Induction Of C-myc Expression Research Articles

FBXL6 is dysregulated in keloids and promotes keloid fibroblast growth by inducing c-Myc expression.

C-MYC-mediated keloid fibroblasts proliferation and collagen deposit may contribute to the development of keloids. F-box and leucine-rich repeat protein 6 (FBXL6) is reported to be involved in tumour progression, while the role of FBXL6 in keloid fibroblasts is not deciphered. Normal control skins, hypertrophic scars and keloid tissues were collected and prepared for FBXL6 detection. FBXL6 short hairpin RNAs (shRNAs) or FBXL6 over-expression plasmids were transfected into keloid fibroblasts, and then c-MYC plasmids were further transfected. Cell viability was assayed with a Cell-Counting Kit-8 kit. The relative expression of FBXL6, Cyclin A1, Cyclin D2, Cyclin E1 and Collagen I was detected with real-time PCR and Western blot. Elevated FBXL6 expression could be observed in keloid tissues and hypertrophic scars. FBXL6 shRNAs transfection could inhibit the viability of keloid fibroblasts with diminished c-MYC expression and down-regulated Cyclin A1, Cyclin D2, Cyclin E1 and Collagen I expression. At the same time, overexpressed FBXL6 could promote the proliferation of keloid fibroblasts. Overexpression of c-MYC could promote the proliferation of keloid fibroblasts reduced by FBXL6 shRNAs with up-regulated Cyclin A1 and Collagen I expression. FBXL6 could promote the growth of keloid fibroblasts by inducing c-MYC expression, which could be targeted in keloids treatment.

Histone demethylase KDM4C controls tumorigenesis of glioblastoma by epigenetically regulating p53 and c-Myc

Glioblastoma is the most lethal brain tumor and its pathogenesis remains incompletely understood. KDM4C is a histone H3K9 demethylase that contributes to epigenetic regulation of both oncogene and tumor suppressor genes and is often overexpressed in human tumors, including glioblastoma. However, KDM4C’s roles in glioblastoma and the underlying molecular mechanisms remain unclear. Here, we show that KDM4C knockdown significantly represses proliferation and tumorigenesis of glioblastoma cells in vitro and in vivo that are rescued by overexpressing wild-type KDM4C but not a catalytic dead mutant. KDM4C protein expression is upregulated in glioblastoma, and its expression correlates with c-Myc expression. KDM4C also binds to the c-Myc promoter and induces c-Myc expression. Importantly, KDM4C suppresses the pro-apoptotic functions of p53 by demethylating p53K372me1, which is pivotal for the stability of chromatin-bound p53. Conversely, depletion or inhibition of KDM4C promotes p53 target gene expression and induces apoptosis in glioblastoma. KDM4C may serve as an oncogene through the dual functions of inactivation of p53 and activation of c-Myc in glioblastoma. Our study demonstrates KDM4C inhibition as a promising therapeutic strategy for targeting glioblastoma.

MEK5/ERK5 signaling mediates IL-4-induced M2 macrophage differentiation through regulation of c-Myc expression.

Macrophages are highly plastic cells, responding to diverse environmental stimuli to acquire different functional phenotypes. Signaling through MAPKs has been reported to regulate the differentiation of macrophages, but the role of ERK5 in IL-4-mediated M2 macrophage differentiation is still unclear. Here, we showed that the ERK5 signaling pathway plays a critical role in IL-4-induced M2 macrophage differentiation. Pharmacologic inhibition of MEK5, an upstream activator of ERK5, markedly reduced the expression of classical M2 markers, such as Arg-1, Ym-1, and Fizz-1, as well as the production of M2-related chemokines and cytokines, CCL22, CCL17, and IGF-1 in IL-4-stimulated macrophages. Moreover, pharmacologic inhibition of ERK5 also decreased the expression of several M2 markers induced by IL-4. In accordance, myeloid cell-specific Erk5 depletion (Erk5∆mye ), using LysMcre /Erk5f/f mice, confirmed the involvement of ERK5 in IL-4-induced M2 polarization. Mechanistically, the inhibition of ERK5 did not affect STAT3 or STAT6 phosphorylation, suggesting that ERK5 signaling regulates M2 differentiation in a STAT3 and STAT6-independent manner. However, genetic deficiency or pharmacologic inhibition of the MEK5/ERK5 pathway reduced the expression of c-Myc in IL-4-activated macrophages, which is a critical transcription factor involved in M2 differentiation. Our study thus suggests that the MEK5/ERK5 signaling pathway is crucial in IL-4-induced M2 macrophage differentiation through the induction of c-Myc expression.

