MYC-dependent downregulation of telomerase by FLT3 inhibitors is required for their therapeutic efficacy on acute myeloid leukemia

8-Hydroxydaidzein Induces Apoptosis and Inhibits AML-Associated Gene Expression in U-937 Cells: Potential Phytochemical for AML Treatment

BACKGROUND

8-hydroxydaidzein (8-OHD) is a compound derived from daidzein, known for its anti-inflammatory and anti-proliferative properties in K562 human chronic myeloid leukemia (CML) cells. However, its effects on acute myeloid leukemia (AML) cells have not been fully understood.

METHOD

To investigate its potential anti-AML mechanism, we employed an integrated in vitro-in silico approach.

RESULTS

Our findings demonstrate that 8-OHD suppresses the expression of CDK6 and CCND2 proteins and induces cell apoptosis in U-937 cells by activating Caspase-7 and cleaving PARP-1. Microarray analysis revealed that 8-OHD downregulates differentially expressed genes (DEGs) associated with rRNA processing and ribosome biogenesis pathways. Moreover, AML-target genes, including CCND2, MYC, NPM1, FLT3, and TERT, were downregulated by 8-OHD. Additionally, molecular docking software predicted that 8-OHD has the potential to interact with CDK6, FLT3, and TERT proteins, thereby reducing their activity and inhibiting cell proliferation. Notably, we discovered a synergic pharmacological interaction between 8-OHD and cytarabine (Ara-C).

CONCLUSIONS

Overall, this study provides insights into the therapeutic applications of 8-OHD in treating AML and elucidates its underlying mechanisms of action.

Dyskerin and telomerase RNA component are sex-differentially associated with outcomes and Sunitinib response in patients with clear cell renal cell carcinoma

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) displays sex-biased incidence, outcomes, molecular alterations and treatment efficacy; however, clinical managements are largely identical in male and female patients. Moreover, many biomarkers have been identified as predictors for ccRCC outcomes and response to therapeutic drugs, such as multitargeted tyrosine-kinase receptor (TKR) inhibitors, but little is known about their sex-specificity. Dyskerin (DKC1), encoded by the DKC1 gene within Xq28, is a telomerase co-factor stabilizing telomerase RNA component (TERC) and overexpressed in various cancers. Here, we determined whether DKC1 and/or TERC affect ccRCC sex-differentially.

METHODS

DKC1 and TERC expression in primary ccRCC tumors was assessed using RNA sequencing and qPCR. DKC1 association with molecular alterations and overall or progression-free survival (OS or PFS) was analyzed in the TCGA cohort of ccRCC. The IMmotion 151 and 150 ccRCC cohorts were analyzed to evaluate impacts of DKC1 and TERC on Sunitinib response and PFS.

RESULTS

DKC1 and TERC expression was significantly upregulated in ccRCC tumors. High DKC1 expression predicts shorter PFS independently in female but not male patients. Tumors in the female DKC1-high group exhibited more frequent alterations in PIK3CA, MYC and TP53 genes. Analyses of the IMmotion 151 ccRCC cohort treated with the TKR inhibitor Sunitinib showed that female patients in the DKC1-high group was significantly associated with lower response rates (P = 0.021) accompanied by markedly shortened PFS (6.1 vs 14.2 months, P = 0.004). DKC1 and TERC expression correlated positively with each other, and higher TERC expression predicted poor Sunitinib response (P = 0.031) and shorter PFS (P = 0.004), too. However, DKC1 rather than TERC acted as an independent predictor (P < 0.001, HR = 2.0, 95% CI 1.480-2.704). In male patients, DKC1 expression was associated with neither Sunitinib response (P = 0.131) nor PFS (P = 0.184), while higher TERC levels did not predict response rates. Similar results were obtained from the analysis of the Sunitinib-treated IMmotion 150 ccRCC patients.

CONCLUSIONS

DKC1 serves as an independent female-specific predictor for survival and Sunitinib efficacy in ccRCC, which contribute to better understanding of the sex-biased ccRCC pathogenesis and improve personalized interventions of ccRCC.

