Hyperacetylation of the C-terminal domain of p53 inhibits the formation of the p53/p21 complex.

Given our previous finding that certain tumor-suppressing functions of p53 are exerted by the p53/p21 complex, rather than p53 alone, cells may have a system to regulate the p53/p21 interaction. As p53 binds to p21 via its C-terminal domain, which contains acetylable lysine residues, we investigated whether the C-terminal acetylation of p53 influences the p53/p21 interaction. Indeed, the p53/p21 interaction was reduced when various types of cells (HCT116 colon cancer, A549 lung cancer, and MCF7 breast cancer cells) were treated with MS-275, an inhibitor of SIRT1 (a p53 deacetylase), or with SIRT1-targeting small interfering RNAs. These treatments also increased the acetylation levels of the five lysine residues (K370, K372, K373, K381, K382) in the C-terminal domain of p53. The p53/p21 interaction was also reduced when these lysine residues were substituted with glutamine (an acetylation memetic), but not arginine (an unacetylable lysine analog). While the inhibitory effect of the lysine-to-glutamine substitution was evident upon the substitution of all the five lysine residues, the substitution of only two (K381, K382) or three residues (K370, K372, K373) was less effective. Consistently, the five substitutions reduced the ability of p53 to regulate cell invasion and death by liberating Bax from Bcl-w. Overall, our data suggest that the acetylation, especially the hyperacetylation, of the p53 C-terminal domain suppresses the p53/p21-complex-dependent functions of p53 by inhibiting the p53/p21 interaction. We propose that cellular components involved in the acetylation or deacetylation of the p53 C-terminus are critical regulators of the formation of p53/p21 complex.

JNC-1043, a Novel Podophyllotoxin Derivative, Exerts Anticancer Drug and Radiosensitizer Effects in Colorectal Cancer Cells.

The objective of this study was to determine whether (5S)-5-(4-benzyloxy-3,5-dimethoxy-phenyl)-5,9-dihydro-8H-furo [3',4':6,7] naphtho [2,3-d] [1,3]dioxol-6-one (JNC-1043), which is a novel chemical derivative of ß-apopicropodophyllin, acts as a novel potential anticancer reagent and radiosensitizer in colorectal cancer (CRC) cells. Firstly, we used MTT assays to assess whether JNC-1043 could inhibit the cell proliferation of HCT116 and DLD-1 cells. The IC50 values of these cell lines were calculated as 114.5 and 157 nM, respectively, at 72 h of treatment. Using doses approximating the IC50 values, we tested whether JNC-1043 had a radiosensitizing effect in the CRC cell lines. Clonogenic assays revealed that the dose-enhancement ratios (DER) of HCT116 and DLD-1 cells were 1.53 and 1.25, respectively. Cell-counting assays showed that the combination of JNC-1043 and γ-ionizing radiation (IR) enhanced cell death. Treatment with JNC-1043 or IR alone induced cell death by 50~60%, whereas the combination of JNC-1043 and IR increased this cell death by more than 20~30%. Annexin V-propidium iodide assays showed that the combination of JNC-1043 and IR increased apoptosis by more 30~40% compared to that induced by JNC-1043 or IR alone. DCFDA- and MitoSOX-based assays revealed that mitochondrial ROS production was enhanced by the combination of JNC-1043 and IR. Finally, we found that suppression of ROS by N-acetylcysteine (NAC) blocked the apoptotic cell death induced by the combination of JNC-1043 and IR. The xenograft model also indicated that the combination of JNC-1043 and IR increased apoptotic cell death in tumor mass. These results collectively suggest that JNC-1043 acts as a radiosensitizer and exerts anticancer effects against CRC cells by promoting apoptosis mediated by mitochondrial ROS.

Involvement of the p53/p21 complex in p53-dependent gene expression.

