Aberrant splicing of the DMP1-ARF-MDM2-p53 pathway in cancer

MDM2- an indispensable player in tumorigenesis

Murine double minute 2 (MDM2) is a well-recognized molecule for its oncogenic potential. Since its identification, various cancer-promoting roles of MDM2 such as growth stimulation, sustained angiogenesis, metabolic reprogramming, apoptosis evasion, metastasis, and immunosuppression have been established. Alterations in the expression levels of MDM2 occur in multiple types of cancers resulting in uncontrolled proliferation. The cellular processes are modulated by MDM2 through transcription, post-translational modifications, protein degradation, binding to cofactors, and subcellular localization. In this review, we discuss the precise role of deregulated MDM2 levels in modulating cellular functions to promote cancer growth. Moreover, we also briefly discuss the role of MDM2 in inducing resistance against anti-cancerous therapies thus limiting the benefits of cancerous treatment.

How Driver Oncogenes Shape and Are Shaped by Alternative Splicing Mechanisms in Tumors

The development of RNA sequencing methods has allowed us to study and better understand the landscape of aberrant pre-mRNA splicing in tumors. Altered splicing patterns are observed in many different tumors and affect all hallmarks of cancer: growth signal independence, avoidance of apoptosis, unlimited proliferation, invasiveness, angiogenesis, and metabolism. In this review, we focus on the interplay between driver oncogenes and alternative splicing in cancer. On one hand, oncogenic proteins-mutant p53, CMYC, KRAS, or PI3K-modify the alternative splicing landscape by regulating expression, phosphorylation, and interaction of splicing factors with spliceosome components. Some splicing factors-SRSF1 and hnRNPA1-are also driver oncogenes. At the same time, aberrant splicing activates key oncogenes and oncogenic pathways: p53 oncogenic isoforms, the RAS-RAF-MAPK pathway, the PI3K-mTOR pathway, the EGF and FGF receptor families, and SRSF1 splicing factor. The ultimate goal of cancer research is a better diagnosis and treatment of cancer patients. In the final part of this review, we discuss present therapeutic opportunities and possible directions of further studies aiming to design therapies targeting alternative splicing mechanisms in the context of driver oncogenes.

Antisense Oligonucleotide-Mediated Splice Switching: Potential Therapeutic Approach for Cancer Mitigation

Splicing is an essential process wherein precursor messenger RNA (pre-mRNA) is reshaped into mature mRNA. In alternative splicing, exons of any pre-mRNA get rearranged to form mRNA variants and subsequently protein isoforms, which are distinct both by structure and function. On the other hand, aberrant splicing is the cause of many disorders, including cancer. In the past few decades, developments in the understanding of the underlying biological basis for cancer progression and therapeutic resistance have identified many oncogenes as well as carcinogenic splice variants of essential genes. These transcripts are involved in various cellular processes, such as apoptosis, cell signaling and proliferation. Strategies to inhibit these carcinogenic isoforms at the mRNA level are promising. Antisense oligonucleotides (AOs) have been developed to inhibit the production of alternatively spliced carcinogenic isoforms through splice modulation or mRNA degradation. AOs can also be used to induce splice switching, where the expression of an oncogenic protein can be inhibited by the induction of a premature stop codon. In general, AOs are modified chemically to increase their stability and binding affinity. One of the major concerns with AOs is efficient delivery. Strategies for the delivery of AOs are constantly being evolved to facilitate the entry of AOs into cells. In this review, the different chemical modifications employed and delivery strategies applied are discussed. In addition to that various AOs in clinical trials and their efficacy are discussed herein with a focus on six distinct studies that use AO-mediated exon skipping as a therapeutic strategy to combat cancer.

Development and structural characterisation of human scFv targeting MDM2 spliced variant MDM215kDa

The murine double minute 2 (MDM2) protein is a major negative regulator of the tumour suppressor protein p53. Under normal conditions, MDM2 constantly binds to p53 transactivation domain and/or ubiquinates p53 via its role as E3 ubiquitin ligase to promote p53 degradation as well as nuclear export to maintain p53 levels in cells. Meanwhile, amplification of MDM2 and appearance of MDM2 spliced variants occur in many tumours and normal tissues making it a prognostic indicator for human cancers. The mutation or deletion of p53 protein in half of human cancers inactivates its tumour suppressor activity. However, cancers with wild type p53 have its function effectively inhibited through direct interaction with MDM2 oncoprotein. Here, we described the construction of a MDM2 spliced variant (rMDM2^15kDa) consisting of SWIB/MDM2 domain and its central region for antibody generation. Biopanning with a human naïve scFv library generated four scFv clones specific to rMDM2^15kDa. Additionally, the selected scFv clones were able to bind to the recombinant full length MDM2 (rMDM2-FL). Computational prediction showed that the selected scFv clones potentially bind to exon 7-8 of MDM2 while leaving the MDM2/SWIB domain free for p53 interaction. The developed antibodies exhibit good specificity can be further investigated for downstream biomedical and research applications.

