Aurora kinase B (AURKB) was reported to assist Aurora kinase A (AURKA) to regulate cellular mitosis. AURKA has been found activated in myeloproliferative neoplasms (MPNs) patients with CALR gene mutation, however, it’s unclear whether AURKB displays a compensatory function of AURKA in regulation of CALR mutant cell growth and differentiation. Here, we found that AURKB, similar with AURKA, was aberrantly activated in CALR mutant patients, and displayed a more tolerance to the aurora kinase inhibitor. Inhibition of AURKA decreased cell growth and colony formation, induced cell differentiation and apoptosis, while, this inhibitive degree was further enhanced when AURKB was blocked by incremental inhibitor. Transcriptomic analyses revealed a more significant gene enrichment in cells with knockdown of AURKB than that of AURKA, mainly reflecting in oxidative phosphorylation, mitosis, proliferation and apoptosis signaling pathway. Moreover, downregulation of AURKB enhanced cell growth arrest and apoptosis more obviously than that of AURKA, and additionally promoted cell differentiation and metabolism-oxygen consumption rate (OCR). Otherwise, overexpression of AURKA or AURKB facilitated the cell proliferation of CALR mutant cells, and made cells more sensitive to the aurora kinase inhibitor. These results suggest that activated AURKB not only supports the functions of AURKA in promoting the growth of CALR mutated cells, but also has impeded the differentiation of these cells.

Objective:To investigate the effects of down-regulation of p21 activated kinase 1(PAK1)on the proliferation,differentiation,and apoptosis of myeloproliferative neoplasm(MPN)cells(6133/MPL)with thrombopoietin receptor MPL mutation at codon 515(MPLW515L)and survival of 6133/MPL mice.Methods:Interference with the protein level of PAK1 in 6133/MPL cells was assessed using lentivirus-mediated shRNA transfection technology.CCK-8 assay was used to detect the effect of down-regulation of PAK1 on the proliferation viability of 6133/MPL cells,and colony-forming ability was measured by cell counting.Flow cytometry was used to detect the PAK1 kinase activity on the ability of polyploid DNA formation and cell apoptosis in 6133/MPL cells.The expression of cyclin D1,cyclin D3 and apoptosis-related protein Bax was detected by Western blot.The infiltration of tumor cells in spleen and bone marrow of 6133/MPL mice were detected by HE staining.Results:Down-regulation of PAK1 inhibited the proliferation and reduced the ability of cell colony formation of 6133/MPL cells.After knocking down PAK1,the content of polyploid DNA in 6133/MPL cells increased from 31.8 to 57.5％and 48.0％,and the proportion of apoptosis increased approximately to 10.8％.Down-regulation of PAK1 led to a reduction of infiltration of tumor cells in liver and bone marrow of 6133/MPL mice,thereby prolonging survival time.Conclusion:Down-regulation of PAK1 can significantly inhibit the growth of 6133/MPL cells,promote the formation of polyploid DNA,induce 6133/MPL cell apoptosis,and prolong the survival time of 6133/MPL mice.

Most thrombopoietin receptor (MPL) mutations result in abnormal megakaryocyte expansion in the spleen or bone marrow (BM), leading to progressive fibrosis. It has been reported that p21 (Rac Family Small GTPase 1 [RAC1])-activated kinase 1 (PAK1) participates in the proliferation and differentiation of megakaryoblasts. PAK1 phosphorylation increased in patients with myeloproliferative neoplasms (MPNs) and murine MPN cells with the Mplw515l mutant gene in this study; however, the function of overactivated PAK1 in MPN cells remains unclear. We found that inhibition of PAK1 caused significant changes in the biological behaviors of MPLW515L mutant cells in vitro, including arrested growth or reduced clonality and increased polyploid DNA and cell apoptosis due to upregulated cleaved caspase 3. In vivo, PAK1 inhibitor treatment caused a slow elevation of leukocytosis and hematocrit (HCT) and a reduction in hepatosplenomegaly in 6133/MPLW515Ltransplanted mice, along with reduced tumor cell infiltration and prolonged survival. Further, deletion of PAK1 sustained a relatively normal HCT and platelet count at the beginning of the disease but did not completely alleviate the splenomegaly of MPLW515L mutant mice. Notably, PAK1 knockout attenuated the destruction of splenic structure, and reduced the megakaryocyte burden within the BM. These results suggest that inhibition of PAK1 may be a useful method for treating MPLW515L mutant MPN by intervening megakaryocytes. (c) 2023 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc. All rights reserved.

