p21WAF1/CIP1 promotes p53 protein degradation by facilitating p53-Wip1 and p53-Mdm2 interaction.

Downregulation of the p53 tumor suppressor in cancers is frequently accompanied by the upregulation of Wip1 (a phosphatase) and Mdm2 (an E3 ubiquitin ligase). Mdm2 binds and ubiquitinates p53, promoting its degradation by the proteasome. As the p53/Mdm2 interaction is alleviated by the phosphorylation of the serine-15 (S15) residue of p53, Wip1, which can directly dephosphorylate phospho-S15, facilitates the Mdm2-mediated degradation of p53. Here, we found that p21WAF1/CIP1, previously shown to bind p53 and Mdm2, reduces the cellular levels of p53 protein by decreasing its stability. This is accompanied by a decrease in p53-S15 phosphorylation levels. In agreement, p21 promotes the p53/Wip1 interaction. Additionally, p21 interacts with Wip1, forming a trimeric complex of p53, p21, and Wip1. Studies using a p21 deletion mutant that cannot bind p53 revealed that the p53/p21 complex is more efficient than p53 alone in facilitating the binding of p53 to Wip1 and Mdm2. These findings indicate that p21 is a novel negative regulator of p53 stability and therefore, may be used as a target to restore p53 activity by preventing the action of Wip1 and Mdm2 on p53.

Anti-inflammatory effects of dabrafenib in vitro and in vivo.

The screening of bioactive compound libraries can be an effective approach for repositioning FDA-approved drugs or discovering new treatments for human diseases (drug repositioning). Drug repositioning refers to the development of existing drugs for new indications. Dabrafenib (DAB) is a B-Raf inhibitor and initially used for the treatment of metastatic melanoma therapy. Here, we tested the possible use of DAB in the treatment of lipopolysaccharide (LPS)-mediated vascular inflammatory responses. The anti-inflammatory activities of DAB were determined by measuring permeability, neutrophils adhesion and migration, and activation of pro-inflammatory proteins in LPS-activated human umbilical vein endothelial cells (HUVECs) and mice. We found that DAB inhibited LPS-induced barrier disruption, expression of cell adhesion molecules (CAMs), and adhesion and transendothelial migration of neutrophils to human endothelial cells. DAB also suppressed LPS-induced hyperpermeability and leukocytes migration in vivo. Furthermore, DAB suppressed the production of tumor necrosis factor-α (TNF-α) or interleukin (IL)-6 and the activation of nuclear factor-κB (NF-κB) or extracellular regulated kinases (ERK) 1/2 by LPS. Moreover, treatment with DAB resulted in reduced LPS-induced lethal endotoxemia. These results suggest that DAB possesses anti-inflammatory functions by inhibiting hyperpermeability, expression of CAMs, and adhesion and migration of leukocytes, thereby endorsing its usefulness as a therapy for vascular inflammatory diseases.

Cooperative actions of p21WAF1 and p53 induce Slug protein degradation and suppress cell invasion.

How the p53 transcription factor/tumor suppressor inhibits cell invasion is poorly understood. We demonstrate that this function of p53 requires its direct interaction with p21(WAF1), a transcriptional target of p53, and that both p21 and p53 bind to Slug, which promotes cell invasion. Functional studies reveal that p21 and p53 cooperate to facilitate Mdm2-dependent Slug degradation and that this p53 function is mimicked by p53(R273H), a mutant lacking trans-activating activity. These actions of p21 and p53 are induced by γ-irradiation of cells and also operate in vivo. This is the first study to elucidate a mechanism involving p53 and p21 cooperation.

Nicotinamide phosphoribosyltransferase is essential for interleukin-1beta-mediated dedifferentiation of articular chondrocytes via SIRT1 and extracellular signal-regulated kinase (ERK) complex signaling.

