GSK-3 promotes conditional association of CREB and its coactivators with MEIS1 to facilitate HOX-mediated transcription and oncogenesis

GSK3β phosphorylates Six1 transcription factor and regulates its APC/CCdh1 mediated proteosomal degradation

Sine oculis homeobox homolog 1 (Six1) is a developmentally important transcription factor that regulates cellular proliferation, apoptosis, and dissemination during embryogenesis. Six1 overexpression as reported in multiple cancers modulates expression of a repertoire of its target genes causing an increase in proliferation, metastasis and survival of cancer cells. Six1 exists as a cell cycle regulated nuclear phosphoprotein and its cellular turnover is regulated by APC/C (Anaphase promoting complex / Cyclosome) complex mediated proteolysis. However, the kinases that regulate Six1 proteolysis have not been identified and the mechanistic details that cause its overproduction in various cancers are lacking. Here, we report that Six1 is a physiological GSK3β substrate. GSK3β interacts with Six1 and phosphorylates it at Ser221 within the conserved consensus sequence in its carboxy terminus. Using pharmacological inhibition, siRNA mediated knockdown and protein overexpression of GSK3β; we show that GSK3β regulates Six1 protein stability. Pulse chase analysis of Six1 revealed that GSK3β regulates its ubiquitin proteolysis such that Six1 phosphomimicking mutant (Six1S221E) for Ser221 site had dramatically increased half-life than its phosphodeficient (Six1S221A) and wild type variants. Furthermore, we demonstrate that GSK3β rescues Six1 from APC dependent proteolysis by regulating its binding with APC/C co-activator protein Cdh1. Importantly, strong positive correlation exists between GSK3β and Six1 protein levels throughout the cell cycle and in multiple cancers indicating that GSK3β activation may in part contribute to Six1 overproduction in a subset of human cancers.

Elongation of very long chain fatty acids-3 (Elovl3) is activated by ZHX2 and is a regulator of cell cycle progression

Zinc fingers and homeoboxes 2 (Zhx2) are transcriptional regulators of liver gene expression with key functions in embryonic development as well as tissue regeneration in response to damage and disease, presumably through its control of target genes. Previous microarray data suggested that elongation of very long chain fatty acids-3 (Elovl3), a member of the ELOVL family of enzymes that synthesize very long chain fatty acids (VLCFAs), is a putative Zhx2 target gene. VLCFAs are core component of ceramides and other bioactive sphingolipids that are often dysregulated in diseases and regulate key cellular processes including proliferation. Since several previously identified Zhx2 targets become dysregulated in liver damage, we investigated the relationship between Zhx2 and Elovl3 in liver development, damage, and regeneration. Here, using mouse and cell models, we demonstrate that Zhx2 positively regulates Elovl3 expression in the liver and that male-biased hepatic Elovl3 expression is established between 4 and 8 wk of age in mice. Elovl3 is dramatically repressed in mouse models of liver regeneration, and the reduced Elovl3 levels in the regenerating liver are associated with changes in hepatic VLCFAs. Human hepatoma cell lines with forced Elovl3 expression have lower rates of cell growth; analysis of synchronized cells indicates that this reduced proliferation correlates with cells stalling in S-phase and lower mRNA levels of cell cyclins. Taken together, these data indicate that Elovl3 expression helps regulate cellular proliferation during liver development and regeneration, possibly through control of VLCFAs.NEW & NOTEWORTHY Numerous targets of the transcription factor Zhx2 are dysregulated in liver disease. We show that the elongase Elovl3 is a novel Zhx2 target. Elovl3 and Zhx2 expression change during liver regeneration, which is associated with changes in very long chain fatty acids. Forced Elovl3 expression reduces cell growth and blocks cell cycle progression. This suggests that Elovl3 may account, at least in part, for the relationship between Zhx2 and proliferation during liver development and disease.

Cytarabine-induced destabilization of MCL1 mRNA and protein triggers apoptosis in leukemia cells

Although cytarabine (Ara-C) is the mainstay of treatment for acute myeloid leukemia (AML), its cytotoxic mechanisms for inducing apoptosis are poorly understood. Therefore, we investigated the Ara-C-induced cell death pathway in human AML U937 cells. Ara-C-induced downregulation of MCL1 is associated with the induction of mitochondrial depolarization and apoptosis. Ara-C triggered NOX4-mediated ROS production, which in turn activated p38 MAPK but inactivated AKT. Ara-C-induced DNA damage modulates p38 MAPK activation without affecting AKT inactivation in U937 cells. Inactivated AKT promotes GSK3β-dependent CREB phosphorylation, which in turn increases NOXA transcription, thereby triggering the degradation of MCL1 protein. Activated p38 MAPK induces HuR downregulation, leading to accelerated MCL1 mRNA turnover. A similar pathway also explains the Ara-C-induced THP-1 cell death. Collectively, our data confirm that Ara-C-triggered apoptosis in the AML cell lines U937 and THP-1 is mediated through the destabilization of MCL1 mRNA and protein. Furthermore, Ara-C acts synergistically with the BCL2 inhibitor ABT-199 to induce cell death in ABT-199-resistant and parental U937 cells by inhibiting MCL1 expression.

Npm1 haploinsufficiency in collaboration with MEIS1 is sufficient to induce AML in mice

NPM1 is among the most frequently mutated genes in acute myeloid leukemia (AML). Mutations in the NPM1 gene result in the increased export of NPM1 to the cytoplasm (NPM1c) and are associated with multiple transforming events including the aberrant upregulation of MEIS1 that maintains stem cell and cell cycle-associated pathways in NPM1c AML. However, another consequence of the NPM1c mutation is the inadequate levels of NPM1 wild-type in the nucleus and nucleolus, caused by the loss of one wild-type allele in addition to enforced NPM1 nuclear export. The contribution of NPM1 haploinsufficiency independently of the NPM1 mutation to AML development and its relationship with MEIS1 function is poorly understood. Using mouse models, our study shows that NPM1 haploinsufficiency paired with MEIS1 overexpression is sufficient to induce a fully penetrant AML in mice that transcriptionally resembles human NPM1c AML. NPM1 haploinsufficiency alters MEIS1-binding occupancies such that it binds the promoter of the oncogene structural maintenance of chromosome protein 4 (SMC4) in NPM1 haploinsufficient AML cells but not in NPM1 wild-type-harboring Hoxa9/Meis1-transformed cells. SMC4 is higher expressed in haploinsufficient and NPM1c+ AML cells, which are more vulnerable to the disruption of the MEIS1-SMC4 axis compared with AML cells with nonmutated NPM1. Taken together, our study underlines that NPM1 haploinsufficiency on its own is a key factor of myeloid leukemogenesis and characterizes the MEIS1-SMC4 axis as a potential therapeutic target in this AML subtype.

GSK-3β phosphorylation of DHX33 leads to its ubiquitination mediated protein degradation

DHX33 is a member of DEAD/H box protein family, and is involved in both RNA and DNA metabolism. It plays diverse roles in multiple cellular activities. DHX33 overexpression has been found to promote the development of many human cancers. However, the underlying mechanism to explain its high expression in cancer cells remains incompletely resolved. In this study, with both human cancer cell lines and normal fibroblasts, we found glycogen synthase kinase 3β (GSK-3β) regulates DHX33 protein stability. This is through its direct phosphorylation of DHX33 on T482, which triggers ubiquitination mediate protein degradation. We further identified one of the major ubiquitination sites of DHX33 to be on its N-terminal K94, a critical residue previously found to be important and highly conserved for ATP binding and helicase activity. Our study for the first time reveals an important upstream regulator, GSK-3β, as a critical kinase to phosphorylate DHX33 at the post-translational level leading to its degradation. Moreover, cancer cells have frequent GSK3β deactivation to disrupt this signaling cascade. Therefore, DHX33 is stabilized in many cancer cells as compared to normal cells. Our study unveils an important post-translational regulation of DHX33 in cells and further unveils a novel mechanism for DHX33 overexpression in cancer cells.

