c-Myc augments gamma irradiation-induced apoptosis by suppressing Bcl-XL

CEMIP promotes small cell lung cancer proliferation by activation of glutamine metabolism via FBXW7/c-Myc-dependent axis

Small cell lung cancer (SCLC) is the most malignant lung cancer with rapid growth and early metastasis, but still lacks effective targeted therapies to improve the prognosis. Here, we demonstrated that a novel oncogenic protein, cell migration inducing hyaluronic binding protein (CEMIP), was robustly overexpressed in SCLC tissues than that in noncancerous tissues and high expression of CEMIP predicted poor outcomes in clinical specimens and in large sample size cohorts from public databases (GEPIA 2 and CPTAC). Liquid chromatography mass spectrometry (LC-MS) and in vitro/in vivo functional assays indicated that CEMIP contributed to the proliferation by increasing glutamine consumption and their metabolites (glutamate and glutathione) levels in SCLC cells. Moreover, the addition of a GLS1 inhibitor CB-839 dramatically reduced CEMIP-induced SCLC cell proliferation. Mechanistically, beyond as a scaffold protein, CEMIP facilitates glutamine-dependent cell proliferation through inhibiting c-Myc ubiquitination and increasing c-Myc stabilization and nuclear accumulation via hindering the interaction between FBXW7 (a E3 ubiquitin ligase) and its target substrate c-Myc. Taken together, our findings reveal a novel oncogenic role of CEMIP in sustaining SCLC growth via FBXW7/c-Myc-dependent axis, and provide new evidence that inhibition of CEMIP might be a potential therapeutic strategy for the treatment of SCLC.

The "Superoncogene" Myc at the Crossroad between Metabolism and Gene Expression in Glioblastoma Multiforme

The concept of the Myc (c-myc, n-myc, l-myc) oncogene as a canonical, DNA-bound transcription factor has consistently changed over the past few years. Indeed, Myc controls gene expression programs at multiple levels: directly binding chromatin and recruiting transcriptional coregulators; modulating the activity of RNA polymerases (RNAPs); and drawing chromatin topology. Therefore, it is evident that Myc deregulation in cancer is a dramatic event. Glioblastoma multiforme (GBM) is the most lethal, still incurable, brain cancer in adults, and it is characterized in most cases by Myc deregulation. Metabolic rewiring typically occurs in cancer cells, and GBM undergoes profound metabolic changes to supply increased energy demand. In nontransformed cells, Myc tightly controls metabolic pathways to maintain cellular homeostasis. Consistently, in Myc-overexpressing cancer cells, including GBM cells, these highly controlled metabolic routes are affected by enhanced Myc activity and show substantial alterations. On the other hand, deregulated cancer metabolism impacts Myc expression and function, placing Myc at the intersection between metabolic pathway activation and gene expression. In this review paper, we summarize the available information on GBM metabolism with a specific focus on the control of the Myc oncogene that, in turn, rules the activation of metabolic signals, ensuring GBM growth.

Targeting the MYC interaction network in B-cell lymphoma via histone deacetylase 6 inhibition

Overexpression of MYC is a genuine cancer driver in lymphomas and related to poor prognosis. However, therapeutic targeting of the transcription factor MYC remains challenging. Here, we show that inhibition of the histone deacetylase 6 (HDAC6) using the HDAC6 inhibitor Marbostat-100 (M-100) reduces oncogenic MYC levels and prevents lymphomagenesis in a mouse model of MYC-induced aggressive B-cell lymphoma. M-100 specifically alters protein-protein interactions by switching the acetylation state of HDAC6 substrates, such as tubulin. Tubulin facilitates nuclear import of MYC, and MYC-dependent B-cell lymphoma cells rely on continuous import of MYC due to its high turn-over. Acetylation of tubulin impairs this mechanism and enables proteasomal degradation of MYC. M-100 targets almost exclusively B-cell lymphoma cells with high levels of MYC whereas non-tumor cells are not affected. M-100 induces massive apoptosis in human and murine MYC-overexpressing B-cell lymphoma cells. We identified the heat-shock protein DNAJA3 as an interactor of tubulin in an acetylation-dependent manner and overexpression of DNAJA3 resulted in a pronounced degradation of MYC. We propose a mechanism by which DNAJA3 associates with hyperacetylated tubulin in the cytoplasm to control MYC turnover. Taken together, our data demonstrate a beneficial role of HDAC6 inhibition in MYC-dependent B-cell lymphoma.

5,7,2,5-tetrahydroxy-8,6-dimethoxyflavone up-regulates miR-145 expression and inhibits proliferation of gastric cancer cells

INTRODUCTION

Gastric cancer is a frequently detected malignancy, and its incidence has increased over the past decades in East Asia. The present study investigated the effect of 5,7,2, 5-tetrahydroxy-8,6-dimethoxyflavone (THDMF) on gastric cancer cells and explored the underlying mechanism. The study analysed cell viability changes, apoptotic features, and metastasis potential of treatment with THDMF.

MATERIAL AND METHODS

MTT colorimetric assay was used for measurement of MKN28, MKN45, and GES-1 cell proliferation and flow cytometry for the detection of apoptosis. Transwell and wound healing assays were used to observe the invasion and migration abilities of MKN28 cells. The expression of p21, MMP2/-9, PI3K, and c-Myc proteins was detected by western blotting.

RESULTS

The THDMF treatment significantly (p < 0.05) reduced MKN28 and MKN45 cell proliferation without changing GES-1 cell viability. A significant increase in apoptotic cell population on treatment with THDMF was observed. Treatment of MKN28 cells with THDMF increased the percentage of cells in the G1 phase. Exposure of MKN28 cells to THDMF caused a marked decrease in invasion and migration potential in comparison to control cells. The expression of miR-145 was markedly increased in MKN28 cells on treatment with THDMF. In MKN28 cells expression of c-Myc, PI3K, p-AKT, MMP-2, and MMP-9 was suppressed markedly on exposure to THDMF. The expression of p21 protein in MKN28 cells was markedly promoted on exposure to THDMF.

CONCLUSIONS

THDMF exhibits anti-cancer effect on gastric cancer cells in vitro by activation of cell apoptosis and arrest of cell cycle. In addition, THDMF promoted miR-145 expression and down-regulation of PI3K/AKT signalling pathway in MKN28 cells. Therefore, THDMF may be utilised as a potential novel therapeutic agent for the treatment of gastric cancer.

CEMIP, a novel adaptor protein of OGT, promotes colorectal cancer metastasis through glutamine metabolic reprogramming via reciprocal regulation of β-catenin

Metastasis is the leading cause of colorectal cancer (CRC)-induced death. However, the underlying molecular mechanisms of CRC metastasis are poorly understood. Metabolic reprogramming is an intrinsic feature of cancer, which have complicated effects on cancer metastasis. Here, we find that a novel metastasis-related protein, cell migration-inducing and hyaluronan-binding protein (CEMIP), can act as a novel adaptor protein of O-GlcNAc transferase (OGT) to promote CRC metastasis through glutamine metabolic reprogramming. Mechanistically, CEMIP interacts with OGT and β-catenin, which leads to elevated O-GlcNAcylation of β-catenin and enhanced β-catenin nuclear translocation from cytomembrane. Furthermore, accumulated β-catenin in nucleus enhances the transcription of CEMIP to reciprocally regulate β-catenin and contributes to over-expression of glutaminase 1 and glutamine transporters (SLC1A5 and SLC38A2). Combinational inhibition of CEMIP and glutamine metabolism could dramatically attenuate the metastasis of CRC in vivo. Collectively, this study reveals the importance of glutamine metabolic reprogramming in CEMIP-induced CRC metastasis, indicating the great potential of CEMIP and glutamine metabolism for CRC metastasis prevention.

