Loss of the tissue-specific proapoptotic BH3-only protein Nbk/Bik is a unifying feature of renal cell carcinoma

MyoD1 promotes the transcription of BIK and plays an apoptosis-promoting role in the development of gastric cancer

Myogenic differentiation (MyoD) 1, which is known as a pivotal transcription factor during myogenesis, has been proven dysregulated in several cancers. However, litter is known about the precise role and downstream genes of MyoD1 in gastric cancer (GC) cells. Here, we report that MyoD1 is lowly expressed in primary GC tissues and cells. In our experiments, overexpression of MyoD1 inhibited cell proliferation. Downstream genes of MyoD1 regulation were investigated using RNA-Seq. As a result, 138 up-regulated genes and 20 down-regulated genes and 27 up-regulated lncRNAs and 20 down-regulated lncRNAs were identified in MyoD1 overexpressed MKN-45 cells, which participated in epithelial cell signaling in Helicobacter pylori infection, glycosaminoglycan biosynthesis (keratan sulfate), notch signaling pathway, and others. Among these genes, BIK was directly regulated by MyoD1 in GC cells and inhibited cancer cell proliferation. The BIK knockdown rescued the effects of MyoD1 overexpression on GC cells. In conclusion, MyoD1 inhibited cell proliferation via 158 genes and 47 lncRNAs downstream directly or indirectly that participated in multiple signaling pathways in GC, and among these, MyoD1 promotes BIK transcription by binding to its promoter, then promotes BIK-Bcl2-caspase 3 axis and regulates GC cell apoptosis.

Overcoming Chemotherapy Resistance in Metastatic Cancer: A Comprehensive Review

The management of metastatic cancer is complicated by chemotherapy resistance. This manuscript provides a comprehensive academic review of strategies to overcome chemotherapy resistance in metastatic cancer. The manuscript presents background information on chemotherapy resistance in metastatic cancer cells, highlighting its clinical significance and the current challenges associated with using chemotherapy to treat metastatic cancer. The manuscript delves into the molecular mechanisms underlying chemotherapy resistance in subsequent sections. It discusses the genetic alterations, mutations, and epigenetic modifications that contribute to the development of resistance. Additionally, the role of altered drug metabolism and efflux mechanisms, as well as the activation of survival pathways and evasion of cell death, are explored in detail. The strategies to overcome chemotherapy resistance are thoroughly examined, covering various approaches that have shown promise. These include combination therapy approaches, targeted therapies, immunotherapeutic strategies, and the repurposing of existing drugs. Each strategy is discussed in terms of its rationale and potential effectiveness. Strategies for early detection and monitoring of chemotherapy drug resistance, rational drug design vis-a-vis personalized medicine approaches, the role of predictive biomarkers in guiding treatment decisions, and the importance of lifestyle modifications and supportive therapies in improving treatment outcomes are discussed. Lastly, the manuscript outlines the clinical implications of the discussed strategies. It provides insights into ongoing clinical trials and emerging therapies that address chemotherapy resistance in metastatic cancer cells. The manuscript also explores the challenges and opportunities in translating laboratory findings into clinical practice and identifies potential future directions and novel therapeutic avenues. This comprehensive review provides a detailed analysis of strategies to overcome chemotherapy resistance in metastatic cancer. It emphasizes the importance of understanding the molecular mechanisms underlying resistance and presents a range of approaches for addressing this critical issue in treating metastatic cancer.

Apoptosis evasion via long non-coding RNAs in colorectal cancer

Long non-coding RNA (LncRNA) is a novel and diverse class of regulatory transcripts that are frequently dysregulated in numerous tumor types. LncRNAs are involved in a complicated molecular network, regulating gene expression, and modulating diverse cellular activities in different cancers including colorectal cancer (CRC). Evidence indicates that lncRNAs can be used as a potential biomarker for the prognosis and diagnosis of CRC as they are aberrantly expressed in CRC cells. The high expression or silencing of lncRNAs is associated with cell proliferation, invasion, metastasis, chemoresistance and apoptosis in CRC. LncRNAs exert both pro-apoptotic and anti-apoptotic functions in CRC. The expression of some oncogene lncRNAs is upregulated which leads to the inhibition of apoptotic pathways, similarly, the tumor suppressor lncRNAs are downregulated in CRC. In this review, we describe the function and mechanisms of lncRNAs to regulate the expression of genes that are involved directly or indirectly in controlling cellular apoptosis in CRC. Furthermore, we also discussed the different apoptotic pathways in normal cells and the mechanisms by which CRC evade apoptosis.

A prognosis model for clear cell renal cell carcinoma based on four necroptosis-related genes

Necroptosis is a type of caspase-independent cell death, and it plays a critical role in regulating the development of cancer. To date, little is known about the role of necroptosis-related genes (NRGs) in clear cell renal cell carcinoma (ccRCC). In this study, we downloaded data regarding the expression of NRGs and overall survival (OS) from The Cancer Genome Atlas (TCGA) database and constructed a risk model to determine the prognostic features of necroptosis using COX regression analysis. Patients with ccRCC were divided into low-risk and high-risk groups based on their risk scores. Thereafter, Kaplan–Meier curves were used to evaluate OS, and receiver operating characteristic (ROC) curves were used to determine the accuracy of prediction. Stratified analyses were performed according to different clinical variables. Furthermore, we assessed the correlation between clinical variables and risk scores; the NRGs with differential expression were mainly enriched in positive regulation of intracellular transport and platinum resistance pathways. We constructed prognostic signatures for OS based on four NRGs and showed that the survival time was significantly longer in the low-risk groups than in the high-risk groups (p < 0.001). The area of the ROC curve for OS was 0.717, indicating excellent predictive accuracy of the established model. Therefore, a predictive model based on NRGs was constructed, which can predict the prognosis of patients and provides insights into the biological mechanisms underlying necroptosis in patients with ccRCC.

Epigenetic Deregulation of Apoptosis in Cancers

Cancer cells possess the ability to evade apoptosis. Genetic alterations through mutations in key genes of the apoptotic signaling pathway represent a major adaptive mechanism of apoptosis evasion. In parallel, epigenetic changes via aberrant modifications of DNA and histones to regulate the expression of pro- and antiapoptotic signal mediators represent a major complementary mechanism in apoptosis regulation and therapy response. Most epigenetic changes are governed by the activity of chromatin modifying enzymes that add, remove, or recognize different marks on histones and DNA. Here, we discuss how apoptosis signaling components are deregulated at epigenetic levels, particularly focusing on the roles of chromatin-modifying enzymes in this process. We also review the advances in cancer therapies with epigenetic drugs such as DNMT, HMT, HDAC, and BET inhibitors, as well as their effects on apoptosis modulation in cancer cells. Rewiring the epigenome by drug interventions can provide therapeutic advantage for various cancers by reverting therapy resistance and leading cancer cells to undergo apoptotic cell death.

Activity-Dependent Regulation of the Proapoptotic BH3-Only Gene egl-1 in a Living Neuron Pair in Caenorhabditis elegans

The BH3-only family of proteins is key for initiating apoptosis in a variety of contexts, and may also contribute to non-apoptotic cellular processes. Historically, the nematode Caenorhabditis elegans has provided a powerful system for studying and identifying conserved regulators of BH3-only proteins. In C. elegans, the BH3-only protein egl-1 is expressed during development to cell-autonomously trigger most developmental cell deaths. Here we provide evidence that egl-1 is also transcribed after development in the sensory neuron pair URX without inducing apoptosis. We used genetic screening and epistasis analysis to determine that its transcription is regulated in URX by neuronal activity and/or in parallel by orthologs of Protein Kinase G and the Salt-Inducible Kinase family. Because several BH3-only family proteins are also expressed in the adult nervous system of mammals, we suggest that studying egl-1 expression in URX may shed light on mechanisms that regulate conserved family members in higher organisms.