Therapeutic Targeting of FLT3 in Acute Myeloid Leukemia: Current Status and Novel Approaches

FMS-like tyrosine kinase 3 (FLT3) is mutated in approximately 30% of acute myeloid leukemia (AML) patients. The presence of FLT3-ITD (internal tandem duplication, 20-25%) mutation and, to a lesser extent, FLT3-TKD (tyrosine kinase domain, 5-10%) mutation is associated with poorer diagnosis and therapy response since the leukemic cells become hyperproliferative and resistant to apoptosis after continuous activation of FLT3 signaling. Targeting FLT3 has been the focus of many pre-clinical and clinical studies. Hence, many small-molecule FLT3 inhibitors (FLT3is) have been developed, some of which are approved such as midostaurin and gilteritinib to be used in different clinical settings, either in combination with chemotherapy or alone. However, many questions regarding the best treatment strategy remain to be answered. On the other hand, various FLT3-dependent and -independent resistance mechanisms could be evolved during FLT3i therapy which limit their clinical impact. Therefore, identifying molecular mechanisms of resistance and developing novel strategies to overcome this obstacle is a current interest in the field. In this review, recent studies of approved FLT3i and knowledge about major resistance mechanisms of clinically approved FLT3i's will be discussed together with novel treatment approaches such as designing novel FLT3i and dual FLT3i and combination strategies including approved FLT3i plus small-molecule agents targeting altered molecules in the resistant cells to abrogate resistance. Moreover, how to choose an appropriate FLT3i for the patients will be summarized based on what is currently known from available clinical data. In addition, strategies beyond FLT3i's including immunotherapeutics, small-molecule FLT3 degraders, and flavonoids will be summarized to highlight potential alternatives in FLT3-mutated AML therapy.

Genomic, epigenomic, and transcriptomic signatures for telomerase complex components: a pan-cancer analysis

Telomerase activation is required for malignant transformation. Recent advances in high-throughput technologies have enabled the generation of complex datasets, thus providing alternative approaches to exploring telomerase biology more comprehensively, which has proven to be challenging due to the need for laborious assays required to test for telomerase activity. To solve these issues, several groups have analyzed TCGA pan-cancer tumor datasets by investigating telomerase reverse transcriptase (TERT), the catalytic subunit for telomerase activity, or its surrogates. However, telomerase is a multiunit complex containing not only TERT, but also numerus cofactors required for telomerase function. Here we determined genomic and molecular alterations of 10 well-characterized telomerase components in the TCGA and CCLE datasets. We calculated a telomerase score (TS) based on their expression profiles and clustered tumors into low, high, and intermediate subtypes. To validate the in silico analysis result, we used immunoblotting and telomerase assays. High TS subtypes were significantly associated with stemness, proliferation, epithelial to mesenchymal transition, hyperactivation of oncogenic signaling pathways, shorter patient survival, and infiltration of dysfunctional T-cells or poor response to immunotherapy. Copy number alterations in 10 telomerase components were widespread and associated with the level of their expression. Surprisingly, primary tumors and cancer cell lines frequently displayed a homozygous deletion of the TCAB1 gene, encoding a telomerase protein essential for telomerase trafficking, assembling, and function, as previously reported. However, tumors or cells carrying a TCAB1 deletion still exhibited telomerase activity comparable to or even higher than their wildtype counterparts. Collectively, applying telomerase component-based TS in complex datasets provided a robust tool for telomerase analyses. Our findings also reveal a tight connection between telomerase and other oncogenic signaling pathways; TCAB1 may acts as a dispensable telomerase component. Moreover, TS may serve as a useful biomarker to predict patient outcomes and response to immunotherapy.

Antiproliferative Effects of Ferulic, Coumaric, and Caffeic Acids in HepG2 Cells by hTERT Downregulation

Objective

Phenolic acids are well-known phytochemicals that are detected in a wide variety of medicinal plants, and their antiproliferative effects on cancer cells are known, but their mechanisms are poorly revealed. In most of cancer cells, telomerase reverse transcriptase (hTERT) is a dominant factor of telomere length regulation. The hTERT expression promotes invasiveness in tumor cells and is a hallmark of cancer. Therefore, in this study, the probable inhibitory effects of caffeic (Caf), coumaric (Cum), and ferulic acids (Fer) are investigated on the hTERT expression pattern in HepG2 cells.

