Twins with different personalities: STAT5B-but not STAT5A-has a key role in BCR/ABL-induced leukemia

A novel function of STAT3β in suppressing interferon response improves outcome in acute myeloid leukemia

Signal transducer and activator of transcription 3 (STAT3) is frequently overexpressed in patients with acute myeloid leukemia (AML). STAT3 exists in two distinct alternatively spliced isoforms, the full-length isoform STAT3α and the C-terminally truncated isoform STAT3β. While STAT3α is predominantly described as an oncogenic driver, STAT3β has been suggested to act as a tumor suppressor. To elucidate the role of STAT3β in AML, we established a mouse model of STAT3β-deficient, MLL-AF9-driven AML. STAT3β deficiency significantly shortened survival of leukemic mice confirming its role as a tumor suppressor. Furthermore, RNA sequencing revealed enhanced STAT1 expression and interferon (IFN) signaling upon loss of STAT3β. Accordingly, STAT3β-deficient leukemia cells displayed enhanced sensitivity to blockade of IFN signaling through both an IFNAR1 blocking antibody and the JAK1/2 inhibitor Ruxolitinib. Analysis of human AML patient samples confirmed that elevated expression of IFN-inducible genes correlated with poor overall survival and low STAT3β expression. Together, our data corroborate the tumor suppressive role of STAT3β in a mouse model in vivo. Moreover, they provide evidence that its tumor suppressive function is linked to repression of the STAT1-mediated IFN response. These findings suggest that the STAT3β/α mRNA ratio is a significant prognostic marker in AML and holds crucial information for targeted treatment approaches. Patients displaying a low STAT3β/α mRNA ratio and unfavorable prognosis could benefit from therapeutic interventions directed at STAT1/IFN signaling.

JAK/STAT in leukemia: a clinical update

Over the past three decades, considerable efforts have been expended on understanding the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway in leukemia, following the identification of the JAK2V617F mutation in myeloproliferative neoplasms (MPNs). The aim of this review is to summarize the latest progress in our understanding of the involvement of the JAK/STAT signaling pathway in the development of leukemia. We also attempt to provide insights into the current use of JAK/STAT inhibitors in leukemia therapy and explore pertinent clinical trials in this field.

Myeloproliferative Neoplasms: Diseases Mediated by Chronic Activation of Signal Transducer and Activator of Transcription (STAT) Proteins

Myeloproliferative neoplasms (MPNs) are hematopoietic diseases characterized by the clonal expansion of single or multiple lineages of differentiated myeloid cells that accumulate in the blood and bone marrow. MPNs are grouped into distinct categories based on key clinical presentations and distinctive mutational hallmarks. These include chronic myeloid leukemia (CML), which is strongly associated with the signature BCR::ABL1 gene translocation, polycythemia vera (PV), essential thrombocythemia (ET), and primary (idiopathic) myelofibrosis (PMF), typically accompanied by molecular alterations in the JAK2, MPL, or CALR genes. There are also rarer forms such as chronic neutrophilic leukemia (CNL), which involves mutations in the CSF3R gene. However, rather than focusing on the differences between these alternate disease categories, this review aims to present a unifying molecular etiology in which these overlapping diseases are best understood as disruptions of normal hematopoietic signaling: specifically, the chronic activation of signaling pathways, particularly involving signal transducer and activator of transcription (STAT) transcription factors, most notably STAT5B, leading to the sustained stimulation of myelopoiesis, which underpins the various disease sequalae.

Interplay between signal transducers and activators of transcription (STAT) proteins and cancer: involvement, therapeutic and prognostic perspective

Signal transducers and activators of transcription or STAT are proteins that consist of various transcription factors that are responsible for activating genes regarding cell proliferation, differentiation, and apoptosis. They commonly activate several cytokine, growth, or hormone factors via the JAK-STAT signaling pathway by tyrosine phosphorylation which are responsible for giving rise to numerous immune responses. Mutations within the Janus-Kinases (JAKs) or the STATs can set off the commencement of various malfunctions of the immune system of the body; carcinogenesis being an inevitable outcome. STATs are known to act as both oncogenes and tumor suppressor genes which makes it a hot topic of investigation. Various STATs related mechanisms are currently being investigated to analyze its potential of serving as a therapeutic base for numerous immune diseases and cancer; a deeper understanding of the molecular mechanisms involved in the signaling pathways can contribute to the same. This review will throw light upon each STAT member in causing cancer malignancies by affecting subsequent signaling pathways and its genetic and epigenetic associations as well as various inhibitors that could be used to target these pathways thereby devising new treatment options. The review will also focus upon the therapeutic advances made in cancers that most commonly affect people and discuss how STAT genes are identified as prognostic markers.

STAT5b gain-of-function disease in a child with mycobacterial osteomyelitis of the skull: rare presentation of an emerging disease entity

PURPOSE

STAT proteins play a key role in several cellular functions related to cell development, differentiation, proliferation, and survival. Persistent STAT activation due to somatic STAT5b^N642H gain-of-function mutation is a rare mechanism of STAT dysregulation that results in hypereosinophilia, frequent infections, leukemias, and pulmonary diseases. Herein, we describe a case of a child with a rare early onset STAT5b gain-of-function disease treated with targeted JAK inhibition who developed a cranial Mycobacterium avium osteomyelitis.

METHODS

A 3-year-old male with a known STAT5b gain-of-function mutation presented with a 10-day history of a firm, immobile, non-painful cranial mycobacterium mass with dural infiltration located anterior to the coronal suture. Stepwise management finalized with complete resection of the lesion with calvarial reconstruction. A case-based literature review was performed evaluating all patients with this mutation who developed cranial disease.

RESULTS

The patient was symptom and lesion-free at 1 year since surgical resection and initiation of triple mycobacterial pharmacotherapy. Our literature review demonstrated the rarity of this disease, as well as other presentations of this disease in other patients.

CONCLUSION

Patients with STAT5b gain-of-function mutations have attenuated Th1 responses and are treated with medications, such as JAK inhibitors, which further inhibit other STAT proteins that regulate immunity against rare infectious entities, such as mycobacterium. Our case highlights the importance of considering these rare infections in patients on JAK inhibitors and with STAT protein mutations. Possessing a clear mechanistic understanding of this genetic mutation, its downstream effect, and the consequences of treatment may enhance a physician's diagnostic and clinical management of similar patients in the future.