LncRNA H19 confers chemoresistance in ERα-positive breast cancer through epigenetic silencing of the pro-apoptotic gene BIK

Breast cancer is a common malignancy in women. Acquisition of drug resistance is one of the main obstacles encountered in breast cancer therapy. Long non-coding RNA (lncRNA) has been demonstrated to play vital roles in both development and tumorigenesis. However, the relationship between lncRNAs and the development of chemoresistance is not well established. In the present study, the high expression of lncRNA H19 was identified as a powerful factor associated with paclitaxel (PTX) resistance in ERα-positive breast cancer cells, but not in ERα-negative breast cancer cells. LncRNA H19 attenuated cell apoptosis in response to PTX treatment by inhibiting transcription of pro-apoptotic genes BIK and NOXA. H19 was further confirmed to suppress the promoter activity of BIK by recruiting EZH2 and by trimethylating the histone H3 at lysine 27. Interestingly, our data showed that lncRNA H19 was one of the downstream target molecules of ERα. Altered ERα expression may therefore change H19 levels to modulate the apoptosis response to chemotherapy in breast cancer cells. Our data suggest that the ERα-H19-BIK signaling axis plays an important role in promoting chemoresistance.

Increased Expression of Endonuclease G in Gastric and Colorectal Carcinomas

Aims

Endonuclease G (EndoG) is a mitochondrial protein that plays a role in DNA fragmentation during apoptosis. In addition, EndoG plays a role in cell proliferation and survival. It may be important to identify EndoG protein expression to predict its function in human cancers. The aim of this study was to explore whether alteration of EndoG expression might be a characteristic of colorectal or gastric carcinoma.

Methods

We investigated EndoG protein expression in 103 colorectal and 60 gastric carcinoma tissues by immunohistochemistry using a tissue microarray approach.

Results

Expression of EndoG was detected in 72 (70%) of the colorectal carcinomas and 41 (68%) of the gastric carcinomas in cytoplasm. By contrast, normal mucosal cells of both stomach and colon tissues showed no or very weak expression of EndoG. There was no significant association of EndoG expression with clinocopathological characteristics, including invasion, metastasis and stage.

Conclusion

Our data indicate that EndoG inactivation by loss of expression may not occur in colorectal and gastric cancers. Rather, increased expression of EndoG in colorectal and gastric cancer cells compared to their normal mucosal epithelial counterparts suggests that neo-expression of EndoG may play a role in both colorectal and gastric tumorigenesis.

Repression of TCF3/E2A contributes to Hodgkin lymphomagenesis

Although Hodgkin and Reed-Sternberg (HRS) cells of classical Hodgkin lymphoma (cHL) derived from germinal or post germinal B cells, they have lost the B cell phenotype in the process of lymphomagenesis. The phenomenon can be at least partially explained by repression of B-cell-specific transcription factors including TCF3, early B-cell factor 1 (EBF1), SPI1/PU.1, and FOXO1, which are down-regulated by genetic and epigenetic mechanisms. The unique phenotype has been suspected to be advantageous for survival of HRS cells. Ectopic expression of some of these transcription factors (EBF1, PU.1, FOXO1) indeed impaired survival of cHL cells. Here we show that forced expression of TCF3 causes cell death and cell cycle arrest in cHL cell lines. Mechanistically, TCF3 overexpression modulated expression of multiple pro-apoptotic genes including BIK, APAF1, FASLG, BOK, and TNFRSF10A/DR4. We conclude that TCF3 inactivation contributes not only to extinguishing of B cell phenotype but also to cHL oncogenesis.

The pro-apoptotic paradox: the BH3-only protein Bcl-2 interacting killer (Bik) is prognostic for unfavorable outcomes in breast cancer

Breast cancer is the leading cause of cancer-associated deaths in women worldwide. Clinical biomarkers give information on disease progression and identify relevant biological pathways. A confounding factor that uncouples markers from disease outcome is the ability of tumor cells to mutate and evade clinical intervention. Therefore, we focussed on apoptotic genes that modulate tumor regression. Using gene and tissue microarray analyses, we identified an association of Bcl-2 interacting killer (Bik) with poor breast cancer prognosis. Bik prognostic ability was independent of Estrogen Receptor/Progesterone Receptor and Her2 status. Additionally, Bik was independent of anti-apoptotic Bcl-2, Bcl-xL, Mcl-1 and Bcl-w suggesting a complex mechanism of tumor promotion identified by Bik high tumors. Bik also stimulates autophagy, which can contribute to enhanced tumor fitness. We found a significant association between the autophagy marker ATG5 and Bik. Combined high expression level of ATG5 and Bik was a stronger predictor of outcome than either alone. Thus, our study identifies Bik as a novel, independent prognostic biomarker for poor outcomes in breast cancer and suggests that Bik-mediated autophagy contributes to disease recurrence.

Molecular mechanisms for tumour resistance to chemotherapy

Chemotherapy is one of the prevailing methods used to treat malignant tumours, but the outcome and prognosis of tumour patients are not optimistic. Cancer cells gradually generate resistance to almost all chemotherapeutic drugs via a variety of distinct mechanisms and pathways. Chemotherapeutic resistance, either intrinsic or acquired, is caused and sustained by reduced drug accumulation and increased drug export, alterations in drug targets and signalling transduction molecules, increased repair of drug-induced DNA damage, and evasion of apoptosis. In order to better understand the mechanisms of chemoresistance, this review highlights our current knowledge of the role of altered drug metabolism and transport and deregulation of apoptosis and autophagy in the development of tumour chemoresistance. Reduced intracellular activation of prodrugs (e.g. thiotepa and tegafur) or enhanced drug inactivation by Phase I and II enzymes contributes to the development of chemoresistance. Both primary and acquired resistance can be caused by alterations in the transport of anticancer drugs which is mediated by a variety of drug transporters such as P-glycoprotein (P-gp), multidrug resistance associated proteins, and breast cancer resistance protein. Presently there is a line of evidence indicating that deregulation of programmed cell death including apoptosis and autophagy is also an important mechanism for tumour resistance to anticancer drugs. Reversal of chemoresistance is likely via pharmacological and biological approaches. Further studies are warranted to grasp the full picture of how each type of cancer cells develop resistance to anticancer drugs and to identify novel strategies to overcome it.

BIK is involved in BRAF/MEK inhibitor induced apoptosis in melanoma cell lines

In patients with BRAF-mutated melanoma specific inhibitors of BRAF^V600E and MEK1/2 frequently induce initial tumor reduction, frequently followed by relapse. As demonstrated previously, BRAF^V600E-inhibition induces apoptosis only in a fraction of treated cells, while the remaining arrest and survive providing a source or a niche for relapse. To identify factors contributing to the differential initial response towards BRAF/MEK inhibition, we established M14 melanoma cell line-derived single cell clones responding to treatment with BRAF inhibitor vemurafenib and MEK inhibitor trametinib predominantly with either cell cycle arrest (CCA-cells) or apoptosis (A-cells). Screening for differentially expressed apoptosis-related genes revealed loss of BCL2-Interacting Killer (BIK) mRNA in CCA-cells. Importantly, ectopic expression of BIK in CCA-cells resulted in increased apoptosis rates following vemurafenib/trametinib treatment, while knockdown/knockout of BIK in A-cells attenuated the apoptotic response. Furthermore, we demonstrate reversible epigenetic silencing of BIK mRNA expression in CCA-cells. Importantly, HDAC inhibitor treatment associated with re-expression of BIK augmented sensitivity of CCA-cells towards vemurafenib/trametinib treatment both in vitro and in vivo. In conclusion, our results suggest that BIK can be a critical mediator of melanoma cell fate determination in response to MAPK pathway inhibition.

Bax/Bak-independent mitochondrial depolarization and reactive oxygen species induction by sorafenib overcome resistance to apoptosis in renal cell carcinoma

Renal cell carcinoma (RCC) is polyresistant to chemo- and radiotherapy and biologicals, including TNF-related apoptosis-inducing ligand (TRAIL). Sorafenib, a multikinase inhibitor approved for the treatment of RCC, has been shown to sensitize cancer cells to TRAIL-induced apoptosis, in particular by down-regulation of the Bak-inhibitory Bcl-2 family protein Mcl-1. Here we demonstrate that sorafenib overcomes TRAIL resistance in RCC by a mechanism that does not rely on Mcl-1 down-regulation. Instead, sorafenib induces rapid dissipation of the mitochondrial membrane potential (ΔΨ_m) that is accompanied by the accumulation of reactive oxygen species (ROS). Loss of ΔΨ_m and ROS production induced by sorafenib are independent of caspase activities and do not depend on the presence of the proapoptotic Bcl-2 family proteins Bax or Bak, indicating that both events are functionally upstream of the mitochondrial apoptosis signaling cascade. More intriguingly, we find that it is sorafenib-induced ROS accumulation that enables TRAIL to activate caspase-8 in RCC. This leads to apoptosis that involves activation of an amplification loop via the mitochondrial apoptosis pathway. Thus, our mechanistic data indicate that sorafenib bypasses central resistance mechanisms through a direct induction of ΔΨ_m breakdown and ROS production. Activation of this pathway might represent a useful strategy to overcome the cell-inherent resistance to cancer therapeutics, including TRAIL, in multiresistant cancers such as RCC.