The p53 tumor suppressor regulates cell functions either by acting as a transcription factor or by interacting with other proteins. Previously, we reported that the non-transcriptional actions of p53 can be facilitated by the binding of p53 to p21. Herein, we investigated whether p53/p21 interaction influences the transcriptional activity of p53. We observed that the expression of the p53 promoter-based reporter gene is dependent on p21 levels. Moreover, using a p21 variant that is unable to bind p53, we showed that p53 promoter activity requires p53/p21 interaction. To investigate the possible role of p21 in regulating the expression of endogenous p53 targets, we analyzed mRNA levels of Puma, Mdm2, and Gadd45a in untreated control and γ-ray-irradiated cells. We observed that while Puma expression is dependent on p53 regardless of γ-irradiation, p53 mediates the expression of Mdm2 and Gadd45a only in irradiated cells. Notably, p53/p21 interaction is required only for the p53-dependent expression of the tested genes and not Mdm2 and Gadd45a in non-irradiated cells. Moreover, chromatin immunoprecipitation assay revealed that p21 is required for the binding of p53 to the promoters of Puma, Mdm2, and Gadd45a. Collectively, our data support the view that the p53/p21 complex is involved in regulating p53-dependent gene expression. These findings provide a new foundation for understanding the transcriptional action of p53.

Radiosensitizer Effect of ß-Apopicropodophyllin against Colorectal Cancer via Induction of Reactive Oxygen Species and Apoptosis.

ß-apopicropodophyllin (APP), a derivative of podophyllotoxin (PPT), has been identified as a potential anti-cancer drug. This study tested whether APP acts as an anti-cancer drug and can sensitize colorectal cancer (CRC) cells to radiation treatment. APP exerted an anti-cancer effect against the CRC cell lines HCT116, DLD-1, SW480, and COLO320DM, with IC50 values of 7.88 nM, 8.22 nM, 9.84 nM, and 7.757 nM, respectively, for the induction of DNA damage. Clonogenic and cell counting assays indicated that the combined treatment of APP and γ-ionizing radiation (IR) showed greater retardation of cell growth than either treatment alone, suggesting that APP sensitized CRC cells to IR. Annexin V-propidium iodide (PI) assays and immunoblot analysis showed that the combined treatment of APP and IR increased apoptosis in CRC cells compared with either APP or IR alone. Results obtained from the xenograft experiments also indicated that the combination of APP and IR enhanced apoptosis in the in vivo animal model. Apoptosis induction by the combined treatment of APP and IR resulted from reactive oxygen species (ROS). Inhibition of ROS by N-acetylcysteine (NAC) restored cell viability and decreased the induction of apoptosis by APP and IR in CRC cells. Taken together, these results indicate that a combined treatment of APP and IR might promote apoptosis by inducing ROS in CRC cells.

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.

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.

Radiation-induced IL-1ß expression and secretion promote cancer cell migration/invasion via activation of the NF-κB-RIP1 pathway.

Here, we demonstrate that interleukin-1ß (IL-1ß) contributes to the γ-ionizing radiation (IR)-induced increase of migration/invasion in A549 lung cancer cells, and that this occurs via RIP1 upregulation. We initially observed that the protein expression and secreted concentration of IL-1ß were increased upon exposure of A549 cells to IR. We then demonstrated that IR-induced IL-1ß is located downstream of the NF-κB-RIP1 signaling pathway. Treatments with siRNA and specific pharmaceutical inhibitors of RIP1 and NF-κB suppressed the IR-induced increases in the protein expression and secreted concentration of IL-1ß. IL-1Ra, an antagonist of IL-1ß, treatment suppressed the IR-induced epithelial-mesenchymal transition (EMT) and IR-induced invasion/migration in vitro. These results suggest that IL-1ß could regulate IR-induced EMT. We also found that IR could induce the expression of IL-1ß expression in vivo and that of IL-1 receptor (R) I/II in vitro and in vivo. The IR-induced increases in the protein levels of IL-1 RI/II and IL-1ß suggest that an autocrine loop between IL-1ß and IL-1 RI/II might play important roles in IR-induced EMT and migration/invasion. Based on these collective results, we propose that IR concomitantly activates NF-κB and RIP1 to trigger the NF-κB-RIP1-IL-1ß-IL-1RI/II-EMT pathway, ultimately promoting metastasis.

RIP1 Is a Novel Component of γ-ionizing Radiation-Induced Invasion of Non-Small Cell Lung Cancer Cells.

