Discrepant NOXA (PMAIP1) transcript and NOXA protein levels: a potential Achilles' heel in mantle cell lymphoma

Metabolic Reprogramming and Potential Therapeutic Targets in Lymphoma

Lymphoma is a heterogeneous group of diseases that often require their metabolism program to fulfill the demand of cell proliferation. Features of metabolism in lymphoma cells include high glucose uptake, deregulated expression of enzymes related to glycolysis, dual capacity for glycolytic and oxidative metabolism, elevated glutamine metabolism, and fatty acid synthesis. These aberrant metabolic changes lead to tumorigenesis, disease progression, and resistance to lymphoma chemotherapy. This metabolic reprogramming, including glucose, nucleic acid, fatty acid, and amino acid metabolism, is a dynamic process caused not only by genetic and epigenetic changes, but also by changes in the microenvironment affected by viral infections. Notably, some critical metabolic enzymes and metabolites may play vital roles in lymphomagenesis and progression. Recent studies have uncovered that metabolic pathways might have clinical impacts on the diagnosis, characterization, and treatment of lymphoma subtypes. However, determining the clinical relevance of biomarkers and therapeutic targets related to lymphoma metabolism is still challenging. In this review, we systematically summarize current studies on metabolism reprogramming in lymphoma, and we mainly focus on disorders of glucose, amino acids, and lipid metabolisms, as well as dysregulation of molecules in metabolic pathways, oncometabolites, and potential metabolic biomarkers. We then discuss strategies directly or indirectly for those potential therapeutic targets. Finally, we prospect the future directions of lymphoma treatment on metabolic reprogramming.

SMG1, a nonsense-mediated mRNA decay (NMD) regulator, as a candidate therapeutic target in multiple myeloma

Early data suggested that CC-115, a clinical molecule, already known to inhibit the mammalian target of rapamycin kinase (TORK) and DNA-dependent protein kinase (DNA-PK) may have additional targets beyond TORK and DNA-PK. Therefore, we aimed to identify such target(s) and investigate a potential therapeutic applicability. Functional profiling of 141 cancer cell lines revealed inhibition of kinase suppressor of morphogenesis in genitalia 1 (SMG1), a key regulator of the RNA degradation mechanism nonsense-mediated mRNA decay (NMD), as an additional target of CC-115. CC-115 treatment showed a dose-dependent increase of SMG1-mediated NMD transcripts. A subset of cell lines, including multiple myeloma (MM) cell lines sensitive to the endoplasmic reticulum stress-inducing compound thapsigargin, were highly susceptible to SMG1 inhibition. CC-115 caused the induction of UPR transcripts and cell death by mitochondrial apoptosis, requiring the presence of BAX/BAK and caspase activity. Superior antitumor activity of CC-115 over TORK inhibitors in primary human MM cells and three xenograft mouse models appeared to be via inhibition of SMG1. Our data support further development of SMG1 inhibitors as possible therapeutics in MM.

Pituitary adenomas evade apoptosis via noxa deregulation in Cushing's disease

Sporadic pituitary adenomas occur in over 10% of the population. Hormone-secreting adenomas, including those causing Cushing’s disease (CD), cause severe morbidity and early mortality. Mechanistic studies of CD are hindered by a lack of in vitro models and control normal human pituitary glands. Here, we surgically annotate adenomas and adjacent normal glands in 25 of 34 patients. Using single-cell RNA sequencing (RNA-seq) analysis of 27594 cells, we identify CD adenoma transcriptomic signatures compared with adjacent normal cells, with validation by bulk RNA-seq, DNA methylation, qRT-PCR, and immunohistochemistry. CD adenoma cells include a subpopulation of proliferating, terminally differentiated corticotrophs. In CD adenomas, we find recurrent promoter hypomethylation and transcriptional upregulation of PMAIP1 (encoding pro-apoptotic BH3-only bcl-2 protein noxa) but paradoxical noxa downregulation. Using primary CD adenoma cell cultures and a corticotroph-enriched mouse cell line, we find that selective proteasomal inhibition with bortezomib stabilizes noxa and induces apoptosis, indicating its utility as an anti-tumor agent.

Asuzu et al. perform single-cell transcriptomic profiling in Cushing’s disease (CD) adenomas and find overexpression and DNA hypomethylation of PMAIP1, which encodes the pro-apoptotic protein noxa. Noxa is degraded by the proteasome. Proteasomal inhibition rescues noxa and induces apoptosis in CD.

The whole blood transcriptional regulation landscape in 465 COVID-19 infected samples from Japan COVID-19 Task Force

Coronavirus disease 2019 (COVID-19) is a recently-emerged infectious disease that has caused millions of deaths, where comprehensive understanding of disease mechanisms is still unestablished. In particular, studies of gene expression dynamics and regulation landscape in COVID-19 infected individuals are limited. Here, we report on a thorough analysis of whole blood RNA-seq data from 465 genotyped samples from the Japan COVID-19 Task Force, including 359 severe and 106 non-severe COVID-19 cases. We discover 1169 putative causal expression quantitative trait loci (eQTLs) including 34 possible colocalizations with biobank fine-mapping results of hematopoietic traits in a Japanese population, 1549 putative causal splice QTLs (sQTLs; e.g. two independent sQTLs at TOR1AIP1), as well as biologically interpretable trans-eQTL examples (e.g., REST and STING1), all fine-mapped at single variant resolution. We perform differential gene expression analysis to elucidate 198 genes with increased expression in severe COVID-19 cases and enriched for innate immune-related functions. Finally, we evaluate the limited but non-zero effect of COVID-19 phenotype on eQTL discovery, and highlight the presence of COVID-19 severity-interaction eQTLs (ieQTLs; e.g., CLEC4C and MYBL2). Our study provides a comprehensive catalog of whole blood regulatory variants in Japanese, as well as a reference for transcriptional landscapes in response to COVID-19 infection.

Data-Driven Mathematical Model of Apoptosis Regulation in Memory Plasma Cells

Memory plasma cells constitutively produce copious amounts of antibodies, imposing a critical risk factor for autoimmune disease. We previously found that plasma cell survival requires secreted factors such as APRIL and direct contact to stromal cells, which act in concert to activate NF-κB- and PI3K-dependent signaling pathways to prevent cell death. However, the regulatory properties of the underlying biochemical network are confounded by the complexity of potential interaction and cross-regulation pathways. Here, based on flow-cytometric quantification of key signaling proteins in the presence or absence of the survival signals APRIL and contact to the stromal cell line ST2, we generated a quantitative model of plasma cell survival. Our model emphasizes the non-redundant nature of the two plasma cell survival signals APRIL and stromal cell contact, and highlights a requirement for differential regulation of individual caspases. The modeling approach allowed us to unify distinct data sets and derive a consistent picture of the intertwined signaling and apoptosis pathways regulating plasma cell survival.