Methods

The MTT, apoptosis assays, and real-time PCR analysis were applied to evaluate viability, cytotoxicity, and hTERT gene expression level, respectively.

Results

All of the studied phenolic acids showed cytotoxic effects on HepG2 cells in a timely manner and presented a time-dependent inhibitory effect on the growth of HepG2 cells. They reduced percentage of viable cells and induced apoptosis. Also, these phenolic acids had significant inhibitory effects on hTERT gene expression.

Conclusion

These findings suggest that cell viability along with hTERT gene expression in HepG2 cells could be reduced by Cum, Caf, and Fer. As different cancer cells are resistant to conventional chemotherapeutics, this type of results proposes the telomerase as a proper target of cancer therapy development by natural products.

Mechanism of Human Telomerase Reverse Transcriptase (hTERT) Regulation and Clinical Impacts in Leukemia

The proliferative capacity and continuous survival of cells are highly dependent on telomerase expression and the maintenance of telomere length. For this reason, elevated expression of telomerase has been identified in virtually all cancers, including leukemias; however, it should be noted that expression of telomerase is sometimes observed later in malignant development. This time point of activation is highly dependent on the type of leukemia and its causative factors. Many recent studies in this field have contributed to the elucidation of the mechanisms by which the various forms of leukemias increase telomerase activity. These include the dysregulation of telomerase reverse transcriptase (TERT) at various levels which include transcriptional, post-transcriptional, and post-translational stages. The pathways and biological molecules involved in these processes are also being deciphered with the advent of enabling technologies such as next-generation sequencing (NGS), ribonucleic acid sequencing (RNA-Seq), liquid chromatography-mass spectrometry (LCMS/MS), and many others. It has also been established that TERT possess diagnostic value as most adult cells do not express high levels of telomerase. Indeed, studies have shown that prognosis is not favorable in patients who have leukemias expressing high levels of telomerase. Recent research has indicated that targeting of this gene is able to control the survival of malignant cells and therefore offers a potential treatment for TERT-dependent leukemias. Here we review the mechanisms of hTERT regulation and deliberate their association in malignant states of leukemic cells. Further, we also cover the clinical implications of this gene including its use in diagnostic, prognostic, and therapeutic discoveries.

Thyroid Carcinoma: Phenotypic Features, Underlying Biology and Potential Relevance for Targeting Therapy

Thyroid carcinoma consists a group of phenotypically heterogeneous cancers. Recent advances in biological technologies have been advancing the delineation of genetic, epigenetic, and non-genetic factors that contribute to the heterogeneities of these cancers. In this review article, we discuss new findings that are greatly improving the understanding of thyroid cancer biology and facilitating the identification of novel targets for therapeutic intervention. We review the phenotypic features of different subtypes of thyroid cancers and their underlying biology. We discuss recent discoveries in thyroid cancer heterogeneities and the critical mechanisms contributing to the heterogeneity with emphases on genetic and epigenetic factors, cancer stemness traits, and tumor microenvironments. We also discuss the potential relevance of the intratumor heterogeneity in understanding therapeutic resistance and how new findings in tumor biology can facilitate designing novel targeting therapies for thyroid cancer.

Telomere-related Markers for Cancer

Telomeres are structurally nucleoprotein complexes at termini of linear chromosomes and essential to chromosome stability/integrity. In normal human cells, telomere length erodes progressively with each round of cell divisions, which serves as an important barrier to uncontrolled proliferation and malignant transformation. In sharp contrast, telomere maintenance is a key feature of human malignant cells and required for their infinite proliferation and maintenance of other cancer hallmarks as well. Thus, a telomere-based anti-cancer strategy has long been suggested. However, clinically efficient and specific drugs targeting cancer telomere-maintenance have still been in their infancy thus far. To achieve this goal, it is highly necessary to elucidate how exactly cancer cells maintain functional telomeres. In the last two decades, numerous studies have provided profound mechanistic insights, and the identified mechanisms include the aberrant activation of telomerase or the alternative lengthening of telomere pathway responsible for telomere elongation, dysregulation and mutation of telomere-associated factors, and other telomere homeostasis-related signaling nodes. In the present review, these various strategies employed by malignant cells to regulate their telomere length, structure and function have been summarized, and potential implications of these findings in the rational development of telomere-based cancer therapy and other clinical applications for precision oncology have been discussed.