Although much is known about interleukin (IL)-1ß and its role as a key mediator of cartilage destruction in osteoarthritis, only limited information is available on IL-1ß signaling in chondrocyte dedifferentiation. Here, we have characterized the molecular mechanisms leading to the dedifferentiation of primary cultured articular chondrocytes by IL-1ß treatment. IL-1ß or lipopolysaccharide, but not phorbol 12-myristate 13-acetate, retinoic acid, or epidermal growth factor, induced nicotinamide phosphoribosyltransferase (NAMPT) expression, showing the association of inflammatory cytokines with NAMPT regulation. SIRT1, in turn, was activated NAMPT-dependently, without any alteration in the expression level. Activation or inhibition of SIRT1 oppositevely regulates IL-1ß-mediated chondrocyte dedifferentiation, suggesting this protein as a key regulator of chondrocytes phenotype. SIRT1 activation promotes induction of ERK and p38 kinase activities, but not JNK, in response to IL-1ß. Subsequently, ERK and p38 kinase activated by SIRT1 also induce SIRT1 activation, forming a positive feedback loop to sustain downstream signaling of these kinases. Moreover, we found that the SIRT1-ERK complex, but not SIRT1-p38, is engaged in IL-1ß-induced chondrocyte dedifferentiation via a Sox-9-mediated mechanism. JNK is activated by IL-1ß and modulates dedifferentiation of chondrocytes, but this pathway is independent on NAMPT-SIRT1 signaling. Based on these findings, we propose that IL-1ß induces dedifferentiation of articular chondrocytes by up-regulation of SIRT1 activity enhanced by both NAMPT and ERK signaling.

Roles of human INO80 chromatin remodeling enzyme in DNA replication and chromosome segregation suppress genome instability.

Although INO80 chromatin remodeling enzyme has been shown in yeast to play roles in non-transcriptional nuclear processes such as DNA replication, its cellular functions in higher eukaryotes have remained largely unexplored. Here, we provide evidence that human INO80 (hINO80) participates in both DNA replication and chromosome segregation during the normal cell division cycle. hINO80 binds to chromatin localizing at replication forks during the S-phase, and is required for efficient DNA synthesis and S-phase progression. Unexpectedly, hINO80 associates with spindle microtubule during mitosis, and its deficiency leads to defective microtubule assembly and abnormal chromosome segregation. Consistent with these results, hINO80 is critical for suppressing aneuploidy and structural chromosome abnormalities. This work therefore not only emphasizes the evolutionary importance of INO80 in DNA replication but also reveals a new role for this remodeler in chromosome segregation, both of which likely come into play in maintaining the genome integrity.

Slug promotes p53 and p21 protein degradation by inducing Mdm2 expression in HCT116 colon cancer cells.

Our previous study revealed that the tumor suppressor/transcription factor p53 directly binds to its transcriptional target, p21, and that the p53/p21 complex binds to zinc finger protein SNAI2 (Slug), a tumor promoter/transcription factor; thereby promoting the degradation of Slug by Mdm2, an E3 ligase. The present study demonstrated that Slug reduced the cellular expression levels of p53 and p21 in HCT116 colon cancer by decreasing their protein stability. In parallel, Slug increased the mRNA and protein expression levels of Mdm2 in these cells. Moreover, knockdown of Mdm2 using specific small interfering RNAs abolished the ability of Slug to induce the degradation of p53 and p21. Considering the well-known function of Mdm2 in facilitating p53 and p21 degradation, these data suggested that Slug promoted p53 and p21 degradation by inducing Mdm2 expression. Moreover, Slug increased ubiquitination levels of p53 in HCT116 cells. This is consistent with the fact that Mdm2 induces p53 degradation by ubiquitinating p53, and further confirmed that Mdm2 acted downstream of Slug. Comparative studies using HCT116 cells and their p53- or p21-knockout variants have revealed that Slug requires p21 to induce p53 degradation. This result is consistent with our previous study, which revealed that Mdm2 acts more efficiently on p53 in the p53/p21 complex compared with on p53 alone. By contrast, Slug did not require p53 to induce p21 degradation, suggesting that p53 was dispensable in Mdm2-mediated p21 degradation. Notably, the ability of Slug to increase/decrease Mdm2/p53 and p21 levels, respectively, was not confined to HCT116 cells alone, but was also confirmed in A549 and H460 lung cancer cells. Collectively, the results of the present study suggested that Slug could counter p53 and p21. The balance between these two opposing groups (Slug vs. p53/p21) may depend on environmental stresses and the internal physiology of cells.