Of the many cellular responses activated by TP53, which ones are critical for tumour suppression?

The tumour suppressor TP53 is a master regulator of several cellular processes that collectively suppress tumorigenesis. The TP53 gene is mutated in ~50% of human cancers and these defects usually confer poor responses to therapy. The TP53 protein functions as a homo-tetrameric transcription factor, directly regulating the expression of ~500 target genes, some of them involved in cell death, cell cycling, cell senescence, DNA repair and metabolism. Originally, it was thought that the induction of apoptotic cell death was the principal mechanism by which TP53 prevents the development of tumours. However, gene targeted mice lacking the critical effectors of TP53-induced apoptosis (PUMA and NOXA) do not spontaneously develop tumours. Indeed, even mice lacking the critical mediators for TP53-induced apoptosis, G1/S cell cycle arrest and cell senescence, namely PUMA, NOXA and p21, do not spontaneously develop tumours. This suggests that TP53 must activate additional cellular responses to mediate tumour suppression. In this review, we will discuss the processes by which TP53 regulates cell death, cell cycling/cell senescence, DNA damage repair and metabolic adaptation, and place this in context of current understanding of TP53-mediated tumour suppression.

NOXA expression drives synthetic lethality to RUNX1 inhibition in pancreatic cancer

Recent evidence demonstrated the existence of molecular subtypes in pancreatic ductal adenocarcinoma (PDAC), which resist all current therapies. The paucity of therapeutic options, including a complete lack of targeted therapies, underscores the urgent and unmet medical need for the identification of targets and novel treatment strategies for PDAC. Our study unravels a function of the transcription factor RUNX1 in apoptosis regulation in PDAC. We show that pharmacological RUNX1 inhibition in PDAC is feasible and leads to NOXA-dependent apoptosis. The development of targeted therapies that influence the transcriptional landscape of PDAC might have great benefits for patients who are resistant to conventional therapies. RUNX1 inhibition as a new therapeutic intervention offers an attractive strategy for future therapies.

Evasion from drug-induced apoptosis is a crucial mechanism of cancer treatment resistance. The proapoptotic protein NOXA marks an aggressive pancreatic ductal adenocarcinoma (PDAC) subtype. To identify drugs that unleash the death-inducing potential of NOXA, we performed an unbiased drug screening experiment. In NOXA-deficient isogenic cellular models, we identified an inhibitor of the transcription factor heterodimer CBFβ/RUNX1. By genetic gain and loss of function experiments, we validated that the mode of action depends on RUNX1 and NOXA. Of note is that RUNX1 expression is significantly higher in PDACs compared to normal pancreas. We show that pharmacological RUNX1 inhibition significantly blocks tumor growth in vivo and in primary patient-derived PDAC organoids. Through genome-wide analysis, we detected that RUNX1-loss reshapes the epigenetic landscape, which gains H3K27ac enrichment at the NOXA promoter. Our study demonstrates a previously unknown mechanism of NOXA-dependent cell death, which can be triggered pharmaceutically. Therefore, our data show a way to target a therapy-resistant PDAC, an unmet clinical need.

Chronic lymphocytic leukemia (CLL) risk is mediated by multiple enhancer variants within CLL risk loci

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in Western countries. It has a strong genetic basis, showing a ~ 8-fold increased risk of CLL in first-degree relatives. Genome-wide association studies (GWAS) have identified 41 risk variants across 41 loci. However, for a majority of the loci, the functional variants and the mechanisms underlying their causal roles remain undefined. Here, we examined the genetic and epigenetic features associated with 12 index variants, along with any correlated (r2 ≥ 0.5) variants, at the CLL risk loci located outside of gene promoters. Based on publicly available ChIP-seq and chromatin accessibility data as well as our own ChIP-seq data from CLL patients, we identified six candidate functional variants at six loci and at least two candidate functional variants at each of the remaining six loci. The functional variants are predominantly located within enhancers or super-enhancers, including bi-directionally transcribed enhancers, which are often restricted to immune cell types. Furthermore, we found that, at 78% of the functional variants, the alternative alleles altered the transcription factor binding motifs or histone modifications, indicating the involvement of these variants in the change of local chromatin state. Finally, the enhancers carrying functional variants physically interacted with genes enriched in the type I interferon signaling pathway, apoptosis, or TP53 network that are known to play key roles in CLL. These results support the regulatory roles for inherited noncoding variants in the pathogenesis of CLL.

Autophagic degradation of NOXA underlies stromal cell-mediated resistance to proteasome inhibitors in mantle cell lymphoma

Mantle cell lymphoma (MCL) is usually resistant to the current standard-of-care regimens and also to novel agents such as the proteasome inhibitor bortezomib. A better prognosis of leukemic variants of MCL suggests that MCL cells acquire drug resistance in nodal and/or bone marrow microenvironments via interaction with supporting cells. Bortezomib exerts cytotoxic action in MCL cells via stabilization of the pro-apoptotic BCL-2 family protein NOXA. Here we show that autophagic degradation of NOXA is a mechanism of bortezomib resistance in MCL cells in a tumor microenvironment. First, we demonstrated that interaction with bone marrow-derived or nodal stromal cells conferred bortezomib resistance to MCL cells in vitro and in a murine model. Co-culture of MCL cells with stromal cells enhanced bortezomib-induced ubiquitination and subsequent binding of NOXA to the p62 adaptor, which escorted NOXA to the lysosome for autophagic degradation. Finally, we found that not only direct contact with stromal cells but also stroma-derived humoral factors, especially interleukin-6, promoted selective autophagy and NOXA degradation in MCL cells. Targeting protective autophagy, for example, using the lysosome inhibitor chloroquine, might increase the efficacy of bortezomib-containing regimens in MCL.

Pharmacologic Targeting of Mcl-1 Induces Mitochondrial Dysfunction and Apoptosis in B-Cell Lymphoma Cells in a TP53- and BAX-Dependent Manner

PURPOSE

Bcl-2 has been effectively targeted in lymphoid malignancies. However, resistance is inevitable, and novel approaches to target mitochondrial apoptosis are necessary. AZD5991, a selective BH3-mimetic in clinical trials, inhibits Mcl-1 with high potency.

EXPERIMENTAL DESIGN

We explored the preclinical activity of AZD5991 in diffuse large B-cell lymphoma (DLBCL) and ibrutinib-resistant mantle cell lymphoma (MCL) cell lines, MCL patient samples, and mice bearing DLBCL and MCL xenografts using flow cytometry, immunoblotting, and Seahorse respirometry assay. Cas9 gene editing and ex vivo functional drug screen assays helped identify mechanisms of resistance to Mcl-1 inhibition.