BH3-Only Proteins in Health and Disease

BH3-only proteins are proapoptotic members of the broader Bcl-2 family, which promote cell death by directly or indirectly activating Bax and Bak. The expression of BH3-only proteins is regulated both transcriptionally and posttranscriptionally in a cell type-specific and a tissue-specific manner. Research over the last 20 years has provided significant insights into their roles in tissue homeostasis and various pathologies, which in turn has led to the development of novel therapeutics for numerous diseases. In this review, a snapshot of the progress over this period is given, including our current understanding of their regulation, mode of action, role in mammalian development, and pathology.

RAG-induced DNA lesions activate proapoptotic BIM to suppress lymphomagenesis in p53-deficient mice

Delbridge, Strasser, and collaborators show that potentially oncogenic RAG1/2-dependent DNA lesions trigger apoptosis through the induction of BIM, which functions as an efficient tumor suppressor.

Neoplastic transformation is driven by oncogenic lesions that facilitate unrestrained cell expansion and resistance to antiproliferative signals. These oncogenic DNA lesions, acquired through errors in DNA replication, gene recombination, or extrinsically imposed damage, are thought to activate multiple tumor suppressive pathways, particularly apoptotic cell death. DNA damage induces apoptosis through well-described p53-mediated induction of PUMA and NOXA. However, loss of both these mediators (even together with defects in p53-mediated induction of cell cycle arrest and cell senescence) does not recapitulate the tumor susceptibility observed in p53^−/− mice. Thus, potentially oncogenic DNA lesions are likely to also trigger apoptosis through additional, p53-independent processes. We found that loss of the BH3-only protein BIM accelerated lymphoma development in p53-deficient mice. This process was negated by concomitant loss of RAG1/2-mediated antigen receptor gene rearrangement. This demonstrates that BIM is critical for the induction of apoptosis caused by potentially oncogenic DNA lesions elicited by RAG1/2-induced gene rearrangement. Furthermore, this highlights the role of a BIM-mediated tumor suppressor pathway that acts in parallel to the p53 pathway and remains active even in the absence of wild-type p53 function, suggesting this may be exploited in the treatment of p53-deficient cancers.

The deubiquitinase Usp27x stabilizes the BH3-only protein Bim and enhances apoptosis

Bim is a pro-apoptotic Bcl-2 family member of the BH3-only protein subgroup. Expression levels of Bim determine apoptosis susceptibility in non-malignant and in tumour cells. Bim protein expression is downregulated by proteasomal degradation following ERK-dependent phosphorylation and ubiquitination. Here, we report the identification of a deubiquitinase, Usp27x, that binds Bim upon its ERK-dependent phosphorylation and can upregulate its expression levels. Overexpression of Usp27x reduces ERK-dependent Bim ubiquitination, stabilizes phosphorylated Bim, and induces apoptosis in PMA-stimulated cells, as well as in tumour cells with a constitutively active Raf/ERK pathway. Loss of endogenous Usp27x enhances the Bim-degrading activity of oncogenic Raf. Overexpression of Usp27x induces low levels of apoptosis in melanoma and non-small cell lung cancer (NSCLC) cells and substantially enhances apoptosis induced in these cells by the inhibition of ERK signalling. Finally, deletion of Usp27x reduces apoptosis in NSCLC cells treated with an EGFR inhibitor. Thus, Usp27x can trigger via its proteolytic activity the deubiquitination of Bim and enhance its levels, counteracting the anti-apoptotic effects of ERK activity, and therefore acts as a tumour suppressor.

Uncoupling of PUMA Expression and Apoptosis Contributes to Functional Heterogeneity in Renal Cell Carcinoma - Prognostic and Translational Implications

Renal cell carcinoma (RCC) is characterized by a profound disruption of proapoptotic signaling networks leading to chemo- and radioresistance. A key mediator of DNA damage-induced apoptosis is the BH3-only protein PUMA. Given its central role in proapoptotic signaling, we analyzed a series of more than 600 precision-annotated primary RCC specimens for PUMA protein expression. We found a reduced expression of PUMA in 22.6% of RCCs analyzed. Unexpectedly, however, PUMA deficiency was not associated with more aggressive tumor characteristic as expected. Instead, a reduced PUMA expression was associated with a lower TNM stage, lower histopathologic grade, and more favorable cancer-specific patient survival. A direct correlation in a separate patient cohort revealed a profound disconnection between PUMA expression and apoptosis as exemplified by the fact that the tumor with the highest level of apoptotic cells was PUMA deficient. In a series of in vitro studies, we corroborated these results and discovered the highest propensity to undergo apoptosis in an RCC cell line with virtually undetectable PUMA expression. At the same time, PUMA expression was not necessarily associated with stronger apoptosis induction, which underscores the striking functional heterogeneity of PUMA expression and apoptosis in RCC. Collectively, our findings suggest that PUMA-independent mechanisms of cell death exist and may play an important role in suppressing malignant progression. They underscore the functional heterogeneity of RCCs and suggest that PUMA expression alone may not be a suitable predictive biomarker. A better understanding of alternative proapoptotic pathways, however, may help to design novel therapeutic strategies for patients with advanced RCC.

Breast cancer cell line MDA-MB-231 miRNA profile expression after BIK interference: BIK involvement in autophagy

B-cell lymphoma 2 (BCL2)-interacting killer (apoptosis inducing) (BIK) has been proposed as a tumor suppressor in diverse types of cancers. However, BIK's overexpression in breast cancer (BC) and in non-small lung cancer cells (NSCLCs), associated with a poor prognosis, suggests its participation in tumor progression. In this study, we evaluated the global expression pattern of microRNAs (miRNAs), messenger RNA (mRNA) expression changes in autophagy, and autophagic flux after BIK interference. BIK gene expression was silenced by small interfering RNA (siRNA) in BC cell MDA-MB-231, and BIK interference efficiency was tested by real-time PCR and by Western blotting. BIK expression levels decreased by 75 ± 18 % in the presence of 600 nM siRNA, resulting in the abolishment of BIK expression by 94 ± 30 %. BIK interference resulted in the overexpression of 17 miRNAs that, according to the DIANA-miRPath v3.0 database, are mainly implied in the control of cell signaling, gene expression, and autophagy. The autophagy array revealed downregulation of transcripts which participate in autophagy, and their interactome revealed a complex network, where hepatocyte growth factor-regulated tyrosine kinase substrate (HGS), α-synuclein (SNCA), unc-51-like autophagy activating kinase 1/2 (ULK1/2), and mitogen-activated protein kinase 3 (MAPK3) were shown to be signaling hubs. LC3-II expression-an autophagy marker-was increased by 169 ± 25 % after BIK interference, which indicates the involvement of BIK in autophagy. Altogether, our results indicate-for the first time-that BIK controls the expression of miRNAs, as well as the autophagic flux in MDA-MB-231 cells.

Far upstream element-binding protein 1 (FUBP1) is a potential c-Myc regulator in esophageal squamous cell carcinoma (ESCC) and its expression promotes ESCC progression

The human far upstream element (FUSE) binding protein 1 (FUBP1) belongs to an ancient family which is required for proper regulation of the c-Myc proto-oncogene. Although c-Myc plays an important role in development of various carcinomas, the relevance of FUBP1 and their contribution to esophageal squamous cell carcinoma (ESCC) development remain unclear. In this study, we aimed to investigate the relationship between FUBP1 and c-Myc as well as their contribution to ESCC development. Western blot and immunohistochemical analyses were performed to evaluate FUBP1 expression. Coimmunoprecipitation analysis was performed to explore the correlation between FUBP1 and c-Myc in ESCC. In addition, the role of FUBP1 in ESCC proliferation was studied in ESCC cells through knocking FUBP1 down. The regulation of FUBP1 on proliferation was confirmed by Cell Counting Kit-8 (CCK-8) assay, flow cytometric assays, and clone formation assays. The expressions of FUBP1 and c-Myc were both upregulated in ESCC tissues. In addition to correlation between expression of FUBP1 and tumor grade, we also confirmed the correlation of FUBP1, c-Myc, and Ki-67 expression by twos. Moreover, upregulation of FUBP1 and c-Myc in ESCC was associated with poor survival. FUBP1 was confirmed to activate c-Myc in ESCC tissues and cells. FUBP1 was demonstrated to promote proliferation of ESCC cells. Moreover, downregulation of both FUBP1 and c-Myc was confirmed to inhibit proliferation of ESCC cells. Our results indicated that FUBP1 may potentially stimulate c-Myc expression in ESCC and its expression may promote ESCC progression.

