Allele-specific CRISPR-Cas9 editing of dominant epidermolysis bullosa simplex in human epidermal stem cells.

Epidermolysis bullosa simplex (EBS) is a rare skin disease inherited mostly in an autosomal dominant manner. Patients display a skin fragility that leads to blisters and erosions caused by minor mechanical trauma. EBS phenotypic and genotypic variants are caused by genetic defects in intracellular proteins whose function is to provide the attachment of basal keratinocytes to the basement membrane zone and most EBS cases display mutations in keratin 5 (KRT5) and keratin 14 (KRT14) genes. Besides palliative treatments, there is still no long-lasting effective cure to correct the mutant gene and abolish the dominant negative effect of the pathogenic protein over its wild-type counterpart. Here, we propose a molecular strategy for EBS01 patient's keratinocytes carrying a monoallelic c.475/495del21 mutation in KRT14 exon 1. Through the CRISPR-Cas9 system, we perform a specific cleavage only on the mutant allele and restore a normal cellular phenotype and a correct intermediate filament network, without affecting the epidermal stem cell, referred to as holoclones, which play a crucial role in epidermal regeneration.

Involvement of MAF/SPP1 axis in the development of bone marrow fibrosis in PMF patients.

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by hyperplastic megakaryopoiesis and myelofibrosis. We recently described the upregulation of MAF (v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog) in PMF CD34+ hematopoietic progenitor cells (HPCs) compared to healthy donor. Here we demonstrated that MAF is also upregulated in PMF compared with the essential thrombocytemia (ET) and polycytemia vera (PV) HPCs. MAF overexpression and knockdown experiments shed some light into the role of MAF in PMF pathogenesis, by demonstrating that MAF favors the megakaryocyte and monocyte/macrophage commitment of HPCs and leads to the increased expression of proinflammatory and profibrotic mediators. Among them, we focused our further studies on SPP1 and LGALS3. We assessed SPP1 and LGALS3 protein levels in 115 PMF, 47 ET and 24 PV patients plasma samples and we found that SPP1 plasma levels are significantly higher in PMF compared with ET and PV patients. Furthermore, in vitro assays demonstrated that SPP1 promotes fibroblasts and mesenchymal stromal cells proliferation and collagen production. Strikingly, clinical correlation analyses uncovered that higher SPP1 plasma levels in PMF patients correlate with a more severe fibrosis degree and a shorter overall survival. Collectively our data unveil that MAF overexpression contributes to PMF pathogenesis by driving the deranged production of the profibrotic mediator SPP1.

Integrated evaluation of PAM50 subtypes and immune modulation of pCR in HER2-positive breast cancer patients treated with chemotherapy and HER2-targeted agents in the CherLOB trial.

BACKGROUND: The aim of this work was to evaluate the impact of (and relative contribution of) tumor-related and immune-related diversity of HER2-positive disease on the response to neoadjuvant chemotherapy plus anti-HER2 agents. PATIENTS AND METHODS: The CherLOB phase II study randomized 121 HER2-positive breast cancer patients to neoadjuvant chemotherapy plus trastuzumab, lapatinib or both. Tumor samples from diagnostic core biopsy were centralized. Tumor-infiltrating lymphocytes (TILs) were evaluated on H&E slides. Intrinsic subtyping was carried out using the research-based 50-gene prediction analysis of a microarray (PAM50) subtype predictor. Immune-related gene signatures were also evaluated. RESULTS: Continuous Str-TILs and It-TILs were significantly associated with pCR [OR 1.03, 95% CI 1.02-1.05 (P < 0.001) and OR 1.09, 95% CI 1.04-1.15 (P < 0.001) for Str-TILs and It-TILs, respectively]. According to PAM50, the subtype distribution was as follows: HER2-enriched 26.7%, Luminal A 25.6%, Luminal B 16.3%, Basal-like 14% and Normal-like 17.4%. The highest rate of pCR was observed for the HER2-enriched subtype (50%), followed by Basal-like, Luminal B and Luminal A (χ(2) test, P = 0.026). Immune gene signatures significantly associated with pCR in univariate analyses were identified: most of them maintained a significant association with pCR in multivariate analyses corrected for PAM50 subtypes, whereas TILs did not. CONCLUSIONS: In this study, both tumor-related and immune-related features contribute to the modulation of pCR after neoadjuvant chemotherapy plus anti-HER2 agents. Immune signatures rather than TILs added significant prediction of pCR beyond PAM50 intrinsic subtypes.

