Molecular mechanisms and anti-cancer aspects of the medicinal phytochemicals rocaglamides (=flavaglines)

Rocaglamide regulates iron homeostasis by suppressing hepcidin expression

The anemia of inflammation (AI) is characterized by the presence of inflammation and abnormal elevation of hepcidin. Accumulating evidence has proved that Rocaglamide (RocA) was involved in inflammation regulation. Nevertheless, the role of RocA in AI, especially in iron metabolism, has not been investigated, and its underlying mechanism remains elusive. Here, we demonstrated that RocA dramatically suppressed the elevation of hepcidin and ferritin in LPS-treated mice cell line RAW264.7 and peritoneal macrophages. In vivo study showed that RocA can restrain the depletion of serum iron (SI) and transferrin (Tf) saturation caused by LPS. Further investigation showed that RocA suppressed the upregulation of hepcidin mRNA and downregulation of Fpn1 protein expression in the spleen and liver of LPS-treated mice. Mechanistically, this effect was attributed to RocA's ability to inhibit the IL-6/STAT3 pathway, resulting in the suppression of hepcidin mRNA and subsequent increase in Fpn1 and TfR1 expression in LPS-treated macrophages. Moreover, RocA inhibited the elevation of the cellular labile iron pool (LIP) and reactive oxygen species (ROS) induced by LPS in RAW264.7 cells. These findings reveal a pivotal mechanism underlying the roles of RocA in modulating iron homeostasis and also provide a candidate natural product on alleviating AI.

Rocaglamide promotes infiltration and differentiation of T cells and coordinates with PD-1 inhibitor to overcome checkpoint resistance in multiple tumor models

Tumor-infiltrating lymphocyte (TIL) deficiency is the most conspicuous obstacle to limit the cancer immunotherapy. Immune checkpoint inhibitors (ICIs), such as anti-PD-1 antibody, have achieved great success in clinical practice. However, due to the limitation of response rates of ICIs, some patients fail to benefit from monotherapy. Thus, novel combination therapy that could improve the response rates emerges as new strategies for cancer treatment. Here, we reported that the natural product rocaglamide (RocA) increased tumor-infiltrating T cells and promoted Th17 differentiation of CD4+ TILs. Despite RocA monotherapy upregulated PD-1 expression of TILs, which was considered as the consequence of T cell activation, combining RocA with anti-PD-1 antibody significantly downregulated the expression of PD-1 and promoted proliferation of TILs. Taken together, these findings demonstrated that RocA could fuel the T cell anti-tumor immunity and revealed the remarkable potential of RocA as a therapeutic candidate when combining with the ICIs.

Thioredoxin (Trx): A redox target and modulator of cellular senescence and aging-related diseases

Thioredoxin (Trx) is a compact redox-regulatory protein that modulates cellular redox state by reducing oxidized proteins. Trx exhibits dual functionality as an antioxidant and a cofactor for diverse enzymes and transcription factors, thereby exerting influence over their activity and function. Trx has emerged as a pivotal biomarker for various diseases, particularly those associated with oxidative stress, inflammation, and aging. Recent clinical investigations have underscored the significance of Trx in disease diagnosis, treatment, and mechanistic elucidation. Despite its paramount importance, the intricate interplay between Trx and cellular senescence-a condition characterized by irreversible growth arrest induced by multiple aging stimuli-remains inadequately understood. In this review, our objective is to present a comprehensive and up-to-date overview of the structure and function of Trx, its involvement in redox signaling pathways and cellular senescence, its association with aging and age-related diseases, as well as its potential as a therapeutic target. Our review aims to elucidate the novel and extensive role of Trx in senescence while highlighting its implications for aging and age-related diseases.

The mechanism of UNC-51-like kinase 1 and the applications of small molecule modulators in cancer treatment

Autophagy is a process of self-renewal in cells, which not only provides the necessary nutrients for cells, but also clears necrotic organelles. Autophagy disorders are closely related to diseases such as cancer. UNC-51-like kinase 1 (ULK1) is a serine/threonine protein kinase that plays a crucial role in receiving input from energy and nutrient sensors, activating autophagy to maintain cellular homeostasis under stressful conditions. In recent years, targeting ULK1 has become a highly promising strategy for cancer treatment. This review introduces the regulatory mechanism of ULK1 in autophagy through the AMPK/mTOR/ULK1 pathway and reviews the research progress of ULK1 activators and inhibitors and their applications in cancer treatment. In addition, we analyze the binding modes between ULK1 and modulators through virtual molecular docking, which will provide a reliable basis and theoretical guidance for the design and development of new therapeutic drugs targeting ULK1.

Natural compounds modulating mitophagy: Implications for cancer therapy

Cancer is considered as the second leading cause of mortality, and cancer incidence is still growing rapidly worldwide, which poses an increasing global health burden. Although chemotherapy is the most widely used treatment for cancer, its effectiveness is limited by drug resistance and severe side effects. Mitophagy is the principal mechanism that degrades damaged mitochondria via the autophagy/lysosome pathway to maintain mitochondrial homeostasis. Emerging evidence indicates that mitophagy plays crucial roles in tumorigenesis, particularly in cancer therapy. Mitophagy can exhibit dual effects in cancer, with both cancer-inhibiting or cancer-promoting function in a context-dependent manner. A variety of natural compounds have been found to affect cancer cell death and display anticancer properties by modulating mitophagy. In this review, we provide a systematic overview of mitophagy signaling pathways, and examine recent advances in the utilization of natural compounds for cancer therapy through the modulation of mitophagy. Furthermore, we address the inquiries and challenges associated with ongoing investigations concerning the application of natural compounds in cancer therapy based on mitophagy. Overcoming these limitations will provide opportunities to develop novel interventional strategies for cancer treatment.

Galectin-3 and prohibitin 1 are autoantigens in IgG4-related cholangitis without clear-cut protective effects against toxic bile acids

Background and aims

IgG4-related cholangitis (IRC) is the hepatobiliary manifestation of IgG4-related disease, a systemic B cell-driven fibro-inflammatory disorder. Four autoantigens have recently been described in IgG4-RD: annexin A11, galectin-3, laminin 511-E8, and prohibitin 1. We have previously reported a protective role of annexin A11 and laminin 511-E8 in human cholangiocytes against toxic bile acids. Here, we explored the potentially protective role of the carbohydrate-binding lectin galectin-3 and the scaffold proteins prohibitins 1 and 2.

