Tyrosine kinase fusion genes in chronic myeloproliferative diseases

Rare and potentially fatal - Cytogenetically cryptic TNIP1::PDGFRB and PCM1::FGFR1 fusion leading to myeloid/lymphoid neoplasms with eosinophilia in children

Myeloid/lymphoid neoplasms with eosinophilia (MLN-eos) are rare haematological neoplasms primarily affecting adults. The heterogeneous clinical picture and the rarity of the disease, especially in children, may delay an early diagnosis. MLN-eos are characterized by constitutive tyrosine kinase (TK) activity due to gene fusions. It is thus of importance to obtain a prompt genetic diagnosis to start a specific therapy. Here, we outline the clinical, genetic, and biochemical background of TK driven MLN-eos and report two extremely rare paediatric cases of MLN-eo, the used diagnostic methods, therapy and clinical outcomes. Our results demonstrate that, standard cytogenetic and molecular methods may not be sufficient to diagnose MLN-eo due to cytogenetically cryptic aberrations. We therefore recommend performing additional evaluation with fluorescence in-situ hybridization and molecular genetic methods (array-based comparative genomic hybridization and RNA sequencing) which will lead to the correct diagnosis. Following this diagnostic route we detected a TNIP1::PDGFRB and a PCM1::FGFR1 fusion in our patients. Thus, genetic diagnosis must be precise and quick in order to initiate adequate therapies with tyrosine kinase inhibitors or HSCT.

JAK2 and Beyond: Mutational Study of JAK2V617 in Myeloproliferative Disorders and Haematological Malignancies in Kashmiri population

BACKGROUND

Janus Tyrosine Kinase-2 (JAK2 V617F), a novel point mutation affecting the MPD'S is a somatic gain-of-function mutation. It alters a highly conserved amino acid valine in the negative regulatory JH2 domain to phenylalanine predicted to dysregulate kinase activity.

AIM

To evaluate the prevalence and clinical significance of JAK2 V617F mutation in various MPD's as well as in hematological malignancies.

SUBJECTS AND METHODS

JAK2 mutation was assessed in 90 patients with myeloproliferative disorders and 47 leukemic patients. In addition, peripheral blood samples from 90 healthy donors were also collected as control. We used a highly sensitive Allele-Specific polymerase chain reaction (AS-PCR) for the detection and confirmed the mutation further by direct sequencing.

RESULTS

Our results showed significant differences between various disorders with respect to either the proportion of positivity or that of mutant alleles. JAK2-V617F was detected in 67/90 MPD patients and 02/17 for AML,01/11 for ALL-L1,02/12 for ALL-L2 and 02/07 for CML and 90 healthy controls.

CONCLUSION

From the above findings it is evident that the JAK2 V617F mutation is widespread not only in MPD's but also in hematological malignancies, which might as well lead to the new classification of MPD'S. Our data also suggest that different genetic events may lead to JAK-STAT pathway activation in different malignancies.

Myeloid/Lymphoid Neoplasm with PDGFRB Rearrangement with t (5;10) (q33;q22) Harboring a Novel Breakpoint of the CCDC6-PDGFRB Fusion Gene

Myeloid/lymphoid neoplasms with PDGFRB rearrangement are a distinct type of myeloid neoplasms that occur in association with rearrangement of PDGFRB at 5q32. The hematological features most often show prominent eosinophilia. We herein report a patient with myeloid/lymphoid neoplasms with PDGFRB rearrangement with t (5;10) (q33;q22) who showed atypical chronic myeloid leukemia-like clinical features without eosinophilia and achieved an optimal response to imatinib. A sequence analysis showed a CCDC6-PDGFRB fusion gene with a new break point in the PDGFRB gene. This is the sixth case of myeloid/lymphoid neoplasm with PDGFRB rearrangement harboring a CCDC6-PDGFRB fusion gene, and it has a new breakpoint in the PDGFRB fusion gene.

Kinomic profiling identifies focal adhesion kinase 1 as a therapeutic target in advanced clear cell renal cell carcinoma

The introduction of targeted therapies has caused a paradigm shift in the treatment of metastatic clear cell (cc)-renal cell carcinoma (RCC). We hypothesized that determining differential kinase activity between primary and metastatic tumor sites may identify critical drivers of progression and relevant therapeutic targets in metastatic disease. Kinomic profiling was performed on primary tumor and metastatic tumor deposits utilizing a peptide substrate microarray to detect relative tyrosine phosphorylation activity. Pharmacologic and genetic loss of function experiments were used to assess the biologic significance of the top scoring kinase on in vitro and in vivo tumor phenotypes. Kinomics identified 7 peptides with increased tyrosine phosphorylation in metastases that were significantly altered (p<0.005). Based on these peptides, bioinformatics analyses identified several candidate kinases activated in metastases compared to primary tumors. The highest ranked upstream kinase was Focal Adhesion Kinase 1 (FAK1). RCC lines demonstrate evidence of elevated FAK1 activation relative to non-transformed renal epithelial cells. Pharmacologic inhibition of FAK1 with GSK2256098 suppresses in vitro tumor phenotypes. In turn, FAK1 knockdown in RCC cells suppresses both in vitro phenotypes and in vivo tumor growth. Collectively, these data demonstrate functional activation of FAK1 in metastases and provide preclinical rationale for targeting this kinase in the setting of advanced ccRCC.

Marked response to imatinib mesylate in a patient with platelet-derived growth factor receptor beta-associated acute myeloid leukemia

Abnormal platelet-derived growth factor receptor (PDGFR)-mediated signaling may cause hematologic neoplasm. The PDGFR beta (PDGFRB) gene, located at chromosome band 5q31-33, forms a fusion gene as a result of chromosome translocation. Although patients with PDGFRB rearrangement mostly present with myeloproliferative neoplasm and eosinophilia, acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) have also been reported in this population. Treatment with imatinib mesylate alone has been shown to have excellent long-term efficacy against myeloproliferative neoplasms; however, its long-term effects on ALL and AML have not been elucidated. A 75-year-old man was diagnosed with acute myeloid leukemia having the PDGFRB and cGMP-dependent protein kinase 2 fusion gene with additional genetic abnormalities. Continuous therapy with single-agent imatinib mesylate resulted in cytogenetic remission and decreased molecular burden for 9 months; however, the leukemia subsequently recurred, and the patient died 1 year after initiation of treatment. This case report supports the importance of cytogenetic analysis during patient screening.