Harnessing the p53-PUMA axis to overcome DNA damage resistance in renal cell carcinoma

Resistance to DNA damage–induced apoptosis is a hallmark of cancer and a major cause of treatment failure and lethal disease outcome. A tumor entity that is largely resistant to DNA-damaging therapies including chemo- or radiotherapy is renal cell carcinoma (RCC). This study was designed to explore the underlying molecular mechanisms of DNA damage resistance in RCC to develop strategies to resensitize tumor cells to DNA damage–induced apoptosis. Here, we show that apoptosis-resistant RCC cells have a disconnect between activation of p53 and upregulation of the downstream proapoptotic protein p53 upregulated modulator of apoptosis (PUMA). We demonstrate that this disconnect is not caused by gene-specific repression through CCCTC-binding factor (CTCF) but instead by aberrant chromatin compaction. Treatment with an HDAC inhibitor was found to effectively reactivate PUMA expression on the mRNA and protein level and to revert resistance to DNA damage–induced cell death. Ectopic expression of PUMA was found to resensitize a panel of RCC cell lines to four different DNA-damaging agents tested. Remarkably, all RCC cell lines analyzed were wild-type for p53, and a knockdown was likewise able to sensitize RCC cells to acute genotoxic stress. Taken together, our results indicate that DNA damage resistance in RCC is reversible, involves the p53-PUMA axis, and is potentially targetable to improve the oncological outcomes of RCC patients.

FBP1 and p27kip1 expression after sciatic nerve injury: implications for Schwann cells proliferation and differentiation

Far Upstream Element (FUSE) Binding Protein 1 (FBP1), first identified as a single-stranded DNA (ssDNA) binding protein that binds to the FUSE, could modulate c-myc mRNA levels and also has been shown to regulate tumor cell proliferation and replication of virus. Typically, FBP1 could active the translation of p27kip1 (p27) and participate in tumor growth. However, the expression and roles of FBP1 in peripheral system lesions and repair are still unknown. In our study, we found that FBP1 protein levels was relatively higher in the normal sciatic nerves, significantly decreased and reached a minimal level at Day 3, and then returned to the normal level at 4 weeks. Spatially, we observed that FBP1 had a major colocation in Schwann cells and FBP1 was connected with Ki-67 and Oct-6. In vitro, we detected the decreased level of FBP1 and p27 in the TNF-α-induced Schwann cells proliferation model, while increased expression in cAMP-induced Schwann cells differentiation system. Specially, FBP1-specific siRNA-transfected SCs did not show fine and longer morphological change after cAMP treatment and had a decreased motility compared with normal. At 3 days after cAMP treatment and SC/neuron co-cultures, p27 was transported to cytoplasm to form CDK4/6-p27 to participate in SCs differentiation. In conclusion, we speculated that FBP1 and p27 were involved in SCs proliferation and the following differentiation in the sciatic nerve after crush by transporting p27 from nucleus to cytoplasm.

Patient samples of renal cell carcinoma show reduced expression of TRAF1 compared with normal kidney and functional studies in vitro indicate TRAF1 promotes apoptosis: potential for targeted therapy

AIMS

The tumour necrosis factor (TNF) receptor-associated factor (TRAF) family of proteins links the TNF receptor superfamily to cell signalling cascades. TRAF1 is involved in regulation of apoptosis, proliferation, differentiation and stress responses. It has a role in development of several malignancies, but no information for renal cell carcinoma (RCC) is available.

METHODS

Expression profiles for TRAF1 were investigated in 121 samples of human RCC of various subtypes plus paired normal kidney prepared in tissue microarrays, in comparison with apoptosis (morphology, ApopTag) and mitosis (morphology, proliferating cell nuclear antigen/PCNA). TRAF1 function was tested in vitro in RCC ACHN cells. TRAF1 short interfering RNA (siRNA) was used to inhibit expression of TRAF1 in ACHN cells untreated or treated with cancer therapies known to induce apoptosis (20 Gy X-irradiation and/or 500 IU/mL interferon-alpha).

RESULTS

In patient samples, TRAF1 localised to proximal tubular epithelium in normal kidney and was significantly decreased in clear cell RCC as one group (p < 0.01) and all other RCC subclassifications grouped together (p < 0.05). There was little apoptosis identified in any RCC samples. In vitro, TRAF1 siRNA caused significant reduction in TRAF1 expression and a concurrent decrease in apoptosis and increase in proliferative activity (both p < 0.05) in the ACHN RCC cells treated with radiation and interferon-alpha.

CONCLUSION

TRAF1 may have a pro-apoptotic, anti-mitotic role in RCC. The low TRAF1 expression in untreated RCC patient samples compared with normal kidney, and the localisation of TRAF1 to the proximal tubular epithelium from which many RCC originate, may indicate a potential for targeted therapy in RCC.

Combination of lenalidomide with vitamin D3 induces apoptosis in mantle cell lymphoma via demethylation of BIK

Mantle cell lymphoma (MCL) is a currently incurable B-cell malignancy. Lenalidomide (Len) has been demonstrated to be one of the most efficient new treatment options. Because Len and 1α,25-dihydroxyvitamin (VD3) synergize to kill breast cancer cells, we investigated whether VD3 could increase the ability of Len to induce MCL cell death. While MCL cells were weakly sensitive to Len (1 μM), the addition of VD3 at physiological dose (100 nM) strongly increased cell death, accompanied by slowdown in cell cycle progression in MCL cell lines (n=4 out of 6) and primary samples (n=5 out of 7). The Len/VD3 treatment markedly increased the expression of the BH3-only BCL2-interacting killer (Bik) without affecting the expression of other Bcl-2 molecules. Immunoprecipitation assays demonstrated that Bik was free from anti-apoptotic partners, Bcl-2 and Bcl-x_L, in treated cells. Moreover, silencing of BIK prevented apoptosis induced by Len/VD3, confirming the direct involvement of Bik in cell death. Bik accumulation induced by Len/VD3 was related to an increase in BIK mRNA levels, which resulted from a demethylation of BIK CpG islands. The sensitivity of MCL cells to Len/VD3 was similar to the response to 5-azacytidine, which also induced demethylation of BIK CpG islands. These preclinical data provide the rationale to investigate the role of VD3 in vivo in the response to Len.

Repression of the proapoptotic cellular BIK/NBK gene by Epstein-Barr virus antagonizes transforming growth factor β1-induced B-cell apoptosis

The Epstein-Barr virus (EBV) establishes a lifelong latent infection in humans. EBV infection of primary B cells causes cell activation and proliferation, a process driven by the viral latency III gene expression program, which includes EBV nuclear proteins (EBNAs), latent membrane proteins, and untranslated RNAs, including microRNAs. Some latently infected cells enter the long-lived memory B-cell compartment and express only EBNA1 transiently (Lat I) or no EBV protein at all (Lat 0). Targeting the molecular machinery that controls B-cell fate decisions, including the Bcl-2 family of apoptosis-regulating proteins, is crucial to the EBV cycle of infection. Here, we show that BIK (also known as NBK), which encodes a proapoptotic "sensitizer" protein, is repressed by the EBNA2-driven Lat III program but not the Lat I program. BIK repression occurred soon after infection of primary B cells by EBV but not by a recombinant EBV in which the EBNA2 gene had been knocked out. Ectopic BIK induced apoptosis in Lat III cells by a mechanism dependent on its BH3 domain and the activation of caspases. We show that EBNA2 represses BIK in EBV-negative B-cell lymphoma-derived cell lines and that this host-virus interaction can inhibit the proapoptotic effect of transforming growth factor β1 (TGF-β1), a key physiological mediator of B-cell homeostasis. Reduced levels of TGF-β1-associated regulatory SMAD proteins were bound to the BIK promoter in response to EBV Lat III or ectopic EBNA2. These data are evidence of an additional mechanism used by EBV to promote B-cell survival, namely, the transcriptional repression of the BH3-only sensitizer BIK.