MiR-6838-5p facilitates the proliferation and invasion of renal cell carcinoma cells through inhibiting the DMTF1/ARF-p53 axis

Renal cell carcinoma (RCC) is one of the most common renal malignancies in the urinary system. Numerous studies have demonstrated that miRNAs can regulate tumorigenesis and progression. This study aims to investigate the role and regulatory mechanism of miR-6838-5p in RCC. Our study confirmed that miR-6838-5p was upregulated in human RCC tissues (30/42, 77.43%, P < 0.01) and RCC cell lines (P < 0.05) compared to adjacent non-neoplastic tissues and normal renal epithelial cells. In vitro, overexpression of miR-6838-5p enhanced cell proliferation and invasion in human RCC cell lines (ACHN and 786-O), which were detected by CCK-8, Transwell and Colony formation assays (P < 0.05), and knockdown of miR-6838-5p suppressed cell proliferation and invasion (P < 0.05). Results of Bioinformatics analysis combined with Dual-luciferase reporter gene assay demonstrated that miR-6838-5p could bind to Cyclin D binding myb-like transcription factor 1 (DMTF1). In addition, RT-qPCR and Western blotting confirmed that DMTF1 was downregulated in RCC tissues and cell lines. Meanwhile, it was demonstrated that overexpression of miR-6838-5p inhibited DMTF1 level in ACHN cells. Next, we confirmed that DMTF1 overexpression reversed the inhibitory effects of overexpression of miR-6838-5p on phosphatase and tensin homolog (PTEN), tumor protein 53(p53), murine double minute 2 (MDM2) and alternative reading frame (ARF) protein levels in the ARF-p53 signaling pathway. In conclusion, our research showed that miR-6838-5p enhanced the proliferation and invasion of RCC cells by inhibiting the DMTF1/ARF-p53 axis.

A prognosis-related molecular subtype for early-stage non-small lung cell carcinoma by multi-omics integration analysis

Background

Early-stage non-small cell lung carcinoma (NSCLC) accounts for more than 80% of lung cancer, which is a kind of cancer with high heterogeneity, so the genetic heterogeneity and molecular subtype should be explored.

Methods

Partitioning Around Medoid algorithm was used to acquire the molecular subtype for early-stage NSCLC based on prognosis-related mRNAs and methylation sites. Random forest (RF) and support vector machine (SVM) were used to build prediction models for subtypes.

Results

Six prognosis-related subtypes for early-stage NSCLC, including 4 subtypes for lung squamous cell carcinoma (LUSC) and 2 subtypes for lung adenocarcinoma (LUAD), were identified. There were highly expressed and hypermethylated gene regions for LUSC-C1 and LUAD-C2, highly expressed region for LUAD-C1, and hypermethylated regions for LUSC-C3 and LUSC-C4. Molecular subtypes for LUSC were mainly determined by DNA methylation (14 mRNAs and 362 methylation sites). Molecular subtypes for LUAD were determined by both mRNA and DNA methylation information (143 mRNAs and 458 methylation sites). Ten methylation sites were selected as biomarkers for prediction of LUSC-C1 and LUSC-C3, respectively. Nine genes and 1 methylation site were selected as biomarkers for LUAD subtype prediction. These subtypes can be predicted by the selected biomarkers with RF and SVM models.

Conclusions

In conclusion, we proposed a prognosis-related molecular subtype for early-stage NSCLC, which can provide important information for personalized therapy of patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-07846-0.

RNA-binding protein CELF1 enhances cell migration, invasion, and chemoresistance by targeting ETS2 in colorectal cancer

Colorectal cancer (CRC) is often diagnosed at later stages after it has metastasized to other organs. The development of chemoresistance also contributes to a poor prognosis. Therefore, an increased understanding of the metastatic properties of CRC and chemoresistance could improve patient survival. CUGBP elav-like family member 1 (CELF1) is an RNA-binding protein, which is overexpressed in many human malignant tumors. However, the influence of CELF1 in CRC is unclear. V-ets erythroblastosis virus E26 oncogene homologue 2 (ETS2) is an evolutionarily conserved proto-oncogene known to be overexpressed in a variety of human cancers including CRC. In thespresent tudy, we investigated the association between CELF1 and ETS2 in CRC tumorigenesis and oxaliplatin (L-OHP) resistance. We found a positive correlation between the elevated expression of CELF1 and ETS2 in human CRC tissues. Overexpression of CELF1 increased CRC cell proliferation, migration, and invasion in vitro and in a xenograft tumor growth model in vivo, and induced resistance to L-OHP. In contrast, CELF1 knockdown improved the response of CRC cells to L-OHP. Overexpression of ETS2 increased the malignant behavior of CRC cells (growth, migration, and invasion) and L-OHP resistance in vitro. Moreover, L-OHP resistance induced by CELF1 overexpression was reversed by ETS2 knockdown. The results of luciferase reporter and ribonucleoprotein immunoprecipitation assays indicated that CELF1 up-regulates ETS2 by binding to its 3'-UTR. Taken together, our findings have identified that CELF1 regulates ETS2 in a mechanism that results in CRC tumorigenesis and L-OHP resistance, and CELF1 may be a promising target for overcoming chemoresistance in CRC.

Expression of p53 is associated with microbial acetaldehyde production in oralsquamous cell carcinoma

OBJECTIVES

The objective of this study was to investigate the association between p53 expression and microbial acetaldehyde production in patients with oral squamous cell carcinoma (OSCC).

STUDY DESIGN

Oral mucosal biopsies from 22 patients with OSCC and 24 healthy controls (HCs) were collected. p53 expression was analyzed by immunohistochemistry. Microbial samples were collected from the mucosa and microbial acetaldehyde production from ethanol was measured by gas chromatography.

RESULTS

The majority of all OSCC (77%) and HC samples (67%) produced mutagenic levels of acetaldehyde (>100 µM). A significant positive correlation between microbial acetaldehyde production and p53 expression levels in OSCC samples was seen in the intermediate and superficial layers of the epithelium of the infiltrative zone (P = .0005 and P = .0004, respectively) and in the superficial layer of the healthy appearing mucosa next to the tumor (P = .0391). There was no significant correlation between acetaldehyde levels and p53 expression in HC samples.

CONCLUSIONS

Our results show an association between microbial acetaldehyde production and immunostaining of p53 in OSCC samples.