MicroRNA-139-5p mediates BMSCs impairment in diabetes by targeting HOXA9/c-Fos

The properties and functions of BMSCs were altered by the diabetic microenvironment, and its mechanism was not very clear. In recent years, the regulation of the function of BMSCs by microRNA has become a research hotspot, meanwhile, HOX genes also have been focused on and involved in multiple functions of stem cells. In this study, we investigated the role of miR-139-5p in diabetes-induced BMSC impairment. Since HOXA9 may be a target gene of miR-139-5p, we speculated that miR-139-5p/HOXA9 might be involved in regulating the biological characteristics and the function of BMSCs in diabetes. We demonstrated that the miR-139-5p expression was increased in BMSCs derived from STZ-induced diabetic rats. MiR-139-5p mimics were able to inhibit cell proliferation, and migration and promoted senescence and apoptosis in vitro. MiR-139-5p induced the down-regulated expression of HOXA9 and c-Fos in BMSCs derived from normal rats. Moreover, miR-139-5p inhibitors reversed the tendency in diabetic-derived BMSCs. Further, gain-and-loss function experiments indicated that miR-139-5p regulated the functions of BMSCs by targeting HOXA9 and c-Fos. In vivo wound model experiments showed that the downregulation of miR-139-5p further promoted the epithelialization and angiogenesis of diabetic BMSC-mediated skin. In conclusion, induction of miR-139-5p upregulation mediated the impairment of BMSCs through the HOXA9/c-Fos pathway in diabetic rats. Therefore, miR-139-5p/HOXA9 might be an important therapeutic target in treating diabetic BMSCs and diabetic complications in the future.

Mammalian eIF4E2-GSK3β maintains basal phosphorylation of p53 to resist senescence under hypoxia

Hypoxia modulates senescence, but their physiological link remains unclear. Here, we found that eIF4E2, a hypoxia-activated translation initiation factor, interacted with GSK3β to maintain phosphorylation of p53, thus resisting senescence under hypoxia. RNA-binding protein RBM38 interacted with eIF4E to inhibit the translation of p53, but GSK3β-mediated Ser195 phosphorylation disrupted the RBM38-eIF4E interaction. Through investigation of RBM38 phosphorylation, we found that the eIF4E2-GSK3β pathway specifically regulated proline-directed serine/threonine phosphorylation (S/T-P). Importantly, peptides e2-I or G3-I that blocking eIF4E2-GSK3β interaction can inhibit the basal S/T-P phosphorylation of p53 at multiple sites, therby inducing senescence through transcriptional inhibition. Additionally, a nanobody was screened via the domain where eIF4E2 bound to GSK3β, and this nanobody inhibited S/T-P phosphorylation to promote senescence. Furthermore, hypoxia inhibited eIF4E2-GSK3β pathway by mediating S-Nitrosylation of GSK3β. Blocking eIF4E2-GSK3β interaction promoted liver senescence under hypoxia, thus leading to liver fibrosis, eventually accelerating N, N-diethylnitrosamine (DEN)-induced tumorigenesis. Interestingly, eIF4E2 isoforms with GSK3β-binding motif exclusively exist in mammals, which protect zebrafish heart against hypoxia. Together, this study reveals a mammalian eIF4E2-GSK3β pathway that prevents senescence by maintaining basal S/T-P phosphorylation of p53, which underlies hypoxia adaptation of tissues.

Nuclear GSK-3β and Oncogenic KRas Lead to the Retention of Pancreatic Ductal Progenitor Cells Phenotypically Similar to Those Seen in IPMN

Glycogen synthase kinase-3β (GSK-3β) is a downstream target of oncogenic KRas and can accumulate in the nucleus in pancreatic ductal adenocarcinoma (PDA). To determine the interplay between oncogenic KRas and nuclear GSK-3β in PDA development, we generated Lox-STOP-Lox (LSL) nuclear-targeted GSK-3β animals and crossed them with LSL-KRas^G12D mice under the control of the Pdx1-cre transgene—referred to as KNGC. Interestingly, 4-week-old KNGC animals show a profound loss of acinar cells, the expansion of ductal cells, and the rapid development of cystic-like lesions reminiscent of intraductal papillary mucinous neoplasm (IPMN). RNA-sequencing identified the expression of several ductal cell lineage genes including AQP5. Significantly, the Aqp5⁺ ductal cell pool was proliferative, phenotypically distinct from quiescent pancreatic ductal cells, and deletion of AQP5 limited expansion of the ductal pool. Aqp5 is also highly expressed in human IPMN along with GSK-3β highlighting the putative role of Aqp5⁺ ductal cells in human preneoplastic lesion development. Altogether, these data identify nGSK-3β and KRas^G12D as an important signaling node promoting the retention of pancreatic ductal progenitor cells, which could be used to further characterize pancreatic ductal development as well as lineage biomarkers related to IPMN and PDA.

Re-Expression of ERα and AR in Receptor Negative Endocrine Cancers via GSK3 Inhibition

DNA methylation, catalyzed by DNA methyltransferase (DNMT), is a well-characterized epigenetic modification in cancer cells. In particular, promoter hypermethylation of AR and ESR1 results in loss of expression on Androgen Receptor (AR) and Estrogen Receptor (ER), respectively, and is associated with a hormone refractory state. We now report that Glycogen Synthase Kinase 3 (GSK3) phosphorylates DNMT1 at S714, which is localized to a 62 amino acid region referred to as auto-inhibitory linker, which functions to occlude the DNA from the active site of DNMT1 to prevent the methylation of unmethylated DNA. Molecular Dynamics simulation indicates that phosphorylation at S714 resulted in conformational rearrangement of the autoinhibitory domain that inactivated its ability to block the methylation of unmethylated DNA and resulted in enhanced DNA binding. Treatment with a novel and more selective inhibitor of GSK3 resulted in decreased methylation of the promoter region of genes encoding the Androgen Receptor (AR) and Estrogen Receptor alpha (ERa) and re-expression of the AR and ERa in AR negative prostate cancer and ER negative breast cancer cells, respectively. As a result, concurrent treatment with the GSK3 inhibitor resulted in responsiveness of AR negative prostate cancer and ER negative breast cancer cells to inhibitors of the AR or ER, respectively, in in vitro and in vivo experimental models.

Proteasome Inhibitors Interrupt the Activation of Non-Canonical NF-κB Signaling Pathway and Induce Cell Apoptosis in Cytarabine-Resistant HL60 Cells

Over half of older patients with acute myeloid leukemia (AML) do not respond to cytotoxic chemotherapy, and most responders relapse because of drug resistance. Cytarabine is the main drug used for the treatment of AML. Intensive treatment with high-dose cytarabine can increase the overall survival rate and reduce the relapse rate, but it also increases the likelihood of drug-related side effects. To optimize cytarabine treatment, understanding the mechanism underlying cytarabine resistance in leukemia is necessary. In this study, the gene expression profiles of parental HL60 cells and cytarabine-resistant HL60 (R-HL60) cells were compared through gene expression arrays. Then, the differential gene expression between parental HL60 and R-HL60 cells was measured using KEGG software. The expression of numerous genes associated with the nuclear factor κB (NF-κB) signaling pathway changed during the development of cytarabine resistance. Proteasome inhibitors inhibited the activity of non-canonical NF-κB signaling pathway and induced the apoptosis of R-HL60 cells. The study results support the application and possible mechanism of proteasome inhibitors in patients with relapsed or refractory leukemia.

