Critical role of retinoid/rexinoid signaling in mediating transformation and therapeutic response of NUP98-RARG leukemia

Acute myeloid leukemia with NUP98::RARG rearrangement: a case report and review of the relevant literature

We herein report a rare case of acute myeloid leukemia (AML) with t(11;12)(p15;q13) and NUP98::RARG, which seems to be involved in the development of AML. The morphological features were similar to those of classic acute promyelocytic leukemia (APL), but unlike classic APL, this leukemia was resistant to treatment with all-trans retinoic acid (ATRA). We decided to use standard chemotherapy for AML with monitoring of minimal residual disease (MRD) by qualitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for NUP98::RARG mRNA. Although MRD disappeared after induction chemotherapy, it later reappeared, and hematological relapse occurred during subsequent chemotherapies. The patient received haploidentical hematopoietic stem cell transplantation while not in remission and achieved a second molecular remission. However, relapse occurred 4 months after transplantation. The specific mechanism of ATRA resistance in this unique case of AML remains unclear, and no standard treatment has been determined. This is the first case report of AML with NUP98::RARG rearrangement in Japan. Qualitative RT-PCR analysis for NUP98::RARG mRNA was helpful for the accurate diagnosis and evaluation of MRD to choose an adequate treatment for this type of AML.

Oncogenic role of RARG rearrangements in acute myeloid leukemia resembling acute promyelocytic leukemia

Acute myeloid leukemia (AML) featuring retinoic acid receptor-gamma (RARG) rearrangements exhibits morphological features resembling those of acute promyelocytic leukemia but is associated with drug resistance and poor clinical outcomes. However, the mechanisms underlying the role of RARG fusions in leukemogenesis remain elusive. Here, we show that RARG fusions disrupt myeloid differentiation and promote proliferation and self-renewal of hematopoietic stem and progenitor cells (HSPCs) by upregulating BCL2 and ATF3. RARG fusions overexpression leads to preleukemic phenotypes but fails to induce oncogenic transformation. However, the co-occurrence of RARG fusions and heterozygous Wt1 loss induce fully penetrant AML by activating MYC and HOXA9/MEIS1 targets. Leveraging Connectivity Map resources and high-throughput screening, we identify venetoclax, homoharringtonine, and daunorubicin as potential therapeutic options for RARG-AML. Overall, our findings provide pivotal insights into the molecular mechanisms governed by RARG fusions and enhanced by WT1 loss in AML development and propose a rational therapeutic strategy for RARG-AML.

Critical role of tripartite fusion and LBD truncation in certain RARA- and all RARG-related atypical APL

Atypical acute promyelocytic leukemia (aAPL) presents a complex landscape of retinoic acid receptor (RAR) fusion genes beyond the well-known PML::RARA fusion. Among these, 31 individually rare RARA and RARG fusion genes have been documented, often reported in the canonical X::RAR bipartite fusion form. Intriguingly, some artificially mimicked bipartite X::RAR fusions respond well to all-trans retinoic acid (ATRA) in vitro, contrasting with the ATRA resistance observed in patients. To unravel the underlying mechanisms, we conducted a comprehensive molecular investigation into the fusion transcripts in 27 RARA fusion gene-positive aAPL (RARA-aAPL) and 21 RARG-aAPL cases. Our analysis revealed an unexpected novel form of X::RAR::X- or X::RAR::Y-type tripartite fusions in certain RARA-aAPL and all RARG-aAPL cases, with shared features and notable differences between these 2 disease subgroups. In RARA-aAPL cases, the occurrence of RARA 3' splices was associated with their 5' fusion partner genes, mapping across the coding region of helix 11_12 (H11_12) within the ligand-binding domain (LBD), resulting in LBD-H12 or H11_12 truncation. In RARG-aAPL cases, RARG 3' splices were consistently localized to the terminus of exon 9, leading to LBD-H11_12 truncation. Significant differences were also observed between RARA and RARG 5' splice patterns. Our analysis also revealed extensive involvement of transposable elements in constructing RARA and RARG 3' fusions, suggesting transposition mechanisms for fusion gene ontogeny. Both protein structural analysis and experimental results highlighted the pivotal role of LBD-H11_12/H12 truncation in driving ATRA unresponsiveness and leukemogenesis in tripartite fusion-positive aAPL, through a protein allosteric dysfunction mechanism.

