Alessandra Boe

Constitutive activation of the ETS‐1‐miR‐222 circuitry in metastatic melanoma

MicroRNAs‐221 and ‐222 are highly upregulated in several solid tumors, including melanomas. We demonstrate that the proto‐oncogene ETS‐1, involved in the pathogenesis of cancers of different origin, is a transcriptional regulator of miR‐222 by direct binding to its promoter region. Differently from 293FT cells or early stage melanomas, where unphosphorylated ETS‐1 represses miR‐222 transcription, in metastatic melanoma the constitutively Thr‐38 phosphorylated fraction of ETS‐1 induces miR‐222. Despite its stepwise decreased expression along with melanoma progression, the oncogenic activity of ETS‐1 relies on its RAS/RAF/ERK‐dependent phosphorylation status more than on its total amount. To close the loop, we demonstrate ETS‐1 as a direct target of miR‐222, but not miR‐221, showing the novel option of their uncoupled functions. In addition, a spatial redistribution of ETS‐1 protein from the nucleus to the cytoplasm is also evidenced in advanced melanoma cells. Finally, in vivo studies confirmed the contribution of miR‐222 to the increased invasive potential obtained by ETS‐ silencing.

M4 and M5 acute myeloid leukaemias display a high sensitivity to Bortezomib-mediated apoptosis

The present study explored the sensitivity of leukaemic blasts derived from 30 acute myeloid leukaemia (AML) patients to Bortezomib. Bortezomib induced apoptosis of primary AML blasts: 18/30 AMLs were clearly sensitive to the proapoptotic effects of Bortezomib, while the remaining cases were moderately sensitive to this molecule. The addition of tumour necrosis factor‐related‐apoptosis‐inducing ligand, when used alone, did not induce apoptosis of AML blasts and further potentiated the cytotoxic effects of Bortezomib. The majority of AMLs sensitive to Bortezomib showed immunophenotypic features of the M4 and M5 French–American–British classification subtypes and displayed myelomonocytic features. All AMLs with mutated FLT3 were in the Bortezomib‐sensitive group. Biochemical studies showed that: (i) Bortezomib activated caspase‐8 and caspase‐3 and decreased cellular FLICE [Fas‐associated death domain (FADD)‐like interleukin‐1β‐converting enzyme]‐inhibitory protein (c‐FLIP) levels in AML blasts; (ii) high c‐FLIP levels in AML blasts were associated with low Bortezomib sensitivity. Finally, analysis of the effects of Bortezomib on leukaemic cells displaying high aldehyde dehydrogenase activity suggested that this drug induced in vitro killing of leukaemic stem cells. The findings of the present study, further support the development of Bortezomib as an anti‐leukaemic drug and provide simple tools to predict the sensitivity of AML cells to this drug.

MicroRNA-146a and AMD3100, two ways to control CXCR4 expression in acute myeloid leukemias

CXCR4 is a negative prognostic marker in acute myeloid leukemias (AMLs). Therefore, it is necessary to develop novel ways to inhibit CXCR4 expression in leukemia. AMD3100 is an inhibitor of CXCR4 currently used to mobilize cancer cells. CXCR4 is a target of microRNA (miR)-146a that may represent a new tool to inhibit CXCR4 expression. We then investigated CXCR4 regulation by miR-146a in primary AMLs and found an inverse correlation between miR-146a and CXCR4 protein expression levels in all AML subtypes. As the lowest miR-146a expression levels were observed in M5 AML, we analyzed the control of CXCR4 expression by miR-146a in normal and leukemic monocytic cells and showed that the regulatory miR-146a/CXCR4 pathway operates during monocytopoiesis, but is deregulated in AMLs. AMD3100 treatment and miR-146a overexpression were used to inhibit CXCR4 in leukemic cells. AMD3100 treatment induces the decrease of CXCR4 protein expression, associated with miR-146a increase, and increases sensitivity of leukemic blast cells to cytotoxic drugs, this effect being further enhanced by miR-146a overexpression. Altogether our data indicate that miR-146a and AMD3100, acting through different mechanism, downmodulate CXCR4 protein levels, impair leukemic cell proliferation and then may be used in combination with anti-leukemia drugs, for development of new therapeutic strategies.

