Hippo kinase loss contributes to del(20q) hematologic malignancies through chronic innate immune activation

YAP1 regulates thrombopoiesis by binding to MYH9 in immune thrombocytopenia

ABSTRACT

Immune thrombocytopenia (ITP) is a complicated bleeding disease characterized by a sharp platelet reduction. As a dominating element involved in ITP, megakaryocytes (MKs) are responsible for thrombopoiesis. However, the mechanism underlying the dysregulation of thrombopoiesis that occurs in ITP remains unidentified. In this study, we examined the role of Yes-associated protein 1 (YAP1) in thrombopoiesis during ITP. We observed reduced YAP1 expression with cytoskeletal actin misalignment in MKs from patients with ITP. Using an experimental ITP mouse model, we showed that reduced YAP1 expression induced aberrant MK distribution, reduced the percentage of late MKs among the total MKs, and caused submaximal platelet recovery. Mechanistically, YAP1 upregulation by binding of GATA-binding protein 1 to its promoter promoted MK maturation. Phosphorylated YAP1 promoted cytoskeletal activation by binding its WW2 domain to myosin heavy chain 9, thereby facilitating thrombopoiesis. Targeting YAP1 with its activator XMU-MP-1 was sufficient to rescue cytoskeletal defects and thrombopoiesis dysregulation in YAP1+/- mice with ITP and patients. Taken together, these results demonstrate the crucial role of YAP1 in thrombopoiesis, providing potential for the development of diagnostic markers and therapeutic options for ITP.

MST1/2: Important regulators of Hippo pathway in immune system associated diseases

The Hippo signaling pathway is first found in Drosophila and is highly conserved in evolution. Previous studies on this pathway in mammals have revealed its key role in cell proliferation and differentiation, organ size control, and carcinogenesis. Apart from these, recent findings indicate that mammalian Ste20-like kinases 1 and 2 (MST1/2) have significant effects on immune regulation. In this review, we summarize the updated understanding of how MST1/2 affect the regulation of the immune system and the specific mechanism. The effect of MST1/2 on immune cells and its role in the tumor immune microenvironment can alter the body's response to tumor cells. The relationship between MST1/2 and the immune system suggests new directions in the manipulation of immune responses for clinical immunotherapy, especially for tumor treatment.

Paralog-specific signaling by IRAK1/4 maintains MyD88-independent functions in MDS/AML

Dysregulation of innate immune signaling is a hallmark of hematologic malignancies. Recent therapeutic efforts to subvert aberrant innate immune signaling in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) have focused on the kinase IRAK4. IRAK4 inhibitors have achieved promising, though moderate, responses in preclinical studies and clinical trials for MDS and AML. The reasons underlying the limited responses to IRAK4 inhibitors remain unknown. In this study, we reveal that inhibiting IRAK4 in leukemic cells elicits functional complementation and compensation by its paralog, IRAK1. Using genetic approaches, we demonstrate that cotargeting IRAK1 and IRAK4 is required to suppress leukemic stem/progenitor cell (LSPC) function and induce differentiation in cell lines and patient-derived cells. Although IRAK1 and IRAK4 are presumed to function primarily downstream of the proximal adapter MyD88, we found that complementary and compensatory IRAK1 and IRAK4 dependencies in MDS/AML occur via noncanonical MyD88-independent pathways. Genomic and proteomic analyses revealed that IRAK1 and IRAK4 preserve the undifferentiated state of MDS/AML LSPCs by coordinating a network of pathways, including ones that converge on the polycomb repressive complex 2 complex and JAK-STAT signaling. To translate these findings, we implemented a structure-based design of a potent and selective dual IRAK1 and IRAK4 inhibitor KME-2780. MDS/AML cell lines and patient-derived samples showed significant suppression of LSPCs in xenograft and in vitro studies when treated with KME-2780 as compared with selective IRAK4 inhibitors. Our results provide a mechanistic basis and rationale for cotargeting IRAK1 and IRAK4 for the treatment of cancers, including MDS/AML.