Tilting MYC toward cancer cell death

MYC oncoprotein promotes cell proliferation and serves as the key driver in many human cancers; therefore, considerable effort has been expended to develop reliable pharmacological methods to suppress its expression or function. Despite impressive progress, MYC-targeting drugs have not reached the clinic. Recent advances suggest that within a limited expression range unique to each tumor, MYC oncoprotein can have a paradoxical, proapoptotic function. Here we introduce a counterintuitive idea that modestly and transiently elevating MYC levels could aid chemotherapy-induced apoptosis and thus benefit the patients as much, if not more than MYC inhibition.

Targeting mitochondrial respiration and the BCL2 family in high-grade MYC-associated B-cell lymphoma

Multiple molecular features, such as activation of specific oncogenes (e.g., MYC, BCL2) or a variety of gene expression signatures, have been associated with disease course in diffuse large B‐cell lymphoma (DLBCL), although their relationships and implications for targeted therapy remain to be fully unraveled. We report that MYC activity is closely correlated with—and most likely a driver of—gene signatures related to oxidative phosphorylation (OxPhos) in DLBCL, pointing to OxPhos enzymes, in particular mitochondrial electron transport chain (ETC) complexes, as possible therapeutic targets in high‐grade MYC‐associated lymphomas. In our experiments, indeed, MYC sensitized B cells to the ETC complex I inhibitor IACS‐010759. Mechanistically, IACS‐010759 triggered the integrated stress response (ISR) pathway, driven by the transcription factors ATF4 and CHOP, which engaged the intrinsic apoptosis pathway and lowered the apoptotic threshold in MYC‐overexpressing cells. In line with these findings, the BCL2‐inhibitory compound venetoclax synergized with IACS‐010759 against double‐hit lymphoma (DHL), a high‐grade malignancy with concurrent activation of MYC and BCL2. In BCL2‐negative lymphoma cells, instead, killing by IACS‐010759 was potentiated by the Mcl‐1 inhibitor S63845. Thus, combining an OxPhos inhibitor with select BH3‐mimetic drugs provides a novel therapeutic principle against aggressive, MYC‐associated DLBCL variants.

Crosstalk of the Wnt/β-Catenin Signaling Pathway in the Induction of Apoptosis on Cancer Cells

The Wnt/β-catenin signaling pathway plays a major role in cell survival and proliferation, as well as in angiogenesis, migration, invasion, metastasis, and stem cell renewal in various cancer types. However, the modulation (either up- or downregulation) of this pathway can inhibit cell proliferation and apoptosis both through β-catenin-dependent and independent mechanisms, and by crosstalk with other signaling pathways in a wide range of malignant tumors. Existing studies have reported conflicting results, indicating that the Wnt signaling can have both oncogenic and tumor-suppressing roles, depending on the cellular context. This review summarizes the available information on the role of the Wnt/β-catenin pathway and its crosstalk with other signaling pathways in apoptosis induction in cancer cells and presents a modified dual-signal model for the function of β-catenin. Understanding the proapoptotic mechanisms induced by the Wnt/β-catenin pathway could open new therapeutic opportunities.

MYC: a multipurpose oncogene with prognostic and therapeutic implications in blood malignancies

MYC oncogene is a transcription factor with a wide array of functions affecting cellular activities such as cell cycle, apoptosis, DNA damage response, and hematopoiesis. Due to the multi-functionality of MYC, its expression is regulated at multiple levels. Deregulation of this oncogene can give rise to a variety of cancers. In this review, MYC regulation and the mechanisms by which MYC adjusts cellular functions and its implication in hematologic malignancies are summarized. Further, we also discuss potential inhibitors of MYC that could be beneficial for treating hematologic malignancies.

Myc is involved in Genistein protecting against LPS-induced myocarditis in vitro through mediating MAPK/JNK signaling pathway

BACKGROUND

Genistein is widely used as a pharmacological compound as well as a food additive. However, the pharmaceutical effects of Genistein on myocarditis and its potential mechanisms have not been studied in detail.

METHODS

H9c2 cells were continuously stimulated by lipopolysaccharide (LPS) for 12 h to simulate the in vitro model of myocarditis injury. DrugBank, String, and GEO dataset were used to investigate specific genes that interacting with Genistein. KEGG and GO enrichment analysis were employed to explore Myc-related signaling pathways. Biological behaviors of H9c2 cells were observed with the support of cell counting kit-8, MTT and flow cytometry. Expression levels of cytokines including TNF-α and ILs were evaluated by enzyme-linked immunosorbent assay. Western blot was applied to detect the expression of Myc and MAPK pathway related proteins.

RESULTS

Genistein alleviated the damage of H9c2 cells subjected to LPS from the perspective of elevating cells growth ability, and inhibiting cells apoptosis and inflammatory response. Through bioinformatics analysis, we identified Myc as the potential target of Genistein in myocarditis, and MAPK as the signaling pathway. Significantly, Myc was highly up-regulated in myocarditis samples. More importantly, by performing biological experiments, we discovered that Genistein relieved H9c2 cells apoptosis and inflammatory reaction which caused by LPS stimulation through inhibiting Myc expression. Additionally, the marked augmentation of p-P38 MAPK and p-JNK expression in LPS-induced cardiomyocyte model were blocked by Genistein and si-Myc.

CONCLUSIONS

Our research revealed that Myc mediated the protective effects of Genistein on H9c2 cells damage caused by LPS partly through modulation of MAPK/JNK signaling pathway.

Co-Operativity between MYC and BCL-2 Pro-Survival Proteins in Cancer

B-Cell Lymphoma 2 (BCL-2), c-MYC and related proteins are arguably amongst the most widely studied in all of biology. Every year there are thousands of papers reporting on different aspects of their biochemistry, cellular and physiological mechanisms and functions. This plethora of literature can be attributed to both proteins playing essential roles in the normal functioning of a cell, and by extension a whole organism, but also due to their central role in disease, most notably, cancer. Many cancers arise due to genetic lesions resulting in deregulation of both proteins, and indeed the development and survival of tumours is often dependent on co-operativity between these protein families. In this review we will discuss the individual roles of both proteins in cancer, describe cancers where co-operativity between them has been well-characterised and finally, some strategies to target these proteins therapeutically.

Dimethoxycurcumin reduces proliferation and induces apoptosis in renal tumor cells more efficiently than demethoxycurcumin and curcumin

Curcumin (Cur), is a pigment with antiproliferative activity but has some pharmacokinetic limitations, which led researchers to look for more effective structure analogs. This work investigated the effects of Cur and compared them with the two analogs, demethoxycurcumin (DeMC) and dimethoxycurcumin (DiMC), to elucidate their mechanisms of action. The cytotoxic, antiproliferative, and genotoxic effects these compounds were correlated based on gene expression analysis in the human renal adenocarcinoma cells (786-O). Cur decreased CYP2D6 expression and exhibited cytotoxic effects, such as inducing monopolar spindle formation and mitotic arrest mediated by the increase in CDKN1A (p21) mRNA. This dysregulation induced cell death through a caspase-independent pathway but was mediated by decrease in MTOR and BCL2 mRNA expression, suggesting that apoptosis occurred by autophagy. DeMC and DiMC had similar effects in that they induced monopolar spindle and mitotic arrest, were genotoxic, and activated GADD45A, an important molecule in repair mechanisms, and CDKN1A. However, the induction of apoptosis by DeMC was delayed and regulated by the decrease of antiapoptotic mRNA BCL.XL and subsequent activation of caspase 9 and caspase 3/7. DiMC treatment increased the expression of CYP1A2, CYP2C19, and CYP3A4 and exhibited higher cytotoxicity compared with other compounds. It induced apoptosis by increasing mRNA expression of BBC3, MYC, and CASP7 and activation of caspase 9 and caspase 3/7. These data revealed that different gene regulation processes are involved in cell death induced by Cur, DeMC, and DiMC. All three can be considered as promising chemotherapy candidates, with DiMC showing the greatest potency.