CircRNA_010763 promotes growth and invasion of lung cancer through serving as a molecular sponge of miR-715 to induce c-Myc expression.

This study aims to investigate the regulatory effect of circRNA_010763 on the growth and invasion of non-small cell lung cancer (NSCLC). qRT-PCR was performed to detect the expressions of circRNA_010763 and c-Myc in human NSCLC tissues and cells. CCK-8 assay was performed to evaluate the A549 cells proliferation and transwell assay was performed to evaluate the A549 cells migration. The correlation between miR-715 and circRNA_010763 was detected by statistical analysis. Bioinformatics prediction and Luciferase assay were performed to explore the interaction and binding site of circRNA_010763 and miR-715, miR-715 and c-Myc, respectively. We found that both circRNA_010763 and c-Myc were upregulated in human NSCLC tissues and cells. qRT-PCR and CCK-8 assay showed that circRNA_010763 expression is associated with the proliferation of NSCLC cells. Transwell assay showed that circRNA_010763 regulated the migration ability of NSCLC cells. The bioinformatics prediction and Luciferase assay demonstrated that circRNA_010763 can sponge with miR-715, serving as a molecular sponge to further regulate the expression of c-Myc. In this study, we found that circRNA_010763 was highly expressed in human NSCLC tissues, which could promote tumor proliferation, migration and invasion through serving as a molecular sponge by modulating the inhibitory effect of miR-715 on oncogene c-Myc.

Salt-inducible kinase 1 maintains HDAC7 stability to promote pathologic cardiac remodeling.

Salt-inducible kinases (SIKs) are key regulators of cellular metabolism and growth, but their role in cardiomyocyte plasticity and heart failure pathogenesis remains unknown. Here, we showed that loss of SIK1 kinase activity protected against adverse cardiac remodeling and heart failure pathogenesis in rodent models and cardiomyocytes derived from human induced pluripotent stem cells. We found that SIK1 phosphorylated and stabilized histone deacetylase 7 (HDAC7) protein during cardiac stress, an event that is required for pathologic cardiomyocyte remodeling. Gain- and loss-of-function studies of HDAC7 in cultured cardiomyocytes implicated HDAC7 as a prohypertrophic signaling effector that can induce c-Myc expression, indicating a functional departure from the canonical MEF2 corepressor function of class IIa HDACs. Taken together, our findings reveal what we believe to be a previously unrecognized role for a SIK1/HDAC7 axis in regulating cardiac stress responses and implicate this pathway as a potential target in human heart failure.

EREG-driven oncogenesis of Head and Neck Squamous Cell Carcinoma exhibits higher sensitivity to Erlotinib therapy.

Rationale: The oncogenesis of head and neck squamous cell carcinoma (HNSCC) is believed to result from oncogene activation and tumor suppressor inactivation. Here, we identified a new oncogenic role for the EREG gene in HNSCC.Methods: The TCGA database and immunohistochemistry assay were used to analyze expression of EREG in HNSCC tissues. Immunoblotting was performed to identify the EGFR-mediated pathways altered by EREG. The role of EREG in oncogenesis was investigated in vivo and in vitro.Results: Upregulated EREG expression predicted a poor prognosis and triggered HNSCC oncogenic transformation by activating the epidermal growth factor receptor (EGFR) signaling pathway. We also demonstrated the direct association of EREG with EGFR and that this binding required EGFR domains I and III and the N57 residue of EREG. Moreover, EREG overexpression was shown to promote HNSCC oncogenesis by inducing C-Myc expression, and the pharmacological inhibition of C-Myc rescued EREG-promoted HNSCC oncogenesis. Unlike other EGFR ligands, EREG could mimic EGFR mutations by sustaining the activation of the EGFR-Erk pathway, and high EREG expression was positively associated with the response to treatment with the EGFR inhibitor erlotinib. Furthermore, knockdown of EREG decreased sensitivity to erlotinib treatment in vitro and in vivo.Conclusions: These results identify the EREG-EGFR-C-Myc pathway as a crucial axis that drives HNSCC oncogenesis and show that EREG expression could be a predictive functional marker of sensitivity to erlotinib therapy in HNSCC.

