Wnt signaling in leukemias and myeloma: T-cell factors are in control

PRUNE1 (located on chromosome 1q21.3) promotes multiple myeloma with 1q21 Gain by enhancing the links between purine and mitochondrion

Patients with multiple myeloma (MM) with chromosome 1q21 Gain (1q21+) are clinically and biologically heterogeneous. 1q21+ in the real world actually reflects the prognosis for gain/amplification of the CKS1B gene. In this study, we found that the copy number of prune exopolyphosphatase 1 (PRUNE1), located on chromosome 1q21.3, could further stratify the prognosis of MM patients with 1q21+. Using selected reaction monitoring/multiple reaction monitoring (SRM/MRM) analysis, liquid chromatography-tandem mass spectrometry (LC-MS/MS), transmission electron microscopy (TEM), confocal fluorescence microscopy, calculation of adenosine triphosphate (ATP), intracellular reactive oxygen species (ROS) and mitochondrial oxygen consumption rates (OCRs), we demonstrated for the first time that PRUNE1 promotes the proliferation and invasion of MM cells by stimulating purine metabolism, purine synthesis enzymes and mitochondrial functions, enhancing links between purinosomes and mitochondria. SOX11 was identified as a transcription factor for PRUNE1. Through integrated analysis of the transcriptome and proteome, CD73 was determined to be the downstream target of PRUNE1. Furthermore, it has been determined that dipyridamole can effectively suppress the proliferation of MM cells with high-expression levels of PRUNE1 in vitro and in vivo. These findings provide insights into disease-causing mechanisms and new therapeutic targets for MM patients with 1q21+.

Splicing factor arginine/serine-rich 8 promotes multiple myeloma malignancy and bone lesion through alternative splicing of CACYBP and exosome-based cellular communication

BACKGROUND

Multiple myeloma (MM) is a distinctive malignancy of plasma cell within the bone marrow (BM), of which alternative splicing factors play vital roles in the progression. Splicing factor arginine/serine-rich 8 (SFRS8) is the exclusive factor associated with MM prognosis, however its role in MM remains undefined.

METHODS

The analyses of 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide (MTT) assay, immunohistochemistry, flow cytometry and xenograft model were performed to examine cell proliferation, cell cycle and apoptosis in SFRS8 overexpression or knockdown MM cells in vitro and in vivo. The SFRS8-regulated alternative splicing events were identified by RNA immunoprecipitation sequencing (RIP-seq) and validated by RIP-qPCR and Co-IP methods. Exosomes were extracted from the supernatant of myeloma cells by ultracentrifugation. Bone lesion was evaluated by TRAP staining in vitro and SCID/NOD-TIBIA mouse model. A neon electroporation system was utilised to deliver siRNA through exosomes. The effect of siRNA-loaded exosomes in vivo was evaluated by using a patient-derived tumor xenograft (PDX) model and SCID/NOD-TIBIA mouse model.

RESULTS

SFRS8 was significantly upregulated in MM samples and positively associated with poor overall survival (OS) in MM patients. SFRS8 promoted MM cell proliferation in vitro and in vivo. Furthermore, calcyclin binding protein (CACYBP) was identified as the downstream target of SFRS8. Particularly, SFRS8 could reduce CACYBP isoform1 (NM_014412.3) and increase CACYBP isoform2 (NM_001007214.1) by mediating the alternative splicing of CACYBP, thereby altering the ubiquitination degradation of β-catenin to promote MM progression. In addition, SFRS8 promoted osteoclast differentiation through exosomes in vitro and in vivo. More importantly, exosomal siRNA targeting CACYBP isoform2 inhibited tumour growth in PDX and SCID/NOD-TIBIA mouse models.

CONCLUSION

Our findings demonstrate that targeting the SFRS8/CACYBP/β-catenin axis may be a promising strategy for MM diagnosis and treatment.

Exogenous Expression of WNT7A in Leukemia-Derived Cell Lines Induces Resistance to Chemotherapeutic Agents

BACKGROUND

Dysregulations of the WNT pathway are implicated in the malignant transformation of different types of neoplasia. WNT7A is expressed in normal peripheral lymphocytes, but is decreased in the tumoral counterpart. Furthermore, the treatment of leukemic cells with recombinant WNT7A decreases proliferation, suggesting its possible use as a therapeutic biomolecule. This study aimed to evaluate the concomitant action of WNT7A and different chemotherapeutic agents over proliferation and cell death of leukemia/ lymphoma derived cell lines.

METHODS

Ectopic expression of WNT7A was induced in CEM and BJAB cell lines by using a lentiviral system. RNA expression was analyzed by microarrays and qPCR, and protein expression was determined by Western Blot. Cell proliferation was measured by cell counting, metabolic activity by WST-1 assay, cell death and DNA content by flow cytometry.

RESULTS

WNT7A ectopic expression was shown to decrease cell proliferation, but the apoptosis rate of leukemic cells was not altered. Moreover, these cells acquired resistance to doxorubicin, vincristine and MG-132. Cell cycle analysis reveals a decrease in G1 and an increase in S and G2 phases with a further upregulation of senescence- associated genes. Microarray analysis reveals that most gene expression changes were related to cancer and metabolic associated pathways. All those changes appear to be independent of the WNT canonical pathway regulation.

CONCLUSION

WNT7A negatively regulates cell proliferation in leukemic cell lines and promotes resistance to chemotherapeutic agents by inducing a senescence-like phenotype independently of the WNT canonical pathway.