RESULTS

Mcl-1 was expressed in DLBCL and MCL cell lines and primary tumors. Treatment with AZD5991 restricted growth of DLBCL cells independent of cell of origin and overcame ibrutinib resistance in MCL cells. Mcl-1 inhibition led to mitochondrial dysfunction as manifested by mitochondrial membrane depolarization, decreased mitochondrial mass, and induction of mitophagy. This was accompanied by impairment of oxidative phosphorylation. TP53 and BAX were essential for sensitivity to Mcl-1, and oxidative phosphorylation was implicated in resistance to Mcl-1 inhibition. Induction of prosurvival proteins (e.g., Bcl-xL) in stromal conditions that mimic the tumor microenvironment rendered protection of primary MCL cells from Mcl-1 inhibition, while BH3-mimetics targeting Bcl-2/xL sensitized lymphoid cells to AZD5991. Treatment with AZD5991 reduced tumor growth in murine lymphoma models and prolonged survival of MCL PDX mice.

CONCLUSIONS

Selective targeting Mcl-1 is a promising therapeutic approach in lymphoid malignancies. TP53 apoptotic network and metabolic reprogramming underlie susceptibility to Mcl-1 inhibition.

Advances in Cancer Treatment by Targeting the Neddylation Pathway

Developmental down-regulation protein 8 (NEDD8), expressed by neural progenitors, is a ubiquitin-like protein that conjugates to and regulates the biological function of its substrates. The main target of NEDD8 is cullin-RING E3 ligases. Upregulation of the neddylation pathway is closely associated with the progression of various tumors, and MLN4924, which inhibits NEDD8-activating enzyme (NAE), is a promising new antitumor compound for combination therapy. Here, we summarize the latest progress in anticancer strategies targeting the neddylation pathway and their combined applications, providing a theoretical reference for developing antitumor drugs and combination therapies.

Targeting H3K9 methyltransferase G9a and its related molecule GLP as a potential therapeutic strategy for cancer

H3K9 methyltransferase (G9a) and its relevant molecule GLP are the SET domain proteins that specifically add mono, di and trimethyl groups on to the histone H3K9, which lead to the transcriptional inactivation of chromatin and reduce the expression of cancer suppressor genes, which trigger growth and progress of several cancer types. Various studies have demonstrated that overexpression of H3K9 methyltransferase G9a and GLP in different kinds of tumors, like lung, breast, bladder, colon, cervical, gastric, skin cancers, hepatocellular carcinoma and hematological malignancies. Several G9a and GLP inhibitors such as BIX-01294, UNC0642, A-366 and DCG066 were developed to combat various cancers; however, there is a need for more effective and less toxic compounds. The current molecular docking study suggested that the selected new compounds such as ninhydrin, naphthoquinone, cysteamine and disulfide cysteamine could be suitable molecules as a G9a and GLP inhibitors. Furthermore, detailed cell based and preclinical animal studies are required to confirm their properties. In the current review, we discussed the role of G9a and GLP mediated epigenetic regulation in the cancers. A thorough literature review was done related to G9a and GLP. The databases used extensively for retrieval of information were PubMed, Medline, Scopus and Science-direct. Further, molecular docking was performed using Maestro Schrodinger version 9.2 software to investigate the binding profile of compounds with Human G9a HMT (PDB ID: 3FPD, 3RJW) and Human GLP MT (PDB ID: 6MBO, 6MBP).

Homeostasis: apoptosis and cell cycle in normal and pathological prostate

Prostatic diseases such as hyperplasia and cancer are a consequence of glandular aging due to the loss of homeostasis. Glandular homeostasis is guaranteed by the delicate balance between production and cell death. Both cell renewal and apoptosis are part of this delicate balance. We will explore the predictive capacity for biochemical progression, following prostatectomy, of some members of the Bcl-2 family and of proteins involved in cell cycle inhibition in conjunction with established classical markers. The expression of Bcl-2, Bcl-xL, Mcl-1, Bax, Bim, Bad, PUMA, Noxa, p21, p27, Rb and p53 were analyzed by immunochemistry in 86 samples of radical prostatectomy and correlated with each of the markers established clinicopathological tests using statistical tests such as Sperman, Kaplan-Meier curves, unifactorial Cox, and multifactorial. The most relevant results are: (1) Positive correlation between: p27 with clinical T stage; and PUMA with pathological T stage; (2) Negative correlation between: Bcl-2 with clinical T stage, Bcl-xL with survival, Noxa and pRb with Gleason score.Our results suggest that the expression of Bcl-2, Bcl-xL, PUMA, Noxa, p27, and Rb were related to some of the classic markers established to predict biochemical progression after prostatectomy.

E1 Enzymes as Therapeutic Targets in Cancer

Post-translational modifications of cellular substrates with ubiquitin and ubiquitin-like proteins (UBLs), including ubiquitin, SUMOs, and neural precursor cell-expressed developmentally downregulated protein 8, play a central role in regulating many aspects of cell biology. The UBL conjugation cascade is initiated by a family of ATP-dependent enzymes termed E1 activating enzymes and executed by the downstream E2-conjugating enzymes and E3 ligases. Despite their druggability and their key position at the apex of the cascade, pharmacologic modulation of E1s with potent and selective drugs has remained elusive until 2009. Among the eight E1 enzymes identified so far, those initiating ubiquitylation (UBA1), SUMOylation (SAE), and neddylation (NAE) are the most characterized and are implicated in various aspects of cancer biology. To date, over 40 inhibitors have been reported to target UBA1, SAE, and NAE, including the NAE inhibitor pevonedistat, evaluated in more than 30 clinical trials. In this Review, we discuss E1 enzymes, the rationale for their therapeutic targeting in cancer, and their different inhibitors, with emphasis on the pharmacologic properties of adenosine sulfamates and their unique mechanism of action, termed substrate-assisted inhibition. Moreover, we highlight other less-characterized E1s-UBA6, UBA7, UBA4, UBA5, and autophagy-related protein 7-and the opportunities for targeting these enzymes in cancer. SIGNIFICANCE STATEMENT: The clinical successes of proteasome inhibitors in cancer therapy and the emerging resistance to these agents have prompted the exploration of other signaling nodes in the ubiquitin-proteasome system including E1 enzymes. Therefore, it is crucial to understand the biology of different E1 enzymes, their roles in cancer, and how to translate this knowledge into novel therapeutic strategies with potential implications in cancer treatment.