Drug Repurposing for Targeting Acute Leukemia With KMT2A (MLL)-Gene Rearrangements

The treatment failure rates of acute leukemia with rearrangements of the Mixed Lineage Leukemia (MLL) gene highlight the need for novel therapeutic approaches. Taking into consideration the limitations of the current therapies and the advantages of novel strategies for drug discovery, drug repurposing offers valuable opportunities to identify treatments and develop therapeutic approaches quickly and effectively for acute leukemia with MLL-rearrangements. These approaches are complimentary to de novo drug discovery and have taken advantage of increased knowledge of the mechanistic basis of MLL-fusion protein complex function as well as refined drug repurposing screens. Despite the vast number of different leukemia associated MLL-rearrangements, the existence of common core oncogenic pathways holds the promise that many such therapies will be broadly applicable to MLL-rearranged leukemia as a whole.

Discovery of Novel Benzothiazepinones as Irreversible Covalent Glycogen Synthase Kinase 3β Inhibitors for the Treatment of Acute Promyelocytic Leukemia

Recently, irreversible inhibitors have attracted great interest in antitumors due to their advantages of forming covalent bonds to target proteins. Herein, some benzothiazepinone compounds (BTZs) have been designed and synthesized as novel covalent GSK-3β inhibitors with high selectivity for the kinase panel. The irreversible covalent binding mode was identified by kinetics and mass spectrometry, and the main labeled residue was confirmed to be the unique Cys14 that exists only in GSK-3β. The candidate 4-3 (IC₅₀ = 6.6 μM) showed good proliferation inhibition and apoptosis-inducing ability to leukemia cell lines, low cytotoxicity on normal cell lines, and no hERG inhibition, which hinted the potential efficacy and safety. Furthermore, 4-3 exhibited decent pharmacokinetic properties in vivo and remarkably inhibited tumor growth in the acute promyelocytic leukemia (APL) mouse model. All the results suggest that these newly irreversible BTZ compounds might be useful in the treatment of cancer such as APL.

NOXA-mediated degradation of MCL1 and BCL2L1 causes apoptosis of daunorubicin-treated human acute myeloid leukemia cells

Daunorubicin (DNR) is used clinically to treat acute myeloid leukemia (AML), while the signaling pathways associated with its cytotoxicity are not fully elucidated. Thus, we investigated the DNR-induced death pathway in the human AML cell lines U937 and HL-60. DNR-induced apoptosis in U937 cells accompanied by downregulation of MCL1 and BCL2L1, upregulation of Phorbol-12-myristate-13-acetate-induced protein 1 (NOXA), and mitochondrial depolarization. DNR induced NOX4-mediated reactive reactive oxygen species (ROS) production, which in turn inactivated Akt and simultaneously activated p38 mitogen-activated protein kinase (MAPK). Activated p38 MAPK and inactivated Akt coordinately increased GSK3β-mediated cAMP response element-binding protein (CREB) phosphorylation, which promoted NOXA transcription. NOXA upregulation critically increased the proteasomal degradation of MCL1 and BCL2L1. The same pathway was also responsible for the DNR-induced death of HL-60 cells. Restoration of MCL1 or BCL2L1 expression alleviated DNR-induced mitochondrial depolarization and cell death. Furthermore, ABT-199 (a BCL2 inhibitor) synergistically enhanced the cytotoxicity of DNR in AML cell lines. Notably, DNR-induced DNA damage was not related to NOXA-mediated degradation of MCL1 and BCL2L1. Collectively, these results indicate that the upregulation of NOXA expression through the NOX4-ROS-p38 MAPK-GSK3β-CREB axis results in the degradation of MCL1 and BCL2L1 in DNR-treated U937 and HL-60 cells. This signaling pathway may provide insights into the mechanism underlying DNR-triggered apoptosis in AML cells.

A Gene Expression Signature to Predict Nucleotide Excision Repair Defects and Novel Therapeutic Approaches

Nucleotide excision repair (NER) resolves DNA adducts, such as those caused by ultraviolet light. Deficient NER (dNER) results in a higher mutation rate that can predispose to cancer development and premature ageing phenotypes. Here, we used isogenic dNER model cell lines to establish a gene expression signature that can accurately predict functional NER capacity in both cell lines and patient samples. Critically, none of the identified NER deficient cell lines harbored mutations in any NER genes, suggesting that the prevalence of NER defects may currently be underestimated. Identification of compounds that induce the dNER gene expression signature led to the discovery that NER can be functionally impaired by GSK3 inhibition, leading to synergy when combined with cisplatin treatment. Furthermore, we predicted and validated multiple novel drugs that are synthetically lethal with NER defects using the dNER gene signature as a drug discovery platform. Taken together, our work provides a dynamic predictor of NER function that may be applied for therapeutic stratification as well as development of novel biological insights in human tumors.

Shaggy functions downstream of dMyc and their concurrent downregulation confers additive rescue against tau toxicity in Drosophila

Neurodegenerative tauopathies such as Alzheimer's and Parkinson's diseases are characterized by hyperphosphorylation of tau protein and their subsequent aggregation in the forms of paired helical filaments and/or neurofibrillary tangles in specific areas of the brain. Despite several attempts, it remains a challenge to develop reliable biomarkers or effective drugs against tauopathies. It is increasingly evident now that due to the involvement of multiple cellular cascades affected by the pathogenic tau molecules, a single genetic modifier or a molecule is unlikely to be efficient enough to provide an inclusive rescue. Hence, multitargets based combinatorial approach(s) have been suggested to provide an efficient rescue against tauopathies. We have reported earlier that targeted downregulation of dmyc (a Drosophila homolog of human cmyc proto-oncogene) restricts tau etiology by limiting tau hyperphosphorylation and heterochromatin loss. Although, dmyc generates a significant rescue; however, it is not proficient enough to provide a complete alleviation against tauopathies. Here, we report that tissue-specific concurrent downregulation of dmyc and gsk3β conveys a near-complete rescue against tau toxicity in Drosophila. We noted that combinatorial downregulation of dmyc and gsk3β reduces tau hyperphosphorylation, restricts the formation of neurofibrillary tangles, and restores heterochromatin loss to the physiological level. Our subsequent investigations revealed that dmyc regulates gsk3β via protein phosphatase 2A (dPP2A) in a dose-dependent manner to regulate tau pathogenesis. We propose that dmyc and gsk3β candidates can be utilized in a synergistic manner for the development of an efficient combinatorial therapeutic approach against the devastating human tauopathies.

Lithium and Therapeutic Targeting of GSK-3

Lithium salts have been in the therapeutic toolbox for better or worse since the 19th century, with purported benefit in gout, hangover, insomnia, and early suggestions that lithium improved psychiatric disorders. However, the remarkable effects of lithium reported by John Cade and subsequently by Mogens Schou revolutionized the treatment of bipolar disorder. The known molecular targets of lithium are surprisingly few and include the signaling kinase glycogen synthase kinase-3 (GSK-3), a group of structurally related phosphomonoesterases that includes inositol monophosphatases, and phosphoglucomutase. Here we present a brief history of the therapeutic uses of lithium and then focus on GSK-3 as a therapeutic target in diverse diseases, including bipolar disorder, cancer, and coronavirus infections.

Derivation of stable embryonic stem cell-like, but transcriptionally heterogenous, induced pluripotent stem cells from non-permissive mouse strains

Genetic background is known to play a role in the ability to derive pluripotent, embryonic stem cells (ESC), a trait referred to as permissiveness. Previously we demonstrated that induced pluripotent stem cells (iPSC) can be readily derived from non-permissive mouse strains by addition of serum-based media supplemented with GSK3B and MEK inhibitors, termed 2iS media, 3 days into reprogramming. Here, we describe the derivation of second type of iPSC colony from non-permissive mouse strains that can be stably maintained independently of 2iS media. The resulting cells display transcriptional heterogeneity similar to that observed in ESC from permissive genetic backgrounds derived in conventional serum containing media supplemented with leukemia inhibitor factor. However, unlike previous studies that report exclusive subpopulations, we observe both exclusive and simultaneous expression of naive and primed cell surface markers. Herein, we explore shifts in pluripotency in the presence of 2iS and characterize heterogenous subpopulations to determine their pluripotent state and role in heterogenous iPSCs derived from the non-permissive NOD/ShiLtJ strain. We conclude that heterogeneity is a naturally occurring, necessary quality of stem cells that allows for the maintenance of pluripotency. This study further demonstrates the efficacy of the 2iS reprogramming technique. It is also the first study to derive stable ESC-like stem cells from the non-permissive NOD/ShiLtJ and WSB/EiJ strains, enabling easier and broader research possibilities into pluripotency for these and similar non-permissive mouse strains and species.