Methods

Anti-galectin-3, anti-prohibitin 1 and 2 autoantibody positivity in IRC and healthy and disease (primary sclerosing cholangitis (PSC)) control sera was assessed by ELISA/liquid chromatography-tandem mass spectrometry (LC-MS/MS). Human H69 cholangiocytes were subjected to short hairpin RNA (shRNA) knockdown targeting galectin-3 (LGALS3), prohibitin 1 (PHB1), and prohibitin 2 (PHB2). H69 cholangiocytes were also exposed to recombinant galectin-3, the inhibitor GB1107, recombinant prohibitin 1, and the pan-prohibitin inhibitor rocaglamide. Protection against bile acid toxicity was assessed by intracellular pH (pHi) measurements using BCECF-AM, 22,23-3H-glycochenodeoxycholic acid (3H-GCDC) influx, and GCDC-induced apoptosis using Caspase-3/7 assays.

Results

Anti-galectin-3 autoantibodies were detected in 13.5% of individuals with IRC but not in PSC. Knockdown of LGALS3 and galectin-3 inhibition with GB1107 did not affect pHi, whereas recombinant galectin-3 incubation lowered pHi. LGALS3 knockdown increased GCDC-influx but not GCDC-induced apoptosis. GB1107 reduced GCDC-influx and GCDC-induced apoptosis. Recombinant galectin-3 tended to decrease GCDC-influx and GCDC-induced apoptosis. Anti-prohibitin 1 autoantibodies were detected in 61.5% and 35.7% of individuals with IRC and PSC, respectively. Knockdown of PHB1, combined PHB1/2 KD, treatment with rocaglamide, and recombinant prohibitin 1 all lowered pHi. Knockdown of PHB1, PHB2, or combined PHB1/2 did not alter GCDC-influx, yet knockdown of PHB1 increased GCDC-induced apoptosis. Conversely, rocaglamide reduced GCDC-influx but did not attenuate GCDC-induced apoptosis. Recombinant prohibitin 1 did not affect GCDC-influx or GCDC-induced apoptosis. Finally, anti-galectin-3 and anti-prohibitin 1 autoantibody pretreatment did not lead to increased GCDC-influx.

Conclusions

A subset of individuals with IRC have autoantibodies against galectin-3 and prohibitin 1. Gene-specific knockdown, pharmacological inhibition, and recombinant protein substitution did not clearly disclose a protective role of these autoantigens in human cholangiocytes against toxic bile acids. The involvement of these autoantibodies in processes surpassing epithelial secretion remains to be elucidated.

The prohibitin-binding compound fluorizoline induces the pro-inflammatory cytokines interleukin-8 and interleukin-6 through the activation of JNK and p38 MAP kinases

Fluorizoline is a prohibitin (PHB)-binding compound that induces apoptosis in several cancer cell lines as well as in primary cells from hematologic malignancies. In this study, we show that fluorizoline treatment triggers the activation of the stress-activated kinases c-Jun N-terminal kinase (JNK) and p38 prior to caspase activation in human cell lines. However, the blockage of p38 and JNK activity with chemical inhibitors or siRNA-mediated downregulation of MAPK14 (p38) does not prevent fluorizoline-induced apoptosis, suggesting that the activation of these kinases plays an alternative role in the cell response to fluorizoline treatment. Here, we describe that fluorizoline treatment leads to the secretion of pro-inflammatory cytokines interleukin-8 (IL-8) and interleukin-6 (IL-6). Importantly, we demonstrate that the activation of the stress-activated kinases JNK and p38 mediates the secretion of both IL-8 and IL-6. This study shows novel insights into the pro-inflammatory role exhibited by a compound that binds to PHB, thus supporting the potential of PHBs as anti-inflammatory proteins.

Essential Protein PHB2 and Its Regulatory Mechanisms in Cancer

Prohibitins (PHBs) are a highly conserved class of proteins and have an essential role in transcription, epigenetic regulation, nuclear signaling, mitochondrial structural integrity, cell division, and cellular membrane metabolism. Prohibitins form a heterodimeric complex, consisting of two proteins, prohibitin 1 (PHB1) and prohibitin 2 (PHB2). They have been discovered to have crucial roles in regulating cancer and other metabolic diseases, functioning both together and independently. As there have been many previously published reviews on PHB1, this review focuses on the lesser studied prohibitin, PHB2. The role of PHB2 in cancer is controversial. In most human cancers, overexpressed PHB2 enhances tumor progression, while in some cancers, it suppresses tumor progression. In this review, we focus on (1) the history, family, and structure of prohibitins, (2) the essential location-dependent functions of PHB2, (3) dysfunction in cancer, and (4) the promising modulators to target PHB2. At the end, we discuss future directions and the clinical significance of this common essential gene in cancer.

Mitomycin C enhanced the antitumor efficacy of Rocaglamide in colorectal cancer

Rocaglamide (ROC), a natural phytochemical isolated from Aglaia species, is a translational inhibitor of de novo c-FLIP synthesis, which relieves the inhibition of c-FLIP dimerization with procasoase-8 and downstream activation. Unfortunately, a lot of cancer cells, especially colorectal cancer cells (CRC), exhibit marked resistance to Rocaglamide-induced cell death. Research has demonstrated that mitomycin C (MMC) has broad-spectrum anti-tumor activity that it can synergize with a wide range of clinical drugs to inhibit tumor growth. The current study investigated whether MMC combined with ROC could sensitize CRC cells with different ROC resistance to apoptosis. HCT116 and HT29, two different CRC cells, were treated with ROC and/or MMC, and the induction of apoptosis, inhibition of cell migration and invasion, arrest of cell cycle, induction of reactive oxygen species, and effects on Bcl-2 family signaling pathway were investigated. The results showed that low concentration of MMC combined with ROC significantly promoted HCT116 and HT29 cell apoptosis and inhibited cell proliferation by downregulating the expression of Bcl-2 and c-FLIP, upregulating the expression of Bax, activating the caspase cascade (involving the mitochondrial apoptosis pathway), arresting cell cycle in G1 phase, and increasing the level of reactive oxygen species (ROS). In addition, the viability and morphology of MRC-5 cells were not significantly affected by the combined treatment with ROC and MMC, indicating its safety. Therefore, it is concluded that the combination treatment of ROC and MMC is a highly effective tumor therapy and may offer a promising therapeutic strategy for the treatment of CRC.

