A novel missense (M206K) STAT3 mutation in diffuse large B cell lymphoma deregulates STAT3 signaling

Dependence of peripheral T-cell lymphoma on constitutively activated JAK3: Implication for JAK3 inhibition as a therapeutic approach

Peripheral T-cell lymphoma (PTCL) is a clinically heterogeneous group that represents 10%-15% of all lymphomas. Despite improved genetic and molecular understanding, treatment outcomes for PTCL have not shown significant improvement. Although Janus kinase-2 (JAK2) plays an important role in myeloproliferative neoplasms, the critical role of JAK isoforms in mediating prosurvival signaling in PTCL cells is not well defined. Immunohistochemical analysis of PTCL tumors (n = 96) revealed high levels of constitutively active JAK3 (pJAK3) that significantly (p < 0.04) correlated with the activation state of its canonical substrate STAT3. Furthermore, constitutive activation of JAK3 and STAT3 positively correlated, at least in part, with an oncogenic tyrosine phosphatase PTPN11. Pharmacological inhibition of JAK3 but not JAK1/JAK2 significantly (p < 0.001) decreased PTCL proliferation, survival and STAT3 activation. A sharp contrast was observed in the pJAK3 positivity between ALK+ (85.7%) versus ALK-negative (10.0%) in human PTCL tumors and PTCL cell lines. Moreover, JAK3 and ALK reciprocally interacted in PTCL cells, forming a complex to possibly regulate STAT3 signaling. Finally, combined inhibition of JAK3 (by WHI-P154) and ALK (by crizotinib or alectinib) significantly (p < 0.01) decreased the survival of PTCL cells as compared to either agent alone by inhibiting STAT3 downstream signaling. Collectively, our findings establish that JAK3 is a therapeutic target for a subset of PTCL, and provide rationale for the clinical evaluation of JAK3 inhibitors combined with ALK-targeted therapy in PTCL.

Untwining Anti-Tumor and Immunosuppressive Effects of JAK Inhibitors-A Strategy for Hematological Malignancies?

Simple Summary

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway is aberrantly activated in many malignancies. Inhibition of this pathway via JAK inhibitors (JAKinibs) is therefore an attractive therapeutic strategy underlined by Ruxolitinib (JAK1/2 inhibitor) being approved for the treatment of myeloproliferative neoplasms. As a consequence of the crucial role of the JAK-STAT pathway in the regulation of immune responses, inhibition of JAKs suppresses the immune system. This review article provides a thorough overview of the current knowledge on JAKinibs’ effects on immune cells in the context of hematological malignancies. We also discuss the potential use of JAKinibs for the treatment of diseases in which lymphocytes are the source of the malignancy.

Abstract

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway propagates signals from a variety of cytokines, contributing to cellular responses in health and disease. Gain of function mutations in JAKs or STATs are associated with malignancies, with JAK2^V617F being the main driver mutation in myeloproliferative neoplasms (MPN). Therefore, inhibition of this pathway is an attractive therapeutic strategy for different types of cancer. Numerous JAK inhibitors (JAKinibs) have entered clinical trials, including the JAK1/2 inhibitor Ruxolitinib approved for the treatment of MPN. Importantly, loss of function mutations in JAK-STAT members are a cause of immune suppression or deficiencies. MPN patients undergoing Ruxolitinib treatment are more susceptible to infections and secondary malignancies. This highlights the suppressive effects of JAKinibs on immune responses, which renders them successful in the treatment of autoimmune diseases but potentially detrimental for cancer patients. Here, we review the current knowledge on the effects of JAKinibs on immune cells in the context of hematological malignancies. Furthermore, we discuss the potential use of JAKinibs for the treatment of diseases in which lymphocytes are the source of malignancies. In summary, this review underlines the necessity of a robust immune profiling to provide the best benefit for JAKinib-treated patients.

STAT3 Activation and Oncogenesis in Lymphoma

Signal transducer and activator of transcription 3 (STAT3) is an important and the most studied transcription factor in the Janus kinase (JAK)/STAT signaling pathway. STAT3 mediates the expression of various genes that play a critical role in many cellular and biological processes, such as cell proliferation, survival, differentiation, migration, angiogenesis, and inflammation. STAT3 and associated JAKs are activated and tightly regulated by a variety of cytokines and growth factors and their receptors in normal immune responses. However, abnormal expression of STAT3 leads to its constitutive activation, which promotes malignant transformation and tumor progression through oncogenic gene expression in numerous human cancers. Human lymphoma is a heterogeneous malignancy of T and B lymphocytes. Constitutive signaling by STAT3 is an oncogenic driver in several types of B-cell lymphoma and most of T-cell lymphomas. Aberrant STAT3 activation can also induce inappropriate expression of genes involved in tumor immune evasion such as PD-L1. In this review, we focus on the oncogenic role of STAT3 in human lymphoma and highlight potential therapeutic intervention by targeting JAK/STAT3 signaling.

