Mutant p53 disrupts the stress MAPK activation circuit induced by ASK1-dependent stabilization of Daxx

Oncogenic pathways activated by pro-inflammatory cytokines promote mutant p53 stability: clue for novel anticancer therapies

Inflammation and cancerogenesis are strongly interconnected processes, not only because inflammation promotes DNA instability, but also because both processes are driven by pathways such as NF-kB, STAT3, mTOR and MAPKs. Interestingly, these pathways regulate the release of pro-inflammatory cytokines such as IL-6, TNF-α and IL-1β that in turn control their activation and play a crucial role in shaping immune response. The transcription factor p53 is the major tumor suppressor that is often mutated in cancer, contributing to tumor progression. In this overview, we highlight how the interplay between pro-inflammatory cytokines and pro-inflammatory/pro-oncogenic pathways, regulating and being regulated by UPR signaling and autophagy, affects the stability of mutp53 that in turn is able to control autophagy, UPR signaling, cytokine release and the activation of the same oncogenic pathways to preserve its own stability and promote tumorigenesis. Interrupting these positive feedback loops may represent a promising strategy in anticancer therapy, particularly against cancers carrying mutp53.

Understanding MAPK Signaling Pathways in Apoptosis

MAPK (mitogen-activated protein kinase) signaling pathways regulate a variety of biological processes through multiple cellular mechanisms. In most of these processes, such as apoptosis, MAPKs have a dual role since they can act as activators or inhibitors, depending on the cell type and the stimulus. In this review, we present the main pro- and anti-apoptotic mechanisms regulated by MAPKs, as well as the crosstalk observed between some MAPKs. We also describe the basic signaling properties of MAPKs (ultrasensitivity, hysteresis, digital response), and the presence of different positive feedback loops in apoptosis. We provide a simple guide to predict MAPKs’ behavior, based on the intensity and duration of the stimulus. Finally, we consider the role of MAPKs in osmostress-induced apoptosis by using Xenopus oocytes as a cell model. As we will see, apoptosis is plagued with multiple positive feedback loops. We hope this review will help to understand how MAPK signaling pathways engage irreversible cellular decisions.

DAXX in cancer: phenomena, processes, mechanisms and regulation

DAXX displays complex biological functions. Remarkably, DAXX overexpression is a common feature in diverse cancers, which correlates with tumorigenesis, disease progression and treatment resistance. Structurally, DAXX is modular with an N-terminal helical bundle, a docking site for many DAXX interactors (e.g. p53 and ATRX). DAXX's central region folds with the H3.3/H4 dimer, providing a H3.3-specific chaperoning function. DAXX has two functionally critical SUMO-interacting motifs. These modules are connected by disordered regions. DAXX's structural features provide a framework for deciphering how DAXX mechanistically imparts its functions and how its activity is regulated. DAXX modulates transcription through binding to transcription factors, epigenetic modifiers, and chromatin remodelers. DAXX's localization in the PML nuclear bodies also plays roles in transcriptional regulation. DAXX-regulated genes are likely important effectors of its biological functions. Deposition of H3.3 and its interactions with epigenetic modifiers are likely key events for DAXX to regulate transcription, DNA repair, and viral infection. Interactions between DAXX and its partners directly impact apoptosis and cell signaling. DAXX's activity is regulated by posttranslational modifications and ubiquitin-dependent degradation. Notably, the tumor suppressor SPOP promotes DAXX degradation in phase-separated droplets. We summarize here our current understanding of DAXX's complex functions with a focus on how it promotes oncogenesis.

Apolipoprotein E4 Elicits Lysosomal Cathepsin D Release, Decreased Thioredoxin-1 Levels, and Apoptosis

The major genetic risk factor for Alzheimer’s disease (AD), apolipoprotein E4 (ApoE4), has been suggested to have detrimental effects on neurons, including direct toxicity via apoptosis. Thioredoxin-1 (Trx1) is an endogenous antioxidant protein important for redox regulation and participates in the regulation of apoptosis through the inhibition of apoptosis signal-regulating kinase-1 (Ask-1). In this study, we have investigated the effects of ApoE on Trx1 in the brain. Our results showed that the protein levels of Trx1 were reduced in the hippocampus of ApoE4 targeted replacement (TR) mice compared to ApoE3 TR mice. The reduction was also seen in vitro after treatment of both human primary cortical neurons and neuroblastoma cells with human recombinant ApoE4 (rApoE4). Furthermore, ApoE4 caused a disruption of lysosomal integrity and a shift in the localization of Cathepsin D, an enzyme known to degrade Trx1. ApoE4 treatment induced in addition apoptosis through translocation of Death-domain associated protein-6 (Daxx) from the nucleus to the cytosol, suggesting an activation of the Ask-1 pathway. This toxicity was prevented by overexpression of Trx1 and other endogenous Ask-1 inhibitors. Our data suggests that down-regulation of Trx1 is involved in the toxicity caused by ApoE4. An activated ASK-1 pathway might indeed make cells more vulnerable to other insults such as amyloid-β, which could partially explain the mechanism behind the strongest genetic risk factor for AD.