Case report: Successful therapy with azacitidine for acute myeloid leukemia with NUP98::RARG resembling acute promyelocytic leukemia

We report a case of acute myeloid leukemia (AML) with retinoic acid receptor gamma (RARG) rearrangement, exhibiting clinical, morphological, and immunophenotypic features similar to classic acute promyelocytic leukemia (APL). RNA sequencing analysis of the patient's bone marrow samples revealed the presence of nucleoporin 98 (NUP98)-RARG caused by translocation. AML with RARG rearrangement is insensitive to all-trans retinoic acid (ATRA) and arsenic trioxide. The patient received azacitidine therapy after failing ATRA and standard 3 + 7 therapy (idarubicin and cytarabine) and achieved complete remission. Conclusively, this acute myeloid leukemia subtype may benefit from azacitidine.

Single-cell RNA sequencing reveals the heterogeneity of epithelial cell and fibroblast cells from non- to metastatic lymph node OTSCC

Lymph node metastasis (LNM) is one of the common features of oral tongue squamous cell carcinoma (OTSCC). LNM is also taken as a sign of advanced OTSCC and poor survival rate. Recently, single-cell RNA sequencing has been applied in investigating the heterogeneity of tumor microenvironment and discovering the potential biomarkers for helping the diagnosis and prognosticating. Pathogenesis of LNM in OTSCC remains unknown. Specifically, cancer-associated fibroblasts (CAFs) and epithelial tumor cells could foster the progression of tumors. Thus, in this study, we aimed to comprehensively analyze the roles of subpopulations of CAFs and epithelial tumor cells in lymph node metastatic OTSCC using the integration of OTSCC single-cell RNA sequencing datasets. Four distinct subtypes of CAFs, namely vascular CAFs, myofibroblast CAFs, inflammatory CAFs, and growth arrest CAFs were successfully discovered in LNM tumor and confirmed the roles of GAS and PTN pathways in the progression of tumor metastasis. In addition, NKAIN2+ epithelial cells and FN1+ epithelial cells specifically exhibited an upregulation of PTN, NRG, MIF, and SPP1 signaling pathways in the metastatic OTSCC. In doing so, we put forth some potential biomarkers that could be utilized for the purpose of diagnosing and prognosticating OTSCC during its metastatic phase and tried to confirm by immunofluorescence assays.

A global study for acute myeloid leukemia with RARG rearrangement

Acute myeloid leukemia (AML) with retinoic acid receptor γ (RARG) rearrangement has clinical, morphologic, and immunophenotypic features similar to classic acute promyelocytic leukemia. However, AML with RARG rearrangement is insensitive to alltrans retinoic acid (ATRA) and arsenic trioxide (ATO) and carries a poor prognosis. We initiated a global cooperative study to define the clinicopathological features, genomic and transcriptomic landscape, and outcomes of AML with RARG rearrangements collected from 29 study groups/institutions worldwide. Thirty-four patients with AML with RARG rearrangements were identified. Bleeding or ecchymosis was present in 18 (54.5%) patients. Morphology diagnosed as M3 and M3v accounted for 73.5% and 26.5% of the cases, respectively. Immunophenotyping showed the following characteristics: positive for CD33, CD13, and MPO but negative for CD38, CD11b, CD34, and HLA-DR. Cytogenetics showed normal karyotype in 38% and t(11;12) in 26% of patients. The partner genes of RARG were diverse and included CPSF6, NUP98, HNRNPc, HNRNPm, PML, and NPM1. WT1- and NRAS/KRAS-mutations were common comutations. None of the 34 patients responded to ATRA and/or ATO. Death within 45 days from diagnosis occurred in 10 patients (∼29%). At the last follow-up, 23 patients had died, and the estimated 2-year cumulative incidence of relapse, event-free survival, and overall survival were 68.7%, 26.7%, and 33.5%, respectively. Unsupervised hierarchical clustering using RNA sequencing data from 201 patients with AML showed that 81.8% of the RARG fusion samples clustered together, suggesting a new molecular subtype. RARG rearrangement is a novel entity of AML that confers a poor prognosis. This study is registered with the Chinese Clinical Trial Registry (ChiCTR2200055810).

