a b s t r a c t JAK2 V617F mutant induces transformation through aberrant activation of various transcription factors. We found that the expression of Aurora kinase A (Aurka) was significantly induced by mutant JAK2 through c-Myc expression. Interestingly, mutant JAK2 enhanced resistance to cisplatin (CDDP)-induced DNA damage, and effectively suppressed apoptosis. Ectopic expression of Aurka in Ba/F3 cells exhibited similar resistance to CDDP, and this required kinase activity. Conversely, knockdown and inhibition of Aurka in cells expressing mutant JAK2 abolished the resistance to CDDP. Taken together, Aurka is most likely critical for resistance to DNA damage in cells transformed by JAK2 V617F mutant.
The acquired mutation (V617F) of Janus kinase 2 (JAK2) is observed in the majority of patients with myeloproliferative neoplasms (MPNs). In the screening of genes whose expression was induced by JAK2 (V617F), we found the significant induction of c-Myc mRNA expression mediated by STAT5 activation. Interestingly, GSK-3β was inactivated in transformed Ba/F3 cells by JAK2 (V617F), and this enhanced the protein expression of c-Myc. The enforced expression of c-Myc accelerated cell proliferation but failed to inhibit apoptotic cell death caused by growth factor deprivation; however, the inhibition of GSK-3β completely inhibited the apoptosis of cells expressing c-Myc. Strikingly, c-Myc T58A mutant exhibited higher proliferative activity in a growth-factor-independent manner; however, this mutant failed to induce apoptosis. In addition, knockdown of c-Myc significantly inhibited the proliferation of transformed cells by JAK2 (V617F), suggesting that c-Myc plays an important role in oncogenic activity of JAK2 (V617F). Furthermore, JAK2 (V617F) induced the expression of a target gene of c-Myc, ornithine decarboxylase (ODC), known as the rate-limiting enzyme in polyamine biosynthesis. An ODC inhibitor, difluoromethylornithine (DFMO), prevented the proliferation of transformed cells by JAK2 (V617F). Importantly, administration of DFMO effectively delayed tumor formation in nude mice inoculated with transformed cells by JAK2 (V617F), resulting in prolonged survival; therefore, ODC expression through c-Myc is a critical step for JAK2 (V617F)-induced transformation and DFMO could be used as effective therapy for MPNs.
JAK2 plays important roles in the regulation of a variety of cellular processes including cell migration, proliferation, and protection from apoptosis. Recently the L611S point mutation in JAK2 has been identified in a child with acute lymphoblastic leukemia. Here we analyzed the mechanism by which JAK2 exhibits its oncogenicity. In BaF3 murine hematopoietic cells, L611S mutant increased the expression of antiapoptotic proteins including X chromosome-linked inhibitor of apoptosis protein, inhibitor of apoptosis protein, and Bcl-XL. We also showed that JAK2 L611S mutant protects BaF3 cells from cytokine withdrawal-induced apoptotic cell death and leads to cytokine-independent cell growth. Furthermore BaF3 cells expressing JAK2 L611S mutant gained the ability to induce tumorigenesis in nude mice. The L611S mutant also exhibited malignancy, including prompt invasion and spreading into various organs, leading to rapid lethality of the mice. Finally we showed that a specific JAK2 inhibitor, AG490, potently inhibited cytokine-independent cell growth induced by JAK2 L611S mutant via the induction of apoptotic cell death. In addition, treatment with AG490 significantly inhibited the JAK2 L611S mutant-induced tumorigenesis in nude mice. Thus, our results both in vitro and in vivo strongly suggest that L611S mutant of JAK2 harbors potent oncogenic activity, and this probably requires the antiapoptotic signaling pathway.The tyrosine kinase Janus kinase 2 (JAK2) 2 is the essential component of various cytokine signal transductions. Recent studies showed that JAK2 activates the mitogen-activated protein kinase family (ERK, c-Jun NH 2 -terminal kinase (JNK), and p38), Akt, and the signal transducers and activators of transcription (Stat) family in various tissues and is involved in numerous biological functions such as cell growth, cell survival, and differentiation (1, 2). Therefore, it has been reported that the disruption of the regulation of JAK2 activity is associated with hematopoietic disorders and oncogenesis (3-5).JAK2 contains seven regions with significant sequence homology between the kinases, termed Jak homology (JH) domains (1, 2). The JH1 domain is located within the carboxyl terminus of the protein and contains the tyrosine kinase domain. The adjacent JH2 domain shows close homology to the JH1 domain; however, it lacks critical residues required for tyrosine kinase activity. Under normal conditions, this JH2 domain negatively regulates kinase activity. Theoretical models of JAK2 structure suggest that the JH1 and JH2 domains are facing each other and that the activation loop of JAK2 is buried at this interface (6). Upon activation of JAK2, phosphorylation of the activation loop at Tyr 1007/1008 occurs and is believed to prevent this JH1-JH2 interaction and therefore relieve inhibition (7-9).The JAK2 deletion mutant lacking JH2 domain exhibited receptor-independent constitutive activation (8, 9). Furthermore JH2 domain mutations have been demonstrated to be involved in various myeloproliferative diseases (10 -1...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.