Mammalian STE20-like kinase-1/2 are activated in human platelets stimulated by collagen or thrombin and play a vital role in collagen-activated platelets

INTRODUCTION

Mammalian ste20-like kinases-1/2 (MST1/2), the core kinases of the Hippo pathway, play critical roles in the biology of hematopoietic cells via noncanonical mechanisms and contributes to megakaryocyte differentiation, polyploidization, and maturation to produce platelets. However, the role of MST1/2 in platelet functions remains unclear.

MATERIALS AND METHODS

In this study, we investigated this topic by determining platelet aggregation and through flow cytometry, ATP release assay, clot retraction assay, and immunoblotting analysis.

RESULTS

We found that MST1/2 were rapidly phosphorylated and activated upon platelet stimulation by thrombin and collagen. XMU-MP-1, a specific inhibitor of MST1/2, blocks the activation of MST1/2 in platelets. Inhibitor-pretreated platelets showed impaired platelet aggregation and dense-granule secretion mediated by collagen, thrombin, and U46619, whereas ristocetin or ADP mediated platelet aggregation was unaffected by XMU-MP-1. Although platelet-mediated clot retraction was not affected by MST1/2 inhibitors, integrin αIIbβ3 activation was significantly attenuated in XMU-MP-1-treated platelets. Moreover, MST1/2 inhibition significantly attenuated the mobilization of platelet calcium ions and the secretion of α-granules induced by convulxin.

CONCLUSIONS

This study is the first to demonstrate that MST1/2 play vital roles in human platelets and contributes to collagen-induced platelet activation and aggregation.

Diagnosis of Myelodysplastic Syndromes: From Immunological Observations to Clinical Applications

Myelodysplastic syndromes (MDS) constitute a very heterogeneous group of diseases with a high prevalence in elderly patients and a propensity for progression to acute myeloid leukemia. The complexity of these hematopoietic malignancies is revealed by the multiple recurrent somatic mutations involved in MDS pathogenesis and the paradoxical common phenotype observed in these patients characterized by ineffective hematopoiesis and cytopenia. In the context of population aging, the incidence of MDS will strongly increase in the future. Thus, precise diagnosis and evaluation of the progression risk of these diseases are imperative to adapt the treatment. Dysregulations of both innate and adaptive immune systems are frequently detected in MDS patients, and their critical role in MDS pathogenesis is now commonly accepted. However, different immune dysregulations and/or dysfunctions can be dynamically observed during the course of the disease. Monitoring the immune system therefore represents a new attractive tool for a more precise characterization of MDS at diagnosis and for identifying patients who may benefit from immunotherapy. We review here the current knowledge of the critical role of immune dysfunctions in both MDS and MDS precursor conditions and discuss the opportunities offered by the detection of these dysregulations for patient stratification.

Myelodysplastic Syndromes with Isolated 20q Deletion: A New Clinical-Biological Entity?

Aims: To define the peculiar features of patients with the deletion of the chromosome 20 long arm (del20q), data from 69 patients with myelodysplastic syndromes (MDSs) and isolated del20q, followed by the Gruppo Romano-Laziale Sindromi Mielodisplastiche (GROM-L) and Ospedale Torrette of Ancona, were collected and compared with those of 502 MDS patients with normal karyotype (NK-MDS). Results: Compared to the NK-MDS group, patients with del20q at diagnosis were older (p = 0.020) and mainly male (p = 0.006). They also had a higher rate of bone marrow blast < 5% (p = 0.004), a higher proportion of low and int-1 risk according to IPSS score (p = 0.023), and lower median platelet (PLT) count (p < 0.001). To date, in the del20q cohort, 21 patients (30.4%) received no treatment, 42 (61.0%) were treated with erythropoiesis-stimulating agents (ESA), 3 (4.3%) with hypomethylating agents, and 3 (4.3%) with other treatments. Among 34 patients evaluable for response to ESA, 21 (61.7%) achieved stable erythroid response according to IWG 2006 criteria and 13 (38.2%) were resistant. Nine patients (13.0%) progressed to acute myeloid leukaemia (AML) after a median time from diagnosis of 28 months (IR 4.1−51.7). The median overall survival (OS) of the entire cohort was 60.6 months (95% CI 54.7−66.4). the 5-year cumulative OS was 55.9% (95% CI 40.6−71.2). Conclusion: According to our results, we hypothesize that MDSs with isolated del 20q may represent a distinct biological entity, with peculiar clinical and prognostic features. The physio-pathological mechanisms underlying the deletion of the chromosome 20 long arm are still unclear and warrant future molecular analysis.