Regulation of ASK1 signaling by scaffold and adaptor proteins

The mitogen-activated protein kinase (MAPK) signaling pathway is a three-tiered kinase cascade where mitogen-activated protein kinase kinase kinases (MAP3Ks) lead to the activation of mitogen-activated protein kinase kinases (MAP2K), and ultimately MAPK proteins. MAPK signaling can promote a diverse set of biological outcomes, ranging from cell death to proliferation. There are multiple mechanisms which govern MAPK output, such as the duration and strength of the signal, cellular localization to upstream and downstream binding partners, pathway crosstalk and the binding to scaffold and adaptor molecules. This review will focus on scaffold and adaptor proteins that bind to and regulate apoptosis signal-regulating kinase 1 (ASK1), a MAP3K protein with a critical role in mediating stress response pathways.

ASK family and cancer

Cancer is a major problem in public health and is one of the leading causes of mortality worldwide. Many types of cancer cells exhibit aberrant cellular signal transduction in response to stress, which often leads to oncogenesis. Mitogen-activated protein kinase (MAPK) signal cascades are one of the important intracellular stress signaling pathways closely related to cancer. The key molecules in MAPK signal cascades that respond to various types of stressors are apoptosis signal-regulating kinase (ASK) family members; ASK1, ASK2 and ASK3. ASK family members are activated by a wide variety of stressors, and they regulate various cellular responses, such as cell proliferation, inflammation and apoptosis. In this review, we will discuss both the oncogenic and anti-oncogenic roles of the ASK family members in various contexts of cancer development with deeper insights into the involvement of ASK family members in cancer pathology.

The regulatory and signaling mechanisms of the ASK family

Apoptosis signal-regulating kinase 1 (ASK1) was identified as a MAP3K that activates the JNK and p38 pathways, and subsequent studies have reported ASK2 and ASK3 as members of the ASK family. The ASK family is activated by various intrinsic and extrinsic stresses, including oxidative stress, ER stress and osmotic stress. Numerous lines of evidence have revealed that members of the ASK family are critical for signal transduction systems to control a wide range of stress responses such as cell death, differentiation and cytokine induction. In this review, we focus on the precise signaling mechanisms of the ASK family in response to diverse stressors.

Apigenin enhances the cisplatin cytotoxic effect through p53-modulated apoptosis

Epidemiological and experimental evidence suggests that dietary flavonoids, including apigenin, have anticancer roles. Apigenin has been reported to elevate p53, a critical molecule in the induction of apoptosis. The present study aimed to investigate whether apigenin, a dietary flavonoid, improves the cytotoxic effect of cisplatin in a cancer cell culture system, and to elucidate the mechanism of this effect. Multiple tumor cell types were treated with apigenin, cisplatin or both drugs. Cell viability was evaluated, and the cytotoxic effect was determined biochemically and microscopically. Treatment with apigenin increased cisplatin-induced DNA damage and the apoptosis of tumor cells in a p53-dependent manner. Apigenin, when used with cisplatin, inhibited cell proliferation and promoted mitogen-activated protein kinase activation and subsequent p53 phosphorylation, leading to p53 accumulation and upregulation of proapoptotic proteins. Cisplatin is one of the most commonly used chemotherapeutic drugs for malignant tumors, but resistance to this drug occurs. The current results therefore demonstrate that dietary flavonoids may diminish the resistance of cancers to cisplatin.

Silencing Daxx increases the anti-tumor activity of a TRAIL/shRNA Bcl-xL-expressing oncolytic adenovirus through enhanced viral replication and cellular arrest

We previously showed that an increase of cellular Bcl-xL mediates acquired resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and knockdown of Bcl-xL expression greatly sensitized TRAIL-induced cytotoxicity. Here, we show that Daxx downregulation increases the anti-tumorigenic activity through enhancement of viral replication and cellular arrest with combination of TRAIL/shBcl-xL-induced apoptosis. This study was conducted to determine the effect of Daxx downregulation on the anti-tumorigenesis induced by oncolytic adenovirus arming TRAIL or TRAIL/shRNA of Bcl-xL genes. Unlike the enhanced cancer cell death induced by exogenous TRAIL or TRAIL plus shRNA of Bcl-xL, oncolytic adenovirus expressing TRAIL or TRAIL plus shRNA of Bcl-xL did not show much enhanced cancer cell death compared to oncolytic adenovirus itself. On the other hand, enhanced cytotoxic cell death and viral replication was observed after infection with oncolytic adenovirus expressing TRAIL plus shRNA of Bcl-xL and shRNA of Daxx at the same construct. Then we realized that enhanced adenoviral replication through Daxx downregulation was caused by increased adenoviral E1A protein expression and Daxx downregulation also stimulated cellular arrest through p21/p53 accumulation. Taken all together, we have shown here that Daxx downregulation should be essentially needed for the increase of anti-tumor activity through enhancement of viral replication and cellular arrest with the combination of TRAIL/shBcl-xL-induced apoptosis and oncolytic adenovirus.