Fibroblast growth factor receptor 1 and cytokeratin 20 expressions and their relation to prognostic variables in bladder cancer

BACKGROUND

Tumor grade and stage are currently the most important prognostic variables in bladder cancer but establishing additional criteria is still needed for effective treatment.

OBJECTIVES

The aim of the study was to assess the expression of fibroblast growth factor receptor 1 (FGFR1) and cytokeratin 20 (CK20) in cancer bladder (CB) and to evaluate their association with the clinicopathological features of the disease.

PATIENTS AND METHODS

The study included 80 patients diagnosed as bladder cancer of different stages and grades and 80 patients with nonmalignant urothelial diseases of matched age and sex to the malignant group. The expressions of FGFR1 and CK20 in tissue samples were determined by RT-PCR and immunohistochemistry.

RESULTS

The expression levels of FGFR1 and CK20 were increased in the malignant group when compared to the control group (P<0.001 for each). Analysis of their expression showed that levels of FGFR1 and CK20 were significantly higher in invasive tumor stages (pT2-pT4) than in non-invasive stages (pTis, pTa, pT1) (P<0.001). Interestingly, the sensitivity and specificity of combined detection with CK20 and FGFR1 for the differentiation between invasive and non-invasive stages of bladder cancer reached 97.5% and 92.5%, respectively.

CONCLUSION

Our results determined overexpression of both FGFR1 and CK20 in CB specimens. The alterations in the expression of FGFR1 and CK20 were associated with disease stage and grade. Lastly, combined detection of FGFR1 and CK20 had a high predictive prognostic value in differentiating invasive from non-invasive carcinoma.

Fusion of platelet-derived growth factor receptor β to CEV14 gene in chronic myelomonocytic leukemia: A case report and review of the literature

Myeloid tumor possessing platelet-derived growth factor receptor β (PDGFRβ) gene rearrangement is a rare hematological malignancy, which presents with typical characteristics of myeloid proliferation disorders and eosinophilia. In the present study, an elderly chronic myelomonocytic leukemia patient was diagnosed with chromosome rearrangement. Fluorescence in situ hybridization (FISH) was conducted with a PDGFRβ isolate probe, and gene translocation between PDGFRβ on chromosome 5 and genes on the chromosomes of group D (13-15) was detected. Karyotype analysis revealed a chromosome 5 break, and PDGFRβ-thyroid hormone receptor interactor 11 (CEV14) gene fusion was confirmed via reverse transcription-polymerase chain reaction (RT-PCR), which additionally revealed the chromosome rearrangement t(5;14)(q33;q32). Due to the correlation between PDGFRβ-CEV14 expression and effectiveness of treatment with tyrosine kinase inhibitors, this fusion gene is considered to be an oncogene. In the present study, an elderly patient was diagnosed with a myeloid tumor associated with the fusion gene PDGFRβ-CEV14, using the methods of FISH and RT-PCR. These methods were confirmed to be of significant value in improving diagnosis, guiding treatment and increasing the cure rate of patients, due to their ability to detect multiple rearrangement genes associated with PDGFRβ in myelodysplastic and myeloproliferative neoplasms.

Fusion of PDGFRB to MPRIP, CPSF6, and GOLGB1 in three patients with eosinophilia-associated myeloproliferative neoplasms

In eosinophilia-associated myeloproliferative neoplasms (MPN-eo), constitutive activation of protein tyrosine kinases (TK) as consequence of translocations, inversions, or insertions and creation of TK fusion genes is recurrently observed. The most commonly involved TK and their potential TK inhibitors include PDGFRA at 4q12 or PDGFRB at 5q33 (imatinib), FGFR1 at 8p11 (ponatinib), and JAK2 at 9p24 (ruxolitinib). We here report the identification of three new PDGFRB fusion genes in three male MPN-eo patients: MPRIP-PDGFRB in a case with t(5;17)(q33;p11), CPSF6-PDGFRB in a case with t(5;12)(q33;q15), and GOLGB1-PDGFRB in a case with t(3;5)(q13;q33). The fusion proteins identified by 5'-rapid amplification of cDNA ends polymerase chain reaction (PCR) or DNA-based long distance inverse PCR are predicted to contain the TK domain of PDGFRB. The partner genes contain domains like coiled-coil structures, which are likely to cause dimerization and activation of the TK. In all patients, imatinib induced rapid and durable complete remissions.

Class III Receptor Tyrosine Kinases in Acute Leukemia - Biological Functions and Modern Laboratory Analysis

Acute myeloid leukemia (AML) is a complex disease caused by deregulation of multiple signaling pathways. Mutations in class III receptor tyrosine kinases (RTKs) have been implicated in alteration of cell signals concerning the growth and differentiation of leukemic cells. Point mutations, insertions, or deletions of RTKs as well as chromosomal translocations induce constitutive activation of the receptor, leading to uncontrolled proliferation of undifferentiated myeloid blasts. Aberrations can occur in all domains of RTKs causing either the ligand-independent activation or mimicking the activated conformation. The World Health Organization recommended including RTK mutations in the AML classification since their detection in routine laboratory diagnostics is a major factor for prognostic stratification of patients. Polymerase chain reaction (PCR)-based methods are well-validated for the detection of fms-related tyrosine kinase 3 (FLT3) mutations and can easily be applied for other RTKs. However, when methodological limitations are reached, accessory techniques can be applied. For a higher resolution and more quantitative approach compared to agarose gel electrophoresis, PCR fragments can be separated by capillary electrophoresis. Furthermore, high-resolution melting and denaturing high-pressure liquid chromatography are reliable presequencing screening methods that reduce the sample amount for Sanger sequencing. Because traditional DNA sequencing is time-consuming, next-generation sequencing (NGS) is an innovative modern possibility to analyze a high amount of samples simultaneously in a short period of time. At present, standardized procedures for NGS are not established, but when this barrier is resolved, it will provide a new platform for rapid and reliable laboratory diagnostic of RTK mutations in patients with AML. In this article, the biological and physiological role of RTK mutations in AML as well as possible laboratory methods for their detection will be reviewed.

