The acute lymphoblastic leukemia-associated JAK2 L611S mutant induces tumorigenesis in nude mice

Therapeutic advances of targeting receptor tyrosine kinases in cancer

Receptor tyrosine kinases (RTKs), a category of transmembrane receptors, have gained significant clinical attention in oncology due to their central role in cancer pathogenesis. Genetic alterations, including mutations, amplifications, and overexpression of certain RTKs, are critical in creating environments conducive to tumor development. Following their discovery, extensive research has revealed how RTK dysregulation contributes to oncogenesis, with many cancer subtypes showing dependency on aberrant RTK signaling for their proliferation, survival and progression. These findings paved the way for targeted therapies that aim to inhibit crucial biological pathways in cancer. As a result, RTKs have emerged as primary targets in anticancer therapeutic development. Over the past two decades, this has led to the synthesis and clinical validation of numerous small molecule tyrosine kinase inhibitors (TKIs), now effectively utilized in treating various cancer types. In this manuscript we aim to provide a comprehensive understanding of the RTKs in the context of cancer. We explored the various alterations and overexpression of specific receptors across different malignancies, with special attention dedicated to the examination of current RTK inhibitors, highlighting their role as potential targeted therapies. By integrating the latest research findings and clinical evidence, we seek to elucidate the pivotal role of RTKs in cancer biology and the therapeutic efficacy of RTK inhibition with promising treatment outcomes.

The acetylation of STAT3 at K685 attenuates NPM-ALK-induced tumorigenesis

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), a fusion protein generated by a chromosomal translocation, is a causative gene product of anaplastic large cell lymphoma (ALCL). It induces cell proliferation and tumorigenesis by activating the transcription factor, signal transducer and activator of transcription factor 3 (STAT3). We herein demonstrated that STAT3 underwent acetylation at K685 in a manner that was dependent on the kinase activity of NPM-ALK. To investigate the role of STAT3 acetylation in NPM-ALK-induced oncogenesis, we generated Ba/F3 cells expressing NPM-ALK in which STAT3 was silenced by shRNA, named STAT3-KD cells, and then reconstituted wild-type STAT3 or the STAT3 K685R mutant into these cells. The phosphorylation level of the K685R mutant at Y705 and S727 was significantly higher than that of wild-type STAT3 in STAT3-KD cells. The expression of STAT3 target genes, such as IL-6, Pim1, Pim2, and Socs3, was more strongly induced by the reconstitution of the K685R mutant than wild-type STAT3. In addition, the proliferative ability of STAT3-KD cells reconstituted with the K685R mutant was slightly higher than that of STAT3-KD cells reconstituted with wild-type STAT3. In comparisons with the inoculation of STAT3-KD cells reconstituted with wild-type STAT3, the inoculation of STAT3-KD cells reconstituted with the K685R mutant significantly enhanced tumorigenesis and hepatosplenomegaly in nude mice. Collectively, these results revealed for the first time that the acetylation of STAT3 at K685 attenuated NPM-ALK-induced oncogenesis.

JAK2 Alterations in Acute Lymphoblastic Leukemia: Molecular Insights for Superior Precision Medicine Strategies

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer, arising from immature lymphocytes that show uncontrolled proliferation and arrested differentiation. Genomic alterations affecting Janus kinase 2 (JAK2) correlate with some of the poorest outcomes within the Philadelphia-like subtype of ALL. Given the success of kinase inhibitors in the treatment of chronic myeloid leukemia, the discovery of activating JAK2 point mutations and JAK2 fusion genes in ALL, was a breakthrough for potential targeted therapies. However, the molecular mechanisms by which these alterations activate JAK2 and promote downstream signaling is poorly understood. Furthermore, as clinical data regarding the limitations of approved JAK inhibitors in myeloproliferative disorders matures, there is a growing awareness of the need for alternative precision medicine approaches for specific JAK2 lesions. This review focuses on the molecular mechanisms behind ALL-associated JAK2 mutations and JAK2 fusion genes, known and potential causes of JAK-inhibitor resistance, and how JAK2 alterations could be targeted using alternative and novel rationally designed therapies to guide precision medicine approaches for these high-risk subtypes of ALL.