CHIP ubiquitylates NOXA and induces its lysosomal degradation in response to DNA damage

The BH3-only protein NOXA is a regulator of mitochondrial apoptosis by specifically antagonizing the anti-apoptotic protein MCL-1. Here we show that the E3 ubiquitin ligase CHIP controls NOXA stability after DNA damage. Our findings reveal that CHIP and MCL-1 are binding partners of NOXA and differentially define the fate of NOXA. Whereas NOXA is initially targeted to mitochondria upon MCL-1-binding, CHIP mediates ubiquitylation of cytosolic NOXA and promotes lysosomal degradation of NOXA, which is not bound by MCL-1. Our data indicate that MCL-1 defines NOXA abundance and its pro-apoptotic activity. Increased NOXA levels beyond this threshold are effectively removed by lysosomal protein degradation triggered via CHIP-mediated ubiquitylation. Together, these results shed new light on regulatory circuits controlling DNA damage response and identified the E3 ligase CHIP as a new molecular guardian, which restricts the cytosolic accumulation of NOXA upon genotoxic stress.

Function and regulation of lipid signaling in lymphomagenesis: A novel target in cancer research and therapy

To survive under the challenging conditions, cancer cells adapt their own metabolic mechanism(s) to be able steady supplying energy and metabolites for synthesis of new biomass. Aberrant lipid metabolism in cancer cells becomes a hall marker of carcinogenesis. Epidemiologic evidence indicates that fat intake, in particular saturated or animal fat, may increase the risk of lymphoma. Understanding the specific alterations of lymphoma metabolism becomes essential to address malignant transformation, progression, and therapeutic approaches. This review is focused on the lipid metabolism, with emphasis on fatty acid synthase, lipid rafts, exosomes, and metabolic diseases, in distinct lymphoma entities.

Dysregulated metabolic pathways in age-related macular degeneration

Age-related macular degeneration is a major cause of vision impairment in the Western world among people of 55 years and older. Recently we have shown that autophagy is dysfunctional in the retinal pigment epithelium (RPE) of the AMD donor eyes (AMD RPE). We also showed increased reactive oxygen (ROS) production, increased cytoplasmic glycogen accumulation, mitochondrial dysfunction and disintegration, and enlarged and annular LAMP-1-positive organelles in AMD RPE. However, the underlying mechanisms inducing these abnormalities remain to be elucidated. Here, by performing a comprehensive study, we show increased PAPR2 expression, deceased NAD+, and SIRT1, increased PGC-1α acetylation (inactive form), lower AMPK activity, and overactive mTOR pathway in AMD RPE as compared to normal RPE. Metabolomics and lipidomics revealed dysregulated metabolites in AMD RPE as compared to normal RPE, including glycerophospholipid metabolism, involved in autophagy, lipid, and protein metabolisms, glutathione, guanosine, and L-glutamic acid, which are implicated in protection against oxidative stress and neurotoxicity, further supporting our observations. Our data show dysregulated metabolic pathways as important contributors to AMD pathophysiology, and facilitate the development of new treatment strategies for this debilitating disease of the visual system.

Targeting Protein Neddylation for Cancer Therapy

Neddylation is a posttranslational modification that conjugates a ubiquitin-like protein NEDD8 to substrate proteins. The best-characterized substrates of neddylation are the cullin subunits of cullin-RING E3 ubiquitin ligase complexes (CRLs). CRLs as the largest family of E3 ubiquitin ligases control many important biological processes, including tumorigenesis, through promoting ubiquitylation and subsequent degradation of a variety of key regulatory proteins. The process of protein neddylation is overactivated in multiple types of human cancers, providing a sound rationale as an attractive anticancer therapeutic strategy, evidenced by the development of the NEDD8-activating enzyme (NAE) inhibitor MLN4924 (also known as pevonedistat). Recently, increasing evidence strongly indicates that neddylation inhibition by MLN4924 exerts anticancer effects mainly by triggering cell apoptosis, senescence, and autophagy and causing angiogenesis suppression, inflammatory responses, and chemo-/radiosensitization in a context-dependent manner. Here, we briefly summarize the latest progresses in this field, focusing on the preclinical studies to validate neddylation modification as a promising anticancer target.

Potent efficacy of MCL-1 inhibitor-based therapies in preclinical models of mantle cell lymphoma

Apoptosis-regulating BCL-2 family members, which can promote malignant transformation and resistance to therapy, have become prime therapeutic targets, as illustrated by the striking efficacy in certain lymphoid malignancies of the BCL-2-specific inhibitor venetoclax. In other lymphoid malignancies, however, such as the aggressive mantle cell lymphoma (MCL), cell survival might rely instead or also on BCL-2 relative MCL-1. We have explored MCL-1 as a target for killing MCL cells by both genetic and pharmacologic approaches. In several MCL cell lines, MCL-1 knockout with an inducible CRISPR/Cas9 system triggered spontaneous apoptosis. Accordingly, most MCL cell lines proved sensitive to the specific MCL-1 inhibitor S63845, and MCL-1 inhibition also proved efficacious in an MCL xenograft model. Furthermore, its killing efficacy rose on combination with venetoclax, the BCL-X_L-specific inhibitor A-1331852, or Bruton's tyrosine kinase (BTK) inhibitor ibrutinib, which reduced pro-survival signals. We also tested the MCL-1 inhibitor in primary samples from 13 MCL patients, using CD40L-expressing feeder cells to model their microenvironmental support. Notably, all unstimulated primary MCL samples were very sensitive to S63845, but the CD40L stimulation attenuated their sensitivity. Mass cytometric analysis revealed that the stimulation likely conveyed protection by elevating BCL-X_L and MCL-1. Accordingly, sensitivity of the CD40L-stimulated cells to S63845 was substantially restored by co-treatment with venetoclax, the BCL-X_L-specific inhibitor or ibrutinib. Overall, our findings indicate that MCL-1 is very important for survival of MCL cells and that the MCL-1 inhibitor, both alone and together with ibrutinib, venetoclax or a BCL-X_L inhibitor, offers promise for novel improved MCL therapies.

