c-Myc Transcriptional Activity Research Articles

Wnt/IL-1β/IL-8 autocrine circuitries control chemoresistance in mesothelioma initiating cells by inducing ABCB5.

Malignant pleural mesothelioma (MPM) is a tumor with high chemoresistance and poor prognosis. MPM-initiating cells (ICs) are known to be drug resistant, but it is unknown if and how stemness-related pathways determine chemoresistance. Moreover, there are no predictive markers of IC-associated chemoresistance. Aim of this work is to clarify if and by which mechanisms the chemoresistant phenotype of MPM IC was due to specific stemness-related pathways. We generated MPM IC from primary MPM samples and compared the gene expression and chemo-sensitivity profile of IC and differentiated/adherent cells (AC) of the same patient. Compared to AC, IC had upregulated the drug efflux transporter ABCB5 that determined resistance to cisplatin and pemetrexed. ABCB5-knocked-out (KO) IC clones were resensitized to the drugs in vitro and in patient-derived xenografts. ABCB5 was transcriptionally activated by the Wnt/GSK3β/β-catenin/c-myc axis that also increased IL-8 and IL-1β production. IL-8 and IL-1β-KO IC clones reduced the c-myc-driven transcription of ABCB5 and reacquired chemosensitivity. ABCB5-KO clones had lower IL-8 and IL-1β secretion, and c-myc transcriptional activity, suggesting that either Wnt/GSK3β/β-catenin and IL-8/IL-1β signaling drive c-myc-mediated transcription of ABCB5. ABCB5 correlated with lower time-to-progression and overall survival in MPM patients treated with cisplatin and pemetrexed. Our work identified multiple autocrine loops linking stemness pathways and resistance to cisplatin and pemetrexed in MPM IC. ABCB5 may represent a new target to chemosensitize MPM IC and a potential biomarker to predict the response to the first-line chemotherapy in MPM patients.

Zinc-finger protein YY1 suppresses tumor growth of human nasopharyngeal carcinoma by inactivating c-Myc–mediated microRNA-141 transcription

Yin Yang 1 (YY1) is a zinc-finger protein that plays critical roles in various biological processes by interacting with DNA and numerous protein partners. YY1 has been reported to play dual biological functions as either an oncogene or tumor suppressor in the development and progression of multiple cancers, but its role in human nasopharyngeal carcinoma (NPC) has not yet been revealed. In this study, we found that YY1 overexpression significantly inhibits cell proliferation and cell-cycle progression from G1 to S and promotes apoptosis in NPC cells. Moreover, we identified YY1 as a component of the c-Myc complex and observed that ectopic expression of YY1 inhibits c-Myc transcriptional activity, as well as the promoter activity and expression of the c-Myc target gene microRNA-141 (miR-141). Furthermore, restoring miR-141 expression could at least partially reverse the inhibitory effect of YY1 on cell proliferation and tumor growth and on the expression of some critical c-Myc targets, such as PTEN/AKT pathway components both in vitro and in vivo We also found that YY1 expression is reduced in NPC tissues, negatively correlates with miR-141 expression and clinical stages in NPC patients, and positively correlates with survival prognosis. Our results reveal a previously unappreciated mechanism in which the YY1/c-Myc/miR-141 axis plays a critical role in NPC progression and may provide some potential and valuable targets for the diagnosis and treatment of NPC.

SPAG5 upregulation contributes to enhanced c-MYC transcriptional activity via interaction with c-MYC binding protein in triple-negative breast cancer