A Rare Co-Occurrence of Triple Mutations in JAK2, CALR, and MPL in the Same Patient with Myelofibrosis

Background. The diagnosis and prognostication of myeloproliferative neoplasm rely on the presence of driver mutations in JAK2, calreticulin (CALR), and MPL mutations. In the past, the presence of these mutations was thought to be mutually exclusive. Since then, there have been multiple reports of the presence of dual mutations. The presence of all three driver mutations in the same patient with myelofibrosis has not been previously described.

CASE

A 73-year-old female underwent a hematological workup in our facility after a routine hemogram performed prior to complex ophthalmological surgery revealed severe thrombocytosis. A comprehensive workup including an NGS panel for MPN driver mutations demonstrated that she had a calreticulin type-1 mutation, a JAK2 exon 14 (JAK2L611S) mutation, and an abnormal hotspot variant for MPL with VAF1%. A bone marrow biopsy confirmed a myeloproliferative neoplasm with grade 2 reticulin fibrosis suggesting primary myelofibrosis. Molecular profiling of bone marrow confirmed the previously noted mutations and an MPLW515R mutation. The patient was started on treatment with hydroxyurea and aspirin with improvement in platelet count and resolution of anemia.

DISCUSSION

The clinical significance of the presence of multiple driver mutations in the same patient is not well understood at this time. There have been 11 publications between 2014 and 2020 that have described dual mutations of JAK2V617F, MPL, and CALR mutations. The JAK2 exon 14 mutation noted, in this case, is JAK2L611S which has not previously been reported in MPN and only reported in 5 cases in the COSMIC database. The JAK2 exon 14 mutation identified in this case is not an established driver mutation for myeloproliferative neoplasm, and its clinical implication remains unknown.

CONCLUSIONS

The above case in addition to recent case reports and case series supports the use of broader NGS sequencing panels for diagnosis and prognostication of MPN. These mutations should not be considered mutually exclusive. The clinical behavior and prognosis of the subgroup with multiple mutations need to be studied in larger series.

EBP2, a novel NPM-ALK-interacting protein in the nucleolus, contributes to the proliferation of ALCL cells by regulating tumor suppressor p53

The oncogenic fusion protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), found in anaplastic large-cell lymphoma (ALCL), localizes to the cytosol, nucleoplasm, and nucleolus. However, the relationship between its localization and transforming activity remains unclear. We herein demonstrated that NPM-ALK localized to the nucleolus by binding to nucleophosmin 1 (NPM1), a nucleolar protein that exhibits shuttling activity between the nucleolus and cytoplasm, in a manner that was dependent on its kinase activity. In the nucleolus, NPM-ALK interacted with Epstein-Barr virus nuclear antigen 1-binding protein 2 (EBP2), which is involved in rRNA biosynthesis. Moreover, enforced expression of NPM-ALK induced tyrosine phosphorylation of EBP2. Knockdown of EBP2 promoted the activation of the tumor suppressor p53, leading to G0 /G1 -phase cell cycle arrest in Ba/F3 cells transformed by NPM-ALK and ALCL patient-derived Ki-JK cells, but not ALCL patient-derived SUDH-L1 cells harboring p53 gene mutation. In Ba/F3 cells transformed by NPM-ALK and Ki-JK cells, p53 activation induced by knockdown of EBP2 was significantly inhibited by Akt inhibitor GDC-0068, mTORC1 inhibitor rapamycin, and knockdown of Raptor, an essential component of mTORC1. These results suggest that the knockdown of EBP2 triggered p53 activation through the Akt-mTORC1 pathway in NPM-ALK-positive cells. Collectively, the present results revealed the critical repressive mechanism of p53 activity by EBP2 and provide a novel therapeutic strategy for the treatment of ALCL.