Role of receptor tyrosine kinases and their ligands in glioblastoma

Glioblastoma multiforme is the most frequent, aggressive and fatal type of brain tumor. Glioblastomas are characterized by their infiltrating nature, high proliferation rate and resistance to chemotherapy and radiation. Recently, oncologic therapy experienced a rapid evolution towards “targeted therapy,” which is the employment of drugs directed against particular targets that play essential roles in proliferation, survival and invasiveness of cancer cells. A number of molecules involved in signal transduction pathways are used as molecular targets for the treatment of various tumors. In fact, inhibitors of these molecules have already entered the clinic or are undergoing clinical trials. Cellular receptors are clear examples of such targets and in the case of glioblastoma multiforme, some of these receptors and their ligands have become relevant. In this review, the importance of glioblastoma multiforme in signaling pathways initiated by extracellular tyrosine kinase receptors such as EGFR, PDGFR and IGF-1R will be discussed. We will describe their ligands, family members, structure, activation mechanism, downstream molecules, as well as the interaction among these pathways. Lastly, we will provide an up-to-date review of the current targeted therapies in cancer, in particular glioblastoma that employ inhibitors of these pathways and their benefits.

Molecular therapeutic approaches to acute myeloid leukemia: targeting aberrant chromatin dynamics and signal transduction

Acute myeloid leukemia research and clinical management have greatly benefited from the achievements in molecular biology regarding the identification of the underlying pathogenetic mechanisms of transformation and resistance to therapy. In particular, two categories of alterations, the aberrant activity of transcription/chromatin-remodeling factors and the deregulated activation of signal transduction pathways, have been demonstrated to play a pivotal role in leukemic cell differentiation, proliferation and resistance to apoptosis. These molecular lesions have proven to be suitable therapeutic targets in acute promyelocytic leukemia and chronic myeloid leukemia and are now also seen as therapeutic targets for a wider group of leukemic disorders. The development of novel drugs such as histone deacetylase inhibitors, demethylating agents and inhibitors of receptor tyrosine kinases may potentially benefit acute myeloid leukemia patients.

Kinase activation in circulating cells: opportunities for biomarkers for diagnosis and therapeutic monitoring

A clinically useful tool to assay phosphorylation-dependent signaling in circulating cells has the potential to provide a wealth of information about a patient's health, including information unavailable by any other method. Patterns of kinase activation, such as the abnormal signaling characteristic of myeloproliferative disorders, may offer highly specific biomarkers for diagnosis or monitoring the efficacy of therapeutics. For assays of kinase activity in circulating leukocytes to be standardized, let alone made practical for the clinic, numerous technical hurdles must be overcome. In this review the current status of analysis of kinase signaling in circulating cells and recent progress in biomarker discovery and validation is discussed. Looking forward, the potential value of signaling patterns as complex biomarkers and the resulting need for future development of robust, multiplexed assays of kinase activation is addressed.

Incidence and clinical characteristics of myeloproliferative neoplasms displaying a PDGFRB rearrangement

OBJECTIVES

The myeloproliferative neoplasms displaying a PDGFRB rearrangement are rare diseases derived from a haematopoietic stem cell. The goals of the study were to assess the incidence of these disorders and to define the clinical and biological characteristics as well as the response to the imatinib therapy.

METHODS

A total of 556 patients with myeloproliferative neoplasms were studied by means of molecular cytogenetics.

RESULTS

The incidence of myeloproliferative neoplasms (MPN) with PDGFRB rearrangement was low (10 cases, 1.8% of all MPN). Most of the patients showed moderate anaemia (median Hb was 10.0 gr/dL; range from 7.5 to 13 g/dL), leukocytosis (median white blood cells was 21.7 × 10(9) /L with a range from 4 to 43 × 10(9) /L) and eosinophilia (median circulating eosinophils was 2.4 × 10(9) /L with a range of 1.1-5.7 × 10(9) /L) with a median of bone marrow infiltration cells displaying PDGFRB rearrangement of 55% (range, 37-85%). In three cases, a t(5;12) was observed while two patients showed rearrangements of 17q21 region. In two cases, a del(5)(q31) was observed. Most of the patients responded to standard dosage of imatinib, and the response was maintained in the time in those patients with a follow-up higher than 9 years.

CONCLUSIONS

The incidence of patients with PDGFRB rearrangement is low. These patients showed leukocytosis with eosinophilia and anaemia. The efficacy of imatinib therapy in patients showing PDGFRB rearrangement is high. For this reason, in all patients with MPN without any other molecular aberration, PDGFRB rearrangement should be ascertained.

A Decade of FGF Receptor Research in Bladder Cancer: Past, Present, and Future Challenges

Fibroblast growth factors (FGFs) orchestrate a variety of cellular functions by binding to their transmembrane tyrosine-kinase receptors (FGFRs) and activating downstream signalling pathways, including RAS/MAPK, PLCγ1, PI3K, and STATs. In the last ten years, it has become clear that FGF signalling is altered in a high proportion of bladder tumours. Activating mutations and/or overexpression of FGFR3 are common in urothelial tumours with low malignant potential and low-stage and -grade urothelial carcinomas (UCs) and are associated with a lower risk of progression and better survival in some subgroups. FGFR1 is not mutated in UC, but overexpression is frequent in all grades and stages and recent data indicate a role in urothelial epithelial-mesenchymal transition. In vitro and in vivo studies have shown that FGFR inhibition has cytotoxic and/or cytostatic effects in FGFR-dependent bladder cancer cells and FGFR-targeted agents are currently being investigated in clinical studies for the treatment of UC. Urine-based tests detecting common FGFR3 mutations are also under development for surveillance of low-grade and -stage tumours and for general population screening. Overall, FGFRs hold promise as therapeutic targets, diagnostic and prognostic markers, and screening tools for early detection and clinical management of UC.