BackgroundTriple-negative breast cancer (TNBC) is an aggressive breast cancer subtype that lacks effective therapeutic targets. Sperm-associated antigen 5 (SPAG5) is a mitotic spindle-associated protein that is involved in various biological processes in cervical cancer and bladder urothelial carcinoma. However, the role of SPAG5 in TNBC remains undefined.MethodsThe expression of SPAG5 was examined in TNBC patients via quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and immunohistochemistry (IHC). The biological functions of SPAG5 in TNBC and the underlying mechanisms were investigated in vitro and in vivo.ResultsSPAG5 expression was significantly upregulated in TNBC tissues compared with that in paired adjacent noncancerous tissues (ANTs). High SPAG5 expression was associated with increased lymph node metastasis and high risk of local recurrence. SPAG5 protein expression was significantly associated with poor disease-free survival in TNBC. Gene set enrichment analysis of TNBC data from The Cancer Genome Atlas (TCGA) indicated that high SPAG5 expression was significantly associated with cell cycle and the ATR-BRCA pathway. Functional assays demonstrated that SPAG5 expression promoted tumor growth in vitro and in vivo. In addition, SPAG5-silenced cells were more sensitive to the PARP inhibitor (PARPi) olaparib. Mechanistically, SPAG5 interacted with c-MYC binding protein (MYCBP), thereby increasing MYCBP protein levels and leading to increased c-MYC transcriptional activity, which promoted the expression of the c-MYC target genes: CDC20, CDC25C, BRCA1, BRCA2, and RAD51.Knockdown of MYCBP or c-MYC abolished the SPAG5-induced cell-cycle progression and cell proliferation of TNBC.ConclusionsCollectively, our results indict that SPAG5 is an efficient prognostic factor in TNBC, and that SPAG5 knockdown increases the sensitivity of TNBC to the PARPi olaparib. SPAG5 promotes tumor growth and DNA repair by increasing c-MYC transcriptional activity via interaction with MYCBP. The SPAG5/MYCBP/c-MYC axis may represent a potential therapeutic target for TNBC treatment.

Effect of resveratrol on Sertoli cell proliferation.

Resveratrol (RSV), a polyphenolic compound largely found in red grape skin, has been used as a nutritional supplement as it exhibits beneficial health effects, such as anticancer, cardioprotective, antiaging, and anti-inflammatory. Particularly, it has been shown that it participates in the mechanisms involved in cell proliferation. Sirtuin 1 (SIRT1) is considered a well-known RSV effector. Noteworthy, Sirt1-knockout animals are infertile. The aim of this study was, first, to determine whether RSV has any effect on Sertoli cell proliferation and, second, whether SIRT1, a putative target of RSV, is present in immature Sertoli cells. Sertoli cell cultures obtained from 8-day-old rats, which actively proliferate, were treated with RSV (10 and 50 µM) under basal and follicle-stimulating hormone (FSH)-stimulated conditions. Bromodeoxyuridine (BrdU) incorporation and the expression of cyclins D1, D2, D3, E1, and E2 and the Cip/Kip cell cycle inhibitors p21Cip and p27Kip were analyzed. RSV decreased BrdU incorporation and cyclins D1, D2, E1, and E2 expression and increased p21Cip and p27Kip messenger RNA (mRNA) levels. RSV also decreased FSH-stimulated BrdU incorporation and cyclins D1 and D2 mRNA levels. The effect of RSV on cMYC was also analyzed. RSV treatment did not modify basal and FSH-stimulated cMyc expression; however, it inhibited basal and FSH-stimulated cMYC transcriptional activity, suggesting a role of cMYC in RSV effects. Additionally, Sirt1 was detected in immature Sertoli cells. Altogether, these results suggest that RSV possibly, by activating SIRT1 and regulating cMYC transcriptional activity, participates in the regulation of immature Sertoli cell proliferation.

HIF involvement in the regulation of rat Sertoli cell proliferation by FSH

The final number of Sertoli cells reached during the proliferative periods determines sperm production capacity in adulthood. It is well known that FSH increases the rate of proliferation of Sertoli cells; however, little is known about the transcription factors that are activated by the hormone in order to regulate Sertoli cell proliferation. On the other hand, Hypoxia Inducible Factors (HIFs) are master regulators of cell growth. HIFs are dimers of HIF-β and HIF-α subunits. Considering that HIF-β is constitutively expressed, HIF transcriptional activity is regulated through the abundance of HIF-α subunits. To date, three HIF-α isoforms have been described. The association of the different HIF-α subunits with HIF-β subunit constitutes three active transcription factors —HIF-1, HIF-2 and HIF-3— which interact with consensus hypoxia-response elements in the promoter region of target genes. Hypoxia has been classically considered the main stimulus that increases HIF transcriptional activity, however, regulation by hormones under normoxic conditions was also demonstrated. The aim of this work has been to investigate whether HIFs participate in the regulation of rat Sertoli cell proliferation by FSH. Sertoli cells obtained from 8-day old rats were cultured in the absence or presence of FSH. It has been observed that FSH increases HIF transcriptional activity and HIF-2α mRNA levels without modifying either HIF-1α or HIF-3α expression. Incubations with FSH have been also performed in the absence or presence of a pharmacological agent that promotes HIF-α subunit degradation, LW6. It has been observed that LW6 inhibits the FSH effect on proliferation, CCND1 expression and c-Myc transcriptional activity. Altogether, these results suggest that HIFs might be involved in the regulation of Sertoli cell proliferation by FSH.

