c-Myc Activity Research Articles

Iron-mediated oxidative stress induces PD-L1 expression via activation of c-Myc in lung adenocarcinoma.

Introduction: The PD-1/PD-L1 axis is hijacked by lung adenocarcinoma (LUAD) cells to escape immune surveillance. PD-L1 expression in LUAD is affected, among others, by the metabolic trafficking between tumor cells and the tumor microenvironment (TME). Methods: Correlation between PD-L1 expression and iron content within the TME was established on FFPE LUAD tissue samples. The effects of an iron rich microenvironment on PD-L1 mRNA and protein levels were assessed in vitro in H460 and A549 LUAD by using qPCR, western blot and flow citometry. c-Myc knockdown was performed to validate the role of this transcription factor on PD-L1 expression. The effects of iron-induced PD-L1 on T cell immune function was assessed by quantifying IFN-γ release in a co-colture system. TCGA dataset was used to analyse the correlation between PD-L1 and CD71 mRNA expression in LUAD patients. Results: In this study, we highlight a significant correlation between iron density within the TME and PD-L1 expression in 16 LUAD tissue specimens. In agreement, we show that a more pronounced innate iron-addicted phenotype, indicated by a higher transferrin receptor CD71 levels, significantly correlates with higher PD-L1 mRNA expression levels in LUAD dataset obtained from TCGA database. In vitro, we demonstrate that the addition of Fe3+ within the culture media promotes the significant overexpression of PD-L1 in A549 and H460 LUAD cells, through the modulation of its gene transcription mediated by c-Myc. The effects of iron lean on its redox activity since PD-L1 up-regulation is counteracted by treatment with the antioxidant compound trolox. When LUAD cells are co-cultured with CD3/CD28-stimulated T cells in an iron-rich culture condition, PD-L1 up-regulation causes the inhibition of T-lymphocytes activity, as demonstrated by the significant reduction of IFN-γ release. Discussion: Overall, in this study we demonstrate that iron abundance within the TME may enhance PD-L1 expression in LUAD and, thus, open the way for the identification of possible combinatorial strategies that take into account the iron levels within the TME to improve the outcomes of LUAD patients treated with anti-PD-1/PD-L1-based therapies.

MDB-24. A DATA-DRIVEN APPROACH FOR THE IDENTIFICATION OF NEW SYNERGISTIC DRUG COMBINATIONS AGAINST NEURAL CANCERS

Abstract High-risk medulloblastomas are tumours with a poor survival prognosis (≤ 50%), which are currently treated with radiation therapy and DNA-damaging chemotherapy. The severe side effects of these treatments, including developmental problems and secondary tumours, underscore the need for new treatments with reduced toxicity. An attractive target for such therapy is the Myc-family proteins since high-risk medulloblastomas amplify either N-Myc (SHH-MB, G4-MB) or c-Myc (G3-MB). While the proteins from the Myc family themselves are often referred to as pharmacologically intractable, their levels and activity can be modulated by indirect targeting, e.g. inhibition of proteins located upstream or downstream of c-Myc/N-Myc. The diverse cellular processes and pathways that c-Myc and N-Myc are involved in, however, suggest that several Myc pathways must be interrupted simultaneously to achieve a lasting effect. To identify such multimodal interventions against Myc, we performed a principal component analysis of RNA sequencing data from patient-derived medulloblastoma cells (MB002, G3, MYC-amplified) and DAOY cells (SHH-group, no MYC amplification) that were treated with 120 small molecules. In the subsequent analysis, we focused on a selection of ~ 40 genes that represent common upstream regulators and downstream targets of either c-Myc or N-Myc. Applying a principal component analysis to these particular markers, we expect that the drugs that affect different pathways associated with c-Myc activity and are located at the opposite ends of the PC1 and PC2 axis should have a synergistic effect. Additionally, we expected that the drugs located closer to each other, which affect closely related pathways, would either have no effect or would be antagonistic. Our PCA distribution method can be used to select synergistic combinations in a manner that is easily extended to new compounds. This approach may allow fast screening of compounds for estimation of the treatment effect.

Tg(Δ113p53:cmyc) Transgene Upregulates glut1 Expression to Promote Zebrafish Heart Regeneration.