Transcriptional fine-tuning of microRNA-223 levels directs lineage choice of human hematopoietic progenitors

MicroRNAs (miRNAs) regulate cell proliferation, differentiation and death during development and postnatal life. The expression level of mature miRNAs results from complex molecular mechanisms, including the transcriptional regulation of their genes. MiR-223 is a hematopoietic-specific miRNA participating in regulatory signaling networks involving lineage-specific transcription factors (TFs). However, the transcriptional mechanisms governing its expression levels and its functional role in lineage fate decision of human hematopoietic progenitors (HPCs) have not yet been clarified. We found that in CD34+HPCs undergoing unilineage differentiation/maturation, miR-223 is upregulated more than 10-fold during granulopoiesis, 3-fold during monocytopoiesis and maintained at low levels during erythropoiesis. Chromatin immunoprecipitation and promoter luciferase assays showed that the lineage-specific expression level of mature miR-223 is controlled by the coordinated binding of TFs to their DNA-responsive elements located in ‘distal’ and ‘proximal’ regulatory regions of the miR-223 gene, differentially regulating the transcription of two primary transcripts (pri-miRs). All this drives myeloid progenitor maturation into specific lineages. Accordingly, modulation of miR-223 activity in CD34+HPCs and myeloid cell lines significantly affects their differentiation/maturation into erythroid, granulocytic and monocytic/macrophagic lineages. MiR-223 overexpression increases granulopoiesis and impairs erythroid and monocytic/macrophagic differentiation. Its knockdown, meanwhile, impairs granulopoiesis and facilitates erythropoiesis and monocytic/macrophagic differentiation. Overall, our data reveal that transcriptional pathways acting on the differential regulation of two pri-miR transcripts results in the fine-tuning of a single mature miRNA expression level, which dictates the lineage fate decision of hematopoietic myeloid progenitors.

Salinomycin Potentiates the Cytotoxic Effects of TRAIL on Glioblastoma Cell Lines

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been reported to exhibit therapeutic activity in cancer. However, many tumors remain resistant to treatment with TRAIL. Therefore, small molecules that potentiate the cytotoxic effects of TRAIL could be used for combinatorial therapy. Here we found that the ionophore antibiotic salinomycin acts in synergism with TRAIL, enhancing TRAIL-induced apoptosis in glioma cells. Treatment with low doses of salinomycin in combination with TRAIL augmented the activation of caspase-3 and increased TRAIL-R2 cell surface expression. TRAIL-R2 upmodulation was required for mediating the stimulatory effect of salinomycin on TRAIL-mediated apoptosis, since it was abrogated by siRNA-mediated TRAIL-R2 knockdown. Salinomycin in synergism with TRAIL exerts a marked anti-tumor effect in nude mice xenografted with human glioblastoma cells. Our results suggest that the combination of TRAIL and salinomycin may be a useful tool to overcome TRAIL resistance in glioma cells and may represent a potential drug for treatment of these tumors. Importantly, salinomycin+TRAIL were able to induce cell death of well-defined glioblastoma stem-like lines.

Resistance of acute myeloid leukemic cells to the triterpenoid CDDO-Imidazolide is associated with low caspase-8 and FADD levels

The synthetic triterpenoid CDDO-Im-induced apoptosis of patient-derived AML blasts: 11/25 AMLs were highly sensitive, while the remaining were moderately sensitive to CDDO-Im. The addition of TRAIL significantly potentiated the cytotoxic effect of CDDO-Im, through mechanisms involving the induction of TRAIL-R1/TRAIL-R2 and downmodulation of TRAIL-R3/TRAIL-R4. Biochemical studies showed that CDDO-Im: induced a rapid and marked GSH depletion and antioxidants (GSH or NAC) completely inhibited its pro-apoptotic effect; sequentially activated caspase-8, -9 and -3; caspase inhibitors partially protected AML blasts from CDDO-Im-induced apoptosis; resistance of AML blasts to CDDO-Im-induced apoptosis correlated with low caspase-8/FADD and high Bcl-X(L) expression in leukemic blasts.

Cancer Stem Cell-Based Models of Colorectal Cancer Reveal Molecular Determinants of Therapy Resistance

Colorectal cancer (CRC) therapy mainly relies on the use of conventional chemotherapeutic drugs combined, in a subset of patients, with epidermal growth factor receptor [EGFR]‐targeting agents. Although CRC is considered a prototype of a cancer stem cell (CSC)‐driven tumor, the effects of both conventional and targeted therapies on the CSC compartment are largely unknown. We have optimized a protocol for colorectal CSC isolation that allowed us to obtain CSC‐enriched cultures from primary tumor specimens, with high efficiency. CSC isolation was followed by in vitro and in vivo validation, genetic characterization, and drug sensitivity analysis, thus generating panels of CSC lines with defined patterns of genetic mutations and therapy sensitivity. Colorectal CSC lines were polyclonal and maintained intratumor heterogeneity in terms of somatically acquired mutations and differentiation state. Such CSC‐enriched cultures were used to investigate the effects of both conventional and targeted therapies on the CSC compartment in vivo and to generate a proteomic picture of signaling pathways implicated in sensitivity/resistance to anti‐EGFR agents. We propose CSC lines as a sound preclinical framework to test the effects of therapies in vitro and in vivo and to identify novel determinants of therapy resistance.