IMPORTANCE

Over 90% of adult humans are infected with the Epstein-Barr virus (EBV). EBV establishes a lifelong silent infection, with its DNA residing in small numbers of blood B cells that are a reservoir from which low-level virus reactivation and shedding in saliva intermittently occur. Importantly, EBV DNA is found in some B-cell-derived tumors in which viral genes play a key role in tumor cell emergence and progression. Here, we report for the first time that EBV can shut off a B-cell gene called BIK. When activated by a molecular signal called transforming growth factor β1 (TGF-β1), BIK plays an important role in killing unwanted B cells, including those infected by viruses. We describe the key EBV-B-cell molecular interactions that lead to BIK shutoff. These findings further our knowledge of how EBV prevents the death of its host cell during infection. They are also relevant to certain posttransplant lymphomas where unregulated cell growth is caused by EBV genes.

Apoptotic machinery diversity in multiple myeloma molecular subtypes

Multiple myeloma (MM) is a plasma-cell (PC) malignancy that is heterogeneous in its clinical presentation and prognosis. Monoclonal gammopathy of undetermined significance (MGUS) consistently preceded development of MM. The presence of primary IgH translocations and the universal overexpression of cyclin D genes led to a molecular classification of MM patients into different disease subtypes. Since Bcl-2 family proteins determine cell fate, we analyzed a publicly available Affymetrix gene expression of 44 MGUS and 414 newly diagnosed MM patients to investigate (1) the global change of Bcl-2 family members in MM versus MGUS (2) whether the four major subtypes defined as hyperdiploid, CyclinD1, MAF, and MMSET, display specific apoptotic machineries. We showed that among the main anti-apoptotic members (Bcl-2, Bcl-x_L, and Mcl-1), Mcl-1 up-regulation discriminated MM from MGUS, in agreement with the prominent role of Mcl-1 in PC differentiation. Surprisingly, the expression of multi-domain pro-apoptotic Bak and Bax were increased during the progression of MGUS to MM. The combined profile of Bcl-2, Bcl-x_L, and Mcl-1 was sufficient to distinguish MM molecular groups. While specific pro-apoptotic members expression was observed for each MM subtypes, CyclinD1 subgroup, was identified as a particular entity characterized by a low expression of BH3-only (Puma, Bik, and Bad) and multi-domain pro-apoptotic members (Bax and Bak). Our analysis supports the notion that MM heterogeneity is extended to the differential expression of the Bcl-2 family content in each MM subgroup. The influence of Bcl-2 family profile in the survival of the different patient groups will be further discussed to establish the potential consequences for therapeutic interventions. Finally, the use of distinct pro-survival members in the different steps of immune responses to antigen raises also the question of whether the different Bcl-2 anti-apoptotic profile could reflect a different origin of MM cells.

Suppression of the death gene BIK is a critical factor for resistance to tamoxifen in MCF-7 breast cancer cells

Apoptosis is controlled by the BCL-2 family of proteins, which can be divided into three different subclasses based on the conservation of BCL-2 homology domains. BIK is a founding member of the BH3-only pro-apoptotic protein family. BIK is predominantly localized in the endoplasmic reticulum (ER) and induces apoptosis through the mitochondrial pathway by mobilizing calcium from the ER to the mitochondria. In this study, we determined that suppression of the death gene Bik promotes resistance to tamoxifen (TAM) in MCF-7 breast cancer cells. We utilized small interfering (siRNA) to specifically knockdown BIK in MCF-7 cells and studied their response to tamoxifen. The levels of cell apoptosis, the potential mitochondrial membrane (ΔΨ_m), and the activation of total caspases were analyzed. Western blot analysis was used to determine the expression of some BCL-2 family proteins. Flow cytometry studies revealed an increase in apoptosis level in MCF-7 cells and a 2-fold increase in relative BIK messenger RNA (mRNA) expression at a concentration of 6.0 μM of TAM. BIK silencing, with a specific RNAi, blocked TAM-induced apoptosis in 45±6.78% of cells. Moreover, it decreased mitochondrial membrane potential (Ψ_m) and total caspase activity, and exhibited low expression of pro-apoptotic proteins BAX, BAK, PUMA and a high expression of BCl-2 and MCL-1. The above suggests resistance to TAM, regulating the intrinsic pathway and indicate that BIK comprises an important factor in the process of apoptosis, which may exert an influence the ER pathway, which regulates mitochondrial integrity. Collectively, our results show that BIK is a central component of the programmed cell death of TAM-induced MCF-7 breast cancer cells. The silencing of BIK gene will be useful for future studies to establish the mechanisms of regulation of resistance to TAM.

DNA methylation and apoptosis resistance in cancer cells

Apoptosis is a cell death programme primordial to cellular homeostasis efficiency. This normal cell suicide program is the result of the activation of a cascade of events in response to death stimuli. Apoptosis occurs in normal cells to maintain a balance between cell proliferation and cell death. A deregulation of this balance due to modifications in the apoptosic pathway leads to different human diseases including cancers. Apoptosis resistance is one of the most important hallmarks of cancer and some new therapeutical strategies focus on inducing cell death in cancer cells. Nevertheless, cancer cells are resistant to treatment inducing cell death because of different mechanisms, such as DNA mutations in gene coding for pro-apoptotic proteins, increased expression of anti-apoptotic proteins and/or pro-survival signals, or pro-apoptic gene silencing mediated by DNA hypermethylation. In this context, aberrant DNA methylation patterns, hypermethylation and hypomethylation of gene coding for proteins implicated in apoptotic pathways are possible causes of cancer cell resistance. This review highlights the role of DNA methylation of apoptosis-related genes in cancer cell resistance.

The sensitivity of diffuse large B-cell lymphoma cell lines to histone deacetylase inhibitor-induced apoptosis is modulated by BCL-2 family protein activity

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) is a genetically heterogeneous disease and this variation can often be used to explain the response of individual patients to chemotherapy. One cancer therapeutic approach currently in clinical trials uses histone deacetylase inhibitors (HDACi's) as monotherapy or in combination with other agents.

METHODOLOGY/PRINCIPAL FINDINGS

We have used a variety of cell-based and molecular/biochemical assays to show that two pan-HDAC inhibitors, trichostatin A and vorinostat, induce apoptosis in seven of eight human DLBCL cell lines. Consistent with previous reports implicating the BCL-2 family in regulating HDACi-induced apoptosis, ectopic over-expression of anti-apoptotic proteins BCL-2 and BCL-XL or pro-apoptotic protein BIM in these cell lines conferred further resistance or sensitivity, respectively, to HDACi treatment. Additionally, BCL-2 family antgonist ABT-737 increased the sensitivity of several DLBCL cell lines to vorinostat-induced apoptosis, including one cell line (SUDHL6) that is resistant to vorinostat alone. Moreover, two variants of the HDACi-sensitive SUDHL4 cell line that have decreased sensitivity to vorinostat showed up-regulation of BCL-2 family anti-apoptotic proteins such as BCL-XL and MCL-1, as well as decreased sensitivity to ABT-737. These results suggest that the regulation and overall balance of anti- to pro-apoptotic BCL-2 family protein expression is important in defining the sensitivity of DLBCL to HDACi-induced apoptosis. However, the sensitivity of DLBCL cell lines to HDACi treatment does not correlate with expression of any individual BCL-2 family member.

CONCLUSIONS/SIGNIFICANCE

These studies indicate that the sensitivity of DLBCL to treatment with HDACi's is dependent on the complex regulation of BCL-2 family members and that BCL-2 antagonists may enhance the response of a subset of DLBCL patients to HDACi treatment.

BIK (NBK) is a mediator of the sensitivity of Fanconi anaemia group C lymphoblastoid cell lines to interstrand DNA cross-linking agents

FA (Fanconi anaemia) is a rare hereditary disorder characterized by congenital malformations, progressive bone marrow failure and an extraordinary predisposition to develop cancer. At present, 15 genes have been related to this condition and mutations of them have also been found in different types of cancer. Bone marrow failure threatens the life of FA patients during the first decade of their life, but the mechanisms underlying this process are not completely understood. In the present study we investigate a possible imbalance between the expression of pro- and anti-apoptotic proteins as a cause for the hypersensitivity of FANCC (FA, complementation group C)-deficient cells to genotoxic stress. We found a BIK (Bcl-2 interacting killer) over-expression in lymphoblastoid cell lines derived from FA-C patients when compared with their phenotypically corrected counterparts. This overexpression has a transcriptional basis since the regulatory region of the gene shows higher activity in FANCC-deficient cells. We demonstrate the involvement of BIK in the sensitivity of FA-C lymphoblasts to interstrand DNA cross-linking agents as it is induced by these drugs and interference of its expression in these cells preserves their viability and reduces apoptosis. We investigate the mechanism of BIK overexpression in FANCC-deficient cells by analysing the activity of many different signalling pathways in these cells. Finally, we provide evidence of a previously undescribed indirect epigenetic regulation of BIK in FA-C lymphoblasts mediated by ΔNp73, an isoform of p73 lacking its transactivation domain that activates BIK through a proximal element in its promoter.

