The role of β-catenin in chronic myeloproliferative disorders

A proteomic study of myeloproliferative neoplasms using reverse-phase protein arrays

Myeloproliferative neoplasms polycythemia vera (PV), essential thrombocythaemia (ET) and primary myelofibrosis constitute a group of haematological diseases. The comprehensive assessment of signaling pathway activation in blood cells may aid the understanding of MPN pathophysiology. Thus, levels of post-translational protein modifications and total protein expression were determined in MPN patients and control leukocytes by using reverse-phase protein arrays (RPPA). Compared to control samples, p-SRC, p-CTNNB1, c-MYC, MCL-1, p-MDM2, BAX and CCNB1 showed higher expression in PV samples than controls. P-JAK2/JAK2 and pro-apoptotic BIM showed differential expression between JAK2V617F-positive and -negative ET patients. Apoptosis, cancer and PI3K/AKT pathways proteins showed differential expression among the studied groups. For most of the proteins analyzed using Western-Blot and RPPA, RPPA showed higher sensitivity to detect subtle differences. Taken together, our data indicate deregulated protein expression in MPN patients compared to controls. Thus, RPPA may be a useful method for broad proteome analysis in MPN patients´ leukocytes.

Defective WNT signaling associates with bone marrow fibrosis-a cross-sectional cohort study in a family with WNT1 osteoporosis

This study explores bone marrow function in patients with defective WNT1 signaling. Bone marrow samples showed increased reticulin and altered granulopoiesis while overall hematopoiesis was normal. Findings did not associate with severity of osteoporosis. These observations provide new insight into the role of WNT signaling in bone marrow homeostasis.

INTRODUCTION

WNT signaling regulates bone homeostasis and survival and self-renewal of hematopoietic stem cells. Aberrant activation may lead to osteoporosis and bone marrow pathology. We aimed to explore bone marrow findings in a large family with early-onset osteoporosis due to a heterozygous WNT1 mutation.

METHODS

We analyzed peripheral blood samples, and bone marrow aspirates and biopsies from 10 subjects with WNT1 mutation p.C218G. One subject was previously diagnosed with idiopathic myelofibrosis and others had no previously diagnosed hematologic disorders. The findings were correlated with the skeletal phenotype, as evaluated by number of peripheral and spinal fractures and bone mineral density.

RESULTS

Peripheral blood samples showed no abnormalities in cell counts, morphology or distributions but mild increase in platelet count. Bone marrow aspirates (from 8/10 subjects) showed mild decrease in bone marrow iron storages in 6 and variation in cell distributions in 5 subjects. Bone marrow biopsies (from 6/10 subjects) showed increased bone marrow reticulin (grade MF-2 in the myelofibrosis subject and grade MF-1 in 4 others), and an increase in overall, and a shift towards early-phase, granulopoiesis. The bone marrow findings did not associate with the severity of skeletal phenotype.

CONCLUSIONS

Defective WNT signaling associates with a mild increase in bone marrow reticulin and may predispose to myelofibrosis, while overall hematopoiesis and peripheral blood values are unaltered in individuals with a WNT1 mutation. In this family with WNT1 osteoporosis, bone marrow findings were not related to the severity of osteoporosis.

β-catenin induces expression of prohibitin gene in acute leukemic cells

Prohibitin (PHB) is a multifunctional protein conserved in eukaryotic systems and shows various expression levels in tumor cells. However, regulation of PHB is not clearly understood. Here, we focused on the regulation of PHB expression by Wnt signaling, one of dominant regulatory signals in various leukemic cells. High mRNA levels of PHB were found in half of clinical leukemia samples. PHB expression was increased by inhibition of the MAPK pathway and decreased by activation of EGF signal. Although cell proliferating signals downregulated the transcription of PHB, treatment with lithium chloride, an analog of the Wnt signal, induced PHB level in various cell types. We identified the TCF-4/LEF-1 binding motif, CATCTG, in the promoter region of PHB by site-directed mutagenesis and ChIP assay. This β-catenin-mediated activation of PHB expression was independent of c‑MYC activation, a product of Wnt signaling. These data indicate that PHB is a direct target of β-catenin and the increased level of PHB in leukemia can be regulated by Wnt signaling.