The heart switches its main metabolic substrate from glucose to fatty acids shortly after birth, which is one of reasons for the loss of heart regeneration capability in adult mammals. On the contrary, metabolic shifts from oxidative phosphorylation to glucose metabolism promote cardiomyocyte (CM) proliferation after heart injury. However, how glucose transportation in CMs is regulated during heart regeneration is still not fully understood. In this report, we found that the expression of Glut1 (slc2a1) was upregulated around the injury site of zebrafish heart, accompanied by an increase in glucose uptake at the injury area. Knockout of slc2a1a impaired zebrafish heart regeneration. Our previous study has demonstrated that the expression of Δ113p53 is activated after heart injury and Δ113p53+ CMs undergo proliferation to contribute to zebrafish heart regeneration. Next, we used the Δ113p53 promoter to generate the Tg(Δ113p53:cmyc) zebrafish transgenic line. Conditional overexpression of cmyc not only significantly promoted zebrafish CM proliferation and heart regeneration but also significantly enhanced glut1 expression at the injury site. Inhibiting Glut1 diminished the increase in CM proliferation in Tg(Δ113p53:cmyc) injured hearts of zebrafish. Therefore, our results suggest that the activation of cmyc promotes heart regeneration through upregulating the expression of glut1 to speed up glucose transportation.

Abstract A008: Elucidating the effects of the Alzheimer's disease associated gene BIN1 on cancer tumorigenesis

Abstract Purpose- BIN1 is in deleted in ~5% of all prostate cancer (PC) patients and interestingly is highly enriched in the Speckle-type POZ protein (SPOP) mutant subclass (15%) of PC. BIN1 was originally identified as a repressor of cMYC activity and our lab has shown that patients with SPOPmut;MYChigh PC have worse clinical outcomes. Our observation of BIN1 deletion in the SPOP mutant subclass leads us to hypothesize that BIN1 deletion leads to enhanced AR signaling and more aggressive PC. Experimental Procedures- We analyzed baseline protein and mRNA levels of BIN1 in 13 PC cell lines via quantitative polymerase chain reaction (qPCR) and immunoblot. To understand the role of BIN1 in PC cells, we overexpressed BIN1 and evaluated changes in cell proliferation, migration, and AR target gene expression. To elucidate the role of BIN1 in vivo prostate development, we also generated a prostate-specific knockout of BIN1 and investigated changes in prostate development and AR signaling axis over time in this mouse model. Results- Our results show that none of the 13 PC cell lines analyzed had strong protein expression at baseline, but all had detectable mRNA levels. Interestingly, the three cell lines with the highest mRNA expression were AR negative (DU-145), AR independent (LN95) or castration resistant (MDVR). We also saw a decrease in downstream AR target genes (KLK3 and NKX3.1) measured using qPCR after BIN1 overexpression in 22Rv1 cells. We further corroborated this finding by measuring KLK3 expression using a KLK3-luc reporter assay after BIN1 overexpression. BIN1 overexpression also reduced invasive activity of 22Rv1 measured using a Matrigel invasion assay system. Since BIN1 deletion was enriched in SPOP mutant PC clinical data, we evaluated changes in cell proliferation in the wildtype and mutant SPOP cell lines with and without BIN1OE and found that BIN1OEhindered growth of SPOP mutant PC cells. Analysis of the TCGA primary PC dataset illustrate that PC patients harboring BIN1 deletion had higher AR activity compared to PC patients expressing wildtype BIN1. Importantly, mice with prostate specific BIN1 deletion had larger prostate mass at 2 months of age compared to age matched controls and several mice at the 6&9 month had severely enlarged prostates. Conclusion- Our findings show for the first time that BIN1 functions as an inhibitor of the AR signaling axis and deletion of BIN1 leads to higher levels of AR signaling. We also show that BIN1 deletion in mice affects prostate development and leads to enlarged prostates. These novel findings illustrate the clinical significance of BIN1 deletion in PC patients and highlights the AR-signaling axis as a potential target for PC patients with BIN1 deletion Citation Format: Collin McColl, Darlene Skapura, Elisa Echartea, Jenny Deng, Cristian Coarfa, Salma Kaochar, Brian Simons, Aleksandra Rusin. Elucidating the effects of the Alzheimer's disease associated gene BIN1 on cancer tumorigenesis [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A008.

Association between intra-tumoral microbiome and clinical benefit (CB) from immunotherapy (IO) in patients with metastatic renal cell carcinoma (mRCC).