Flavonoid-rich extracts from okra flowers exert antitumor activity in colorectal cancer through induction of mitochondrial dysfunction-associated apoptosis, senescence and autophagy

Okra flowers contain a higher content of total flavonoids than most other flowers; however little research has been conducted on their potential benefits, including antitumor activity. In this study, we extracted and purified flavonoids from okra flower (AFE), and aimed to evaluate the effect of AFE and its underlying mechanism on colorectal cancer (CRC) cell growth in vitro and in vivo. Here, we identify that AFE is a safe, natural antioxidant and exerts significant antitumor efficacy on the inhibition of CRC cell proliferation and metastasis as well as tumour growth in vivo. We further reveal that AFE inhibits CRC cell proliferation by inducing mitochondrial dysfunction, which results from the activation of p53 and induction of apoptosis and senescence, and inhibits autophagic degradation. Furthermore, AFE inhibited migration and invasion of CRC cells by regulating the balance of MMP2/TIMP2 and MMP9 expression levels. Of note, administration of AFE as a preventive agent achieves a more effective antitumor effect than the therapeutic agent in a xenograft mouse model. Our results reveal, for the first time, that AFE is a safe, natural antioxidant with significant antitumor efficacy, which has great potential in the application for CRC prevention and treatment.

c-Myc promotes tubular cell apoptosis in ischemia-reperfusion-induced renal injury by negatively regulating c-FLIP and enhancing FasL/Fas-mediated apoptosis pathway

c-Myc plays an important role in cell proliferation, differentiation, and cell apoptosis. FasL/Fas pathway is a key regulator of cell apoptosis. This study was aimed to investigate the effects of c-Myc on the FasL/Fas pathway in ischemia-reperfusion (I/R)-induced renal injury. Rats were objected to bilateral renal ischemia for 60 min and reperfused for 24 or 48 h. NRK-52E cells were treated with hypoxia-reoxygenation (H/R) or FasL. Immunohistochemistry was used to identify the distribution of c-Myc. Cell apoptosis was assessed by TUNEL staining. Ad-c-Myc and recombinant pcDAN 3.0 were used to overexpress c-Myc and c-FLIP, respectively. ChIP assay and luciferase assay were used to detect the binding of c-Myc to c-FLIP promoter. In I/R rats, c-Myc was increased significantly and mainly located in renal tubular epithelial cells; meanwhile, c-FLIP was decreased, cleaved caspase-8, cleaved caspase-3 and TUNEL-positive staining cells were increased. Treatment of I/R rats with c-Myc inhibitor 10058-F4 significantly attenuated the decrease in c-FLIP, the increase in cleaved caspase-8, cleaved caspase-3, TUNEL-positive cells, Scr and BUN in I/R rats. In NRK-52E cells, hypoxia and reoxygen induced the increase in c-Myc and decrease in c-FLIP. ChIP and luciferase assay results indicated that c-Myc binds to the promoter region of c-FLIP gene. Overexpression of c-Myc markedly decreased c-FLIP. Overexpression of c-FLIP inhibited the increase in cleaved caspase-8 and caspase-3 induced by FasL. Data indicated that c-Myc is increased in kidneys of I/R rats and negatively regulates the expression of c-FLIP, then enhanced FasL-induced cell apoptosis in I/R stress.

Apoptosis regulation in adrenocortical carcinoma

Apoptosis evading is a hallmark of cancer. Tumor cells are characterized by having an impaired apoptosis signaling, a fact that deregulates the balance between cell death and survival, leading to tumor development, invasion and resistance to treatment. In general, patients with adrenocortical carcinomas (ACC) have an extremely bad prognosis, which is related to disease progression and significant resistance to treatments. In this report, we performed an integrative review about the disruption of apoptosis in ACC that may underlie the characteristic poor prognosis in these patients. Although the apoptosis has been scarcely studied in ACC, the majority of the deregulation phenomena already described are anti-apoptotic. Most importantly, in a near future, targeting apoptosis modulation in ACC patients may become a promising therapeutic.

Effect of miR‑145 on gastric cancer cells

Gastric cancer is one of the most common malignant tumors in the world. Due to the lack of early diagnosis and effective treatment, the outcome of treatment and prognosis is poor. MicroRNA-145 (miR-145) is downregulated in various cancer types. In the present study, miR-145 expression was detected by reverse transcription-quantitative polymerase chain reaction in gastric cancer cell lines and normal gastric epithelial cells. The function of miR-145 in the gastric cancer cell line SGC-7901 was investigated. The present results demonstrated that the expression of miR-145 was downregulated in gastric cancer cells. Further analysis identified that upregulation of miR-145 significantly suppressed SGC-7901 cell proliferation, increased cellular apoptosis and blocked the cell cycle in the G₁ phase. Additionally, overexpression of miR-145 reduced SGC-7901 cell invasion and metastasis in vitro. Western blot analysis demonstrated that overexpression of miR-145 downregulated Myc proto-oncogene protein, phosphoinositide 3-kinase/protein kinase B and matrix metalloproteinase 2/9, and upregulated p21 in SGC-7901 cells. The present results revealed potential signaling pathways that miR-145 may use to regulate gastric cancer cell proliferation, apoptosis and metastasis. Collectively, the present results suggest that miR-145 is a tumor suppressor for gastric cancer and it may be a potential therapeutic target for gastric cancer treatment.

MYC-Induced miR-203b-3p and miR-203a-3p Control Bcl-xL Expression and Paclitaxel Sensitivity in Tumor Cells

Taxanes are chemotherapeutic agents used in the treatment of solid tumors, particularly of breast, ovarian, and lung origin. However, patients show divergent therapy responses, and the molecular determinants of taxane sensitivity have remained elusive. Especially the signaling pathways that promote death of the taxane-treated cells are poorly characterized. Here we describe a novel part of a signaling route in which c-Myc enhances paclitaxel sensitivity through upregulation of miR-203b-3p and miR-203a-3p; two clustered antiapoptosis protein Bcl-xL controlling microRNAs. In vitro, the miR-203b-3p decreases the expression of Bcl-xL by direct targeting of the gene's mRNA 3'UTR. Notably, overexpression of the miR-203b-3p changed the fate of paclitaxel-treated breast and ovarian cancer cells from mitotic slippage to cell death. In breast tumors, high expression of the miR-203b-3p and MYC was associated with better therapy response and patient survival. Interestingly, in the breast tumors, MYC expression correlated negatively with BCL2L1 expression but positively with miR-203b-3p and miR-203a-3p. Finally, silencing of MYC suppressed the transcription of both miRNAs in breast tumor cells. Pending further validation, these results may assist in patient stratification for taxane therapy.

Combination therapy with protein kinase inhibitor H89 and Tetrandrine elicits enhanced synergistic antitumor efficacy

BACKGROUND

Tetrandrine, a bisbenzylisoquinoline alkaloid that was isolated from the medicinal plant Stephania tetrandrine S. Moore, was recently identified as a novel chemotherapy drug. Tetrandrine exhibited a potential antitumor effect on multiple types of cancer. Notably, an enhanced therapeutic efficacy was identified when tetrandrine was combined with a molecularly targeted agent. H89 is a potent inhibitor of protein kinase A and is an isoquinoline sulfonamide.

METHODS

The effects of H89 combined with tetrandrine were investigated in vitro with respect to cell viability, apoptosis and autophagy, and synergy was assessed by calculation of the combination index. The mechanism was examined by western blot, flow cytometry and fluorescence microscopy. This combination was also evaluated in a mouse xenograft model; tumor growth and tumor lysates were analyzed, and a TUNEL assay was performed.

RESULTS

Combined treatment with H89 and tetrandrine exerts a mostly synergistic anti-tumor effect on human cancer cells in vitro and in vivo while sparing normal cells. Mechanistically, the combined therapy significantly induced cancer cell apoptosis and autophagy, which were mediated by ROS regulated PKA and ERK signaling. Moreover, Mcl-1 and c-Myc were shown to play a critical role in H89/tetrandrine combined treatment. Mcl-1 ectopic expression significantly diminished H89/tetrandrine sensitivity and amplified c-Myc sensitized cancer cells in the combined treatment.