Loss of FOXP3 and TSC1 Accelerates Prostate Cancer Progression through Synergistic Transcriptional and Posttranslational Regulation of c-MYC.

Although c-MYC and mTOR are frequently activated proteins in prostate cancer, any interaction between the two is largely untested. Here, we characterize the functional cross-talk between FOXP3-c-MYC and TSC1-mTOR signaling during tumor progression. Deletion of Tsc1 in mouse embryonic fibroblasts (MEF) decreased phosphorylation of c-MYC at threonine 58 (pT58) and increased phosphorylation at serine 62 (pS62), an observation validated in prostate cancer cells. Conversely, inhibition of mTOR increased pT58 but decreased pS62. Loss of both FOXP3 and TSC1 in prostate cancer cells synergistically enhanced c-MYC expression via regulation of c-Myc transcription and protein phosphorylation. This crosstalk between FOXP3 and TSC1 appeared to be mediated by both the mTOR-4EBP1-c-MYC and FOXP3-c-MYC pathways. In mice, Tsc1 and Foxp3 double deletions in the prostate led to prostate carcinomas at an early age; this did not occur in these mice with an added c-Myc deletion. In addition, we observed synergistic antitumor effects of cotreating mice with inhibitors of mTOR and c-MYC in prostate cancer cells and in Foxp3 and Tsc1 double-mutant mice. In human prostate cancer, loss of nuclear FOXP3 is often accompanied by low expression of TSC1. Because loss of FOXP3 transcriptionally induces c-Myc expression and loss of TSC1 activates mTOR signaling, these data suggest cross-talk between FOXP3-c-MYC and TSC1-mTOR signaling that converges on c-MYC to regulate tumor progression. Coadministration of c-MYC and mTOR inhibitors may overcome the resistance to mTOR inhibition commonly observed in prostate cancer cells. SIGNIFICANCE: These results establish the principle of a synergistic action of TSC1 and FOXP3 during prostate cancer progression and provide new therapeutic targets for patients who have prostate cancer with two signaling defects.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/7/1413/F1.large.jpg.

Integrin CD11b activation drives anti-tumor innate immunity

Myeloid cells are recruited to damaged tissues where they can resolve infections and tumor growth or stimulate wound healing and tumor progression. Recruitment of these cells is regulated by integrins, a family of adhesion receptors that includes integrin CD11b. Here we report that, unexpectedly, integrin CD11b does not regulate myeloid cell recruitment to tumors but instead controls myeloid cell polarization and tumor growth. CD11b activation promotes pro-inflammatory macrophage polarization by stimulating expression of microRNA Let7a. In contrast, inhibition of CD11b prevents Let7a expression and induces cMyc expression, leading to immune suppressive macrophage polarization, vascular maturation, and accelerated tumor growth. Pharmacological activation of CD11b with a small molecule agonist, Leukadherin 1 (LA1), promotes pro-inflammatory macrophage polarization and suppresses tumor growth in animal models of murine and human cancer. These studies identify CD11b as negative regulator of immune suppression and a target for cancer immune therapy.

PIM1 overexpression in T-cell lymphomas protects tumor cells from apoptosis and confers doxorubicin resistance by upregulating c-myc expression.

T-cell lymphomas (TCLs) are a malignancy characterized by tumor aggression and resistance to traditional chemotherapy. Disruption of the extrinsic cell death pathway is essential for resistance to chemotherapy. PIM1 serves as a crucial modulator in cancers. However, the role of PIM1 in TCLs remains unclear. In this study, we studied the roles of PIM1 in established T-lymphoma cell lines Jurkat and HUT-78. CCK-8 assay was conducted to evaluate cell survival and flow cytometry was performed to evaluate cell death of TCL cells. siRNAs were used to knockdown the expression of PIM1 and c-myc. qRT-PCR was used to evaluate the mRNA expression levels of c-myc and PIM1. Western blot analysis was used to evaluate the protein expression levels of PIM1, c-myc, STAT3, and phospho-STAT3. Doxorubicin was used to determine the effect of PIM1 on apoptosis. Our results showed that PIM1 expression was markedly enhanced and induced c-myc expression in TCL cells. Doxorubicin inhibited the expressions of c-myc and PIM1, and triggered the extrinsic cell death of TCLs by suppressing the JAK-STAT3 signaling pathway. Moreover, PIM1 silencing via siRNA suppressed c-myc expression, promoted the cell death of TCLs, and increased doxorubicin sensitivity. Conversely, PIM1 overexpression in TCL cells induced c-myc expression, suppressed TCL cell death, and promoted doxorubicin resistance. Collectively, our results demonstrate that PIM1 overexpression in TCLs participates in cancer cell protection from apoptosis and leads to doxorubicin resistance by inducing c-myc expression, indicating that PIM1 may be a promising target in TCL treatment.

