Molecular signature of retinoic acid treatment in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia characterized by a block of differentiation at the promyelocytic stage. APL patients respond to pharmacological concentrations of all-trans retinoic acid ( RA) and disease remission correlates with terminal differentiation of leukemic blasts. The PML/RAR oncogenic transcription factor is responsible for both the pathogenesis of APL and for its sensitivity to RA. In order to identify physiological targets of RA therapy, we analysed gene expression profiles of RA-treated APL blasts and found 1056 common target genes. Comparing these results to those obtained in RA-treated U937 cell lines revealed that transcriptional response to RA is largely dependent on the expression of PML/RAR. Several genes involved in the control of differentiation and stem cell renewal are early targets of RA regulation, and may be important effectors of RA response. Modulation of chromatin modifying genes was also observed, suggesting that specific structural changes in local chromatin domains may be required to promote RA-mediated differentiation. Computational analysis of upstream genomic regions in RA target genes revealed nonrandom distribution of transcription factor binding sites, indicating that specific transcriptional regulatory complexes may be involved in determining RA response

Single-cell imaging and transcriptomic analyses of firm adhesion between patient-derived cancer and endothelial cells under shear stress

Data availability: All data underlying the results are available as part of the article and no additional source data are required.Reporting guidelines: Open Science Framework: ARRIVE checklist for ‘Single-cell imaging and transcriptomic analyses of firm adhesion between patient-derived cancer and endothelial cells under shear stress’ https://doi.org/10.17605/OSF.IO/FAM5Z28. Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).Copyright: © 2023 Cerutti C et al. Adhesion between cancer cells and endothelial cells, lining the blood vessels, is a key event during tumour progression and metastasis formation. However, the analysis of its underlying cellular and molecular mechanisms is largely limited by the intrinsic difficulties to study the interactions between circulating cancer cells and endothelial cells in vivo, and in vitro under conditions that mimic the in vivo blood flow. Here, we developed a method to study cell:cell firm adhesion under shear-stress conditions coupled to high-content live-cell imaging, and single-cell RNAseq analysis. As the model system, we used cancer cells freshly isolated from patient-derived xenografts (PDXs) and human primary endothelial cells. Breast cancer is the most common cancer in women worldwide and the leading cause of cancer-related deaths among women. Therefore, we set up protocols for breast cancer PDX tumour dissociation, isolation and purification to obtain freshly isolated PDX-derived human cancer single cell suspension. We then implemented an in vitro assay to study cancer to endothelial cells firm adhesion under shear-stress, using an all–human microfluidic model coupled to time-lapse and live-cell imaging. Finally, we developed a method to successfully retrieve, separate and enrich alive endothelial and cancer cells from the flow-based firm adhesion assay. Most notably, we used retrieved cells for single-cell RNAseq analysis and showed that samples quality, number of cells and transcripts per cell were consistent and optimal for downstream discovery analyses. In conclusion, we developed a workflow method that can provide insights into the mechanisms of cancer adhesion to endothelial cells, and identify new targets for personalized treatments development for the clinic to prevent and/or treat breast cancer metastasis formation.European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 800924 (International Cancer Research Fellowships – 2 [iCARE-2]) to CC, AIRC Grant AIRC-IG-2017-20162, Ricerca Corrente (Italian Ministry of Health), AIRCIG 2022 - ID. 27716 and PRIN17 n PRIN201719PPELI_01 to PGP

PO-299 In vivo shRNA screening to identify quiescence-related genes required for AML growth

Introduction AML is hierarchically organised with at the apex Leukaemia Stem Cells (LSCs), a rare cell population able to initiate and sustain the tumour growth. LSCs share many functional properties with normal Hematopoietic Stem Cells (HSCs) including self-renewal capacity and quiescence. Quiescent LSCs can survive to radiation and chemotherapy acting as a reservoir for leukaemia relapse, the major cause of death for AML patients. Therefore, LSCs quiescence is critical for leukaemia maintenance and few evidences suggest that quiescence regulation in pre-leukemic phase plays a pivotal role for leukemogenic process as well. Material and methods We analysed the transcriptional deregulations induced by the expression of different leukemic oncogenes in HSCs and we examined the contribution of representative quiescence related genes in AML growth by in vivo RNA interference screening. Results and discussions The transcriptional profile of oncogene-expressing HSCs is enriched in a quiescent stem cell gene signature, compared to normal HSCs. Therefore, we hypothesised that enhancement of the quiescent phenotype in HSCs could be a shared mechanism for leukaemia development and maintenance. The in vivo shRNA screening allowed the identification of genes whose silencing in AML blasts was sufficient to significantly decrease in vitro self-renewal and delay leukaemia growth in vivo . Conclusion We identified quiescence-related genes, commonly deregulated by leukemic oncogenes at pre-leukemic level, which may offer new therapeutic targets in a wide group of AML patients

PO-272 Leukemia-associated NPM mutations promote quiescence of hematopoietic stem cells and prevent their functional exhaustion upon oncogene-induced hyper-proliferation