Identification of a novel functional JAK1 S646P mutation in acute lymphoblastic leukemia

The survival rate of childhood acute lymphoblastic leukemia (ALL) is approaching 90%, while the prognosis of adults remains poor due to the limited therapeutic approaches. In order to identify new targets for ALL, we performed whole-exome sequencing on four adults with B-ALL and discovered a somatic JAK1 S646P mutation. Sanger sequencing of JAK1 was conducted on 53 ALL patients, and two cases exhibited A639G and P960S mutations separately. Functional studies demonstrated that only JAK1 S646P mutation could activate multiple signaling pathways, drive cytokine-independent cell growth, and promote proliferation of malignant cells in nude mice. Moreover, a high sensitivity to the JAK1/2 inhibitor ruxolitinib was observed in S646P mutant model. Exploration in a total of 209 ALL cases showed that JAK1 mutations occur at a frequency of 10.5% in T-ALL (2/19) and 1.6% in B-ALL (3/190). Collectively, our results suggested that JAK1 S646P is an activating mutation in vitro and in vivo. JAK-STAT pathway might represent a promising therapeutic target for ALL.

[Study of cytokine signaling: the quest for immunomodulatory drugs interacting with cytokine production and activity]

I have been engaged in research and education in the fields of immunology and biochemistry at a medical college and college of pharmacy for 40 years. The original reasons why I began studying cytokines and some of the interests that have motivated me to continue working in the field of cytokine research are described: 1) the roles of cytokines in various immunological and inflammatory diseases (e.g., chemokines in bacterial infections and inflammatory diseases, particularly the role of interleukin-5 and eotaxins in eosinophilia); 2) the role of focal adhesion kinase in antiapoptosis and metastasis of melanoma; 3) recent findings on the role of JAK2/STAT pathways, particularly how JAK2V617F mutation induces dysregulated proliferation and tumorigenesis; and 4) the interactions of various chemical compounds and natural products in cytokine gene activation and signaling. Previous discoveries and published findings by my research group are described, along with comments and discussion pertaining to recent developments in the field.

ASC-associated inflammation promotes cecal tumorigenesis in aryl hydrocarbon receptor-deficient mice

The aryl hydrocarbon receptor (AhR) plays a suppressive role in cecal carcinogenesis by CUL4B/AhR-mediated ubiquitylation and degradation of β-catenin, which is activated by xenobiotics and natural ligands. AhR-deficient (AhR(-)(/-)) mice develop cecal tumors with severe inflammation. To elucidate whether the tumors develop autonomously in AhR(-/-) mice due to impaired β-catenin degradation or in association with accelerated inflammation, we performed two kinds of experiments using germ-free (GF) AhR(-/-) mice and compound mutant mice lacking genes for AhR and apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), which plays an essential role in caspase-1 activation in inflammasomes. Both GF AhR(-/-) and AhR(-/-)•ASC(-/-) mice showed considerably reduced tumor development compared with that in AhR(-/-) mice albeit in a 'cancer-prone' state with aberrant β-catenin accumulation. Blocking of the interleukin (IL)-1β signaling pathway by treatment with a caspase-1 inhibitor, YVAD, reduced cecal tumorigenesis in AhR(-/-) mice. Signal transducers and activators of transcription 3 (STAT3) activation was detected in the cecal epithelium of the AhR(-/-) mice due to enhanced IL-6 production. An inhibitor of the STAT3 signaling pathway, AG490 suppressed the tumor formation. ASC-mediated inflammation was also found to play a critical role in tumor development in Apc(Min/+) mice, a mouse model of familial adenomatous polyposis. Collectively, these results revealed an important role of the bacteria-triggered or ASC-mediated inflammation signaling pathway in the intestinal tumorigenesis of mice and suggest a possible chemical therapeutic intervention, including AhR ligands and inhibitors of the inflammation pathway.

Critical roles of Myc-ODC axis in the cellular transformation induced by myeloproliferative neoplasm-associated 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.