ALDH1A1 in Cancers: Bidirectional Function, Drug Resistance, and Regulatory Mechanism

Aldehyde dehydrogenases 1 family member A1(ALDH1A1) gene codes a cytoplasmic enzyme and shows vital physiological and pathophysiological functions in many areas. ALDH1A1 plays important roles in various diseases, especially in cancers. We reviewed and summarized representative correlative studies and found that ALDH1A1 could induce cancers via the maintenance of cancer stem cell properties, modification of metabolism, promotion of DNA repair. ALDH1A1 expression is regulated by several epigenetic processes. ALDH1A1 also acted as a tumor suppressor in certain cancers. The detoxification of ALDH1A1 often causes chemotherapy failure. Currently, ALDH1A1-targeted therapy is widely used in cancer treatment, but the mechanism by which ALDH1A1 regulates cancer development is not fully understood. This review will provide insight into the status of ALDH1A1 research and new viewpoint for cancer therapy.

A Novel NUP98/RARG Gene Fusion in Pediatric Acute Myeloid Leukemia Resembling Acute Promyelocytic Leukemia

Here, we introduced the first case of acute myeloid leukemia (AML) with RARG-NUP98 in a pediatric patient. The young male presented with structural and functional abnormalities similar to hypergranular acute promyelocytic leukemia, but was resistant to all transretinoic acids and arsenic trioxide. Till date, only 12 adult AML cases involving RARG rearrangement have been reported. At present, there is no standardized or optimal treatment option for this AML subtype. Disease management may typically require a joint treatment strategy involving chemotherapy, immunotherapy, and support therapy. In this study, we report the clinical manifestations and experimental results of a 10-year-old male and review other cases of RARG gene rearrangement reported in the literature.

Rexinoids Modulate Effector T Cell Expression of Mucosal Homing Markers CCR9 and α4β7 Integrin and Direct Their Migration In Vitro

Altering T cell trafficking to mucosal regions can enhance immune responses towards pathogenic infections and cancers at these sites, leading to better outcomes. All-trans-retinoic acid (ATRA) promotes T cell migration to mucosal surfaces by inducing transcription of the mucosal-homing receptors CCR9 and α4β7 via binding to retinoic acid receptors (RARs), which heterodimerize with retinoid X receptors (RXRs) to function. However, the unstable nature and toxicity of ATRA limit its use as a widespread treatment modality for mucosal diseases. Therefore, identifying alternatives that could reduce or eliminate the use of ATRA are needed. Rexinoids are synthetically derived compounds structurally similar to ATRA. Originally named for their ability to bind RXRs, rexinoids can enhance RAR-mediated gene transcription. Furthermore, rexinoids are more stable than ATRA and possess an improved safety profile, making them attractive candidates for use in clinical settings. Here we show that select novel rexinoids act as ATRA mimics, as they cause increased CCR9 and α4β7 expression and enhanced migration to the CCR9 ligand, CCL25 in vitro, even in the absence of ATRA. Conversely, other rexinoids act synergistically with ATRA, as culturing cells with suboptimal doses of both compounds resulted in CCR9 expression and migration to CCL25. Overall, our findings show that rexinoids can be used independently or synergistically with ATRA to promote mucosal homing of T cells in vitro, and lends support for the prospective clinical use of these compounds in immunotherapeutic approaches for pathogenic infections or cancers at mucosal surfaces.

Current views on the genetic landscape and management of variant acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by the accumulation of promyelocytes in bone marrow. More than 95% of patients with this disease belong to typical APL, which express PML-RARA and are sensitive to differentiation induction therapy containing all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), and they exhibit an excellent clinical outcome. Compared to typical APL, variant APL showed quite different aspects, and how to recognize, diagnose, and treat variant APL remained still challenged at present. Herein, we drew the genetic landscape of variant APL according to recent progresses, then discussed how they contributed to generate APL, and further shared our clinical experiences about variant APL treatment. In practice, when APL phenotype was exhibited but PML-RARA and t(15;17) were negative, variant APL needed to be considered, and fusion gene screen as well as RNA-sequencing should be displayed for making the diagnosis as soon as possible. Strikingly, we found that besides of RARA rearrangements, RARB or RARG rearrangements also generated the phenotype of APL. In addition, some MLL rearrangements, NPM1 rearrangements or others could also drove variant APL in absence of RARA/RARB/RARG rearrangements. These results indicated that one great heterogeneity existed in the genetics of variant APL. Among them, only NPM1-RARA, NUMA-RARA, FIP1L1-RARA, IRF2BP2-RARA, and TFG-RARA have been demonstrated to be sensitive to ATRA, so combined chemotherapy rather than differentiation induction therapy was the standard care for variant APL and these patients would benefit from the quick switch between them. If ATRA-sensitive RARA rearrangement was identified, ATRA could be added back for re-induction of differentiation. Through this review, we hoped to provide one integrated view on the genetic landscape of variant APL and helped to remove the barriers for managing this type of disease.