Jak2/STAT6/c-Myc pathway is vital to the pathogenicity of Philadelphia-positive acute lymphoblastic leukemia caused by P190BCR-ABL

BACKGROUND

The Philadelphia chromosome encodes the BCR-ABL fusion protein, which has two primary subtypes, P210 and P190. P210 and P190 cause Philadelphia-positive chronic myeloid leukemia (Ph+ CML) and Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL), respectively. The Ph+ ALL is more malignant than Ph+ CML in disease phenotype and progression. This implies the key pathogenic molecules and regulatory mechanisms caused by BCR-ABL in two types of leukemia are different. It is reported that STAT6 was significantly activated only in P190 transformed cells. However, the potential role and the mechanism of STAT6 activation in Ph+ ALL and its activation mechanism by P190 are still unknown.

METHODS

The protein and mRNA levels of STAT6, c-Myc, and other molecules were measured by western blot and quantitative real-time PCR. The STAT6 inhibitor AS1517499 was used to specifically inhibit p-STAT6. The effect of p-STAT6 inhibition on Ph+ CML and Ph+ ALL cells was identified by CCK-8 and FCM assay. Dual luciferase reporter and ChIP assay were performed to confirm the direct binding between STAT6 and c-Myc. The impact of STAT6 inhibition on tumor progression was detected in Ph+ CML and Ph+ ALL mouse models.

RESULTS

Our results demonstrated that P210 induced CML-like disease, and P190 caused the more malignant ALL-like disease in mouse models. STAT6 was activated in P190 cell lines but not in P210 cell lines. Inhibition of STAT6 suppressed the malignancy of Ph+ ALL in vitro and in vivo, whereas it had little effect on Ph+ CML. We confirmed that p-STAT6 regulated the transcription of c-Myc, and STAT6 was phosphorylated by p-Jak2 in P190 cell lines, which accounted for the discrepant expression of p-STAT6 in P190 and P210 cell lines. STAT6 inhibition synergized with imatinib in Ph+ ALL cells.

CONCLUSIONS

Our study suggests that STAT6 activation plays an essential role in the development of Ph+ ALL and may be a potential therapeutic target in Ph+ ALL. Video abstract.

Stafiba: A STAT5-Selective Small-Molecule Inhibitor

The transcription factors STAT5a and STAT5b are constitutively active in many human tumors. Combined inhibition of both STAT5 proteins is a valuable approach with promising applications in tumor biology. We recently reported resorcinol bisphosphate as a moderately active inhibitor of the protein-protein interaction domains, the SH2 domains, of both STAT5a and STAT5b. Here, we describe the development of resorcinol bisphosphate to Stafiba, a phosphatase-stable inhibitor of STAT5a and STAT5b with activity in the low micromolar concentration range. Our data provide insights into the structure-activity relationships of resorcinol bisphosphates and the corresponding bisphosphonates for use as inhibitors of both STAT5a and STAT5b.

Genetics of Immune Dysregulation and Cancer Predisposition: Two Sides of the Same Coin

Approximately 10% of cancers have a hereditary predisposition. However, no genetic diagnosis is available in 60%-80% of familial cancers. In some of these families, immune dysregulation-mediated disease is frequent. The immune system plays a critical role in identifying and eliminating tumors; thus, dysregulation of the immune system can increase the risk of developing cancer. This review focuses on some of the genes involved in immune dysregulation the promote the risk for cancer. Genetic counseling for patients with cancer currently focuses on known genes that raise the risk of cancer. In missing hereditary familial cases, the history family of immune dysregulation should be recorded, and genes related to the immune system should be analyzed in relevant families. On the other hand, patients with immune disorders diagnosed with a pathogenic mutation in an immune regulatory gene may have an increased risk of cancer. Therefore, those patients need to be under surveillance for cancer. Gene panel and exome sequencing are currently standard methods for genetic diagnosis, providing an excellent opportunity to jointly test cancer and immune genes.

Down-regulation of hepatic expression of GHR/STAT5/IGF-1 signaling pathway fosters development and aggressiveness of HCV-related hepatocellular carcinoma: Crosstalk with Snail-1 and type 2 transforming growth factor-beta receptor

Background and aims

So far, few clinical trials are available concerning the role of growth hormone receptor (GHR)/signal transducer and activator of transcription 5 (STAT5)/insulin like growth factor-1 (IGF-1) axis in hepatocarcinogenesis. The aim of this study was to evaluate the hepatic expression of GHR/STAT5/IGF-1 signaling pathway in hepatocellular carcinoma (HCC) patients and to correlate the results with the clinico-pathological features and disease outcome. The interaction between this signaling pathway and some inducers of epithelial-mesenchymal transition (EMT), namely Snail-1 and type 2 transforming growth factor-beta receptor (TGFBR2) was studied too.

Material and methods

A total of 40 patients with HCV-associated HCC were included in this study. They were compared to 40 patients with HCV-related cirrhosis without HCC, and 20 healthy controls. The hepatic expression of GHR, STAT5, IGF-1, Snail-1 and TGFBR2 proteins were assessed by immunohistochemistry.

Results

Compared with cirrhotic patients without HCC and healthy controls, cirrhotic patients with HCC had significantly lower hepatic expression of GHR, STAT5, and IGF-1proteins. They also displayed significantly lower hepatic expression of TGFBR2, but higher expression of Snail-1 versus the non-HCC cirrhotic patients and controls. Serum levels of alpha-fetoprotein (AFP) showed significant negative correlations with hepatic expression of GHR (r = -0.31; p = 0.029) and STAT5 (r = -0.29; p = 0.04). Hepatic expression of Snail-1 also showed negative correlations with GHR, STAT5, and IGF-1 expression (r = -0.55, p = 0.02; r = -0.472, p = 0.035, and r = -0.51, p = 0.009, respectively), whereas, hepatic expression of TGFBR2 was correlated positively with the expression of all these proteins (r = 0.47, p = 0.034; 0.49, p = 0.023, and r = 0.57, p<0.001, respectively). Moreover, we reported that decreased expression of GHR was significantly associated with serum AFP level>100 ng/ml (p = 0.048), increased tumor size (p = 0.02), vascular invasion (p = 0.002), and advanced pathological stage (p = 0.01). Similar significant associations were found between down-regulation of STAT5 expression and AFP level > 100 ng/ml (p = 0.006), vascular invasion (p = 0.009), and advanced tumor stage (p = 0.007). Also, attenuated expression of IGF-1 showed a significant association with vascular invasion (p < 0.001). Intriguingly, we detected that lower expression of GHR, STAT5 and IGF-1 were considered independent predictors for worse outcome in HCC.