Abstract: Previously, we demonstrated that γ-ionizing radiation (IR) triggers the invasion/migration of A549 cells via activation of an EGFR-p38/ERK-STAT3/CREB-1-EMT pathway. Here, we have demonstrated the involvement of a novel intracellular signaling mechanism in γ-ionizing radiation (IR)-induced migration/invasion. Expression of receptor-interacting protein (RIP) 1 was initially increased upon exposure of A549, a non-small cell lung cancer (NSCLC) cell line, to IR. IR-induced RIP1 is located downstream of EGFR and involved in the expression/activity of matrix metalloproteases (MMP-2 and MMP-9) and vimentin, suggesting a role in epithelial-mesenchymal transition (EMT). Our experiments showed that IR-induced RIP1 sequentially induces Src-STAT3-EMT to promote invasion/migration. Inhibition of RIP1 kinase activity and expression blocked induction of EMT by IR and suppressed the levels and activities of MMP-2, MMP-9 and vimentin. IR-induced RIP1 activation was additionally associated with stimulation of the transcriptional factor NF-κB. Specifically, exposure to IR triggered NF-κB activation and inhibition of NF-κB suppressed IR-induced RIP1 expression, followed by a decrease in invasion/migration as well as EMT. Based on the collective results, we propose that IR concomitantly activates EGFR and NF-κB and subsequently triggers the RIP1-Src/STAT3-EMT pathway, ultimately promoting metastasis.

Radiosensitizing Effect of Novel Phenylpyrimidine Derivatives on Human Lung Cancer Cells via Cell Cycle Perturbation.

Radiotherapy is one of the most common treatments for cancer, but radioresistance and injury to normal tissue are considered major obstacles to successful radiotherapy. Thus, there is an urgent need to develop radiosensitizers to improve the therapeutic outcomes of radiotherapy in cancer patients. Our previous efforts to identify novel radiosensitizers, using high-throughput screening targeting p53 and Nrf2 revealed a promising N-phenylpyrimidin-2-amine (PPA) lead compound. In the present study, 17 derivatives of this lead compound were examined, and it was found that 4-(4-fluorophenyl)-N-(4-nitrophenyl)-6-phenylpyrimidin-2-amine (PPA5), 4-((4-(4-fluorophenyl)pyrimidin-2-yl)amino)-3-methoxy-N-methyl -benzamide (PPA13), 4-((4-(4-fluorophenyl)pyrimidin-2-yl)amino)benzenesulfonamide (PPA14), 4-((4-(2-chlorophenyl)pyrimidin-2-yl)amino)benzenesulfonamide (PPA15), and 4-((4-(2-chlorophenyl)pyrimidin-2-yl)amino)-N-methylbenzamide (PPA17) inhibited cell viability by more than 50%, with a marked increase in the proportion of cells arrested at the G2/M phase of cell cycle. Among these compounds, PPA15 markedly increased the sub-G1 cell population and increased the levels of cyclin B1 and the phosphorylation levels of cyclin-dependent kinase (CDK) 1. Combined treatment with radiation and PPA14 or PPA15 significantly decreased clonogenic survival. An in vitro kinase assay revealed that PPA15 inhibited multiple CDKs involved in cell cycle regulation. Compared with drug or radiation treatment alone, combined treatment with PPA15 and radiation resulted in the suppression of A549 tumor growth in mice by 59.5% and 52.7%, respectively. Treatment with PPA15 alone directly inhibited tumor growth by 25.7%. These findings suggest that the novel pan CDK inhibitor, PPA15, may be a promising treatment to improve the effectiveness of radiotherapy for the treatment of cancer. SIGNIFICANCE STATEMENT: Several inhibitors of CDK have been successfully evaluated in combination with other chemotherapeutics in clinical trials, but negative side effects have partially restricted their clinical use. In this study, we identified a novel pan-CDK inhibitor to increase radiosensitivity, and we hope this work will encourage the development of promising small-molecule radiosensitizers.

Inhibition of Karyopherin-α2 Augments Radiation-Induced Cell Death by Perturbing BRCA1-Mediated DNA Repair.