Reanalysis of ribosome profiling datasets reveals a function of rocaglamide A in perturbing the dynamics of translation elongation via eIF4A

The quickly accumulating ribosome profiling data is an insightful resource for studying the critical details of translation regulation under various biological contexts. Rocaglamide A (RocA), an antitumor heterotricyclic natural compound, has been shown to inhibit translation initiation of a large group of mRNA species by clamping eIF4A onto poly-purine motifs in the 5' UTRs. However, reanalysis of previous ribosome profiling datasets reveals an unexpected shift of the ribosome occupancy pattern, upon RocA treatment in various types of cells, during early translation elongation for a specific group of mRNA transcripts without poly-purine motifs over-represented in their 5' UTRs. Such perturbation of translation elongation dynamics can be attributed to the blockage of translating ribosomes due to the binding of eIF4A to the poly-purine sequence in coding regions. In summary, our study presents the complete dual modes of RocA in blocking translation initiation and elongation, which underlie the potent antitumor effect of RocA.

Regulatory T cells suppress CD4+ effector T cell activation by controlling protein synthesis

Regulatory T cells (Tregs) suppress the activation and subsequent effector functions of CD4 effector T cells (Teffs). However, molecular mechanisms that enforce Treg-mediated suppression in CD4 Teff are unclear. We found that Tregs suppressed activation-induced global protein synthesis in CD4 Teffs prior to cell division. We analyzed genome-wide changes in the transcriptome and translatome of activated CD4 Teffs. We show that mRNAs encoding for the protein synthesis machinery are regulated at the level of translation in activated CD4 Teffs by Tregs. Tregs suppressed global protein synthesis of CD4 Teffs by specifically inhibiting mRNAs of the translation machinery at the level of mTORC1-mediated translation control through concerted action of immunosuppressive cytokines IL-10 and TGFβ. Lastly, we found that the therapeutic targeting of protein synthesis with the RNA helicase eIF4A inhibitor rocaglamide A can alleviate inflammatory CD4 Teff activation caused by acute Treg depletion in vivo. These data show that peripheral tolerance is enforced by Tregs through mRNA translational control in CD4 Teffs.

Potential Phytochemicals for Prevention of Familial Breast Cancer with BRCA Mutations

Breast cancer has remained a global challenge and the second leading cause of cancer mortality in women and family history. Hereditary factors are some of the major risk factors associated with breast cancer. Out of total breast cancer cases, 5-10% account only for familial breast cancer, and nearly 50% of all hereditary breast cancer are due to BRCA1/BRCA2 germline mutations. BRCA1/2 mutations play an important role not only in determining the clinical prognosis of breast cancer but also in the survival curves. Since this risk factor is known, a significant amount of the healthcare burden can be reduced by taking preventive measures among people with a known history of familial breast cancer. There is increasing evidence that phytochemicals of nutrients and supplements help in the prevention and cure of BRCA-related cancers by different mechanisms such as limiting DNA damage, altering estrogen metabolism, or upregulating expression of the normal BRCA allele, and ultimately enhancing DNA repair. This manuscript reviews different approaches used to identify potential phytochemicals to mitigate the risk of familial breast cancer with BRCA mutations. The findings of this review can be extended for the prevention and cure of any BRCAmutated cancer after proper experimental and clinical validation of the data.

Hierarchical Virtual Screening Based on Rocaglamide Derivatives to Discover New Potential Anti-Skin Cancer Agents

Skin Cancer (SC) is among the most common type of cancers worldwide. The search for SC therapeutics using molecular modeling strategies as well as considering natural plant-derived products seems to be a promising strategy. The phytochemical Rocaglamide A (Roc-A) and its derivatives rise as an interesting set of reference compounds due to their in vitro cytotoxic activity with SC cell lines. In view of this, we performed a hierarchical virtual screening study considering Roc-A and its derivatives, with the aim to find new chemical entities with potential activity against SC. For this, we selected 15 molecules (Roc-A and 14 derivatives) and initially used them in docking studies to predict their interactions with Checkpoint kinase 1 (Chk1) as a target for SC. This allowed us to compile and use them as a training set to build robust pharmacophore models, validated by Pearson’s correlation (p) values and hierarchical cluster analysis (HCA), subsequentially submitted to prospective virtual screening using the Molport^® database. Outputted compounds were then selected considering their similarities to Roc-A, followed by analyses of predicted toxicity and pharmacokinetic properties as well as of consensus molecular docking using three software. 10 promising compounds were selected and analyzed in terms of their properties and structural features and, also, considering their previous reports in literature. In this way, the 10 promising virtual hits found in this work may represent potential anti-SC agents and further investigations concerning their biological tests shall be conducted.

Comparative phytochemistry of flavaglines (= rocaglamides), a group of highly bioactive flavolignans from Aglaia species (Meliaceae)

Flavaglines are formed by cycloaddition of a flavonoid nucleus with a cinnamic acid moiety representing a typical chemical character of the genus Aglaia of the family Meliaceae. Based on biosynthetic considerations 148 derivatives are grouped together into three skeletal types representing 77 cyclopenta[b]benzofurans, 61 cyclopenta[bc]benzopyrans, and 10 benzo[b]oxepines. Apart from different hydroxy, methoxy, and methylenedioxy groups of the aromatic rings, important structural variation is created by different substitutions and stereochemistries of the central cyclopentane ring. Putrescine-derived bisamides constitute important building blocks occurring as cyclic 2-aminopyrrolidines or in an open-chained form, and are involved in the formation of pyrimidinone flavaglines. Regarding the central role of cinnamic acid in the formation of the basic skeleton, rocagloic acid represents a biosynthetic precursor from which aglafoline- and rocaglamide-type cyclopentabenzofurans can be derived, while those of the rocaglaol-type are the result of decarboxylation. Broad-based comparison revealed characteristic substitution trends which contribute as chemical markers to natural delimitation and grouping of taxonomically problematic Aglaia species. A wide variety of biological activities ranges from insecticidal, antifungal, antiprotozoal, and anti-inflammatory properties, especially to pronounced anticancer and antiviral activities. The high insecticidal activity of flavaglines is comparable with that of the well-known natural insecticide azadirachtin. Comparative feeding experiments informed about structure-activity relationships and exhibited different substitutions of the cyclopentane ring essential for insecticidal activity. Parallel studies on the antiproliferative activity of flavaglines in various tumor cell lines revealed similar structural prerequisites that let expect corresponding molecular mechanisms. An important structural modification with very high cytotoxic potency was found in the benzofuran silvestrol characterized by an unusual dioxanyloxy subunit. It possessed comparable cytotoxicity to that of the natural anticancer compounds paclitaxel (Taxol®) and camptothecin without effecting normal cells. The primary effect was the inhibition of protein synthesis by binding to the translation initiation factor eIF4A, an ATP-dependent DEAD-box RNA helicase. Flavaglines were also shown to bind to prohibitins (PHB) responsible for regulation of important signaling pathways, and to inhibit the transcriptional factor HSF1 deeply involved in metabolic programming, survival, and proliferation of cancer cells. Flavaglines were shown to be not only promising anticancer agents but gained now also high expectations as agents against emerging RNA viruses like SARS-CoV-2. Targeting the helicase eIF4A with flavaglines was recently described as pan-viral strategy for minimizing the impact of future RNA virus pandemics.