Inhibition of Glycolysis in Prostate Cancer Chemoprevention by Phenethyl Isothiocyanate.

We have shown previously that dietary administration of phenethyl isothiocyanate (PEITC), a small molecule from edible cruciferous vegetables, significantly decreases the incidence of poorly differentiated prostate cancer in Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) mice without any side effects. In this study, we investigated the role of c-Myc-regulated glycolysis in prostate cancer chemoprevention by PEITC. Exposure of LNCaP (androgen-responsive) and 22Rv1 (castration-resistant) human prostate cancer cells to PEITC resulted in suppression of expression as well as transcriptional activity of c-Myc. Prostate cancer cell growth inhibition by PEITC was significantly attenuated by stable overexpression of c-Myc. Analysis of the RNA-Seq data from The Cancer Genome Atlas indicated a significant positive association between Myc expression and gene expression of many glycolysis-related genes, including hexokinase II and lactate dehydrogenase A Expression of these enzyme proteins and lactate levels were decreased upon PEITC treatment in prostate cancer cells, and these effects were significantly attenuated by ectopic expression of c-Myc. A normal prostate stromal cell line (PrSC) was resistant to lactic acid suppression by PEITC treatment. Prostate cancer chemoprevention by PEITC in TRAMP mice was associated with a significant decrease in plasma lactate and pyruvate levels. However, a 1-week intervention with 10 mg PEITC (orally, 4 times/day) was not sufficient to decrease lactate levels in the serum of human subjects. These results indicated that although prostate cancer prevention by PEITC in TRAMP mice was associated with suppression of glycolysis, longer than 1-week intervention might be necessary to observe such an effect in human subjects. Cancer Prev Res; 11(6); 337-46. ©2018 AACR.

Regulation of c-MYC transcriptional activity by transforming growth factor-beta 1-stimulated clone 22.

c‐MYC stimulates cell proliferation through the suppression of cyclin‐dependent kinase (CDK) inhibitors including P15 (CDKN2B) and P21 (CDKN1A). It also activates E‐box‐mediated transcription of various target genes including telomerase reverse transcriptase (TERT) that is involved in cellular immortality and tumorigenesis. Transforming growth factor‐beta 1 (TGF‐β1)‐stimulated clone 22 (TSC‐22/TSC22D1) encodes a highly conserved leucine zipper protein that is induced by various stimuli, including TGF‐β. TSC‐22 inhibits cell growth in mammalian cells and in Xenopus embryos. However, underlying mechanisms of growth inhibition by TSC‐22 remain unclear. Here, we show that TSC‐22 physically interacts with c‐MYC to inhibit the recruitment of c‐MYC on the P15 (CDKN2B) and P21 (CDKN1A) promoters, effectively inhibiting c‐MYC‐mediated suppression of P15 (CDKN2B) and also P21 (CDKN1A) promoter activities. In contrast, TSC‐22 enhances c‐MYC‐mediated activation of the TERT promoter. Additionally, the expression of TSC‐22 in embryonic stem cells inhibits cell growth without affecting its pluripotency‐related gene expression. These results indicate that TSC‐22 differentially regulates c‐MYC‐mediated transcriptional activity to regulate cell proliferation.

Abstract 5795: Functional and mechanistic interrogation of BET Bromodomain degraders for the treatment of metastatic castration resistant prostate cancer