Therapeutic Target Discovery Using High-Throughput Genetic Screens in Acute Myeloid Leukemia

The development of high-throughput gene manipulating tools such as short hairpin RNA (shRNA) and CRISPR/Cas9 libraries has enabled robust characterization of novel functional genes contributing to the pathological states of the diseases. In acute myeloid leukemia (AML), these genetic screen approaches have been used to identify effector genes with previously unknown roles in AML. These AML-related genes centralize alongside the cellular pathways mediating epigenetics, signaling transduction, transcriptional regulation, and energy metabolism. The shRNA/CRISPR genetic screens also realized an array of candidate genes amenable to pharmaceutical targeting. This review aims to summarize genes, mechanisms, and potential therapeutic strategies found via high-throughput genetic screens in AML. We also discuss the potential of these findings to instruct novel AML therapies for combating drug resistance in this genetically heterogeneous disease.

Glycogen Synthase Kinase 3β in Cancer Biology and Treatment

Glycogen synthase kinase (GSK)3β is a multifunctional serine/threonine protein kinase with more than 100 substrates and interacting molecules. GSK3β is normally active in cells and negative regulation of GSK3β activity via phosphorylation of its serine 9 residue is required for most normal cells to maintain homeostasis. Aberrant expression and activity of GSK3β contributes to the pathogenesis and progression of common recalcitrant diseases such as glucose intolerance, neurodegenerative disorders and cancer. Despite recognized roles against several proto-oncoproteins and mediators of the epithelial–mesenchymal transition, deregulated GSK3β also participates in tumor cell survival, evasion of apoptosis, proliferation and invasion, as well as sustaining cancer stemness and inducing therapy resistance. A therapeutic effect from GSK3β inhibition has been demonstrated in 25 different cancer types. Moreover, there is increasing evidence that GSK3β inhibition protects normal cells and tissues from the harmful effects associated with conventional cancer therapies. Here, we review the evidence supporting aberrant GSK3β as a hallmark property of cancer and highlight the beneficial effects of GSK3β inhibition on normal cells and tissues during cancer therapy. The biological rationale for targeting GSK3β in the treatment of cancer is also discussed at length.

MBNL1 regulates essential alternative RNA splicing patterns in MLL-rearranged leukemia

Despite growing awareness of the biologic features underlying MLL-rearranged leukemia, targeted therapies for this leukemia have remained elusive and clinical outcomes remain dismal. MBNL1, a protein involved in alternative splicing, is consistently overexpressed in MLL-rearranged leukemias. We found that MBNL1 loss significantly impairs propagation of murine and human MLL-rearranged leukemia in vitro and in vivo. Through transcriptomic profiling of our experimental systems, we show that in leukemic cells, MBNL1 regulates alternative splicing (predominantly intron exclusion) of several genes including those essential for MLL-rearranged leukemogenesis, such as DOT1L and SETD1A. We finally show that selective leukemic cell death is achievable with a small molecule inhibitor of MBNL1. These findings provide the basis for a new therapeutic target in MLL-rearranged leukemia and act as further validation of a burgeoning paradigm in targeted therapy, namely the disruption of cancer-specific splicing programs through the targeting of selectively essential RNA binding proteins.

Crosstalk between MEIS1 and markers of different cell signaling pathways in esophageal squamous cell carcinoma

The homeobox transcription factor MEIS1 is involved in cell fate decision, stem cells properties, gastrointestinal (GI) tract development, and progression of several malignancies such as esophageal squamous cell carcinoma (ESCC). Increasing evidences suggest the crosstalk between MEIS1 and cell signaling pathways. Therefore, our aim in present study was to investigate the probable linkage of MEIS1 expression with key genes of different cell signaling pathways in ESCC tumorigenesis, and their correlation with clinicopathological feature of the patients. The gene expression profiling of MEIS1 and different cell signaling genes including SALL4, SIZN1, and HEY1 (stemness state, BMP, and NOTCH signaling pathways, respectively) was performed using quantitative real-time reverse transcription polymerase chain reaction (PCR) in fresh tumoral compared to margin normal tissues of 50 treatment-naive ESCC samples. The mRNA expression of MEIS1/SIZN1, SIZN1/HEY1, and SIZN1/SALL4 were significantly associated to each other (P < 0.05). There were remarkable correlations between concomitant mRNA expression of MEIS1 and SIZN1 in tumors with invasion to adventitia, early stages of tumor progression and poorly differentiated tumors. Moreover, expression of MEIS1 and HEY1 was correlated to each other in primary stages of tumor progression and non-invaded tumors. Expression of MEIS1 was significantly associated with SALL4 in poorly differentiated tumors. Our results indicated that correlation between different cell signaling pathway-related genes may lead to esophageal tumorigenesis. It is illustrated that MEIS1 as a HOX gene has a significant correlation with stemness state, BMP, and NOTCH signaling pathways via the SIZN1.

HOX family transcription factors: Related signaling pathways and post-translational modifications in cancer

HOX family transcription factors belong to a highly conserved subgroup of the homeobox superfamily that determines cellular fates in embryonic morphogenesis and the maintenance of adult tissue architecture. HOX family transcription factors play key roles in numerous cellular processes including cell growth, differentiation, apoptosis, motility, and angiogenesis. As tumor promoters or suppressors HOX family members have been reported to be closely related with a variety of cancers. They closely regulate tumor initiation and growth, invasion and metastasis, angiogenesis, anti-cancer drug resistance and stem cell origin. Here, we firstly described the pivotal roles of HOX transcription factors in tumorigenesis. Then, we summarized the main signaling pathways regulated by HOX transcription factors, including Wnt/β-catenin, transforming growth factor β, mitogen-activated protein kinase, phosphoinositide 3-kinase/Akt, and nuclear factor-κB signalings. Finally, we outlined the important post-translational modifications of HOX transcription factors and their regulation in cancers. Future research directions on the HOX transcription factors are also discussed.

The role of exosomes and MYC in therapy resistance of acute myeloid leukemia: Challenges and opportunities

Acute myeloid leukemia (AML) is caused by abnormal production of white blood cells, red blood cells or platelets. The leukemia cells communicate with their microenvironment through nano-vesicle exosomes that are 30-100 nm in diameter. These nano-vesicles are released from body fluids upon fusion of an endocytic compartment with the cell membrane. Exosomes function as cargo to deliver signaling molecules to distant cells. This allows cross-talk between hematopoietic cells and other distant target cell environments. Exosomes support leukemia growth by acting as messengers between tumor cells and the microenvironment as well as inducing oncogenic factors such as c-Myc. Exosomes have also been used as biomarkers in the clinical diagnosis of leukemia. Glycogen synthase kinase-3 (GSK-3) and protein phosphatase 2A (PP2A) are two crucial signaling molecules involved in the AML pathogenesis and MYC stability. GSK-3 is a serine/threonine protein kinase that coordinates with over 40 different proteins during physiological/pathological conditions in blood cells. The dysregulation in GSK-3 has been reported during hematological malignancies. GSK-3 acts as a tumor suppressor by targeting c-MYC, MCL-1 and β-catenin. Conversely, GSK-3 can also act as tumor promoter in some instances. The pharmacological modulators of GSK-3 such as ABT-869, 6-Bromoindirubin-3'-oxime (BIO), GS-87 and LY2090314 have shown promise in the treatment of hematological malignancy. PP2A is a heterotrimeric serine/threonine phosphatase involved in the regulation of hematological malignancy. PP2A-activating drugs (PADs) can effectively antagonize leukemogenesis. The discovery of exosomes, kinase inhibitors and phosphatase activators have provided new hope to the leukemia patients. This review discusses the role of exosomes, GSK-3 and PP2A in the pathogenesis of leukemia. We provide evidence from both preclinical and clinical studies.