Mechanisms of FGFR-mediated carcinogenesis

In this review, the evidence for a role of fibroblast growth factor receptor (FGFR) mediated signalling in carcinogenesis are considered and relevant underlying mechanisms highlighted. FGF signalling mediated by FGFR follows a classic receptor tyrosine kinase signalling pathway and its deregulation at various points of its cascade could result in malignancy. Here we review the accumulating reports that revealed the association of FGF/FGFRs to various types of cancer at a genetic level, along with in vitro and in vivo evidences available so far, which indicates the functional involvement of FGF signalling in tumour formation and progression. An increasing number of drugs against the FGF pathways is currently in clinical testing. We will discuss the strategies for future FGF research in cancer and translational approaches.

Genomic profiling of B-progenitor acute lymphoblastic leukemia

Childhood acute lymphoblastic leukemia (ALL) is comprised of multiple subtypes defined by recurring chromosomal alterations that are important events in leukemogenesis and are widely used in diagnosis and risk stratification, yet fail to fully explain the biology of this disease. In the last 5 years, genome-wide profiling of gene expression, structural DNA alterations and sequence variations has yielded important insights into the nature of submicroscopic genetic alterations that define novel subgroups of acute lymphoblastic leukemia and cooperate with known cytogenetic alterations in leukemogenesis. Importantly, several of these alterations are important determinants of risk of relapse and are potential targets for therapeutic intervention. Here, these advances and future directions in the genomic analysis of ALL are discussed.

The driver of malignancy in KG-1a leukemic cells, FGFR1OP2-FGFR1, encodes an HSP90 addicted oncoprotein

The KG-1a cell line is developed from a human stem cell myeloproliferative neoplasm as the result of intragenic disruption and a chromosomal translocation of the FGFR1 gene and the FGFR1OP2 gene encoding a protein of unknown function called FOP2 (FGFR1 Oncogene Partner 2). The resulting fusion protein FOP2-FGFR1 is soluble and has constitutive tyrosine kinase activity. Since the heat shock protein HSP90 and its co-chaperone CDC37 have been shown to stabilize many oncogenic proteins, we investigated the requirement for HSP90 or HSP90-CDC37 assistance to maintain the stability or activity of FOP2-FGFR1 expressed in KG-1a cells. We found that HSP90-CDC37 forms a permanent complex with FOP2-FGFR1. This results in protection against degradation of FOP2-FGFR1 and holds the oncoprotein in a permanently active conformation. Inhibition of HSP90 or depletion of CDC37 or heat shock factor 1 (HSF1) reduced the expression level of FOP2-FGFR1 and was sufficient to block the oncoprotein induced proliferation of KG-1a cells. We conclude that the driver of malignancy in KG-1a leukemic cells, FOP2-FGFR1, is an HSP90 addicted oncoprotein. This provides a rationale for the therapeutic use of HSP90 inhibitors in myeloid leukemias that contain FGFR fusion proteins.

Fusion of PDGFRB to two distinct loci at 3p21 and a third at 12q13 in imatinib-responsive myeloproliferative neoplasms

We identified four patients who presented with BCR-ABL1 negative myeloproliferative neoplasms and cytogenetically visible abnormalities of chromosome band 5q31-35. Fluorescence in situ hybridization indicated that the platelet-derived growth factor receptor beta gene (PDGFRB) was disrupted in all four cases and 5' rapid amplification of cDNA ends identified in-frame mRNA fusions between PDGFRB and WDR48 (3p21), GOLGA4 (3p21) and BIN2 (12q13). Strikingly, all three genes encode proteins involving intracellular trafficking. Imatinib, a known inhibitor of PDGFRbeta, selectively blocked the growth of t(3;5) myeloid colonies and produced clinically significant responses in all patients. We conclude that PDGFRB fuses to diverse partner genes in atypical myeloproliferative neoplasms (MPNs). Although very rare, identification of these fusions is critical for proper management of affected individuals.

Hypereosinophilic syndrome and clonal eosinophilia: point-of-care diagnostic algorithm and treatment update

Acquired eosinophilia is operationally categorized into secondary, clonal, and idiopathic types. Causes of secondary eosinophilia include parasite infections, allergic or vasculitis conditions, drugs, and lymphoma. Clonal eosinophilia is distinguished from idiopathic eosinophilia by the presence of histologic, cytogenetic, or molecular evidence of an underlying myeloid malignancy. The World Health Organization classification system for hematologic malignancies recognizes 2 distinct subcategories of clonal eosinophilia: chronic eosinophilic leukemia, not otherwise specified and myeloid/lymphoid neoplasms with eosinophilia and mutations involving platelet-derived growth factor receptor alpha/beta or fibroblast growth factor receptor 1. Clonal eosinophilia might also accompany other World Health Organization-defined myeloid malignancies, including chronic myelogenous leukemia, myelodysplastic syndromes, chronic myelomonocytic leukemia, and systemic mastocytosis. Hypereosinophilic syndrome, a subcategory of idiopathic eosinophilia, is defined by the presence of a peripheral blood eosinophil count of 1.5 x 10(9)/L or greater for at least 6 months (a shorter duration is acceptable in the presence of symptoms that require eosinophil-lowering therapy), exclusion of both secondary and clonal eosinophilia, evidence of organ involvement, and absence of phenotypically abnormal and/or clonal T lymphocytes. The presence of the latter defines lymphocytic variant hyper eosinophilia, which is best classified under secondary eosinophilia. In the current review, we provide a simplified algorithm for distinguishing the various causes of clonal and idiopathic eosinophilia and discuss current therapy, including new drugs (imatinib mesylate, alemtuzumab, and mepolizumab).

Fibroblast growth factor signalling: from development to cancer

Fibroblast growth factors (FGFs) and their receptors control a wide range of biological functions, regulating cellular proliferation, survival, migration and differentiation. Although targeting FGF signalling as a cancer therapeutic target has lagged behind that of other receptor tyrosine kinases, there is now substantial evidence for the importance of FGF signalling in the pathogenesis of diverse tumour types, and clinical reagents that specifically target the FGFs or FGF receptors are being developed. Although FGF signalling can drive tumorigenesis, in different contexts FGF signalling can mediate tumour protective functions; the identification of the mechanisms that underlie these differential effects will be important to understand how FGF signalling can be most appropriately therapeutically targeted.