Dynamic regulation of the cancer stem cell compartment by Cripto-1 in colorectal cancer

Stemness was recently depicted as a dynamic condition in normal and tumor cells. We found that the embryonic protein Cripto-1 (CR1) was expressed by normal stem cells at the bottom of colonic crypts and by cancer stem cells (CSCs) in colorectal tumor tissues. CR1-positive populations isolated from patient-derived tumor spheroids exhibited increased clonogenic capacity and expression of stem-cell-related genes. CR1 expression in tumor spheroids was variable over time, being subject to a complex regulation of the intracellular, surface and secreted protein, which was related to changes of the clonogenic capacity at the population level. CR1 silencing induced CSC growth arrest in vitro with a concomitant decrease of Src/Akt signaling, while in vivo it inhibited the growth of CSC-derived tumor xenografts and reduced CSC numbers. Importantly, CR1 silencing in established xenografts through an inducible expression system decreased CSC growth in both primary and metastatic tumors, indicating an essential role of CR1 in the regulation the CSC compartment. These results point to CR1 as a novel and dynamically regulated effector of stem cell functions in colorectal cancer.

Identity and ranking of colonic mesenchymal stromal cells.

Although ongoing clinical trials utilize systemic administration of bone‐marrow mesenchymal stromal cells (BM‐MSCs) in Crohns disease (CD), nothing is known about the presence and the function of mesenchymal stromal cells (MSCs) in the normal human bowel. MSCs are bone marrow (BM) multipotent cells supporting hematopoiesis with the potential to differentiate into multiple skeletal phenotypes. A recently identified new marker, CD146, allowing to prospectively isolate MSCs from BM, renders also possible their identification in different tissues. In order to elucidate the presence and functional role of MSCs in human bowel we analyzed normal adult colon sections and isolated MSCs from them. In colon (C) sections, resident MSCs form a net enveloping crypts in lamina propria, coinciding with structural myofibroblasts or interstitial stromal cells. Nine sub‐clonal CD146+ MSC lines were derived and characterized from colon biopsies, in addition to MSC lines from five other human tissues. In spite of a phenotype qualitative identity between the BM‐ and C‐MSC populations, they were discriminated and categorized. Similarities between C‐MSC and BM‐MSCs are represented by: Osteogenic differentiation, hematopoietic supporting activity, immune‐modulation, and surface‐antigen qualitative expression. The differences between these populations are: C‐MSCs mean intensity expression is lower for CD13, CD29, and CD49c surface‐antigens, proliferative rate faster, life‐span shorter, chondrogenic differentiation rare, and adipogenic differentiation completely blocked. Briefly, BM‐MSCs, deserve the rank of progenitors, whereas C‐MSCs belong to the restricted precursor hierarchy. The presence and functional role of MSCs in human colon provide a rationale for BM‐MSC replacement therapy in CD, where resident bowel MSCs might be exhausted or diverted from their physiological functions. J. Cell. Physiol. 227: 3291–3300, 2012.

Transcriptional silencing of the ETS1 oncogene contributes to human granulocytic differentiation

Background Ets-1 is a widely expressed transcription factor implicated in several biological processes including hematopoiesis, where it contributes to the regulation of cellular differentiation. The functions of Ets-1 are regulated by transcription factors as well as by phosphorylation events: phosphorylation of threonine 38 activates Ets-1, whereas phosphorylation of a cluster of serines within exon VII reduces DNA binding activity. This study focuses on the role of Ets-1 during granulocytic differentiation of NB4 promyelocytic and HL60 myeloblastic leukemia cell lines induced by all-trans retinoic acid. Design and Methods Ets-1 expression was measured by real-time reverse transcriptase polymerase chain reaction and western blotting. The role of Ets-1 during all-trans retinoic acid-induced differentiation was analyzed by using a transdominant negative molecule or small interfering RNA. Results NB4 and HL60 cell lines expressed high levels of p51 Ets-1, while the splice variant isoform that lacks exon VII (p42) was almost undetectable. The addition of all-trans retinoic acid reduced p51 Ets-1 levels and induced inhibitory phosphorylation of the remaining protein. Expression of Ets-1 was also reduced during dimethylsulfoxide-induced differentiation and during granulocytic differentiation of human CD34+ hematopoietic progenitor cells but not in NB4.R2 and HL60R cells resistant to all-trans retinoic acid. In line with these observations, transduction of a transdominant negative molecule of Ets-1, which inhibited DNA binding and transcriptional activity of the wild-type Ets-1, significantly increased chemical-induced differentiation. Consistently, Ets-1 knockdown by small interfering RNA increased the number of mature neutrophils upon addition of all-trans retinoic acid. Interestingly, p51 Ets-1 over-expression was frequently observed in CD34+ hematopoietic progenitor cells derived from patients with acute myeloid leukemia, as compared to its expression in normal CD34+ cells. Conclusions Our results indicated that a decreased expression of Ets-1 protein generalizes to granulocytic differentiation and may represent a crucial event for granulocytic maturation.