4561 Background: Specific bacteria and microbial diversity in the gut may drive response to IO in patients (pts) with mRCC (Routy et al Science 2018; Salgia et al Eur Urol 2020). Despite the evidence of bacterial proliferation in RCC tumors (Heidler et al Urol Int 2020), the impact of the intra-tumoral microbiome in RCC has been poorly delineated. Here, we explored its association to CB in mRCC pts receiving IO-based regimens. Methods: We identified pts with mRCC and available RNA sequencing (RNA-seq) data from tumor tissue collected prior to start of IO.Intra-tumoral microbiome analysis was performed on formalin-fixed paraffin-embedded samples. Following quality and adapter trimming, RNA-seq reads were mapped to a human genome to filter host reads using the STAR alignment tool. Taxonomic classification was performed using Kraken2 and Bracken. Following removal of common contaminants, the relative abundances among all non-human species were calculated. Microbial diversity was assessed using the Shannon index and statistical analysis performed using a t-test. Relative microbial abundance was compared between tumors from pts with or without CB from 1st line IO treatment using the Kruskal-Wallis test. P-values less than 0.05 were considered significant. Results: A total of 96 pts (71:25, M:F) with mRCC were included in this analysis. Of these, 85 (89%) had clear cell histology and 68 (71%) were IMDC intermediate/poor risk. The median age at the time of tissue sampling was 62.7 yrs old and most of the samples analyzed (57%) were collected from the primary site. IO, alone or in combination, was received as 1st line treatment in 57 pts (59%), with the most common regimen being nivolumab/ipilimumab (47%). CB from 1st line IO was observed in 39 (68%) pts. Tumors from pts achieving CB from 1st line IO had elevated microbial diversity compared to tumors from pts without CB (p=0.01). Tumor samples from these pts also had a significantly higher relative abundance of several bacterial genera compared to tumors from pts without CB. These included Pasteurella, Escherichia, and Cloacibacterium (p<0.05). No significant differences in bacterial diversity were observed between CB and no-CB pts receiving IO as 2nd line or beyond. Conclusions: This is the largest study exploring the association between the intra-tumoral microbiome of mRCC and CB from IO. In line with gut microbiome studies, an increased intra-tumoral Shannon diversity index was also associated with CB to IO in our 1st line cohort, further suggesting that bacterial diversity could be a driver of response. Additionally, several genera associated with CB are particularly relevant. For instance, members of the Pasteurella genus have been implicated in the activation of c-myc, a proto-oncogene that has been shown to induce PD-L1 expression.

ATAD2 promotes glycolysis and tumor progression in clear cell renal cell carcinoma by regulating the transcriptional activity of c-Myc

Clear cell renal cell carcinoma (ccRCC) is a common malignant tumor of the urogenital tract. Given that ccRCC is often resistant to radiotherapy and traditional chemotherapy, the clinical treatment of patients with ccRCC remains a challenge. The present study found that ATAD2 was significantly upregulated in ccRCC tissues. In vitro and in vivo experiments showed that the inhibition of ATAD2 expression mitigated the aggressive phenotype of ccRCC. ATAD2 was also associated with glycolysis in ccRCC. Interestingly, we found that ATAD2 could physically interact with c-Myc and promote the expression of its downstream target gene, thereby enhancing the Warburg effect of ccRCC. Overall, our study emphasizes the role of ATAD2 in ccRCC. The targeted expression or functional regulation of ATAD2 could be a promising method to reduce the proliferation and progression of ccRCC.

Heat shock factor 1 (HSF1) specifically potentiates c-MYC-mediated transcription independently of the canonical heat shock response

Despite its pivotal roles in biology, how the transcriptional activity of c-MYC is tuned quantitatively remains poorly defined. Here, we show that heat shock factor 1 (HSF1), the master transcriptional regulator of the heat shock response, acts as a prime modifier of the c-MYC-mediated transcription. HSF1 deficiency diminishes c-MYC DNA binding and dampens its transcriptional activity genome wide. Mechanistically, c-MYC, MAX, and HSF1 assemble into a transcription factor complex on genomic DNAs, and surprisingly, the DNA binding of HSF1 is dispensable. Instead, HSF1 physically recruits the histone acetyltransferase general control nonderepressible 5 (GCN5), promoting histone acetylation and augmenting c-MYC transcriptional activity. Thus, we find that HSF1 specifically potentiates the c-MYC-mediated transcription, discrete from its canonical role in countering proteotoxic stress. Importantly, this mechanism of action engenders two distinct c-MYC activation states, primary and advanced, which may be important to accommodate diverse physiological and pathological conditions.

Targeting SMYD2 inhibits prostate cancer cell growth by regulating c-Myc signaling.

SMYD2 is a lysine histone methyl transferase involved in various cancers epigenetically via methylating histone H3K4, and H3K36. c-Myc is one of the major drivers ofprostate cancer (PCa) initiation and progression. The roles of SMYD2 in PCa and the regulators of c-Myc activity in PCa are still under-researched.SMYD2 expression and survival outcomes in PCa cohorts were analyzed by bioinformatics analysis. SMYD2 protein levels were detected in PCa tissues by immunohistochemistry. SMYD2 knockdown cells were established to identify the effects of SMYD2 on cell growth in vitro and in vivo. GSEA and RNA sequencing were adopted to reconnoiter the signaling regulated by SMYD2 in PCa. The relationship between SMYD2 and c-Myc was examined by western blot analysis, qPCR, and immunohistochemistry. SMYD2 specific inhibitor-AZ505 was used to pharmacologically inhibit SMYD2 function in vitro and in vivo.SMYD2 expression increased in PCa tissues compared with benign prostate tissues and higher SMYD2 expression was associated with a higher risk of biochemical relapse after radical prostatectomy. SMYD2 knockdown inhibited the growth of PCa cells both in vitro and in vivo. Furthermore, high SMYD2 levels conduced to activated c-Myc signaling in PCa cells. Importantly, the pharmacological intervention of SMYD2 by AZ505 significantly repressed PCa cell growth both in vitro and in vivo. Our findings indicate that SMYD2 inhibition restrains PCa cell proliferation by regulating c-Myc signaling and provide evidence for the potential practice of SMYD2 targeting in the treatment of PCa.