Balancing STAT Activity as a Therapeutic Strategy

Driven by dysregulated IL-6 family member cytokine signaling in the tumor microenvironment (TME), aberrant signal transducer and activator of transcription (STAT3) and (STAT5) activation have been identified as key contributors to tumorigenesis. Following transformation, persistent STAT3 activation drives the emergence of mesenchymal/cancer-stem cell (CSC) properties, important determinants of metastatic potential and therapy failure. Moreover, STAT3 signaling within tumor-associated macrophages and neutrophils drives secretion of factors that facilitate metastasis and suppress immune cell function. Persistent STAT5 activation is responsible for cancer cell maintenance through suppression of apoptosis and tumor suppressor signaling. Furthermore, STAT5-mediated CD4+/CD25+ regulatory T cells (T_regs) have been implicated in suppression of immunosurveillance. We discuss these roles for STAT3 and STAT5, and weigh the attractiveness of different modes of targeting each cancer therapy. Moreover, we discuss how anti-tumorigenic STATs, including STAT1 and STAT2, may be leveraged to suppress the pro-tumorigenic functions of STAT3/STAT5 signaling.

Mutations in the signal transducer and activator of transcription family of genes in cancer

In recent years, it has become clear that members of the signal transducer and activator of transcription (STAT) family of genes play an important role in cancer. The STAT family consists of seven genes, STAT1‐4,STAT5A, STAT5B and STAT6, that are involved in regulating cellular proliferation, apoptosis, angiogenesis and the immune system response. Constitutive activation of STAT3, via mutational changes, is important in oncogenesis in both solid and hematopoietic cancers. In the case of hematopoietic neoplasms, STAT3 driver mutations have been described in T‐cell large granular lymphocytic (T‐LGL) leukemia and chronic natural killer lymphoproliferative disorders (CLPD‐NK) and are seen in 30%‐40% of T‐LGL leukemia patients. STAT5B is also mutated in T‐LGL leukemia and CLPD‐NK, but in a much smaller proportion. Here we review past and current research on STAT genes in hematopoietic and solid cancers with emphasis on STAT3 and STAT5B and their roles in the pathogenesis of hematopoietic malignancies, particularly T‐LGL leukemia and CLPD‐NK.

The role of STAT3 in glioblastoma progression through dual influences on tumor cells and the immune microenvironment

Glioblastoma multiforme (GBM) is the most aggressive form of cancer that begins within the brain; generally, the patient has a dismal prognosis and limited therapeutic options. Signal transducer and activator of transcription 3 (STAT3) is a critical mediator of tumorigenesis, tumor progression, and suppression of anti-tumor immunity in GBM. In a high percentage of GBM cells and tumor microenvironments, persistent activation of STAT3 induces cell proliferation, anti-apoptosis, glioma stem cell maintenance, tumor invasion, angiogenesis, and immune evasion. This makes STAT3 an attractive therapeutic target and a prognostic indicator in GBM. Targeting STAT3 affords an opportunity to disrupt multiple pro-oncogenic pathways at a single molecular hub. Unfortunately, there are no successful STAT3 inhibitors currently in clinical trials. However, strong clinical evidence implicating STAT3 as a major factor in GBM justifies the identification of safe and effective strategies for inhibiting STAT3.

Loss of function mutations in PTPN6 promote STAT3 deregulation via JAK3 kinase in diffuse large B-cell lymphoma