Regulation of Canonical Oncogenic Signaling Pathways in Cancer via DNA Methylation

Disruption of signaling pathways that plays a role in the normal development and cellular homeostasis may lead to the dysregulation of cellular signaling and bring about the onset of different diseases, including cancer. In addition to genetic aberrations, DNA methylation also acts as an epigenetic modifier to drive the onset and progression of cancer by mediating the reversible transcription of related genes. Although the role of DNA methylation as an alternative driver of carcinogenesis has been well-established, the global effects of DNA methylation on oncogenic signaling pathways and the presentation of cancer is only emerging. In this article, we introduced a differential methylation parsing pipeline (MethylMine) which mined for epigenetic biomarkers based on feature selection. This pipeline was used to mine for biomarkers, which presented a substantial difference in methylation between the tumor and the matching normal tissue samples. Combined with the Data Integration Analysis for Biomarker discovery (DIABLO) framework for machine learning and multi-omic analysis, we revisited the TCGA DNA methylation and RNA-Seq datasets for breast, colorectal, lung, and prostate cancer, and identified differentially methylated genes within the NRF2-KEAP1/PI3K oncogenic pathway, which regulates the expression of cytoprotective genes, that serve as potential therapeutic targets to treat different cancers.

Survival of Lung Cancer Patients Dependent on the LOH Status for DMP1, ARF, and p53

Lung cancer is the leading cause of cancer deaths in the world, and accounts for more solid tumor deaths than any other carcinomas. The prognostic values of DMP1, ARF, and p53-loss are unknown in lung cancer. We have conducted survival analyses of non-small cell lung cancer (NSCLC) patients from the University of Minnesota VA hospital and those from the Wake Forest University Hospital. Loss of Heterozygosity (LOH) for hDMP1 was found in 26 of 70 cases (37.1%), that of the ARF/INK4a locus was found in 33 of 70 (47.1%), and that of the p53 locus in 43 cases (61.4%) in the University of Minnesota samples. LOH for hDMP1 was associated with favorable prognosis while that of p53 predicted worse prognosis. The survival was much shorter for ARF-loss than INK4a-loss, emphasizing the importance of ARF in human NSCLC. The adverse effect of p53 LOH on NSCLC patients' survival was neutralized by simultaneous loss of the hDMP1 locus in NSCLC and breast cancer, suggesting the possible therapy of epithelial cancers with metastatic ability.

Post-Translational Regulation of ARF: Perspective in Cancer

Tumorigenesis can be induced by various stresses that cause aberrant DNA mutations and unhindered cell proliferation. Under such conditions, normal cells autonomously induce defense mechanisms, thereby stimulating tumor suppressor activation. ARF, encoded by the CDKN2a locus, is one of the most frequently mutated or deleted tumor suppressors in human cancer. The safeguard roles of ARF in tumorigenesis are mainly mediated via the MDM2-p53 axis, which plays a prominent role in tumor suppression. Under normal conditions, low p53 expression is stringently regulated by its target gene, MDM2 E3 ligase, which induces p53 degradation in a ubiquitin-proteasome-dependent manner. Oncogenic signals induced by MYC, RAS, and E2Fs trap MDM2 in the inhibited state by inducing ARF expression as a safeguard measure, thereby activating the tumor-suppressive function of p53. In addition to the MDM2-p53 axis, ARF can also interact with diverse proteins and regulate various cellular functions, such as cellular senescence, apoptosis, and anoikis, in a p53-independent manner. As the evidence indicating ARF as a key tumor suppressor has been accumulated, there is growing evidence that ARF is sophisticatedly fine-tuned by the diverse factors through transcriptional and post-translational regulatory mechanisms. In this review, we mainly focused on how cancer cells employ transcriptional and post-translational regulatory mechanisms to manipulate ARF activities to circumvent the tumor-suppressive function of ARF. We further discussed the clinical implications of ARF in human cancer.

Therapeutic Approaches Targeting Nucleolus in Cancer

The nucleolus is a distinct sub-cellular compartment structure in the nucleus. First observed more than 200 years ago, the nucleolus is detectable by microscopy in eukaryotic cells and visible during the interphase as a sub-nuclear structure immersed in the nucleoplasm, from which it is not separated from any membrane. A huge number of studies, spanning over a century, have identified ribosome biogenesis as the main function of the nucleolus. Recently, novel functions, independent from ribosome biogenesis, have been proposed by several proteomic, genomic, and functional studies. Several works have confirmed the non-canonical role for nucleoli in regulating important cellular processes including genome stability, cell-cycle control, the cellular senescence, stress responses, and biogenesis of ribonucleoprotein particles (RNPs). Many authors have shown that both canonical and non-canonical functions of the nucleolus are associated with several cancer-related processes. The association between the nucleolus and cancer, first proposed by cytological and histopathological studies showing that the number and shape of nucleoli are commonly altered in almost any type of cancer, has been confirmed at the molecular level by several authors who demonstrated that numerous mechanisms occurring in the nucleolus are altered in tumors. Recently, therapeutic approaches targeting the nucleolus in cancer have started to be considered as an emerging "hallmark" of cancer and several therapeutic interventions have been developed. This review proposes an up-to-date overview of available strategies targeting the nucleolus, focusing on novel targeted therapeutic approaches. Finally, a target-based classification of currently available treatment will be proposed.