Ionizing radiation (IR) has been widely used in the treatment of cancer. Radiation-induced DNA damage triggers the DNA damage response (DDR), which can confer radioresistance and early local recurrence by activating DNA repair pathways. Since karyopherin-α2 (KPNA2), playing an important role in nucleocytoplasmic transport, was significantly increased by IR in our previous study, we aimed to determine the function of KPNA2 with regard to DDR. Exposure to radiation upregulated KPNA2 expression in human colorectal cancer HT29 and HCT116 cells and breast carcinoma MDA-MB-231 cells together with the increased expression of DNA repair protein BRCA1. The knockdown of KPNA2 effectively increased apoptotic cell death via inhibition of BRCA1 nuclear import following IR. Therefore, we propose that KPNA2 is a potential target for overcoming radioresistance via interruption to DDR.

ß-Apopicropodophyllin functions as a radiosensitizer targeting ER stress in non-small cell lung cancer.

AIMS: In this study, we examined whether ß-apopicropodophyllin (APP) could act as a radiosensitizer in non-small cell lung cancer (NSCLC) cells. MAIN METHODS: The in vitro radiosensitizing activity of APP was demonstrated with clonogenic assay, immunoblotting, Annexin V-Propidium iodide (PI) assay, BrdU incorporation, detection of mitochondrial ROS/intracellular of H2O2, mitochondrial membrane potential detection, and performing of isolation of mitochondrial and cytosolic fractions. The in vivo radiosensitizing activity of APP was determined in xenografted mice with co-treatment of APP and IR based on measurement of tumor volumes and apoptotic cell death. KEY FINDINGS: The results of a clonogenic assay indicated that a combination of APP and γ-ionizing radiation (IR) inhibits cell growth and increases cell death in NSCLC cells. Several signal transduction pathways were examined for their potential involvement in the apparent radiosensitization effect of APP, as assessed by immunoblotting analyses and mitochondrial potential determination in vitro. Treatment of NCI-H460 cells with 15 nM APP and NCI-H1299 cells with 10 nM APP yielded dose-enhancement ratios of 1.44 and 1.24, respectively. Enhanced ER stress, disrupted mitochondrial membrane potential, and increased reactive oxygen species (ROS) were observed in cells co-treated with APP and IR, and this was followed by the cytosolic release of cytochrome c and consequent activation of caspase-3 and -9. Notably, inhibition of JNK, which prevents caspase activation, blocked the APP/IR-induced activations of ER stress and apoptotic cell death. In NCI-H460 or NCI-H1299 cell-xenografted mice, APP/IR treatment delayed the time it took tumors to reach a threshold size by 22.38 and 16.83 days, respectively, compared with controls, to yield enhancement factors of 1.53 and 1.38, respectively. SIGNIFICANCE: APP has a radiosensitizing function derived from its ability to induce apoptotic cell death via activation of ER stress, disruption of mitochondrial membrane potential, and induction of the caspase pathway.

Mitochondrial superoxide dismutase 2 mediates γ-irradiation-induced cancer cell invasion.

Sublethal doses of γ-rays promote cancer cell invasion by stimulating a signaling pathway that sequentially involves p53, sulfatase 2 (SULF2), ß-catenin, interleukin-6 (IL-6), signal transducer and activator of transcription 3 (STAT3), and Bcl-XL. Given that Bcl-XL can increase O2•- production by stimulating respiratory complex I, the possible role of mitochondrial reactive oxygen species (ROS) in γ-irradiation-induced cell invasion was investigated. Indeed, γ-irradiation promoted cell invasion by increasing mitochondrial ROS levels, which was prevented by metformin, an inhibitor of complex I. γ-Irradiation-stimulated STAT3 increased the expression of superoxide dismutase 2 (SOD2), a mitochondrial enzyme that catalyzes the conversion of O2•- to hydrogen peroxide (H2O2). In contrast to O2•-, H2O2 functions as a signaling molecule. γ-Irradiation consistently stimulated the Src-dependent invasion pathway in a manner dependent on both complex I and SOD2. SOD2 was also essential for the invasion of un-irradiated cancer cells induced by upregulation of Bcl-XL, an intracellular oncogene, or extracellular factors, such as SULF2 and IL-6. Overall, these data suggested that SOD2 is critical for the malignant effects of radiotherapy and tumor progression through diverse endogenous factors.