Advances in plant-derived natural products for antitumor immunotherapy

In recent years, immunotherapy has emerged as a novel antitumor strategy in addition to traditional surgery, radiotherapy and chemotherapy. It uniquely focuses on immune cells and immunomodulators in the tumor microenvironment and helps eliminate tumors at the root by rebuilding the immune system. Despite remarkable breakthroughs, cancer immunotherapy still faces many challenges: lack of predictable and prognostic biomarkers, adverse side effects, acquired treatment resistance, high costs, etc. Therefore, more efficacious and efficient, safer and cheaper antitumor immunomodulatory drugs have become an urgent requirement. For decades, plant-derived natural products obtained from land and sea have provided the most important source for the development of antitumor drugs. Currently, more attention is being paid to the discovery of potential cancer immunotherapy modulators from plant-derived natural products, such as polysaccharides, phenols, terpenoids, quinones and alkaloids. Some of these agents have outstanding advantages of multitargeting and low side effects and low cost compared to conventional immunotherapeutic agents. We intend to summarize the progress of comprehensive research on these plant-derived natural products and their derivatives and discuss their possible mechanisms in regulating the immune system and their efficacy as monotherapies or in combination with regular chemotherapeutic agents.

Treatment resistance analysis reveals GLUT-1-mediated glucose uptake as a major target of synthetic rocaglates in cancer cells

Rocaglates are natural compounds that have been extensively studied for their ability to inhibit translation initiation. Rocaglates represent promising drug candidates for tumor treatment due to their growth‐inhibitory effects on neoplastic cells. In contrast to natural rocaglates, synthetic analogues of rocaglates have been less comprehensively characterized, but were also shown to have similar effects on the process of protein translation. Here, we demonstrate an enhanced growth‐inhibitory effect of synthetic rocaglates when combined with glucose anti‐metabolite 2‐deoxy‐D‐glucose (2DG) in different cancer cell lines. Moreover, we unravel a new aspect in the mechanism of action of synthetic rocaglates involving reduction of glucose uptake mediated by downregulation or abrogation of glucose transporter GLUT‐1 expression. Importantly, cells with genetically induced resistance to synthetic rocaglates showed substantially less pronounced treatment effect on glucose metabolism and did not demonstrate GLUT‐1 downregulation, pointing at the crucial role of this mechanism for the anti‐tumor activity of the synthetic rocaglates. Transcriptome profiling revealed glycolysis as one of the major pathways differentially regulated in sensitive and resistant cells. Analysis of synthetic rocaglate efficacy in a 3D tissue context with a co‐culture of tumor and normal cells demonstrated a selective effect on tumor cells and substantiated the mechanistic observations obtained in cancer cell lines. Increased glucose uptake and metabolism is a universal feature across different tumor types. Therefore, targeting this feature by synthetic rocaglates could represent a promising direction for exploitation of rocaglates in novel anti‐tumor therapies.

1-Aminomethyl SAR in a novel series of flavagline-inspired eIF4A inhibitors: Effects of amine substitution on cell potency and in vitro PK properties

Flavaglines such as silvestrol (1) and rocaglamide (2) constitute an interesting class of natural products with promising anticancer activities. Their mode of action is based on inhibition of eukaryotic initiation factor 4A (eIF4A) dependent translation through formation of a stable ternary complex with eIF4A and mRNA, thus blocking ribosome scanning. Herein we describe initial SAR studies in a novel series of 1-aminomethyl substituted flavagline-inspired eIF4A inhibitors. We discovered that a variety of N-substitutions at the 1-aminomethyl group are tolerated, making this position pertinent for property and ADME profile tuning. The findings presented herein are relevant to future drug design efforts towards novel eIF4A inhibitors with drug-like properties.

Cotranslational prolyl hydroxylation is essential for flavivirus biogenesis

Viral pathogens are an ongoing threat to public health worldwide. Analysing their dependence on host biosynthetic pathways could lead to effective antiviral therapies1. Here we integrate proteomic analyses of polysomes with functional genomics and pharmacological interventions to define how enteroviruses and flaviviruses remodel host polysomes to synthesize viral proteins and disable host protein production. We find that infection with polio, dengue or Zika virus markedly modifies polysome composition, without major changes to core ribosome stoichiometry. These viruses use different strategies to evict a common set of translation initiation and RNA surveillance factors from polysomes while recruiting host machineries that are specifically required for viral biogenesis. Targeting these specialized viral polysomes could provide a new approach for antiviral interventions. For example, we find that both Zika and dengue use the collagen proline hydroxylation machinery to mediate cotranslational modification of conserved proline residues in the viral polyprotein. Genetic or pharmacological inhibition of proline hydroxylation impairs nascent viral polyprotein folding and induces its aggregation and degradation. Notably, such interventions prevent viral polysome remodelling and lower virus production. Our findings delineate the modular nature of polysome specialization at the virus-host interface and establish a powerful strategy to identify targets for selective antiviral interventions.

Biological and biorational management of blast diseases in cereals caused by Magnaporthe oryzae

Blast diseases, caused by the fungal pathogen Magnaporthe oryzae, are among the most destructive diseases that occur on at least 50 species of grasses, including cultivated cereals wheat, and rice. Although fungicidal control of blast diseases has widely been researched, development of resistance of the pathogen against commercially available products makes this approach unreliable. Novel approaches such as the application of biopesticides against the blast fungus are needed for sustainable management of this economically important disease. Antagonistic microorganisms, such as fungi and probiotic bacteria from diverse taxonomic genera were found to suppress blast fungi both in vitro and in vivo. Various classes of secondary metabolites, such as alkaloids, phenolics, and terpenoids of plant and microbial origin significantly inhibit fungal growth and may also be effective in managing blast diseases. Common modes of action of microbial biocontrol agents include: antibiosis, production of lytic enzymes, induction of systemic resistance in host plant, and competition for nutrients or space. However, the precise mechanism of biocontrol of the blast fungus by antagonistic microorganisms and/or their bioactive secondary metabolites is not well understood. Commercial formulations of biocontrol agents and bioactive natural products could be cost-effective and sustainable but their availability at this time is extremely limited. This review updates our knowledge on the infection pathway of the wheat blast fungus, catalogs naturally occurring biocontrol agents that may be effective against blast diseases, and discusses their role in sustainable management of the disease.