The genomics of acute myeloid leukemia in children

Acute myeloid leukemia (AML) is a clinically, morphologically, and genetically heterogeneous disorder. Like many malignancies, the genomic landscape of pediatric AML has been mapped recently through sequencing of large cohorts of patients. Much has been learned about the biology of AML through studies of specific recurrent genetic lesions. Further, genetic lesions have been linked to specific clinical features, response to therapy, and outcome, leading to improvements in risk stratification. Lastly, targeted therapeutic approaches have been developed for the treatment of specific genetic lesions, some of which are already having a positive impact on outcomes. While the advances made based on the discoveries of sequencing studies are significant, much work is left. The biologic, clinical, and prognostic impact of a number of genetic lesions, including several seemingly unique to pediatric patients, remains undefined. While targeted approaches are being explored, for most, the efficacy and tolerability when incorporated into standard therapy is yet to be determined. Furthermore, the challenge of how to study small subpopulations with rare genetic lesions in an already rare disease will have to be considered. In all, while questions and challenges remain, precisely defining the genomic landscape of AML, holds great promise for ultimately leading to improved outcomes for affected patients.

Acute Myeloid Leukemia with NUP98-RARG Gene Fusion Similar to Acute Promyelocytic Leukemia: Case Report and Literature Review

Retinoic acid receptor gamma (RARG) belongs to the nuclear receptor superfamily and has 90% homology to RAR alpha (RARA) and RAR beta. The promyelocytic leukemia (PML)–RARA fusion gene has been implicated in acute promyelocytic leukemia (APL). RARG gene rearrangement has been identified in a rare subtype of acute myeloid leukemia (AML) that resembles APL. To date, only 10 cases of gene rearrangements involving RARG (nucleoporin [NUP]98–RARG, promyelocytic leukemia protein–RARG, cleavage and polyadenylation-specific factor 6–RARG, or nucleophosmin [NPM]1–RARG–NPM1) have been reported. These patients show characteristics similar to APL, including bone marrow morphology, coagulation abnormality, and immunophenotype; however, they are resistant to all-trans retinoic acid and arsenic trioxide treatment. Moreover, there is no optimal therapeutic regimen for this subtype of AML. In this study, we report the clinical presentation and experimental findings of a case of AML with NUP98–RARG gene fusion similar to APL and review other cases of RARG gene rearrangement described in the literature.

Alkaloid-based regimen is beneficial for acute myeloid leukemia resembling acute promyelocytic leukemia with NUP98/RARG fusion and RUNX1 mutation: A case report

RATIONALE

Some acute myeloid leukemia (AML) patients present with features mimicking the classical hypergranular subtype of acute promyelocytic leukemia (APL) but without the typical promyelocytic leukemia/retinoic acid receptor α (PML/RARα) rearrangement. Herein, we report an AML patient resembling APL but with nucleoporin 98/retinoid acid receptor gamma gene (NUP98/RARG) fusion transcript and Runt-related transcription factor 1 (RUNX1) mutation.

PATIENT CONCERNS

An 18-year-old male presented at the hospital with a diagnosis of AML.

DIAGNOSES

The patient was diagnosed with bone marrow examination. Bone marrow smear displayed 90.5% promyelocytes. Fluorescence in situ hybridization analysis failed to detect the PML/RARα fusion transcript or RARα amplification. While real-time polymerase chain reaction showed positivity for the NUP98/RARG fusion transcript. G-banding karyotype analysis showed a normal karyotype.

INTERVENTIONS

The patient showed resistance to arsenic trioxide and standard 3 + 7 chemotherapy, but eventually achieved complete remission through the Homoharringtonine, Cytarabine, and Aclarubicin chemotherapy.

OUTCOMES

These measures resulted in a rapid response and disease control.

LESSONS

Acute myeloid leukemia with the NUP98/RARG fusion gene and the RUNX1 mutation may be a special subtype of AML and may benefit from the alkaloid-based regimen.