Bcl-XL and STAT3 mediate malignant actions of gamma-irradiation in lung cancer cells.

Previous reports suggest that, in addition to its therapeutic effects, ionizing radiation (IR) increases the invasiveness of surviving cancer cells. Here, we demonstrate that this activity of IR in lung cancer cells is mediated by a signaling pathway involving p38 kinase, phosphoinositide 3-kinase, Akt, and matrix metalloproteinase (MMP-2). The invasion-promoting doses of IR also increased and reduced the levels of vimentin and E-cadherin, respectively, both of which are markers for the epithelial-mesenchymal transition (EMT). Interestingly, all of these malignant actions of IR were mimicked by the overexpression of Bcl-X(L), a pro-survival member of the Bcl-2 family, in lung cancer cells. Moreover, both RNA and protein levels of Bcl-X(L) were elevated upon irradiation of the cells, and the prevention of this event using small-interfering RNAs of Bcl-X(L) reduced the ability of IR to promote invasion signals and EMT-associated events. This suggests that Bcl-X(L) functions as a signaling mediator of the malignant effects of IR. It was also demonstrated that IR enhances signal transducer and activator of transcription 3 (STAT3) phosphorylation, and the reduction of STAT3 levels via RNA interference prevented IR-induced Bcl-X(L) accumulation, and thus all the tested Bcl-X(L)-dependent events. Overall, the data suggest that IR induces Bcl-X(L) accumulation via STAT3, which then promotes cancer cell invasion and EMT-associated markers. Our findings demonstrate a novel function of Bcl-X(L) in cancer, and also advance our understanding of the malignant actions of IR significantly.

Suppressive effects of dabrafenib on endothelial protein C receptor shedding.

Beyond its role in the activation of protein C, the endothelial cell protein C receptor (EPCR) plays an important role in the cytoprotective pathway. EPCR can be shed from the cell surface, which is mediated by tumor necrosis factor-α converting enzyme (TACE). Dabrafenib (DAB) is a B-Raf inhibitor and initially used for the treatment of metastatic melanoma therapy. However, little is known about the effects of DAB on EPCR shedding. We investigated this issue by monitoring the effects of DAB on phorbol-12-myristate 13-acetate (PMA)-, tumor necrosis factor (TNF)-α-, interleukin (IL)-1ß-induced EPCR shedding in human umbilical vein endothelial cells (HUVECs), and cecal ligation and puncture (CLP)-mediated EPCR shedding in mice and underlying mechanism. Data demonstrate that DAB induced potent inhibition of PMA-, TNF-α-, IL-1ß- (in HUVECs), and CLP-induced EPCR shedding (in mice) via inhibition of phosphorylation of mitogen-activated protein kinases (MAPKs) such as p38, janus kinase (JNK), and extracellular signal-regulated kinase (ERK) 1/2. DAB also inhibited the expression and activity of PMA-induced TACE in HUVECs suggesting that p38, ERK1/2, and JNK could be molecular targets of DAB. These results demonstrate the potential of DAB as an anti-EPCR shedding reagent against PMA-mediated and CLP-mediated EPCR shedding.

The p53/p21 Complex Regulates Cancer Cell Invasion and Apoptosis by Targeting Bcl-2 Family Proteins.