Effects of arecoline on proliferation of oral squamous cell carcinoma cells by dysregulating c-Myc and miR-22, directly targeting oncostatin M.

Arecoline, the major alkaloid of areca nut, is known to induce oral carcinogenesis, however, its mechanism is still needed to elucidate. This study investigated the effects of arecoline on cell viability and cell-cycle progression of oral squamous cell carcinoma (OSCC) cells as well as a relevant cellular gene expression. The results showed that a low concentration of arecoline (0.025 μg/ml) increased OSCC cell viability, proportion of cells in G2/M phase and cell proliferation. Simultaneously, it induced IL-6, STAT3 and c-Myc expression. Interestingly, c-myc promoter activity was also induced by arecoline. MiR-22 expression in arecoline-treated OSCC cells was suppressed and comparable to an upregulated c-Myc expression. In arecoline-treated OSCC cells, oncostatin M (OSM) expression was significantly upregulated and inversely correlated with miR-22 expression. Likewise, OSM expression and its post-transcriptional activity were significantly decreased in miR-22-transfected OSCC and 293FT cells. This result demonstrated that miR-22 directly targeted OSM. Interestingly, miR-22 played an important role as a tumor suppresser on suppressing cell proliferation, migration and cell-cycle progression of OSCC cells. This result suggested the effect of arecoline to promote cell proliferation and cell-cycle progression of OSCC cells might be involved in induction of c-Myc expression and reduction of miR-22 resulting in OSM upregulation.

Clinical significance of NS1-BP expression in esophageal squamous cell carcinoma

Objective: To investigate the clinical significance of NS1-BP expression in patients with esophageal squamous cell carcinoma (ESCC), and to study the roles of NS1-BP in proliferation and apoptosis of ESCC cells. Methods: A total of 98 tumor tissues and 30 adjacent normal tissues from 98 ESCC patients were used as study group and control group, and these samples were collected in Sun Yat-Sen University Cancer Center between 2002 and 2008. In addition, 46 ESCC tissues which were collected in Cancer Institute and Hospital of Tianjin Medical University were used as validation group. Expression of mucosal NS1-BP was detected by immunohistochemistry. Kaplan-Meier curve and log-rank test were used to analyze the survival rate. Multivariate Cox proportional hazard model was used to analyze the prognostic factors. Furthermore, NS1-BP was over expressed or knocked down in ESCC cells by transient transfection. Protein levels of c-Myc were detected by western blot. Cell viability and apoptosis was analyzed by MTT assay and flow cytometry. Results: Among all of tested samples, NS1-BP were down-regulated in 9 out of 30 non-tumorous normal esophageal tissues (30.0%) and 85 out of 144 ESCC tissues (59.0%), respectively, showing a statistically significant difference (P=0.012). In the study group, three-year disease-free survival rate of NS1-BP high expression group (53.2%) was significantly higher than that of NS1-BP low expression group (27.6%; P=0.009). In the validation group, the three-year disease-free survival rates were 57.8% and 25.5% in NS1-BP high and low levels groups, respectively, showing a similar results (P=0.016). Importantly, multivariate analyses showed that low expression of NS1-BP was an independent predictor for chemoradiotherapy sensitivity and shorter disease-free survival time in ESCC patients(P<0.05 for all). Furthermore, overexpressed NS1-BP in TE-1 cells repressed c-Myc expression, inhibited cell proliferation and promoted apoptosis. In contrast, knockdown NS1-BP in KYSE510 cells induced c-Myc expression, increased cell proliferation and repressed apoptosis. Conclusions: NS1-BP is an independent favorable prognostic factor in ESCC. It inhibits cell proliferation and enhances cell apoptosis via repressing c-Myc. Targeting NS1-BP may be a new therapeutic strategy for ESCC patients.