Inhibitors of Eukaryotic Translational Machinery as Therapeutic Agents

Inhibiting eukaryotic protein translation with small molecules is emerging as a powerful therapeutic strategy. The advantage of targeting cellular translational machinery is that it is required for the highly proliferative state of many neoplastic cells, replication of certain viruses, and ultimately the expression of a wide variety of protein targets. Although, this approach has been exploited to develop clinical agents, such as homoharringtonine (HHT, 1), used to treat chronic myeloid leukemia (CML), inhibiting components of the translational machinery is often associated with cytotoxic phenotypes. However, recent studies have demonstrated that certain small molecules can inhibit the translation of specific subsets of proteins, leading to lower cytotoxicity, and opening-up therapeutic opportunities for translation inhibitors to be deployed in indications beyond oncology and infectious disease. This review summarizes efforts to develop inhibitors of the eukaryotic translational machinery as therapeutic agents and highlights emerging opportunities for translation inhibitors in the future.

The multifaceted functions of RNA helicases in the adaptive cellular response to hypoxia: From mechanisms to therapeutics

Hypoxia is a hallmark of cancer. Hypoxia-inducible factor (HIF), a master player for sensing and adapting to hypoxia, profoundly influences genome instability, tumor progression and metastasis, metabolic reprogramming, and resistance to chemotherapies and radiotherapies. High levels and activity of HIF result in poor clinical outcomes in cancer patients. Thus, HIFs provide ideal therapeutic targets for cancers. However, HIF biology is sophisticated, and currently available HIF inhibitors have limited clinical utility owing to their low efficacy or side effects. RNA helicases, which are master players in cellular RNA metabolism, are usually highly expressed in tumors to meet the increased oncoprotein biosynthesis demand. Intriguingly, recent findings provide convincing evidence that RNA helicases are crucial for the adaptive cellular response to hypoxia via a mutual regulation with HIFs. More importantly, some RNA helicase inhibitors may suppress HIF signaling by blocking the translation of HIF-responsive genes. Therefore, RNA helicase inhibitors may work synergistically with HIF inhibitors in cancer to improve treatment efficacy. In this review, we discuss current knowledge of how cells sense and adapt to hypoxia through HIFs. However, our primary focus is on the multiple functions of RNA helicases in the adaptive response to hypoxia. We also highlight how these hypoxia-related RNA helicases can be exploited for anti-cancer therapeutics.

In silico and in vitro studies on the anti-cancer activity of andrographolide targeting survivin in human breast cancer stem cells

Breast cancer stem cells (BCSCs) express high levels of the anti-apoptotic protein, survivin. This study aimed to discover a natural active compound with anti-cancer properties that targeted survivin in human breast cancer stem cells. From the seven examined compounds, andrographolide was selected as a lead compound through in silico molecular docking with survivin, caspase-9, and caspase-3. We found that the affinity between andrographolide and survivin is higher than that with caspase-9 and caspase-3. Human CD24-/CD44+ BCSCs were treated with andrographolide in vitro for 24 hours. The cytotoxic effect of andrographolide on BCSCs was compared to that on human mesenchymal stem cells (MSCs). The expression of survivin, caspase-9, and caspase-3 mRNA was analyzed using qRT-PCR, while Thr34-phosphorylated survivin and total survivin levels were determined using ELISA and Immunoblotting assay. Annexin-V/PI flow cytometry assays were performed to evaluate the apoptotic activity of andrographolide. Our results demonstrate that the CC50 of andrographolide in BCSCs was 0.32mM, whereas there was no cytotoxic effect in MSCs. Moreover, andrographolide decreased survivin and Thr34-phosphorylated survivin, thus inhibiting survivin activation and increasing survivin mRNA in BCSCs. The apoptotic activity of andrographolide was revealed by the increase of caspase-3 mRNA and protein, as well as the increase in both the early and late phases of apoptosis. In conclusion, andrographolide can be considered an anti-cancer compound that targets BCSCs due to its molecular interactions with survivin, caspase-9, and caspase-3, which induce apoptosis. We suggest that the binding of andrographolide to survivin is a critical aspect of the effect of andrographolide.

The Synthetic Small Molecule FL3 Combats Intestinal Tumorigenesis via Axin1-Mediated Inhibition of Wnt/β-Catenin Signaling

Colorectal cancer exhibits aberrant activation of Wnt/β-catenin signaling. Many inhibitors of the Wnt/β-catenin pathway have been tested for Wnt-dependent cancers including colorectal cancer, but are unsuccessful due to severe adverse reactions. FL3 is a synthetic derivative of natural products called flavaglines, which exhibit anti-inflammatory and cytoprotective properties in intestinal epithelial cells, but has not been previously tested in cell or preclinical models of intestinal tumorigenesis. In vitro studies suggest that flavaglines target prohibitin 1 (PHB1) as a ligand, but this has not been established in the intestine. PHB1 is a highly conserved protein with diverse functions that depend on its posttranslational modifications and subcellular localization. Here, we demonstrate that FL3 combats intestinal tumorigenesis in the azoxymethane-dextran sodium sulfate and Apc^Min/+ mouse models and in human colorectal cancer tumor organoids (tumoroids) by inhibiting Wnt/β-catenin signaling via induction of Axin1 expression. FL3 exhibited no change in cell viability in normal intestinal epithelial cells or human matched-normal colonoids. FL3 response was diminished in colorectal cancer cell lines and human colorectal cancer tumoroids harboring a mutation at S45 of β-catenin. PHB1 deficiency in mice or in human colorectal cancer tumoroids abolished FL3-induced expression of Axin1 and drove tumoroid death. In colorectal cancer cells, FL3 treatment blocked phosphorylation of PHB1 at Thr258, resulting in its nuclear translocation and binding to the Axin1 promoter. These results suggest that FL3 inhibits Wnt/β-catenin signaling via PHB1-dependent activation of Axin1. FL3, therefore, represents a novel compound that combats Wnt pathway-dependent cancers, such as colorectal cancer. SIGNIFICANCE: Targeting of PHB1 by FL3 provides a novel mechanism to combat Wnt-driven cancers, with limited intestinal toxicity. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/17/3519/F1.large.jpg.