CONCLUSION

Our findings demonstrate that the combination of tetrandrine and H89 exhibits an enhanced therapeutic effect and may become a promising therapeutic strategy for cancer patients. They also indicate a significant clinical application of tetrandrine in the treatment of human cancer. Moreover, the combination of H89/tetrandrine provides new selectively targeted therapeutic strategies for patients with c-Myc amplification.

EBV and Apoptosis: The Viral Master Regulator of Cell Fate?

Epstein-Barr virus (EBV) was first discovered in cells from a patient with Burkitt lymphoma (BL), and is now known to be a contributory factor in 1-2% of all cancers, for which there are as yet, no EBV-targeted therapies available. Like other herpesviruses, EBV adopts a persistent latent infection in vivo and only rarely reactivates into replicative lytic cycle. Although latency is associated with restricted patterns of gene expression, genes are never expressed in isolation; always in groups. Here, we discuss (1) the ways in which the latent genes of EBV are known to modulate cell death, (2) how these mechanisms relate to growth transformation and lymphomagenesis, and (3) how EBV genes cooperate to coordinately regulate key cell death pathways in BL and lymphoblastoid cell lines (LCLs). Since manipulation of the cell death machinery is critical in EBV pathogenesis, understanding the mechanisms that underpin EBV regulation of apoptosis therefore provides opportunities for novel therapeutic interventions.

Global Inhibition with Specific Activation: How p53 and MYC Redistribute the Transcriptome in the DNA Double-Strand Break Response

In response to stresses, cells often halt normal cellular processes, yet stress-specific pathways must bypass such inhibition to generate effective responses. We investigated how cells redistribute global transcriptional activity in response to DNA damage. We show that an oscillatory increase of p53 levels in response to double-strand breaks drives a counter-oscillatory decrease of MYC levels. Using RNA sequencing (RNA-seq) of newly synthesized transcripts, we found that p53-mediated reduction of MYC suppressed general transcription, with the most highly expressed transcripts reduced to a greater extent. In contrast, upregulation of p53 targets was relatively unaffected by MYC suppression. Reducing MYC during the DNA damage response was important for cell-fate regulation, as counteracting MYC repression reduced cell-cycle arrest and elevated apoptosis. Our study shows that global inhibition with specific activation of transcriptional pathways is important for the proper response to DNA damage; this mechanism may be a general principle used in many stress responses.

PUMA decreases the growth of prostate cancer PC-3 cells independent of p53

PUMA (p53 upregulated modulator of apoptosis), a member of the B-cell lymphoma 2 (Bcl-2) protein family, is a pro-apoptotic protein. PUMA expression is modulated by the tumor suppressor p53. PUMA has a role in rapid cell death via p53-dependent and -independent mechanisms. To evaluate whether p53 is required for PUMA-mediated apoptosis in prostate cancer cells, p53 protein was silenced in human prostate cancer PC-3 cells by using p53 small interfering RNA (siRNA). The interference efficiency of p53 on RNA and protein levels was detected by reverse transcription-quantitative polymerase chain reaction and western blotting. Cell proliferation and p21 expression were subsequently examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and western blot analysis, respectively. p53-silenced or control PC-3 cells were transfected with pCEP4-(hemagglutinin)-PUMA plasmid, or non-carrier plasmid. Enzyme-linked immunosorbent assay was used to determine cell apoptosis by measuring histone release and caspase-3 activation, and MTT assay was used to measure cell viability. In addition, the expression of pro-apoptosis protein Bax and anti-apoptosis protein Bcl-2 were evaluated. The results of the present study revealed that p53 siRNA significantly suppressed p53 RNA and protein expression in PC-3 cells. Deficiency of p53 increased the cell growth rate and decreased p21 expression. However, PUMA overexpression remained able to induce apoptosis in p53-silenced and control cells by increasing Bax expression and decreasing Bcl-2 expression, leading to the activation of caspase-3. These results suggest that PUMA may mediate apoptosis of prostate cancer PC-3 cells, potentially independently of p53. Furthermore, PUMA gene treatment to induce cancer cell apoptosis may be more efficient compared with p53-dependent apoptosis, where loss of p53 expression or function may lead to limited efficacy of PUMA expression. Therefore, the present study proposes the significant hypothesis that increasing PUMA expression may be an effective approach for the treatment of prostate cancer, regardless of p53 status.

Therapeutic aspects of c-MYC signaling in inflammatory and cancerous colonic diseases

Colonic inflammation is required to heal infections, wounds, and maintain tissue homeostasis. As the seventh hallmark of cancer, however, it may affect all phases of tumor development, including tumor initiation, promotion, invasion and metastatic dissemination, and also evasion immune surveillance. Inflammation acts as a cellular stressor and may trigger DNA damage or genetic instability, and, further, chronic inflammation can provoke genetic mutations and epigenetic mechanisms that promote malignant cell transformation. Both sporadical and colitis-associated colorectal carcinogenesis are multi-step, complex processes arising from the uncontrolled proliferation and spreading of malignantly transformed cell clones with the obvious ability to evade the host’s protective immunity. In cells upon DNA damage several proto-oncogenes, including c-MYC are activated in parelell with the inactivation of tumor suppressor genes. The target genes of the c-MYC protein participate in different cellular functions, including cell cycle, survival, protein synthesis, cell adhesion, and micro-RNA expression. The transcriptional program regulated by c-MYC is context dependent, therefore the final cellular response to elevated c-MYC levels may range from increased proliferation to augmented apoptosis. Considering physiological intestinal homeostasis, c-MYC displays a fundamental role in the regulation of cell proliferation and crypt cell number. However, c-MYC gene is frequently deregulated in inflammation, and overexpressed in both sporadic and colitis-associated colon adenocarcinomas. Recent results demonstrated that endogenous c-MYC is essential for efficient induction of p53-dependent apoptosis following DNA damage, but c-MYC function is also involved in and regulated by autophagy-related mechanisms, while its expression is affected by DNA-methylation, or histone acetylation. Molecules directly targeting c-MYC, or agents acting on other genes involved in the c-MYC pathway could be selected for combined regiments. However, due to its context-dependent cellular function, it is clinically essential to consider which cytotoxic drugs are used in combination with c-MYC targeted agents in various tissues. Increasing our knowledge about MYC-dependent pathways might provide direction to novel anti-inflammatory and colorectal cancer therapies.

Cooperation of ETV6/RUNX1 and BCL2 enhances immunoglobulin production and accelerates glomerulonephritis in transgenic mice

The t(12;21) translocation generating the ETV6/RUNX1 fusion gene represents the most frequent chromosomal rearrangement in childhood leukemia. Presence of ETV6/RUNX1 alone is usually not sufficient for leukemia onset, and additional genetic alterations have to occur in ETV6/RUNX1-positive cells to cause transformation. We have previously generated an ETV6/RUNX1 transgenic mouse model where the expression of the fusion gene is restricted to CD19-positive B cells. Since BCL2 family members have been proposed to play a role in leukemogenesis, we investigated combined effects of ETV6/RUNX1 with exogenous expression of the antiapoptotic protein BCL2 by crossing ETV6/RUNX1 transgenic animals with Vav-BCL2 transgenic mice. Strikingly, co-expression of ETV6/RUNX1 and BCL2 resulted in significantly shorter disease latency in mice, indicating oncogene cooperativity. This was associated with faster development of follicular B cell lymphoma and exacerbated immune complex glomerulonephritis. ETV6/RUNX1-BCL2 double transgenic animals displayed increased B cell numbers and immunoglobulin titers compared to Vav-BCL2 transgenic mice. This led to pronounced deposition of immune complexes in glomeruli followed by accelerated development of immune complex glomerulonephritis. Thus, our study reveals a previously unrecognized synergism between ETV6/RUNX1 and BCL2 impacting on malignant disease and autoimmunity.

MYC: connecting selective transcriptional control to global RNA production

Two opposing models have been proposed to describe the function of the MYC oncoprotein in shaping cellular transcriptomes: one posits that MYC amplifies transcription at all active loci; the other that MYC differentially controls discrete sets of genes, the products of which affect global transcript levels. Here, we argue that differential gene regulation by MYC is the sole unifying model that is consistent with all available data. Among other effects, MYC endows cells with physiological and metabolic changes that have the potential to feed back on global RNA production, processing and turnover. The field is progressing steadily towards a full characterization of the MYC-regulated genes and pathways that mediate these biological effects and - by the same token - endow MYC with its pervasive oncogenic potential.