Abstract Metastatic castration-resistant prostate cancer (mCRPC), a lethal disease primarily driven by androgen receptor (AR) signaling, results in approximately 30,000 annual deaths in the U.S. While the AR is necessary for the function, survival, and differentiation of normal prostatic tissue, AR function and signaling shift from tumor suppressive to tumor promoting during prostate carcinogenesis. Surgical or chemical castration targeting the AR signaling axis has been the mainstay of prostate cancer (PCa) treatment. Unfortunately, despite castration, PCa will inevitably progress into castration resistant prostate cancer (CRPC) in which AR remains an important oncogene. Current CRPC therapeutics, such as second-generation AR antagonists, elicit only temporary responses and patients eventually succumb to the disease. Therefore, new therapeutics against the AR axis in CRPC are urgently needed. One such novel strategy for targeting the AR-pathway and inhibiting the growth of CRPC has been the use of bromodomain and extraterminal (BET) protein inhibitors such a JQ1, which disrupt AR and oncogenic c-MYC transcriptional activity. While BET inhibitors may seem to be attractive candidate drugs for clinical translation, their off-target effects, such as binding to other proteins, toxicity, and the rapid development of treatment resistance, limit their translation. However, a new class of molecules that target BET proteins through proteasomal degradation can improve efficacy and specificity over standard inhibitors. Based on our preliminary findings, we have hypothesized that pharmacologic BET degradation represents an important advance in CRPC treatment and may provide a novel therapeutic strategy that can enhance efficacy and disrupt resistance to AR-targeted therapy. Utilizing prostate cancer cell lines, organoids, and patient derived xenografts, we performed RNA-seq, ChIP-seq, and proteomic studies to assay the effects of BET inhibitors and degrader compounds in preclinical models. These inhibitors affected AR-positive prostate cancer cells preferentially over AR-negative cells, and proteomic and genomic mechanistic studies confirmed the disruption of oncogenic AR and MYC signaling both in vivo and in vitro. In conclusion, we are developing highly potent, small molecules that lead to the proteasomal-degradation of BET proteins. With optimized in vivo properties, BET degraders promise to be a novel potential therapeutic strategy for patients with mCRPC. Citation Format: Steven Kregel, Rohit Malik, Irfan A. Asangani, Ester Fernandez-Salas, Kari Wilder-Romans, Xia Jiang, Thekkelnaycke Rajendiran, Xuhong Cao, Corey Speers, Shaomeng Wang, Arul M. Chinnaiyan. Functional and mechanistic interrogation of BET Bromodomain degraders for the treatment of metastatic castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5795.

Abstract 1470: Fine-tuning the expression of heterogeneous network of genes involved in androgen signaling, aerobic glycolysis, apoptosis and epithelial-mesenchymal transition by microRNA-644a in prostate cancer potentiation of AR signaling therapy by miR-644a: Selective manipulation of the prostate cancer transcriptome by miR-644a

Abstract Intratumoral Prostate cancer (PCa) heterogeneity is characterized by multiple intrinsic mechanisms including Androgen signaling, aerobic glycolysis, aberrant transcriptional activation of c-Myc and dysregulation of miRNAs. The ability of prostate cancer cells to alter growth and metabolism in a manner distinct from benign cells is a major concern in the treatment of castration-resistant prostate cancer. Therefore, targeting the diverse oncogenesis promoting pathways involved in PCa progression and resistance at the posttranscriptional level using micro RNAs (miRNAs) offers a novel therapeutic option. Using a miRNA mimic screen, we identified a human-specific miRNA miR-644a, which modulates expression of a diverse set of oncogenic pathways in PCa including androgen signaling, AKT/IGF-1R signaling, c-myc mediated signaling and EMT pathways. We have also demonstrated a potent tumor suppressive function of miR-644a in mouse prostate cancer xenograft model. miR-644a also sensitizes the PCa tumors to current therapeutic options including AR antagonist Enzalutamide by regulating the key modulators in development of drug resistance. In conclusion, our study demonstrates that miR-644a is a novel tumor suppressor miRNA regulating key prostate carcinogenesis promoting pathways. Citation Format: Jey Sabith Ebron, Jagjit Singh, Eswar Shankar, Crystal Weyman, Sanjay Gupta, Daniel J. Lindner, Girish C. Shukla. Fine-tuning the expression of heterogeneous network of genes involved in androgen signaling, aerobic glycolysis, apoptosis and epithelial-mesenchymal transition by microRNA-644a in prostate cancer potentiation of AR signaling therapy by miR-644a: Selective manipulation of the prostate cancer transcriptome by miR-644a [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1470. doi:10.1158/1538-7445.AM2017-1470

The secreted protein WNT5A regulates condylar chondrocyte proliferation, hypertrophy and migration