Silencing lncRNA LOC101928963 Inhibits Proliferation and Promotes Apoptosis in Spinal Cord Glioma Cells by Binding to PMAIP1

Long non-coding RNAs (lncRNAs) have been widely highlighted due to their involvement in various types of cancers, including glioma; however, the exact mechanism and function by which they operate in regard to spinal cord glioma remain poorly understood. LOC101928963 was screened out for its differential expression in spinal cord glioma by microarray analysis. Therefore, this study was conducted to investigate the modulatory effects of LOC101928963 on spinal cord glioma by binding to phorbol-12-myristate-13-acetate-induced protein 1 (PMAIP1). The expression of LOC101928963 and LOC101928963 was characterized in spinal cord glioma tissues, and their interaction was examined by dual-luciferase reporter gene assay. Cells with LOC101928963 that exhibited elevated or suppressed levels of PMAIP1 were established to substantiate the mechanism between LOC101928963 and PMAIP1. qRT-PCR and western blot methods were subsequently applied to determine the expression of cell-proliferation- and apoptosis-related genes in response to the alterations of LOC101928963 and PMAIP1. Glioma cell proliferation and apoptosis were assessed by MTT assay and flow cytometry. Decreased cell apoptosis and PMAIP1 expression, as well as overexpressed LOC101928963, were exhibited among spinal cord glioma tissues. LOC101928963 overexpression was observed to promote cell proliferation and cell-cycle entry and inhibit the process of apoptosis. PMAIP1, a target of LOC101928963, displayed a downregulated level following the elevation of LOC101928963. The present results strongly emphasize the neutralization effect of PMAIP1 overexpression on spinal cord glioma progression induced by the overexpression of LOC101928963. The data obtained during the study highlighted the inhibitory role of LOC101928963 silencing in spinal cord glioma through the increase in PMAIP1, which suggests a potential target in the treatment of spinal cord glioma.

SIRT7 regulates hepatocellular carcinoma response to therapy by altering the p53-dependent cell death pathway

Background

Optimal therapeutic strategies for hepatocellular carcinoma (HCC) patients are still challenging due to the high recurrence rate after surgical resection and chemotherapy resistance. Growing evidence shows that genetic and epigenetic alterations are involved in HCC progression and resistance to therapy, however the molecular mechanisms underlying resistance to therapy have not been fully understood.

Methods

Expression of SIRT7 in 17 paired paraffin-embedded HCC tissues and adjacent nontumoral liver tissues was examined by immunohistochemistry and Western blot. The mRNA expression of SIRT7 in 20 paired frozen HCC tissues and adjacent nontumoral liver tissues was analyzed by quantitative RT-PCR. The biologic consequences of overexpression and knockdown of SIRT7 in HCC therapy sensitivity were studied in vitro and in vivo. Interaction between SIRT7 and p53 were studied in HCC cell lines.

Results

SIRT7 expression was frequently upregulated in clinical HCC samples, and its expression was highly associated with TACE-resistance and poor survival (P = 0.008.) Depletion of SIRT7 from multiple liver cancer cell lines significantly increased doxorubicin toxicity while overexpression of SIRT7 largely abolished doxorubicin induced apoptosis. At the molecular level, we observed that SIRT7 interacts with and induces deacetylation of p53 at lysines 320 and 373. Deacetylated p53 showed significantly less affinity for the NOXA promoter and its transcription. In mouse xenografts, SIRT7 suppression increased doxorubicin induced p53 activation, inhibited tumor growth and induced apoptosis.

Conclusion

The newly identified SIRT7-p53-NOXA axis partially illustrates the molecular mechanism of HCC resistance to therapy and represents a novel potential therapeutic target for HCC treatment.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1246-4) contains supplementary material, which is available to authorized users.

Cyclin D1-CDK4 activity drives sensitivity to bortezomib in mantle cell lymphoma by blocking autophagy-mediated proteolysis of NOXA

BACKGROUND

Mantle cell lymphoma (MCL) is an aggressive B-non-Hodgkin lymphoma with generally poor outcome. MCL is characterized by an aberrantly high cyclin D1-driven CDK4 activity. New molecular targeted therapies such as inhibitors of the ubiquitin-proteasome system (UPS) have shown promising results in preclinical studies and MCL patients. Our previous research revealed stabilization of the short-lived pro-apoptotic NOXA as a critical determinant for sensitivity to these inhibitors. It is currently unclear how cyclin D1 overexpression and aberrant CDK4 activity affect NOXA stabilization and treatment efficacy of UPS inhibitors in MCL.

METHODS

The effect of cyclin D1-driven CDK4 activity on response of MCL cell lines and primary cells to proteasome inhibitor treatment was investigated using survival assays (Flow cytometry, AnnexinV/PI) and Western blot analysis of NOXA protein. Half-life of NOXA protein was determined by cycloheximide treatment and subsequent Western blot analysis. The role of autophagy was analyzed by LC3-II protein expression and autophagolysosome detection. Furthermore, silencing of autophagy-related genes was performed using siRNA and MCL cells were treated with autophagy inhibitors in combination with proteasome and CDK4 inhibition.

RESULTS

In this study, we show that proteasome inhibitor-mediated cell death in MCL depends on cyclin D1-driven CDK4 activity. Inhibition of cyclin D1/CDK4 activity significantly reduced proteasome inhibitor-mediated stabilization of NOXA protein, mainly driven by an autophagy-mediated proteolysis. Bortezomib-induced cell death was significantly potentiated by compounds that interfere with autophagosomal function. Combined treatment with bortezomib and autophagy inhibitors enhanced NOXA stability leading to super-induction of NOXA protein. In addition to established autophagy modulators, we identified the fatty acid synthase inhibitor orlistat to be an efficient autophagy inhibitor when used in combination with bortezomib. Accordingly, this combination synergistically induced apoptosis both in MCL cell lines and in patient samples.

CONCLUSION

Our data demonstrate that CDK4 activity in MCL is critical for NOXA stabilization upon treatment with UPS inhibitors allowing preferential induction of cell death in cyclin D transformed cells. Under UPS blocked conditions, autophagy appears as the critical regulator of NOXA induction. Therefore, inhibitors of autophagy are promising candidates to increase the activity of proteasome inhibitors in MCL.

Phenotypic miRNA Screen Identifies miR-26b to Promote the Growth and Survival of Endothelial Cells

Endothelial cell (EC) proliferation is a crucial event in physiological and pathological angiogenesis. MicroRNAs (miRNAs) have emerged as important modulators of the angiogenic switch. Here we conducted high-content screening of a human miRNA mimic library to identify novel regulators of EC growth systematically. Several miRNAs were nominated that enhanced or inhibited EC growth. Of these, we focused on miR-26b, which is a conserved candidate and expressed in multiple human EC types. miR-26b overexpression enhanced EC proliferation, migration, and tube formation, while inhibition of miR-26b suppressed the proliferative and angiogenic capacity of ECs. A combinatory functional small interfering RNA (siRNA) screening of 48 predicted gene targets revealed that miR-26b enhanced EC growth and survival through inhibiting PTEN expression. Local administration of miR-26b mimics promoted the growth of new microvessels in the Matrigel plug model. In the mouse model of hindlimb ischemia, miR-26b was found to be downregulated in endothelium in the first week following ischemia, and local overexpression of miR-26b improved the survival of capillaries and muscle fibers in ischemic muscles. Our findings suggest that miR-26b enhances EC proliferation, survival, and angiogenesis. miR-26b is a potential target for developing novel pro-angiogenic therapeutics in ischemic disease.