The involvement of c-Myc in the DNA double-strand break repair via regulating radiation-induced phosphorylation of ATM and DNA-PKcs activity

Deregulation of c-Myc often occurs in various human cancers, which not only contributes to the genesis and progression of cancers but also affects the outcomes of cancer radio- or chemotherapy. In this study, we have investigated the function of c-Myc in the repair of DNA double-strand break (DSB) induced by γ-ray irradiation. A c-Myc-silenced Hela-630 cell line was generated from HeLa cells using RNA interference technology. The DNA DSBs were detected by γ-H2AX foci, neutral comet assay and pulsed-field gel electrophoresis. We found that the capability of DNA DSB repair in Hela-630 cells was significantly reduced, and the repair kinetics of DSB was delayed as compared to the control Hela-NC cells. Silence of c-myc sensitized the cellular sensitivity to ionizing radiation. The phosphorylated c-Myc (Thr58/pSer62) formed the consistent co-localisation foci with γ-H2AX as well as the phosphorylated DNA-PKcs/S2056 in the irradiated cells. Moreover, depression of c-Myc largely attenuated the ionizing radiation-induced phosphorylation of the ataxia telangiectasia mutated (ATM) and decreased the in vitro kinase activity of DNA-PKcs. Taken together, our results demonstrated that c-Myc protein functions in the process of DNA double-strand break repair, at least partially, through affecting the ATM phosphorylation and DNA-PKcs kinase activity. The overexpression of c-Myc in tumours can account for the radioresistance of some tumour cell types.

GP130 activation induces myeloma and collaborates with MYC

Multiple myeloma (MM) is a plasma cell neoplasm that results from clonal expansion of an Ig-secreting terminally differentiated B cell. Advanced MM is characterized by tissue damage that involves bone, kidney, and other organs and is typically associated with recurrent genetic abnormalities. IL-6 signaling via the IL-6 signal transducer GP130 has been implicated as an important driver of MM pathogenesis. Here, we demonstrated that ectopic expression of constitutively active GP130 (L-GP130) in a murine retroviral transduction-transplantation model induces rapid MM development of high penetrance. L-GP130-expressing mice recapitulated all of the characteristics of human disease, including monoclonal gammopathy, BM infiltration with lytic bone lesions, and protein deposition in the kidney. Moreover, the disease was easily transplantable and allowed different therapeutic options to be evaluated in vitro and in vivo. Using this model, we determined that GP130 signaling collaborated with MYC to induce MM and was responsible and sufficient for directing the plasma cell phenotype. Accordingly, we identified Myc aberrations in the L-GP130 MM model. Evaluation of human MM samples revealed recurrent activation of STAT3, a downstream target of GP130 signaling. Together, our results indicate that deregulated GP130 activity contributes to MM pathogenesis and that pathways downstream of GP130 activity have potential as therapeutic targets in MM.

BIM is the primary mediator of MYC-induced apoptosis in multiple solid tissues

MYC is one of the most frequently overexpressed oncogenes in human cancer, and even modestly deregulated MYC can initiate ectopic proliferation in many postmitotic cell types in vivo. Sensitization of cells to apoptosis limits MYC's oncogenic potential. However, the mechanism through which MYC induces apoptosis is controversial. Some studies implicate p19ARF-mediated stabilization of p53, followed by induction of proapoptotic BH3 proteins NOXA and PUMA, whereas others argue for direct regulation of BH3 proteins, especially BIM. Here, we use a single experimental system to systematically evaluate the roles of p19ARF and BIM during MYC-induced apoptosis, in vitro, in vivo, and in combination with a widely used chemotherapeutic, doxorubicin. We find a common specific requirement for BIM during MYC-induced apoptosis in multiple settings, which does not extend to the p53-responsive BH3 family member PUMA, and find no evidence of a role for p19ARF during MYC-induced apoptosis in the tissues examined.

JNK signalling in cancer: in need of new, smarter therapeutic targets

The JNKs are master protein kinases that regulate many physiological processes, including inflammatory responses, morphogenesis, cell proliferation, differentiation, survival and death. It is increasingly apparent that persistent activation of JNKs is involved in cancer development and progression. Therefore, JNKs represent attractive targets for therapeutic intervention with small molecule kinase inhibitors. However, evidence supportive of a tumour suppressor role for the JNK proteins has also been documented. Recent studies showed that the two major JNK proteins, JNK1 and JNK2, have distinct or even opposing functions in different types of cancer. As such, close consideration of which JNK proteins are beneficial targets and, more importantly, what effect small molecule inhibitors of JNKs have on physiological processes, are essential. A number of ATP-competitive and ATP-non-competitive JNK inhibitors have been developed, but have several limitations such as a lack of specificity and cellular toxicity. In this review, we summarize the accumulating evidence supporting a role for the JNK proteins in the pathogenesis of different solid and haematological malignancies, and discuss many challenges and scientific opportunities in the targeting of JNKs in cancer.

C-Myc participates in β-catenin-mediated drug resistance in A549/DDP lung adenocarcinoma cells

The aim of this study was to investigate c-Myc and β-catenin-mediated drug resistance in A549/DDP lung adenocarcinoma cells. Cisplatin sensitivity was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) toxicity assay. β-Catenin and c-Myc protein expression following cisplatin treatment were determined using western blotting and immunofluorescence. Flow cytometry was performed to detect cell cycle and apoptosis in A549, A549/DDP, and c-Myc small interfering RNA (siRNA)-transfected A549/DDP cells before and after treatment with different doses of cisplatin. The median inhibitory concentration (IC50 ) in cisplatin-treated A549 and A549/DDP cells was 5.769 ± 0.24 μmol/L and 28.373 ± 0.96 μmol/L, respectively; the cisplatin resistance of A549 cells was about five times that of A549/DDP cells. Endogenous β-catenin and c-Myc expression in A549/DDP cells were higher than that in A549 cells, and were upregulated in A549/DDP cells (p < 0.05) and downregulated in A549 cells after 48 h cisplatin treatment (p < 0.05). β-catenin localization transferred from membrane/cytoplasmic/nuclear to cytoplasmic/nuclear, and c-Myc localization transferred from cytoplasmic/nuclear to nuclear in both cell lines following cisplatin treatment. The rate of apoptosis increased in a dose-dependent manner with cisplatin. After 48-h transfection with c-myc siRNA, A549/DDP cells were blocked in the S phase, and G0/G1-phase cells increased. Simultaneously, the apoptotic rate was increased (p < 0.05) and the IC50 decreased significantly (p < 0.05). C-myc, the downstream target gene of β-catenin, plays an important role in regulating cisplatin resistance in A549/DDP cells. C-Myc siRNA improved the sensitivity of A549/DDP cells to cisplatin.

Endogenous c-Myc is essential for p53-induced apoptosis in response to DNA damage in vivo

Recent studies have suggested that C-MYC may be an excellent therapeutic cancer target and a number of new agents targeting C-MYC are in preclinical development. Given most therapeutic regimes would combine C-MYC inhibition with genotoxic damage, it is important to assess the importance of C-MYC function for DNA damage signalling in vivo. In this study, we have conditionally deleted the c-Myc gene in the adult murine intestine and investigated the apoptotic response of intestinal enterocytes to DNA damage. Remarkably, c-Myc deletion completely abrogated the immediate wave of apoptosis following both ionizing irradiation and cisplatin treatment, recapitulating the phenotype of p53 deficiency in the intestine. Consistent with this, c-Myc-deficient intestinal enterocytes did not upregulate p53. Mechanistically, this was linked to an upregulation of the E3 Ubiquitin ligase Mdm2, which targets p53 for degradation in c-Myc-deficient intestinal enterocytes. Further, low level overexpression of c-Myc, which does not impact on basal levels of apoptosis, elicited sustained apoptosis in response to DNA damage, suggesting c-Myc activity acts as a crucial cell survival rheostat following DNA damage. We also identify the importance of MYC during DNA damage-induced apoptosis in several other tissues, including the thymus and spleen, using systemic deletion of c-Myc throughout the adult mouse. Together, we have elucidated for the first time in vivo an essential role for endogenous c-Myc in signalling DNA damage-induced apoptosis through the control of the p53 tumour suppressor protein.