Transcriptional addiction in mixed lineage leukemia: new avenues for target therapies

Mixed lineage leukemia (MLL) is an aggressive and refractory blood cancer that predominantly occurs in pediatric patients and is often associated with poor prognosis and dismal outcomes. Thus far, no effective target therapy for the treatment of MLL leukemia is available. MLL leukemia is caused by the rearrangement of MLL genes at 11q23, which generates various MLL chimeric proteins that promote leukemogenesis through transcriptional misregulation of MLL target genes. Biochemical studies on MLL chimeras have identified that the most common partners exist in the superelongation complex (SEC) and DOT1L complex, which activate or sustain MLL target gene expression through processive transcription elongation. The results of these studies indicate a transcription-related mechanism for MLL leukemogenesis and maintenance. In this study, we first review the history of MLL leukemia and its related clinical features. Then, we discuss the biological functions of MLL and MLL chimeras, significant cooperating events, and transcriptional addiction mechanisms in MLL leukemia with an emphasis on potential and rational therapy development. Collectively, we believe that targeting the transcriptional addiction mediated by SEC and the DOT1L complex will provide new avenues for target therapies in MLL leukemia and serve as a novel paradigm for targeting transcriptional addiction in other cancers.

Transcription factor Oct1 protects against hematopoietic stress and promotes acute myeloid leukemia

A better understanding of the development and progression of acute myelogenous leukemia (AML) is necessary to improve patient outcome. Here we define roles for the transcription factor Oct1/Pou2f1 in AML and normal hematopoiesis. Inappropriate reactivation of the CDX2 gene is widely observed in leukemia patients and in leukemia mouse models. We show that Oct1 associates with the CDX2 promoter in both normal and AML primary patient samples, but recruits the histone demethylase Jmjd1a/Kdm3a to remove the repressive H3K9me2 mark only in malignant specimens. The CpG DNA immediately adjacent to the Oct1 binding site within the CDX2 promoter exhibits variable DNA methylation in healthy control blood and bone marrow samples, but complete demethylation in AML samples. In MLL-AF9-driven mouse models, partial loss of Oct1 protects from myeloid leukemia. Complete Oct1 loss completely suppresses leukemia but results in lethality from bone marrow failure. Loss of Oct1 in normal hematopoietic transplants results in superficially normal long-term reconstitution; however, animals become acutely sensitive to 5-fluorouracil, indicating that Oct1 is dispensable for normal hematopoiesis but protects blood progenitor cells against external chemotoxic stress. These findings elucidate a novel and important role for Oct1 in AML.

Adaptive Transcriptional Responses by CRTC Coactivators in Cancer

Adaptive stress signaling networks directly influence tumor development and progression. These pathways mediate responses that allow cancer cells to cope with both tumor cell-intrinsic and cell-extrinsic insults and develop acquired resistance to therapeutic interventions. This is mediated in part by constant oncogenic rewiring at the transcriptional level by integration of extracellular cues that promote cell survival and malignant transformation. The cAMP-regulated transcriptional coactivators (CRTCs) are a newly discovered family of intracellular signaling integrators that serve as the conduit to the basic transcriptional machinery to regulate a host of adaptive response genes. Thus, somatic alterations that lead to CRTC activation are emerging as key driver events in the development and progression of many tumor subtypes.

Off-target based drug repurposing opportunities for tivantinib in acute myeloid leukemia

GSK3α has been identified as a new target in the treatment of acute myeloid leukemia (AML). However, most GSK3 inhibitors lack specificity for GSK3α over GSK3β and other kinases. We have previously shown in lung cancer cells that GSK3α and to a lesser extent GSK3β are inhibited by the advanced clinical candidate tivantinib (ARQ197), which was designed as a MET inhibitor. Thus, we hypothesized that tivantinib would be an effective therapy for the treatment of AML. Here, we show that tivantinib has potent anticancer activity across several AML cell lines and primary patient cells. Tivantinib strongly induced apoptosis, differentiation and G2/M cell cycle arrest and caused less undesirable stabilization of β-catenin compared to the pan-GSK3 inhibitor LiCl. Subsequent drug combination studies identified the BCL-2 inhibitor ABT-199 to synergize with tivantinib while cytarabine combination with tivantinib was antagonistic. Interestingly, the addition of ABT-199 to tivantinib completely abrogated tivantinib induced β-catenin stabilization. Tivantinib alone, or in combination with ABT-199, downregulated anti-apoptotic MCL-1 and BCL-XL levels, which likely contribute to the observed synergy. Importantly, tivantinib as single agent or in combination with ABT-199 significantly inhibited the colony forming capacity of primary patient AML bone marrow mononuclear cells. In summary, tivantinib is a novel GSK3α/β inhibitor that potently kills AML cells and tivantinib single agent or combination therapy with ABT-199 may represent attractive new therapeutic opportunities for AML.

Aberrant GSK3β nuclear localization promotes AML growth and drug resistance

Acute myeloid leukemia (AML) is a devastating disease with poor patient survival. As targetable mutations in AML are rare, novel oncogenic mechanisms are needed to define new therapeutic targets. We identified AML cells that exhibit an aberrant pool of nuclear glycogen synthase kinase 3β (GSK3β). This nuclear fraction drives AML growth and drug resistance. Nuclear, but not cytoplasmic, GSK3β enhances AML colony formation and AML growth in mouse models. Nuclear GSK3β drives AML partially by promoting nuclear localization of the NF-κB subunit, p65. Finally, nuclear GSK3β localization has clinical significance as it strongly correlates to worse patient survival (n = 86; hazard ratio = 2.2; P < .01) and mediates drug resistance in cell and animal models. Nuclear localization of GSK3β may define a novel oncogenic mechanism in AML and represent a new therapeutic target.

HOXA9 Reprograms the Enhancer Landscape to Promote Leukemogenesis

Aberrant expression of HOXA9 is a prominent feature of acute leukemia driven by diverse oncogenes. Here we show that HOXA9 overexpression in myeloid and B progenitor cells leads to significant enhancer reorganizations with prominent emergence of leukemia-specific de novo enhancers. Alterations in the enhancer landscape lead to activation of an ectopic embryonic gene program. We show that HOXA9 functions as a pioneer factor at de novo enhancers and recruits CEBPα and the MLL3/MLL4 complex. Genetic deletion of MLL3/MLL4 blocks histone H3K4 methylation at de novo enhancers and inhibits HOXA9/MEIS1-mediated leukemogenesis in vivo. These results suggest that therapeutic targeting of HOXA9-dependent enhancer reorganization can be an effective therapeutic strategy in acute leukemia with HOXA9 overexpression.