OBJECTIVE:To construct a myeloproliferative neoplasms (MPN) transplanted mouse model with JAK2-V617F, MPLW515L or CALR-Type I gene mutation, and establish a systematic evaluation system to verify the success of model construction.METHODS:The bone marrow c-kit+ cells of the mice were obtained by the following steps: The mice were killed by cervical dislocation, the femur, tibia and ilium were separated, and the bone marrow cells were collected. The c-kit+ cells were sorted after incubation with CD117 magnetic beads. The method of constructing mouse primary mutant cells is as follows: A gene mutation vector with a GFP tag was constructed by the retroviral system, and the retroviral vector was packaged into the Platinum-E cells to obtain the virus supernatant, and then used it to infect the c-kit+ cells of mice. The MPN mouse model was constructed as follows: the mouse primary c-kit+ cells containing the mutant genes were collected after infection, and then transplanted them via the tail vein into the female recipient mice of the same species which were irradiated with a lethal dose of gamma rays (8.0 Gy). The MPN mouse model was evaluated as follows: After transplantation, the peripheral blood of the mice was regularly collected from the tail vein to perform the complete blood count test, and the size of spleen and the degree of bone marrow fibrosis were estimated.RESULTS:The mouse c-kit+ cells with the mutant genes were successfully obtained from the bone marrow. MPN mouse model was successfully constructed: The peripheral blood cells of the MPN-transplanted mice carried exogenous implanted GFP-positive cells, and the white blood cells (WBC), platelet (PLT) and hematocrit (HCT) were all increased; the body weight loss, and the water and food intake were reduced in the transplanted mice; further pathological analysis showed that the transplanted mice displayed splenomegaly and bone marrow fibrosis. These results suggested that the MPN mouse model was successfully constructed. According to the common and different characteristics of the three MPN mouse model, a preliminary evaluation system for judging the success of MPN mouse model construction was summarized, which mainly included the following indicators, for example, the proportion of GFP-positive cells in the peripheral blood of mice; WBC, PLT and HCT; the degree of spleen enlargement and the bone marrow fibrosis.CONCLUSION:The MPN mouse model with JAK2-V617F, MPLW515L or CALR-Type I gene mutation is successfully established by retroviral system, which can provide an important experimental animal model for the research of MPN pathogenesis and drug-targeted therapy.