Classic and Variants APLs, as Viewed from a Therapy Response

Most acute promyelocytic leukemia (APL) are caused by PML-RARA, a translocation-driven fusion oncoprotein discovered three decades ago. Over the years, several other types of rare X-RARA fusions have been described, while recently, oncogenic fusion proteins involving other retinoic acid receptors (RARB or RARG) have been associated to very rare cases of acute promyelocytic leukemia. PML-RARA driven pathogenesis and the molecular basis for therapy response have been the focus of many studies, which have now converged into an integrated physio-pathological model. The latter is well supported by clinical and molecular studies on patients, making APL one of the rare hematological disorder cured by targeted therapies. Here we review recent data on APL-like diseases not driven by the PML-RARA fusion and discuss these in view of current understanding of "classic" APL pathogenesis and therapy response.

WITER: a powerful method for estimation of cancer-driver genes using a weighted iterative regression modelling background mutation counts

Genomic identification of driver mutations and genes in cancer cells are critical for precision medicine. Due to difficulty in modelling distribution of background mutation counts, existing statistical methods are often underpowered to discriminate cancer-driver genes from passenger genes. Here we propose a novel statistical approach, weighted iterative zero-truncated negative-binomial regression (WITER, http://grass.cgs.hku.hk/limx/witer or KGGSeq,http://grass.cgs.hku.hk/limx/kggseq/), to detect cancer-driver genes showing an excess of somatic mutations. By fitting the distribution of background mutation counts properly, this approach works well even in small or moderate samples. Compared to alternative methods, it detected more significant and cancer-consensus genes in most tested cancers. Applying this approach, we estimated 229 driver genes in 26 different types of cancers. In silico validation confirmed 78% of predicted genes as likely known drivers and many other genes as very likely new drivers for corresponding cancers. The technical advances of WITER enable the detection of driver genes in TCGA datasets as small as 30 subjects and rescue of more genes missed by alternative tools in moderate or small samples.

RARG Gene Dysregulation in Acute Myeloid Leukemia

Retinoic acid receptor γ (RARγ) belongs to the nuclear receptor superfamily and shares 90% homology with retinoic acid receptor α (RARα) and retinoic acid receptor β (RARβ). RARA rearrangements are well-known to be involved in acute promyelocytic leukemia (APL), but RARG rearrangements can also resemble this kind of leukemia. In this review we trace the role of RARγ, considering both its physiological and oncogenic contribution; from 2011 to date, nine cases of patients harboring RARG fusions have been reported. These patients showed typical APL features, including the clinical presentation, coagulation abnormalities and morphological features of bone marrow (BM), but are not responsive to APL standard therapy. We stress the urgent need for a better comprehension of the critical role of RARG dysregulation in the leukemogenesis process, since optimum therapy strategies have not yet been established.

The Pleiotropic Role of Retinoic Acid/Retinoic Acid Receptors Signaling: From Vitamin A Metabolism to Gene Rearrangements in Acute Promyelocytic Leukemia

The family of retinoic acid receptors (RARs: RARα, -β, and -γ) has remarkable pleiotropy characteristics, since the retinoic acid/RARs pathway is involved in numerous biological processes not only during embryonic development, but also in the postnatal phase and during adulthood. In this review, we trace the roles of RA/RARs signaling in the immune system (where this pathway has both an immunosuppressive role or is involved in the inflammatory response), in hematopoiesis (enhancing hematopoietic stem cell self-renewal, progenitor cells differentiation or maintaining the bone marrow microenvironment homeostasis), and in bone remodeling (where this pathway seems to have controversial effects on bone formation or osteoclast activation). Moreover, in this review is shown the involvement of RAR genes in multiple chromosomal rearrangements generating different fusion genes in hematological neoplasms, with a particular focus on acute promyelocytic leukemia and its variant subtypes. The effect of different RARs fusion proteins on leukemic transformation, on patients’ outcome, and on therapy response is also discussed.

A case of acute myeloid leukemia with promyelocytic features characterized by expression of a novel RARG-CPSF6 fusion

Novel RARG-CPSF6 fusion in an AML case with promyelocytic features and no evidence of PML-RARA or X-RARA fusion. Gene fusions involving RARG can initiate AML with promyelocytic morphological features.