Targeting the overexpressed ROC1 induces G2 cell cycle arrest and apoptosis in esophageal cancer cells

Recent reports showed that regulator of Cullins-1 (ROC1) play an important role in tumor progression in a tumor-specific manner. However, the role and mechanism of ROC1 in esophageal cancer remains elusive. Here we demonstrated that ROC1 was overexpressed in esophageal squamous cell carcinomas, which was positive associated with poor prognosis of esophageal cancer patients. ROC1 knockdown significantly inhibited the growth of esophageal cancer cells in vitro and in vivo. Mechanistically, ROC1 silencing induced G2 cell cycle arrest and triggered apoptosis by accumulating the pro-apoptotic protein NOXA. Consistently, the downregulation of NOXA expression via siRNA substantially attenuated apoptosis induced by ROC1 silencing. These findings suggest that ROC1 is an appealing drug target for esophageal cancer.

MLN4924 suppresses neddylation and induces cell cycle arrest, senescence, and apoptosis in human osteosarcoma

Neddylation is a post-translational protein modification process associated with carcinogenesis and cancer development. MLN4924, a pharmaceutical neddylation inhibitor, induces potent anti-cancer effects in multiple types of cancers. In this study, we investigated the effects of MLN4924 on human osteosarcoma (OS). Levels of both NEDD8 activating enzyme E1 (NAE1) and ubiquitin-conjugating enzyme E2M (Ube2M), two critical components of the neddylation pathway, were much higher in OS tissues and cells than in normal osseous tissues and cells. MLN4924 treatment led to DNA damage, reduced cell viability, senescence and apoptosis in OS cells. Moreover, MLN4924 inhibited OS xenograft tumor growth in mice. Mechanistically, MLN4924 blocked the neddylation of cullins and induced accumulation of several tumor-suppressive substrates of Cullin-RING E3 ubiquitin ligases (CRLs), including CDT1, Wee1, p21, p27, Noxa, and p16. These results suggest clinical studies investigating the utility of MLN4924 for the treatment of OS are warranted.

Mantle cell lymphoma in the era of precision medicine-diagnosis, biomarkers and therapeutic agents

Despite advances in the development of clinical agents for treating Mantle Cell Lymphoma (MCL), treatment of MCL remains a challenge due to complexity and frequent relapse associated with MCL. The incorporation of conventional and novel diagnostic approaches such as genomic sequencing have helped improve understanding of the pathogenesis of MCL, and have led to development of specific agents targeting signaling pathways that have recently been shown to be involved in MCL. In this review, we first provide a general overview of MCL and then discuss about the role of biomarkers in the pathogenesis, diagnosis, prognosis, and treatment for MCL. We attempt to discuss major biomarkers for MCL and highlight published and ongoing clinical trials in an effort to evaluate the dominant signaling pathways as drugable targets for treating MCL so as to determine the potential combination of drugs for both untreated and relapse/refractory cases. Our analysis indicates that incorporation of biomarkers is crucial for patient stratification and improve diagnosis and predictability of disease outcome thus help us in designing future precision therapies. The evidence indicates that a combination of conventional chemotherapeutic agents and novel drugs designed to target specific dysregulated signaling pathways can provide the effective therapeutic options for both untreated and relapse/refractory MCL.

Protein neddylation and its alterations in human cancers for targeted therapy

Neddylation, a post-translational modification that conjugates an ubiquitin-like protein NEDD8 to substrate proteins, is an important biochemical process that regulates protein function. The best-characterized substrates of neddylation are the cullin subunits of Cullin-RING ligases (CRLs), which, as the largest family of E3 ubiquitin ligases, control many important biological processes, including tumorigenesis, through promoting ubiquitylation and subsequent degradation of a variety of key regulatory proteins. Recently, increasing pieces of experimental evidence strongly indicate that the process of protein neddylation modification is elevated in multiple human cancers, providing sound rationale for its targeting as an attractive anticancer therapeutic strategy. Indeed, neddylation inactivation by MLN4924 (also known as pevonedistat), a small molecule inhibitor of E1 NEDD8-activating enzyme currently in phase I/II clinical trials, exerts significant anticancer effects by inducing cell cycle arrest, apoptosis, senescence and autophagy in a cell-type and context dependent manner. Here, we summarize the latest progresses in the field with a major focus on preclinical studies in validation of neddylation modification as a promising anticancer target.

MLN4924 (Pevonedistat), a protein neddylation inhibitor, suppresses proliferation and migration of human clear cell renal cell carcinoma

Neddylation is a post-translational protein modification associated with cancer development. MLN4924 is a neddylation inhibitor currently under investigation in multiple phase I studies on various malignancies, and its clincal name is Pevonedistat. It has been documented that MLN4924 blocks Cullins neddylation and inactivates CRLs and, in turn, triggers cell-cycle arrest, apoptosis, senescence and autophagy in many cancer cells. In this study, we investigated the anti-tumor effect of MLN4924 in human clear cell renal carcinoma (ccRCC). Levels of both Nedd8 activating enzyme E1 and Nedd8-conjugating enzyme E2 were higher in ccRCC tissues and RCC cancer cells than in normal. Moreover, MLN4924 treatment led to rapid inhibition of Cullin1 neddylation and notably suppressed growth and survival as well as migration in a dose-and time-dependent manner. Mechanistic studies revealed that MLN4924 induced the accumulation of a number of CRL substrates, including p21, p27 and Wee1 to trigger DNA damage and induce growth arrest at the G2/M phase. MLN4924 also induced anti-migration and anti-invasion by activating E-cadherin and repressing Vimentin. Taken together, this study provides the first evidence that neddylation pathway is overactive in ccRCC and that MLN4924 induces dose-dependent anti-proliferation, anti-migration, anti-invasion in ccRCC cells. The study thus indicates that MLN4924 has potential therapeutic value for the clinical treatment of renal cancer.