Expression of µ-protocadherin is negatively regulated by the activation of the ß-catenin signaling pathway in normal and cancer colorectal enterocytes.

Mu-protocadherin (MUCDHL) is an adhesion molecule predominantly expressed by colorectal epithelial cells which is markedly downregulated upon malignant transformation. Notably, treatment of colorectal cancer (CRC) cells with mesalazine lead to increased expression of MUCDHL, and is associated with sequestration of ß-catenin on the plasma membrane and inhibition of its transcriptional activity. To better characterize the causal relationship between ß-catenin and MUCDHL expression, we performed various experiments in which CRC cell lines and normal colonic organoids were subjected to culture conditions inhibiting (FH535 treatment, transcription factor 7-like 2 siRNA inactivation, Wnt withdrawal) or stimulating (LiCl treatment) ß-catenin activity. We show here that expression of MUCDHL is negatively regulated by functional activation of the ß-catenin signaling pathway. This finding was observed in cell culture systems representing conditions of physiological stimulation and upon constitutive activation of ß-catenin in CRC. The ability of MUCDHL to sequester and inhibit ß-catenin appears to provide a positive feedback enforcing the effect of ß-catenin inhibitors rather than serving as the primary mechanism responsible for ß-catenin inhibition. Moreover, MUCDHL might have a role as biomarker in the development of CRC chemoprevention drugs endowed with ß-catenin inhibitory activity.

Amplicon-based next-generation sequencing: an effective approach for the molecular diagnosis of epidermolysis bullosa.

BACKGROUND: Epidermolysis bullosa (EB) is caused by mutations in genes that encode proteins belonging to the epidermal-dermal junction assembly. Due to the extreme clinical/genetic heterogeneity of the disease, the current methods available for diagnosing EB involve immunohistochemistry of biopsy samples and transmission electron microscopy followed by single-candidate gene Sanger sequencing (SS), which are labour-intensive and expensive clinical pathways. OBJECTIVES: According to the recently published recommendations for the diagnosis and treatment of EB, the assessment of the mutational landscape is now a fundamental step for developing a comprehensive diagnostic path. We aimed to develop a customized, cost-effective amplicon panel for the complete and accurate sequencing of all the pathogenic genes already identified in EB, and to minimize the processing time required for the execution of the test and to refine the analysis pipeline to achieve cost-effective results from the perspective of a routine laboratory set-up. Next-generation sequencing (NGS) via the parallel ultra-deep sequencing of many genes represents a proper method for reducing the processing time and costs of EB diagnostics. MATERIALS AND METHODS: We developed an EB disease-comprehensive AmpliSeq panel to accomplish the NGS on an Ion Torrent Personal Genome Machine platform. The panel was performed on 10 patients with known genetic diagnoses and was then employed in eight family trios with unknown molecular footprints. RESULTS: The panel was successful in finding the causative mutations in all 10 patients with known mutations, fully confirming the SS data and providing proof of concept of the sensitivity, specificity and accuracy of this procedure. In addition to being consistent with the clinical diagnosis, it was also effective in the trios, identifying all of the variants, including ones that the SS missed or de novo mutations. CONCLUSIONS: The NGS and AmpliSeq were shown to be an effective approach for the diagnosis of EB, resulting in a cost- and time-effective 72-h procedure.

Targeted cancer exome sequencing reveals recurrent mutations in myeloproliferative neoplasms.

With the intent of dissecting the molecular complexity of Philadelphia-negative myeloproliferative neoplasms (MPN), we designed a target enrichment panel to explore, using next-generation sequencing (NGS), the mutational status of an extensive list of 2000 cancer-associated genes and microRNAs. The genomic DNA of granulocytes and in vitro-expanded CD3+T-lymphocytes, as a germline control, was target-enriched and sequenced in a learning cohort of 20 MPN patients using Roche 454 technology. We identified 141 genuine somatic mutations, most of which were not previously described. To test the frequency of the identified variants, a larger validation cohort of 189 MPN patients was additionally screened for these mutations using Ion Torrent AmpliSeq NGS. Excluding the genes already described in MPN, for 8 genes (SCRIB, MIR662, BARD1, TCF12, FAT4, DAP3, POLG and NRAS), we demonstrated a mutation frequency between 3 and 8%. We also found that mutations at codon 12 of NRAS (NRASG12V and NRASG12D) were significantly associated, for primary myelofibrosis (PMF), with highest dynamic international prognostic scoring system (DIPSS)-plus score categories. This association was then confirmed in 66 additional PMF patients composing a final dataset of 168 PMF showing a NRAS mutation frequency of 4.7%, which was associated with a worse outcome, as defined by the DIPSS plus score.