Dual inhibition of Bcl-2 and Bcl-xL strikingly enhances PI3K inhibition-induced apoptosis in human myeloid leukemia cells through a GSK3- and Bim-dependent mechanism

Effects of concomitant inhibition of the PI3K/AKT/mTOR pathway and Bcl-2/Bcl-xL (BCL2L1) were examined in human myeloid leukemia cells. Tetracycline-inducible Bcl-2 and Bcl-xL dual knockdown sharply increased PI3K/AKT/mTOR inhibitor lethality. Conversely, inducible knockdown or dominant-negative AKT increased, whereas constitutively active AKT reduced lethality of the Bcl-2/Bcl-xL inhibitor ABT-737. Furthermore, PI3K/mTOR inhibitors (e.g., BEZ235 and PI-103) synergistically increased ABT-737-mediated cell death in multiple leukemia cell lines and reduced colony formation in leukemic, but not normal, CD34+ cells. Notably, increased lethality was observed in four of six primary acute myelogenous leukemia (AML) specimens. Responding, but not nonresponding, samples exhibited basal AKT phosphorylation. PI3K/mTOR inhibitors markedly downregulated Mcl-1 but increased Bim binding to Bcl-2/Bcl-xL; the latter effect was abrogated by ABT-737. Combined treatment also markedly diminished Bax/Bak binding to Mcl-1, Bcl-2, or Bcl-xL. Bax, Bak, or Bim (BCL2L11) knockdown or Mcl-1 overexpression significantly diminished regimen-induced apoptosis. Interestingly, pharmacologic inhibition or short hairpin RNA knockdown of GSK3α/β significantly attenuated Mcl-1 downregulation and decreased apoptosis. In a systemic AML xenograft model, dual tetracycline-inducible knockdown of Bcl-2/Bcl-xL sharply increased BEZ235 antileukemic effects. In a subcutaneous xenograft model, BEZ235 and ABT-737 coadministration significantly diminished tumor growth, downregulated Mcl-1, activated caspases, and prolonged survival. Together, these findings suggest that antileukemic synergism between PI3K/AKT/mTOR inhibitors and BH3 mimetics involves multiple mechanisms, including Mcl-1 downregulation, release of Bim from Bcl-2/Bcl-xL as well as Bak and Bax from Mcl-1/Bcl-2/Bcl-xL, and GSK3α/β, culminating in Bax/Bak activation and apoptosis. They also argue that combining PI3K/AKT/mTOR inhibitors with BH3 mimetics warrants attention in AML, particularly in the setting of basal AKT activation and/or addiction.

Synergistic silencing by promoter methylation and reduced AP-2α transactivation of the proapoptotic HRK gene confers apoptosis resistance and enhanced tumor growth

The Harakiri (HRK) gene encodes an important proapoptotic mitochondrial protein of the Bcl-2 family. HRK is expressed in normal tissues but is decreased in many cancers such as melanoma, the mechanisms of which have not been fully elucidated. Here, we demonstrate that HRK is silenced by hypermethylation of a major proximal CpG island in the HRK promoter. Furthermore, we show that HRK is a novel target gene regulated by the transcription factor AP-2α, which interacts with an AP-2α binding site in the HRK promoter. Hypermethylation of the major proximal CpG island (which contains the AP-2α binding site within the most densely methylated -218- to -194-bp region) inhibited AP-2α binding and transcriptional activity. Artificial overexpression of AP-2α in melanoma cells up-regulated HRK transcription, which was further restored by treatment with DNA methyltransferase inhibitor 5-azacytidine. Artificial overexpression of HRK by recombinant adenovirus induced caspase-dependent apoptosis, inhibited melanoma cell growth in vitro, and markedly reduced in vivo melanoma growth in a nude mouse xenograft model. RNA interference by siHRK or siAP-2α reversed the above effects. We conclude that the synergistic effects of HRK promoter hypermethylation and loss of AP-2α transactivation lead to HRK gene silencing and confer resistance to apoptosis and enhanced tumor growth. These novel molecular lesions may provide the basis for new therapeutic approaches to treating AP-2α- and HRK-deficient cancers.

Mitochondria in cancer: at the crossroads of life and death

Mitochondrial processes play an important role in tumor initiation and progression. In this review, we focus on three critical processes by which mitochondrial function may contribute to cancer: through alterations in glucose metabolism, the production of reactive oxygen species (ROS) and compromise of intrinsic apoptotic function. Alterations in cancer glucose metabolism include the Warburg effect, leading to a shift in metabolism away from aerobic respiration toward glycolysis, even when sufficient oxygen is present to support respiration. Such alterations in cellular metabolism may favor tumor cell growth by increasing the availability of biosynthetic intermediates needed for cellular growth and proliferation. Mutations in specific metabolic enzymes, namely succinate dehydrogenase, fumarate hydratase and the isocitrate dehydrogenases, have been linked to human cancer. Mitochondrial ROS may contribute to cancer via DNA damage and the activation of aberrant signaling pathways. ROS-dependent stabilization of the transcription factor hypoxia-inducible factor (HIF) may be a particularly important event for tumorigenesis. Compromised function of intrinsic apoptosis removes an important cellular safeguard against cancer and has been implicated in tumorigenesis, tumor metastasis, and chemoresistance. Each of the major mitochondrial processes is linked. In this review, we outline the connections between them and address ways these mitochondrial pathways may be targeted for cancer therapy.

Bcl-2 family of proteins as therapeutic targets in genitourinary neoplasms

INTRODUCTION

Overexpression of antiapoptotic B-cell lymphoma (Bcl-2) proteins confers the dysregulation of apoptosis and results in drug resistance in a variety of cancers, including those of the genitourinary tract. Inhibitors that target prosurvival Bcl-2 proteins are in preclinical and clinical development. The objective of this review is to assess the involvement of Bcl-2 proteins as well as the preclinical and clinical activity of Bcl-2 inhibitors under evaluation for genitourinary neoplasms.

MATERIALS AND METHODS

PubMed was used with both medical subject heading terms and free search to identify the relevant literature. Information on clinical trials was obtained using http://Clincaltrials.gov, EU Clinical Trials Register, and meeting abstracts of the American Society of Clinical Oncology.

RESULTS

To date, 2 Bcl-2 inhibitors have been evaluated in clinical trials for genitourinary tumors (oblimersen and AT-101 (R-(-)-gossypol)). Both agents demonstrated some success in early stages of development, but their clinical activity did not meet expectations. Preclinical studies are under way for other Bcl-2 inhibitors including ABT-737, HA14-1, and Bcl-2 homology 3 inhibitors.

CONCLUSION

Antiapoptotic Bcl-2 proteins are potential molecular targets in genitourinary cancers. Bcl-2 inhibitors might be effective as single agents or in combination with conventional therapies. However, the biology of the Bcl-2 family in genitourinary cancers remains poorly understood and robust preclinical studies are needed to inform clinical development. Such studies should aim to identify: (1) pharmacodynamic markers that could help guide patient selection for treatment with Bcl-2 inhibitors, and (2) optimal combinations of Bcl-2 inhibitors with other anticancer agents for future clinical investigation.