Fibroblast growth factor receptor 1 promotes proliferation and survival via activation of the mitogen-activated protein kinase pathway in bladder cancer

Fibroblast growth factor receptors (FGFR) play key roles in proliferation, differentiation, and tumorigenesis. Many urothelial carcinomas contain activating point mutations or increased expression of FGFR3. However, little is known about the role of other FGFRs. We examined FGFR expression in telomerase-immortalized normal human urothelial cells, urothelial carcinoma cell lines, and tumor samples and showed that FGFR1 expression is increased in a high proportion of cell lines and tumors independent of stage and grade. To determine the role of FGFR1 in low-stage bladder cancer, we overexpressed FGFR1 in telomerase-immortalized normal human urothelial cells and examined changes in proliferation and cell survival in response to FGF2. FGFR1 stimulation increased proliferation and reduced apoptosis. To elucidate the mechanistic basis for these alterations, we examined the signaling cascades activated by FGFR1. FRS2alpha and PLCgamma were activated in response to FGF2, leading to activation of the mitogen-activated protein kinase pathway. The level of mitogen-activated protein kinase activation correlated with the level of cyclin D1, MCL1, and phospho-BAD, which also correlated with FGFR-induced proliferation and survival. Knockdown of FGFR1 in urothelial carcinoma cell lines revealed differential FGFR1 dependence. JMSU1 cells were dependent on FGFR1 expression for survival but three other cell lines were not. Two cell lines (JMSU1 and UMUC3) were dependent on FGFR1 for growth in soft agar. Only one of the cell lines tested (UMUC3) was frankly tumorigenic; here, FGFR1 knockdown inhibited tumor growth. Our results indicate that FGFR1 has significant effects on urothelial cell phenotype and may represent a useful therapeutic target in some cases of urothelial carcinoma.

Transcription and signalling pathways involved in BCR-ABL-mediated misregulation of 24p3 and 24p3R

Lipocalin 24p3 is a secreted protein that can induce apoptosis in cells containing the 24p3 cell surface receptor, 24p3R. The oncoprotein BCR-ABL activates 24p3 and represses 24p3R expression. Thus, BCR-ABL(+) cells synthesise and secrete 24p3, which induces apoptosis in normal 24p3R-containing cells but not in BCR-ABL(+) cells. The cell signalling and transcription factor pathways by which BCR-ABL misregulates expression of 24p3 and 24p3R remain to be elucidated. Here we show that BCR-ABL upregulates 24p3 expression through activation of the JAK/STAT pathway, which culminates in binding of Stat5 to the 24p3 promoter. We find that 24p3R expression is regulated by Runx transcription factors, and that BCR-ABL induces a switch in binding from Runx3, an activator of 24p3R expression, to Runx1, a repressor of 24p3R expression, through a Ras signalling pathway. Finally, we show that repression of 24p3R by BCR-ABL is a critical feature of the mechanism by which imatinib kills BCR-ABL(+) cells. Our results reveal diverse signalling/transcription pathways that regulate 24p3 and 24p3R expression in response to BCR-ABL and are directly relevant to the treatment of BCR-ABL(+) disease.

Intrinsic differences between the catalytic properties of the oncogenic NUP214-ABL1 and BCR-ABL1 fusion protein kinases

The NUP214-ABL1 fusion kinase has recently been identified in 6% of patients with T-cell acute lymphoblastic leukemia. In contrast to the more common oncogenic ABL1 fusion BCR-ABL1, NUP214-ABL1 localizes to the nuclear pore complexes and has attenuated transforming properties in hematopoietic cells and in mouse bone marrow transplant models. We have performed a thorough biochemical comparative analysis of NUP214-ABL1 and BCR-ABL1 and show that, despite their common tyrosine kinase domain, the two fusion proteins differ in many critical catalytic properties. NUP214-ABL1 has lower in vitro tyrosine kinase activity, which is in agreement with the absence of phosphorylation on its activation loop. NUP214-ABL1 was more sensitive to imatinib (Glivec) than BCR-ABL1 in vitro and in cells, indicating a different activation state and conformation of the two ABL1 fusion kinases. Using a peptide array, we identified differences in the spectrum and efficiency of substrate peptide phosphorylation and a differential involvement of Src kinases in downstream signaling. These results clearly indicate that different fusion partners of the same kinase can determine not only localization, but also critical functional properties of the enzyme such as inhibitor sensitivity and substrate preference, with subsequent differences in downstream signaling effectors and likely consequences in disease pathogenesis.

8p11 myeloproliferative syndrome preceded by t(8;9)(p11;q33), CEP110/FGFR1 fusion transcript: morphologic, molecular, and cytogenetic characterization of myeloid neoplasms associated with eosinophilia and FGFR1 abnormality

We report a rare case of t(8;9)(p11;q33) in a patient with 8p11 myeloproliferative syndrome (EMS) that was preceded by centrosomal protein 110kDa (CEP110; previously CEP1)/fibroblast growth factor receptor 1 (FGFR1) fusion transcript. A 36-year-old man was brought to Severance Hospital with a nasopharyngeal mass and eosinophilia. Biopsy of the left tonsil and nasopharynx revealed diffuse infiltration of atypical lymphoid cells, and he was diagnosed with precursor T-cell lymphoma with hypereosinophilic syndrome. Two months later, chromosome study revealed a 46,XY,t(8;9)(p11;q33) karyotype, and the CEP110/FGFR1 fusion transcript was detected by reverse transcription-polymerase chain reaction (RT-PCR) in both this and the previous bone marrow specimen. Timely molecular and cytogenetic tests are of value for diagnosis and treatment of the newly classified "myeloid neoplasms associated with clonal eosinophilic disorders" (according to 2008 World Health Organization criteria).