Acute myeloid leukemia cell membrane-coated nanoparticles for cancer vaccination immunotherapy

Cancer vaccines are promising treatments to prevent relapse after chemotherapy in acute myeloid leukemia (AML) patients, particularly for those who cannot tolerate intensive consolidation therapies. Here, we report the development of an AML cell membrane-coated nanoparticle (AMCNP) vaccine platform, in which immune-stimulatory adjuvant-loaded nanoparticles are coated with leukemic cell membrane material. This AMCNP vaccination strategy stimulates leukemia-specific immune responses by co-delivering membrane-associated antigens along with adjuvants to antigen-presenting cells. To demonstrate that this AMCNP vaccine enhances leukemia-specific antigen presentation and T cell responses, we modified a murine AML cell line to express membrane-bound chicken ovalbumin as a model antigen. AMCNPs were efficiently acquired by antigen-presenting cells in vitro and in vivo and stimulated antigen cross-presentation. Vaccination with AMCNPs significantly enhanced antigen-specific T cell expansion and effector function compared with control vaccines. Prophylactic vaccination with AMCNPs enhanced cellular immunity and protected against AML challenge. Moreover, in an AML post-remission vaccination model, AMCNP vaccination significantly enhanced survival in comparison to vaccination with whole leukemia cell lysates. Collectively, AMCNPs retained AML-specific antigens, elicited enhanced antigen-specific immune responses, and provided therapeutic benefit against AML challenge.

Innate immune pathways and inflammation in hematopoietic aging, clonal hematopoiesis, and MDS

With a growing aged population, there is an imminent need to develop new therapeutic strategies to ameliorate disorders of hematopoietic aging, including clonal hematopoiesis and myelodysplastic syndrome (MDS). Cell-intrinsic dysregulation of innate immune- and inflammatory-related pathways as well as systemic inflammation have been implicated in hematopoietic defects associated with aging, clonal hematopoiesis, and MDS. Here, we review and discuss the role of dysregulated innate immune and inflammatory signaling that contribute to the competitive advantage and clonal dominance of preleukemic and MDS-derived hematopoietic cells. We also propose how emerging concepts will further reveal critical biology and novel therapeutic opportunities.

Murine Modeling of Myeloproliferative Neoplasms

Myeloproliferative neoplasms, such as polycythemia vera, essential thrombocythemia, and primary myelofibrosis, are bone marrow disorders that result in the overproduction of mature clonal myeloid elements. Identification of recurrent genetic mutations has been described and aid in diagnosis and prognostic determination. Mouse models of these mutations have confirmed the biologic significance of these mutations in myeloproliferative neoplasm disease biology and provided greater insights on the pathways that are dysregulated with each mutation. The models are useful tools that have led to preclinical testing and provided data as validation for future myeloproliferative neoplasm clinical trials.

Comparison of SYK Signaling Networks Reveals the Potential Molecular Determinants of Its Tumor-Promoting and Suppressing Functions

Spleen tyrosine kinase (SYK) can behave as an oncogene or a tumor suppressor, depending on the cell and tissue type. As pharmacological SYK inhibitors are currently evaluated in clinical trials, it is important to gain more information on the molecular mechanisms underpinning these opposite roles. To this aim, we reconstructed and compared its signaling networks using phosphoproteomic data from breast cancer and Burkitt lymphoma cell lines where SYK behaves as a tumor suppressor and promoter. Bioinformatic analyses allowed for unveiling the main differences in signaling pathways, network topology and signal propagation from SYK to its potential effectors. In breast cancer cells, the SYK target-enriched signaling pathways included intercellular adhesion and Hippo signaling components that are often linked to tumor suppression. In Burkitt lymphoma cells, the SYK target-enriched signaling pathways included molecules that could play a role in SYK pro-oncogenic function in B-cell lymphomas. Several protein interactions were profoundly rewired in the breast cancer network compared with the Burkitt lymphoma network. These data demonstrate that proteomic profiling combined with mathematical network modeling allows untangling complex pathway interplays and revealing difficult to discern interactions among the SYK pathways that positively and negatively affect tumor formation and progression.