Mutations and prognosis in primary myelofibrosis.

Patient outcome in primary myelofibrosis (PMF) is significantly influenced by karyotype. We studied 879 PMF patients to determine the individual and combinatorial prognostic relevance of somatic mutations. Analysis was performed in 483 European patients and the seminal observations were validated in 396 Mayo Clinic patients. Samples from the European cohort, collected at time of diagnosis, were analyzed for mutations in ASXL1, SRSF2, EZH2, TET2, DNMT3A, CBL, IDH1, IDH2, MPL and JAK2. Of these, ASXL1, SRSF2 and EZH2 mutations inter-independently predicted shortened survival. However, only ASXL1 mutations (HR: 2.02; P<0.001) remained significant in the context of the International Prognostic Scoring System (IPSS). These observations were validated in the Mayo Clinic cohort where mutation and survival analyses were performed from time of referral. ASXL1, SRSF2 and EZH2 mutations were independently associated with poor survival, but only ASXL1 mutations held their prognostic relevance (HR: 1.4; P=0.04) independent of the Dynamic IPSS (DIPSS)-plus model, which incorporates cytogenetic risk. In the European cohort, leukemia-free survival was negatively affected by IDH1/2, SRSF2 and ASXL1 mutations and in the Mayo cohort by IDH1 and SRSF2 mutations. Mutational profiling for ASXL1, EZH2, SRSF2 and IDH identifies PMF patients who are at risk for premature death or leukemic transformation.

Gene expression profiling in MDS and AML: potential and future avenues.

Today, the classification systems for myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) already incorporate cytogenetic and molecular genetic aberrations in an attempt to better reflect disease biology. However, in many MDS/AML patients no genetic aberrations have been identified yet, and even within some cytogenetically well-defined subclasses there is considerable clinical heterogeneity. Recent advances in genomics technologies such as gene expression profiling (GEP) provide powerful tools to further characterize myeloid malignancies at the molecular level, with the goal to refine the MDS/AML classification system, incorporating as yet unknown molecular genetic and epigenetic pathomechanisms, which are likely reflected by aberrant gene expression patterns. In this study, we provide a comprehensive review on how GEP has contributed to a refined molecular taxonomy of MDS and AML with regard to diagnosis, prediction of clinical outcome, discovery of novel subclasses and identification of novel therapeutic targets and novel drugs. As many challenges remain ahead, we discuss the pitfalls of this technology and its potential including future integrative studies with other genomics technologies, which will continue to improve our understanding of malignant transformation in myeloid malignancies and thereby contribute to individualized risk-adapted treatment strategies for MDS and AML patients.

Integrated analysis of microRNA and mRNA expression profiles in physiological myelopoiesis: role of hsa-mir-299-5p in CD34+ progenitor cells commitment.

Hematopoiesis entails a series of hierarchically organized events that proceed throughout cell specification and terminates with cell differentiation. Commitment needs the transcription factors' effort, which, in concert with microRNAs, drives cell fate and responds to promiscuous patterns of gene expression by turning on lineage-specific genes and repressing alternate lineage transcripts. We obtained microRNA profiles from human CD34+ hematopoietic progenitor cells and in vitro differentiated erythroblasts, megakaryoblasts, monoblasts and myeloblast precursors that we analyzed together with their gene expression profiles. The integrated analysis of microRNA-mRNA expression levels highlighted an inverse correlation between microRNAs specifically upregulated in one single-cell progeny and their putative target genes, which resulted in downregulation. Among the upregulated lineage-enriched microRNAs, hsa-miR-299-5p emerged as having a role in controlling CD34+ progenitor fate, grown in multilineage culture conditions. Gain- and loss-of-function experiments revealed that hsa-miR-299-5p participates in the regulation of hematopoietic progenitor fate, modulating megakaryocytic-granulocytic versus erythroid-monocytic differentiation.

The homeobox gene Arx is a novel positive regulator of embryonic myogenesis.