Central role of the p53 pathway in the noncoding-RNA response to oxidative stress

Oxidative stress plays a fundamental role in many conditions. Specifically, redox imbalance inhibits endothelial cell (EC) growth, inducing cell death and senescence. We used global transcriptome profiling to investigate the involvement of noncoding-RNAs in these phenotypes. By RNA-sequencing, transcriptome changes were analyzed in human ECs exposed to H₂O₂, highlighting a pivotal role of p53-signaling. Bioinformatic analysis and validation in p53-silenced ECs, identified several p53-targets among both mRNAs and long noncoding-RNAs (lncRNAs), including MALAT1 and NEAT1. Among microRNAs (miRNAs), miR-192-5p was the most induced by H₂O₂ treatment, in a p53-dependent manner. Down-modulated mRNA-targets of miR-192-5p were involved in cell cycle, DNA repair and stress response. Accordingly, miR-192-5p overexpression significantly decreased EC proliferation, inducing cell death. A central role of the p53-pathway was also confirmed by the analysis of differential exon usage: Upon H₂O₂ treatment, the expression of p53-dependent 5'-isoforms of MDM2 and PVT1 increased selectively. The transcriptomic alterations identified in H₂O₂-treated ECs were also observed in other physiological and pathological conditions where redox control plays a fundamental role, such as ECs undergoing replicative senescence, skeletal muscles of critical limb-ischemia patients and the peripheral-blood mononuclear cells of long-living individuals. Collectively, these findings indicate a prominent role of noncoding-RNAs in oxidative stress response.

c-MYB and DMTF1 in Cancer

The c-Myb gene encodes a transcription factor that regulates cell proliferation, differentiation, and apoptosis through protein-protein interaction and transcriptional regulation of signaling pathways. The protein is frequently overexpressed in human leukemias, breast cancers, and other solid tumors suggesting that it is a bona fide oncogene. c-MYB is often overexpressed by translocation in human tumors with t(6;7)(q23;q34) resulting in c-MYB-TCRβ in T cell ALL, t(X;6)(p11;q23) with c-MYB-GATA1 in acute basophilic leukemia, and t(6;9)(q22-23;p23-24) with c-MYB-NF1B in adenoid cystic carcinoma. Antisense oligonucleotides to c-MYB were developed to purge bone marrow cells to eliminate tumor cells in leukemias. Recently, small molecules that inhibit c-MYB activity have been developed to disrupt its interaction with p300. The Dmp1 (cyclin D binding myb-like protein 1; Dmtf1) gene was isolated through its virtue for binding to cyclin D2. It is a transcription factor that has a Myb-like repeat for DNA binding. The Dmtf1 protein directly binds to the Arf promoter for transactivation and physically interacts with p53 to activate the p53 pathway. The gene is hemizygously deleted in 35-42% of human cancers and is associated with longer survival. The significances of aberrant expression of c-MYB and DMTF1 proteins in human cancers and their clinical significances are discussed.

Aberrant RNA Splicing in Cancer and Drug Resistance

More than 95% of the 20,000 to 25,000 transcribed human genes undergo alternative RNA splicing, which increases the diversity of the proteome. Isoforms derived from the same gene can have distinct and, in some cases, opposing functions. Accumulating evidence suggests that aberrant RNA splicing is a common and driving event in cancer development and progression. Moreover, aberrant splicing events conferring drug/therapy resistance in cancer is far more common than previously envisioned. In this review, aberrant splicing events in cancer-associated genes, namely BCL2L1, FAS, HRAS, CD44, Cyclin D1, CASP2, TMPRSS2-ERG, FGFR2, VEGF, AR and KLF6, will be discussed. Also highlighted are the functional consequences of aberrant splice variants (BCR-Abl35INS, BIM-γ, IK6, p61 BRAF V600E, CD19-∆2, AR-V7 and PIK3CD-S) in promoting resistance to cancer targeted therapy or immunotherapy. To overcome drug resistance, we discuss opportunities for developing novel strategies to specifically target the aberrant splice variants or splicing machinery that generates the splice variants. Therapeutic approaches include the development of splice variant-specific siRNAs, splice switching antisense oligonucleotides, and small molecule inhibitors targeting splicing factors, splicing factor kinases or the aberrant oncogenic protein isoforms.

Plumbagin from a tropical pitcher plant (Nepenthes alata Blanco) induces apoptotic cell death via a p53-dependent pathway in MCF-7 human breast cancer cells

Plumbagin (5-hydroxy-2-methyl-1,4-naphthaquinone) has displayed antitumor activity in vitro and in animal models; however, the underlying molecular mechanisms have not been fully explored. The aim of this study was to investigate the anticancer effects of plumbagin isolated from Nepenthes alata against MCF-7 breast cancer cells. We examined the cytotoxicity, cell cycle regulation, apoptotic cell death, and generation of intracellular reactive oxygen species (ROS) in MCF-7 cells. Plumbagin exhibited potent cytotoxicity in MCF-7 cells (wild-type p53) compared to that in SK-OV-3 (null-type) human epithelial ovarian cancer cells. Specifically, plumbagin upregulated the expression of p21^CIP1/WAF1 in MCF-7 cells, causing cell cycle arrest in the G2/M phase through inhibition of cyclin B1 levels. Plumbagin also significantly increased the ratio of Bax/Bcl-2 and release of cytochrome c, resulting in apoptotic cell death in MCF-7 cells. Furthermore, plumbagin dramatically increased the intracellular ROS level, whereas pretreatment with the ROS scavenger N-acetyl cysteine protected against plumbagin-induced cytotoxicity, suggesting that ROS formation plays a pivotal role in antitumor activity in MCF-7 cells. In mice bearing MCF-7 cell xenografts, plumbagin significantly reduced tumor growth and weight without apparent side effects. We therefore concluded that plumbagin exerts anticancer activity against MCF-7 cells through the generation of intracellular ROS, resulting in the induction of apoptosis via a p53-dependent pathway. This study thus identifies a new anticancer mechanism of plumbagin against p53-dependent breast cancer cells and suggests a novel strategy for overcoming of breast cancer therapy.