Roles for deregulated receptor tyrosine kinases and their downstream signaling molecules in hematologic malignancies

Growth, survival and differentiation of hematopoietic cells are regulated by the interactions between hematopoietic growth factors and their receptors. The defect in these interactions results in a failure of hematopoiesis, while aberrantly elevated and/or sustained activation of these signals cause hematologic malignancies. Among them, constitutively activating mutations of the receptor tyrosine kinases (RTKs), such as c-Kit, platelet-derived growth factor receptor (PDGFR) and FLT3, are often involved in the pathogenesis of various types of hematologic malignancies. Constitutive activation of RTKs is provoked by several mechanisms including chromosomal translocations and various mutations involving their regulatory regions. Chromosomal translocations commonly generate chimeric proteins consisting of the cytoplasmic domain of RTKs and the dimerization or multimerization motif of the fusion partner, resulting in the constitutive dimerization of RTKs. On the other hand, missense, insertion or deletion mutations in the regulatory regions, such as juxtamembrane domain, activation loop, and extracellular domain, also cause constitutive activation of RTKs mainly by preventing the auto-inhibitory regulation. Oncogenic RTKs activate downstream signaling molecules such as Ras/MAPK, PI3-K/Akt/mTOR, and STATs as well as ligand-activated wild type RTKs. However, their signals are quantitatively and qualitatively different from wild type RTKs. Based on these findings, several agents that target oncogenic RTKs or their downstream molecules have been developed: imatinib and FLT3 inhibitors for RTKs themselves, farnesyltransferase inhibitors, mTOR inhibitors and MEK inhibitors for the downstream signaling molecules. As promising results have been obtained in several clinical trials using these agents, the establishment of these molecular targeted agents is expected.

Extramedullary molecular evidence of the 5′KIAA1509/3′PDGFRB fusion gene in chronic eosinophilic leukemia

We report a case of chronic eosinophilic leukemia (CEL), demonstrating for the first time: (i) the association of CEL with the 5'KIAA1509/3'PDGFRB fusion gene as a consequence of a t(5;14)(q33;q32); (ii) the molecular detection of this rearrangement in an extramedullary site; (iii) the cloning and sequencing of the KIAA1509 and PDGFRB genomic breakpoints. The 5'KIAA1509/3'PDGFRB fusion gene is predicted to encode a protein of 2059 amino acids. The genomic breakpoints were localized inside KIAA1509 intron 11 and PDGFRB intron 10. Sequence analysis in correspondence with these breakpoints revealed the presence of repetitive DNA, such Alu elements, which could promote chromosomal rearrangements.

The diagnosis of BCR/ABL-negative chronic myeloproliferative diseases (CMPD): a comprehensive approach based on morphology, cytogenetics, and molecular markers

Recent years showed significant progress in the molecular characterization of the chronic myeloproliferative disorders (CMPD) which are classified according to the WHO classification of 2001 as polycythemia vera (PV), chronic idiopathic myelofibrosis (CIMF), essential thrombocythemia (ET), CMPD/unclassifiable (CMPD-U), chronic neutrophilic leukemia, and chronic eosinophilic leukemia (CEL)/hypereosinophilic syndrome, all to be delineated from BCR/ABL-positive chronic myeloid leukemia (CML). After 2001, the detection of the high frequency of the JAK2V617F mutation in PV, CIMF, and ET, and of the FIP1L1–PDGFRA fusion gene in CEL further added important information in the diagnosis of CMPD. These findings also enhanced the importance of tyrosine kinase mutations in CMPD and paved the way to a more detailed classification and to an improved definition of prognosis using also novel minimal residual disease (MRD) markers. Simultaneously, the broadening of therapeutic strategies in the CMPD, e.g., due to reduced intensity conditioning in allogeneic hematopoietic stem cell transplantation and the introduction of tyrosine kinase inhibitors in CML, in CEL, and in other ABL and PDGRFB rearrangements, increased the demands to diagnostics. Therefore, today, a multimodal diagnostic approach combining cytomorphology, cytogenetics, and individual molecular methods is needed in BCR/ABL-negative CMPD. A stringent diagnostic algorithm for characterization, choice of treatment, and monitoring of MRD will be proposed in this review.

Recurrent finding of the FIP1L1-PDGFRA fusion gene in eosinophilia-associated acute myeloid leukemia and lymphoblastic T-cell lymphoma

The FIP1L1-PDGFRA fusion gene has been described in patients with eosinophilia-associated myeloproliferative disorders (Eos-MPD). Here, we report on seven FIP1L1-PDGFRA-positive patients who presented with acute myeloid leukemia (AML, n=5) or lymphoblastic T-cell non-Hodgkin-lymphoma (n=2) in conjunction with AML or Eos-MPD. All patients were male, the median age was 58 years (range, 40-66). AML patients were negative for common mutations of FLT3, NRAS, NPM1, KIT, MLL and JAK2; one patient revealed a splice mutation of RUNX1 exon 7. Patients were treated with imatinib (100 mg, n=5; 400 mg, n=2) either as monotherapy (n=2), as maintenance treatment after intensive chemotherapy (n=3) or in overt relapse 43 and 72 months, respectively, after primary diagnosis and treatment of FIP1L1-PDGFRA-positive disease (n=2). All patients are alive, disease-free and in complete hematologic and complete molecular remission after a median time of 20 months (range, 9-36) on imatinib. The median time to achievement of complete molecular remission was 6 months (range, 1-14). We conclude that all eosinophilia-associated hematological malignancies should be screened for the presence of the FIP1L1-PDGFRA fusion gene as they are excellent candidates for treatment with tyrosine kinase inhibitors even if they present with an aggressive phenotype such as AML.

Bone Marrow Phospho-STAT5 Expression in Non-CML Chronic Myeloproliferative Disorders Correlates With JAK2 V617F Mutation and Provides Evidence of In Vivo JAK2 Activation

The recently described JAK2 V617F mutation, present in a substantial proportion of nonchronic myelogenous leukemia chronic myeloproliferative disorders (non-CML CMPDs), is changing the way we conceptualize and diagnose these diseases. We hypothesized that the activation of this tyrosine kinase might result in activation of downstream mediators such as STAT5, which would be detectable in bone marrow biopsies. We examined the expression of activated STAT5 (nuclear phospho-STAT5) in 73 bone marrow biopsies from patients with CMPDs [20 essential thrombocythemia (ET), 26 chronic idiopathic myelofibrosis (CIMF), and 27 polycythemia vera] and 39 controls. We compared the results with the JAK2 mutational status and clinical parameters. The frequency of the JAK2 V617F was 73% (85% in PV, 65% in ET, and 65% in CIMF). All patients with the JAK2 V617F showed abnormal nuclear megakaryocytic phospho-STAT5 (nMEG pSTAT5) expression. In the JAK2 wild-type group, nMEG pSTAT5 was observed in 2/7 ET, and 3/9 CIMF patients. nMEG pSTAT5 staining was 100% sensitive and 88% specific for JAK2 V617F. Clinically, nMEG pSTAT5+ patients seemed to require cytoreductive therapy more often than those without nMEG p-STAT expression. pSTAT5 immunohistochemistry is a useful diagnostic test in bone marrow biopsies from suspected non-CML CMPD patients. It identifies most of the patients with the JAK2 V617F but also other JAK2 wild-type CMPD patients. The presence of nMEG pSTAT5 in a subset of CMPD patients lacking the mutation suggests that alternate tyrosine kinase/phosphatase pathways may be involved and warrant further investigation. Phosphoprotein detection represents a new area for diagnostic pathology that exploits specific functional characteristics of cells within the context of a tissue section.