Objective:To investigate the effects of down-regulation of aurora kinase (AURK) B on the proliferation and apoptosis of CALR-mutated MARIMO cells, as well as changes in related genes and signalling. Methods:MARIMO cells derived from a 68-year-old female patient with CALR mutation-positive myeloproliferative neoplasms(MPN) were selected for the study. Lentivirus-mediated short hairpin RNA (shRNA) was used to transfect MARIMO cells, and the cells were categorized into sh-AURKA group, sh-AURKB group and control shRNA (sh-CTRL) group according to the difference of shRNA. The MARIMO cell lines in each group were observed by inverted fluorescence microscope, and their green fluorescent protein (GFP) positivity was detected by flow cytometry (FCM). The reproduction and apoptosis of MARIMO cells in sh-AURKB group and sh-CTRL group were analyzed by FCM, 5-ethynyl-2′-deoxyuridine (EdU)/4′, 6-diamidino-2-phenylindole dihydrochloride (DAPI) staining, and Annexin V/PE reagent. The enrichment of differentially expressed genes (DEG) in sh-AURKB group and sh-CTRL group was analyzed by RNA sequencing (RNA-Seq), and gene ontology (GO) functional annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were carried out to screen for significant DEG. The relative expression of mRNA and proteins of DEG were validated by real-time fluorescence quantitative-PCR (RT-qPCR) and Western blotting. Relative expression levels were verified. The comparison of measurement data between two groups was performed by t test. The overall comparison among 3 groups were conducted by one-way analysis of variance, pairwise comparisons between groups were conducted by least-significant difference (LSD) test. This study was in line with World Medical Association Declaration of Helsinki revised in 2013. Results:① The number of MARIMO cells 72 h after transfection was reduced in sh-AURKB group compared with sh-CTRL group [ (0.62±0.03) ×10 5vs (12.44±0.08) ×10 5], and the difference was statistically significant ( t=257.20, P<0.000 1).Compared with sh-CTRL group, the proportion of MARIMO cells in the S-stage in sh-AURKB group was decreased [(33.37 ± 0.75)% vs (42.77 ± 0.91)%], and the proportion of MARIMO cells in G2-M stage was increased [(27.83 ± 0.69)% vs (17.90 ± 0.40)%], the proportion of apoptosis was increased [(16.47 ± 0.70)% vs (2.75 ± 0.13)%], all the differences were statistically significant ( t=13.83, P=0.000 2; t= 23.78, P<0.000 1); t=33.28, P<0.000 1). ② RNA-Seq assay showed that compared to sh-CTRL group, there were 2 787 genes up-regulated and 2 420 genes down-regulated in MARIMO cells in sh-AURKB group. ③ The DEG of sh-AURKB group and sh-CTRL group were mainly annotated in GO nodes such as intracellular region, intracellular membrane border organelle, membrane border organelle, intracellular organelle part, organelle part, etc.. KEGG enrichment analysis showed that a total of 89 signal pathways were significantly enriched. Further screening of DEG-related pathways showed that the 2 groups of significant DEG were NDUFV1, NPRL2, MAP2K4, and CPEB1. ④ RT-qPCR results showed that the relative mRNA expression levels of NPRL2, MAP2K4 and CPEB1 in sh-AURKB group were lower than those in sh-CTRL group, and the differences were statistically significant (LSD- t=14.13, 9.13, 3.10; P<0.000 1, <0.000 1, =0.021). Western blotting results showed that compared with SH-CTRL group, the protein strip grayscale value of NDUFV1/GAPDH in sh-AURKB group increased, while NPRL2/GAPDH, CPEB1/GAPDH, MAP2K4/GAPDH and p-MAP2K4/GAPDH reduced, and the differences were statistically significant (LSD- t=22.60、12.09、7.48、20.48、8.22, P<0.000 1、<0.000 1、=0.000 3、<0.000 1、=0.000 2) Conclusions:AURKB is involved in the proliferation, differentiation and apoptosis of CALR mutant MARIMO cells, and down-regulation of AURKB could induce significant changes in gene expression levels. DEG are mainly enriched in the cell metabolism, cell cycle and apoptosis related pathways.

Acute megakaryoblastic leukaemia (AMKL) is characterized by expansion of megakaryoblasts, which are hyper-proliferative cells that fail to undergo differentiation. Insight to the cell-cycle regulation revealed important events in early or late megakaryocytes (MKs) maturation; the cyclin-dependent kinases 4 and 6 (CDK4/6) have been reported to participate in the development of progenitor megakaryocytes, mainly by promoting cell cycle progression and DNA polyploidization. However, it remains unclear whether the continuous proliferation, but not differentiation, of megakaryoblasts is related to an aberrant regulation of CDK4/6 in AMKL. Here, we found that CDK4/6 were up regulated in patients with AMKL, and persistently maintained at a high level during the differentiation of abnormal megakaryocytes in vitro, according to a database and western blot. Additionally, AMKL cells were exceptionally reliant on the cell cycle regulators CDK4 or 6, as blocking their activity using an inhibitor or short hairpin RNA (shRNA) significantly reduced the proliferation of 6133/MPL megakaryocytes, reduced DNA polyploidy, induced apoptosis, decreased the level of phosphorylated retinoblastoma protein (p-Rb), and activation of caspase 3. Additionally, CDK4/6 inhibitors and shRNA reduced the numbers of leukemia cells in the liver and bone marrow (BM), alleviated hepatosplenomegaly, and prolonged the survival of AMKL-transplanted mice. These results suggested that blocking the activity of CDK4/6 may represent an effective approach to control megakaryoblasts in AMKL.