Canonical Wnt/β-Catenin Signaling Pathway Is Dysregulated in Patients With Primary and Secondary Myelofibrosis

INTRODUCTION

β-Catenin is a central effector molecule of the canonical wingless-related integration site (Wnt) signaling pathway. It is important for maintenance of stem cell homeostasis and its aberrant activation has been implicated in a wide array of malignant hematological disorders. There are few reports suggesting its dysregulation in Philadelphia chromosome-negative (Ph-) myeloproliferative neoplasms (MPNs).

PATIENTS AND METHODS

We analyzed β-catenin mRNA expression in bone marrow (BM) aspirates of 29 patients with primary (PMF) and 4 patients with secondary, post Ph- MPN, myelofibrosis (SMF) using quantitative real-time polymerase chain reaction (qRT PCR). The control group consisted of 16 BM aspirates from patients with limited-stage aggressive non-Hodgkin lymphoma without BM involvement. We compared relative gene expression with clinical and hematological parameters.

RESULTS

Relative expression of β-catenin differed significantly among groups (P = .0002), it was significantly higher in patients with PMF and SMF than in the control group, but did not differ between patients with PMF and SMF. A negative correlation was found regarding hemoglobin level in PMF (P = .017). No association according to Janus kinase 2 (JAK2) V617F mutational status or JAK2 V617F allele burden was detected.

CONCLUSION

Our results show for the first time that β-catenin mRNA expression is increased in patients with PMF and SMF and its upregulation might potentiate anemia. A number of inflammatory cytokines associated with PMF are capable of mediating their effects through increased β-catenin expression. Accordingly, β-catenin can induce expression of a number of genes implicated in processes of cell cycle control, fibrosis, and angiogenesis, which are central to the PMF pathogenesis. Therefore, β-catenin might represent an interesting new therapeutic target in these diseases.

The Role of β-Catenin in Bcr/Abl Negative Myeloproliferative Neoplasms: An Immunohistochemical Study

INTRODUCTION

β-Catenin is a multifunctional protein that acts as a central effector molecule in the Wnt signaling pathway. Aberrant activation of the Wnt/β-catenin signaling pathway causes various diseases including cancer. In this study we evaluated β-catenin expression in bcr/abl-negative myeloproliferative neoplasms (MPNs).

MATERIALS AND METHODS

The expression of β-catenin was evaluated in bone marrow using immunohistochemical methods in 66 patients with bcr/abl-negative myeloproliferative neoplasms (MPNs) and in 30 healthy control subjects. Immunreactive score (IRS; staining intensity × percentage of positive stained cells) was used for the evaluation of the cell staining reaction.

RESULTS

IRS of megakaryocytes (IRSmega) was higher in essential thrombocytemia (ET) compared with the control group (P = .022) and primary myelofibrosis (PMF; P = .001). IRS of vascular endothelial cells (IRSvas) was higher in the bcr/abl negative MPN compared with the control group (P = .024). Also, IRSvas was higher in the PMF compared with the control group (P = .001), policythemia vera (PV; P = .005), and ET (P = .006). A positive correlation was detected between IRSmega and platelet counts (P = .019).

CONCLUSION

Results of this study suggest that the Wnt/β-catenin signaling pathway has a role in the angiogenesis of PMF and in the thrombopoiesis of PV and ET. Hence, targeting the Wnt/β-catenin signaling pathway could open new avenues for novel therapeutic approaches in bcr/abl-negative MPNs.

Dual role of wingless signaling in stem-like hematopoietic precursor maintenance in Drosophila

In Drosophila, blood development occurs in a specialized larval hematopoietic organ, the lymph gland (LG), within which stem-like hemocyte precursors or prohemocytes differentiate to multiple blood cell types. Here we show that components of the Wingless (Wg) signaling pathway are expressed in prohemocytes. Loss- and gain-of-function analysis indicates that canonical Wg signaling is required for maintenance of prohemocytes and negatively regulates their differentiation. Wg signals locally in a short-range fashion within different compartments of the LG. In addition, Wg signaling positively regulates the proliferation and maintenance of cells that function as a hematopoietic niche in Drosophila, the posterior signaling center (PSC), and in the proliferation of crystal cells. Our studies reveal a conserved function of Wg signaling in the maintenance of stem-like blood progenitors and reveal an involvement of this pathway in the regulation of hemocyte differentiation through its action in the hematopoietic niche.