Tumor suppression by the EGR1, DMP1, ARF, p53, and PTEN Network

Recent studies have indicated that EGR1 is a direct regulator of tumor suppressors including TGFβ1, PTEN, and p53. The Myb-like transcription factor Dmp1 is a physiological regulator of the Arf-p53 pathway through transactivation of the Arf promoter and physical interaction of p53. The Dmp1 promoter has binding sites for Egr proteins, and Egr1 is a target for Dmp1. Crosstalks between p53 and PTEN have been reported. The Egr1-Dmp1-Arf-p53-Pten pathway displays multiple modes of interaction with each other, suggesting the existence of a functional network of tumor suppressors that maintain normal cell growth and prevent the emergence of incipient cancer cells.

Differential Effects of Autophagy-Related 10 Protein on HCV Replication and Autophagy Flux Are Mediated by Its Cysteine44 and Cysteine135

Autophagy-related 10 (ATG10) is essential for autophagy since it promotes ATG5-ATG12 complex formation. Our previous study found that there are two isoforms of the ATG10 protein, ATG10 (a longer one) and ATG10S, which have identical sequences except an absence of a 36-amino acid fragment (peptide B) in ATG10S, yet exhibit distinct effects on HCV genome replication. Here, we report the existence of two amino acids, cysteine at residue 44 and 135 (Cys⁴⁴ and Cys¹³⁵, respectively), in ATG10 being related to differential effects of ATG10 on HCV replication and autophagy flux. Through a series of ATG10 mutation experiments and protein modeling prediction, we found that Cys⁴⁴ was involved in the dual role of the two isoforms of ATG10 protein on HCV replication and autophagy flux, and that Cys¹³⁵ plays similar roles as Cys⁴⁴, but the disulfide bond of Cys⁴⁴-Cys¹³⁵ was not verified in the ATG10 protein. Further analyses by full HCV virion infection confirmed the roles of -SH of Cys⁴⁴ and Cys¹³⁵ on HCV replication. ATG10 with deleted or mutated Cys⁴⁴ and/or Cys¹³⁵ could activate expression of innate immunity-related genes, including il28a, irf-3, irf-7, and promote complete autophagy by driving autophagosomes to interact with lysosomes via IL28A-mediation. Subcellular localization assay and chromatin immunoprecipitation assay showed that ATG10 with the sulfydryl deletion or substitution of Cys⁴⁴ and Cys¹³⁵ could translocate into the nucleus and bind to promoter of IL28A gene; the results indicated that ATG10 with Cys⁴⁴ and/or Cys¹³⁵ absence might act as transcriptional factors to trigger the expression of anti-HCV immunological genes, too. In conclusion, our findings provide important information for understanding the differential roles on HCV replication and autophagy flux between ATG10 and ATG10S, and how the structure-function relationship of ATG10 transformed by a single -SH group loss on Cys⁴⁴ and Cys¹³⁵ in ATG10 protein, which may be a new target against HCV replication.

Role of transmembrane glycoprotein mucin 1 (MUC1) in various types of colorectal cancer and therapies: Current research status and updates

Colorectal carcinoma (CRC) is the third most common malignant tumor in the world. In recent years, the morbidity and mortality of CRC have increased in the world due to increasingly ageing population, modern dietary habits, environmental change, genetic disorders and chronic intestinal inflammation. Despite recent advances in earlier detection and improvements in chemotherapy, the 5-year survival rate of patients with metastatic CRC remains low. Therefore, novel effective treatment strategies for primary or metastatic CRC have emerged to enhance cure rate as well as elongation of patient's survival. Immunotherapy has been proposed for a potentially effective therapeutic approach to the treatment of CRC. Tumor vaccination in preclinical and clinical studies has supported the antitumor activity induced by immunization with CRC cell vaccines. Epithelial cell molecule Mucin 1 (MUC1), a transmembrane glycoprotein aberrantly overexpressed in various cancers including CRC, has been used as a candidate target antigen in the peptide, dendritic cell, and whole tumor vaccines. Several clinical trials in progress reveal the immunogenicity and suitability of MUC1 that acted as immunotherapeutic vaccines for CRC/colorectal cancer stem cells (CCSC). The present review summarizes the potential roles of MUC1 on CRC/CCSC vaccines according to the latest data. Moreover, this review also discusses the novel strategies for targeting CCSC via inducing an immune response against MUC1 to achieve the best prevention and treatment effects in animal models and clinical trails.

Cisplatin sensitivity in breast cancer cells is associated with particular DMTF1 splice variant expression

The cyclin D binding myb-like transcription factor 1 (DMTF1) is a tumor suppressor gene that activates p14^ARF transcription and thereby stabilizing the p53 tumor suppressor. The DMTF1 gene locus encodes for three different alternatively spliced isoforms, namely DMTF1α, β and γ. The oncogenic DMTF1β isoform negatively interferes with the transcriptional activity of DMTF1α. Increased DMTF1β is associated with increased cell proliferation in a variety of cancer cell types. In this study, we aimed at identifying the role of DMTF1 isoforms in response to cisplatin treatment in breast cancer cells. First, we used SKBR3 (cisplatin sensitive) and MCF7 (cisplatin resistant) breast cancer cell lines to quantify DMTF1 expression in response to cisplatin treatment. Total DMTF1 mRNA levels increased in a dose dependent manner in both cell lines upon cisplatin treatment. However, the mRNA levels of the isoforms revealed that the sensitive cell line, SKBR3, showed increased levels of both isoforms, whereas the resistant cell, MCF7, only showed increased levels of the oncogenic DMTF1β isoform. Silencing all DMTF1 isoforms led to increased cell survival upon cisplatin treatment. Furthermore, we found a significant increase in the percentage of quiescent cells in SKBR3 shDMTF1. Together, our data suggest that DMTF1 expression levels are associated with increased cisplatin resistance.