Conclusion

Decreased expression of GHR/STAT5/IGF-1 signaling pathway may have a role in development, aggressiveness, and worse outcome of HCV-associated HCC irrespective of the liver functional status. Snail-1 and TGFBR2 as inducers of EMT may be key players. However, large prospective multicenter studies are needed to validate these results.

Dissection of the MEF2D-IRF8 transcriptional circuit dependency in acute myeloid leukemia

Transcriptional dysregulation is a prominent feature in leukemia. Here, we systematically surveyed transcription factor (TF) vulnerabilities in leukemia and uncovered TF clusters that exhibit context-specific vulnerabilities within and between different subtypes of leukemia. Among these TF clusters, we demonstrated that acute myeloid leukemia (AML) with high IRF8 expression was addicted to MEF2D. MEF2D and IRF8 form an autoregulatory loop via direct binding to mutual enhancer elements. One important function of this circuit in AML is to sustain PU.1/MEIS1 co-regulated transcriptional outputs via stabilizing PU.1’s chromatin occupancy. We illustrated that AML could acquire dependency on this circuit through various oncogenic mechanisms that results in the activation of their enhancers. In addition to forming a circuit, MEF2D and IRF8 can also separately regulate gene expression, and dual perturbation of these two TFs leads to a more robust inhibition of AML proliferation. Collectively, our results revealed a TF circuit essential for AML survival.

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MEF2D is a context-specific vulnerability in IRF8^hi AML

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MEF2D and IRF8 form a transcriptional circuit via binding to each other’s enhancers

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MEF2D-IRF8 circuit supports PU.1’s chromatin occupancy and transcriptional output

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MEF2D and IRF8 can regulate separate gene expression programs alongside the circuit

Comparing machine learning algorithms to predict 5-year survival in patients with chronic myeloid leukemia

Introduction

Chronic myeloid leukemia (CML) is a myeloproliferative disorder resulting from the translocation of chromosomes 19 and 22. CML includes 15–20% of all cases of leukemia. Although bone marrow transplant and, more recently, tyrosine kinase inhibitors (TKIs) as a first-line treatment have significantly prolonged survival in CML patients, accurate prediction using available patient-level factors can be challenging. We intended to predict 5-year survival among CML patients via eight machine learning (ML) algorithms and compare their performance.

Methods

The data of 837 CML patients were retrospectively extracted and randomly split into training and test segments (70:30 ratio). The outcome variable was 5-year survival with potential values of alive or deceased. The dataset for the full features and important features selected by minimal redundancy maximal relevance (mRMR) feature selection were fed into eight ML techniques, including eXtreme gradient boosting (XGBoost), multilayer perceptron (MLP), pattern recognition network, k-nearest neighborhood (KNN), probabilistic neural network, support vector machine (SVM) (kernel = linear), SVM (kernel = RBF), and J-48. The scikit-learn library in Python was used to implement the models. Finally, the performance of the developed models was measured using some evaluation criteria with 95% confidence intervals (CI).

Results

Spleen palpable, age, and unexplained hemorrhage were identified as the top three effective features affecting CML 5-year survival. The performance of ML models using the selected-features was superior to that of the full-features dataset. Among the eight ML algorithms, SVM (kernel = RBF) had the best performance in tenfold cross-validation with an accuracy of 85.7%, specificity of 85%, sensitivity of 86%, F-measure of 87%, kappa statistic of 86.1%, and area under the curve (AUC) of 85% for the selected-features. Using the full-features dataset yielded an accuracy of 69.7%, specificity of 69.1%, sensitivity of 71.3%, F-measure of 72%, kappa statistic of 75.2%, and AUC of 70.1%.

Conclusions

Accurate prediction of the survival likelihood of CML patients can inform caregivers to promote patient prognostication and choose the best possible treatment path. While external validation is required, our developed models will offer customized treatment and may guide the prescription of personalized medicine for CML patients.

PDGFRβ promotes oncogenic progression via STAT3/STAT5 hyperactivation in anaplastic large cell lymphoma

BACKGROUND

Anaplastic large cell lymphoma (ALCL) is an aggressive non-Hodgkin T cell lymphoma commonly driven by NPM-ALK. AP-1 transcription factors, cJUN and JUNb, act as downstream effectors of NPM-ALK and transcriptionally regulate PDGFRβ. Blocking PDGFRβ kinase activity with imatinib effectively reduces tumor burden and prolongs survival, although the downstream molecular mechanisms remain elusive.

METHODS AND RESULTS

In a transgenic mouse model that mimics PDGFRβ-driven human ALCL in vivo, we identify PDGFRβ as a driver of aggressive tumor growth. Mechanistically, PDGFRβ induces the pro-survival factor Bcl-xL and the growth-enhancing cytokine IL-10 via STAT5 activation. CRISPR/Cas9 deletion of both STAT5 gene products, STAT5A and STAT5B, results in the significant impairment of cell viability compared to deletion of STAT5A, STAT5B or STAT3 alone. Moreover, combined blockade of STAT3/5 activity with a selective SH2 domain inhibitor, AC-4-130, effectively obstructs tumor development in vivo.

CONCLUSIONS

We therefore propose PDGFRβ as a novel biomarker and introduce PDGFRβ-STAT3/5 signaling as an important axis in aggressive ALCL. Furthermore, we suggest that inhibition of PDGFRβ or STAT3/5 improve existing therapies for both previously untreated and relapsed/refractory ALK+ ALCL patients.

Recent research on the association between signal transducer and activator of transcription 5 and childhood acute lymphoblastic leukemia

Signal transducer and activator of transcription 5 (STAT5) can be involved in the processes such as cell proliferation, differentiation, apoptosis, and hematopoiesis, and its dysregulation is closely associated with the development and progression of malignant tumors including leukemia and may affect the treatment outcome and prognosis of pediatric patients. Identification of STAT5 can facilitate targeted therapy to improve the response rate of children with acute lymphoblastic leukemia. This article reviews the impact of STAT5 on the development/progression, targeted therapy strategies and the prognosis of childhood acute lymphoblastic leukemia.