Design of Development Candidate eFT226, a First in Class Inhibitor of Eukaryotic Initiation Factor 4A RNA Helicase

Dysregulation of protein translation is a key driver for the pathogenesis of many cancers. Eukaryotic initiation factor 4A (eIF4A), an ATP-dependent DEAD-box RNA helicase, is a critical component of the eIF4F complex, which regulates cap-dependent protein synthesis. The flavagline class of natural products (i.e., rocaglamide A) has been shown to inhibit protein synthesis by stabilizing a translation-incompetent complex for select messenger RNAs (mRNAs) with eIF4A. Despite showing promising anticancer phenotypes, the development of flavagline derivatives as therapeutic agents has been hampered because of poor drug-like properties as well as synthetic complexity. A focused effort was undertaken utilizing a ligand-based design strategy to identify a chemotype with optimized physicochemical properties. Also, detailed mechanistic studies were undertaken to further elucidate mRNA sequence selectivity, key regulated target genes, and the associated antitumor phenotype. This work led to the design of eFT226 (Zotatifin), a compound with excellent physicochemical properties and significant antitumor activity that supports clinical development.

Licochalcone H Synthesized by Modifying Structure of Licochalcone C Extracted from Glycyrrhiza inflata Induces Apoptosis of Esophageal Squamous Cell Carcinoma Cells

Esophageal cancer is one of the malignant cancers with a low 5-year survival rate. Licochalcone (LC) H, a chemically synthesized substance, is a regioisomer of LCC extracted from licorice. The purpose of this study was to determine whether LCH might have anticancer effect on human esophageal squamous cell carcinoma (ESCC) cell lines via apoptosis signaling pathway. After 48 h of treatment, IC₅₀ of LCH in KYSE 30, KYSE 70, KYSE 410, KYSE 450, and KYSE 510 cells were 15, 14, 18, 15, and 16 μM, respectively. This study demonstrated that LCH potently suppressed proliferation of ESCC cells in a concentration- and time-dependent manner. LCH triggered G2/M-phase arrest by modulating expression levels of cdc2, cyclin B1, p21, and p27. LCH also induced apoptosis of ESCC cells through reactive oxygen species-mediated endoplasmic reticulum (ER) stress via JNK/p38 activation pathways. The anticancer effect of LCH was associated with ER stress and mitochondrial dysfunction. It also affected protein levels of Mcl-1, tBid, Bax, Bcl-2, cytochrome c, Apaf-1, PARP, cleaved-PARP, and ER stress-related proteins (GRP78 and CHOP). Our findings provide the first demonstration that LCH has anticancer effect on ESCC. Thus, LCH might have potential for preventing and/or treating human ESCC.

PINK1/Parkin-Mediated Mitophagy Regulation by Reactive Oxygen Species Alleviates Rocaglamide A-Induced Apoptosis in Pancreatic Cancer Cells

Pancreatic cancer (PC) is one of the most lethal diseases, and effective treatment of PC patients remains an enormous challenge. Rocaglamide A (Roc-A), a bioactive molecule extracted from the plant Aglaia elliptifolia, has aroused considerable attention as a therapeutic choice for numerous cancer treatments. Nevertheless, the effects and underlying mechanism of Roc-A in PC are still poorly understood. Here, we found that Roc-A inhibited growth and stimulated apoptosis by induction of mitochondria dysfunction in PC. Moreover, Roc-A accelerated autophagosome synthesis and triggered mitophagy involving the PTEN-induced putative kinase 1 (PINK1)/Parkin signal pathway. We also demonstrated that inhibition of autophagy/mitophagy can sensitize PC cells to Roc-A. Finally, Roc-A treatment results in an obvious accumulation of reactive oxygen species (ROS), and pretreatment of cells with the reactive oxygen species scavenger N-acetylcysteine reversed the apoptosis and autophagy/mitophagy induced by Roc-A. Together, our results elucidate the potential mechanisms of action of Roc-A. Our findings indicate Roc-A as a potential therapeutic agent against PC and suggest that combination inhibition of autophagy/mitophagy may be a promising therapeutic strategy in PC.

PHB2 (prohibitin 2) promotes PINK1-PRKN/Parkin-dependent mitophagy by the PARL-PGAM5-PINK1 axis

Mitophagy, which is a conserved cellular process for selectively removing damaged or unwanted mitochondria, is critical for mitochondrial quality control and the maintenance of normal cellular physiology. However, the precise mechanisms underlying mitophagy remain largely unknown. Prior studies on mitophagy focused on the events in the mitochondrial outer membrane. PHB2 (prohibitin 2), which is a highly conserved membrane scaffold protein, was recently identified as a novel inner membrane mitophagy receptor that mediates mitophagy. Here, we report a new signaling pathway for PHB2-mediated mitophagy. Upon mitochondrial membrane depolarization or misfolded protein aggregation, PHB2 depletion destabilizes PINK1 in the mitochondria, which blocks the mitochondrial recruitment of PRKN/Parkin, ubiquitin and OPTN (optineurin), leading to an inhibition of mitophagy. In addition, PHB2 overexpression directly induces PRKN recruitment to the mitochondria. Moreover, PHB2-mediated mitophagy is dependent on the mitochondrial inner membrane protease PARL, which interacts with PHB2 and is activated upon PHB2 depletion. Furthermore, PGAM5, which is processed by PARL, participates in PHB2-mediated PINK1 stabilization. Finally, a ligand of PHB proteins that we synthesized, called FL3, was found to strongly inhibit PHB2-mediated mitophagy and to effectively block cancer cell growth and energy production at nanomolar concentrations. Thus, our findings reveal that the PHB2-PARL-PGAM5-PINK1 axis is a novel pathway of PHB2-mediated mitophagy and that targeting PHB2 with the chemical compound FL3 is a promising strategy for cancer therapy.Abbreviations: AIFM1: apoptosis inducing factor mitochondria associated 1; ATP5F1A/ATP5A1: ATP synthase F1 subunit alpha; BAF: bafilomycin A₁; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CCCP: chemical reagent carbonyl cyanide m-chlorophenyl hydrazine; FL3: flavaglines compound 3; HSPD1/HSP60: heat shock protein family D (Hsp60) member 1; LC3B/MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MEF: mouse embryo fibroblasts; MPP: mitochondrial-processing peptidase; MT-CO2/COX2: mitochondrially encoded cytochrome c oxidase II; MTS: mitochondrial targeting sequence; OA: oligomycin and antimycin A; OPTN: optineurin; OTC: ornithine carbamoyltransferase; PARL: presenilin associated rhomboid like; PBS: phosphate-buffered saline; PGAM5: PGAM family member 5, mitochondrial serine/threonine protein phosphatase; PHB: prohibitin; PHB2: prohibitin 2; PINK1: PTEN induced kinase 1; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; Roc-A: rocaglamide A; TOMM20: translocase of outer mitochondrial membrane 20; TUBB: tubulin beta class I.