The tumor suppressor p53 binds prosurvival Bcl-2 family proteins such as Bcl-w and Bcl-XL to liberate Bax, which in turn exerts proapoptotic or anti-invasive functions depending on stress context. On the basis of our previous finding that p53 interacts with p21, we investigated the possible involvement of p21 in these functions. Here, we report that although p53 can bind Bcl-w alone, it requires p21 to liberate Bax to suppress cell invasion and promote cell death. p21 bound Bcl-w, forming a p53/p21/Bcl-w complex in a manner that maintained all pairwise p53/p21, p21/Bcl-w, and p53/Bcl-w interactions. This allowed Bax liberation from the complex. Accordingly, a p53 derivative incapable of binding p21 failed to mediate radiotherapy-induced tumor cell death in mice. Bcl-XL also served as a target of the cooperative action of p53 and p21. Overall, our findings indicate that the p53/p21 complex rather than p53 itself regulates cell invasion and death by targeting Bcl-2 proteins. We propose that the p53/p21 complex is a functional unit that acts on multiple cell components, providing a new foundation for understanding the tumor-suppressing functions of p53 and p21. Cancer Res; 77(11); 3092-100. ©2017 AACR.

Anti-vascular inflammatory effects of pentacyclic triterpenoids from Astilbe rivularis in vitro and in vivo.

Sepsis is a systemic inflammatory condition resulting from bacterial infections. It is associated with high mortality rates, and its therapeutic options are limited. Transforming growth factor ß induced protein (TGFBIp) is an extracellular matrix protein that functions as a mediator of experimental sepsis. C-27-carboxylated pentacyclic triterpenoids are specifically found in species of the genus Astilbe, and show several biological effects. Given the anti-inflammatory effects of pentacyclic triterpenoids, we investigated the effects of 3ß-trans-p-coumaroyloxy-olean-12-en-27-oic acid (1) and 6ß-hydroxy-3-oxoolean-12-en-27-oic acid (2) on TGFBIp-mediated vascular inflammatory responses. The anti-inflammatory activities of compounds 1 and 2 were determined by measuring the permeability, leukocyte adhesion and migration, and activation of pro-inflammatory proteins in TGFBIp-activated human umbilical vein endothelial cells (HUVECs) and mice. We found that compounds 1 and 2 inhibited lipopolysaccharide (LPS)-induced TGFBIp secretion, TGFBIp-induced barrier disruption, expression of cell adhesion molecules (CAMs), and the adhesion/transendothelial migration of the neutrophils to the human endothelial cells. Compounds 1 and 2 also suppressed TGFBIp-induced hyperpermeability and leukocyte migration in vivo. These results suggested that C-27-carboxylated pentacyclic triterpenoids 1 and 2 have anti-inflammatory functions by inhibiting hyperpermeability, CAM expression, and leukocyte adhesion/migration. Therefore, these compounds can be considered as a potential therapy for vascular inflammatory diseases.

ROS homeostasis and metabolism: a critical liaison for cancer therapy.

Evidence indicates that hypoxia and oxidative stress can control metabolic reprogramming of cancer cells and other cells in tumor microenvironments and that the reprogrammed metabolic pathways in cancer tissue can also alter the redox balance. Thus, important steps toward developing novel cancer therapy approaches would be to identify and modulate critical biochemical nodes that are deregulated in cancer metabolism and determine if the therapeutic efficiency can be influenced by changes in redox homeostasis in cancer tissues. In this review, we will explore the molecular mechanisms responsible for the metabolic reprogramming of tumor microenvironments, the functional modulation of which may disrupt the effects of or may be disrupted by redox homeostasis modulating cancer therapy.

Podophyllotoxin acetate triggers anticancer effects against non-small cell lung cancer cells by promoting cell death via cell cycle arrest, ER stress and autophagy.