Targeting IGF1R signaling enhances the sensitivity of cisplatin by inhibiting proline and arginine metabolism in oesophageal squamous cell carcinoma under hypoxia

BackgroundCisplatin (DDP)-based chemotherapy is commonly adopted as the first-line treatment for patients with oesophageal squamous cell carcinoma (OSCC), but the high rate of drug resistance limits its clinical application and the underlying mechanisms at play remain unclear. The aims of this study were to elucidate the role of abnormal signal transmission and metabolism in the chemoresistance of OSCC under hypoxia and to identify targeted drugs that enhance the sensitivity of DDP chemotherapy.MethodsUpregulated genes in OSCC were determined by RNA sequencing (RNA-seq), the Cancer Genome Atlas (TCGA) database, immunohistochemistry (IHC), real-time quantitative PCR (RT-qPCR), and western blotting (WB). The clinicopathological significance of insulin-like growth factor-I receptor (IGF1R), argininosuccinate synthetase 1 (ASS1), and pyrroline-5-carboxylate reductase 1 (PYCR1) in OSCC was analysed using tissue micriarray (TMA). Metabolic abnormalities were determined by untargeted metabolomics analysis. The DDP-resistance role of IGF1R, ASS1, and PYCR1 in OSCC was investigated in vitro and in vivo.ResultsGenerally, tumour cells exist in a hypoxic microenvironment. By genomic profiling, we determined that IGF1R, as a receptor tyrosine kinase (RTK), was upregulated in OSCC under low-oxygen conditions. Clinically, enhanced IGF1R expression was associated with higher tumour stages and a poorer prognosis in OSCC patients, and its inhibitor, linsitinib, showed synergistic effects with DDP therapy in vivo and in vitro. Since oxygen-deprivation frequently lead to metabolic reprogramming, we further learned via metabolomics analysis that abnormal IGF1R pathways promoted the expression of metabolic enzymes ASS1 and PYCR1 by the transcriptional activity of c-MYC. In detail, enhanced expression of ASS1 promotes arginine metabolism for biological anabolism, whereas PYCR1 activates proline metabolism for redox balance, which maintains the proliferation ability of OSCC cells during DDP treatment under hypoxic conditions.ConclusionEnhanced expression of ASS1 and PYCR1 via IGF1R pathways rewired arginine and proline metabolism, promoting DDP resistance in OSCC under hypoxia. Linsitinib targeting IGF1R signaling may lead to promising combination therapy options for OSCC patients with DDP resistance.

The RNA helicase DDX3 and its role in c-MYC driven germinal center-derived B-cell lymphoma.

DDX3X is an RNA helicase with many functions in RNA metabolism such as mRNA translation, alternative pre-mRNA splicing and mRNA stability, but also plays a role as a regulator of transcription as well as in the Wnt/beta-catenin- and Nf-κB signaling pathways. The gene encoding DDX3X is located on the X-chromosome, but escapes X-inactivation. Hence females have two active copies and males only one. However, the Y chromosome contains the gene for the male DDX3 homologue, called DDX3Y, which has a very high sequence similarity and functional redundancy with DDX3X, but shows a more restricted protein expression pattern than DDX3X. High throughput sequencing of germinal center (GC)-derived B-cell malignancies such as Burkitt Lymphoma (BL) and Diffuse large B-cell lymphoma (DLBCL) samples showed a high frequency of loss-of-function (LOF) mutations in the DDX3X gene revealing several features that distinguish this gene from others. First, DDX3X mutations occur with high frequency particularly in those GC-derived B-cell lymphomas that also show translocations of the c-MYC proto-oncogene, which occurs in almost all BL and a subset of DLBCL. Second, DDX3X LOF mutations occur almost exclusively in males and is very rarely found in females. Third, mutations in the male homologue DDX3Y have never been found in any type of malignancy. Studies with human primary GC B cells from male donors showed that a loss of DDX3X function helps the initial process of B-cell lymphomagenesis by buffering the proteotoxic stress induced by c-MYC activation. However, full lymphomagenesis requires DDX3 activity since an upregulation of DDX3Y expression is invariably found in GC derived B-cell lymphoma with DDX3X LOF mutation. Other studies with male transgenic mice that lack Ddx3x, but constitutively express activated c-Myc transgenes in B cells and are therefore prone to develop B-cell malignancies, also showed upregulation of the DDX3Y protein expression during the process of lymphomagenesis. Since DDX3Y is not expressed in normal human cells, these data suggest that DDX3Y may represent a new cancer cell specific target to develop adjuvant therapies for male patients with BL and DLBCL and LOF mutations in the DDX3X gene.