Objective: To investigate the effect of blocking P21 activated kinase 1 (PAK1) activity on the proliferation, differentiation, and apoptosis of acute megakaryocytic leukemia (AMKL) cell lines (CHRF and CMK) . Methods: Cell counts were used to detect the effects of PAK1 inhibitors (IPA-3 and G5555) on AMKL cell proliferation inhibition and colony formation, and flow cytometry was used to detect its effects on AMKL cell cycle. The effect of PAK1 inhibitor on the expression of cyclin D1 and apoptosis-related protein Cleaved caspase 3 was detected using Western blot, while interference with the protein expression level of PAK1 in AMKL cells was assessed using lentivirus-mediated shRNA transfection technology. Flow cytometry was used to detect the effects of knockdown of PAK1 kinase activity on the ability of polyploid DNA formation and cell apoptosis in AMKL cells. Results: PAK1 inhibitors inhibited the proliferation of AMKL cells in a dose-dependent manner and reduced the ability of cell colony formation, and the difference was statistically significant when compared with the control group (P<0.05) . Moreover, they also reduced the percentage of AMKL cells in S phase, and Western blot detection showed that the expression levels of phosphorylated PAK1 and cyclin D1 decreased significantly. Finally, PAK1 inhibitors induced AMKL cell apoptosis by up-regulating Cleaved caspase 3 and showed different abilities to increase the content of polyploid DNA in megakaryocytes. Only high concentrations of IPA-3 and low doses of G5555 increased the number of polyploid megakaryocytes, while knockdown of PAK1 kinase activity promoted AMKL cell differentiation and increased the apoptosis rate. Conclusion: PAK1 inhibitor significantly arrests AMKL cell growth and promotes cell apoptosis. Knocking down the expression of PAK1 promotes the formation of polyploid DNA and induces AMKL cell apoptosis. The above findings indicate that inhibiting the activity of PAK1 may control AMKL effectively.

Abstract The authors have requested that this preprint be removed from Research Square.

INTRODUCTION:Somatic mutations in the calreticulin (CALR) gene occur in most myeloproliferative neoplasm (MPN) patients who lack Janus kinase 2 or thrombopoietin receptor (MPL) mutations, but the molecular pathogenesis of MPN with mutated CALR is unclear, which limited the further treatment for CALR gene mutant patients.OBJECTIVES:Previous studies showed that CALR mutations not only activated serine/threonine protein kinase (AKT) in primary mouse bone marrow cells but also mitogen-activated protein kinases (MAPKs) in MARIMO cells harboring a heterozygous 61-bp deletion in CALR exon 9, which were responsible for mutant CALR cell survival, respectively. Hence, we aimed to initially explore the mechanism of AKT activation and observe the synergistic inhibitory effect of combining AKT (MK-2206) and MAPK kinase (AZD 6244) inhibitors in MARIMO cells.METHODS:We detected the expression of phosphorylated AKT in MARIMO cells treated with inhibitors for 24 or 48 h by western blotting and analyzed cell proliferation, cell cycle, and apoptosis by flow cytometry. We further examined the synergistic inhibitory effect of combining MK-2206 and AZD 6244 in MARIMO cells using the median effect principle of Chou and Talalay.RESULTS:We found that the AKT was activated in MARIMO cells, and blocking its activity significantly inhibited MARIMO cell growth with downregulation of cyclin D and E, and accelerated cell apoptosis by decreasing Bcl-2 but increasing Bax and cleaved caspase-3 levels in a dose-dependent manner. Further analysis showed that AKT activation was dependent on mammalian target of rapamycin but not on the JAK signaling pathway in MARIMO cells, displaying that inhibition of JAK activity by ruxolitinib (RUX) did not decrease the AKT phosphorylation. Furthermore, the combination of MK-2206 and AZD 6244 produced a significantly synergistic inhibitory effect on MARIMO cells.CONCLUSIONS:AKT activation is a feature of MARIMO cells and co-targeting of AKT and MAPKs signaling pathways synergistically inhibits MARIMO cell growth.