We previously reported that podophyllotoxin acetate (PA) radiosensitizes NCI-H460 cells. Here, we confirmed that PA treatment also induces cell death among two other non-small cell lung cancer (NSCLC) cell lines: NCI-H1299 and A549 cells (IC50 values = 7.6 and 16.1 nM, respectively). Our experiments further showed that PA treatment was able to induce cell death via various mechanisms. First, PA dose-dependently induced cell cycle arrest at G2/M phase, as shown by accumulation of the mitosis-related proteins, p21, survivin and Aurora B. This G2/M phase arrest was due to the PA-induced inhibition of microtubule polymerization. Together, the decreased microtubule polymerization and increased cell cycle arrest induced DNA damage (reflected by accumulation of γ-H2AX) and triggered the induction of intrinsic and extrinsic apoptotic pathways, as shown by the time-dependent activations of caspase-3, -8 and -9. Second, PA time-dependently activated the pro-apoptotic ER stress pathway, as evidenced by increased expression levels of BiP, CHOP, IRE1-α, phospho-PERK, and phospho-JNK. Third, PA activated autophagy, as reflected by time-dependent increases in the expression levels of beclin-1, Atg3, Atg5 and Atg7, and the cleavage of LC3. Collectively, these results suggest a model wherein PA decreases microtubule polymerization and increases cell cycle arrest, thereby inducing apoptotic cell death via the activation of DNA damage, ER stress and autophagy.

Mdm2 increases cellular invasiveness by binding to and stabilizing the Slug mRNA.

Mdm2 is an oncoprotein that induces the degradation of the tumor suppressor, p53. Here, we show that Mdm2 increases the mRNA levels of Slug by binding to and stabilizing the Slug mRNA. While this effect of Mdm2 was observed in both p53-null and p53-expressing cancer cells, it increased the protein levels of Slug only in the former cells. Mdm2 consistently induced Slug-dependent events, such as decreases in E-cadherin levels and increases in cellular invasiveness, only in p53-null cells. Therefore, the binding of Mdm2 to the Slug mRNA appears to provide a novel mechanism through which Mdm2 promotes tumor progression in a manner independent of the presence of p53.

Bcl-w promotes cell invasion by blocking the invasion-suppressing action of Bax.

The Bcl-2 family members are key regulators of cellular viability, either promoting or suppressing cell death. Recent reports have indicated that the pro-survival members (Bcl-w, Bcl-XL, and others) also enhance the migratory and invasive potentials of cancer cells, although the mechanisms underlying this phenomenon have yet to be adequately elucidated. Herein, by using human cancer cells and mouse embryonic fibroblasts, we demonstrate that Bcl-w functions in the mitochondria to increase the levels of reactive oxygen species (ROS), which subsequently stimulates the invasion-promoting signaling pathway. By way of contrast, Bax,a member of the multidomain pro-apoptotic group (Bax and Bak), was found to reduce ROS levels, thereby suppressing cell invasion. Analyses of the functional relationship between Bcl-w and Bax have shown that Bcl-w requires Bax for promoting cell invasion, whereas Bax suppresses cell invasion in a Bcl-win dependent manner. By using a Bcl-w mutant (Bcl-w/G94A) that was found not to bind to Bax, we have further determined that Bcl-w should bind to Bax to promote cell invasion. Overall, the results indicate that Bcl-w enhances cellular invasiveness by binding to Bax and subsequently blocking its invasion suppressing actions. Moreover, these functions of Bcl-w and Bax are mimicked by other pro-survival and pro-apoptotic members, such as Bcl-XL and Bak, respectively. We propose the balance between prosurvival and multidomain pro-apoptotic members as a novel determinant of cellular invasiveness.

Akt is negatively regulated by the MULAN E3 ligase.

The serine/threonine kinase Akt functions in multiple cellular processes, including cell survival and tumor development. Studies of the mechanisms that negatively regulate Akt have focused on dephosphorylation-mediated inactivation. In this study, we identified a negative regulator of Akt, MULAN, which possesses both a RING finger domain and E3 ubiquitin ligase activity. Akt was found to directly interact with MULAN and to be ubiquitinated by MULAN in vitro and in vivo. Other molecular assays demonstrated that phosphorylated Akt is a substantive target for both interaction with MULAN and ubiquitination by MULAN. The results of the functional studies suggest that the degradation of Akt by MULAN suppresses cell proliferation and viability. These data provide insight into the Akt ubiquitination signaling network.