Pharmacological impact of FLT3 mutations on receptor activity and responsiveness to tyrosine kinase inhibitors

Acute myelogenous leukaemia (AML) is an aggressive blood cancer characterized by the rapid proliferation of immature myeloid blast cells, resulting in a high mortality rate. The 5-year overall survival rate for AML patients is approximately 25%. Circa 35% of all patients carry a mutation in the FLT3 gene which have a poor prognosis. Targeting FLT3 receptor tyrosine kinase has become a treatment strategy in AML patients possessing FLT3 mutations. The most common mutations are internal tandem duplications (ITD) within exon 14 and a single nucleotide polymorphism (SNP) that leads to a point mutation in the D835 of the tyrosine kinase domain (TKD). Variations in the ITD sequence and the occurrence of other point mutations that lead to ligand-independent FLT3 receptor activation create difficulties in developing personalized therapeutic strategies to overcome observed mutation-driven drug resistance. Midostaurin and quizartinib are tyrosine kinase inhibitors (TKIs) with inhibitory efficacy against FLT3-ITD, but exhibit limited clinical impact. In this review, we focus on the structural aspects of the FLT3 receptor and correlate those mutations with receptor activation and the consequences for molecular and clinical responsiveness towards therapies targeting FLT3-ITD positive AML.

Telomerase reverse transcriptase promoter mutations in thyroid carcinomas: implications in precision oncology-a narrative review

Telomerase is a ribonucleoprotein enzyme with telomerase reverse transcriptase (TERT) as a catalytic component. In normal human follicular thyroid cells or thyrocytes, telomerase is silent due to the TERT gene being tightly repressed. However, during the formation of thyroid carcinoma (TC), telomerase becomes activated via TERT induction. The TERT promoter’s gain-of-function mutation has recently been identified in TCs and many other malignancies. The mutation creates a de novo ETS-binding motif through which TERT transcription is de-repressed and telomerase is activated; through this, the mutant TERT promoter promotes the development of TC, contributes to disease aggressiveness and treatment resistance, and thereby leads to poor patient outcomes. From a clinical point of view, the strong association between the TERT promoter mutation and disease malignancy and aggressiveness holds great promise for its value in TC diagnostics, risk stratification, prognostication, treatment decision, and follow-up design. In the present review article, we summarize the recent findings of studies of TERT promoter mutations in TC and underscore the implications of TERT hyperactivity driven by genetic events in the pathogenesis and management of TC. Finally, the targeting of TERT promoter mutations and the disruption of telomere maintenance are considered as potential therapeutic strategies against TC.

TERT promoter mutations and GABP transcription factors in carcinogenesis: More foes than friends

The transcriptional de-repression of the telomerase reverse transcriptase (TERT) gene and subsequent activation of telomerase is a prerequisite step in malignant transformation and progression. Recently, the gain-of-function mutation of the TERT promoter was identified in many types of human malignancies, and the mutated promoter acquires de novo ETS binding motifs through which the TERT transcription is activated. The ETS family transcription factors GABPA and GABPB1 have been shown to act as master drivers for the mutant TERT promoter activity. Indeed, GABPA or GABPB1 depletion leads to the down-regulation of TERT expression in the mutant TERT promoter-bearing cancer cells, and is thus proposed as targets for cancer therapy. Surprisingly, however, despite its key role in activating the mutant TERT promoter and telomerase, GABPA may itself function as a potent tumor suppressor in several malignancies. In this review, we address the collaboration between GABPA and mutant TERT promoter in cancer development, discuss selection trade-offs among different activities of GABPA in cancer evolution, and underscore the suppressive function of GABPA in cancer progression and implications in precision oncology.

