Abstract
JAK2-V617F plays a key role in the pathogenesis of myeloproliferative neoplasm. However, its inhibitor ruxolitinib has shown limited clinical efficacies because of the ruxolitinib-persistent proliferation of JAK2-V617F-positive cells. We here demonstrate that the USP9X inhibitor WP1130 or EOAI3402143 (G9) inhibited proliferation and induced apoptosis more efficiently in cells dependent on JAK2-V617F than on cytokine-activated JAK2. WP1130 preferentially downregulated activated and autophosphorylated JAK2-V617F by enhancing its K63-linked polyubiquitination and inducing its aggresomal translocation to block downstream signaling. Furthermore, JAK2-V617F associated physically with USP9X in leukemic HEL cells. Induction of apoptosis by inhibition of USP9X was mediated through the intrinsic mitochondria-mediated pathway, synergistically enhanced by BH3 mimetics, prevented by overexpression of Bcl-xL, and required oxidative stress to activate stress-related MAP kinases p38 and JNK as well as DNA damage responses in HEL cells. Although autophosphorylated JAK2-V617F was resistant to WP1130 in the ruxolitinib-persistent HEL-R cells, these cells expressed Bcl-2 and Bcl-xL at lower levels and showed an increased sensitivity to WP1130 as well as BH3 mimetics as compared with ruxolitinib-naive HEL cells. Thus, USP9X represents a promising target along with anti-apoptotic Bcl-2 family members for novel therapeutic strategies against JAK2-V617F-positive myeloproliferative neoplasms, particularly under the ruxolitinib persistence conditions.
Highlights
The Janus kinases (JAKs) are nonreceptor tyrosine kinases involved in transduction of cytokine-mediated signaling in various hematopoietic cells [1]
We examined the anti-proliferative effect of WP1130 against JAK2-V617F-driven leukemic cell lines
The antiproliferative effects against these cell lines were more prominent than those against BCR-ABL-driven K562, a leukemic cell line derived from patients with chronic myelogenous leukemia (CML) in blastic phase reported to be susceptible to WP1130 [17,18]
Summary
The Janus kinases (JAKs) are nonreceptor tyrosine kinases involved in transduction of cytokine-mediated signaling in various hematopoietic cells [1]. JAK2 activated by these cytokine receptors regulates proliferation, differentiation, and survival of myeloid cells through stimulation of various signaling events, such as activation of STATs and Cancers 2020, 12, 406; doi:10.3390/cancers12020406 www.mdpi.com/journal/cancers. Aberrant activation of these pathways results in cytokine-independent cell growth seen in hematopoietic malignancies including myeloproliferative neoplasms (MPNs) [2,3]. The somatic mutation JAK2-V617F is the most frequently observed driver mutation in BCR/ABL-negative MPNs, such as polycythemia vera (PV) and primary myelofibrosis (PMF) [4]. Some cases of PMF or PV progress and transform into secondary acute myeloid leukemia (post-MPN sAML) with its frequency increased up to 20% in patients treated with chemotherapy
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