PTPN6 (SHP1) is a tyrosine phosphatase that negatively controls the activity of multiple signaling pathways including STAT signaling, however role of mutated PTPN6 is not much known. Here we investigated whether PTPN6 might also be a potential target for diffuse large B cell lymphoma (DLBCL) and performed Sanger sequencing of the PTPN6 gene. We have identified missense mutations within PTPN6 (N225K and A550V) in 5% (2/38) of DLBCL tumors. Site directed mutagenesis was performed to mutate wild type (WT) PTPN6 and stable cell lines were generated by lentiviral transduction of PTPN6(WT), PTPN6(N225K) and PTPN6(A550V) constructs, and effects of WT or mutated PTPN6 on STAT3 signaling were analyzed. WT PTPN6 dephosphorylated STAT3, but had no effect on STAT1, STAT5 or STAT6 phosphorylation. Both PTPN6 mutants were unable to inhibit constitutive, as well as cytokines induced STAT3 activation. Both PTPN6 mutants also demonstrated reduced tyrosine phosphatase activity and exhibited enhanced STAT3 transactivation activity. Intriguingly, a lack of direct binding between STAT3 and WT or mutated PTPN6 was observed. However, compared to WT PTPN6, cells expressing PTPN6 mutants exhibited increased binding between JAK3 and PTPN6 suggesting a more dynamic interaction of PTPN6 with upstream regulators of STAT3. Consistent with this notion, both the mutants demonstrated increased resistance to JAK3 inhibitor, WHIP-154 relative to WT PTPN6. Overall, this is the first study, which demonstrates that N225K and A550V PTPN6 mutations cause loss-of-function leading to JAK3 mediated deregulation of STAT3 pathway and uncovers a mechanism that tumor cells can use to control PTPN6 substrate specificity.

Panel sequencing for clinically oriented variant screening and copy number detection in 142 untreated multiple myeloma patients

We employed a customized Multiple Myeloma (MM)-specific Mutation Panel (M³P) to screen a homogenous cohort of 142 untreated MM patients for relevant mutations in a selection of disease-specific genes. M³Pv2.0 includes 77 genes selected for being either actionable targets, potentially related to drug–response or part of known key pathways in MM biology. We identified mutations in potentially actionable genes in 49% of patients and provided prognostic evidence of STAT3 mutations. This panel may serve as a practical alternative to more comprehensive sequencing approaches, providing genomic information in a timely and cost-effective manner, thus allowing clinically oriented variant screening in MM.

Translation initiation complex eIF4F is a therapeutic target for dual mTOR kinase inhibitors in non-Hodgkin lymphoma

Deregulated mRNA translation has been implicated in disease development and in part is controlled by a eukaryotic initiation complex eIF4F (composed of eIF4E, eIF4G and eIF4A). We demonstrate here that the cap bound fraction from lymphoma cells was enriched with eIF4G and eIF4E indicating that lymphoma cells exist in an activated translational state. Moreover, 77% (110/142) of diffuse large B cell lymphoma tumors expressed eIF4E and this was associated with an inferior event free survival. Over-expression of wild-type eIF4E (eIF4E(WT)) but not cap-mutant eIF4E (eIF4E(cap mutant)) increased the activation of the eIF4F complex. Treatment with the active-site dual mTOR inhibitor CC214-1 reduced the level of the eIF4F complex by decreasing the cap bound fraction of eIF4G and increasing the levels of 4E-BP1. CC214-1 inhibited both the cap dependent and global protein translation. CC214-1 inhibited c-Myc, and cyclin D3 translation by decreasing polysomal fractions from lymphoma cells. Inhibition of eIF4E with shRNA further decreased the CC214-1 induced inhibition of the eIF4F complex, c-Myc, cyclin D3 translation, and colony formation. These studies demonstrate that the eIF4F complex is deregulated in aggressive lymphoma and that dual mTOR therapy has therapeutic potential in these patients.

Novel drug targets for personalized precision medicine in relapsed/refractory diffuse large B-cell lymphoma: a comprehensive review

Diffuse large B-cell lymphoma (DLBCL) is a clinically heterogeneous lymphoid malignancy and the most common subtype of non-Hodgkin's lymphoma in adults, with one of the highest mortality rates in most developed areas of the world. More than half of DLBLC patients can be cured with standard R-CHOP regimens, however approximately 30 to 40 % of patients will develop relapsed/refractory disease that remains a major cause of morbidity and mortality due to the limited therapeutic options.Recent advances in gene expression profiling have led to the identification of at least three distinct molecular subtypes of DLBCL: a germinal center B cell-like subtype, an activated B cell-like subtype, and a primary mediastinal B-cell lymphoma subtype. Moreover, recent findings have not only increased our understanding of the molecular basis of chemotherapy resistance but have also helped identify molecular subsets of DLBCL and rational targets for drug interventions that may allow for subtype/subset-specific molecularly targeted precision medicine and personalized combinations to both prevent and treat relapsed/refractory DLBCL. Novel agents such as lenalidomide, ibrutinib, bortezomib, CC-122, epratuzumab or pidilizumab used as single-agent or in combination with (rituximab-based) chemotherapy have already demonstrated promising activity in patients with relapsed/refractory DLBCL. Several novel potential drug targets have been recently identified such as the BET bromodomain protein (BRD)-4, phosphoribosyl-pyrophosphate synthetase (PRPS)-2, macrodomain-containing mono-ADP-ribosyltransferase (ARTD)-9 (also known as PARP9), deltex-3-like E3 ubiquitin ligase (DTX3L) (also known as BBAP), NF-kappaB inducing kinase (NIK) and transforming growth factor beta receptor (TGFβR).This review highlights the new insights into the molecular basis of relapsed/refractory DLBCL and summarizes the most promising drug targets and experimental treatments for relapsed/refractory DLBCL, including the use of novel agents such as lenalidomide, ibrutinib, bortezomib, pidilizumab, epratuzumab, brentuximab-vedotin or CAR T cells, dual inhibitors, as well as mechanism-based combinatorial experimental therapies. We also provide a comprehensive and updated list of current drugs, drug targets and preclinical and clinical experimental studies in DLBCL. A special focus is given on STAT1, ARTD9, DTX3L and ARTD8 (also known as PARP14) as novel potential drug targets in distinct molecular subsets of DLBCL.