Transient response to imatinib in a chronic eosinophilic leukemia associated with ins(9;4)(q33;q12q25) and a CDK5RAP2-PDGFRA fusion gene

Chronic myeloproliferative disorders with rearrangements of the platelet-derived growth factor receptor A (PDGFRA) gene at chromosome band 4q12 have shown excellent responses to targeted therapy with imatinib. Here we report a female patient who presented with advanced phase of a chronic eosinophilic leukemia. Cytogenetic analysis revealed an ins(9;4)(q33;q12q25) in 5 of 21 metaphases. FISH analysis with flanking BAC probes indicated that PDGFRA was disrupted. A novel mRNA in-frame fusion between exon 13 of the CDK5 regulatory subunit associated protein 2 (CDK5RAP2) gene, a 40-bp insert that was partially derived from an inverted sequence stretch of PDGFRA intron 9, and a truncated PDGFRA exon 12 was identified by 5'-RACE-PCR. CDK5RAP2 encodes a protein that is believed to be involved in centrosomal regulation. The predicted CDK5RAP2-PDGFRA protein consists of 1,003 amino acids and retains both tyrosine kinase domains of PDGFRA and several potential dimerization domains of CDK5RAP2. Despite achieving complete cytogenetic and molecular remission on imatinib, the patient relapsed with imatinib-resistant acute myeloid leukemia that was characterized by a normal karyotype, absence of detectable CDK5RAP2-PDGFRA mRNA, and a newly acquired G12D NRAS mutation.

Identification of a novel imatinib responsive KIF5B-PDGFRA fusion gene following screening for PDGFRA overexpression in patients with hypereosinophilia

Idiopathic hypereosinophilic syndrome (IHES) is a disease that is difficult to classify, and diagnosis is one of exclusion. The identification of a cytogenetically invisible interstitial deletion resulting in the fusion of FIP1-Like-1 (FIP1L1) to platelet-derived growth factor receptor alpha (PDGFRA) has enabled many IHES cases to be reclassified as chronic eosinophilic leukemia. As it is likely that PDGFRA may fuse to other partner genes, we established a reverse transcriptase-PCR test to detect specific overexpression of the PDGFRA kinase domain as an indicator of the presence of a fusion gene. Overexpression was detected in 12/12 FIP1L1-PDGFRA-positive patients, plus 9/217 (4%) patients with hypereosinophilia who had tested negative for FIP1L1-PDGFRA. One of the positive cases was investigated in detail and found to have a complex karyotype involving chromosomes 3, 4 and 10. Amplification of the genomic breakpoint by bubble PCR revealed a novel fusion between KIF5B at 10p11 and PDGFRA at 4q12. Imatinib, a known inhibitor of PDGFRalpha, produced a complete cytogenetic response and disappearance of the KIF5B-PDGFRA fusion by PCR, from both genomic DNA and mRNA. This study demonstrates the utility of screening for PDGFRA kinase domain overexpression in patients with IHES and has identified a third PDGFRA fusion partner in chronic myeloproliferative disorders.

Biology of platelet-derived growth factor and its involvement in disease

Platelet-derived growth factor (PDGF) is mainly believed to be an important mitogen for connective tissue, especially for fibroblasts that serve in wound healing. However, PDGF also has important roles during embryonal development, and its overexpression has been linked to different types of fibrotic disorders and malignancies. Platelet-derived growth factor is synthesized by many different cell types, and its expression is broad. Its synthesis is in response to external stimuli, such as exposure to low oxygen tension, thrombin, or stimulation by other cytokines and growth factors. In addition, PDGF may function in autocrine stimulation of tumor cells, regulation of interstitial fluid pressure, and angiogenesis. Recently, several drugs were developed that are potent inhibitors of the tyrosine kinase activity of PDGF receptors. Thus, it is important to understand the physiology of PDGF and its receptors and the role of PDGF in different diseases. This review summarizes the physiologic activity of PDGF, the expression of PDGF during embryonal development, and the roles of PDGF expression in nonmalignant disease and in different tumors.

Classification of chronic myeloid disorders: From Dameshek towards a semi-molecular system

Hematological malignancies are phenotypically organized into lymphoid and myeloid disorders, although such a distinction might not be precise from the standpoint of lineage clonality. In turn, myeloid malignancies are broadly categorized into either acute myeloid leukemia (AML) or chronic myeloid disorder (CMD), depending on the presence or absence, respectively, of AML-defining cytomorphologic and cytogenetic features. The CMD are traditionally classified by their morphologic appearances into discrete clinicopathologic entities based primarily on subjective technologies. It has now become evident that most CMD represent clonal stem cell processes where the primary oncogenic event has been characterized in certain instances; Bcr/Abl in chronic myeloid leukemia, FIP1L1-PDGFRA or c-kit(D816V) in systemic mastocytosis, rearrangements of PDGFRB in chronic eosinophilic leukemia, and rearrangements of FGFR1 in stem cell leukemia/lymphoma syndrome. In addition, Bcr/Abl-negative classic myeloproliferative disorders are characterized by recurrent JAK2(V617F) mutations, whereas other mutations affecting the RAS signaling pathway molecules have been associated with juvenile myelomonocytic leukemia. Such progress is paving the way for a transition from a histologic to a semi-molecular classification system that preserves conventional terminology, while incorporating new information on molecular pathogenesis.