JAK2 inhibition in JAK2V617F-bearing leukemia cells enriches CD34+ leukemic stem cells that are abolished by the telomerase inhibitor GRN163L

The activating-mutation of JAK2V617F drives the development of myeloproliferative neoplasms (MPNs). Several JAK2 inhibitors such as ruxolitinib and gandotinib (LY2784544) currently in clinical trials and, provide improvements in MPNs including myelofibrosis. However, JAK2 inhibitors are non-curative and murine experiments show that JAK2 inhibitors don't eradicate MPN stem cells and it is currently unclear how they escape. We thus determined the effect of the specific JAK2V617F inhibitor LY2784544 on leukemic stem (CD34⁺) cells (LSCs) using the JAK2V617F-bearing erythroleukemia cell line HEL. The LY2784544 treatment caused a transient proliferation inhibition and apoptosis of HEL cells, but a recovery occurred within a week. Thereafter, the continuous LY2784544 exposure induced the accumulation of CD34⁺ LSCs, and the CD34⁺ cells increased from 2% to >90% by week 9, which was accompanied by increased clonogenic potentials. LY2784544 was capable of stimulating CD34 expression even in CD34^- HEL cells, which indicated cellular de-differentiation. A significantly enhanced expression of the stem cell factor KLF4 was observed in LY2784544-treated HEL cells. Inhibiting KLF4 expression attenuated LY2784544-mediated accumulation of CD34⁺ LSCs. Moreover, the telomerase inhibitor GRN163L abolished the LY2784544-effect. JAK2 inhibitors thus cause enrichment of LSCs and are unlikely to cure MPN as a monotherapy. Simultaneously targeting JAK2V617F and KLF4 or telomerase may be a novel strategy for MPN therapy, which should be of significance both biologically and clinically.

FMS-like Tyrosine Kinase 3/FLT3: From Basic Science to Clinical Implications

FMS-like tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase that is expressed almost exclusively in the hematopoietic compartment. Its ligand, FLT3 ligand (FL), induces dimerization and activation of its intrinsic tyrosine kinase activity. Activation of FLT3 leads to its autophosphorylation and initiation of several signal transduction cascades. Signaling is initiated by the recruitment of signal transduction molecules to activated FLT3 through binding to specific phosphorylated tyrosine residues in the intracellular region of FLT3. Activation of FLT3 mediates cell survival, cell proliferation, and differentiation of hematopoietic progenitor cells. It acts in synergy with several other cytokines to promote its biological effects. Deregulated FLT3 activity has been implicated in several diseases, most prominently in acute myeloid leukemia where around one-third of patients carry an activating mutant of FLT3 which drives the disease and is correlated with poor prognosis. Overactivity of FLT3 has also been implicated in autoimmune diseases, such as rheumatoid arthritis. The observation that gain-of-function mutations of FLT3 can promote leukemogenesis has stimulated the development of inhibitors that target this receptor. Many of these are in clinical trials, and some have been approved for clinical use. However, problems with acquired resistance to these inhibitors are common and, furthermore, only a fraction of patients respond to these selective treatments. This review provides a summary of our current knowledge regarding structural and functional aspects of FLT3 signaling, both under normal and pathological conditions, and discusses challenges for the future regarding the use of targeted inhibition of these pathways for the treatment of patients.

Telomerase Reverse Transcriptase (TERT) in Action: Cross-Talking with Epigenetics

Telomerase, an RNA-dependent DNA polymerase with telomerase reverse transcriptase (TERT) as the catalytic component, is silent due to the tight repression of the TERT gene in most normal human somatic cells, whereas activated only in small subsets of cells, including stem cells, activated lymphocytes, and other highly proliferative cells. In contrast, telomerase activation via TERT induction is widespread in human malignant cells, which is a prerequisite for malignant transformation. It is well established that TERT/telomerase extends telomere length, thereby conferring sustained proliferation capacity to both normal and cancerous cells. The recent evidence has also accumulated that TERT/telomerase may participate in the physiological process and oncogenesis independently of its telomere-lengthening function. For instance, TERT is shown to interact with chromatin remodeling factors and to regulate DNA methylation, through which multiple cellular functions are attained. In the present review article, we summarize the non-canonical functions of TERT with a special emphasis on its cross-talk with epigenetics: How TERT contributes to epigenetic alterations in physiological processes and cancer, and how the aberrant epigenetics in turn facilitate TERT expression and function, eventually promoting cancer either initiation or progression or both. Finally, we briefly discuss clinical implications of the TERT-related methylation.