Effects of β-estradiol on cold-sensitive receptor channel TRPM8 in ovariectomized rats

Transient receptor potential cation channel subfamily M member 8 (TRPM8) is associated with sensitivity to cold sensation in mammals. A previous study demonstrated that TRPM8 was overexpressed in the skin of ovariectomized (OVX) rats due to the loss of estrogen. In the present study, we investigated whether estrogen replacement restricts overexpression of the TRPM8 channel in the skin of OVX rats. We divided 15 Sprague Dawley rats into three groups: a non-operated group (NON-OPE), an ovariectomy group (OVX), and a group subjected to estrogen replacement during 4 weeks beginning 7 days after ovariectomy (OVX + E2). Five weeks later, TRPM8 channel mRNA and protein in lumbar skin were quantified by real-time RT-PCR, protein ELISA, and immunohistochemistry. The OVX + E2 group exhibited a trend for decreased expression of the TRPM8 channel in the lumbar skin in comparison with the OVX group, whereas ELISA data and immunohistochemistry data and immunohistochemistry graphs relating to TRPM8 protein did not show any obvious differences between the OVX group and the OVX + E2 group. Estrogen replacement may restrict the overexpression of TRPM8 in the dermis of OVX rats.

Selective targeting of BCL6 induces oncogene addiction switching to BCL2 in B-cell lymphoma

The BCL6 oncogene plays a crucial role in sustaining diffuse large B-cell lymphomas (DLBCL) through transcriptional repression of key checkpoint genes. BCL6-targeted therapy kills lymphoma cells by releasing these checkpoints. However BCL6 also directly represses several DLBCL oncogenes such as BCL2 and BCL-XL that promote lymphoma survival. Herein we show that DLBCL cells that survive BCL6-targeted therapy induce a phenomenon of “oncogene-addiction switching” by reactivating BCL2-family dependent anti-apoptotic pathways. Thus, most DLBCL cells require concomitant inhibition of BCL6 and BCL2-family members for effective lymphoma killing. Moreover, in DLBCL cells initially resistant to BH3 mimetic drugs, BCL6 inhibition induces a newly developed reliance on anti-apoptotic BCL2-family members for survival that translates in acquired susceptibility to BH3 mimetic drugs ABT-737 and obatoclax. In germinal center B cell-like (GCB)-DLBCL cells, the proteasome inhibitor bortezomib and the NEDD inhibitor MLN4924 post-transcriptionally activated the BH3-only sensitizer NOXA thus counteracting the oncogenic switch to BCL2 induced by BCL6-targeting. Hence our study indicates that BCL6 inhibition induces an on-target feedback mechanism based on the activation of anti-apoptotic BH3 members. This oncogene-addition switching mechanism was harnessed to develop rational combinatorial therapies for GCB-DLBCL.

Methylomes of renal cell lines and tumors or metastases differ significantly with impact on pharmacogenes

Current therapies for metastatic clear cell renal cell carcinoma (ccRCC) show limited efficacy. Drug efficacy, typically investigated in preclinical cell line models during drug development, is influenced by pharmacogenes involved in targeting and disposition of drugs. Here we show through genome-wide DNA methylation profiling, that methylation patterns are concordant between primary ccRCC and macro-metastases irrespective of metastatic sites (rs ≥ 0.92). However, 195,038 (41%) of all investigated CpG sites, including sites within pharmacogenes, were differentially methylated (adjusted P < 0.05) in five established RCC cell lines compared to primary tumors, resulting in altered transcriptional expression. Exemplarily, gene-specific analyses of DNA methylation, mRNA and protein expression demonstrate lack of expression of the clinically important drug transporter OCT2 (encoded by SLC22A2) in cell lines due to hypermethylation compared to tumors or metastases. Our findings provide evidence that RCC cell lines are of limited benefit for prediction of drug effects due to epigenetic alterations. Similar epigenetic landscape of ccRCC-metastases and tumors opens new avenue for future therapeutic strategies.

Targeting protein neddylation with an NEDD8-activating enzyme inhibitor MLN4924 induced apoptosis or senescence in human lymphoma cells

Recent studies indicate that post-translational protein neddylation is required for the maintenance of cell viability in several lymphoma cell lines, while inhibition of the neddylation pathway with an NEDD8-activating enzyme (NAE) inhibitor MLN4924 induces apoptosis in lymphoma cells. However, the mechanism by which neddylation inhibition induces apoptosis in lymphoma cells has not been fully elucidated. Moreover, it is unknown whether neddylation inhibition triggers non-apoptotic cell-killing responses, such as cell senescence, in lymphoma cells. Here, we report that MLN4924 specifically inhibited protein neddylation, inactivated cullin-RING E3 ligase (CRL), the best-known neddylation substrate, and induced the accumulation of tumor-suppressive CRL substrates in lymphoma cells. Moreover, MLN4924 potently suppressed the growth of lymphoma cells by inducing G2 cell-cycle arrest, followed by apoptosis or senescence in a cell line-dependent manner. MLN4924-induced apoptosis was mediated by intrinsic apoptotic signaling with substantial up-regulation of pro-apoptotic Bik and Noxa as well as down-regulation of anti-apoptotic XIAP, c-IAP1 and c-IAP2, while senescence induction upon neddylation inhibition seemed dependent on the expression of tumor suppressor p21/p27. Together, these findings expand our understanding on how lymphoma cells respond to neddylation inhibition and support the development of neddylation inhibitors (e.g. MLN4924) for the treatment of lymphoma.

Targeting neddylation induces DNA damage and checkpoint activation and sensitizes chronic lymphocytic leukemia B cells to alkylating agents

Microenvironment-mediated upregulation of the B-cell receptor (BCR) and nuclear factor-κB (NF-κB) signaling in CLL cells resident in the lymph node and bone marrow promotes apoptosis evasion and clonal expansion. We recently reported that MLN4924 (pevonedistat), an investigational agent that inhibits the NEDD8-activating enzyme (NAE), abrogates stromal-mediated NF-κB pathway activity and CLL cell survival. However, the NAE pathway also assists degradation of multiple other substrates. MLN4924 has been shown to induce DNA damage and cell cycle arrest, but the importance of this mechanism in primary neoplastic B cells has not been studied. Here we mimicked the lymph node microenvironment using CD40 ligand (CD40L)-expressing stroma and interleukin-21 (IL-21) to find that inducing proliferation of the primary CLL cells conferred enhanced sensitivity to NAE inhibition. Treatment of the CD40-stimulated CLL cells with MLN4924 resulted in deregulation of Cdt1, a DNA replication licensing factor, and cell cycle inhibitors p21 and p27. This led to DNA damage, checkpoint activation and G2 arrest. Alkylating agents bendamustine and chlorambucil enhanced MLN4924-mediated DNA damage and apoptosis. These events were more prominent in cells stimulated with IL-21 compared with CD40L alone, indicating that, following NAE inhibition, the culture conditions were able to direct CLL cell fate from an NF-κB inhibition to a Cdt1 induction program. Our data provide insight into the biological consequences of targeting NAE in CLL and serves as further rationale for studying the clinical activity of MLN4924 in CLL, particularly in combination with alkylating agents.