In vivo impact of JAK3 A573V mutation revealed using zebrafish

Background

Janus kinase 3 (JAK3) acts downstream of the interleukin-2 (IL-2) receptor family to play a pivotal role in the regulation of lymphoid cell development. Activating JAK3 mutations are associated with a number of lymphoid and other malignancies, with mutations within the regulatory pseudokinase domain common.

Methods

The pseudokinase domain mutations A572V and A573V were separately introduced into the highly conserved zebrafish Jak3 and transiently expressed in cell lines and zebrafish embryos to examine their activity and impact on early T cells. Genome editing was subsequently used to introduce the A573V mutation into the zebrafish genome to study the effects of JAK3 activation on lymphoid cells in a physiologically relevant context throughout the life-course.

Results

Zebrafish Jak3 A573V produced the strongest activation of downstream STAT5 in vitro and elicited a significant increase in T cells in zebrafish embryos. Zebrafish carrying just a single copy of the Jak3 A573V allele displayed elevated embryonic T cells, which continued into adulthood. Hematopoietic precursors and NK cells were also increased, but not B cells. The lymphoproliferative effects of Jak3 A573V in embryos was shown to be dependent on zebrafish IL-2Rγc, JAK1 and STAT5B equivalents, and could be suppressed with the JAK3 inhibitor Tofacitinib.

Conclusions

This study demonstrates that a single JAK3 A573V allele expressed from the endogenous locus was able to enhance lymphopoiesis throughout the life-course, which was mediated via an IL-2Rγc/JAK1/JAK3/STAT5 signaling pathway and was sensitive to Tofacitinib. This extends our understanding of oncogenic JAK3 mutations and creates a novel model to underpin further translational investigations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00018-022-04361-8.

STAT5A modulates CDYL2/SLC7A6 pathway to inhibit the proliferation and invasion of hepatocellular carcinoma by targeting to mTORC1

Chromodomain Y-like 2 (CDYL2), as a member of CDY family known to be involved in spermatogenesis, has been reported to participate in breast cancer development recently, but its exact biological role in hepatocellular carcinoma (HCC) remains unclear. Here, we observed that CDYL2 was down-regulated in human primary HCC tissues and the low levels of CDYL2 expression were correlated with poor survival. Gain- and loss-of-function experiments showed that CDYL2 inhibited the proliferation and metastasis of HCC cells in vitro and in vivo. Mechanistically, CDYL2 down-regulates solute carrier family 7 member 6 (SLC7A6) by decreasing the enrichment of H3K4me3 on the promoter region of SLC7A6. Additionally, we also found that signal transducer and activator of transcription 5A (STAT5A) could directly and positively regulate the expression of CDYL2. Thus, CDYL2 was regulated by STAT5A, and suppressed the amino acid transportation through down-regulation of SLC7A6, and then inhibits the mTORC1/S6K pathway, a master regulator of cell growth. Consistently, CDYL2 expression correlated significantly with STAT5A and SLC7A6 expression in HCC. Collectively, we propose a model for a STAT5A/CDYL2/SLC7A6 axis that provides novel insight into CDYL2, which may serve as a potential factor for predicting prognosis and a therapeutic target for HCC patients.

Stat5b inhibition blocks proliferation and tumorigenicity of glioblastoma stem cells derived from a de novo murine brain cancer model

Glioblastoma (GBM) is the most common and malignant type of brain cancer in adults with poor prognosis. GBM stem cells (GSCs) reside within niches in GBM tissues and contribute to recurrence and therapy resistance. Previous studies have shown that expression of leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5), a Wnt pathway-related stem cell marker, correlates with a poor prognosis in GBM, and its knockdown in GSCs induces apoptosis accompanied with downregulation of signal transducer and activator of transcription 5b (Stat5b). Here, we show that Stat5b co-localizes with Lgr5 in hypoxia-inducible factor 2α (Hif2α)-positive regions in GBM tissues. Functional analyses using GSCs derived from a murine de novo GBM model induced by oncogenic genes transduction using the Sleeping-Beauty transposon system revealed that expression of Stat5b was induced by culturing under hypoxia together with Lgr5, repressed by Hif2α knockdown, and reduced by Lgr5 knockdown or a Wnt/β-catenin signaling inhibitor ICG-001 treatment. Stat5b inhibition in the GSCs induced apoptosis and caused downregulation of Cyclin E2 resulted in blockade of entry into S-phase in the cell cycle. Disruption of Stat5b in an orthotopic transplantation model significantly prolongs event-free survival. These results suggest that Stat5b, regulated by hypoxia and the Wnt pathway, plays an important role in the maintenance and tumorigenicity of GSCs and may be a promising therapeutic molecular target to attack GSCs.

Clinicopathological and molecular genomic features of monomorphic epitheliotropic intestinal T-cell lymphoma in the Chinese population: a study of 20 cases

Background

Monomorphic epitheliotropic T-cell lymphoma (MEITL) is an aggressive non-Hodgkin lymphoma with a high fatality rate. This study was aimed to explore the clinicopathological and molecular genetic features of MEITL in the Chinese population.

Methods

A retrospective analysis was performed based on the clinical manifestations and pathological features of 20 Chinese MEITL. 9 cases with paired diseased-normal tissues were also analyzed for molecular information by whole-exome sequencing.

Results

There were 14 men and 6 women with a median age of 58.5 (28-81) years. 17(17/20) lesions were located in the jejunum or ileum; 13(13/20) cases had ulcers or perforations. Microscopically, except for 1(1/20) case of pleomorphic cells, the monomorphic, middle-sized tumor cells infiltrating into the intestinal epithelial and peripheral intestinal mucosa recess could be seen in the other 19 cases. Immunohistochemistry showed that most of the tumor cells in MEITL were positive for CD3(20/20), CD8(17/20), CD43(19/20), and CD56(15/20), but negative for CD5(20/20). The most frequently mutated genes of these Chinese cases were STAT5B (4/9) and TP53 (4/9), not SETD2(2/9). JAK3 mutations (3/9) were also detected with a high mutated frequency. We demonstrated that mutations of JAK-STAT pathway-related genes and the amplification of Chromosome 9q appeared at the same time in most cases(5/9).

Conclusions

The clinicopathological features were consistent with that in previous western studies, but a special case with pleomorphic cells was found in this study. The co-occurrence of JAK-STAT pathway-related gene mutations and the amplification of Chr9q is a molecular feature of MEITL.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13000-021-01173-5.