YAP1 and its fusion proteins in cancer initiation, progression and therapeutic resistance

YAP1 is a transcriptional co-activator whose activity is controlled by the Hippo signaling pathway. In addition to important functions in normal tissue homeostasis and regeneration, YAP1 has also prominent functions in cancer initiation, aggressiveness, metastasis, and therapy resistance. In this review we are discussing the molecular functions of YAP1 and its roles in cancer, with a focus on the different mechanisms of de-regulation of YAP1 activity in human cancers, including inactivation of upstream Hippo pathway tumor suppressors, regulation by intersecting pathways, miRNAs, and viral oncogenes. We are also discussing new findings on the function and biology of the recently identified family of YAP1 gene fusions, that constitute a new type of activating mutation of YAP1 and that are the likely oncogenic drivers in several subtypes of human cancers. Lastly, we also discuss different strategies of therapeutic inhibition of YAP1 functions.

The Genomics of Myelodysplastic Syndromes: Origins of Disease Evolution, Biological Pathways, and Prognostic Implications

The molecular pathogenesis of myelodysplastic syndrome (MDS) is complex due to the high rate of genomic heterogeneity. Significant advances have been made in the last decade which elucidated the landscape of molecular alterations (cytogenetic abnormalities, gene mutations) in MDS. Seminal experimental studies have clarified the role of diverse gene mutations in the context of disease phenotypes, but the lack of faithful murine models and/or cell lines spontaneously carrying certain gene mutations have hampered the knowledge on how and why specific pathways are associated with MDS pathogenesis. Here, we summarize the genomics of MDS and provide an overview on the deregulation of pathways and the latest molecular targeted therapeutics.

Chromosome Abnormalities: New Insights into Their Clinical Significance in Cancer

Chromosomal abnormalities, consisting of numerical and structural chromosome abnormalities, are a common characteristic of cancer. Numerical chromosome abnormalities, mainly including aneuploidy and chromosome instability, are caused by chromosome segregation errors in mitosis, whereas structural chromosome abnormalities are a consequence of DNA damage and comprise focal/arm-level chromosome gain or loss. Recent advances have started to unveil the mechanisms by which chromosomal abnormalities can facilitate tumorigenesis and change the cellular fitness and the expression or function of RNAs and proteins. Accumulating evidence suggests that chromosome abnormalities represent a genomic signature that is linked to cancer prognosis and reaction to chemotherapy and immunotherapy. In this review, we discuss the most recent findings on the role of chromosome abnormalities in tumorigenesis and cancer progression, with a particular emphasis on how aneuploidy and chromosome instability influence cancer therapy and prognosis. We also highlight the distribution and clinical application of the structural chromosome abnormalities in various cancer types. A better understanding of the role of chromosome abnormalities will be beneficial to the development of precision oncology and suggest future directions for the field.

The RUNX1-ETO target gene RASSF2 suppresses t(8;21) AML development and regulates Rac GTPase signaling

Large-scale chromosomal translocations are frequent oncogenic drivers in acute myeloid leukemia (AML). These translocations often occur in critical transcriptional/epigenetic regulators and contribute to malignant cell growth through alteration of normal gene expression. Despite this knowledge, the specific gene expression alterations that contribute to the development of leukemia remain incompletely understood. Here, through characterization of transcriptional regulation by the RUNX1-ETO fusion protein, we have identified Ras-association domain family member 2 (RASSF2) as a critical gene that is aberrantly transcriptionally repressed in t(8;21)-associated AML. Re-expression of RASSF2 specifically inhibits t(8;21) AML development in multiple models. Through biochemical and functional studies, we demonstrate RASSF2-mediated functions to be dependent on interaction with Hippo kinases, MST1 and MST2, but independent of canonical Hippo pathway signaling. Using proximity-based biotin labeling we define the RASSF2-proximal proteome in leukemia cells and reveal association with Rac GTPase-related proteins, including an interaction with the guanine nucleotide exchange factor, DOCK2. Importantly, RASSF2 knockdown impairs Rac GTPase activation, and RASSF2 expression is broadly correlated with Rac-mediated signal transduction in AML patients. Together, these data reveal a previously unappreciated mechanistic link between RASSF2, Hippo kinases, and Rac activity with potentially broad functional consequences in leukemia.