Transcriptional Basis of Ca2+ Remodeling Reversal Induced by Polyamine Synthesis Inhibition in Colorectal Cancer Cells.

Colorectal cancer (CRC) is associated with mutations in APC/Wnt leading to c-myc activation and the overexpression of ODC1, the limiting step in polyamine synthesis. CRC cells also display a remodeling of intracellular Ca2+ homeostasis that contributes to cancer hallmarks. As polyamines may modulate Ca2+ homeostasis during epithelial tissue repair, we investigated whether polyamine synthesis inhibition may reverse Ca2+ remodeling in CRC cells and, if so, the molecular basis for this reversal. To this end, we used calcium imaging and transcriptomic analysis in normal and CRC cells treated with DFMO, an ODC1 suicide inhibitor. We found that polyamine synthesis inhibition partially reversed changes in Ca2+ homeostasis associated with CRC, including a decrease in resting Ca2+ and SOCE along with an increased Ca2+ store content. We also found that polyamine synthesis inhibition reversed transcriptomic changes in CRC cells without affecting normal cells. Specifically, DFMO treatment enhanced the transcription of SOCE modulators CRACR2A; ORMDL3; and SEPTINS 6, 7, 8, 9, and 11, whereas it decreased SPCA2, involved in store-independent Orai1 activation. Therefore, DFMO treatment probably decreased store-independent Ca2+ entry and enhanced SOCE control. Conversely, DFMO treatment decreased the transcription of the TRP channels TRPC1 and 5, TRPV6, and TRPP1 while increasing TRPP2, thus probably decreasing Ca2+ entry through TRP channels. Finally, DFMO treatment enhanced the transcription of the PMCA4 Ca2+ pump and mitochondrial channels MCU and VDAC3 for enhanced Ca2+ extrusion through the plasma membrane and mitochondria. Collectively, these findings suggested the critical role of polyamines in Ca2+ remodeling in colorectal cancer.

Fibroblast-derived Extracellular Vesicles Induce Lung Cancer Progression in the Idiopathic Pulmonary Fibrosis Microenvironment.

Idiopathic pulmonary fibrosis (IPF) is a progressive aging-related lung disease associated with increased lung cancer risk. Although previous studies have shown that IPF worsens the survival of patients with lung cancer, whether IPF independently affects cancer malignancy and prognosis remains inconclusive. Extracellular vesicles (EVs) have recently emerged as active carriers of molecular biomarkers and mediators of intercellular communication in lung homeostasis and pathogenesis. EV cargo-mediated fibroblast-tumor cell communication might participate in the development and progression of lung cancer by modulating various signaling pathways. In this study, we examined the impact of lung fibroblast (LF)-derived EVs on non-small cell lung cancer (NSCLC) malignancy in the IPF microenvironment. Here, we showed that LFs derived from patients with IPF have phenotypes of myofibroblast differentiation and cellular senescence. Furthermore, we found that IPF LF-derived EVs have markedly altered microRNA compositions and exert proproliferative functions on NSCLC cells. Mechanistically, the phenotype was attributed mainly to the enrichment of miR-19a in IPF LF-derived EVs. As a downstream signaling pathway, mir-19a in IPF LF-derived EVs regulates ZMYND11-mediated c-Myc activation in NSCLC, potentially contributing to the poor prognosis of patients with NSCLC with IPF. Our discoveries provide novel mechanistic insights for understanding lung cancer progression in the IPF microenvironment. Accordingly, blocking the secretion of IPF LF-derived EV miR-19a and their signaling pathways is a potential therapeutic strategy for managing IPF and lung cancer progression.