High STAT5A Expression is Associated with Major Molecular Response Achievement Failure of Chronic Phase Chronic Myeloid Leukemia Patients Receiving Hydroxyurea before Imatinib: A Cross-sectional Study

BACKGROUND: STAT5 is a transcriptional factor which when highly expressed in chronic myeloid leukemia (CML) cells stimulate proliferation and mediate resistance from tyrosine kinase inhibitors, resulting in major molecular response (MMR) failure. STAT5 has two isoforms, STAT5A and STAT5B. However, prolonged use of imatinib appears to only upregulate STAT5A pathway. In addition, the resistance conferred by STAT5A does not extend to other drugs such as hydroxyurea. Hence, STAT5A and STAT5B might have different functions in CML cells. AIM: The objective of the study was to determine the association of STAT5A and STAT5B expression with MMR failure in CML patients. METHODS: This was a cross-sectional study of CML patients in chronic phase with age ≥ 18 years old, receiving IM therapy ≥ 12 months, and previously given hydroxyurea. MMR status was evaluated and patients were categorized as achieved or failed to achieve MMR. Expression levels of STAT5A and STAT5B were conducted using RT-PCR methods. Associations between STAT5A expression, STAT5B expression, hydroxyurea duration, and imatinib duration with MMR achievement were calculated using logistic regression. RESULTS: A total of 118 patients were analyzed; 71.1% failed to achieve MMR. Multivariate logistic regression analysis showed statistically significant association between high STAT5A expression (odds ratio [OR]: 3.852; 95% confidence interval [CI]: 1.420–10.452; p = 0.008), STAT5A/STAT5B interaction (OR: 0.150; 95% CI: 0.038–0.593; p = 0.007), longer hydroxyurea administration (OR: 3.882; 95% CI: 1.023–14.733; p = 0.046), and shorter imatinib administration (OR: 0.333; 95% CI: 0.132–0.840; p = 0.020) with MMR achievement failure. After adjusting STAT5A expression with STAT5A/STAT5B interaction, high STAT5A expression independently increased the likelihood of MMR achievement failure only in high expression STAT5B patients (OR: 3.852; 95% CI: 1.420–10.452; p = 0.008). CONCLUSION: High STAT5A expression which is induced by high STAT5B is associated with MMR achievement failure of chronic phase CML patients who received hydroxyurea before imatinib. Longer duration of hydroxyurea and shorter duration of IM confound of STAT5A expression to MMR achievement failure.

Identification of mutations that cooperate with defects in B cell transcription factors to initiate leukemia

The transcription factors PAX5, IKZF1, and EBF1 are frequently mutated in B cell acute lymphoblastic leukemia (B-ALL). We demonstrate that compound heterozygous loss of multiple genes critical for B and T cell development drives transformation, including Pax5^+/-xEbf1^+/-, Pax5^+/-xIkzf1^+/-, and Ebf1^+/-xIkzf1^+/- mice for B-ALL, or Tcf7^+/-xIkzf1^+/- mice for T-ALL. To identify genetic defects that cooperate with Pax5 and Ebf1 compound heterozygosity to initiate leukemia, we performed a Sleeping Beauty (SB) transposon screen that identified cooperating partners including gain-of-function mutations in Stat5b (~65%) and Jak1 (~68%), or loss-of-function mutations in Cblb (61%) and Myb (32%). These findings underscore the role of JAK/STAT5B signaling in B cell transformation and demonstrate roles for loss-of-function mutations in Cblb and Myb in transformation. RNA-Seq studies demonstrated upregulation of a PDK1>SGK3>MYC pathway; treatment of Pax5^+/-xEbf1^+/- leukemia cells with PDK1 inhibitors blocked proliferation in vitro. In addition, we identified a conserved transcriptional gene signature between human and murine leukemias characterized by upregulation of myeloid genes, most notably involving the GM-CSF pathway, that resemble a B cell/myeloid mixed-lineage leukemia. Thus, our findings identify multiple mechanisms that cooperate with defects in B cell transcription factors to generate either progenitor B cell or mixed B/myeloid-like leukemias.

[Clinical characteristics of T-cell large granular lymphoblastic leukemia with STAT3 gene mutation]

目的

探讨携带STAT3基因突变的T细胞大颗粒淋巴细胞白血病（T-LGLL）患者的临床特征，为此类患者的临床管理提供参考。

方法

回顾性分析2009至2019年就诊于江苏省人民医院的T-LGLL患者的临床资料，比较STAT3突变患者与未突变患者的基线临床数据、治疗反应及生存结局。

结果

共纳入80例患者，STAT3未突变组66例，STAT3突变组14例（17.5％），其中Y640F突变发生频率最高（42.9％）。STAT3突变组与STAT3未突变组相比，HGB减低（67.5 g/L对82.5 g/L，P＝0.018），中性粒细胞计数减少（0.665×10⁹/L对1.465×10⁹/L，P<0.001），乳酸脱氢酶升高（229 U/L对198 U/L，P＝0.041），铁蛋白升高（402.5 g/L对236.0 g/L，P＝0.029），TCR Vβ亚家族表达率升高（89.2％对65.4％，P＝0.014），具备治疗指征患者比例升高（100％对74％，P＝0.033）。STAT3突变组与未突变组一线免疫抑制治疗的完全缓解率分别为38.5％和32.7％，差异无统计学意义（P＝0.748）。STAT3突变组与未突变组一线免疫抑制治疗的总有效率分别为69.2％和69.4％，差异无统计学意义（P＝1.000）。中位随访63（2～121）个月，两组总生存时间（均未达到）的差异无统计学意义（P＝0.170）。

结论

STAT3基因突变的T-LGLL患者可能有更高的肿瘤负荷和治疗需求，一线应用免疫抑制剂疗效良好。STAT3基因突变对T-LGLL患者预后的意义尚需进一步验证。

A STAT5B-CD9 axis determines self-renewal in hematopoietic and leukemic stem cells

The transcription factors STAT5A and STAT5B are critical in hematopoiesis and leukemia. They are widely believed to have redundant functions but we describe a unique role for STAT5B in driving the self-renewal of hematopoietic and leukemic stem cells (HSCs/LSCs). We find STAT5B to be specifically activated in HSCs and LSCs, where it induces many genes associated with quiescence and self-renewal, including the surface marker CD9. Levels of CD9 represent a prognostic marker for patients with STAT5-driven leukemia and our findings suggest that anti-CD9 antibodies may be useful in their treatment to target and eliminate LSCs. We show that it is vital to consider STAT5A and STAT5B as distinct entities in normal and malignant hematopoiesis.

