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RESEARCH PRODUCT

Role of heat shock protein in myeloproliferative neoplasms : involvement of HSP27 in myelofibrosis

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Myelofibrosis (MF) is the most aggressive myeloproliferative neoplasms (MPN) with the highest degree of morbidity and mortality, including progressive bone marrow fibrosis resulting into bone marrow failure. JAK2 kinase inhibitors have been successfully used for a few years in MPN and more particularly for MF treatment. Nevertheless, their beneficial effects are mainly restricted on symptoms and not on the course of the disease. Recently, heat shock protein 90 (HSP90) - known to stabilize JAK2 - has been reported as a promising therapeutic target in MPN. However HSP90 inhibitors show toxicity and induce the expression of stress-inducible proteins such as HSP70 and, most likely HSP27 as previously shown in other cancers. In addition, we and others have shown that HSP27, was strongly expressed in patients with idiopathic pulmonary or kidney tubulointerstitial fibrosis, underlying a relevant role of HSP27 in fibrotic processes. Taking into account both the beneficial effects of HSP inhibitors in leukemia and in MPN, and the possible implication of HSP27 in fibrosis, we have evaluated here the status of HSP27 in MF patient’s samples and assess the effectiveness of an HSP27 oligonucleotide inhibitor called OGX-427 in murine models. We report here the effect of OGX-427 in two murine models of thrombopoietin- and JAKV617F-induced myelofibrosis. OGX-427 limited the progression of the disease associated with a reduction of spleen weight and of megakaryocytic expansion. And more recently, our additional results show a decrease of reticulin fibrosis in JAK2V617F’s bone marrow. We show that HSP27 regulates JAK2/STAT5 proliferative effect through direct interactions, and we report an increase expression of HSP27 both in CD34+ circulating progenitors and in the serum of patients with NMP with fibrosis. Taking altogether, this work supports that extra and intracellular HSP27 plays a key role of in the pathophysiology in MF and highlight the potential therapeutic benefit of HSP27 inhibitors in this disorder.