The TERT locus genotypes of rs2736100-CC/CA and rs2736098-AA predict shorter survival in renal cell carcinoma

OBJECTIVES

The single nucleotide polymorphisms (SNPs) at the TERT rs2736100 and rs2736098 are associated with multicancer susceptibility, however, published findings regarding renal cell carcinoma (RCC) risk are conflicting. In addition, the potential of these SNPs to predict outcomes in RCC remains unclear. The present study is designed to address these questions.

PATIENTS AND METHODS

We recruited 343 patients with RCC and ethnic-/sex-matched healthy controls. TERT rs2736100 and rs2736098 SNPs were analyzed, and their relationships with relapse/survival were evaluated using univariate or multivariate Cox regression.

RESULTS

The genotype distribution did not significantly differ between RCC patients and healthy controls. RCC patients carrying the rs2736100-CC/CA variants had significantly shorter progression-free and overall survival (PFS and OS) than did those AA-carriers (P = 0.009 and 0.032, respectively), while the rs2736098-AA variant was associated with shorter PFS and OS (P = 0.008 and 0.017, respectively). Multivariate analyses showed that rs2736100-CC/CA and rs2736098-AA predicted shorter PFS and OS independently of other established prognostic variables in RCCs. Furthermore, patients carrying both rs2736100-CC/CA and rs2736098-AA had shortest PFS and OS (P = 0.003 and 0.013, respectively) and the hazard ratio of relapse was 7.2 (95% confidence interval: 2.0-26.1).

CONCLUSIONS

There is no significant association between rs2736100/rs2736098 SNPs and RCC risk. rs2736100-CC/CA and rs2736098-AA variants serve as independent predictors of a poor prognosis in RCC. Given that blood or even urinary DNA can be used to genotype these germline variants before treatment, these 2 SNPs may serve as a potential marker for risk stratification.

Melatonin inhibits MLL-rearranged leukemia via RBFOX3/hTERT and NF-κB/COX-2 signaling pathways

MLL-rearranged leukemia is an aggressive malignancy associated with poor outcome, which is refractory to conventional treatment. Melatonin has been proven to exert anti-tumor activity, but the effect of melatonin on MLL-r leukemia and the underlying mechanism remain poorly understood. In this study, melatonin inhibited cell proliferation and induced apoptosis by activating the caspase-dependent apoptotic pathway in MLL-r leukemia cells. Mechanistic investigations revealed that melatonin suppressed the expression of hTERT by abrogating the binding activity of RBFOX3 to the hTERT promoter. Melatonin also blocked NF-κB nuclear translocation and suppressed NF-κB binding to the COX-2 promoter, thereby suppressing the expression of COX-2. In addition, clinical samples revealed that melatonin exerts anti-leukemic activity in primary MLL-r leukemia blasts ex vivo. In vivo, the mice treated with melatonin experienced a larger reduction in leukemic burden than the control group in a MLL-r leukemia xenograft mouse model. Collectively, these results suggest that melatonin inhibits MLL-rearranged leukemia through suppressing the RBFOX3/hTERT and NF-κB/COX-2 signaling pathways. Our findings provide new insights into the role of melatonin for MLL-r leukemia treatment.