Targeting HSPA8 inhibits proliferation via downregulating BCR-ABL and enhances chemosensitivity in imatinib-resistant chronic myeloid leukemia cells

The resistance to tyrosine kinase inhibitors is currently a major problem for chronic myeloid leukemia (CML) treatment and HSPA8 is highly expressed and a hallmark of poor prognosis in several human cancers. However, its role in imatinib-resistant CML (IR-CML) cells remains undetermined. Here, we determined HSPA8 was overexpressed in IR-CML cells and associated with imatinib resistance. HSPA8 ablation could downregulate BCR-ABL/STAT5 and BCR-ABL/AKT signaling pathways, dramatically induce proliferation inhibition, autophagy, G0/G1 phase cell cycle arrest but not apoptosis in IR-CML cells. Significantly, HSPA8 ablation enhanced the antitumor activity of imatinib via promoting apoptosis in vitro and vivo. These findings unraveled that HSPA8 ablation inhibits proliferation via downregulating BCR-ABL and enhances chemosensitivity of imatinib in IR-CML cells, which investigate the role and molecular mechanism of HSPA8 in IR-CML cells and suggest that HSPA8 may be a potential target for IR-CML treatment.

Janus kinase inhibitors ruxolitinib and baricitinib impair glycoprotein-VI mediated platelet function

Several Janus kinase (JAK) inhibitors (jakinibs) have recently been approved to treat inflammatory, autoimmune and hematological conditions. Despite emerging roles for JAKs and downstream signal transducer and activator of transcription (STAT) proteins in platelets, it remains unknown whether jakinibs affect platelet function. Here, we profile platelet biochemical and physiological responses in vitro in the presence of five different clinically relevant jakinibs, including ruxolitinib, upadacitinib, oclacitinib, baricitinib and tofacitinib. Flow cytometry, microscopy and other assays found that potent JAK1/2 inhibitors baricitinib and ruxolitinib reduced platelet adhesion to collagen, as well as platelet aggregation, secretion and integrin α_IIbβ₃ activation in response to the glycoprotein VI (GPVI) agonist collagen-related peptide (CRP-XL). Western blot analysis demonstrated that jakinibs reduced Akt phosphorylation and activation following GPVI activation, where ruxolitinib and baricitinib prevented DAPP1 phosphorylation. In contrast, jakinibs had no effects on platelet responses to thrombin. Inhibitors of GPVI and JAK signaling also abrogated platelet STAT5 phosphorylation following CRP-XL stimulation. Additional pharmacologic experiments supported roles for STAT5 in platelet secretion, integrin activation and cytoskeletal responses. Together, our results demonstrate that ruxolitinib and baricitinib have inhibitory effects on platelet function in vitro and support roles for JAK/STAT5 pathways in GPVI/ITAM mediated platelet function.

JAK-STAT in Early Hematopoiesis and Leukemia

Hematopoietic stem cells (HSCs) produce all the terminally differentiated blood cells and are controlled by extracellular signals from the microenvironment, the bone marrow (BM) niche, as well as intrinsic cell signals. Intrinsic signals include the tightly controlled action of signaling pathways, as the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. Activation of JAK-STAT leads to phosphorylation of members of the STAT family to regulate proliferation, survival, and self-renewal of HSCs. Mutations in components of the JAK-STAT pathway are linked with defects in HSCs and hematologic malignancies. Accumulating mutations in HSCs and aging contribute to leukemia transformation. Here an overview of hematopoiesis, and the role of the JAK-STAT pathway in HSCs and in the promotion of leukemic transformation is presented. Therapeutic targeting of JAK-STAT and clinical implications of the existing research findings are also discussed.

Persistent STAT5 activation reprograms the epigenetic landscape in CD4+ T cells to drive polyfunctionality and antitumor immunity

The presence of polyfunctional CD4+ T cells is often associated with favorable antitumor immunity. We report here that persistent activation of signal transducer and activator of transcription 5 (STAT5) in tumor-specific CD4+ T cells drives the development of polyfunctional T cells. We showed that ectopic expression of a constitutively active form of murine STAT5A (CASTAT5) enabled tumor-specific CD4+ T cells to undergo robust expansion, infiltrate tumors vigorously, and elicit antitumor CD8+ T cell responses in a CD4+ T cell adoptive transfer model system. Integrated epigenomic and transcriptomic analysis revealed that CASTAT5 induced genome-wide chromatin remodeling in CD4+ T cells and established a distinct epigenetic and transcriptional landscape. Single-cell RNA sequencing analysis further identified a subset of CASTAT5-transduced CD4+ T cells with a molecular signature indicative of progenitor polyfunctional T cells. The therapeutic significance of CASTAT5 came from our finding that adoptive transfer of T cells engineered to coexpress CD19-targeting chimeric antigen receptor (CAR) and CASTAT5 gave rise to polyfunctional CD4+ CAR T cells in a mouse B cell lymphoma model. The optimal therapeutic outcome was obtained when both CD4+ and CD8+ CAR T cells were transduced with CASTAT5, indicating that CASTAT5 facilitates productive CD4 help to CD8+ T cells. Furthermore, we provide evidence that CASTAT5 is functional in primary human CD4+ T cells, underscoring its potential clinical relevance. Our results implicate STAT5 as a valid candidate for T cell engineering to generate polyfunctional, exhaustion-resistant, and tumor-tropic antitumor CD4+ T cells to potentiate adoptive T cell therapy for cancer.

Involvement of STAT5 in Oncogenesis

Signal transducer and activator of transcription (STAT) proteins, and in particular STAT3, have been established as heavily implicated in cancer. Recently, the involvement of STAT5 signalling in the pathology of cancer has been shown to be of increasing importance. STAT5 plays a crucial role in the development of the mammary gland and the homeostasis of the immune system. However, in various cancers, aberrant STAT5 signalling promotes the expression of target genes, such as cyclin D, Bcl-2 and MMP-2, that result in increased cell proliferation, survival and metastasis. To target constitutive STAT5 signalling in cancers, there are several STAT5 inhibitors that can prevent STAT5 phosphorylation, dimerisation, or its transcriptional activity. Tyrosine kinase inhibitors (TKIs) that target molecules upstream of STAT5 could also be utilised. Consequently, since STAT5 contributes to tumour aggressiveness and cancer progression, inhibiting STAT5 constitutive activation in cancers that rely on its signalling makes for a promising targeted treatment option.