Introduction Acute Myeloid Leukaemia (AML) is a heterogeneous and multi-step disease. The serial acquisition of mutations and the environmental pressure allow one or more clones to expand and contribute to the disease. In particular, 6% of AMLs are characterised by an initial mutation in the DNMT3a gene, followed by mutations in NPM (NPMc) and FLT3 loci (FLT3-ITD). We previously shown that NPMc can drive AML development in mouse model and highly cooperates with FLT3-ITD. Moreover, it has been reported that normal Hematopoietic Stem Cells (HSCs) of elderly people may bear some somatic early AML mutations and this correlate with an increased risk of hematologic diseases suggesting that mutations can shape pre-leukemic HSCs to be more prone to the acquisition of further mutations giving rise to Leukaemia Initiating Cells (LIC). While the ability of FLT3-ITD to drive HSC compartment exhaustion has been already shown, the impact of NPMc on HSCs remains unclear. Material and methods Taking advantage of the extended pre-leukemic phase of our inducible NPMc mouse model, we elucidate the role of NPMc in HSCs by functional and transcriptional analysis. Moreover, to investigate the basis of NPMc and FLT3-ITD cooperation we generate mice carrying both the conditional NPMc transgene and the FLT3-ITD constitutive mutation and, before AML onset, we analyse double mutant HSCs behaviour. Results and discussions We have found that NPMc expression lead to the expansion of the HSC compartment through the enforcement of a stem-cell transcriptional program that increases self-renewal by promoting quiescence. We then investigated how the NPMc dependent quiescence program is linked to its oncogenic function. The expression of NPMc +in the FLT3-ITD background prevents the HSCs exhaustion imposed by FLT3-ITD and restores their repopulating capacity. Accordingly, gene expression analysis revealed a strong dominance of NPMc +with the restoration of the same transcriptional program observed in the NPMc HSCs. These data strongly suggest that NPMc imposes a HSC-specific program that, in combination with the oncogenic signal provided by FLT3-ITD, allows the selection of the LIC and the occurrence of AML. Conclusion In conclusion, enforcement of quiescence might be a critical function for the maintenance of the transformed clone during both the pre-leukemic and the leukemic phase. As consequence, interfering with quiescence key determinants may eradicate the reservoir of quiescent cells responsible for disease recurrence

Acute MUS81 depletion leads to replication fork slowing and a constitutive DNA damage response

The MUS81 protein belongs to a conserved family of DNA structure-specific nucleases that play important roles in DNA replication and repair. Inactivation of the Mus81 gene in mice has no major deleterious consequences for embryonic development, although cancer susceptibility has been reported. We have investigated the role of MUS81 in human cells by acutely depleting the protein using shRNAs. We found that MUS81 depletion from human fibroblasts leads to accumulation of ssDNA and a constitutive DNA damage response that ultimately activates cellular senescence. Moreover, we show that MUS81 is required for efficient replication fork progression during an unperturbed S-phase, and for recovery of productive replication following replication stalling. These results demonstrate essential roles for the MUS81 nuclease in maintenance of replication fork integrity

Long non‐coding RNA TINCR suppresses metastatic melanoma dissemination by preventing ATF4 translation

Transition from proliferative-to-invasive phenotypes promotes metastasis and therapy resistance in melanoma. Reversion of the invasive phenotype, however, is challenged by the poor understanding of mechanisms underlying its maintenance. Here, we report that the lncRNA TINCR is down-regulated in metastatic melanoma and its silencing increases the expression levels of invasive markers, in vitro migration, in vivo tumor growth, and resistance to BRAF and MEK inhibitors. The critical mediator is ATF4, a central player of the integrated stress response (ISR), which is activated in TINCR-depleted cells in the absence of starvation and eIF2α phosphorylation. TINCR depletion increases global protein synthesis and induces translational reprogramming, leading to increased translation of mRNAs encoding ATF4 and other ISR proteins. Strikingly, re-expression of TINCR in metastatic melanoma suppresses the invasive phenotype, reduces numbers of tumor-initiating cells and metastasis formation, and increases drug sensitivity. Mechanistically, TINCR interacts with mRNAs associated with the invasive phenotype, including ATF4, preventing their binding to ribosomes. Thus, TINCR is a suppressor of the melanoma invasive phenotype, which functions in nutrient-rich conditions by repressing translation of selected ISR RNAs

Translocation detection in lymphoma diagnosis by split-signal FISH: a standardised approach

Lymphomas originating from the lymphatic system comprise about 30 entities classified according to the World Health Organization (WHO). The histopathological diagnosis is generally considered difficult and prone to mistakes. Since non-random chromosomal translocations are specifically involved in different lymphoma entities, their detection will be increasingly important. Hence, a split-signal fluorescence in situ hybridisation (FISH) procedure would be helpful in discriminating the most difficult classifications. The Euro-FISH programme, a concerted action of nine European laboratories, has validated a robust, standardised protocol to improve the diagnostic approach on lymphoma entities. Therefore, 16 fluorescent probes and 10 WHO entities, supplemented with reactive cases, were selected. The results of the Euro-FISH programme show that all probes were correctly cytogenetically located, that the standardised protocol is robust, resulting in reliable results in approximately 90% of cases, and that the procedure could be implemented in every laboratory, bringing the relatively easy interpretation of split-signal probes within the reach of many pathology laboratories