Linarin inhibits radiation-induced cancer invasion by downregulating MMP-9 expression via the suppression of NF-κB activation in human non-small-cell lung cancer A549.

Radiotherapy is routinely used in the treatment of lung cancer patients. However, it often causes malignant effects, such as promoting cancer cell migration and invasion. Previous studies demonstrated that ionizing radiation (IR) promotes cancer cell invasion by stimulating the ß-catenin, IL-6, STAT3, and Bcl-XL signaling pathway or the PI3K, Akt, and NF-κB signaling pathway. Both Bcl-XL and NF-κB stimulate the secretion of matrix metalloproteases (MMPs), including MMP-2 and MMP-9. In the present study, linarin isolated from Chrysanthemum morifolium flowers significantly decreased the IR-induced cell migration and invasion at a concentration of 5 µM in A549 cells. This effect was mediated via MMP-9 downregulation and the suppression of NF-κB activation by inhibiting NF-κB and IκB-α phosphorylation. However, linarin did not affect the STAT3/Bcl-XL pathway or the stabilization of ß-catenin. Overall, these results suggest that linarin repressed the MMP-9-dependent invasion pathway by regulating NF-κB activity, thereby inhibiting IR-induced cancer metastasis.

PLOD3 promotes lung metastasis via regulation of STAT3.

Procollagen-lysine, 2-oxoglutarate 5-dioxygenase (PLOD3), a membrane-bound homodimeric enzyme, hydroxylates lysyl residues in collagen-like peptides; however, its role in lung cancer is unknown. This study aimed to investigate the role of PLOD3 as a pro-metastatic factor and to elucidate the underlying mechanism. First, we experimentally confirmed the release of PLOD3 in circulation in animal models, rendering it a potential serum biomarker for lung cancer in humans. Thereafter, we investigated the effects of PLOD3 overexpression and downregulation on cancer cell invasion and migration in vitro and in vivo, using human lung cancer cell lines and a mouse tumor xenograft model, respectively. Further, PLOD3 levels were determined in lung tissue samples from lung cancer patients. Functional analyses revealed that PLOD3 interacts with STAT3, thereby expressing matrix metalloproteinases (MMP-2 and MMP-9) and with urokinase plasminogen activator (uPA) to enhance tumor metastasis. PLOD3 and the STAT3 pathway were significantly correlated in the metastatic foci of lung cancer patients; PLOD3-STAT3 levels were highly correlated with a poor prognosis. These results indicate that PLOD3 promotes lung cancer metastasis in a RAS-MAP kinase pathway-independent manner. Therefore, secreted PLOD3 serves as a potent inducer of lung cancer metastasis and a potential therapeutic target to enhance survival in lung cancer.

A novel anti-cancer role of ß-apopicropodophyllin against non-small cell lung cancer cells.

We previously reported that podophyllotoxin acetate (PA) inhibits the growth and proliferation of non-small cell lung cancer (NSCLC) cells and also makes them more sensitive to radiation and chemotherapeutic agents. In an attempt to enhance PA activity, we synthesized 34 derivatives based on podophyllotoxin (PPT). Screening of the derivative compounds for anti-cancer activity against NSCLC led to the identification of ß-apopicropodophyllin (APP) as a strong anti-cancer agent. In addition to its role as an immunosuppressive regulator of the T-cell mediated immune response, the compound additionally showed anti-cancer activity against A549, NCI-H1299 and NCI-460 cell lines with IC50 values of 16.9, 13.1 and 17.1 nM, respectively. The intracellular mechanisms underlying the effects of APP were additionally examined. APP treatment caused disruption of microtubule polymerization and DNA damage, which led to cell cycle arrest, as evident from accumulation of phospho-CHK2, p21, and phospho-Cdc2. Moreover, APP stimulated the pro-apoptotic ER stress signaling pathway, indicated by elevated levels of BiP, phospho-PERK, phospho-eIF2α, CHOP and ATF4. We further observed activation of caspase-3, -8 and -9, providing evidence that both intrinsic and extrinsic apoptotic pathways were triggered. In vivo, APP inhibited tumor growth of NSCLC xenografts in nude mice by promoting apoptosis. Our results collectively support a novel role of APP as an anticancer agent that evokes apoptosis by inducing microtubule disruption, DNA damage, cell cycle arrest and ER stress.