Cutting edge: cell-autonomous control of IL-7 response revealed in a novel stage of precursor B cells

During early stages of B-lineage differentiation in bone marrow, signals emanating from IL-7R and pre-BCR are thought to synergistically induce proliferative expansion of progenitor cells. Paradoxically, loss of pre-BCR-signaling components is associated with leukemia in both mice and humans. Exactly how progenitor B cells perform the task of balancing proliferative burst dependent on IL-7 with the termination of IL-7 signals and the initiation of L chain gene rearrangement remains to be elucidated. In this article, we provide genetic and functional evidence that the cessation of the IL-7 response of pre-B cells is controlled via a cell-autonomous mechanism that operates at a discrete developmental transition inside Fraction C' (large pre-BII) marked by transient expression of c-Myc. Our data indicate that pre-BCR cooperates with IL-7R in expanding the pre-B cell pool, but it is also critical to control the differentiation program shutting off the c-Myc gene in large pre-B cells.

The circadian clock in cancer development and therapy

Most aspects of mammalian function display circadian rhythms driven by an endogenous clock. The circadian clock is operated by genes and comprises a central clock in the brain that responds to environmental cues and controls subordinate clocks in peripheral tissues via circadian output pathways. The central and peripheral clocks coordinately generate rhythmic gene expression in a tissue-specific manner in vivo to couple diverse physiological and behavioral processes to periodic changes in the environment. However, with the industrialization of the world, activities that disrupt endogenous homeostasis with external circadian cues have increased. This change in lifestyle has been linked to an increased risk of diseases in all aspects of human health, including cancer. Studies in humans and animal models have revealed that cancer development in vivo is closely associated with the loss of circadian homeostasis in energy balance, immune function, and aging, which are supported by cellular functions important for tumor suppression including cell proliferation, senescence, metabolism, and DNA damage response. The clock controls these cellular functions both locally in cells of peripheral tissues and at the organismal level via extracellular signaling. Thus, the hierarchical mammalian circadian clock provides a unique system to study carcinogenesis as a deregulated physiological process in vivo. The asynchrony between host and malignant tissues in cell proliferation and metabolism also provides new and exciting options for novel anticancer therapies.

Migfilin sensitizes cisplatin-induced apoptosis in human glioma cells in vitro

AIM

Filamin binding LIM protein 1, also known as migfilin, is a skeleton organization protein that binds to mitogen-inducible gene 2 at cell-extracellular matrix adhesions. The aim of this study was to investigate the role of migfilin in cisplatin-induced apoptosis in human glioma cells, to determine the functional domains of migfilin, and to elucidate the molecular mechanisms underlying the regulation of cisplatin-related chemosensitivity.

METHODS

The human glioma cell lines Hs683, H4, and U-87 MG were transfected with pEGFP-C2-migfilin to elevate the expression level of migfilin. RNA interference was used to reduce the expression of migfilin. To determine the functional domains of migfilin, U-87 MG cells were transfected with plasmids of migfilin deletion mutants. After treatment with cisplatin (40 μmol/L) for 24 h, the cell viability was assessed using the MTS assay, and the cell apoptotic was examined using the DAPI staining assay and TUNEL analysis. Expression levels of apoptosis-related proteins were detected by Western blot analysis.

RESULTS

Overexpression of migfilin significantly enhanced cisplatin-induced apoptosis in Hs683, H4, and U-87 MG cells, whereas downregulation of migfilin expression inhibited the chemosensitivity of these cell lines. The N-terminal region of migfilin alone was able to enhance the cisplatin-induced apoptosis. However, despite the existence of the N-terminal region, mutants of migfilin with any one of three LIM domains deleted led to a function loss. Furthermore, apoptotic proteins (PARP and caspase-3) and the anti-apoptotic protein Bcl-xL were modulated by the expression level of migfilin in combination with cisplatin.

CONCLUSION

The LIM1-3 domains of migfilin play a key role in sensitizing glioma cells to cisplatin-induced apoptosis through regulation of apoptosis-related proteins.

SirT1 regulates radiosensitivity of hepatoma cells differently under normoxic and hypoxic conditions

Intratumoral hypoxic cells are more resistant to radiotherapy due to a reduction in lifespan of DNA-damaging free radicals and augmentation of post-irradiation molecular restoration. SirT1, a member of the mammalian sirtuin family, deacetylates various transcription factors to trigger cell defense and survival in response to stresses and DNA damage. In this study, we provide new evidence indicating that overexpression of SirT1 in hepatoma HepG2 cells allowed the cells to become much more resistant to irradiation under hypoxia than under normoxia. When SirT1 was knocked down in both HepG2 and SK-Hep-1 cells, the radiosensitivity was increased, especially under hypoxia. But this enhanced radiosensitivity in SirT1-deficient cells was extensively decreased by infecting cells with c-Myc siRNA. Furthermore, the expression of c-Myc protein and its acetylation were increased in the SirT1 knockdown cells and these increments under hypoxic conditions were much more notable than under normoxia. In addition, c-Myc interference significantly suppressed phosphorylated p53 protein expression after irradiation, especially under hypoxic conditions. The current findings indicate that SirT1 confers a higher radioresistance in hypoxic cells than in normoxic cells due to the decreased levels of c-Myc protein and its acetylation, and that a c-Myc-dependent radiation-induced phosphorylated p53 may be involved. SirT1 could serve as a novel target of radiation damage and thus as a potential strategy to advance the efficiency of radiotherapy in hepatoma entities.

miR-34c may protect lung cancer cells from paclitaxel-induced apoptosis

MicroRNAs (miRNAs) constitute a class of small non-coding RNAs that negatively regulate the expression of their target genes. They are involved in many biological processes, including cell proliferation, apoptosis and differentiation, and are considered as promising new therapeutic targets for cancer. However, the identity of miRNAs involved in apoptosis and their respective targets remain largely unknown. Given the elevated complexity of miRNA regulation of gene expression, we performed a functional screening as an alternative strategy to identify those miRNAs that in lung cancer cells may interfere with the apoptotic process. To this aim, we generated a derivative of the non-small cell lung carcinoma A549 cell line in which caspase-8, a critical upstream initiator of apoptosis, can be activated by administration of the small dimerizer drug AP20187. We found a number of miRNAs that may rescue cell viability from caspase-8 activation. They included miRNAs already described as oncogenic such as miR-17, miR-135 and miR-520, but also some miRNAs such as miR-124-1 and miR-34c for which a tumor-suppressive role has instead been described or expected. Among them, miR-34c-5p markedly increased resistance to paclitaxel-induced apoptosis. We demonstrate that Bmf (Bcl-2-modifying factor) is a target of miR-34c-5p, and that its silencing, together with that of c-myc, a known target of miR-34c-5p, contributes to resistance to apoptosis induced by paclitaxel through p53 downregulation.

Not all sarcomas developed in irradiated tissue are necessarily radiation-induced--spectrum of disease and treatment characteristics

BACKGROUND

Sarcomas in irradiated tissue (SITs) are often considered with second cancers, although they usually present distinct dose-response, genetic and clinical patterns. The contribution of radiation in SIT development is likely, but remains unproven in many cases.

MATERIALS AND METHODS

We reviewed the literature for published data on SITs.