Galectin-3 expression is prognostic in diffuse type gastric adenocarcinoma, confers aggressive phenotype, and can be targeted by YAP1/BET inhibitors

Background:Overexpression of Galectin-3 (Gal-3), a β-galactoside binding protein, has been noted in many tumour types but its functional significance and clinical utility in gastric adenocarcinoma (GAC) are not well known.Methods:We studied 184 GAC patients characterised by histologic grade, sub-phenotypes (diffuse vs intestinal), and ethnicity (Asians vs North Americans). Immunohistochemistry was performed to assess the expression of Gal-3 in human GACs and we correlated it to the clinical outcomes. Cell proliferation, invasion, co-immunoprecipitation and kinase activity assays were done in genetically stable Gal-3 overexpressing GC cell lines and the parental counterparts to delineate the mechanisms of action and activity of inhibitors.Results:Most patients were men, Asian, and had a poorly differentiated GAC. Gal-3 was over-expressed in poorly differentiated (P=0.002) tumours and also in diffuse sub-phenotype (P=0.02). Gal-3 overexpression was associated with shorter overall survival (OS; P=0.026) in all patients. Although, Gal-3 over-expression was not prognostic in the Asian cohort (P=0.337), it was highly prognostic in the North American cohort (P=0.001). In a multivariate analysis, Gal-3 (P=0.001) and N-stage (P=<0.001) were independently prognostic for shorter OS. Mechanistically, Gal-3 induced c-MYC expression through increasing RalA activity and an enhanced YAP1/RalA/RalBP complex to confer an aggressive phenotype. YAP1/BET bromodomain inhibitors reduced Gal-3-mediated aggressive phenotypes in GAC cells.Conclusions:Gal-3 is an independent prognostic marker of shorter OS and a novel therapeutic target particularly in diffuse type GAC in North American patients.

Expression of cell cycle regulators and biomarkers of proliferation and regrowth in human pituitary adenomas.

The pathogenesis of pituitary adenomas (PA) is complex. Ki-67, pituitary tumour transforming gene (PTTG), vascular endothelial growth factor (VEGF), cyclin D1, c-MYC and pituitary adenylate cyclase-activating peptide (PACAP) protein expression were analysed and correlated with tumour and patient characteristics. 74 pituitary tumour samples (48 non-functional PA, 26 functional PAs); Immunohistochemical analysis of protein expression, retrospective analysis of MR images and in vitro analysis of octreotide treatment was carried out on GH3 cells. PTTG expression was negatively associated with age and positively with PA size, regrowth and Ki-67 index. Cyclin D1 correlated with Ki-67 and tumour size. c-MYC negatively correlated with size of tumour and age; and correlated with PTTG expression. Somatostatin analogue treatment was associated with lower Ki-67, PTTG and Cyclin D1 expression while T2 hypointense PAs were associated with lower PTTG, cyclin D1, c-MYC and Ki-67. In vitro analyses confirmed the effect of somatostatin analogue treatment on Pttg and Cyclin D1 expression. Interesting and novel observations on the differences in expression of tumour markers studied are reported. Correlation between Ki-67 expression, PTTG nuclear expression and recurrence/regrowth of PAs, emphasizes the role that Ki-67 and PTTG expression have as markers of increased proliferation. c-MYC and PTTG nuclear expression levels were correlated providing evidence that PTTG induces c-MYC expression in PAs and we propose that c-MYC might principally have a role in early pituitary tumorigenesis. Evidence is shown that the anti-proliferative effect of somatostatin analogue treatment in vivo occurs through regulation of the cell cycle.

