer treatment times, apoptosis is followed in vitro by secondary necrosis due to impaired mitochondrial activity and ATP depletion. Bile acid-induced apoptosis is a result of oxidative stress with increased ROS generation mainly by activation of plasma membrane enzymes, such as NAD(P)H oxidases and, to a lower extent, PLA2. These effects lead to a loss of mitochondrial potential and release of pro-apoptotic factors to the cytosol, which is confirmed by activation of caspase-9 and -3, but not caspase-8. This initial apoptotic steps promote cleavage of Bcl-2, allowing Bax activation and formation of additional pores in the mitochondrial membrane that amplify the apoptotic signal.

Trichostatin A sensitizes HBx-expressing liver cancer cells to etoposide treatment

Agents commonly used in cancer chemotherapy rely on the induction of cell death via apoptosis, mitotic catastrophe, premature senescence and autophagy. Chemoresistance is the major factor limiting long-term treatment success in patients with hepatocellular carcinoma (HCC). Recent studies have revealed that the hepatitis B virus X protein (HBx) exerts anti-apoptotic effects, resulting in an increased drug resistance in HCC cells. In this study, we showed that etoposide treatment activated caspase-8 and caspase-3, leading to cleavages of p53, Bid and PARP, which subsequently induced apoptosis. Furthermore, p53 and Bid were accumulated in cytoplasm following etoposide treatment. However, HBx significantly attenuated etoposide-induced cell death. In HBx-expressing cells, despite the translocation of p53 and Bid to cytoplasm, the activation of caspases was inhibited. Furthermore, the phosphorylation of extracellular-signal-regulated kinase (ERK) was markedly increased in HBx-expressing cells. Moreover, the pretreatment with trichostatin A (TSA, a histone deacetylase inhibitor) or TSA in combination with etoposide significantly sensitized HCC cells to apoptosis by inhibiting ERK phosphorylation, reactivating caspases and PARP, and inducing translocation of p53 and Bid to cytoplasm. Collectively, HBx reduces the sensitivity of HCC cells to chemotherapy. TSA in combination with etoposide can significantly overcome the increased resistance of HBx-expressing HCC cells to chemotherapy.

A quarter century of granzymes

Granzymes (Grs) were discovered just over a quarter century ago. They are produced by cytotoxic T cells and natural killer cells and are released upon interaction with target cells. Intensive biochemical, genetic, and biological studies have been performed in order to study their roles in immunity and inflammation. This review summarizes research on the family of Grs.

Mitochondrial liaisons of p53

Mitochondria play a central role in cell survival and cell death. While producing the bulk of intracellular ATP, mitochondrial respiration represents the most prominent source of harmful reactive oxygen species. Mitochondria participate in many anabolic pathways, including cholesterol and nucleotide biosynthesis, yet also control multiple biochemical cascades that contribute to the programmed demise of cells. The tumor suppressor protein p53 is best known for its ability to orchestrate a transcriptional response to stress that can have multiple outcomes, including cell cycle arrest and cell death. p53-mediated tumor suppression, however, also involves transcription-independent mechanisms. Cytoplasmic p53 can physically interact with members of the BCL-2 protein family, thereby promoting mitochondrial membrane permeabilization. Moreover, extranuclear p53 can suppress autophagy, a major prosurvival mechanism that is activated in response to multiple stress conditions. Thirty years have passed since its discovery, and p53 has been ascribed with an ever-increasing number of functions. For instance, p53 has turned out to influence the cell's redox status, by transactivating either anti- or pro-oxidant factors, and to regulate the metabolic switch between glycolysis and aerobic respiration. In this review, we will analyze the mechanisms by which p53 affects the balance between the vital and lethal functions of mitochondria.