Translocations involving ETS family proteins in human cancer

The ETS transcription factors regulate expression of genes involved in normal cell development, proliferation, differentiation, angiogenesis, and apoptosis, consisting of 28 family members in humans. Dysregulation of these transcription factors facilitates cell proliferation in cancers, and several members participate in invasion and metastasis by activating certain gene transcriptions. ETS1 and ETS2 are the founding members of the ETS family and regulate transcription by binding to ETS sequences. Three chimeric genes involving ETS genes have been identified in human cancers, which are EWS-FLI1 in Ewing's sarcoma, TMPRSS2-ERG in prostate cancer, and ETV6-RUNX1 in acute lymphocytic leukemia. Although these fusion transcripts definitely contribute to the pathogenesis of the disease, the impact of these fusion transcripts on patients' prognosis is highly controversial. In the present review, the roles of ETS protein translocations in human carcinogenesis are discussed.

Aberrant expression of ETS1 and ETS2 proteins in cancer

The ETS transcription factors regulate expression of genes involved in normal cell development, proliferation, differentiation, angiogenesis, and apoptosis, consisting of 28 family members in humans. Dysregulation of these transcription factors facilitates cell proliferation in cancers, and several members participate in invasion and metastasis by activating gene transcription. ETS1 and ETS2 are the founding members of the ETS family and regulate transcription by binding to ETS sequences. They are both involved in oncogenesis and tumor suppression depending on the biological situations used. The essential roles of ETS proteins in human telomere maintenance have been suggested, which have been linked to creation of new Ets binding sites. Recently, preferential binding of ETS2 to gain-of-function mutant p53 and ETS1 to wild type p53 (WTp53) has been suggested, raising the tumor promoting role for the former and tumor suppressive role for the latter. The oncogenic and tumor suppressive functions of ETS1 and 2 proteins have been discussed.

Aberrant Expression of p14ARF in Human Cancers: A New Biomarker?

The ARF and INK4a genes are located on the CDKN2a locus, both showing tumor suppressive activity. ARF has been shown to monitor potentially harmful oncogenic signalings, making early stage cancer cells undergo senescence or programmed cell death to prevent cancer. Conversely, INK4a detects both aging and incipient cancer cell signals, and thus these two gene functions are different. The efficiency of detection of oncogenic signals is more efficient for the for the former than the latter in the mouse system. Both ARF and INK4a genes are inactivated by gene deletion, promoter methylation, frame shift, aberrant splicing although point mutations for the coding region affect only the latter. Recent studies show the splicing alterations that affect only ARF or both ARF and INK4a genes suggesting that ARF is inactivated in human tumors more frequently than what was previously thought. The ARF gene is activated by E2Fs and Dmp1 transcription factors while it is repressed by Bmi1, Tbx2/3, Twist1, and Pokemon nuclear proteins. It is also regulated at protein levels by Arf ubiquitin ligase named ULF, MKRN1, and Siva1. The prognostic value of ARF overexpression is controversial since it is induced in early stage cancer cells to eliminate pre-malignant cells (better prognosis); however, it may also indicate that the tumor cells have mutant p53 associated with worse prognosis. The ARF tumor suppressive protein can be used as a biomarker to detect early stage cancer cells as well as advanced stage tumors with p53 inactivation.

Alternative Splicing as a Target for Cancer Treatment

Alternative splicing is a key mechanism determinant for gene expression in metazoan. During alternative splicing, non-coding sequences are removed to generate different mature messenger RNAs due to a combination of sequence elements and cellular factors that contribute to splicing regulation. A different combination of splicing sites, exonic or intronic sequences, mutually exclusive exons or retained introns could be selected during alternative splicing to generate different mature mRNAs that could in turn produce distinct protein products. Alternative splicing is the main source of protein diversity responsible for 90% of human gene expression, and it has recently become a hallmark for cancer with a full potential as a prognostic and therapeutic tool. Currently, more than 15,000 alternative splicing events have been associated to different aspects of cancer biology, including cell proliferation and invasion, apoptosis resistance and susceptibility to different chemotherapeutic drugs. Here, we present well established and newly discovered splicing events that occur in different cancer-related genes, their modification by several approaches and the current status of key tools developed to target alternative splicing with diagnostic and therapeutic purposes.

Aberrant expression of p16INK4a in human cancers - a new biomarker?

The ARF and INK4a genes are located in the same CDKN2a locus, both showing its tumor suppressive activity. ARF has been shown to detect potentially harmful oncogenic signals, making incipient cancer cells undergo senescence or apoptosis. INK4a, on the other hand, responds to signals from aging in a variety of tissues including islets of Langerhans, neuronal cells, and cancer stem cells in general. It also detects oncogenic signals from incipient cancer cells to induce them senescent to prevent neoplastic transformation. Both of these genes are inactivated by gene deletion, promoter methylation, frame shift, and aberrant splicing although mutations changing the amino acid sequences affect only the latter. Recent studies indicated that polycomb gene products EZH2 and BMI1 repressed p16^INK4a expression in primary cells, but not in cells deficient for pRB protein function. It was also reported that that p14^ARF inhibits the stability of the p16^INK4a protein in human cancer cell lines and mouse embryonic fibroblasts through its interaction with regenerating islet-derived protein 3γ. Overexpression of INK4a is associated with better prognosis of cancer when it is associated with human papilloma virus infection. However, it has a worse prognostic value in other tumors since it is an indicator of pRB loss. The p16^INK4a tumor suppressive protein can thus be used as a biomarker to detect early stage cancer cells as well as advanced tumor cells with pRB inactivation since it is not expressed in normal cells.

