Thus, our study identifies Plek2 as an effector of the JAK2/STAT5 pathway and a key factor in the pathogenesis of JAK2V617F-induced MPNs, pointing to Plek2 as a viable target for the treatment of MPNs.
These include: i) more pronounced expression of phosphoSTAT5 protein in patients with JAK2V617F mutation compared to patients with wild-type of JAK2 kinase ii) different expression pattern of pSTAT5 in the nucleus and the cytoplasm of megakaryocytes and other bone marrow cells; iii) approximately 5-fold higher expression level of STAT5a gene in PV in comparison to patients with PMF and approximately 2-fold higher than in ET patients; iv) different, intracellular expression patterns of ERK2 and ERK1/2 antigens allowed to distinguish each subtype of MPN.
We investigated the JAK2 V617F, CALR and STAT5 activation status in patients with CML and thrombocytosis (CML-T) that mimicked ET, trying to identify a common mechanism for thrombocytosis in MPN.
We found that homozygous Stat5 deficiency extended the lifespan of Nf1-deficient mice and eliminated the development of myeloproliferative neoplasm associated with Nf1 gene loss.
Abnormal expression of several STAT5-p53 target genes (LEP, ATP5J, GTF2A2, VEGFC, NPY1R and NPY5R) is frequently detected in platelets of myeloproliferative neoplasm (MPN) patients, but not in platelets from healthy controls.
Hemopoietic progenitor cells (HPC) from myeloproliferative neoplasms (MPN) such as myelofibrosis commonly express mutant JAK2-V617F or other mutations that are associated with increased activities of JAK-STAT5/3, RAS/RAF/MAPK, and PI3K/AKT/mTOR pathways.
We treated primary cells from normal donors and patients with MPN with JAK2 inhibitors and measured phosphorylation of downstream targets STAT5 and STAT3 by flow cytometry.
These results demonstrate that STAT5a/b is essential for the induction of CML-like leukemia by BCR-ABL1 and of polycythemia by JAK2(V617F), and validate STAT5a/b and the genes they regulate as targets for therapy in these MPNs.
Eliminating STAT5 expression had dramatic effects in both contexts, and this new work and other recent studies support the therapeutic potential of targeting pathways regulated by this important signaling molecule in patients with myeloproliferative neoplasms (MPNs).
These findings also provide strong support for the development of Stat5 inhibitors as targeted therapies for the treatment of PV and other JAK2V617F-positive MPNs.
Monoclonal antibodies to phospho-STAT5 and phospho-Akt were generated and assessed by immunocytochemistry on bone marrow biopsies of MPN patients with JAK2 V617F, JAK2 exon 12, MPL exon 10 and KIT D816V mutations.