Wnt signaling in multiple myeloma: a central player in disease with therapeutic potential

Multiple myeloma is the second most frequent hematological malignancy in the western world and remains incurable, predominantly due to acquired drug resistance and disease relapse. The highly conserved Wnt signal transduction pathway, which plays a key role in regulating cellular processes of proliferation, differentiation, migration, and stem cell self-renewal, is associated with multiple aspects of disease. Bone homeostasis is severely disturbed by Wnt antagonists that are secreted by the malignant plasma cells in the bone marrow. In the vast majority of patients, this results in osteolytic bone disease, which is associated with bone pain and pathological fractures and was reported to facilitate disease progression. More recently, cumulative evidence also indicates the importance of intrinsic Wnt signaling in the survival of multiple myeloma cells. However, Wnt pathway-activating gene mutations could not be identified. The search for factors or processes responsible for Wnt pathway activation currently focuses on aberrant ligand levels in the bone marrow microenvironment, increased expression of Wnt transcriptional co-factors and associated micro-RNAs, and disturbed epigenetics and post-translational modification processes. Furthermore, Wnt pathway activation is associated with acquired cell adhesion-mediated resistance of multiple myeloma cells to conventional drug therapies, including doxorubicin and lenalidomide. In this review, we present an overview of the relevance of Wnt signaling in multiple myeloma and highlight the Wnt pathway as a potential therapeutic target for this disease.

DACT1 overexpression inhibits proliferation, enhances apoptosis, and increases daunorubicin chemosensitivity in KG-1α cells

DACT1 has been shown to participate in the development of many types of tumors; however, its role and precise molecular mechanisms in leukemia are unclear. In this study, we investigated the effect of DACT1 on KG-1α leukemia cells to further understand the mechanisms of DACT1-mediated tumor suppression. We transfected a DACT1 expression plasmid to upregulate DACT1 in KG-1α cells and analyzed the resulting phenotypic changes. The results demonstrated that DACT1 overexpression inhibited KG-1α proliferation, increased apoptosis, and arrested cells in the G0/G1 phase. Mechanistically, DACT1 overexpression inhibited Wnt/β-catenin signaling by reducing nuclear β-catenin levels in KG-1α cells. Furthermore, the viability of KG-1α cells transfected with DACT1 was significantly reduced when treated with daunorubicin. We also found that DACT1 reduced P-glycoprotein expression in KG-1α cells. These findings revealed an inhibitory role for DACT1 in leukemogenesis and provided evidence that DACT1 is an attractive target for the development of novel anti-leukemia therapies.

MEDICI: Mining Essentiality Data to Identify Critical Interactions for Cancer Drug Target Discovery and Development

Protein-protein interactions (PPIs) mediate the transmission and regulation of oncogenic signals that are essential to cellular proliferation and survival, and thus represent potential targets for anti-cancer therapeutic discovery. Despite their significance, there is no method to experimentally disrupt and interrogate the essentiality of individual endogenous PPIs. The ability to computationally predict or infer PPI essentiality would help prioritize PPIs for drug discovery and help advance understanding of cancer biology. Here we introduce a computational method (MEDICI) to predict PPI essentiality by combining gene knockdown studies with network models of protein interaction pathways in an analytic framework. Our method uses network topology to model how gene silencing can disrupt PPIs, relating the unknown essentialities of individual PPIs to experimentally observed protein essentialities. This model is then deconvolved to recover the unknown essentialities of individual PPIs. We demonstrate the validity of our approach via prediction of sensitivities to compounds based on PPI essentiality and differences in essentiality based on genetic mutations. We further show that lung cancer patients have improved overall survival when specific PPIs are no longer present, suggesting that these PPIs may be potentially new targets for therapeutic development. Software is freely available at https://github.com/cooperlab/MEDICI. Datasets are available at https://ctd2.nci.nih.gov/dataPortal.

Discrete roles of canonical and non-canonical Wnt signaling in hematopoiesis and lymphopoiesis

The mechanisms that regulate proliferation, fate decisions and differentiation of hematopoietic stem cells (HSC) and thymic stem cells are highly complex. Several signaling pathways including Wnt signaling have important roles during these processes. Both canonical and non-canonical Wnt signaling are important in normal and malignant hematopoiesis and lymphoid development, yet their precise roles are controversial. In a side-by-side comparison, we investigated the roles of the canonical and non-canonical Wnt pathway in hematopoiesis and thymopoiesis. As complete loss-of-function models for non-canonical Wnt signaling are not yet available and highly complex for canonical Wnt signaling, we decided to use a gain-of-function approach. To this end, Wnt3a and Wn5a, two well-known prototypical canonical and non-canonical Wnt ligands were produced in hematopoiesis supporting stromal assays. High levels of Wnt3a signaling blocked T-cell development at early stages, whereas intermediate levels accelerated T-cell development. In contrast, Wnt5a signaling prompted apoptosis in developing thymocytes, without affecting differentiation at a particular stage. To explore the role of Wnt3a and Wnt5a in vivo, we transduced HSCs isolated from fetal liver, transduced with Wnt3a and Wnt5a vectors, and performed reconstitution assays in irradiated C57Bl/6 mice. Wnt3a overexpression led to increased lymphopoiesis, whereas Wnt5a augments myelopoiesis in the bone marrow (BM) and spleen. Thus, the canonical and non-canonical Wnt signaling have discrete roles in hematopoiesis and thymopoiesis, and understanding their right dose of action is crucial for prospective translational applications.