FLT3 is fused to ETV6 in a myeloproliferative disorder with hypereosinophilia and a t(12;13)(p13;q12) translocation

The FMS-like tyrosine kinase 3 (FLT3) gene, belonging to the receptor tyrosine kinase (TK) subclass III family, plays an important role in normal hematopoiesis and is one of the most frequently mutated genes in hematologic malignancies as well as an attractive target for directed inhibition. Activating mutations of this gene, including internal tandem duplication in the juxtamembrane (JM) domain and point mutations in the TK domain, are found in approximately one-third of patients with acute myeloid leukemia and in a smaller subset of patients with acute lymphoblastic leukemia. We report here that FLT3 may contribute to leukemogenesis in a patient with myeloproliferative disorder and a t(12;13)(p13;q12) translocation through generating a fusion gene with the ETS variant gene 6 (ETV6) gene. ETV6 has been reported to fuse to various partner genes, including TK and transcription factors. Both ETV6/FLT3 and reciprocal FLT3/ETV6 transcripts were detected in the patient mRNA by reverse transcriptase-polymerase chain reaction. At the protein level, however, only ETV6/FLT3 products were expressed. Among them, one retains the helix-loop-helix (HLH) oligomerization domain of ETV6 and the JM as well as TK domain of FLT3. FLT3 receptor in leukemic cells might be inappropriately activated through dimerization by HLH domain of ETV6, which consequently interfered with proliferation and differentiation of hematopoietic cells.

Eosinophilia: secondary, clonal and idiopathic

Blood eosinophilia signifies either a cytokine-mediated reactive phenomenon (secondary) or an integral phenotype of an underlying haematological neoplasm (primary). Secondary eosinophilia is usually associated with parasitosis in Third World countries and allergic conditions in the West. Primary eosinophilia is operationally classified as being clonal or idiopathic, depending on the respective presence or absence of a molecular, cytogenetic or histological evidence for a myeloid malignancy. The current communication features a comprehensive clinical summary of both secondary and primary eosinophilic disorders with emphasis on recent developments in molecular pathogenesis and treatment.

Fusion tyrosine kinases: a result and cause of genomic instability

Reciprocal chromosomal translocations may arise as a result of unfaithful repair of spontaneous DNA double-strand breaks, most probably induced by oxidative stress, radiation, genotoxic chemicals and/or replication stress. Genes encoding tyrosine kinases are targeted by these mechanisms resulting in the generation of chimera genes encoding fusion tyrosine kinases (FTKs). FTKs display transforming activity owing to their constitutive kinase activity causing deregulated proliferation, apoptosis, differentiation and adhesion. Moreover, FTKs are able to facilitate DNA repair, prolong activation of G(2)/M and S cell cycle checkpoints, and elevate expression of antiapoptotic protein Bcl-X(L), making malignant cells less responsive to antitumor treatment. FTKs may also stimulate the generation of reactive oxygen species and enhance spontaneous DNA damage in tumor cells. Unfortunately, FTKs compromise the fidelity of DNA repair mechanisms, which contribute to the accumulation of additional genetic abnormalities leading to the resistance to inhibitors such as imatinib mesylate and malignant progression of the disease.

Molecular regulation of receptor tyrosine kinases in hematopoietic malignancies

Dysregulation of receptor tyrosine kinase (RTK) activity has been implicated in the progression of a variety of human leukemias. Most notably, mutations and chromosomal translocations affecting regulation of tyrosine kinase activity in the Kit receptor, the Flt3 receptor, and the PDGFbeta/FGF1 receptors have been demonstrated in mast cell leukemia, acute myeloid leukemia (AML), and chronic myelogenous leukemias (CML), respectively. In addition, critical but non-overlapping roles for the Ron and Kit receptor tyrosine kinases in the progression of animal models of erythroleukemia have been demonstrated [Persons, D., Paulson, R., Loyd, M., Herley, M., Bodner, S., Bernstein, A., Correll, P. and Ney, P., 1999. Fv2 encodes a truncated form of the Stk receptor tyrosine kinase. Nat. Gen. 23, 159-165.; Subramanian, A., Teal, H.E., Correll, P.H. and Paulson, R.F., 2005. Resistance to friend virus-induced erythroleukemia in W/Wv mice is caused by a spleen-specific defect which results in a severe reduction in target cells and a lack of Sf-Stk expression. J. Virol. 79 (23), 14586-14594.]. The various classes of RTKs implicated in the progression of leukemia have been recently reviewed [Reilly, J., 2003. Receptor tyrosine kinases in normal and malignant haematopoiesis. Blood Rev. 17 (4), 241-248.]. Here, we will discuss the mechanism by which alterations in these receptors result in transformation of hematopoietic cells, in the context of what is known about the molecular regulation of RTK activity, with a focus on our recent studies of the Ron receptor tyrosine kinase.

Atypical myeloproliferative disorders: diagnosis and management

Myeloid disorders constitute a subgroup of hematological malignancies that is separate from lymphoid disorders. The World Health Organization system for classification of tumors of the hematopoietic system divides myeloid disorders into acute myeloid leukemia and chronic myeloid disorders based on the presence or absence, respectively, of acute myeloid leukemia--defining morphological and cytogenetic features including the presence of 20% or more myeloblasts in either the bone marrow or the peripheral blood. A recently proposed semimolecular classification system for chronic myeloid disorders recognizes 3 broad categories: the myelodysplastic syndrome, classic myeloproliferative disorders (MPD), and atypical MPD. Classic MPD includes polycythemia vera, essential thrombocythemia, myelofibrosis with myeloid metaplasia, and chronic myeloid leukemia. Both myelodysplastic syndrome and BCR/ABL-negative classic MPD were previously discussed as part of the current ongoing symposium on hematological malignancies. The current review focuses on the diagnosis and treatment of both molecularly defined and clinicopathologically assigned categories of atypical MPD: chronic myelomonocytic leukemia, juvenile myelomonocytic leukemia, chronic neutrophilic leukemia, chronic basophilic leukemia, chronic eosinophilic leukemia, idiopathic eosinophilia including hypereosinophilic syndrome, systemic mastocytosis, unclassified MPD, and eosinophilic/mast cell disorders associated with mutations of platelet-derived growth factor receptors alpha (PDGFRA) and beta (PDGFRB), FGFR1, and KIT.