Targeting of the Eukaryotic Translation Initiation Factor 4A Against Breast Cancer Stemness

Breast cancer stem cells (BCSCs) are intrinsically chemoresistant and capable of self-renewal. Following chemotherapy, patients can develop minimal residual disease due to BCSCs which can repopulate into a relapsed tumor. Therefore, it is imperative to co-target BCSCs along with the bulk tumor cells to achieve therapeutic success and prevent recurrence. So, it is vital to identify actionable molecular targets against both BCSCs and bulk tumor cells. Previous findings from our lab and others have demonstrated that inhibition of the emerging drug target eIF4A with Rocaglamide A (RocA) was efficacious against triple-negative breast cancer cells (TNBC). RocA specifically targets the pool of eIF4A bound to the oncogenic mRNAs that requires its helicase activity for their translation. This property enables specific targeting of tumor cells. The efficacy of RocA against BCSCs is unknown. In this study, we postulated that eIF4A could be a vulnerable node in BCSCs. In order to test this, we generated a paclitaxel-resistant TNBC cell line which demonstrated an elevated level of eIF4A along with increased levels of cancer stemness markers (ALDH activity and CD44), pluripotency transcription factors (SOX2, OCT4, and NANOG) and drug transporters (ABCB1, ABCG2, and ABCC1). Furthermore, genetic ablation of eIF4A resulted in reduced expression of ALDH1A1, pluripotency transcription factors and drug transporters. This pointed out that eIF4A is likely associated with selected set of proteins that are critical to BCSCs, and hence targeting eIF4A may eliminate BCSCs. Therefore, we isolated BCSCs from two TNBC cell lines: MDA-Bone-Un and SUM-159PT. Following RocA treatment, the self-renewal ability of the BCSCs was significantly reduced as determined by the efficiency of the formation of primary and secondary mammospheres. This was accompanied by a reduction in the levels of NANOG, OCT4, and drug transporters. Exposure to RocA also induced cell death of the BCSCs as evaluated by DRAQ7 and cell viability assays. RocA treatment induced apoptosis with increased levels of cleaved caspase-3. Overall, we identified that RocA is effective in targeting BCSCs, and eIF4A is an actionable molecular target in both BCSCs and bulk tumor cells. Therefore, anti-eIF4A inhibitors could potentially be combined synergistically with existing chemo-, radio- and/or immunotherapies.

Using genomics to define pediatric blood cancers and inform practice

Over the past decade, there has been exponential growth in the number of genome sequencing studies performed across a spectrum of human diseases as sequencing technologies and analytic pipelines improve and costs decline. Pediatric hematologic malignancies have been no exception, with a multitude of next generation sequencing studies conducted on large cohorts of patients in recent years. These efforts have defined the mutational landscape of a number of leukemia subtypes and also identified germ-line genetic variants biologically and clinically relevant to pediatric leukemias. The findings have deepened our understanding of the biology of many childhood leukemias. Additionally, a number of recent discoveries may positively impact the care of pediatric leukemia patients through refinement of risk stratification, identification of targetable genetic lesions, and determination of risk for therapy-related toxicity. Although incredibly promising, many questions remain, including the biologic significance of identified genetic lesions and their clinical implications in the context of contemporary therapy. Importantly, the identification of germ-line mutations and variants with possible implications for members of the patient's family raises challenging ethical questions. Here, we review emerging genomic data germane to pediatric hematologic malignancies.

RARA and RARG gene downregulation associated with EZH2 mutation in acute promyelocytic-like morphology leukemia

Most acute promyelocytic leukemia (APL) patients express PML-RARA fusion; in rare cases, RARA is rearranged with partner genes other than PML. To date, only 2 patients presenting features similar to APL showing the RARG gene rearrangement have been described. We report an acute myeloid leukemia patient with morphology resembling APL without involvement of the RARA gene. Molecular and fluorescent in situ hybridization analyses excluded PML-RARA fusion and variant rearrangements involving RARA and RARG loci. Targeted next-generation sequencing showed EZH2- D185H mutation. As this mutation involved the region of interaction with DNA methyltransferases, we speculate an epigenetic alteration of genes involved in the APL-like phenotype. Expression analysis by droplet digital polymerase chain reaction revealed downregulation of the RARA and RARG genes. We hypothesize a novel mechanism of EZH2 function alteration, which may be responsible for an acute myeloid leukemia with APL-like phenotype featuring dysregulation of the RARA and RARG genes.