TRAILblazing Strategies for Cancer Treatment

In the late 1990s, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF-family, started receiving much attention for its potential in cancer therapy, due to its capacity to induce apoptosis selectively in tumour cells in vivo. TRAIL binds to its membrane-bound death receptors TRAIL-R1 (DR4) and TRAIL-R2 (DR5) inducing the formation of a death-inducing signalling complex (DISC) thereby activating the apoptotic cascade. The ability of TRAIL to also induce apoptosis independently of p53 makes TRAIL a promising anticancer agent, especially in p53-mutated tumour entities. Thus, several so-called TRAIL receptor agonists (TRAs) were developed. Unfortunately, clinical testing of these TRAs did not reveal any significant anticancer activity, presumably due to inherent or acquired TRAIL resistance of most primary tumour cells. Since the potential power of TRAIL-based therapies still lies in TRAIL's explicit cancer cell-selectivity, a desirable approach going forward for TRAIL-based cancer therapy is the identification of substances that sensitise tumour cells for TRAIL-induced apoptosis while sparing normal cells. Numerous of such TRAIL-sensitising strategies have been identified within the last decades. However, many of these approaches have not been verified in animal models, and therefore potential toxicity of these approaches has not been taken into consideration. Here, we critically summarise and discuss the status quo of TRAIL signalling in cancer cells and strategies to force tumour cells into undergoing apoptosis triggered by TRAIL as a cancer therapeutic approach. Moreover, we provide an overview and outlook on innovative and promising future TRAIL-based therapeutic strategies.

The Translation Inhibitor Rocaglamide Targets a Bimolecular Cavity between eIF4A and Polypurine RNA

A class of translation inhibitors, exemplified by the natural product rocaglamide A (RocA), isolated from Aglaia genus plants, exhibits antitumor activity by clamping eukaryotic translation initiation factor 4A (eIF4A) onto polypurine sequences in mRNAs. This unusual inhibitory mechanism raises the question of how the drug imposes sequence selectivity onto a general translation factor. Here, we determined the crystal structure of the human eIF4A1⋅ATP analog⋅RocA⋅polypurine RNA complex. RocA targets the "bi-molecular cavity" formed characteristically by eIF4A1 and a sharply bent pair of consecutive purines in the RNA. Natural amino acid substitutions found in Aglaia eIF4As changed the cavity shape, leading to RocA resistance. This study provides an example of an RNA-sequence-selective interfacial inhibitor fitting into the space shaped cooperatively by protein and RNA with specific sequences.

Sensitization of renal carcinoma cells to TRAIL-induced apoptosis by rocaglamide and analogs

Rocaglamide has been reported to sensitize several cell types to TRAIL-induced apoptosis. In recent years, advances in synthetic techniques have led to generation of novel rocaglamide analogs. However, these have not been extensively analyzed as TRAIL sensitizers, particularly in TRAIL-resistant renal cell carcinoma cells. Evaluation of rocaglamide and analogs identified 29 compounds that are able to sensitize TRAIL-resistant ACHN cells to TRAIL-induced, caspase-dependent apoptosis with sub-µM potency which correlated with their potency as protein synthesis inhibitors and with loss of cFLIP protein in the same cells. Rocaglamide alone induced cell cycle arrest, but not apoptosis. Rocaglates averaged 4–5-fold higher potency as TRAIL sensitizers than as protein synthesis inhibitors suggesting a potential window for maximizing TRAIL sensitization while minimizing effects of general protein synthesis inhibition. A wide range of other rocaglate effects (e.g. on JNK or RAF-MEK-ERK signaling, death receptor levels, ROS, ER stress, eIF4E phosphorylation) were assessed, but did not contribute to TRAIL sensitization. Other than a rapid loss of MCL-1, rocaglates had minimal effects on mitochondrial apoptotic pathway proteins. The identification of structurally diverse/mechanistically similar TRAIL sensitizing rocaglates provides insights into both rocaglate structure and function and potential further development for use in RCC-directed combination therapy.

Rocaglamide enhances NK cell-mediated killing of non-small cell lung cancer cells by inhibiting autophagy

Targeting macroautophagy/autophagy is a novel strategy in cancer immunotherapy. In the present study, we showed that the natural product rocaglamide (RocA) enhanced natural killer (NK) cell-mediated lysis of non-small cell lung cancer (NSCLC) cells in vitro and tumor regression in vivo. Moreover, this effect was not related to the NK cell recognition of target cells or expressions of death receptors. Instead, RocA inhibited autophagy and restored the level of NK cell-derived GZMB (granzyme B) in NSCLC cells, therefore increasing their susceptibility to NK cell-mediated killing. In addition, we further identified that the target of RocA was ULK1 (unc-51 like autophagy activating kinase 1) that is required for autophagy initiation. Using firefly luciferase containing the 5´ untranslated region of ULK1, we found that RocA inhibited the protein translation of ULK1 in a sequence-specific manner. Taken together, RocA could block autophagic immune resistance to NK cell-mediated killing, and our data suggested that RocA was a promising therapeutic candidate in NK cell-based cancer immunotherapy.

Proteomic profiling of human cancer pseudopodia for the identification of anti-metastatic drug candidates

Cancer metastasis causes approximately 90% of all cancer-related death and independent of the advancement of cancer therapy, a majority of late stage patients suffers from metastatic cancer. Metastasis implies cancer cell migration and invasion throughout the body. Migration requires the formation of pseudopodia in the direction of movement, but a detailed understanding of this process and accordingly strategies of prevention remain elusive. Here, we use quantitative proteomic profiling of human cancer pseudopodia to examine this mechanisms essential to metastasis formation, and identify potential candidates for pharmacological interference with the process. We demonstrate that Prohibitins (PHBs) are significantly enriched in the pseudopodia fraction derived from cancer cells, and knockdown of PHBs, as well as their chemical inhibition through Rocaglamide (Roc-A), efficiently reduces cancer cell migration.

Discovering a Reliable Heat-Shock Factor-1 Inhibitor to Treat Human Cancers: Potential Opportunity for Phytochemists

Heat-shock factor-1 (HSF-1) is an important transcription factor that regulates pathogenesis of many human diseases through its extensive transcriptional regulation. Especially, it shows pleiotropic effects in human cancer, and hence it has recently received increased attention of cancer researchers. After myriad investigations on HSF-1, the field has advanced to the phase where there is consensus that finding a potent and selective pharmacological inhibitor for this transcription factor will be a major break-through in the treatment of various human cancers. Presently, all reported inhibitors have their limitations, made evident at different stages of clinical trials. This brief account summarizes the advances with tested natural products as HSF-1 inhibitors and highlights the necessity of phytochemistry in this endeavor of discovering a potent pharmacological HSF-1 inhibitor.