Skeletal muscle fibers form in overlapping, but distinct phases that depend on the generation of temporally different lineages of myogenic cells. During primary myogenesis (E10.5-E12.5 in the mouse), embryonic myoblasts fuse homotypically to generate primary fibers, whereas during later development (E14.5-E17.5), fetal myoblasts differentiate into secondary fibers. How these myogenic waves are regulated remains largely unknown. Studies have been hampered by the lack of markers which would distinguish embryonic from fetal myoblast populations. We show here that the homeobox gene Arx is strongly expressed in differentiating embryonic muscle, downstream of myogenic basic helix-loop-helix (bHLH) genes. Its expression progressively decreases during development. When overexpressed in the C2C12 myogenic cell line, Arx enhances differentiation. Accordingly, it stimulates the transcriptional activity from the Myogenin promoter and from multimerized E-boxes when co-expressed with MyoD and Mef2C in CH310T1/2. Furthermore, Arx co-immunoprecipitates with Mef2C, suggesting that it participates in the transcriptional regulatory network acting in embryonic muscle. Finally, embryonic myoblasts isolated from Arx-deficient embryos show a delayed differentiation in vivo together with an enhanced clonogenic capacity in vitro. We propose here that Arx acts as a novel positive regulator of embryonic myogenesis by synergizing with Mef2C and MyoD and by establishing an activating loop with Myogenin.

Transcriptional profiles in melanocytes from clinically unaffected skin distinguish the neoplastic growth pattern in patients with melanoma.

BACKGROUND: It is generally accepted that sunlight may contribute to the development of melanoma. OBJECTIVES: To analyse gene expression of melanocytes obtained from clinically unaffected skin of patients with melanoma and healthy controls before and after exposure to ultraviolet B radiation. METHODS: Using GeneChip array technology, the gene expression of melanocytes obtained from the two donor groups was profiled, in order to identify transcriptional differences affecting susceptibility to melanoma. RESULTS: The data collected did not show any difference between the expression profiles of melanocytes purified from normal donors and from patients with melanoma that was able to give a statistically significant class separation. However, by means of unsupervised clustering our data could be divided into two main classes. The first class included the transcriptome profiles of melanocytes obtained from skin samples of patients with a vertical growth phase (VGP) melanoma, while the second class included the transcriptome profiles of melanocytes obtained from skin samples of patients with a radial growth phase (RGP) melanoma. CONCLUSIONS: These data suggest that melanocytes in patients with VGP and RGP melanomas show significant differences in gene expression profiles, which allow us to classify patients with melanoma also from clinically unaffected skin.

Identification of a molecular signature for leukemic promyelocytes and their normal counterparts: Focus on DNA repair genes.

Acute promyelocytic leukemia (APL) is a clonal expansion of hematopoietic precursors blocked at the promyelocytic stage. Gene expression profiles of APL cells obtained from 16 patients were compared to eight samples of CD34+-derived normal promyelocytes. Malignant promyelocytes showed widespread changes in transcription in comparison to their normal counterpart and 1020 differentially expressed genes were identified. Discriminating genes include transcriptional regulators (FOS, JUN and HOX genes) and genes involved in cell cycle and DNA repair. The strong upregulation in APL of some transcripts (FLT3, CD33, CD44 and HGF) was also confirmed at protein level. Interestingly, a trend toward a transcriptional repression of genes involved in different DNA repair pathways was found in APL and confirmed by real-time polymerase chain reactor (PCR) in a new set of nine APLs. Our results suggest that both inefficient base excision repair and recombinational repair might play a role in APLs development. To investigate the expression pathways underlying the development of APL occurring as a second malignancy (sAPL), we included in our study eight cases of sAPL. Although both secondary and de novo APL were characterized by a strong homogeneity in expression profiling, we identified a small set of differentially expressed genes that discriminate sAPL from de novo cases.

Identification of a molecular signature predictive of sensitivity to differentiation induction in acute myeloid leukemia.

Acute myeloid leukemia (AML) blasts are immature committed myeloid cells unable to spontaneously undergo terminal maturation, and characterized by heterogeneous sensitivity to natural differentiation inducers. Here, we show a molecular signature predicting the resistance or sensitivity of six myeloid cell lines to differentiation induced in vitro with retinoic acid or vitamin D. The identified signature was further validated by TaqMan assay for the prediction of response to an in vitro differentiation assay performed on 28 freshly isolated AML blast populations. The TaqMan assay successfully predicts the in vitro resistance or responsiveness of AML blasts to differentiation inducers. Furthermore, performing a meta-analysis of publicly available microarray data sets, we also show the accuracy of our prediction on known phenotypes and suggest that our signature could become useful for the identification of patients eligible for new therapeutic strategies.

Virally mediated MafB transduction induces the monocyte commitment of human CD34+ hematopoietic stem/progenitor cells.