The Myc/Max/Mxd Network Is a Target of Mutated Flt3 Signaling in Hematopoietic Stem Cells in Flt3-ITD-Induced Myeloproliferative Disease

Acute myeloid leukemia (AML) has poor prognosis due to various mutations, e.g., in the FLT3 gene. Therefore, it is important to identify pathways regulated by the activated Flt3 receptor for the discovery of new therapeutic targets. The Myc network of oncogenes and tumor suppressor genes is involved in mechanisms regulating proliferation and survival of cells, including that of the hematopoietic system. In this study, we evaluated the expression of the Myc oncogenes and Mxd antagonists in hematopoietic stem cell and myeloid progenitor populations in the Flt3-ITD-knockin myeloproliferative mouse model. Our data shows that the expression of Myc network genes is changed in Flt3-ITD mice compared with the wild type. Mycn is increased in multipotent progenitors and in the pre-GM compartment of myeloid progenitors in the ITD mice while the expression of several genes in the tumor suppressor Mxd family, including Mxd1, Mxd2, and Mxd4, is concomitantly downregulated, as well as the expression of the Mxd-related gene Mnt and the transcriptional activator Miz-1. LSKCD150⁺CD48⁻ hematopoietic long-term stem cells are decreased in the Flt3-ITD cells while multipotent progenitors are increased. Of note, PKC412-mediated inhibition of Flt3-ITD signaling results in downregulation of cMyc and upregulation of the Myc antagonists Mxd1, Mxd2, and Mxd4. Our data provides new mechanistic insights into downstream alterations upon aberrant Flt3 signaling and rationale for combination therapies for tyrosine kinase inhibitors with Myc antagonists in treating AML.

Telomerase reverse transcriptase regulates DNMT3B expression/aberrant DNA methylation phenotype and AKT activation in hepatocellular carcinoma

Telomerase reverse transcriptase (TERT)1 acts as a master regulator of cancer hallmarks, but underlying mechanisms remain incompletely understood. We show that TERT is required for the aberrant DNA methyltransferase 3 B (DNMT3B)2 expression and cancer-specific methylation in hepatocellular carcinoma (HCC)3, through which AKT is activated. TERT depletion inhibited, while its over-expression promoted DNMT3B expression in HCC cells, respectively. Mechanistically, TERT cooperates with the transcription factor Sp1 to stimulate DNMT3B transcription. The tumor suppressors PTEN and RASSF1A were de-repressed following DNMT3B inhibition in TERT-depleted HCC cells. The PTEN promoter analysis demonstrated significantly reduced methylation in these cells. TERT silencing also led to diminished global DNA methylation. The analysis of the Cancer Genome Atlas (TCGA)4 dataset showed that higher levels of TERT and DNMT3B expression predicted significantly shorter survival in HCC patients. Collectively, our findings establish TERT as an important contributor to cancer-specific DNA methylation and AKT hyperactivation in HCC cells. Given critical roles of both the aberrant DNA methylation and AKT activation in carcinogenesis, this TERT-regulated network or the TERT-DNMT3B-PTEN-AKT axis provides a biological explanation for multi-oncogenic activities of TERT and may be exploited in HCC treatment.

PTEN deficiency confers colorectal cancer cell resistance to dual inhibitors of FLT3 and aurora kinase A

PTEN is a tumor suppressor found mutated in many cancers. From a synthetic lethality drug screen with PTEN-isogenic colorectal cancer cells, we found that mutant-PTEN cells were resistant to dual inhibitors of FLT3 and aurora kinase-A, including KW2449 and ENMD-2076. KW2449 significantly reduced the viability of wildtype-PTEN cells causing apoptosis, while little effect was observed in mutant-PTEN counterparts. Transcriptome profiling showed that members of PI3K-AKT signaling pathway were strongly changed in cells after KW2449 treatment, indicating a potential role of the pathway in drug resistance. We found that KW2449 caused a dose-dependent, biphasic induction of AKT phosphorylation at Ser473 in mutant-PTEN cells. Co-treatment with the inhibitors of its upstream signaling completely abolished the reactivation of AKT phosphorylation by KW2449 and reversed the drug resistant phenotype. These data suggest that reactivation of AKT phosphorylation at Ser473 is a key factor to confer drug resistant phenotype of mutant-PTEN cells to the dual inhibitors and that proper drug combinations that shut down AKT reactivation is necessary for the effective treatment of mutant-PTEN cancer with the dual inhibitors in clinical settings.