The anticancer phytochemical rocaglamide inhibits Rho GTPase activity and cancer cell migration

Chemotherapy is one of the pillars of anti-cancer therapy. Although chemotherapeutics cause regression of the primary tumor, many chemotherapeutics are often shown to induce or accelerate metastasis formation. Moreover, metastatic tumors are largely resistant against chemotherapy. As more than 90% of cancer patients die due to metastases and not due to primary tumor formation, novel drugs are needed to overcome these shortcomings. In this study, we identified the anticancer phytochemical Rocaglamide (Roc-A) to be an inhibitor of cancer cell migration, a crucial event in metastasis formation. We show that Roc-A inhibits cellular migration and invasion independently of its anti-proliferative and cytotoxic effects in different types of human cancer cells. Mechanistically, Roc-A treatment induces F-actin-based morphological changes in membrane protrusions. Further investigation of the molecular mechanisms revealed that Roc-A inhibits the activities of the small GTPases RhoA, Rac1 and Cdc42, the master regulators of cellular migration. Taken together, our results provide evidence that Roc-A may be a lead candidate for a new class of anticancer drugs that inhibit metastasis formation.

Rocaglamide breaks TRAIL-resistance in human multiple myeloma and acute T-cell leukemia in vivo in a mouse xenogtraft model

Multiple myeloma (MM) is an incurable malignancy by the presently known therapies. TRAIL is a promising anticancer agent that virtually not shows any toxicity to normal cells. We have recently carried out clinical trials with a human circularly permuted TRAIL, CPT, against MM saw a partial response in approximate 20-30% of patients. In the current study, we investigated the cause of CPT resistance and revealed that the majority of the MM patients express elevated levels of c-FLIP. Knockdown of c-FLIP expression by siRNA alone was sufficient to increase CPT-mediated apoptosis in a CPT-resistant human MM cell line U266. To overcome CPT resistance, we investigated the combination of CPT with Rocaglamides(s) in MM which has been shown to inhibit c-FLIP expression in vitro. We show that Rocaglamide(s) overcomes CPT resistance in U266 in vitro and significant increases in anti-tumor efficacies of CPT in mice xenografted with U266. Similar results were also obtained in mice xenografted with the CPT-resistant human acute T-cell leukemia cell line Molt-4. Our study suggests that the combination of Rocaglamide(s) with CPT may provide a more efficient treatment against myeloma and leukemia.

HTLV-1-associated adult T cell leukemia is highly susceptible to Navitoclax due to enhanced Bax expression

Over-expression of Bcl-2, Bcl-xL and Bcl-w is frequently associated with cancer resistance to chemotherapy. Navitoclax (ABT-263), an orally bio-available small-molecule mimetic of the Bcl-2 homology domain 3, specifically inhibits Bcl-2, Bcl-xL and Bcl-w. Despite promising results obtained from the clinical trials, the use of Navitoclax in patients is dose-limited due to induction of death of platelets via inhibition of Bcl-xL and subsequent thrombocytopenia. This side effect limits the use of Navitoclax in low doses and to very sensitive tumors. In this study, we show that HTLV-1-associated adult T-cell leukemia/lymphoma (ATL) cells, which over-express Bcl-2, Bcl-xL and Bcl-w, show a 10- to 20-fold higher sensitivity (EC50 = ∼ 25-50 nM) to Navitoclax compared to non-HTLV-1-associated leukemic cells (EC50 = ∼ 1 μM). Investigation of the molecular mechanisms revealed that the HTLV-1 oncogenic protein Tax up-regulates expression of the pro-apoptotic protein Bax which enhances the therapeutic efficacy of Navitoclax. In addition, we show that agents that inhibit the transcription elongation or translation initiation such as Wogonin and Roc-A can further decrease the effective dose of Navitoclax. Our study suggests that HTLV-1 ATL may be a good candidate disease for low dose Navitoclax therapy and probably with less risk of thrombocytopenia.

Mutated in colorectal cancer (MCC) is a novel oncogene in B lymphocytes

Background

Identification of novel genetic risk factors is imperative for a better understanding of B lymphomagenesis and for the development of novel therapeutic strategies. TRAF3, a critical regulator of B cell survival, was recently recognized as a tumor suppressor gene in B lymphocytes. The present study aimed to identify novel oncogenes involved in malignant transformation of TRAF3-deficient B cells.

Methods

We used microarray analysis to identify genes differentially expressed in TRAF3^−/− mouse splenic B lymphomas. We employed lentiviral vector-mediated knockdown or overexpression to manipulate gene expression in human multiple myeloma (MM) cell lines. We analyzed cell apoptosis and proliferation using flow cytometry, and performed biochemical studies to investigate signaling mechanisms. To delineate protein-protein interactions, we applied affinity purification followed by mass spectrometry-based sequencing.

Results

We identified mutated in colorectal cancer (MCC) as a gene strikingly up-regulated in TRAF3-deficient mouse B lymphomas and human MM cell lines. Aberrant up-regulation of MCC also occurs in a variety of primary human B cell malignancies, including non-Hodgkin lymphoma (NHL) and MM. In contrast, MCC expression was not detected in normal or premalignant TRAF3^−/− B cells even after treatment with B cell stimuli, suggesting that aberrant up-regulation of MCC is specifically associated with malignant transformation of B cells. In elucidating the functional roles of MCC in malignant B cells, we found that lentiviral shRNA vector-mediated knockdown of MCC induced apoptosis and inhibited proliferation in human MM cells. Experiments of knockdown and overexpression of MCC allowed us to identify several downstream targets of MCC in human MM cells, including phospho-ERK, c-Myc, p27, cyclin B1, Mcl-1, caspases 8 and 3. Furthermore, we identified 365 proteins (including 326 novel MCC-interactors) in the MCC interactome, among which PARP1 and PHB2 were two hubs of MCC signaling pathways in human MM cells.

Conclusions

Our results indicate that in sharp contrast to its tumor suppressive role in colorectal cancer, MCC functions as an oncogene in B cells. Our findings suggest that MCC may serve as a diagnostic marker and therapeutic target in B cell malignancies, including NHL and MM.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-014-0056-6) contains supplementary material, which is available to authorized users.