Discovery and anti-inflammatory evaluation of benzothiazepinones (BTZs) as novel non-ATP competitive inhibitors of glycogen synthase kinase-3β (GSK-3β)

Glycogen synthase kinase-3β (GSK-3β) has been identified to promote inflammation and its inhibitors have also been proven to treat some inflammatory mediated diseases in animal models. Non-ATP competitive inhibitors inherently have better therapeutical value due to their higher specificity than ATP competitive ones. In this paper, we designed and synthesized a series of new BTZ derivatives as non-ATP competitive GSK-3β inhibitors. Kinetic analysis revealed two typical compounds 6j and 3j showed the different non-ATP competitive mechanism of substrate competition or allosteric modulation to GSK-3β, respectively. As expected, the two compounds showed good specificity in a panel test of 16 protein kinases, even to the closest enzymes, like CDK-1/cyclin B and CK-II. The in vivo results proved that both compounds can greatly attenuate the LPS-induced acute lung injury (ALI) and diminish inflammation response in mice by inhibiting the mRNA expression of IL-1β and IL-6. Western blot analysis demonstrated that they negatively regulated GSK-3β, and the mechanism of the observed beneficial effects of the inhibitors may involve both the increased phosphorylation of the Ser9 residue on GSK-3β and protein expression of Sirtuin 1 (SIRT1). The results support that such novel BTZ compounds have a protective role in LPS-induced ALI, and might be attractive candidates for further development of inflammation pharmacotherapy, which greatly thanks to their inherently high selectivities by the non-ATP competitive mode of action. Finally, we proposed suggesting binding modes by Docking study to well explain the impacts of compounds on the target site.

Differential gene expression of a feed-spiked super-producing CHO cell line

Feed supplements are concentrated cell culture media that contain a variety of nutrients, which can be added during a bioprocess. During fed-batch cultivation, feed media are typically added to a growing cell culture to maximize cell and product concentrations. In this study, only a single shot of feed medium was added on day 0 to a basal cell culture medium and compared to non-supplemented basal medium (feed-spiked at day 0 versus control experiments) by cultivation of a recombinant mAb expressing CHO cell line in batch mode under controlled conditions in a bioreactor. Since the feed-spike at day 0 was based on existing medium components without introducing additional supplements, a desirable process with decreased complexity was generated. Unlike cells in basal medium, feed-spiked cultures reached almost 2× higher peak cell concentrations (10 × 10⁶ c/mL vs. 18 × 10⁶ c/mL) and 3× higher antibody concentrations (0.8 g/L vs. 2.4 g/L). Batch process time and the integral over the viable cell count were similar for both process types. Constantly high cell-specific production rates in feed-spiked cultures (70 pg/cell/day) compared to continuously declining rates in basal medium (from 70 to 10 pg/cell/day) were responsible for an overall 70% higher cell-specific production rate and the higher product concentrations. To associate gene expression patterns to different process proceedings, transcriptome analysis was performed using microarrays. Several transcripts that are involved with glutamine de novo synthesis and citric acid cycle were significantly upregulated on several days in feed-spiked cultures. The top identified gene ontology (GO) terms related well to cell cycle and primary metabolism, cellular division as well as nucleobase formation or regulation, which indicated a more active proliferative state for feed-spiked cultures. KEGG biochemical pathway analysis and Gene set enrichment analysis (GSEA) further confirmed these findings from a complementary perspective. Moreover, several interesting gene targets, which have not yet been associated with recombinant protein expression, were identified that related to a higher proliferative state, growth, protein synthesis, cell-size control, metabolism, cell survival as well as genes that are associated with the control of the mammalian target of rapamycin (mTOR) in feed-spiked cultures. Analysis of critical product quality attributes (i.e. glycosylation, charge variants and size distribution) showed that feed-spiking did not change antibody quality.

AMPK/FIS1-Mediated Mitophagy Is Required for Self-Renewal of Human AML Stem Cells

Leukemia stem cells (LSCs) are thought to drive the genesis of acute myeloid leukemia (AML) as well as relapse following chemotherapy. Because of their unique biology, developing effective methods to eradicate LSCs has been a significant challenge. In the present study, we demonstrate that intrinsic overexpression of the mitochondrial dynamics regulator FIS1 mediates mitophagy activity that is essential for primitive AML cells. Depletion of FIS1 attenuates mitophagy and leads to inactivation of GSK3, myeloid differentiation, cell cycle arrest, and a profound loss of LSC self-renewal potential. Further, we report that the central metabolic stress regulator AMPK is also intrinsically activated in LSC populations and is upstream of FIS1. Inhibition of AMPK signaling recapitulates the biological effect of FIS1 loss. These data suggest a model in which LSCs co-opt AMPK/FIS1-mediated mitophagy as a means to maintain stem cell properties that may be otherwise compromised by the stresses induced by oncogenic transformation.

Identification of Upstream Kinases by Fluorescence Complementation Mass Spectrometry

Protein kinases and their substrates comprise extensive signaling networks that regulate many diverse cellular functions. However, methods and techniques to systematically identify kinases directly responsible for specific phosphorylation events have remained elusive. Here we describe a novel proteomic strategy termed fluorescence complementation mass spectrometry (FCMS) to identify kinase-substrate pairs in high throughput. The FCMS strategy employs a specific substrate and a kinase library, both of which are fused with fluorescence complemented protein fragments. Transient and weak kinase-substrate interactions in living cells are stabilized by the association of fluorescence protein fragments. These kinase-substrate pairs are then isolated with high specificity and are identified and quantified by LC-MS. FCMS was applied to the identification of both known and novel kinases of the transcription factor, cAMP response element-binding protein (CREB). Novel CREB kinases were validated by in vitro kinase assays, and the phosphorylation sites were unambiguously located. These results uncovered possible new roles for CREB in multiple important signaling pathways and demonstrated the great potential of this new proteomic strategy.

Deregulation of the HOXA9/MEIS1 axis in acute leukemia

PURPOSE OF REVIEW

HOXA9 is a homeodomain transcription factor that plays an essential role in normal hematopoiesis and acute leukemia, in which its overexpression is strongly correlated with poor prognosis. The present review highlights recent advances in the understanding of genetic alterations leading to deregulation of HOXA9 and the downstream mechanisms of HOXA9-mediated transformation.

RECENT FINDINGS

A variety of genetic alterations including MLL translocations, NUP98-fusions, NPM1 mutations, CDX deregulation, and MOZ-fusions lead to high-level HOXA9 expression in acute leukemias. The mechanisms resulting in HOXA9 overexpression are beginning to be defined and represent attractive therapeutic targets. Small molecules targeting MLL-fusion protein complex members, such as DOT1L and menin, have shown promising results in animal models, and a DOT1L inhibitor is currently being tested in clinical trials. Essential HOXA9 cofactors and collaborators are also being identified, including transcription factors PU.1 and C/EBPα, which are required for HOXA9-driven leukemia. HOXA9 targets including IGF1, CDX4, INK4A/INK4B/ARF, mir-21, and mir-196b and many others provide another avenue for potential drug development.

SUMMARY

HOXA9 deregulation underlies a large subset of aggressive acute leukemias. Understanding the mechanisms regulating the expression and activity of HOXA9, along with its critical downstream targets, shows promise for the development of more selective and effective leukemia therapies.

GSK-3 as a novel prognostic indicator in leukemia

While leukemias represent a diverse set of diseases with malignant cells derived from myeloid or lymphoid origin, a common feature is the dysregulation of signal transduction pathways that influence leukemogeneisis, promote drug resistance, and favor leukemia stem cells. Mutations in PI3K, PTEN, RAS, or other upstream regulators can activate the AKT kinase which has central roles in supporting cell proliferation and survival. A major target of AKT is Glycogen Synthase Kinase 3 (GSK3). GSK3 has two isoforms (alpha and beta) that were studied as regulators of metabolism but emerged as central players in cancer in the early 1990s. GSK3 is unique in that the isoforms are constitutively active. Active GSK3 promotes destruction of oncogenic proteins such as beta Catenin, c-MYC, and MCL-1 and thus has tumor suppressor properties. In AML, inactivation of GSK3 is associated with poor overall survival. Interestingly in some leukemias GSK3 targets a tumor suppressor and thus the kinases can act as tumor promoters in those instances. An example is GSK3 targeting p27Kip1 in AML with MLL translocation. This review will cover the role of GSK3 in various leukemias both as tumor suppressor and tumor promoter. We will also briefly cover current state of GSK3 inhibitors for leukemia therapy.