Silencing Stat3 inhibits viability and induces apoptosis in BGC-823 human gastric cancer cell line

Gastric cancer (GC) is characterized by infrequent early diagnosis, poor prognosis and high mortality. Signal transducer and activator of transcription 3 (Stat3) and signal transducer and activator of transcription 5b (Stat5b) play multiple roles in the development and progression of many human cancers. We investigated the effects of silencing Stat3 and Stat5b on the viability and apoptosis of the human gastric cancer cell line, BGC-823. We found that Stat3 and Stat5b were expressed in both the nucleus and cytoplasm of BGC-823 cells. Silencing of Stat3 caused significantly decreased viability and increased apoptosis, as well as attenuated B-cell lymphoma-2 (Bcl-2) expression in BGC-823 cells. Silencing of Stat5b, however, had no significant effect on these events. Stat3, but not Stat5b, plays an important role in the viability and apoptosis of human gastric cancer cell line, BGC-823, which suggests that Stat3 is a potential target for gastric cancer therapy.

A p53-JAK-STAT connection involved in myeloproliferative neoplasm pathogenesis and progression to secondary acute myeloid leukemia

Since the discovery of JAK2 V617F as a highly prevalent somatic acquired mutation in the majority of myeloproliferative neoplasms (MPNs), it has become clear that these diseases are driven by pathologic activation of JAK2 and eventually of STAT5 and other members of the STAT family. The concept was strengthened by the discovery of the other activating driver mutations in MPL (thrombopoietin receptor, TpoR) and in calreticulin gene, which all lead to persistent activation of wild type JAK2. Although with a rare frequency, MPNs can evolve to secondary acute myeloid leukemia (sAML), a condition that is resistant to treatment. Here we focus on the role of p53 in this transition. In sAML mutations in TP53 or amplification in genes coding for negative regulators of p53 are much more frequent than in de novo AML. We review studies that explore a signaling and biochemical interaction between activated STATs and p53 in MPNs and other cancers. With the development of advanced sequencing efforts, strong evidence has been presented for dominant negative effects of mutated p53 in leukemia. In other studies, gain of function effects have been described that might be cell type specific. A more profound understanding of the potential interaction between p53 and activated STATs is necessary in order to take full advantage of novel p53-targeted therapies.

High activation of STAT5A drives peripheral T-cell lymphoma and leukemia

Recurrent gain-of-function mutations in the transcription factors STAT5A and much more in STAT5B were found in hematopoietic malignancies with the highest proportion in mature T- and natural killer-cell neoplasms (peripheral T-cell lymphoma, PTCL). No targeted therapy exists for these heterogeneous and often aggressive diseases. Given the shortage of models for PTCL, we mimicked graded STAT5A or STAT5B activity by expressing hyperactive Stat5a or STAT5B variants at low or high levels in the hematopoietic system of transgenic mice. Only mice with high activity levels developed a lethal disease resembling human PTCL. Neoplasia displayed massive expansion of CD8⁺ T cells and destructive organ infiltration. T cells were cytokine-hypersensitive with activated memory CD8⁺ T-lymphocyte characteristics. Histopathology and mRNA expression profiles revealed close correlation with distinct subtypes of PTCL. Pronounced STAT5 expression and activity in samples from patients with different subsets underline the relevance of JAK/STAT as a therapeutic target. JAK inhibitors or a selective STAT5 SH₂ domain inhibitor induced cell death and ruxolitinib blocked T-cell neoplasia in vivo. We conclude that enhanced STAT5A or STAT5B action both drive PTCL development, defining both STAT5 molecules as targets for therapeutic intervention.

Pharmacological Inhibition of Oncogenic STAT3 and STAT5 Signaling in Hematopoietic Cancers

Signal Transducer and Activator of Transcription (STAT) 3 and 5 are important effectors of cellular transformation, and aberrant STAT3 and STAT5 signaling have been demonstrated in hematopoietic cancers. STAT3 and STAT5 are common targets for different tyrosine kinase oncogenes (TKOs). In addition, STAT3 and STAT5 proteins were shown to contain activating mutations in some rare but aggressive leukemias/lymphomas. Both proteins also contribute to drug resistance in hematopoietic malignancies and are now well recognized as major targets in cancer treatment. The development of inhibitors targeting STAT3 and STAT5 has been the subject of intense investigations during the last decade. This review summarizes the current knowledge of oncogenic STAT3 and STAT5 functions in hematopoietic cancers as well as advances in preclinical and clinical development of pharmacological inhibitors.

A Novel Inhibitor of STAT5 Signaling Overcomes Chemotherapy Resistance in Myeloid Leukemia Cells

Signal transducers and activators of transcription 5A and 5B (STAT5A and STAT5B) are crucial downstream effectors of tyrosine kinase oncogenes (TKO) such as BCR-ABL in chronic myeloid leukemia (CML) and FLT3-ITD in acute myeloid leukemia (AML). Both proteins have been shown to promote the resistance of CML cells to tyrosine kinase inhibitors (TKI) such as imatinib mesylate (IM). We recently synthesized and discovered a new inhibitor (17f) with promising antileukemic activity. 17f selectively inhibits STAT5 signaling in CML and AML cells by interfering with the phosphorylation and transcriptional activity of these proteins. In this study, the effects of 17f were evaluated on CML and AML cell lines that respectively acquired resistance to IM and cytarabine (Ara-C), a conventional therapeutic agent used in AML treatment. We showed that 17f strongly inhibits the growth and survival of resistant CML and AML cells when associated with IM or Ara-C. We also obtained evidence that 17f inhibits STAT5B but not STAT5A protein expression in resistant CML and AML cells. Furthermore, we demonstrated that 17f also targets oncogenic STAT5B N642H mutant in transformed hematopoietic cells.