Upregulation of specific transcription factors is a generally accepted mechanism to explain the commitment of hematopoietic stem cells along precise maturation lineages. Based on this premise, transduction of primary hematopoietic stem/progenitor cells with viral vectors containing the investigated transcription factors appears as a suitable experimental model to identify such regulators. Although MafB transcription factor is believed to play a role in the regulation of monocytic commitment, no demonstration is, to date, available supporting this function in normal human hematopoiesis. To address this issue, we retrovirally transduced cord blood CD34+ hematopoietic progenitors with a MafB cDNA. Immunophenotypic and morphological analysis of transduced cells demonstrated the induction of a remarkable monomacrophage differentiation. Microarray analysis confirmed these findings and disclosed the upregulation of macrophage-related transcription factors belonging to the AP-1, MAF, PPAR and MiT families. Altogether our data allow to conclude that MafB is a key regulator of human monocytopoiesis.

Correlation between differentiation plasticity and mRNA expression profiling of CD34+-derived CD14- and CD14+ human normal myeloid precursors.

In spite of their apparently restricted differentiation potentiality, hematopoietic precursors are plastic cells able to trans-differentiate from a maturation lineage to another. To better characterize this differentiation plasticity, we purified CD14- and CD14+ myeloid precursors generated by 'in vitro' culture of human CD34+ hematopoietic progenitors. Morphological analysis of the investigated cell populations indicated that, as expected, they consisted of granulocyte and monocyte precursors, respectively. Treatment with differentiation inducers revealed that CD14- cells were bipotent granulo-monocyte precursors, while CD14+ cells appeared univocally committed to a terminal macrophage maturation. Flow cytometry analysis demonstrated that the conversion of granulocyte precursors to the mono-macrophage maturation lineage occurs through a differentiation transition in which the granulocyte-related myeloperoxidase enzyme and the monocyte-specific CD14 antigen are co-expressed. Expression profiling evidenced that the observed trans-differentiation process was accompanied by a remarkable upregulation of the monocyte-related MafB transcription factor.

Gene expression profile of Vitamin D3 treated HL60 cells shows an incomplete molecular phenotypic conversion to monocytes.

By high density oligonucleotide microarrays we have studied the expression profile of proliferating and VD treated HL60 cells and the molecular phenotype of VD monocytes and that of CD14+ peripheral monocytes has been compared. The results indicate that important changes in functional categories of the differentially expressed genes underlie the differentiation transition from myeloblasts to monocytes. This differential gene expression pattern leads to an increased expression of mRNAs involved in surface and external activities since many of the VD induced genes belong to ligand binding, receptors, cell surface antigens, defense/immunity and adhesion molecules functional categories. The results also indicate that the molecular phenotypes of monocytes and VD induced cells diverge for a small but significant set of defense related genes. Particularly, class II MHC genes are not expressed in these cells. Furthermore, the high levels of expression of these genes induced by serum treatment of monocytes are decreased by VD.

Suppression of bile acid synthesis, but not of hepatic cholesterol 7alpha-hydroxylase expression, by obstructive cholestasis in humans.

Regulation of bile acid synthesis, a key determinant of cholesterol homeostasis, is still incompletely understood. To elucidate the feedback control exerted on bile acid biosynthesis in humans with obstructive cholestasis, 16 patients with bile duct obstruction were studied. In vivo 7alpha-hydroxylation, reflecting bile acid synthesis, was assayed in 13 of them by tritium release analysis. Serum 27-hydroxycholesterol was determined by gas chromatography-mass spectrometry. In a subgroup, hepatic cholesterol 7alpha-hydroxylase mRNA was assayed by real-time polymerase chain reaction (PCR), enzyme activity was determined by isotope incorporation, and microsomal cholesterol content was assayed by gas chromatography-mass spectrometry. Age-matched control subjects were studied in parallel. Hydroxylation rates were lower in cholestatic patients (108 +/- 33 mg of cholesterol per day, mean +/- SEM; controls: 297 +/- 40 mg/d; P <.01). The reduction was proportional to the severity of cholestasis, and synthetic rates were normalized in 4 subjects restudied after resolution of biliary obstruction. Consistent findings were obtained by analysis of serum 7alpha-hydroxycholesterol levels. On the other hand, hepatic cholesterol 7alpha-hydroxylase mRNA, microsomal enzyme activity, and cholesterol content tended to be increased in cholestasis. Finally, serum 27-hydroxycholesterol levels were slightly reduced in cholestatic subjects and were not related with the severity of the disease. Suppression of in vivo bile acid synthesis with no corresponding reduction in tissue 7alpha-hydroxylase expression and activity is consistent with nontranscriptional, posttranslational levels of regulation; these may play a role in the feedback control of bile acid synthesis in particular conditions. Alteration of the alternate biosynthetic pathway seems unlikely according to the present data.