C-MYC-Induced AP4 Attenuates DREAM-Mediated Repression by p53

The deregulated expression of the c-MYC oncogene activates p53, which is presumably mediated by ARF/INK4, as well as replication-stress-induced DNA damage. Here, we aimed to determine whether the c-MYC-inducible AP4 transcription factor plays a role in this context using a genetic approach. We used a CRISPR/Cas9 approach to generate AP4- and/or p53-deficient derivatives of MCF-7 breast cancer cells harboring an ectopic, inducible c-MYC allele. Cell proliferation, senescence, DNA damage, and comprehensive RNA expression profiles were determined after activation of c-MYC. In addition, we analyzed the expression data from primary breast cancer samples. Loss of AP4 resulted in elevated levels of both spontaneous and c-MYC-induced DNA damage, senescence, and diminished cell proliferation. Deletion of p53 in AP4-deficient cells reverted senescence and proliferation defects without affecting DNA damage levels. RNA-Seq analyses showed that loss of AP4 enhanced repression of DREAM and E2F target genes after p53 activation by c-MYC. Depletion of p21 or the DREAM complex component LIN37 abrogated this effect. These p53-dependent effects were conserved on the level of clinical and gene expression associations found in primary breast cancer tumors. Our results establish AP4 as a pivotal factor at the crossroads of c-MYC, E2F, and p53 target gene regulation.

Epstein-Barr Virus Synergizes with BRD7 to Conquer c-Myc-Mediated Viral Latency Maintenance via Chromatin Remodeling.

Epstein-Barr virus (EBV) switches between latent and lytic phases in hosts, which is important in the development of related diseases. However, the underlying mechanism of controlling the viral biphasic life cycle and how EBV mediates this regulation remain largely unknown. This study identified bromodomain-containing protein 7 (BRD7) as a crucial host protein in EBV latent infection. Based on the chromatin immunoprecipitation (ChIP) sequencing of endogenous BRD7 in Burkitt lymphoma cells, we found that EBV drove BRD7 to regulate cellular and viral genomic loci, including the transcriptional activation of c-Myc, a recently reported regulator of EBV latency. Additionally, EBV-mediated BRD7 signals were enriched around the FUSE (far-upstream sequence element) site in chromosome 8 and the enhancer LOC108348026 in the lgH locus, which might activate the c-Myc alleles. Mechanically, EBV-encoded nuclear antigen 1 (EBNA1) bound to BRD7 and colocalized at promoter regions of the related genes, thus serving as cofactors for the maintenance of viral latency. Moreover, the disruption of BRD7 decreased the c-Myc expression, induced the BZLF1 expression, and reactivated the lytic cycle. Our findings reveal the unique role of BRD7 to synergize with EBV in maintaining the viral latency state via chromatin remodeling. This study paves the way for understanding the new molecular mechanism of EBV-induced chromatin remodeling and latent-lytic switch, providing novel therapeutic candidate targets for EBV persistent infection. IMPORTANCE When establishing persistent infection in most human hosts, EBV is usually latent. How the viral latency is maintained in cells remains largely unknown. c-Myc was recently reported to act as a controller of the lytic switch, while whether and how EBV regulates it remain to be explored. Here, we identified that BRD7 is involved in controlling EBV latency. We found that EBV-mediated BRD7 was enriched in both the normal promoter regions and the translocation alleles of c-Myc, and disruption of BRD7 decreased c-Myc expression to reactivate the lytic cycle. We also demonstrated that EBV-encoded EBNA1 bound to and regulated BRD7. Therefore, we reveal a novel mechanism by which EBV can regulate its infection state by coordinating with host BRD7 to target c-Myc. Our findings will help future therapeutic intervention strategies for EBV infection and pathogenesis.

B7-H6 enhances F-actin rearrangement by targeting c-MYC activation to promote medulloblastoma migration and invasion.

Medulloblastoma (MB) is children's most common primary malignant primitive neuro-ectodermal tumor. Group 3MB showed a higher propensity to metastasis, which is molecularly characterized by c-MYC gene amplification. The activation of c-MYC promotes the remodeling of the F-actin cytoskeleton to enhance metastasis. The B7 homologue 6 (B7-H6) is associated with the manifold essential hallmarks of tumorigenesis. In this study, we will explore whether B7-H6 regulates the reorganization of F-actin by elevating the c-MYC expression to promote metastasis. The Daoy cell line was used to act as the cell model of medulloblastoma. Small interfering RNA and the plasmid were used to downregulate and upregulate the expression of B7-H6 in Daoy cells. Transwell assays with/without the matrigel matrix were used to detect migration and invasion of Daoy cells. Western blots were used to detect the expression of related proteins. Immunofluorescence staining was used to observe the impact of B7-H6 on the c-MYC /F-actin axis. B7-H6 improved migration and invasion in the Daoy cell line. B7-H6 enhanced the rearrangement of F-actin and activated the expression of MMP-9 and MMP-2. B7-H6 promoted the remodeling of F-actin by targeting c-MYC activation to reinforce migration and invasion. B7-H6 acts as a promoter of migration and invasion in medulloblastoma by activating the c-MYC /F-actin axis.