Haploinsufficiency of SIRT1 Enhances Glutamine Metabolism and Promotes Cancer Development

SIRT1, the most conserved mammalian NAD+-dependent protein deacetylase, plays a vital role in the regulation of metabolism, stress responses, and genome stability. However, the role of SIRT1 in the multi-step process leading to transformation and/or tumorigenesis, as either a tumor suppressor or tumor promoter, is complex and may be dependent upon the context in which SIRT1 activity is altered, and the role of SIRT1 in tumor metabolism is unknown. Here, we demonstrate that SIRT1 dose-dependently regulates cellular glutamine metabolism and apoptosis, which in turn differentially impact cell proliferation and cancer development. Heterozygous deletion of Sirt1 induces c-Myc expression, enhancing glutamine metabolism and subsequent proliferation, autophagy, stress resistance, and cancer formation. In contrast, homozygous deletion of Sirt1 triggers cellular apoptotic pathways, increases cell death, diminishes autophagy, and reduces cancer formation. Consistent with the observed dose dependence in cells, intestine-specific Sirt1 heterozygous mice have enhanced intestinal tumor formation, whereas intestine-specific Sirt1 homozygous knockout mice have reduced development of colon cancer. Furthermore, SIRT1 reduction, but not deletion, is associated with human colorectal tumors, and colorectal cancer patients with low protein expression of SIRT1 have a poor prognosis. Taken together, our findings indicate that the dose-dependent regulation of tumor metabolism and possibly apoptosis by SIRT1 mechanistically contribute to the observed dual roles of SIRT1 in tumorigenesis. Our study highlights the importance of maintenance of a suitable SIRT1 dosage for metabolic and tissue homeostasis, which will have important implications in SIRT1-small-molecule-activator/inhibitor-based therapeutic strategies for cancers.

Telomere length: A possible link between phthalate exposure and cancer development?

Telomere length: A possible link between phthalate exposure and cancer development?

Ibuprofen and Diclofenac Restrict Migration and Proliferation of Human Glioma Cells by Distinct Molecular Mechanisms.

BackgroundNon-steroidal anti-inflammatory drugs (NSAIDs) have been associated with anti-tumorigenic effects in different tumor entities. For glioma, research has generally focused on diclofenac; however data on other NSAIDs, such as ibuprofen, is limited. Therefore, we performed a comprehensive investigation of the cellular, molecular, and metabolic effects of ibuprofen and diclofenac on human glioblastoma cells.MethodsGlioma cell lines were treated with ibuprofen or diclofenac to investigate functional effects on proliferation and cell motility. Cell cycle, extracellular lactate levels, lactate dehydrogenase-A (LDH-A) expression and activity, as well as inhibition of the Signal Transducer and Activator of Transcription 3 (STAT-3) signaling pathway, were determined. Specific effects of diclofenac and ibuprofen on STAT-3 were investigated by comparing their effects with those of the specific STAT-3 inhibitor STATTIC.ResultsIbuprofen treatment led to a stronger inhibition of cell growth and migration than treatment with diclofenac. Proliferation was affected by cell cycle arrest at different checkpoints by both agents. In addition, diclofenac, but not ibuprofen, decreased lactate levels in all concentrations used. Both decreased STAT-3 phosphorylation; however, diclofenac led to decreased c-myc expression and subsequent reduction in LDH-A activity, whereas treatment with ibuprofen in higher doses induced c-myc expression and less LDH-A alteration.ConclusionsThis study indicates that both ibuprofen and diclofenac strongly inhibit glioma cells, but the subsequent metabolic responses of both agents are distinct. We postulate that ibuprofen may inhibit tumor cells also by COX- and lactate-independent mechanisms after long-term treatment in physiological dosages, whereas diclofenac mainly acts by inhibition of STAT-3 signaling and downstream modulation of glycolysis.

Radiofrequency ablation-increased CXCL10 is associated with earlier recurrence of hepatocellular carcinoma by promoting stemness.

Radiofrequency ablation (RFA) represents a valuable choice in hepatocellular carcinoma (HCC); however, local recurrence of HCC is common after RFA. Here, 20 primary HCC patients treated by RFA were enrolled. Before (termed 0d) and after RFA treatment for 1 and 7days (termed 1d and 7d, respectively), plasma and noncancerous tissue were collected. ELISA assay showed that plasma C-X-C motif chemokine 10 (CXCL10) was increased in ten patients (type I patients) but decreased in the other 10 patients (type II patients). The mean interval for HCC recurrence in type I patients was less than the mean interval in type II patients. Interestingly, a significant negative correlation between interval for HCC recurrence and fold change of plasma CXCL10 (1d/0d or 7d/0d) was identified, suggesting that RFA-induced CXCL10 is associated with earlier HCC recurrence. Immunofluorescence assay showed that the receptor of CXCL10, chemokine (C-X-C motif) receptor 3 (CXCR3), was significantly increased in type I, but not type II, patients after RFA. In vitro assay demonstrated that CXCL10 stimulus increased the rate of CD133(+) cancer stem cells (CSCs) in HepG2 cells by binding to CXCR3 and then inducing c-Myc expression. Many studies have reported that induction of CD133(+) CSCs contributes to HCC recurrence. Thus, CXCL10-increased CD133(+) CSCs by activating CXCR3/c-Myc pathway might accelerate HCC recurrence after RFA. These data might have potential implications for HCC therapy.