Overexpression of NAC1 confers drug resistance via HOXA9 in colorectal carcinoma cells

Colorectal carcinoma (CRC) is one of the most common types of malignancy worldwide. Recently, neoadjuvant chemotherapy has become an important treatment strategy for CRC. However, treatment frequently fails due to the development of chemoresistance, which is a major obstacle for positive prognosis. However, the underlying mechanisms of chemoresistance remain unclear. The present study assessed the functions of nucleus accumbens-associated protein 1 (NAC1), an important transcriptional regulator, in CRC progression. Reverse transcription-quantitative polymerase chain reaction, western blot analysis and immunohistochemistry were performed to detect the expression levels of NAC1. It was identified that NAC1 was significantly overexpressed in CRC compared with non-tumorous tissues, indicating an oncogenic role. Following this, gain and loss of function analyses were performed in vitro to further investigate the function of NAC1. Cell viability and caspase-3/7 activity assays were used to assess chemotherapy-induced apoptosis. These results indicated that overexpression of NAC1 in CRC cells increased resistance to chemotherapy and inhibited apoptosis. Additionally, RNA interference-mediated knockdown of NAC1 restored the chemosensitivity of CRC cells. Furthermore, mechanistic investigation revealed that NAC1 increased drug resistance via inducing homeobox A9 (HOXA9) expression, and that knockdown of HOXA9 abrogated NAC1-induced drug resistance. In conclusion, the results of the present study demonstrated that NAC1 may be a critical factor in the development of chemoresistance, offering a potential novel target for the treatment of CRC.

Activation of PERK Elicits Memory Impairment through Inactivation of CREB and Downregulation of PSD95 After Traumatic Brain Injury

The PKR-like ER kinase (PERK), a transmembrane protein, resides in the endoplasmic reticulum (ER). Its activation serves as a key sensor of ER stress, which has been implicated in traumatic brain injury (TBI). The loss of memory is one of the most common symptoms after TBI, but the precise role of PERK activation in memory impairment after TBI has not been well elucidated. Here, we have shown that blocking the activation of PERK using GSK2656157 prevents the loss of dendritic spines and rescues memory deficits after TBI. To elucidate the molecular mechanism, we found that activated PERK phosphorylates CAMP response element binding protein (CREB) and PSD95 directly at the S129 and T19 residues, respectively. Phosphorylation of CREB protein prevents its interaction with a coactivator, CREB-binding protein, and subsequently reduces the BDNF level after TBI. Conversely, phosphorylation of PSD95 leads to its downregulation in pericontusional cortex after TBI in male mice. Treatment with either GSK2656157 or overexpression of a kinase-dead mutant of PERK (PERK-K618A) rescues BDNF and PSD95 levels in the pericontusional cortex by reducing phosphorylation of CREB and PSD95 proteins after TBI. Similarly, administration of either GSK2656157 or overexpression of PERK-K618A in primary neurons rescues the loss of dendritic outgrowth and number of synapses after treatment with a PERK activator, tunicamycin. Therefore, our study suggests that inhibition of PERK phosphorylation could be a potential therapeutic target to restore memory deficits after TBI.SIGNIFICANCE STATEMENT Traumatic brain injury (TBI) is the leading cause of death and disability around the world and affects 1.7 million Americans each year. Here, we have shown that TBI-activated PKR-like ER kinase (PERK) is responsible for memory deficiency, which is the most common problem in TBI patients. A majority of PERK's biological activities have been attributed to its function as an eIF2α kinase. However, our study suggests that activated PERK mediates its function via increasing phosphorylation of CAMP response element binding protein (CREB) and PSD95 after TBI. Blocking PERK phosphorylation rescues spine loss and memory deficits independently of phosphorylation of eIF2α. Therefore, our study suggests that CREB and PSD95 are novel substrates of PERK, so inhibition of PERK phosphorylation using GSK2656157 would be beneficial against memory impairment after TBI.

Taking a Bad Turn: Compromised DNA Damage Response in Leukemia

Genomic integrity is of outmost importance for the survival at the cellular and the organismal level and key to human health. To ensure the integrity of their DNA, cells have evolved maintenance programs collectively known as the DNA damage response. Particularly challenging for genome integrity are DNA double-strand breaks (DSB) and defects in their repair are often associated with human disease, including leukemia. Defective DSB repair may not only be disease-causing, but further contribute to poor treatment outcome and poor prognosis in leukemia. Here, we review current insight into altered DSB repair mechanisms identified in leukemia. While DSB repair is somewhat compromised in all leukemic subtypes, certain key players of DSB repair are particularly targeted: DNA-dependent protein kinase (DNA-PK) and Ku70/80 in the non-homologous end-joining pathway, as well as Rad51 and breast cancer 1/2 (BRCA1/2), key players in homologous recombination. Defects in leukemia-related DSB repair may not only arise from dysfunctional repair components, but also indirectly from mutations in key regulators of gene expression and/or chromatin structure, such as p53, the Kirsten ras oncogene (K-RAS), and isocitrate dehydrogenase 1 and 2 (IDH1/2). A detailed understanding of the basis for defective DNA damage response (DDR) mechanisms for each leukemia subtype may allow to further develop new treatment methods to improve treatment outcome and prognosis for patients.

Role of MAML1 and MEIS1 in Esophageal Squamous Cell Carcinoma Depth of Invasion

Homeobox (HOX) transcription factors and NOTCH signaling pathway are critical regulators of stem cell functions, cell fate in development and homeostasis of gastrointestinal tissues. In the present study, we analyzed cross talk between NOTCH pathway and HOX genes through assessment of probable correlation betweenMAML1 and MEIS1 as the main transcription factor of NOTCH pathway and enhancer of HOX transcriptional machinery, respectively in esophageal squamous cell carcinoma (ESCC) patients. Fifty one ESCC cases were enrolled to assess the levels of Meis1 and Maml1 mRNA expression using real-time polymerase chain reaction (PCR). Only 3 out of 51 (5.9%) cases had MEIS1/MAML1 under expression and 2/51 (3.9%) cases had MEIS1/MAML1over expression. Nine out of 51 samples (17.6%) have shown MEIS1 under expression and MAML1 over expression. There was a significant correlation between MAML1and MEIS1mRNA expressions (p ≤ 0.05). There were significant correlations between MEIS1 under/MAML1 over expressed cases and tumor location (p = 0.05), tumor depth of invasion (p = 0.011), and sex (p = 0.04). Our results showed that MEIS1 may have a negative role in regulation of MAML1expression during the ESCC progression.

Correlation Between Meis1 and Msi1 in Esophageal Squamous Cell Carcinoma

PURPOSE

Homeobox (HOX) transcription factors are critical regulators of cell fate, stem cell functions, and gastrointestinal development. They require three-amino acid loop extension (TALE) homeodomain proteins such as Meis1 to enhance their transcriptional efficiencies. There are complicated associations between different signaling pathways such as the Wnt and NOTCH and tumor progression. It has been investigated that GSK-3 as an important component of the Wnt pathway facilitates the expression of HOX target genes. Therefore, in the present study, we assessed the probable correlation between Wnt, NOTCH, and HOX genes in esophageal squamous cell carcinoma (ESCC) progression and metastasis through the correlational study between the Msi1 as an important activator for both of the NOTCH and Wnt pathways and Meis1.

METHODS

Levels of Meis1 and Msi1 messenger RNA (mRNA) expression in 51 ESCC patients were compared to the normal tissues using real-time polymerase chain reaction.