The beneficial effects of chick embryo extract preconditioning on hair follicle stem cells: A promising strategy to generate Schwann cells.

The beneficial effects of hair follicle stem cells in different animal models of nervous system conditions have been extensively studied. While chick embryo extract (CEE) has been used as a growth medium supplement for these stem cells, this is the first study to show the effect of CEE on them. The rat hair follicle stem cells were isolated and supplemented with 10% fetal bovine serum plus 10% CEE. The migration rate, proliferative capacity and multipotency were evaluated along with morphometric alteration and differentiation direction. The proteome analysis of CEE content identified effective factors of CEE that probably regulate fate and function of stem cells. The CEE enhances the migration rate of stem cells from explanted bulges as well as their proliferation, likely due to activation of AP-1 and translationally controlled tumour protein (TCTP) by thioredoxin found in CEE. The increased length of outgrowth may be the result of cyclic AMP response element binding protein (CREB) phosphorylation triggered by active CamKII contained in CEE. Further, CEE supplementation upregulates the expression of vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor. The elevated expression of target genes and proteins may be due to CREB, AP-1 and c-Myc activation in these stem cells. Given the increased transcript levels of neurotrophins, VEGF, and the expression of PDGFR-α, S100B, MBP and SOX-10 protein, it is possible that CEE promotes the fate of these stem cells towards Schwann cells.

Squalene epoxidase/SQLE is a candidate target for treatment of colorectal cancers with p53 mutation and elevated c-MYC expression.

Elevated expression of c-MYC and inactivation of p53 represent two of the most common alterations in colorectal cancer (CRC). However, c-MYC and defective p53 are difficult to target therapeutically. Therefore, effectors downstream of both c-MYC and p53 may represent attractive, alternative targets for cancer treatment. In a bioinformatics screen we identified Squalene epoxidase/SQLE as a candidate therapeutic target that appeared to be especially relevant for cell survival in CRCs, which display elevated c-MYC expression and loss of p53 function. SQLE is a rate-limiting enzyme in the cholesterol synthesis. Here, we show that p53 supresses SQLE expression, cholesterol levels, and cell viability via the induction of miR-205, which directly targets SQLE. Furthermore, c-MYC induced SQLE expression directly and via its target gene AP4. The transcription factor AP4/TFAP4 directly induced SQLE expression and cholesterol levels, whereas inactivation of AP4 resulted in decreased SQLE expression and caused resistance to Terbinafine, an inhibitor of SQLE. Inhibition of SQLE decreased viability of CRC cells. This effect was enhanced in CRCs cells with p53 inactivation and/or enhanced c-MYC/AP4 expression. Altogether, our results demonstrate that SQLE represents a vulnerability for CRCs with p53 inactivation and elevated c-MYC activity.

Idasanutlin and Navitoclax Induce Synergistic Apoptotic Cell Death in T-Cell Acute Lymphoblastic Leukemia

We report here investigation of the combination of idasanutlin and navitoclax in the context of T-cell acute lymphoblastic leukemia (T-ALL), including detailed mechanistic characterization and in vivo patient derived xenograft results. T-ALL is an aggressive hematologic malignancy with a five-year event-free survival rate that declines with age, ranging from 70-75% for pediatric patients to 21.7% for patients aged 60-79. An unmet clinical need remains for the development of better therapies for T-ALL. Notch pathway activation mutations are present in the majority of T-ALL and are thought to induce transformation, in part, through activation of c-Myc. Typically, increased expression of c-Myc induces apoptosis through the p19(ARF)-Mdm2-p53 tumor suppressor pathway. Unsurprisingly, over 70% of T-ALL cases have inactivating mutations in CDKN2A (p19Arf). However, and critical to our approach, greater than 95% of primary T-ALL cases and 75% of relapsed cases maintain wild type p53. Based on these genetic data, we hypothesized that treatment with MDM2 inhibitors, by bypassing the loss of ARF, would increase p53 expression and lead to T-ALL cell apoptosis. To test this hypothesis, we initially treated T-ALL patient derived xenograft (PDX) lines in vitro with single-agent idasanutlin (a second generation MDM2 inhibitor) and observed upregulation of pro-apoptotic p53 target genes Bax and Puma1. However, only modest T-ALL cell apoptosis was observed in response to MDM2 inhibition alone. Based on these observations, particularly the induction of pro-apoptotic p53 targets, we hypothesized that inhibition of pro-survival BH3 domain proteins would synergize with MDM2 inhibition to kill T-ALL cells. Of note, a prior study showed that most T-ALL (~62%) respond to treatment with navitoclax (ABT-263), an inhibitor of BCL2, BCLXL, and BCLW, although most responses were transient and dose-limiting thrombocytopenia was observed. Combination therapy with idasanutlin could permit on-target inhibition with tolerable dosing. In vitro treatment of a panel of 5 different PDX lines derived from pediatric and adult T-ALL with dual idasanutlin and navitoclax led to robust cell death in all lines. In addition, treatment of a T-ALL PDX line with a matrix of dose combinations showed strong evidence of synergic activity. Synergy was assessed by ZIP (zero interaction potency) score, a statistical method developed by B Yadav et al. (Comput. Struct. Biotechnol. J. 2015) that compares the change in potency of individual dose response curves in the presence of a second agent. Generally, a ZIP score greater than 5 is considered significant; Idasanutlin and navitoclax combination therapy had a global ZIP score=16-18, with the most synergic dose area ZIP score=40-52. Combined treatment resulted in marked apoptosis, with strong induction of pro-apoptotic p53 targets, including PUMA and BAX. Finally, we assessed the in vivo response of four different T-ALL xenografts to dual treatment. In each case, human T-ALL cells were injected into immunodeficient NSG mice and randomized into treatment groups. Monotherapy with idasanutlin or navitoclax resulted in a modest but significant decrease in T-ALL burden in all cases, with the exception of an ETP T-ALL, which was resistant to idasanutlin monotherapy. A marked response to combination treatment with idasanutlin and navitoclax was seen in all four T-ALL xenografts. Specifically, the combination was found to be synergistic in each case based on a modified Bliss Independence test, analyzing average daily change in tumor burden for synergy interaction. Furthermore, overall survival was significantly increased in the combination treatment group. These data suggest that the rational combination of idasanutlin and navitoclax is highly active, with induction of an apoptotic cell death in T-ALL. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Disulfiram/Copper Suppresses Cancer Stem Cell Activity in Differentiated Thyroid Cancer Cells by Inhibiting BMI1 Expression.