Stress Hormone Cortisol Enhances Bcl2 Like-12 Expression to Inhibit p53 in Hepatocellular Carcinoma Cells

BACKGROUND AND AIMS

The pathogenesis of hepatocellular carcinoma (HC) is unclear. It is suggested that psychological stress associates with the pathogenesis of liver cancer. Bcl2-like protein 12 (Bcl2L12) suppresses p53 protein. This study tests a hypothesis that the major stress hormone, cortisol, inhibits the expression of p53 in HC cells (HCC) via up regulating the expression of Bcl2L12.

METHODS

Peripheral blood samples were collected from patients with HC to be analyzed for the levels of cortisol. HCC were cultured to assess the role of cortisol in the regulation of the expression of Bcl2L12 and p53 in HCC.

RESULTS

We observed that the serum cortisol levels were higher in HC patients. Expression of Bcl2L12 in HCC was correlated with serum cortisol. Cortisol enhanced the Bcl2L12 expression in HCC. Bcl2L12 binding to the TP53 promoter was correlated with p53 expression in HCC. Cortisol increased the Bcl2L12 expression in HCC to inhibit p53 expression.

CONCLUSIONS

Stress hormone cortisol suppresses p53 in HCC via enhancing Bcl2L12 expression in HCC. The results suggest that cortisol may be a therapeutic target for the treatment of HC.

Alternative Splicing in Breast Cancer and the Potential Development of Therapeutic Tools

Alternative splicing is a key molecular mechanism now considered as a hallmark of cancer that has been associated with the expression of distinct isoforms during the onset and progression of the disease. The leading cause of cancer-related deaths in women worldwide is breast cancer, and even when the role of alternative splicing in this type of cancer has been established, the function of this mechanism in breast cancer biology is not completely decoded. In order to gain a comprehensive view of the role of alternative splicing in breast cancer biology and development, we summarize here recent findings regarding alternative splicing events that have been well documented for breast cancer evolution, considering its prognostic and therapeutic value. Moreover, we analyze how the response to endocrine and chemical therapies could be affected due to alternative splicing and differential expression of variant isoforms. With all this knowledge, it becomes clear that targeting alternative splicing represents an innovative approach for breast cancer therapeutics and the information derived from current studies could guide clinical decisions with a direct impact in the clinical advances for breast cancer patients nowadays.

MDM2 promotes epithelial-mesenchymal transition and metastasis of ovarian cancer SKOV3 cells

Background:

Metastasis accounts for the most lethal reason for the death of ovarian cancer patients, but remains largely untreated. Epithelial–mesenchymal transition (EMT) is critical for the conversion of early-stage ovarian tumours into metastatic malignancies. Thus the exploration of the signalling pathways promoting EMT would open potential opportunities for the treatment of metastatic ovarian cancer. Herein, the putative role of MDM2 in regulating EMT and metastasis of ovarian cancer SKOV3 cells was investigated.

Methods:

The regulatory effects by MDM2 on cell motility was emulated by wound-healing and transwell assays. The effects on EMT transition and Smad pathway were studied by depicting the expression levels of epithelial marker E-cadherin as well as key components of Smad pathway. To evaluate the clinical relevance of our findings, the correlation of MDM2 expression levels with the stages of 104 ovarian cancer patients was investigated by immunohistochemistry assay.

Results:

We demonstrate that MDM2 functions as a key factor to drive EMT and motility of ovarian SKOV3 cells, by facilitating the activation of TGF-β-Smad pathway, which results in the increased transcription of snail/slug and the subsequent loss of E-cadherin levels. Such induction of EMT is sustained in either E3 ligase-depleted MDM2 or E3 ligase inhibitor HLI-373-treated cells, while being impaired by the N-terminal deletion of MDM2, which is also reflected by the inhibitory effects against EMT by Nutlin-3a, the N-terminal targeting agent. The expression levels of MDM2 is highly correlated with the stages of the ovarian cancer patients, and the higher expression of MDM2 together with TGFB are closely correlated with poor prognosis and predict a high risk of ovarian cancer patients.

Conclusions:

This study suggests that MDM2 activates Smad pathway to promote EMT in ovarian cancer metastasis, and targeting the N-terminal of MDM2 can reprogram EMT and impede the mobility of cancer cells.

Stabilization of the p53-DNA Complex by the Nuclear Protein Dmp1α

We recently reported the existence of a physical interaction between the Myb-like transcription factor Dmp1 (Dmtf1) and p53 in which Dmp1 antagonized polyubiquitination of p53 by Mdm2 and promoted its nuclear localization. Dmp1 significantly stabilized p53-DNA complexes on promoters that contained p53-consensus sequences, which were either supershifted or disrupted with antibodies to Dmp1. Lysates from mice injected with doxorubicin showed that Dmp1 bound to p21Cip1, Bbc3, and Thbs1 gene regulatory regions in a p53-dependent fashion. Our data suggest that acceleration of DNA-binding of p53 by Dmp1 is a critical process for Dmp1 to increase the p53 function in Arf-deficient cells.