Janus kinase deregulation in leukemia and lymphoma

Genetic alterations affecting members of the Janus kinase (JAK) family have been discovered in a wide array of cancers and are particularly prominent in hematological malignancies. In this review, we focus on the role of such lesions in both myeloid and lymphoid tumors. Oncogenic JAK molecules can activate a myriad of canonical downstream signaling pathways as well as directly interact with chromatin in noncanonical processes, the interplay of which results in a plethora of diverse biological consequences. Deciphering these complexities is shedding unexpected light on fundamental cellular mechanisms and will also be important for improved diagnosis, identification of new therapeutic targets, and the development of stratified approaches to therapy.

[Analysis of the mechanism of polycythemia vera by studying JAK2 mutant-induced signaling pathway]

It has been well established that disruption of JAK2 signaling regulation is involved in various hematopoietic disorders; however, the detailed mechanism by which abnormal activation of JAK2 exhibits transforming activity remains to be elucidated. The somatic JAK2 mutation (V617F) was identified in most patients with polycythemia vera (PV). Here, we show that JAK2 V617F mutant was constitutively active and exhibited tumorigenesis activity as a potent oncogene when erythropoietin receptor (EpoR) was co-expressed. To clarify the signaling pathway of JAK2 V617F mutant, we investigated the functional role of downstream transcription factor STAT5 in its induced cellular transformation and tumorigenesis in nude mice. Interestingly, JAK2 V617F mutant failed to exhibit transforming activity when STAT5 activation was inhibited utilizing EpoR mutant (HM). Furthermore, the expression of constitutively active STAT5 mutant (1*6) exhibited transforming activity. Taking these observations together, it is concluded STAT5 plays an essential role in EpoR-JAK2 V617F mutant-induced hematopoietic disorder and would be a good target for the treatment of PV.

ZFP36L1 negatively regulates erythroid differentiation of CD34+ hematopoietic stem cells by interfering with the Stat5b pathway

ZFP36L1 is a member of a family of CCCH tandem zinc finger proteins (TTP family) able to bind to AU-rich elements in the 3'-untranslated region of mRNAs, thereby triggering their degradation. The present study suggests that such mechanism is used during hematopoiesis to regulate differentiation by posttranscriptionally modulating the expression of specific target genes. In particular, it demonstrates that ZFP36L1 negatively regulates erythroid differentiation by directly binding the 3' untranslated region of Stat5b encoding mRNA. Stat5b down-regulation obtained by ZFP36L1 overexpression results, in human hematopoietic progenitors, in a drastic decrease of erythroid colonies formation. These observations have been confirmed by silencing experiments targeting Stat5b and by treating hematopoietic stem/progenitor cells with drugs able to induce ZFP36L1 expression. Moreover, this study shows that different members of ZFP36L1 family act redundantly, because cooverexpression of ZFP36L1 and family member ZFP36 determines a cumulative effect on Stat5b down-regulation. This work describes a mechanism underlying ZFP36L1 capability to regulate hematopoietic differentiation and suggests a new target for the therapy of hematopoietic diseases involving Stat5b/JAK2 pathway, such as chronic myeloproliferative disorders.

Perspectives for the use of structural information and chemical genetics to develop inhibitors of Janus kinases

Gain-of-function mutations in the genes encoding Janus kinases have been discovered in various haematologic diseases. Jaks are composed of a FERM domain, an SH2 domain, a pseudokinase domain and a kinase domain, and a complex interplay of the Jak domains is involved in regulation of catalytic activity and association to cytokine receptors. Most activating mutations are found in the pseudokinase domain. Here we present recently discovered mutations in the context of our structural models of the respective domains. We describe two structural hotspots in the pseudokinase domain of Jak2 that seem to be associated either to myeloproliferation or to lymphoblastic leukaemia, pointing at the involvement of distinct signalling complexes in these disease settings. The different domains of Jaks are discussed as potential drug targets. We present currently available inhibitors targeting Jaks and indicate structural differences in the kinase domains of the different Jaks that may be exploited in the development of specific inhibitors. Moreover, we discuss recent chemical genetic approaches which can be applied to Jaks to better understand the role of these kinases in their biological settings and as drug targets.