Differentiated thyroid carcinomas (DTCs), which have papillary and follicular types, are common endocrine malignancies worldwide. Cancer stem cells (CSCs) are a particular type of cancer cells within bulk tumors involved in cancer initiation, drug resistance, and metastasis. Cells with high intracellular aldehyde hydrogenase (ALDH) activity are a population of CSCs in DTCs. Disulfiram (DSF), an ALDH inhibitor used for the treatment of alcoholism, reportedly targets CSCs in various cancers when combined with copper. This study reported for the first time that DSF/copper can inhibit the proliferation of papillary and follicular DTC lines. DSF/copper suppressed thyrosphere formation, indicating the inhibition of CSC activity. Molecular mechanisms of DSF/copper involved downregulating the expression of B lymphoma Mo-MLV insertion region 1 homolog (BMI1) and cell cycle-related proteins, including cyclin B2, cyclin-dependent kinase (CDK) 2, and CDK4, in a dose-dependent manner. BMI1 overexpression diminished the inhibitory effect of DSF/copper in the thyrosphere formation of DTC cells. BMI1 knockdown by RNA interference in DTC cells also suppressed the self-renewal capability. DSF/copper could inhibit the nuclear localization and transcriptional activity of c-Myc and the binding of E2F1 to the BMI1 promoter. Overexpression of c-Myc or E2F1 further abolished the inhibitory effect of DSF/copper on BMI1 expression, suggesting that the suppression of c-Myc and E2F1 by DSF/copper was involved in the downregulation of BMI1 expression. In conclusion, DSF/copper targets CSCs in DTCs by inhibiting c-Myc- or E2F1-mediated BMI1 expression. Therefore, DSF is a potential therapeutic agent for future therapy in DTCs.

Proviral ALV-LTR Sequence Is Essential for Continued Proliferation of the ALV-Transformed B Cell Line.

Avian leukosis virus (ALV) induces B-cell lymphomas and other malignancies in chickens through insertional activation of oncogenes, and c-myc activation has been commonly identified in ALV-induced tumors. Using ALV-transformed B-lymphoma-derived HP45 cell line, we applied in situ CRISPR-Cas9 editing of integrated proviral long terminal repeat (LTR) to examine the effects on gene expression and cell proliferation. Targeted deletion of LTR resulted in significant reduction in expression of a number of LTR-regulated genes including c-myc. LTR deletion also induced apoptosis of HP45 cells, affecting their proliferation, demonstrating the significance of LTR-mediated regulation of critical genes. Compared to the global effects on expression and functions of multiple genes in LTR-deleted cells, deletion of c-myc had a major effect on the HP45 cells proliferation with the phenotype similar to the LTR deletion, demonstrating the significance of c-myc expression in ALV-induced lymphomagenesis. Overall, our studies have not only shown the potential of targeted editing of the LTR for the global inhibition of retrovirus-induced transformation, but also have provided insights into the roles of LTR-regulated genes in ALV-induced neoplastic transformation.