ObjectiveOur previous study showed that WNT5A, a member of the noncanonical WNT pathway, is involved in interleukin-1beta induced matrix metalloproteinase expression in temporomandibular joint (TMJ) condylar chondrocytes. The purpose of this study is to further explore the roles of WNT5A in cartilage biology of the TMJ. MethodsAn early TMJ osteoarthritis-like rat model was constructed by a mechanical method (steady mouth-opening). The gene and protein levels of WNT5A during the condylar cartilage changes were measured. Effects of WNT5A on chondrocyte proliferation, hypertrophy and migration were analyzed after WNT5A gain or loss of function in vitro. A c-Jun N-terminal kinase (JNK) inhibitor SP600125 was used to evaluate the involvement of JNK pathway in these effects of WNT5A. The expression and transcription activity of cell cycle regulators c-MYC and Cyclin D1 were examined to determine the mechanism behind WNT5A regulation of chondrocyte proliferation. ResultsWNT5A was significantly upregulated in the condylar cartilage of rats in the early TMJ osteoarthritis-like model. Activating WNT5A facilitated condylar chondrocyte proliferation, hypertrophy and migration. Conversely, inhibiting WNT5A activity in chondrocytes decreased their proliferation, hypertrophy and migration. Blockage of the JNK pathway by its inhibitor, SP600125, impaired these effects of WNT5A on chondrocytes. WNT5A regulated both the expression and transcriptional activity of c-MYC and Cyclin D1 in chondrocytes, both of which were upregulated in condylar cartilage of the rat early TMJ osteoarthritis. ConclusionWNT5A regulates condylar chondrocyte proliferation, hypertrophy and migration. These findings provide new insights into the role of WNT5A signaling in TMJ cartilage biology and its potential in future therapy for TMJ degenerative diseases.

The role of c-Myc-RBM38 loop in the growth suppression in breast cancer

BackgroundRNA-binding protein 38 (RBM38) is a member of the RNA recognition motif (RRM) family of RNA-binding proteins (RBPs). RBM38 often exerts its function by forming regulatory loops with relevant genes. c-Myc is an oncogenic transcription factor that is upregulated in one-third of breast cancers and involved in many cellular processes in this malignancy. In our previous study, RBM38 was identified as a tumor suppressor in breast cancer. In the present study, we investigated the mechanisms underlying the regulation of this tumor suppressor.MethodsLentivirus transfections, Western blotting analysis, qRT-PCR and immunohistochemistry were employed to study the expression of c-Myc and RBM38. Chromatin immunoprecipitation and dual-luciferase reporter assays were performed to investigate the direct relationship between c-Myc protein and the RBM38 gene. RNA immunoprecipitation combined with dual-luciferase reporter assays was conducted to confirm the direct relationship between the RBM38 protein and the c-Myc transcript.ResultsKnockdown of c-Myc increased RBM38 expression by binding directly to specific DNA sequences (5′-CACGTG-3′), known as the E-box motif, in the promoter region of RBM38 gene. Additionally, RBM38 destabilized the c-Myc transcript by directly targeting AU-rich elements (AREs) in the 3′-untranslated region (3′-UTR) of c-Myc mRNA to suppress c-Myc expression. Moreover, specific inhibitors of c-Myc transcriptional activity inhibited RBM38-induced suppression of growth, implying that RBM38 acts as a tumor suppressor via a mechanism that depends, at least partially, on the reduction of c-Myc expression in breast cancer.ConclusionsRBM38 and c-Myc form a unique mutually antagonistic RBM38-c-Myc loop in breast cancer.

Overexpression of SLC34A2 is an independent prognostic indicator in bladder cancer and its depletion suppresses tumor growth via decreasing c-Myc expression and transcriptional activity

Solute carrier family 34 member 2 (SLC34A2), a pH-sensitive sodium-dependent phosphate transporter, is associated with several human cancers. In this study, we investigate the clinical significance of SLC34A2 and its function in human bladder cancer (BC). The expression dynamics of SLC34A2 were examined in two independent cohorts of BC samples by quantitative PCR, western blotting and immunohistochemical staining. In the training cohort (156 cases), we applied the X-tile program software to assess the optimal cutoff points for biomarkers in order to accurately classify patients according to clinical outcome. In the validation cohort (130 cases), the cutoff score derived from X-title analysis was investigated to determine the association of SLC34A2 expression with survival outcome. A series of in vitro and in vivo assays were then performed to elucidate the function of SLC34A2 in BC and its underlying mechanisms. Results showed that SLC34A2 was significantly upregulated in BC cell lines and clinical samples. In both two cohorts of BC samples, high expression of SLC34A2 was associated with large tumor size, advanced T status and poor patients’ survival. The depletion of SLC34A2 in BC suppressed cellular viability, colony formation and anchorage-independent growth in vitro, and inhibited xenograft tumor growth in vivo, whereas overexpression of SLC34A2 had the converse effect. Simultaneously, downregulation of SLC34A2 decreased the transcriptional activity and protein expression level of c-Myc in BC cells, whereas restoration of c-Myc expression could compromise the anti-proliferation effect of SLC34A2 depletion. Furthermore, miR-214 was proved as a negative regulator of SLC34A2. Our present study illustrated that SLC34A2 has an important role in promoting proliferation and tumorigenicity of BC, and may represent a novel therapeutic target for this disease.