Structural Implications of STAT3 and STAT5 SH2 Domain Mutations

Src Homology 2 (SH2) domains arose within metazoan signaling pathways and are involved in protein regulation of multiple pleiotropic cascades. In signal transducer and activator of transcription (STAT) proteins, SH2 domain interactions are critical for molecular activation and nuclear accumulation of phosphorylated STAT dimers to drive transcription. Sequencing analysis of patient samples has revealed the SH2 domain as a hotspot in the mutational landscape of STAT proteins although the functional impact for the vast majority of these mutations remains poorly characterized. Despite several well resolved structures for SH2 domain-containing proteins, structural data regarding the distinctive STAT-type SH2 domain is limited. Here, we review the unique features of STAT-type SH2 domains in the context of all currently reported STAT3 and STAT5 SH2 domain clinical mutations. The genetic volatility of specific regions in the SH2 domain can result in either activating or deactivating mutations at the same site in the domain, underscoring the delicate evolutionary balance of wild type STAT structural motifs in maintaining precise levels of cellular activity. Understanding the molecular and biophysical impact of these disease-associated mutations can uncover convergent mechanisms of action for mutations localized within the STAT SH2 domain to facilitate the development of targeted therapeutic interventions.

STAT5A and STAT5B-Twins with Different Personalities in Hematopoiesis and Leukemia

The transcription factors STAT5A and STAT5B have essential roles in survival and proliferation of hematopoietic cells-which have been considered largely redundant. Mutations of upstream kinases, copy number gains, or activating mutations in STAT5A, or more frequently in STAT5B, cause altered hematopoiesis and cancer. Interfering with their activity by pharmacological intervention is an up-and-coming therapeutic avenue. Precision medicine requests detailed knowledge of STAT5A's and STAT5B's individual functions. Recent evidence highlights the privileged role for STAT5B over STAT5A in normal and malignant hematopoiesis. Here, we provide an overview on their individual functions within the hematopoietic system.

ATP Inhibits the Transcription Factor STAT5b

Although naturally occurring low-molecular-weight compounds have many known roles within the cell, these do not usually involve the direct inhibition of protein-protein interactions. Based on the results of high-throughput screening of a library of bioactive compounds and neurotransmitters, we report here that the four nucleoside triphosphates ATP, GTP, CTP and UTP inhibit the SH2 domain of the tumor-related transcription factor STAT5b. ATP and GTP are the most active nucleoside triphosphates and show specificity for STAT5b over STAT5a, STAT3, STAT6 and the p53-binding protein HDM2. As the inhibition constant of ATP against STAT5b is significantly lower than published values for the intracellular ATP concentration, our data suggest that ATP might inhibit the protein-protein interactions of STAT5b in living cells.

Structural and functional consequences of the STAT5BN642H driver mutation

Hyper-activated STAT5B variants are high value oncology targets for pharmacologic intervention. STAT5BN642H, a frequently-occurring oncogenic driver mutation, promotes aggressive T-cell leukemia/lymphoma in patient carriers, although the molecular origins remain unclear. Herein, we emphasize the aggressive nature of STAT5BN642H in driving T-cell neoplasia upon hematopoietic expression in transgenic mice, revealing evidence of multiple T-cell subset organ infiltration. Notably, we demonstrate STAT5BN642H-driven transformation of γδ T-cells in in vivo syngeneic transplant models, comparable to STAT5BN642H patient γδ T-cell entities. Importantly, we present human STAT5B and STAT5BN642H crystal structures, which propose alternative mutation-mediated SH2 domain conformations. Our biophysical data suggests STAT5BN642H can adopt a hyper-activated and hyper-inactivated state with resistance to dephosphorylation. MD simulations support sustained interchain cross-domain interactions in STAT5BN642H, conferring kinetic stability to the mutant anti-parallel dimer. This study provides a molecular explanation for the STAT5BN642H activating potential, and insights into pre-clinical models for targeted intervention of hyper-activated STAT5B.

The STAT5b Linker Domain Mediates the Selectivity of Catechol Bisphosphates for STAT5b over STAT5a

STAT family proteins are important mediators of cell signaling and represent therapeutic targets for the treatment of human diseases. Most STAT inhibitors target the protein-protein interaction domain, the SH2 domain, but specificity for a single STAT protein is often limited. Recently, we developed catechol bisphosphates as the first inhibitors of STAT5b demonstrated to exhibit a high degree of selectivity over the close homologue STAT5a. Here, we show that the amino acid in position 566 of the linker domain, not the SH2 domain, is the main determinant of specificity. Arg566 in wild-type STAT5b favors tight binding of catechol bisphosphates, while Trp566 in wild-type STAT5a does not. Amino acid 566 also determines the affinity for a tyrosine-phosphorylated peptide derived from the EPO receptor for STAT5a and STAT5b, demonstrating the functional relevance of the STAT5 linker domain for the adjacent SH2 domain. These results provide the first demonstration that a residue in the linker domain can determine the affinity of nonpeptidic small-molecule inhibitors for the SH2 domain of STAT proteins. We propose targeting the interface between the SH2 domain and linker domain as a novel design approach for the development of potent and selective STAT inhibitors. In addition, our data suggest that the linker domain could contribute to the enigmatically divergent biological functions of the two STAT5 proteins.

Cell Metabolism Control Through O-GlcNAcylation of STAT5: A Full or Empty Fuel Tank Makes a Big Difference for Cancer Cell Growth and Survival

O-GlcNAcylation is a post-translational modification that influences tyrosine phosphorylation in healthy and malignant cells. O-GlcNAc is a product of the hexosamine biosynthetic pathway, a side pathway of glucose metabolism. It is essential for cell survival and proper gene regulation, mirroring the metabolic status of a cell. STAT3 and STAT5 proteins are essential transcription factors that can act in a mutational context-dependent manner as oncogenes or tumor suppressors. They regulate gene expression for vital processes such as cell differentiation, survival, or growth, and are also critically involved in metabolic control. The role of STAT3/5 proteins in metabolic processes is partly independent of their transcriptional regulatory role, but is still poorly understood. Interestingly, STAT3 and STAT5 are modified by O-GlcNAc in response to the metabolic status of the cell. Here, we discuss and summarize evidence of O-GlcNAcylation-regulating STAT function, focusing in particular on hyperactive STAT5A transplant studies in the hematopoietic system. We emphasize that a single O-GlcNAc modification is essential to promote development of neoplastic cell growth through enhancing STAT5A tyrosine phosphorylation. Inhibition of O-GlcNAcylation of STAT5A on threonine 92 lowers tyrosine phosphorylation of oncogenic STAT5A and ablates malignant transformation. We conclude on strategies for new therapeutic options to block O-GlcNAcylation in combination with tyrosine kinase inhibitors to target neoplastic cancer cell growth and survival.