Inhibition of Bcl-2 antiapoptotic members by obatoclax potently enhances sorafenib-induced apoptosis in human myeloid leukemia cells through a Bim-dependent process

Interactions between the multikinase inhibitor sorafenib and the BH3-mimetic obatoclax (GX15-070) were examined in human acute myeloid leukemia (AML) cells. Treatment with sorafenib/obatoclax induced pronounced apoptosis in and reduced the clonogenic growth of multiple AML lines and primary AML cells but not normal CD34(+) cells. Sorafenib triggered rapid and pronounced Mcl-1 down-regulation accompanied by enhanced binding of Bim to Bcl-2 and Bcl-xL, effects that were abolished by obatoclax coadministration. Notably, shRNA knockdown of Bim, Bak, or Bax, but not Noxa, significantly attenuated obatoclax/sorafenib lethality, whereas ectopic expression of Mcl-1 exerted a protective effect. Furthermore, exposure of leukemia cells to sorafenib and obatoclax markedly induced autophagy, reflected by rapid and pronounced LC3 processing and LC3-green fluorescent protein (GFP) punctate formation. Multiple autophagy inhibitors or VPS34 knockdown, significantly potentiated sorafenib/obatoclax lethality, indicating a cytoprotective role for autophagy in this setting. Finally, studies in a xenograft mouse model revealed that combined sorafenib/obatoclax treatment markedly reduced tumor growth and significantly prolonged survival in association with Mcl-1 down-regulation and apoptosis induction, whereas agents administered individually had only modest effects. These findings suggest that combining sorafenib with agents that inhibit Mcl-1 and Bcl-2/Bcl-xL such as obatoclax may represent a novel and potentially effective strategy in AML.

p14(ARF)-induced apoptosis in p53 protein-deficient cells is mediated by BH3-only protein-independent derepression of Bak protein through down-regulation of Mcl-1 and Bcl-xL proteins

The p14(ARF) tumor suppressor plays a central role in regulating cell cycle arrest and apoptosis. We reported previously that p14(ARF) is capable of triggering apoptosis in a p53-independent manner. However, the mechanism remained unclear. Here we demonstrate that the p53-independent activation of the mitochondrial apoptosis pathway by p14(ARF) is primarily mediated by the pro-apoptotic Bax-homolog Bak. Expression of p14(ARF) exclusively triggers a N-terminal conformational switch of Bak, but not Bax, which allows for mitochondrial permeability shift, release of cytochrome c, activation of caspases, and subsequent fragmentation of genomic DNA. Although forced expression of Bak markedly sensitizes toward p14(ARF)-induced apoptosis, re-expression of Bax has no effect. Vice versa, knockdown of Bak by RNA interference attenuates p14(ARF)-induced apoptosis, whereas down-regulation of Bax has no effect. Bak activation coincides with a prominent, caspase-independent deprivation of the endogenous Bak inhibitors Mcl-1 and Bcl-x(L). In turn, mitochondrial apoptosis is fully blocked by overexpression of either Mcl-1 or Bcl-x(L). Taken together, these data indicate that in the absence of functional p53 and Bax, p14(ARF) triggers mitochondrial apoptosis signaling by activating Bak, which is facilitated by down-regulating anti-apoptotic Mcl-1 and Bcl-x(L). Moreover, our data suggest that the simultaneous inhibition of two central endogenous Bak inhibitors, i.e. Mcl-1 and Bcl-x(L), may be sufficient to activate mitochondrial apoptosis in the absence of BH3-only protein regulation.

MT1-MMP protects breast carcinoma cells against type I collagen-induced apoptosis

As invading breast carcinoma cells breach their underlying basement membrane, they become confronted with a dense three-dimensional reactive stroma dominated by type I collagen. To develop metastatic capabilities, invading tumor cells must acquire the capacity to negotiate this novel microenvironment. Collagen influences the fate of epithelial cells by inducing apoptosis. However, the mechanisms used by invading tumor cells to evade collagen-induced apoptosis remain to be defined. We demonstrate that membrane type-1 matrix metalloproteinase (MT1-MMP/MMP-14) confers breast cancer cells with the ability to escape apoptosis when embedded in a collagen gel and after orthotopic implantation in vivo. In the absence of MMP-14-dependent proteolysis, type I collagen triggers apoptosis by inducing the expression of the pro-apoptotic Bcl-2-interacting killer in luminal-like breast cancer cells. These findings reveal a new mechanism whereby MMP-14 activity promotes tumor progression by circumventing apoptosis.

Apoptotic cell signaling in cancer progression and therapy

Apoptosis is a tightly regulated cell suicide program that plays an essential role in the development and maintenance of tissue homeostasis by eliminating unnecessary or harmful cells. Impairment of this native defense mechanism promotes aberrant cellular proliferation and the accumulation of genetic defects, ultimately resulting in tumorigenesis, and frequently confers drug resistance to cancer cells. The regulation of apoptosis at several levels is essential to maintain the delicate balance between cellular survival and death signaling that is required to prevent disease. Complex networks of signaling pathways act to promote or inhibit apoptosis in response to various cues. Apoptosis can be triggered by signals from within the cell, such as genotoxic stress, or by extrinsic signals, such as the binding of ligands to cell surface death receptors. Various upstream signaling pathways can modulate apoptosis by converging on, and thereby altering the activity of, common central control points within the apoptotic signaling pathways, which involve the BCL-2 family proteins, inhibitor of apoptosis (IAP) proteins, and FLICE-inhibitory protein (c-FLIP). This review highlights the role of these fundamental regulators of apoptosis in the context of both normal apoptotic signaling mechanisms and dysregulated apoptotic pathways that can render cancer cells resistant to cell death. In addition, therapeutic strategies aimed at modulating the activity of BCL-2 family proteins, IAPs, and c-FLIP for the targeted induction of apoptosis are briefly discussed.

In silico analysis and DHPLC screening strategy identifies novel apoptotic gene targets of aberrant promoter hypermethylation in prostate cancer

BACKGROUND

Aberrant DNA methylation has been implicated as a key survival mechanism in cancer, whereby promoter hypermethylation silences genes essential for many cellular processes including apoptosis. Limited data is available on the methylation profile of apoptotic genes in prostate cancer (CaP). The aim of this study was to profile methylation of apoptotic-related genes in CaP using denaturing high performance liquid chromatography (DHPLC).

METHODS

Based on an in silico selection process, 13 genes were screened for methylation in CaP cell lines using DHPLC. Quantitative methylation specific PCR was employed to determine methylation levels in prostate tissue specimens (n = 135), representing tumor, histologically benign prostate, high-grade prostatic intraepithelial neoplasia and benign prostatic hyperplasia. Gene expression was measured by QRT-PCR in cell lines and tissue specimens.

RESULTS

The promoters of BIK, BNIP3, cFLIP, TMS1, DCR1, DCR2, and CDKN2A appeared fully or partially methylated in a number of malignant cell lines. This is the first report of aberrant methylation of BIK, BNIP3, and cFLIP in CaP. Quantitative methylation analysis in prostate tissues identified 5 genes (BNIP3, CDKN2A, DCR1, DCR2 and TMS1) which were frequently methylated in tumors but were unmethylated in 100% of benign tissues. Furthermore, 69% of tumors were methylated in at least one of the five-gene panel. In the case of all genes, except BNIP3, promoter hypermethylation was associated with concurrent downregulation of gene expression.

CONCLUSION

Future examination of this "CaP apoptotic methylation signature" in a larger cohort of patients is justified to further evaluate its value as a diagnostic and prognostic marker.

BH3-only proteins: Orchestrators of apoptosis

The BH3-only proteins of Bcl-2 family are essential initiators of apoptosis that propagate extrinsic and intrinsic cell death signals. The interaction of BH3-only proteins with other Bcl-2 family members is critical for understanding the core machinery that controls commitment to apoptosis by permeabilizing the mitochondrial outer membrane. BH3-only proteins promote apoptosis by both directly activating Bax and Bak and by suppressing the anti-apoptotic proteins at the mitochondria and the endoplasmic reticulum. To prevent constitutive cell death, BH3-only proteins are regulated by a variety of mechanisms including transcription and post-translational modifications that govern specific protein-protein interactions. Furthermore, BH3-only proteins also control the initiation of autophagy, another important pathway regulating cell survival and death. Emerging evidence indicates that the interaction of BH3-only proteins with membranes regulates binding to other Bcl-2 family members, thereby specifying function. Due to the important role of BH3-only proteins in the regulation of cell death, several promising BH3-mimetic drugs that are active in pre-clinical models are currently being tested as anti-cancer agents. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.

BH3-only protein Bik is involved in both apoptosis induction and sensitivity to oxidative stress in multiple myeloma

Background:

Although gene expression profile of multiple myeloma (MM) patients shows a wide range of Bik/Nbk expression, varying from absent to high, its regulation and function in myeloma cells is poorly understood. Thus, we addressed these questions in MM.

Methods:

Human myeloma cell lines (HMCLs) and primary purified myeloma cells were studied for Bcl-2 family protein expression by western blot and further correlation analysis was performed. Correlative study between Bik and thyrotroph embryonic factor (TEF) transcription factor expression was analysed by PCR. Stress oxidative response was analysed by flow cytometry.