Influence of fatty acid synthase inhibitor orlistat on the DNA repair enzyme O6-methylguanine-DNA methyltransferase in human normal or malignant cells in vitro

Tetrahydrolipstatin (orlistat), an inhibitor of lipases and fatty acid synthase, is used orally for long-term treatment of obesity. Although the drug possesses striking antitumor activities in vitro against human cancer cells and in vitro and in vivo against animal tumors, it also induces precancerous lesions in rat colon. Therefore, we tested the in vitro effect of orlistat on the expression of O6-methylguanine-DNA methyltransferase (MGMT), a DNA repair enzyme that plays an essential role in the control of mutagenesis and carcinogenesis. Western blot analysis demonstrated that 2-day continuous exposure to 40 µM orlistat did not affect MGMT levels in a human melanoma cell line, but downregulated the repair protein by 30-70% in human peripheral blood mononuclear cells, in two leukemia and two colon cancer cell lines. On the other hand, orlistat did not alter noticeably MGMT mRNA expression. Differently from lomeguatrib (a false substrate, strong inhibitor of MGMT) orlistat did not reduce substantially MGMT function after 2-h exposure of target cells to the agent, suggesting that this drug is not a competitive inhibitor of the repair protein. Combined treatment with orlistat and lomeguatrib showed additive reduction of MGMT levels. More importantly, orlistat-mediated downregulation of MGMT protein expression was markedly amplified when the drug was combined with a DNA methylating agent endowed with carcinogenic properties such as temozolomide. In conclusion, even if orlistat is scarcely absorbed by oral route, it is possible that this drug could reduce local MGMT-mediated protection against DNA damage provoked by DNA methylating compounds on gastrointestinal tract epithelial cells, thus favoring chemical carcinogenesis.

Regulation of the DNA damage response by ubiquitin conjugation

In response to DNA damage, cells activate a highly conserved and complex kinase-based signaling network, commonly referred to as the DNA damage response (DDR), to safeguard genomic integrity. The DDR consists of a set of tightly regulated events, including detection of DNA damage, accumulation of DNA repair factors at the site of damage, and finally physical repair of the lesion. Upon overwhelming damage the DDR provokes detrimental cellular actions by involving the apoptotic machinery and inducing a coordinated demise of the damaged cells (DNA damage-induced apoptosis, DDIA). These diverse actions involve transcriptional activation of several genes that govern the DDR. Moreover, recent observations highlighted the role of ubiquitylation in orchestrating the DDR, providing a dynamic cellular regulatory circuit helping to guarantee genomic stability and cellular homeostasis (Popovic et al., 2014). One of the hallmarks of human cancer is genomic instability (Hanahan and Weinberg, 2011). Not surprisingly, deregulation of the DDR can lead to human diseases, including cancer, and can induce resistance to genotoxic anti-cancer therapy (Lord and Ashworth, 2012). Here, we summarize the role of ubiquitin-signaling in the DDR with special emphasis on its role in cancer and highlight the therapeutic value of the ubiquitin-conjugation machinery as a target in anti-cancer treatment strategy.

Targeting PI3-kinase (PI3K), AKT and mTOR axis in lymphoma

Targeted therapy represents a transformation in oncology, a field that has relied primarily on non-selective cytotoxic therapies. Phosphatidylinositol 3-kinase (PI3K) is a family of ubiquitous signalling molecules involved in a wide variety of cellular processes and likewise, in a broad selection of human cancers. The discovery that the p110-δ form of PI3K is differentially expressed in normal and malignant lymphocytes has led to the development of specific inhibitors that are currently in clinical trials for lymphoma. Downstream effectors of PI3K, including v-akt murine thymoma viral oncogene homolog 1 (AKT; also termed AKT1) and mechanistic target of rapamycin (serine/threonine kinase) (mTOR) are similarly important in lymphoma, and agents targeting these components of the PI3K-AKT-mTOR axis are also underway, although at earlier stages of development. In this review we examine the role of PI3K-AKT-mTOR in normal and malignant lymphocytes, as well as the preclinical and clinical status of a number of inhibitors of this pathway.

Noxa and cancer therapy: Tuning up the mitochondrial death machinery in response to chemotherapy

Biochemical analyses have characterized the BH3-only protein family member Noxa as a “sensitizer” with weak pro-apoptotic activity. Investigations into cancer cell responses to chemotherapeutic agents have identified Noxa as a pivotal factor mediating the cytotoxic effect of a plethora of anticancer treatments independent of its own pro-apoptotic activity. Accumulating evidence now suggests that tumor cells exert a number of strategies to counteract Noxa function by exploiting diverse cellular regulatory circuits that normally govern Noxa expression during cellular stress responses. Here, we summarize data concerning the role of Noxa in cancer chemosensitivity and highlight the potential of this enigmatic BH3-only protein family member in current and novel anticancer therapies.

IGF expression in HPV-related and HPV-unrelated human cancer cells

The human Igf-1 gene not only produces insulin‑like growth factor-I (IGF-I), but also different carboxy‑terminal extensions, known as E peptides, through alternative splicing. We and others have shown that human Eb peptide (hEb) derived from Igf-1 has intrinsic biological activity and is localized to nuclei of transfected cells. Since hEb actions can complement the activity of IGF-I itself, the aim of the present study was to compare IGF-I isoforms at the endogenous protein and transcript level in cancer cell lines, including HeLa, U2OS, HepG2 and K562 cells. Quantitative real-time PCR (qRT‑PCR) using Igf-1 isoform specific primers was performed to determine expression patterns, using β-actin as a reference gene. The overall relative Igf-1 transcript level was different across the cell lines, with ~80-fold higher expression in K562 (130.2±31.2) than in U2OS cells (1.7±1.1). The relative copy number of Igf-1b was the highest in HepG2 (69.9±28.6) and K562 cells (28.3±6.7), whereas the relative copy numbers of Igf-1a and Igf-1c were significantly higher in K562 cells compared to all other cell lines. Immunoblotting using total cell lysates, cytoplasmic and nuclear fractions were carried out to determine the level and distribution of IGF-I proteins. K562 cells exhibited the highest level of hEb in total cell lysates and nuclear fractions and no cell lines displayed hEb in the cytoplasmic fractions. In contrast, IGF-IA was the highest in HeLa cells and was enriched only in the cytoplasmic fraction. Since relatively low IGF-1A transcript level but relatively high pro‑IGF-1A protein level is plausible, we hypothesized that these transcripts could be processed with higher efficiency and/or the protein product may be stabilized by viral HPV oncogenes in HeLa cells. We assert that while it is important to analyze Igf-1 transcript level, it may be more relevant to determine the IGF isoforms at the protein level.