Miz-1 and Max compete to engage c-Myc: implication for the mechanism of inhibition of c-Myc transcriptional activity by Miz-1.

c-Myc is a basic helix-loop-helix leucine zipper (b-HLH-LZ) transcription factor deregulated in the majority of human cancers. As a heterodimer with Max, another b-HLH-LZ transcription factor, deregulated and persistent c-Myc accumulates at transcriptionally active promoters and enhancers and amplifies transcription. This leads to the so-called transcriptional addiction of tumor cells. Recent studies have showed that c-Myc transcriptional activities can be reversed by its association with Miz-1, a POZ transcription factor containing 13 classical zinc fingers. Although evidences have led to suggest that c-Myc interacts with both Miz-1 and Max to form a ternary repressive complex, earlier evidences also suggest that Miz-1 and Max may compete to engage c-Myc. In such a scenario, the Miz-1/c-Myc complex would be the entity responsible for the inhibition of c-Myc transcriptional amplification. Considering the implications of the Miz-1/c-Myc interaction, it is highly important to solve this duality. While two potential c-Myc interacting domains (hereafter termed MID) have been identified in Miz-1 by yeast two-hybrid, with the b-HLH-LZ as a bait, the biophysical characterization of these interactions has not been reported so far. Here, we report that the MID located between the 12th and 13th zinc finger of Miz-1 and the b-HLH-LZ of Max compete to form a complex with the b-HLH-LZ of c-Myc. Our results support the notion that the repressive action of Miz-1 on c-Myc does not rely on the formation of a ternary complex. The implications of these observations for the mechanism of inhibition of c-Myc transcriptional activity by Miz-1 are discussed. Proteins 2017; 85:199-206. © 2016 Wiley Periodicals, Inc.

Suppression of bromodomain-containing protein 4 by shRNA: A new approach for cancer treatment

MYC is a transcription factor coding gene that is believed to control 15% of the genes in the entire human genome. The central role of c-MYC in cancer pathogenesis makes it a major therapeutic target in field of anticancer agent development. We targeted the acetyl-lysine binding modules or bromodomains, which are associated with c-MYC transcriptional activation. Sequence specific inhibition of BET bromodomains with small hairpin RNAs (shRNAs) resulted in cessation of cellular proliferation in different cancer cell lines. Unlike previous studies on inhibition of bromodomains with selective small-molecule inhibitors, our study revealed the significant role of BET bromodomains in solid tumours and also highlighted the ease of RNA interference (RNAi) methodology for inhibition of bromodomain translation. The degree of influence of BET bromodomain inhibition on proliferation in five cancer cell lines established it as the major target in malignancies characterized by activation of c-MYC.

Wedelolactone, an Anti-inflammatory Botanical, Interrupts c-Myc Oncogenic Signaling and Synergizes with Enzalutamide to Induce Apoptosis in Prostate Cancer Cells.

The c-Myc gene encodes an oncoprotein transcription factor that is frequently upregulated in almost all cancer types and is the subject of intense investigation for management of cancer because of its pleiotropic effects controlling a spectrum of cellular functions. However, due of its nonenzymatic nature, development of suitable strategies to block its protein-protein or protein-DNA interaction is challenging. Thus, c-Myc has been recognized as an elusive molecular target for cancer control, and various approaches are in development to inhibit c-Myc transcriptional activity. We observed that wedelolactone (WDL), an anti-inflammatory botanical compound, severely downregulates the expression of c-Myc mRNA in prostate cancer cells. Moreover, WDL dramatically decreases the protein level, nuclear accumulation, DNA-binding, and transcriptional activities of c-Myc. c-Myc is a transforming oncogene widely expressed in prostate cancer cells and is critical for maintaining their transformed phenotype. Interestingly, WDL was found to strongly affect the viability of Myc-activated prostate cancer cells and completely block their invasion as well as soft agar colony formation in vitro WDL was also found to downregulate c-Myc in vivo in nude mice xenografts. Moreover, WDL synergizes with enzalutamide to decrease the viability of androgen-sensitive prostate cancer cells via induction of apoptosis. These findings reveal a novel anticancer mechanism of the natural compound WDL, and suggest that the oncogenic function of c-Myc in prostate cancer cells can be effectively downregulated by WDL for the development of a new therapeutic strategy against Myc-driven prostate cancer. Mol Cancer Ther; 15(11); 2791-801. ©2016 AACR.