Gas6/Axl in arginine-starvation therapy.

Exploiting abnormal amino acid metabolism for cancer therapy dated back to more than four decades ago by the discovery that L-asparaginase was effective in treating childhood acute lymphocytic leukemia (ALL). ALL lacks asparagine (Asn) because the key enzyme for the biosynthesis of Asn from aspartic acid, asparagine synthetase, is silenced, therefore, ALL requires Asn from the circulation for growth. Asparaginase (trade names Elspa or Concapar) catalyzes the hydrolysis of Asn in the circulation, resulting in Asn starvation and cell death. Asn starvation therapy has shown remarkable treatment efficacies [1]. Another amino acid starvation therapy strategy that has been under development is the use of pegylated arginine deiminase (ADI-PEG20) which degrades arginine (Arg) into citrulline and ammonia. Arg is an important metabolite in the urea cycle for tumor cell growth. De novo biosynthesis of Arg is regulated by the rate-limiting enzyme, argininosuccinate synthetase 1 (ASS1). Reduced levels of ASS1 expression has been found in large subpopulations of solid tumors, including malignant melanoma, hepatocellular carcinoma, prostate cancers, lung cancers and breast cancers. These ASS1low tumors require extracellular Arg to support their highly proliferative activities. ADI-PEG20 treatment causes Arg starvation resulting in tumor cell death of autophagy/apoptosis. ADI-PEG20 has been in clinical investigations for treating ASS1low tumors with promising results [2]. One major problem associated with ADI-PEG20 treatment is drug resistance due mostly to induction of ASS1 expression. Previous studies showed that ASS1 silencing is mediated by an epigenetic mechanism due to DNA methylation at the promoter region of ASS1 [3]. Tsai et al [4] demonstrated that ASS1 silencing in melanoma cells is transcriptional regulated by repressor HIF-1α which binds to the E-box of ASS1 promoter. Arg deprivation induces c-Myc expression which de-represses HIF-1α and induces ASS1 expression. The recent article by Tsai et al [5] presented a comprehensive signaling mechanism of how ASS1low cells response to Arg starvation stress leading to ASS1 activation and ADI-PEG20 resistance. These investigators reported that within minutes after Arg depletion of ASS1low cells, a reactive oxygen species-related mechanism triggers Gas6 externalization to interact with its membrane-bound receptor Axl, which then activates the downstream signal Ras/PI3K/Akt/GSK-3β growth signal, leading to accumulation of c-Myc by protein stabilization. c-Myc can also transcriptionally upregulate itself and Axl, thereby amplifying the Arg stress response signal. Upregulation of ASS1 expression by c-Myc enhances Arg production and relieves Arg-starvation stress pressure; elevated ASS1 can also feedback-downregulate c-Myc and Axl, providing a self-guarding control mechanism for Arg biosynthesis. These results demonstrated that multiple inter-regulatory pathways involving Axl, c-Myc, ASS1 regulate mammalian Arg homeostasis system and sensitivity to Arg starvation therapy using ADI-PEG20. These authors also demonstrated that expression of ASS1, c-Myc, Gas6 and Axl were elevated in primary cultures derived from two melanoma patients failed ADI-PEG20 treatments as correspondingly compared with those derived from the same patients prior to ADI-PEG20 treatment, demonstrating the clinical relevance of the observations. The mechanism that ASS1low cancer cells use Gas6/Axl growth signal in response to Arg starvation differs from the conserved general amino acid control pathway which involves rapid repressing protein synthesis due to phosphorylation of translation initiation factor 2 (eIF2) [6]. Recent studies have demonstrated that high levels of Gas6/Axl are associated with tumor aggressiveness. Moreover, elevated expression of Gas6/Axl can also affect the treatment efficacies with many cancer chemotherapeutics. Many small molecules targeting Gas6/Axl have been under development [7]. Moreover, Gas6/Axl may serve as important therapeutic markers for Arg starvation treatment. Because Gas6 secretion is the early event associated with Arg deprivation treatment, Gas6 in the liquid biopsy could become a non-invasive therapeutic marker, although a sensitive detection method may have to develop because basal level Gas6 levels in human serum is very low. Thus, the work by Tsai et al [5] provides an important rationale for further research on improving the treatment of Arg-auxotrophic tumors.