Recurrent RARB Translocations in Acute Promyelocytic Leukemia Lacking RARA Translocation

Translocations of retinoic acid receptor-α (RARA), typically PML-RARA, are a genetic hallmark of acute promyelocytic leukemia (APL). However, because a small fraction of APL lack translocations of RARA, we focused here on APL cases without RARA translocation to elucidate the molecular etiology of RARA-negative APL. We performed whole-genome sequencing, PCR, and FISH for five APL cases without RARA translocations. Four of five RARA-negative APL cases had translocations involving retinoic acid receptor-β (RARB) translocations, and TBL1XR1-RARB was identified as an in-frame fusion in three cases; one case had an RARB rearrangement detected by FISH, although the partner gene could not be identified. When transduced in cell lines, TBL1XR1-RARB homodimerized and diminished transcriptional activity for the retinoic acid receptor pathway in a dominant-negative manner. TBL1XR1-RARB enhanced the replating capacity of mouse bone marrow cells and inhibited myeloid maturation of human cord blood cells as PML-RARA did. However, the response of APL with RARB translocation to retinoids was attenuated compared with that of PML-RARA, an observation in line with the clinical resistance of RARB-positive APL to ATRA. Our results demonstrate that the majority of RARA-negative APL have RARB translocations, thereby forming a novel, distinct subgroup of APL. TBL1XR1-RARB as an oncogenic protein exerts effects similar to those of PML-RARA, underpinning the importance of retinoic acid pathway alterations in the pathogenesis of APL.Significance: These findings report a novel and distinct genetic subtype of acute promyelocytic leukemia (APL) by illustrating that the majority of APL without RARA translocations harbor RARB translocations. Cancer Res; 78(16); 4452-8. ©2018 AACR.

Aldehyde dehydrogenase 1A1 in stem cells and cancer

The human genome contains 19 putatively functional aldehyde dehydrogenase (ALDH) genes, which encode enzymes critical for detoxification of endogenous and exogenous aldehyde substrates through NAD(P)+-dependent oxidation. ALDH1 has three main isotypes, ALDH1A1, ALDH1A2, and ALDH1A3, and is a marker of normal tissue stem cells (SC) and cancer stem cells (CSC), where it is involved in self-renewal, differentiation and self-protection. Experiments with murine and human cells indicate that ALDH1 activity, predominantly attributed to isotype ALDH1A1, is tissue- and cancer-specific. High ALDH1 activity and ALDH1A1 overexpression are associated with poor cancer prognosis, though high ALDH1 and ALDH1A1 levels do not always correlate with highly malignant phenotypes and poor clinical outcome. In cancer therapy, ALDH1A1 provides a useful therapeutic CSC target in tissue types that normally do not express high levels of ALDH1A1, including breast, lung, esophagus, colon and stomach. Here we review the functions and mechanisms of ALDH1A1, the key ALDH isozyme linked to SC populations and an important contributor to CSC function in cancers, and we outline its potential in future anticancer strategies.

Bridge-Induced Translocation between NUP145 and TOP2 Yeast Genes Models the Genetic Fusion between the Human Orthologs Associated With Acute Myeloid Leukemia

In mammalian organisms liquid tumors such as acute myeloid leukemia (AML) are related to spontaneous chromosomal translocations ensuing in gene fusions. We previously developed a system named bridge-induced translocation (BIT) that allows linking together two different chromosomes exploiting the strong endogenous homologous recombination system of the yeast Saccharomyces cerevisiae. The BIT system generates a heterogeneous population of cells with different aneuploidies and severe aberrant phenotypes reminiscent of a cancerogenic transformation. In this work, thanks to a complex pop-out methodology of the marker used for the selection of translocants, we succeeded by BIT technology to precisely reproduce in yeast the peculiar chromosome translocation that has been associated with AML, characterized by the fusion between the human genes NUP98 and TOP2B. To shed light on the origin of the DNA fragility within NUP98, an extensive analysis of the curvature, bending, thermostability, and B-Z transition aptitude of the breakpoint region of NUP98 and of its yeast ortholog NUP145 has been performed. On this basis, a DNA cassette carrying homologous tails to the two genes was amplified by PCR and allowed the targeted fusion between NUP145 and TOP2, leading to reproduce the chimeric transcript in a diploid strain of S. cerevisiae. The resulting translocated yeast obtained through BIT appears characterized by abnormal spherical bodies of nearly 500 nm of diameter, absence of external membrane and defined cytoplasmic localization. Since Nup98 is a well-known regulator of the post-transcriptional modification of P53 target genes, and P53 mutations are occasionally reported in AML, this translocant yeast strain can be used as a model to test the constitutive expression of human P53. Although the abnormal phenotype of the translocant yeast was never rescued by its expression, an exogenous P53 was recognized to confer increased vitality to the translocants, in spite of its usual and well-documented toxicity to wild-type yeast strains. These results obtained in yeast could provide new grounds for the interpretation of past observations made in leukemic patients indicating a possible involvement of P53 in cell transformation toward AML.