RESULTS

Only 3 out of 51 (5.9 %) cases had Meis1/Msi1 overexpression and also 3/51 (5.9 %) cases had Meis1/Msi1 underexpression. There was a significant correlation between the Msi1 and Mesi1 mRNA expression (p = 0.037). All of the Msi1/Meis1 underexpressed tumors were poorly differentiated (p = 0.003). Meis1 under/Msi1 overexpressed cases also were in T3 tumor depth of invasion (p = 0.019). And there was a significant correlation between the Msi1/Meis1 underexpression and gender (p = 0.045).

CONCLUSIONS

Our results show that Meis1 may have a positive feedback with Msi1 during the ESCC progression.

Animal models of RLS phenotypes

Restless legs syndrome (RLS) is a complex disorder that involves sensory and motor systems. The major pathophysiology of RLS is low iron concentration in the substantia nigra containing the cell bodies of dopamine neurons that project to the striatum, an area that is crucial for modulating movement. People who have RLS often present with normal iron values outside the brain; recent studies implicate several genes are involved in the syndrome. Like most complex diseases, animal models usually do not faithfully capture the full phenotypic spectrum of "disease," which is a uniquely human construct. Nonetheless, animal models have proven useful in helping to unravel the complex pathophysiology of diseases such as RLS and suggesting novel treatment paradigms. For example, hypothesis-independent genome-wide association studies (GWAS) have identified several genes as increasing the risk for RLS, including BTBD9. Independently, the murine homolog Btbd9 was identified as a candidate gene for iron regulation in the midbrain in mice. The relevance of the phenotype of another of the GWAS identified genes, MEIS1, has also been explored. The role of Btbd9 in iron regulation and RLS-like behaviors has been further evaluated in mice carrying a null mutation of the gene and in fruit flies when the BTBD9 protein is degraded. The BTBD9 and MEIS1 stories originate from human GWAS research, supported by work in a genetic reference population of mice (forward genetics) and further verified in mice, fish flies, and worms. Finally, the role of genetics is further supported by an inbred mouse strain that displays many of the phenotypic characteristics of RLS. The role of animal models of RLS phenotypes is also extended to include periodic limb movements.

Nuclear GSK3β promotes tumorigenesis by phosphorylating KDM1A and inducing its deubiquitylation by USP22

Emerging evidences have shown that GSK3β plays oncogenic roles in multiple tumor types; however, the underlying mechanisms remain largely unknown. Herein, we show that nuclear GSK3β is responsible for the accumulation of the histone demethylase KDM1A and critically regulates histone H3K4 methylation during tumorigenesis. GSK3β phosphorylates KDM1A serine 683 upon priming phosphorylation of KDM1A serine 687 by CK1α. Phosphorylation of KDM1A induces its binding with and deubiquitination by USP22, leading to KDM1A stabilization. GSK3β and USP22-dependent KDM1A stabilization is required for the demethylation of histone H3K4, thereby repression of BMP2, CDKN1A, and GATA6 transcription, cancer stem cell self-renewal, and glioblastoma tumorigenesis. In human glioblastoma specimens, KDM1A levels are correlated with nuclear GSK3β and USP22 levels. Furthermore, a GSK3 inhibitor tideglusib sensitizes tumor xenograft to chemotherapy in mice via KDM1A down-regulation and improves survival. Our findings demonstrate that nuclear GSK3β and USP22-mediated KDM1A stabilization is essential for glioblastoma tumorigenesis.

PAR2-dependent activation of GSK3β regulates the survival of colon stem/progenitor cells

Protease-activated receptors PAR1 and PAR2 play an important role in the control of epithelial cell proliferation and migration. However, the survival of normal and tumor intestinal stem/progenitor cells promoted by proinflammatory mediators may be critical in oncogenesis. The glycogen synthase kinase-3β (GSK3β) pathway is overactivated in colon cancer cells and promotes their survival and drug resistance. We thus aimed to determine PAR1 and PAR2 effects on normal and tumor intestinal stem/progenitor cells and whether they involved GSK3β. First, PAR1 and PAR2 were identified in colon stem/progenitor cells by immunofluorescence. In three-dimensional cultures of murine crypt units or single tumor Caco-2 cells, PAR2 activation decreased numbers and size of normal or cancerous spheroids, and PAR2-deficient spheroids showed increased proliferation, indicating that PAR2 represses proliferation. PAR2-stimulated normal cells were more resistant to stress (serum starvation or spheroid passaging), suggesting prosurvival effects of PAR2 Accordingly, active caspase-3 was strongly increased in PAR2-deficient normal spheroids. PAR2 but not PAR1 triggered GSK3β activation through serine-9 dephosphorylation in normal and tumor cells. The PAR2-triggered GSK3β activation implicates an arrestin/PP2A/GSK3β complex that is dependent on the Rho kinase activity. Loss of PAR2 was associated with high levels of GSK3β nonactive form, strengthening the role of PAR2 in GSK3β activation. GSK3 pharmacological inhibition impaired the survival of PAR2-stimulated spheroids and serum-starved cells. Altogether our data identify PAR2/GSK3β as a novel pathway that plays a critical role in the regulation of stem/progenitor cell survival and proliferation in normal colon crypts and colon cancer.

S6K1 regulates hematopoietic stem cell self-renewal and leukemia maintenance

Hyperactivation of the mTOR pathway impairs hematopoietic stem cell (HSC) functions and promotes leukemogenesis. mTORC1 and mTORC2 differentially control normal and leukemic stem cell functions. mTORC1 regulates p70 ribosomal protein S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E-binding (eIF4E-binding) protein 1 (4E-BP1), and mTORC2 modulates AKT activation. Given the extensive crosstalk that occurs between mTORC1 and mTORC2 signaling pathways, we assessed the role of the mTORC1 substrate S6K1 in the regulation of both normal HSC functions and in leukemogenesis driven by the mixed lineage leukemia (MLL) fusion oncogene MLL-AF9. We demonstrated that S6K1 deficiency impairs self-renewal of murine HSCs by reducing p21 expression. Loss of S6K1 also improved survival in mice transplanted with MLL-AF9-positive leukemic stem cells by modulating AKT and 4E-BP1 phosphorylation. Taken together, these results suggest that S6K1 acts through multiple targets of the mTOR pathway to promote self-renewal and leukemia progression. Given the recent interest in S6K1 as a potential therapeutic target in cancer, our results further support targeting this molecule as a potential strategy for treatment of myeloid malignancies.

A Novel Glycogen Synthase Kinase-3 Inhibitor Optimized for Acute Myeloid Leukemia Differentiation Activity

Standard therapies used for the treatment of acute myeloid leukemia (AML) are cytotoxic agents that target rapidly proliferating cells. Unfortunately, this therapeutic approach has limited efficacy and significant toxicity and the majority of AML patients still die of their disease. In contrast to the poor prognosis of most AML patients, most individuals with a rare subtype of AML, acute promyelocytic leukemia, can be cured by differentiation therapy using regimens containing all-trans retinoic acid. GSK3 has been previously identified as a therapeutic target in AML where its inhibition can lead to the differentiation and growth arrest of leukemic cells. Unfortunately, existing GSK3 inhibitors lead to suboptimal differentiation activity making them less useful as clinical AML differentiation agents. Here, we describe the discovery of a novel GSK3 inhibitor, GS87. GS87 was discovered in efforts to optimize GSK3 inhibition for AML differentiation activity. Despite GS87's dramatic ability to induce AML differentiation, kinase profiling reveals its high specificity in targeting GSK3 as compared with other kinases. GS87 demonstrates high efficacy in a mouse AML model system and unlike current AML therapeutics, exhibits little effect on normal bone marrow cells. GS87 induces potent differentiation by more effectively activating GSK3-dependent signaling components including MAPK signaling as compared with other GSK3 inhibitors. GS87 is a novel GSK3 inhibitor with therapeutic potential as a differentiation agent for non-promyelocytic AML. Mol Cancer Ther; 15(7); 1485-94. ©2016 AACR.