From General Aberrant Alternative Splicing in Cancers and Its Therapeutic Application to the Discovery of an Oncogenic DMTF1 Isoform

Alternative pre-mRNA splicing is a crucial process that allows the generation of diversified RNA and protein products from a multi-exon gene. In tumor cells, this mechanism can facilitate cancer development and progression through both creating oncogenic isoforms and reducing the expression of normal or controllable protein species. We recently demonstrated that an alternative cyclin D-binding myb-like transcription factor 1 (DMTF1) pre-mRNA splicing isoform, DMTF1β, is increasingly expressed in breast cancer and promotes mammary tumorigenesis in a transgenic mouse model. Aberrant pre-mRNA splicing is a typical event occurring for many cancer-related functional proteins. In this review, we introduce general aberrant pre-mRNA splicing in cancers and discuss its therapeutic application using our recent discovery of the oncogenic DMTF1 isoform as an example. We also summarize new insights in designing novel targeting strategies of cancer therapies based on the understanding of deregulated pre-mRNA splicing mechanisms.

Oncogenic and tumor-suppressive mouse models for breast cancer engaging HER2/neu

The human c-ErbB2 (HER2) gene is amplified in ∼20% of human breast cancers (BCs), but the protein is overexpressed in ∼30% of the cases indicating that multiple different mechanisms contribute to HER2 overexpression in tumors. It has long been used as a molecular marker of BC for subcategorization for the prediction of prognosis and determination of therapeutic strategies. In comparison to ER(+) BCs, HER2-positive BCs are more invasive, but the patients respond to monoclonal antibody therapy with trastuzumab or tyrosine kinase inhibitors at least at early stages. To understand the pathophysiology of HER2-driven carcinogenesis and test HER2-targeting therapeutic agents in vivo, numerous mouse models have been created that faithfully reproduce HER2(+) BCs in mice. They include MMTV-neu (active mutant or wild type, rat neu or HER2) models, neu promoter-driven neuNT-transgenic mice, neuNT-knock-in mice at the neu locus and doxycycline-inducible neuNT-transgenic models. HER2/neu activates the Phosphatidylinositol-3 kinase-AKT-NF-κB pathway to stimulate the mitogenic cyclin D1/Cdk4-Rb-E2F pathway. Of note, overexpression of HER2 also stimulates the cell autonomous Dmp1-Arf-p53 tumor suppressor pathway to quench oncogenic signals to prevent the emergence of cancer cells. Hence tumor development by MMTV-neu mice was dramatically accelerated in mice that lack Dmp1, Arf or p53 with invasion and metastasis. Expressions of neuNT under the endogenous promoter underwent gene amplification, closely recapitulating human HER2(+) BCs. MMTV-HER2 models have been shown to be useful to test humanized monoclonal antibodies to HER2. These mouse models will be useful for the screening of novel therapeutic agents against BCs with HER2 overexpression.

Clinical applications of mouse models for breast cancer engaging HER2/neu

Human c-ErbB2 (HER2) has long been used as a marker of breast cancer (BC) for sub-categorization for the prediction of prognosis, and determination of therapeutic strategies. HER2 overexpressing BCs are more invasive/metastatic; but patients respond to monoclonal antibody therapy with trastuzumab or tyrosine kinase inhibitors, at least at early stages. To date, numerous mouse models that faithfully reproduce HER2(+) BCs have been created in mice. We recently reviewed different mouse models of BC overexpressing wild type or mutant neu driven by MMTV, neu, or doxycycline-inducible promoters. These mice have been used to demonstrate the histopathology, oncogenic signaling pathways initiated by aberrant overexpression of HER2 in the mammary epithelium, and interaction between oncogenes and tumor suppressor genes at molecular levels. In this review, we focus on their clinical applications. They can be used to test the efficacy of HER(2) inhibitors before starting clinical trials, characterize the tumor-initiating cells that could be the cause of relapse after therapy as well as to analyze the molecular mechanisms of therapeutic resistance targeting HER2. MMTV-human ErbB2 (HER2) mouse models have recently been established since the monoclonal antibody to HER2 (trastuzumab; Herceptin®) does not recognize the rat neu protein. It has been reported that early intervention with HER2 monoclonal antibody would be beneficial for preventing mammary carcinogenesis. MDA-7/IL-24 as well as naturally-occurring chemicals have also been tested using MMTV-neu models. Recent studies have shown that MMTV-neu models are useful to develop vaccines to HER2 for immunotherapy. The mouse models employing HER2/neu will be essential for future antibody or drug screenings to overcome resistance to trastuzumab or HER(2)-specific tyrosine kinase inhibitors.

Novel Molecular Markers for Breast Cancer

The use of molecular biomarkers assures that breast cancer (BC) patients receive optimal treatment. Established biomarkers, such as estrogen receptor, progesterone receptor, HER2, and Ki67, have been playing significant roles in the subcategorization of BC to predict the prognosis and decide the specific therapy to each patient. Antihormonal therapy using 4-hydroxytamoxifen or aromatase inhibitors have been employed in patients whose tumor cells express hormone receptors, while monoclonal antibody to HER2 has been administered to HER2-positive BCs. Although new therapeutic agents have been developed in the past few decades, many patients still die of the disease due to relapse; thus, novel molecular markers that predict therapeutic failure and those that can be targets for specific therapy are expected. We have chosen four of such molecules by reviewing recent publications, which are cyclin E, B-Myb, Twist, and DMP1β. The oncogenicity of these molecules has been demonstrated in vivo and/or in vitro through studies using transgenic mice or siRNAs, and their expressions have been shown to be associated with shortened overall or disease-free survival of BC patients. The former three molecules have been shown to accelerate epithelial-mesenchymal transition that is often associated with cancer stem cell-ness and metastasis; all these four can be novel therapeutic targets as well. Thus, large prospective studies employing immunohistochemistry will be needed to establish the predictive values of these molecules in patients with BC.