RESULTS

SITs incidence ranged between 0.03% and 0.2%. Median latency was 15 years. Angiosarcoma was the second most common subtype after undifferentiated sarcomas of malignant fibrous histiocytoma (MFH). C-Myc overexpression can be used to identify radiation-induced angiosarcoma, and a recently described transcriptomic signature of genes involved in chronic oxidative stress and mitochondrial dysfunction may indicate radiation causality. Osteosarcomas were often associated with genetic predisposition. Five-year survival rates rarely exceeded 30% because the therapeutic possibilities were often limited by the first cancer. Chemotherapy response may differ from that of de novo sarcomas.

CONCLUSION

SITs present different characteristics from non-sarcomatoid second cancers. Reporting of SIT cases and the establishment of tissue and serum banks is necessary to better understand and validate the recently discovered radiation signature.

Cyclin D1 inhibits whereas c-Myc enhances the cytotoxicity of cisplatin in mouse pancreatic cancer cells via regulation of several members of the NF-κB and Bcl-2 families

Background:

Cisplatin (CDDP) is a drug used for treatment of many types of malignancy but pancreatic cancer is relatively resistant to it. This study aims to determine whether and how cyclin D1 (D1) and c-Myc influence the response of pancreatic cancer cells to CDDP.

Materials and Methods:

Ela-mycPT mouse pancreatic cancer cells were transfected with D1 or c-myc cDNA and treated with CDDP alone or together with NPCD, an inhibitor of cyclin dependent ckinase (CDK) 4 and 6. Reverse transcription followed by polymerase chain reaction (RT-PCR) and western blot assays were used to determine the mRNA and protein levels of interested genes. Cell viability was determined using 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay.

Results:

Treatment of Ela-mycPT1 cells with CDDP caused an increase in c-myc expression but a slightly latent decrease in D1 expression, whereas D1 and c-Myc proteins repressed each other. D1 or c-Myc rendered Ela-mycPT1 cells resistant or sensitive, respectively, to CDDP. D1 induced the expression of several members of the NF-κB family, including RelA, RelB, Nfκb1 and Nfκb2. D1 also induced BIRC5 and several pro-survival members of the Bcl-2 gene family, including Bcl-2 , Mcl-1 and Bad while it decreased the level of the pro-apoptotic Noxa. Inhibition of CDK4 or CDK6 kinase activity by NPCD did not affect these effects of D1. In contrast, c-Myc in Ela-mycPT1 and Ela-mycPT4 cells has the opposite effects to D1 on the expression of most of these apoptosis regulating genes.

Conclusion:

Our results suggest that induction of c-Myc and inhibition of D1 may be mechanisms for CDDP to elicit cytotoxicity. On the other hand, D1 induces whereas c-Myc represses the expression of key NF-κB family members to induce and repress, respectively, the expression of BIRC5 and several Bcl-2 family members, in turn inhibiting or enhancing the response to CDDP.

Myc: the beauty and the beast

The iconic history of the Myc oncoprotein encompasses 3 decades of intense scientific discovery. There is no question that Myc has been a pioneer, advancing insight into the molecular basis of cancer as well as functioning as a critical control center for several diverse biological processes and regulatory mechanisms. This narrative chronicles the journey and milestones that have defined the understanding of Myc, and it provides an opportunity to consider future directions in this challenging yet rewarding field.

Comparison of doxorubicin and weekly paclitaxel efficacy in metastatic angiosarcomas

BACKGROUND

Data regarding the role of anthracyclines and taxanes as first-line treatments of metastatic angiosarcoma are limited.

METHODS

Records of 117 metastatic angiosarcoma patients who were treated with either doxorubicin or weekly paclitaxel were reviewed.

RESULTS

Seventy-five patients (64%) were treated with weekly paclitaxel and 42 (36%) with single-agent doxorubicin. Patients in the weekly paclitaxel group were older and more frequently had angiosarcomas arising from the skin. In the doxorubicin group, 34 patients were evaluable for response: 2 (6%) had complete response, 8 (23.5%) had partial response, 10 (29.5%) had stable disease, and 14 (41%) had progressive disease. In the weekly paclitaxel group, 68 patients were evaluable for response: 9 (13%) had complete response, 27 (40%) had partial response, 20 (29.5%) had stable disease, and 12 (17.5%) had progressive disease. Objective responses to weekly paclitaxel were more frequent in cutaneous angiosarcomas, whereas tumor location did not impact response to doxorubicin. Median progression-free survival (PFS) was 4.9 months (95% confidence interval [95% CI], 3.9-6.0 months). Median overall survival (OS) was 8.5 months (95% CI, 6.4-10.7 months). On multivariate analysis, ECOG performance status (PS) was the sole independent factor associated with PFS and OS.

CONCLUSIONS

First-line single-agent doxorubicin and weekly paclitaxel seem to have similar efficacy in metastatic angiosarcomas. Cutaneous angiosarcomas respond favorably to weekly paclitaxel. Best supportive care should be considered in patients with poor PS.

The cooperating mutation or “second hit” determines the immunologic visibility toward MYC-induced murine lymphomas

In Eμ-myc transgenic animals lymphoma formation requires additional genetic alterations, which frequently comprise loss of p53 or overexpression of BCL-2. We describe that the nature of the “second hit” affects the ability of the immune system to contain lymphoma development. Tumors with disrupted p53 signaling killed the host more rapidly than BCL-2 overexpressing ones. Relaxing immunologic control, using Tyk2−/− mice or by Ab-mediated depletion of CD8+ T or natural killer (NK) cells accelerated formation of BCL-2–overexpressing lymphomas but not of those lacking p53. Most strikingly, enforced expression of BCL-2 prolonged disease latency in the absence of p53, whereas blocking p53 function in BCL-2–overexpressing tumors failed to accelerate disease. This shows that blocking apoptosis in p53-deficient cells by enforcing BCL-2 expression can mitigate disease progression increasing the “immunologic visibility.” In vitro cytotoxicity assays confirmed that high expression of BCL-2 protein facilitates NK and T cell–mediated killing. Moreover, we found that high BCL-2 expression is accompanied by significantly increased levels of the NKG2D ligand MULT1, which may account for the enhanced killing. Our findings provide first evidence that the nature of the second hit affects tumor immunosurveillance in c-MYC–driven lymphomas and define a potential shortcoming of antitumor therapies targeting BCL-2.

Chk2 deficiency in Myc overexpressing lymphoma cells elicits a synergistic lethal response in combination with PARP inhibition

Myc is a transcription factor frequently found deregulated in human cancer. The Myc-mediated cellular transformation process is associated with fast proliferative cells and inherent genomic instability, giving rise to malignant, invasive neoplasms with poor prognosis for survival. Transcription-independent functions of Myc include stimulation of replication. Excessive Myc expression stimulates a replication-associated DNA damage response that signals via the phosphoinositide-3-kinase (PI3K)-related protein kinases (PIKKs) ATM and ATR. These, in turn, activate the DNA damage transducers Chk1 and Chk2. Here, we show that Myc can stimulate Chek2 transcript indirectly in vitro as well as in B cells of λ-Myc transgenic mice or in the intestine of Apc (Min) mice. However, Chk2 is dispensable for Myc's ability to transform cells in vitro and for the survival of established lymphoma cells from λ-Myc transgenic mice. Chk2 deficiency induces polyploidy and slow growth, but the cells are viable and protected against DNA damage. Furthermore, inhibition of both Chk1/Chk2 with AZD7762 induces cell death and significantly delays disease progression of transplanted lymphoma cells in vivo. DNA damage recruits PARP family members to sites of DNA breaks that, in turn, facilitate the induction of DNA repair. Strikingly, combining Chk2 and PARP inhibition elicits a synergistic lethal response in the context of Myc overexpression. Our data indicates that only certain types of chemotherapy would give rise to a synergistic lethal response in combination with specific Chk2 inhibitors, which will be important if Chk2 inhibitors enter the clinic.

Therapeutic implications for the induced levels of Chk1 in Myc-expressing cancer cells

PURPOSE

The transcription factor c-Myc (or "Myc") is a master regulator of pathways driving cell growth and proliferation. MYC is deregulated in many human cancers, making its downstream target genes attractive candidates for drug development. We report the unexpected finding that B-cell lymphomas from mice and patients exhibit a striking correlation between high levels of Myc and checkpoint kinase 1 (Chk1).