Results:

A strong expression of Bik protein was found only in one out of three of HMCL and correlated to Bcl-2 expression (P=0.0006). We demonstrated that Bik could be regulated at the protein level by Bcl-2 and at the transcriptional level by TEF. Bik overexpression sensitises myeloma cells to oxidative stress whereas Bik silencing increases resistance to H₂O₂ oxidative stress. Furthermore, Bik ectopic expression disrupts Bim/Bcl-2 and Bim/Bcl-xL endogenous complexes triggering Bim release that could induce Bax and Bak activation.

Conclusions:

Ours results suggest that Bik has a role in both, apoptosis induction and sensitivity to oxidative stress in myeloma cells. Small BH3 mimetic molecules should be considered for further apoptosis-based therapy in myeloma cells expressing endogenous Bik/Bcl-2 complexes.

Therapeutic targeting of C-terminal binding protein in human cancer

The CtBP transcriptional corepressors promote cancer cell survival and migration/invasion. CtBP senses cellular metabolism via a regulatory dehydrogenase domain, and is antagonized by p14/p19(ARF) tumor suppressors. The CtBP dehydrogenase substrate 4-methylthio-2-oxobutyric acid (MTOB) can act as a CtBP inhibitor at high concentrations, and is cytotoxic to cancer cells. MTOB induced apoptosis was p53-independent, correlated with the derepression of the proapoptotic CtBP repression target Bik, and was rescued by CtBP overexpression or Bik silencing. MTOB did not induce apoptosis in mouse embryonic fibroblasts (MEFs), but was increasingly cytotoxic to immortalized and transformed MEFs, suggesting that CtBP inhibition may provide a suitable therapeutic index for cancer therapy. In human colon cancer cell peritoneal xenografts, MTOB treatment decreased tumor burden and induced tumor cell apoptosis. To verify the potential utility of CtBP as a therapeutic target in human cancer, the expression of CtBP and its negative regulator ARF was studied in a series of resected human colon adenocarcinomas. CtBP and ARF levels were inversely-correlated, with elevated CtBP levels (compared with adjacent normal tissue) observed in greater than 60% of specimens, with ARF absent in nearly all specimens exhibiting elevated CtBP levels. Targeting CtBP may represent a useful therapeutic strategy in human malignancies.

Individual and overlapping roles of BH3-only proteins Bim and Bad in apoptosis of lymphocytes and platelets and in suppression of thymic lymphoma development

BH3-only proteins, such as Bim and Bad, contribute to tissue homeostasis by initiating apoptosis in a cell type- and stimulus-specific manner. Loss of Bim provokes lymphocyte accumulation in vivo and renders lymphocytes more resistant to diverse apoptotic stimuli and Bad has been implicated in the apoptosis of haematopoietic cells upon cytokine deprivation. To investigate whether their biological roles in apoptosis overlap, we generated mice lacking both Bim and Bad and compared their haematopoietic phenotype with that of the single-knockout and wild-type (wt) animals. Unexpectedly, bad(-/-) mice had excess platelets due to prolonged platelet life-span. The bim(-/-)bad(-/-) mice were anatomically normal and fertile. Their haematopoietic phenotype resembled that of bim(-/-) mice but lymphocytes were slightly more elevated in their lymph nodes. Although resting B and T lymphocytes from bim(-/-)bad(-/-) and bim(-/-) animals displayed similar resistance to diverse apoptotic stimuli, mitogen activated bim(-/-)bad(-/-) B cells were more refractory to cytokine deprivation. Moreover, combined loss of Bim and Bad-enhanced survival of thymocytes after DNA damage and accelerated development of γ-irradiation-induced thymic lymphoma. Unexpectedly, their cooperation in the thymus depended upon thymocyte-stromal interaction. Collectively, these results show that Bim and Bad can cooperate in the apoptosis of thymocytes and activated B lymphocytes and in the suppression of thymic lymphoma development.

Systematic genetic dissection of p14ARF-mediated mitochondrial cell death signaling reveals a key role for p21CDKN1 and the BH3-only protein Puma/bbc3

Induction of cell death by p14(ARF) is mediated through a Bax/Bak-dependent mitochondrial apoptosis pathway. To investigate the upstream signaling events required for the activation of Bax and/or Bak and to determine the functional impact of de-regulated cell cycle restriction point control in this context, we genetically dissected the impact of BH3-only proteins and the role of the cyclin-dependent kinase (cdk) inhibitor p21(CDKN1). Using isogenic HCT116 colorectal cancer cells, either wild-type or homozygously deleted for the BH3-only protein Puma/bbc3 and/or p21(CDKN1) or p53-reconstituted DU145 prostate cancer cells, we show that p14(ARF)-induced apoptosis is attenuated in the absence of Puma. Upon expression of p14(ARF) in HCT116 cells, Puma is rapidly induced at both the mRNA and protein level. Puma-proficient HCT116 cells undergo apoptotic (nuclear) DNA fragmentation, which is preceded by the N-terminal conformational change of Bax, the breakdown of the mitochondrial membrane potential, and induction of caspase-9 (LEHD)-like and caspase-3/7 (DEVD)-like activities. In contrast, p14(ARF)-induced apoptosis is markedly attenuated in isogenic HCT116 cells bi-allelically deleted for puma. The sensitivity of Puma-deficient cells to p14(ARF)-induced apoptosis is fully restored by functional reconstitution of Puma using a conditional adenoviral expression vector. Notably, the concomitant deletion of p21(CDKN1) strongly enhances p14(ARF)-induced apoptosis in Puma-proficient cells, but not in isogenic Puma-deficient cells. These results indicate that p14(ARF)-induced mitochondrial apoptosis critically depends on the BH3-only protein Puma. In the presence of a functional p53/Puma/Bax-signaling axis, p14(ARF)-triggered apoptosis is enhanced by loss of p21(CDKN1)-mediated cell cycle checkpoint control.

BH3-only proteins: the death-puppeteer's wires

Most cell death in vertebrates proceeds through the intrinsic pathway of apoptosis and results from unregulated increase of mitochondrial membrane permeability. Bcl2-associated X protein (Bax) and Bcl2-antagonist/killer protein (Bak), the effector proapoptotic members of the Bcl-2 family, are, in their active state, the principal accomplices for this permeabilization process. How exactly Bax and Bak are activated has been a matter of major investigation in the last decade, and suitable tools offered by quantitative cytometric methodologies have significantly contributed to the understanding of the function of Bcl-2 family members. Here, we review the most relevant findings in this field and highlight one common trait that has emerged from the diverse new theories: a crucial role in the control of Bax/Bak activation has to be attributed to the BH3-only subset of the Bcl-2 family. BH3-only proteins exert their proapoptotic activity by hierarchical and tightly tuned interactions with other Bcl-2 family members and operate as sensors of intracellular/extracellular death signals and vectors of information to the core apoptotic machinery. Given their essential role in apoptosis, BH3-only molecules are proposed as molecular targets for the cure of diseases associated with abnormal cell death, as in the case with neurodegenerative conditions. As well, they are explored as possible tools for cancer therapy, according to the concept that molecules mimicking the BH3 domain of these proteins could selectively and efficiently cooperate in the cell killing by chemotherapeutic drugs. A few BH3 mimetics are currently being tested in clinical trials of hematologic and solid tumors. Nevertheless, the knowledge about the cellular and molecular mechanisms that regulate responsiveness to BH3 therapy has to be further expanded and will benefit from recent advances in cytometric quantitative technologies.

BH3-only proteins and their effects on cancer

Apoptosis, a form of cellular suicide is a key mechanism involved in the clearance of cells that are dysfunctional, superfluous or infected. For this reason, the cell needs mechanisms o sense death cues and relay death signals to the apoptotic machinery involved in cellular execution. In the intrinsic apoptotic pathway, a subclass of BCL-2 family proteins called the BH3-onlyproteins are responsible for triggering apoptosis in response to varied cellular stress cues. The mechanisms by which they are regulated are tied to the type of cellular stress they sense. Once triggered, they interact with other BCL-2 family proteins to cause mitochondrial outer membrane permeabilization which in turn results in the activation ofserine proteases necessary for cell killing. Failure to properly sense death cues and relay the death signal can have a major impact on cancer. This chapter will discuss our current models of how BH3-only proteins function as well as their impact on carcinogenesis and cancer treatment.