A functionally active RARalpha nuclear receptor is expressed in retinoic acid non responsive early myeloblastic cell lines.

Although all-trans retinoic acid (ATRA) can restore the differentiation capacity of leukemic promyelocytes, early leukemic myeloblasts are conversely not responsive to ATRA induced granulocytic differentiation. To assess whether this resistance to ATRA is related to an impaired function of the Retinoic Acid Receptor alpha (RARalpha), we performed an analysis of RARalpha expression and transactivation activity, in several myeloid leukemic cell lines, representative of different types of spontaneous acute myeloid leukemias. Our results indicate that a functionally active RARalpha nuclear receptor is expressed in all the analyzed cell lines, regardless of their differentiation capacity following exposure to ATRA. The observation that ATRA treatment is able to induce the expression of retinoic acid target genes, in late- but not in early-myeloblastic leukemic cells, raises the possibility that the differentiation block of these cells is achieved through a chromatin mediated mechanism. Acetylation is apparently not involved in this process, since the histone deacetylase inhibitor trichostatin A, is not able to restore the differentiation capacity of early leukemic myeloblasts. Further investigation is needed to clarify whether myeloid transcription factors, distinct to RARalpha, play a role in the resistance of these cells to ATRA treatment.

Regulation of ob gene expression: evidence for epinephrine-induced suppression in human obesity.

Leptin acts as satiety factor and increases energy expenditure. Studies conducted on animals and in vitro on adipocytes culture have shown that infusion of catecholamines leads to a significant reduction of ob gene expression; it appears of interest to evaluate the in vivo effects of adrenergic activation on the expression of the ob gene in humans. We studied ob gene expression in adipose tissue samples from 13 obese subjects before and after epinephrine (25 ng/min x kg ideal body weight for 3 h) and 6 obese patients during saline infusion. Hormonal infusion led to a significant increase in epinephrine plasma levels (from 27 +/- 4 to 339 +/- 75 pg/mL; P < 0.001), plasma free fatty acids (from 0.73 +/- 0.05 to 0.98 +/- 0.07; P < 0.05), heart rate (13.5 +/- 3.1 beats/min; F = 2.9; P < 0.03), and systolic blood pressure (F = 2.7; P < 0.05), whereas diastolic blood pressure did not show significant variation. Plasma leptin levels decreased by the end of the infusion (from 63 +/- 13 to 49 +/- 11 ng/mL; P < 0.05), and ob messenger ribonucleic acid levels were significantly reduced (decrease amounting to 47 +/- 5% of basal values). Our study shows that adrenergic activation contributes to regulate ob messenger ribonucleic acid levels in humans. The interaction between epinephrine and leptin may operate during metabolic and psychological stress to regulate energy expenditure and food intake.

Induction of a functional vitamin D receptor in all-trans-retinoic acid-induced monocytic differentiation of M2-type leukemic blast cells.

Different types of acute myeloid leukemia blast cells were induced to differentiate in vitro with all-trans-retinoic acid (ATRA) and vitamin D3 (VD). M0/M1 leukemic cells are not sensitive to differentiating agents, whereas M3 leukemic cells are induced to undergo granulocytic differentiation after ATRA treatment but are not sensitive to VD. M2 leukemic blast cells behave differently because they undergo monocytic differentiation with both the differentiation inducers. To gain some insight into the maturation of M2-type leukemic cells, we studied the molecular mechanisms underlying monocytic differentiation induced by ATRA and VD in spontaneous M2 blast cells as well as in Kasumi-1 cells (an acute myeloid leukemia M2-type cell line). Our results indicate that ATRA as well as VD efficiently increases the nuclear abundance of VD receptor (VDR) and promotes monocytic differentiation. VDR is functionally active in ATRA-treated Kasumi-1 cells because it efficiently heterodimerizes with retinoid X receptor, binds to a DR3-type vitamin D-responsive element, and activates the transcription of a vitamin D-responsive element-regulated reporter gene. Consistent with these findings, VD-responsive genes are induced by ATRA treatment of Kasumi-1 cells, suggesting that the genetic program underlying monocytic differentiation is activated. The molecular mechanism by which ATRA increases the nuclear abundance of a functional VDR is still unknown, but our data clearly indicate that the M2 leukemic cell context is only permissive of monocytic differentiation.