EXPERIMENTAL DESIGN

By in vitro cell biology studies as well as preclinical studies using a genetically engineered mouse model, we evaluated the role of Chk1 in Myc-overexpressing cells.

RESULTS

We show that Myc indirectly induces Chek1 transcript and protein expression, independently of DNA damage response proteins such as ATM and p53. Importantly, we show that inhibition of Chk1, by either RNA interference or a novel highly selective small molecule inhibitor, results in caspase-dependent apoptosis that affects Myc-overexpressing cells in both in vitro and in vivo mouse models of B-cell lymphoma.

CONCLUSION

Our data suggest that Chk1 inhibitors should be further evaluated as potential drugs against Myc-driven malignancies such as certain B-cell lymphoma/leukemia, neuroblastoma, and some breast and lung cancers.

The MK5/PRAK kinase and Myc form a negative feedback loop that is disrupted during colorectal tumorigenesis

Expression of the Myc oncoprotein is downregulated in response to stress signals to allow cells to cease proliferation and escape apoptosis, but the mechanisms involved in this process are poorly understood. Cell cycle arrest in response to DNA damage requires downregulation of Myc via a p53-independent signaling pathway. Here we have used siRNA screening of the human kinome to identify MAPKAPK5 (MK5, PRAK) as a negative regulator of Myc expression. MK5 regulates translation of Myc, since it is required for expression of miR-34b and miR-34c that bind to the 3'UTR of MYC. MK5 activates miR-34b/c expression via phosphorylation of FoxO3a, thereby promoting nuclear localization of FoxO3a and enabling it to induce miR-34b/c expression and arrest proliferation. Expression of MK5 in turn is directly activated by Myc, forming a negative feedback loop. MK5 is downregulated in colon carcinomas, arguing that this feedback loop is disrupted during colorectal tumorigenesis.

c-Myc induction of programmed cell death may contribute to carcinogenesis: a perspective inspired by several concepts of chemical carcinogenesis

The c-Myc protein, encoded by c-myc gene, in its wild-type form can induce tumors with a high frequency and can induce massive programmed cell death (PCD) in most transgenic mouse models, with greater efficiency than other oncogenes. Evidence also indicates that c-Myc can cause proliferative inhibition, i.e. mitoinhibition. The c-Myc-induced PCD and mitoinhibition, which may be attributable to its inhibition of cyclin D1 and induction of p53, may impose a pressure of compensatory proliferation, i.e. regeneration, onto the initiated cells (cancer progenitor cells) that occur sporadically and are resistant to the mitoinhibition. The initiated cells can thus proliferate robustly and progress to a malignancy. This hypothetical thinking, i.e. the concurrent PCD and mitoinhibition induced by c-Myc can promote carcinogenesis, predicts that an optimal balance is achieved between cell death and ensuing regeneration during oncogenic transformation by c-Myc, which can better promote carcinogenesis. In this perspective, we summarize accumulating evidence and challenge the current model that oncoprotein induces carcinogenesis by promoting cellular proliferation and/or inhibiting PCD. Inspired by c-myc oncogene, we surmise that many tumor-suppressive or growth-inhibitory genes may also be able to promote carcinogenesis in a similar way, i.e. by inducing PCD and/or mitoinhibition of normal cells to create a need for compensatory proliferation that drives a robust replication of initiating cells.

c-MYC expression sensitizes medulloblastoma cells to radio- and chemotherapy and has no impact on response in medulloblastoma patients

Background

To study whether and how c-MYC expression determines response to radio- and chemotherapy in childhood medulloblastoma (MB).

Methods

We used DAOY and UW228 human MB cells engineered to stably express different levels of c-MYC, and tested whether c-MYC expression has an effect on radio- and chemosensitivity using the colorimetric 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt (MTS) assay, clonogenic survival, apoptosis assays, cell cycle analysis, and western blot assessment. In an effort to validate our results, we analyzed c-MYC mRNA expression in formalin-fixed paraffin-embedded tumor samples from well-documented patients with postoperative residual tumor and compared c-MYC mRNA expression with response to radio- and chemotherapy as examined by neuroradiological imaging.

Results

In DAOY - and to a lesser extent in UW228 - cells expressing high levels of c-MYC, the cytotoxicity of cisplatin, and etoposide was significantly higher when compared with DAOY/UW228 cells expressing low levels of c-MYC. Irradiation- and chemotherapy-induced apoptotic cell death was enhanced in DAOY cells expressing high levels of c-MYC. The response of 62 of 66 residual tumors was evaluable and response to postoperative radio- (14 responders (CR, PR) vs. 5 non-responders (SD, PD)) or chemotherapy (23 CR/PR vs. 20 SD/PD) was assessed. c-MYC mRNA expression was similar in primary MB samples of responders and non-responders (Mann-Whitney U test, p = 0.50, ratio 0.49, 95% CI 0.008-30.0 and p = 0.67, ratio 1.8, 95% CI 0.14-23.5, respectively).

Conclusions

c-MYC sensitizes MB cells to some anti-cancer treatments in vitro. As we failed to show evidence for such an effect on postoperative residual tumors when analyzed by imaging, additional investigations in xenografts and larger MB cohorts may help to define the exact function of c-MYC in modulating response to treatment.

Low-dose ionizing radiation effects on differentiation of HL-60 cells

The biological effects of low-dose radiation have attracted attention, but data are currently insufficient to fully understand the beneficial role of the phenomenon. In the present study, we have investigated the effects of low doses of gamma-irradiation alone and in combination with all-trans-retinoic acid (RA) on proliferation, apoptosis and differentiation of the human promyelocytic leukemia HL-60 cells. Changes in cell behavior and protein expression were determined with the use of light and fluorescent microscopy, immunocytochemical and Western blot analysis. Low-dose irradiation with 1–100 cGy caused a dose-dependent inhibition of HL-60 cell proliferation, and induced apoptosis and differentiation to granulocytes with an increase in the number of CD15-positive cells. Pre-irradiation with 1–100 cGy for 24 h before treatment with RA promoted apoptosis but did not impair RA-induced differentiation. Both processes were associated with a decrease in the expression of the proliferating cell nuclear antigen (PCNA), BCL-2, c-MYC, and changes in both cytosolic and nuclear levels of protein tyrosine-phosphorylation as well as protein kinase C alpha or beta isoforms. These results demonstrate the beneficial role of low-dose irradiation in modulating leukemia cell proliferation, differentiation and apoptosis.

Skp2 directs Myc-mediated suppression of p27Kip1 yet has modest effects on Myc-driven lymphomagenesis

The universal cyclin-dependent kinase inhibitor p27(Kip1) functions as a tumor suppressor, and reduced levels of p27(Kip1) connote poor prognosis in several human malignancies. p27(Kip1) levels are predominately regulated by ubiquitin-mediated turnover of the protein, which is marked for destruction by the E3 ubiquitin ligase SCF(Skp2) complex following its phosphorylation by the cyclin E-cyclin-dependent kinase 2 complex. Binding of phospho-p27(Kip1) is directed by the Skp2 F-box protein, and this is greatly augmented by its allosteric regulator Cks1. We have established that programmed expression of c-Myc in the B cells of Emu-Myc transgenic mice triggers p27(Kip1) destruction by inducing Cks1, that this response controls Myc-driven proliferation, and that loss of Cks1 markedly delays Myc-induced lymphomagenesis and cancels the dissemination of these tumors. Here, we report that elevated levels of Skp2 are a characteristic of Emu-Myc lymphomas and of human Burkitt lymphoma that bear MYC/Immunoglobulin chromosomal translocations. As expected, Myc-mediated suppression of p27(Kip1) was abolished in Skp2-null Emu-Myc B cells. However, the effect of Skp2 loss on Myc-driven proliferation and lymphomagenesis was surprisingly modest compared with the effects of Cks1 loss. Collectively, these findings suggest that Cks1 targets, in addition to p27(Kip1), are critical for Myc-driven proliferation and tumorigenesis.