Kinesin light chain-4 depletion induces apoptosis of radioresistant cancer cells by mitochondrial dysfunction via calcium ion influx.

Kinesins act as molecular microtubule-dependent motor proteins and have various important cellular functions related to cell division, intracellular transport, and membrane trafficking. However, the function of kinesin light chain 4 (KLC4) in cancer, especially radioresistance, has not been previously described. Thus, we investigated KLC4 function in lung cancer cells and radioresistant R-H460 cells by analyzing alterations in radiosensitivity after gene knockdown with siRNA and by evaluating cellular phenotypes and xenograft tumor growth. KLC4 was upregulated in human lung cancer cell lines. Moreover, in paired clinical specimens of lung cancer patients, KLC4 expression was significantly higher in tumor tissues than in paired adjacent normal tissues. Fluorescence-activated cell sorting (FACS) analysis showed that apoptosis rates and cleaved poly (ADP-ribose) polymerase (PARP) and cleaved caspase-3 levels in KLC4-knockdown lung cancer cells were significantly increased compared with those in control cells. Colony formation decreased as the radiation dose increased in KLC4-knockdown lung cancer cells, demonstrating an essential role for KLC4 in radioresistance. Importantly, KLC4 silencing suppressed tumor growth in an in vivo xenograft model, accompanied by increased apoptosis. Finally, KLC4-knockdown cells exhibited impaired mitochondrial respiration, increased mitochondrial reactive oxygen species production, and enhanced mitochondrial calcium uptake, resulting in mitochondrial dysfunction. Thus, KLC4 as a kinesin superfamily-targeted therapy may represent a novel, effective anticancer strategy, particularly for patients showing radioresistance.

Pro-apoptotic Bax promotes mesenchymal-epithelial transition by binding to respiratory complex-I and antagonizing the malignant actions of pro-survival Bcl-2 proteins.

The plasticity of solid tumors between the epithelial and mesenchymal states critically influences their malignant progression and metastasis. The epithelial-mesenchymal transition (EMT), which supports cancer cell invasion and metastasis, is promoted by pro-survival members (e.g., Bcl-2 and Bcl-XL) of the Bcl-2 protein family, which are well-known key apoptosis regulators. We found that Bcl-w, another pro-survival member, promotes EMT by increasing respiratory complex-I activity and reactive oxygen species (ROS) levels. In contrast, pro-apoptotic Bax facilitates mesenchymal-epithelial transition by binding to complex-I, which inhibits complex-I-induced ROS production. Functional antagonism between pro-survival and pro-apoptotic proteins in regulating tumor plasticity was directly confirmed by co-expressing Bax with Bcl-w or Bcl-XL. Therefore, the balance between the functionally opposing Bcl-2 proteins appears to be a critical determinant of cancer cell phenotypes. We further showed that sub-lethal doses of γ-radiation induced EMT by increasing Bcl-XL and Bcl-w levels and complex-I activity. We propose that Bcl-2 proteins and complex-I are potential targets for preventing tumor progression and the malignant actions of radiotherapy.

Knockdown of end-binding protein 1 induces apoptosis in radioresistant A549 lung cancer cells via p38 kinase-dependent COX-2 upregulation.

The role of end-binding protein 1 (EB1) in lung cancer tumorigenesis and radiotherapy remains poorly understood. In the present study, we observed that EB1 was highly expressed in lung tumor tissues compared with normal non-tumor tissues based on immunohistochemical analysis of lung cancer tissue samples obtained from human tissue microarrays. EB1 was also highly overexpressed in radioresistant lung and cervical cancer cells, which exhibited increased cell death after EB1 silencing. The cytotoxicity induced by EB1 gene knockdown was due to the activation and generation of reactive oxygen species by p38 mitogen-activated protein kinase. Notably, this signaling cascade, however not nuclear factor-κB-mediated signaling, induced the expression of cyclooxygenase-2, a key effector of apoptotic death. Our results provided new molecular evidence supporting the use of EB1 as a novel target in lung cancer therapy, especially in the case of radioresistance.

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.