STAT5 activation is critical for the transformation mediated by myeloproliferative disorder-associated JAK2 V617F mutant

It has been well established that disruption of JAK2 signaling regulation is involved in various hematopoietic disorders; however, the detailed mechanism by which abnormal activation of JAK2 exhibits transforming activity remains to be elucidated. Here, to clarify the functional role of the erythropoietin receptor (EpoR) and its downstream transcription factor STAT5 in the abnormal activation of JAK2-induced hematopoietic diseases, we generated a stable transfectant of Ba/F3 cells expressing EpoR and analyzed the molecular mechanism of how JAK2 mutation induces cell growth disorder. JAK2 V617F mutant exhibited transforming activity when EpoR was coexpressed. According to a study utilizing several truncated mutants of EpoR, the ability of EpoR to facilitate the transforming activity of JAK2 V617F mutant required the intracellular domain to interact with STAT5. Strikingly, once the truncated EpoR (EpoR-H) was mutated on Tyr-343, the phosphorylation of which is known to be important for interaction with STAT5, JAK2 V617F mutant failed to exhibit transforming activity, suggesting that STAT5 is critical for JAK2 mutant-induced hematopoietic disorder. Furthermore, the expression of the constitutively active STAT5 mutant exhibited transforming activity in Ba/F3 cells, and short hairpin RNA-mediated knockdown of STAT5 significantly inhibited the transforming activity of JAK2 V617F mutant. Taking these observations together, STAT5 plays an essential role in EpoR-JAK2 V617F mutant-induced hematopoietic disorder. Although it remains unclear why the presence of EpoR is required to activate oncogenic signaling via the JAK2 mutant and STAT5, its interacting ability is a target for the treatment of these hematopoietic diseases.

Combined inhibition of Janus kinase 1/2 for the treatment of JAK2V617F-driven neoplasms: selective effects on mutant cells and improvements in measures of disease severity

PURPOSE

Deregulation of the Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathway is a hallmark for the Philadelphia chromosome-negative myeloproliferative diseases polycythemia vera, essential thrombocythemia, and primary myelofibrosis. We tested the efficacy of a selective JAK1/2 inhibitor in cellular and in vivo models of JAK2-driven malignancy.

EXPERIMENTAL DESIGN

A novel inhibitor of JAK1/2 was characterized using kinase assays. Cellular effects of this compound were measured in cell lines bearing the JAK2V617F or JAK1V658F mutation, and its antiproliferative activity against primary polycythemiavera patient cells was determined using clonogenic assays. Antineoplastic activity in vivo was determined using a JAK2V617F-driven xenograft model, and effects of the compound on survival, organomegaly, body weight, and disease-associated inflammatory markers were measured.

RESULTS

INCB16562 potently inhibited proliferation of cell lines and primary cells from PV patients carrying the JAK2V617F or JAK1V658F mutation by blocking JAK-STAT signaling and inducing apoptosis. In vivo, INCB16562 reduced malignant cell burden, reversed splenomegaly and normalized splenic architecture, improved body weight gains, and extended survival in a model of JAK2V617F-driven hematologic malignancy. Moreover, these mice suffered from markedly elevated levels of inflammatory cytokines, similar to advanced myeloproliferative disease patients, which was reversed upon treatment.

CONCLUSIONS

These data showed that administration of the dual JAK1/2 inhibitor INCB16562 reduces malignant cell burden, normalizes spleen size and architecture, suppresses inflammatory cytokines, improves weight gain, and extends survival in a rodent model of JAK2V617F-driven hematologic malignancy. Thus, selective inhibitors of JAK1 and JAK2 represent a novel therapy for the patients with myeloproliferative diseases and other neoplasms associated with JAK dysregulation.