Abstract 2026: G0S2 functions as a tumor suppressor gene through inhibition of c-Myc

Abstract G0/G1 switch gene 2 (G0S2) is a direct retinoic acid target gene that is widely expressed in diverse organs and has been reported to have a role in adipose lipolysis by negatively regulating adipose triglyceride lipase (ATGL). G0S2 is also commonly silenced by DNA methylation in a variety of solid tumors including glioma, head and neck and lung cancers, and G0S2 induction is associated with retinoic acid-mediated clinical remissions in acute promyelocytic leukemia. This evidence suggests that G0S2 may possess tumor suppressor activity although definitive proof and mechanistic details are lacking. We now clearly demonstrate using G0S2 null immortalized mouse embryonic fibroblasts (MEFs) that G0S2 can function to oppose oncogene-induced transformation. G0S2 null MEFs were readily transformed with H-RAS or EGFR while wild-type MEFs were not. Importantly, re-introduction of G0S2 reversed H-RAS transformation of G0S2 null MEFs. Although G0S2 is a known regulator of fat metabolism through attenuating ATGL activity, we found that G0S2 repression of oncogene-induced transformation was independent of ATGL inhibition. Detailed microarray analysis demonstrated that G0S2 knockout alone upregulated gene signatures associated with transformation, proliferation and Myc transcriptional responses. G0S2 knockout also induced c-Myc expression at the transcript and protein level. Finally, transient and stable shRNA-mediated repression of c-Myc completely abrogated oncogene-induced transformation of G0S2 null MEFs. Taken together, these findings indicate that G0S2 can function as a tumor suppressor by opposing Myc. Studies to elucidate the mechanism underlying G0S2 regulation of Myc are ongoing. Understanding the functions and mechanisms of this novel tumor suppressor pathway may lead to new pharmacologic strategies for many cancers where G0S2 is silenced. Citation Format: Christina Y. Yim, David J. Sekula, Sarah J. Freemantle, Ethan Dmitrovsky, Michael J. Spinella. G0S2 functions as a tumor suppressor gene through inhibition of c-Myc. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2026. doi:10.1158/1538-7445.AM2015-2026

C-MYC Generates Repair Errors via Increased Transcription of Alternative-NHEJ Factors, LIG3 and PARP1, in Tyrosine Kinase-Activated Leukemias.

Leukemias expressing the constitutively activated tyrosine kinases (TK) BCR-ABL1 and FLT3/ITD activate signaling pathways that increase genomic instability through generation of reactive oxygen species (ROS), DNA double-strand breaks (DSB), and error-prone repair. The nonhomologous end-joining (NHEJ) pathway is a major pathway for DSB repair and is highly aberrant in TK-activated leukemias; an alternative form of NHEJ (ALT-NHEJ) predominates, evidenced by increased expression of DNA ligase IIIα (LIG3) and PARP1, increased frequency of large genomic deletions, and repair using DNA sequence microhomologies. This study, for the first time, demonstrates that the TK target c-MYC plays a role in transcriptional activation and subsequent expression of LIG3 and PARP1 and contributes to the increased error-prone repair observed in TK-activated leukemias. c-MYC negatively regulates microRNAs miR-150 and miR-22, which demonstrate an inverse correlation with LIG3 and PARP1 expression in primary and cultured leukemia cells and chronic myelogenous leukemia human patient samples. Notably, inhibition of c-MYC and overexpression of miR-150 and -22 decreases ALT-NHEJ activity. Thus, BCR-ABL1 or FLT3/ITD induces c-MYC expression, leading to genomic instability via augmented expression of ALT-NHEJ repair factors that generate repair errors. In the context of TK-activated leukemias, c-MYC contributes to aberrant DNA repair through downstream targets LIG3 and PARP1, which represent viable and attractive therapeutic targets.