The mTORC1 inhibitor everolimus has antitumor activity in vitro and produces tumor responses in patients with relapsed T-cell lymphoma

Everolimus is an oral agent that targets the mammalian target of rapamycin (mTOR) pathway. This study investigated mTOR pathway activation in T-cell lymphoma (TCL) cell lines and assessed antitumor activity in patients with relapsed/refractory TCL in a phase 2 trial. The mTOR pathway was activated in all 6 TCL cell lines tested and everolimus strongly inhibited malignant T-cell proliferation with minimal cytotoxic effects. Everolimus completely inhibited phosphorylation of ribosomal S6, a raptor/mTOR complex 1 (mTORC1) target, without a compensatory activation of the rictor/mTORC2 target Akt (S475). In the clinical trial, 16 patients with relapsed TCL were enrolled and received everolimus 10 mg by mouth daily. Seven patients (44%) had cutaneous (all mycosis fungoides); 4 (25%) had peripheral T cell not otherwise specified; 2 (13%) had anaplastic large cell; and 1 each had extranodal natural killer/T cell, angioimmunoblastic, and precursor T-lymphoblastic leukemia/lymphoma types. The overall response rate was 44% (7/16; 95% confidence interval [CI]: 20% to 70%). The median progression-free survival was 4.1 months (95% CI, 1.5-6.5) and the median overall survival was 10.2 months (95% CI, 2.6-44.3). The median duration of response for the 7 responders was 8.5 months (95% CI, 1.0 to not reached). These studies indicate that everolimus has antitumor activity and provide proof-of-concept that targeting the mTORC1 pathway in TCL is clinically relevant. This trial was registered at www.clinicaltrials.gov as #NCT00436618.

The analysis of clonal diversity and therapy responses using STAT3 mutations as a molecular marker in large granular lymphocytic leukemia

T-cell large granular lymphocytic leukemia and chronic lymphoproliferative disorder of natural killer cells are intriguing entities between benign and malignant lymphoproliferation. The molecular pathogenesis has partly been uncovered by the recent discovery of somatic activating STAT3 and STAT5b mutations. Here we show that 43% (75/174) of patients with T-cell large granular lymphocytic leukemia and 18% (7/39) with chronic lymphoproliferative disorder of natural killer cells harbor STAT3 mutations when analyzed by quantitative deep amplicon sequencing. Surprisingly, 17% of the STAT3-mutated patients carried multiple STAT3 mutations, which were located in different lymphocyte clones. The size of the mutated clone correlated well with the degree of clonal expansion of the T-cell repertoire analyzed by T-cell receptor beta chain deep sequencing. The analysis of sequential samples suggested that current immunosuppressive therapy is not able to reduce the level of the mutated clone in most cases, thus warranting the search for novel targeted therapies. Our findings imply that the clonal landscape of large granular lymphocytic leukemia is more complex than considered before, and a substantial number of patients have multiple lymphocyte subclones harboring different STAT3 mutations, thus mimicking the situation in acute leukemia.