A dp53/JNK-dependant feedback amplification loop is essential for the apoptotic response to stress in Drosophila

Programmed cell death (apoptosis) is a conserved process aimed to eliminate unwanted cells. The key molecules are a group of proteases called caspases that cleave vital proteins, which leads to the death of cells. In Drosophila, the apoptotic pathway is usually represented as a cascade of events in which an initial stimulus activates one or more of the proapoptotic genes (hid, rpr, grim), which in turn activate caspases. In stress-induced apoptosis, the dp53 (Drosophila p53) gene and the Jun N-terminal kinase (JNK) pathway function upstream in the activation of the proapoptotic genes. Here we demonstrate that dp53 and JNK also function downstream of proapoptotic genes and the initiator caspase Dronc (Drosophila NEDD2-like caspase) and that they establish a feedback loop that amplifies the initial apoptotic stimulus. This loop plays a critical role in the apoptotic response because in its absence there is a dramatic decrease in the amount of cell death after a pulse of the proapoptotic proteins Hid and Rpr. Thus, our results indicate that stress-induced apoptosis in Drosophila is dependant on an amplification loop mediated by dp53 and JNK. Furthermore, they also demonstrate a mechanism of mutual activation of proapoptotic genes.

The p53 family: guardians of maternal reproduction

The p53 family of proteins consists of p53, p63 and p73, which are transcription factors that affect both cancer and development. It is now emerging that these proteins also regulate maternal reproduction. Whereas p63 is important for maturation of the egg, p73 ensures normal mitosis in the developing blastocyst. p53 subsequently regulates implantation of the embryo through transcriptional control of leukaemia inhibitory factor. Elucidating the cell biological basis of how these factors regulate female fertility may lead to new approaches to the control of human maternal reproduction.

Wild-type and mutant p53 proteins interact with mitochondrial caspase-3

Caspases play a key role in the apoptotic pathway by virtue of their ability to cleave key protein substrates within the dying cell. Caspases are produced as inactive zymogens, and need to become proteolytically processed in order to become active. A key executioner caspase, caspase-3, has previously been found to exist in both the cytosol and the mitochondria. At the mitochondria, caspase-3 is associated with both the inner and outer mitochondrial membranes, where it interacts with heat shock proteins Hsp60 and Hsp10. Like caspase-3, a small portion of the p53 tumor suppressor protein is localized to mitochondria, particularly after genotoxic stress. p53 interacts with various members of the Bcl2 family at the mitochondria, and this interaction is key to its ability to induce apoptosis. In this study, we sought to determine the identity of other mitochondrial p53-interacting proteins. Using immunoprecipitation from purified mitochondria followed by mass spectrometry we identified caspase-3 as a mitochondrial p53-interacting protein. Interestingly, we find that tumor-derived mutant forms of p53 retain the ability to interact with mitochondrial caspase-3. Further, we find evidence that these mutant forms of p53 may interfere with the ability of procaspase-3 to become proteolytically activated by caspase-9. The combined data suggest that tumor-derived mutants of p53 may be selected for in tumor cells due to their ability to bind and inhibit the activation of caspase-3.

p53 Activates Either Survival or Apoptotic Signaling Responses in Lupulone-Treated Human Colon Adenocarcinoma Cells and Derived Metastatic Cells

The SW480 cell line is derived from a human colon adenocarcinoma, and SW620 cells are derived from a lymph node metastasis of the same patient. We have previously shown that lupulone induces apoptosis in SW480 cells, through a cross talk between the TRAIL-death receptor pathway and the mitochondrial apoptotic pathway. In SW620 cells, lupulone induced apoptosis only through TRAIL-death receptor activation. Both cell lines exhibit the same p53 mutations. Because p53 plays a central role in the response to cellular stresses by upregulating the transcription of several genes controlling apoptosis, we aimed to study the involvement of p53 on lupulone-triggered apoptosis. Our data show that in SW620 cells, lupulone upregulated p53 gene expression and caused a cloistering of p53 in the nucleus, allowing p53 to play a proapoptotic role by activating the TRAIL-death receptor pathway. In contrast, in lupulone-treated SW480 cells, p53 was translocated to the cytoplasm where it initiated a survival response associated with the up-regulation of antiapoptotic Bcl-2 and Mcl-1 proteins in an attempt to preserve mitochondrial integrity. These prosurvival effects of p53 in lupulone-treated SW480 cells were reversed by pifithrin-α, an inhibitor of p53 function, which caused a blocking of p53 in the nucleus leading to the down-regulation of Bcl-2 and Mcl-1, the up-regulation of proapoptotic Bax protein and TRAIL-death receptors leading to enhanced cell death. Our data support different functions of the same mutated p53 in colon adenocarcinoma and derived metastatic cells in response to the chemopreventive agent lupulone.