C-MYC partners with BPTF in human cancer

ABSTRACTThe c-MYC oncogene is deregulated in virtually all human tumors and therefore constitutes an attractive therapeutic target. We found that the chromatin remodeler BPTF is a c-MYC interactor required for c-MYC chromatin recruitment and transcriptional activity. Moreover, inhibition of BPTF delays tumor development both in vitro and in vivo and its levels positively correlate with c-MYC signatures in human tumors. We propose BPTF as a therapeutic target in c-MYC-addicted tumors.

Signal transducer and activator of transcription STAT5 is recruited to c-Myc super-enhancer.

Backgroundc-Myc has been proposed as a putative target gene of signal transducer and activator of transcription 5 (STAT5). No functional STAT5 binding site has been identified so far within the c-Myc gene locus, therefore a direct transcriptional regulation by STAT5 remains uncertain. c-Myc super-enhancer, located 1.7 Mb downstream of the c-Myc gene locus, was recently reported as essential for the regulation of c-Myc gene expression by hematopoietic transcription factors and bromodomain and extra-terminal (BET) proteins and for leukemia maintenance. c-Myc super-enhancer is composed of five regulatory regions (E1–E5) which recruit transcription and chromatin-associated factors, mediating chromatin looping and interaction with the c-Myc promoter.ResultsWe now show that STAT5 strongly binds to c-Myc super-enhancer regions E3 and E4, both in normal and transformed Ba/F3 cells. We also found that the BET protein bromodomain-containing protein 2 (BRD2), a co-factor of STAT5, co-localizes with STAT5 at E3/E4 in Ba/F3 cells transformed by the constitutively active STAT5-1*6 mutant, but not in non-transformed Ba/F3 cells. BRD2 binding at E3/E4 coincides with c-Myc transcriptional activation and is lost upon treatment with deacetylase and BET inhibitors, both of which inhibit STAT5 transcriptional activity and c-Myc gene expression.ConclusionsOur data suggest that constitutive STAT5 binding to c-Myc super-enhancer might contribute to BRD2 maintenance and thus allow sustained expression of c-Myc in Ba/F3 cells transformed by STAT5-1*6.Electronic supplementary materialThe online version of this article (doi:10.1186/s12867-016-0063-y) contains supplementary material, which is available to authorized users.

SREBP-2 promotes stem cell-like properties and metastasis by transcriptional activation of c-Myc in prostate cancer.

Sterol regulatory element-binding protein-2 (SREBP-2) transcription factor mainly controls cholesterol biosynthesis and homeostasis in normal cells. The role of SREBP-2 in lethal prostate cancer (PCa) progression remains to be elucidated. Here, we showed that expression of SREBP-2 was elevated in advanced pathologic grade and metastatic PCa and significantly associated with poor clinical outcomes. Biofunctional analyses demonstrated that SREBP-2 induced PCa cell proliferation, invasion and migration. Furthermore, overexpression of SREBP-2 increased the PCa stem cell population, prostasphere-forming ability and tumor-initiating capability, whereas genetic silencing of SREBP-2 inhibited PCa cell growth, stemness, and xenograft tumor growth and metastasis. Clinical and mechanistic data showed that SREBP-2 was positively correlated with c-Myc and induced c-Myc activation by directly interacting with an SREBP-2-binding element in the 5′-flanking c-Myc promoter region to drive stemness and metastasis. Collectively, these clinical and experimental results reveal a novel role of SREBP-2 in the induction of a stem cell-like phenotype and PCa metastasis, which sheds light on translational potential by targeting SREBP-2 as a promising therapeutic approach in PCa.

BPTF is required for c-MYC transcriptional activity and in vivo tumorigenesis.

c-MYC oncogene is deregulated in most human tumours. Histone marks associated with transcriptionally active genes define high-affinity c-MYC targets. The mechanisms involved in their recognition by c-MYC are unknown. Here we report that c-MYC interacts with BPTF, a core subunit of the NURF chromatin-remodelling complex. BPTF is required for the activation of the full c-MYC transcriptional programme in fibroblasts. BPTF knockdown leads to decreased c-MYC recruitment to DNA and changes in chromatin accessibility. In Bptf-null MEFs, BPTF is necessary for c-MYC-driven proliferation, G1–S progression and replication stress, but not for c-MYC-driven apoptosis. Bioinformatics analyses unveil that BPTF levels correlate positively with c-MYC-driven transcriptional signatures. In vivo, Bptf inactivation in pre-neoplastic pancreatic acinar cells significantly delays tumour development and extends survival. Our findings uncover BPTF as a crucial c-MYC co-factor required for its biological activity and suggest that the BPTF-c-MYC axis is a potential therapeutic target in cancer.