Subcellular localization of DAXX influence ox-LDL induced apoptosis in macrophages

Here we aimed to evaluate the effects of DAXX subcellular localization on ox-LDL induced macrophages apoptosis. Cytoplasmic localization vector DAXX-W621A and nuclear localization vector DAXX-S667A were constructed by point mutation in DAXX. Blank vector, full length DAXX, DAXX-W621A, DAXX-S667A was transfect into RAW264.7 cells, respectively. Then the cells were incubated with 100 mg/ml ox-LDL for 48 h. Immunofluorescent assay was used to assay the localization of DAXX. MTT and Flow cytometry was used to determine cellular viability and apoptosis. RT-PCR and Western blot were used to analyze the expression levels. A significantly increased expression of DAXX was found in transfected cells of DAXX. The content of DAXX in nucleus was significantly increased in DAXX(S667A), and DAXX was significantly increased in cytoplasm of DAXX(W621A). Besides, we found DAXX was mainly expressed in nucleus with a low-level expression in cytoplasm through immunofluorescence. However in DAXX(W621A) group, the DAXX began to transferred to cytoplasm, which exhibited significant florescence. After treated with ox-LDL, the cytoactive of DAXX-W621A exhibited significantly decreased level when compared DAXX group. However, after added inhibitor LMB, the inhibition was relieved. The cell viability was also significantly increased in DAXX-S667A group. The results of apoptosis rates were similar in each group. Furthermore, we found the expression of ASK1 and JNK was also consistent with the apoptosis rates. Cytoplasmic localization of DAXX can increase injury sensitivity of ox-LDL on cells, and nuclear localization can antagonise the effect of ox-LDL. Besides, it is certified ox-LDL induced apoptosis is mainly through ASK1-JNK pathway.

Activation mechanisms of ASK1 in response to various stresses and its significance in intracellular signaling

Apoptosis signal-regulating kinase 1 (ASK1) is a member of the mitogen-activated protein kinase kinase kinase family. ASK1 activates c-jun N-terminal kinase (JNK) and p38 in response to various stimuli such as oxidative stress, endoplasmic reticulum stress, infection and calcium influx. Under these stress conditions, ASK1 plays important roles in intracellular signaling pathways and biological functions. Diverse proteins are known to interact with ASK1 and regulate the activity of ASK1. However, activation mechanisms of ASK1 and ASK1-binding proteins which regulate the activity of ASK1 have not been completely understood. In this review, we focus on the recent findings on ASK1 and update the regulatory mechanisms of ASK1 activity.

The gain of function of p53 cancer mutant in promoting mammary tumorigenesis

Tumor suppressor p53 is critical for suppressing all types of human cancers, including breast cancer. The p53 gene is somatically mutated in over half of all human cancers. The majority of the p53 mutations are missense mutations, leading to the expression of the full-length p53 mutants. Several hotspot mutations, including R175H, are frequently detected in human breast cancer. P53 cancer mutants not only lose tumor suppression activity but, more problematically, also gain new oncogenic activities. Despite correlation of the expression of p53 cancer mutants and the poor prognosis of human breast cancer patients, the roles of p53 cancer mutants in promoting breast cancer remain unclear. We used the humanized p53 cancer mutant knock-in (R175H) mice and mouse mammary tumor virus (MMTV)-Wnt-1 transgenic (mWnt-1) mice to specifically address the gain of function of R175H in promoting breast cancer. Although both R175H/R175HmWnt-1(R175HmWnt-1) and p53(-/-)mWnt-1 mice died from mammary tumor at the same kinetics, which was much earlier than mWnt-1 mice, most of the R175HmWnt-1 mice developed multiple mammary tumors per mouse, whereas p53(-/-)mWnt-1 and mWnt-1 mice mostly developed one tumor per mouse. The multiple mammary tumors arose in the same R175HmWnt-1 mouse exhibited different histological characters. Moreover, R175H gain-of-function mutant expands the mammary epithelial stem cells (MESCs) that give rise to the mammary tumors. As ATM suppresses the expansion of MESCs, the inactivation of ATM by R175H in mammary epithelial cells (MECs) could contribute to the expansion of MESCs in R175HmWnt-1 mice. These findings provide the basis for R175H to promote the initiation of breast cancer by expanding MESCs.