The long non-coding RNA GAS5 cooperates with the eukaryotic translation initiation factor 4E to regulate c-Myc translation

Long noncoding RNAs (lncRNAs) are important regulators of transcription; however, their involvement in protein translation is not well known. Here we explored whether the lncRNA GAS5 is associated with translation initiation machinery and regulates translation. GAS5 was enriched with eukaryotic translation initiation factor-4E (eIF4E) in an RNA-immunoprecipitation assay using lymphoma cell lines. We identified two RNA binding motifs within eIF4E protein and the deletion of each motif inhibited the binding of GAS5 with eIF4E. To confirm the role of GAS5 in translation regulation, GAS5 siRNA and in vitro transcribed GAS5 RNA were used to knock down or overexpress GAS5, respectively. GAS5 siRNA had no effect on global protein translation but did specifically increase c-Myc protein level without an effect on c-Myc mRNA. The mechanism of this increase in c-Myc protein was enhanced association of c-Myc mRNA with the polysome without any effect on protein stability. In contrast, overexpression of in vitro transcribed GAS5 RNA suppressed c-Myc protein without affecting c-Myc mRNA. Interestingly, GAS5 was found to be bound with c-Myc mRNA, suggesting that GAS5 regulates c-Myc translation through lncRNA-mRNA interaction. Our findings have uncovered a role of GAS5 lncRNA in translation regulation through its interactions with eIF4E and c-Myc mRNA.

STAT3 in Cancer-Friend or Foe?

The roles and significance of STAT3 in cancer biology have been extensively studied for more than a decade. Mounting evidence has shown that constitutive activation of STAT3 is a frequent biochemical aberrancy in cancer cells, and this abnormality directly contributes to tumorigenesis and shapes many malignant phenotypes in cancer cells. Nevertheless, results from more recent experimental and clinicopathologic studies have suggested that STAT3 also can exert tumor suppressor effects under specific conditions. Importantly, some of these studies have demonstrated that STAT3 can function either as an oncoprotein or a tumor suppressor in the same cell type, depending on the specific genetic background or presence/absence of specific coexisting biochemical defects. Thus, in the context of cancer biology, STAT3 can be a friend or foe. In the first half of this review, we will highlight the “evil” features of STAT3 by summarizing its oncogenic functions and mechanisms. The differences between the canonical and non-canonical pathway will be highlighted. In the second half, we will summarize the evidence supporting that STAT3 can function as a tumor suppressor. To explain how STAT3 may mediate its tumor suppressor effects, we will discuss several possible mechanisms, one of which is linked to the role of STAT3β, one of the two STAT3 splicing isoforms. Taken together, it is clear that the roles of STAT3 in cancer are multi-faceted and far more complicated than one appreciated previously. The new knowledge has provided us with new approaches and strategies when we evaluate STAT3 as a prognostic biomarker or therapeutic target.

Disease-specific mutations in mature lymphoid neoplasms: recent advances

Mature lymphoid neoplasms (MLN) are clinically and pathologically more complex than precursor lymphoid neoplasms. Until recently, molecular characterization of MLN was mainly based on cytogenetics/fluorescence in situ hybridization, allele copy number, and mRNA expression, approaches that yielded scanty gene mutation information. Use of massive parallel sequencing technologies has changed this outcome, and now many gene mutations have been discovered. Some of these are considerably frequent in, and substantially specific to, distinct MLN subtypes, and occur at single or several hotspots. They include the V600E BRAF mutation in hairy cell leukemia, the L265P MYD88 mutation in Waldenström macroglobulinemia, the G17V RHOA mutation in angioimmunoblastic T-cell lymphoma and peripheral T-cell lymphoma, not otherwise specified, and the Y640F//D661Y/V/H/I//N647I STAT3 mutations in T-cell large granular lymphocytic leukemia. Detecting these mutations is highly valuable in diagnosing MLN subtypes. Defining these mutations also sheds light on the molecular pathogenesis of MLN, furthering development of molecular targeting therapies. In this review, we focus on the disease-specific gene mutations in MLN discovered by recent massive sequencing technologies.

Uncovering the pathogenesis of large granular lymphocytic leukemia-novel STAT3 and STAT5b mutations

Large granular lymphocytic (LGL) leukemia is an incurable chronic disease, characterized by clonal expansion of cytotoxic T- or NK-cells in blood and bone marrow. Cytopenias (anemia, neutropenia) and autoimmune disorders such as rheumatoid arthritis are the most common clinical manifestations of LGL leukemia. Recently, somatic activating STAT3 gene mutations were shown to be specific for LGL leukemia with a prevalence of up to 70%. Analogous mutations in the STAT5b gene were seen in a smaller proportion of patients. These gain-of-function mutations are located in the SH2 domain of STAT3 and affect the phosphotyrosine-SH2 interaction required for dimerization of STAT3. The mutations increase the phosphorylation of STAT3 and STAT5b and enhance the transcriptional activity of the mutated proteins. STAT3 and STAT5b mutations can be used as molecular markers for LGL leukemia diagnostics, and they present novel therapeutic targets for STAT3 and STAT5b inhibitors, which currently are in development for treatment of cancer and autoimmune disorders.