MYC Protein Expression Correlates with C-MYC Transcriptional Activity in Absence of Gene Rearrangement in Diffuse Large B-Cell Lymphoma

Introduction. MYC increases proliferative capacity of malignant B-cells, independently from mechanisms led to increased protein expression. Tumors with solely MYC expression are highly effective curable with doses intensification. Ability of cells to escape apoptosis by several mechanisms like BCL2 or P53 соехpression promotes malignant B-cells growth and survival and represents a big therapeutic problem.Aim. To investigate mechanism of MYC hyperexpression in absence of c-MYC -rearrangement in DLBCL (diffuse large B-cell lymphoma). To analyze efficacy of intensive chemotherapy in pts with DLBCL who underwent modified NHL-BFM-90 (m-NHL-BFM-90) plus rituximab (R) in correspondence with MYC and BCL2 protein expression.Patients and methods. Data of 62 DLBCL pts (35 males and 27 females) who underwent m-NHL-BFM-90+R in National Research Center for Hematology (Moscow) between 2004 and 2013 years were analyzed. Tumor samples were stained with antibody to BCL2 (clone 124, Dako) and MYC (clone Y69, Epitomics). We used a previously reported cut off for MYC expression ≥40% and BCL2 ≥50% (N. Johnson et al., 2012). G-banding data were available in 19 pts. In one case was revealed c-MYC rearrangement into heavy chain locus t(8;14)(q24;q32). In all other cases FISH didn't reveal c-MYC orBCL2 rearrangements with DNA probes Vysis LSI MYC Dual color, Break Apart Rearrangement Probe, Vysis LSI BCL2 Dual color, Break Apart Rearrangement Probe. RQ-PCR was performed in 17 cases to estimate mRNA level of c-MYC expression relatively to ABL. To assess relation between mRNA of c-MYC and MYC protein expression was used correlation analysis (R²). To estimate treatment results were performed Kaplan-Meyer and Cox regression analyses (SAS 9.3).Results: Majority of pts - 48/62 (78%) attended to a high-risk group according IPI (3-5). 9/62 (14,5%) patients had MYC+/BCL2- tumors, 15 (24%) - "double-expressor" (DE) MYC+/BCL2+, 21 (34%) - MYC-/BCL2+, 17 (27,5%) - MYC-/BCL2-. Median age of DE pts was statistically higher than others (61 (25-73) vs 47 (15-73) years old, P<0,05). In case with t(8;14)(q24;q32) MYC protein expression was ≥40%. In 18/50 (36 %) cases in absence of c-MYC -rearrangement MYC protein expression was ≥40%. In 27/43 (63 %) cases in absence of BCL2 rearrangement BCL2 expression was ≥50%. Median level c-MYC mRNA-expression was 1748 % (492 % - 5408 %). There was a tendency to increase MYC expression level with rising quantity of c-MYC mRNA (R2 = 0,13, P = 0,08). In case with t(8;14)(q24;q32) c-MYC mRNA level was higher than median (3940 %). 45 (78%) of pts achieved a complete remission, 4 from them had second remission. Relapses and progression of DLBCL developed in 9 (15%) and 7 (11%) pts. 5 (8%) pts died because of other reasons. DE DLBCL pts had the highest risk of relapse or progression within 4 years: MYC+/BCL2- - 14%, MYC-/BCL2 - 14%, MYC+/BCL2+ - 65%, MYC-/BCL2+ - 24% (P=0,02). In multivariate analysis MYC/BCL2 double expression had an independent prognostic power (HR 4,717, P=0, 0024) from IPI.Conclusion. We illustrated that MYC protein expression level correlates with c-MYC transcriptional activity in absence of c-MYC rearrangement. MYC hyperexpression alone didn't influence on prognosis, only coexpression of MYC and BCL2 had a crucial role increasing probability of relapse or progression in DLBCL patients. DisclosuresNo relevant conflicts of interest to declare.