Metazoan Nuclear Pores Provide a Scaffold for Poised Genes and Mediate Induced Enhancer-Promoter Contacts

Nuclear pore complex components (Nups) have been implicated in transcriptional regulation, yet what regulatory steps are controlled by metazoan Nups remains unclear. We identified the presence of multiple Nups at promoters, enhancers, and insulators in the Drosophila genome. In line with this binding, we uncovered a functional role for Nup98 in mediating enhancer-promoter looping at ecdysone-inducible genes. These genes were found to be stably associated with nuclear pores before and after activation. Although changing levels of Nup98 disrupted enhancer-promoter contacts, it did not affect ongoing transcription but instead compromised subsequent transcriptional activation or transcriptional memory. In support of the enhancer-looping role, we found Nup98 to gain and retain physical interactions with architectural proteins upon stimulation with ecdysone. Together, our data identify Nups as a class of architectural proteins for enhancers and supports a model in which animal genomes use the nuclear pore as an organizing scaffold for inducible poised genes.

Expression of Leukemia-Associated Nup98 Fusion Proteins Generates an Aberrant Nuclear Envelope Phenotype

Chromosomal translocations involving the nucleoporin NUP98 have been described in several hematopoietic malignancies, in particular acute myeloid leukemia (AML). In the resulting chimeric proteins, Nup98's N-terminal region is fused to the C-terminal region of about 30 different partners, including homeodomain (HD) transcription factors. While transcriptional targets of distinct Nup98 chimeras related to immortalization are relatively well described, little is known about other potential cellular effects of these fusion proteins. By comparing the sub-nuclear localization of a large number of Nup98 fusions with HD and non-HD partners throughout the cell cycle we found that while all Nup98 chimeras were nuclear during interphase, only Nup98-HD fusion proteins exhibited a characteristic speckled appearance. During mitosis, only Nup98-HD fusions were concentrated on chromosomes. Despite the difference in localization, all tested Nup98 chimera provoked morphological alterations in the nuclear envelope (NE), in particular affecting the nuclear lamina and the lamina-associated polypeptide 2α (LAP2α). Importantly, such aberrations were not only observed in transiently transfected HeLa cells but also in mouse bone marrow cells immortalized by Nup98 fusions and in cells derived from leukemia patients harboring Nup98 fusions. Our findings unravel Nup98 fusion-associated NE alterations that may contribute to leukemogenesis.

Effects of LG268 on Cell Proliferation and Apoptosis of NB4 Cells

AIMS

To investigate the effect of LG100268 (LG268) on cell proliferation and apoptosis in NB4 cells.

METHODS

NB4 cells were treated with LG268 for 24 h or 48 h. The effect of LG268 on cell proliferation was assessed by the CCK-8 assay and colony-forming assay. Apoptosis and cell cycle were evaluated by flow cytometry. The protein expression levels of Survivin, PARP, c-Myc, cyclin D1, ERK, p-ERK, p38 MAPK, and p- p38 MAPK were detected by western blot.

RESULTS

We found that LG268 inhibited the proliferation of NB4 cells in a dose-dependent manner. Flow cytometry analysis showed that LG268 accelerated apoptosis in NB4 cells in a time- dependent manner and that LG268 treatment led to cell cycle arrest at G0/G1 phase. Moreover, LG268 significantly decreased the protein levels of Survivin, c-Myc, and cyclinD1. Cleaved PARP was observed in the LG268 treatment group but not in the control group. In addition, LG268 increased the phosphorylation level of p38 MAPK and decreased the phosphorylation level of ERK.

CONCLUSIONS

LG268 inhibited cell proliferation and promoted cell apoptosis in NB4 cells.

Aldehyde dehydrogenases and cancer stem cells

Aldehyde dehydrogenases (ALDHs), as essential regulators of aldehyde metabolism in the human body, protect organisms from damage induced by active aldehydes. Given their roles in different cancer types, ALDHs have been evaluated as potential prognostic markers of cancer. ALDHs exhibit high activity in cancer stem cells (CSCs) and may serve as markers of CSCs. Moreover, studies indicated that ALDHs and their regulated retinoic acid, reactive oxygen species and reactive aldehydes metabolism were strongly related with various properties of CSCs. Besides, recent research evidences have demonstrated the transcriptional and post-translational regulation of ALDH expression and activation in CSCs. Thus, this review focuses on the function and regulation of ALDHs in CSCs, particularly ALDH1A1 and ALDH1A3.