Translocation t(8;13)(p11;q11-12) in stem cell leukemia/lymphoma of T-cell and myeloid lineages

Molecular monitoring of 8p11 myeloproliferative syndrome in an infant

The 8p11 myeloproliferative syndrome is a rare hematologic malignancy derived from a pluripotent hematopoietic stem cell associated with rearrangements involving the fibroblast growth factor receptor 1 (FGFR1) gene located on chromosome 8p11. The most common translocation, t(8;13) (p11;q13), results in a ZNF198-FGFR1 fusion gene and constitutively active FGFR1 tyrosine kinase activity. Typical pathologic findings include myeloid hyperplasia, lymphadenopathy, precursor T-lymphoblastic lymphoma, and eosinophilia. The disease is usually associated with an aggressive course and progression to acute myeloid leukemia is frequent. We report here the first case of 8p11 myeloproliferative syndrome in an infant and demonstrate the value of molecular testing in the diagnosis and minimal disease monitoring of this rare disease.

ZNF198, a zinc finger protein rearranged in myeloproliferative disease, localizes to the PML nuclear bodies and interacts with SUMO-1 and PML

The ZNF198/FGFR1 fusion gene in atypical myeloproliferative disease produces a constitutively active cytoplasmic tyrosine kinase, unlike ZNF198 which is normally a nuclear protein. We have now shown that the ZNF198/FGFR1 fusion kinase interacts with the endogenous ZNF198 protein suggesting that the function of ZNF198 may be compromised in cells expressing it. Little is currently known about the endogenous function of ZNF198 and to investigate this further we performed a yeast two-hybrid analysis and identified SUMO-1 as a binding partner of ZNF198. These observations were confirmed using co-immunoprecipitation which demonstrated that ZNF198 is covalently modified by SUMO-1. Since many of the SUMO-1-modified proteins are targeted to the PML nuclear bodies we used confocal microscopy to show that SUMO-1, PML and ZNF198 colocalize to punctate structures, shown by immunocytochemistry to be PML bodies. Using co-immunoprecipitation we now show that PML and sumoylated ZNF198 can be found in a protein complex in the cell. Mutation of the SUMO-1 binding site in wild-type ZNF198 resulted in loss of distinct PML bodies, reduced PML levels and a more dispersed nuclear localization of the PML protein. In cells expressing ZNF198/FGFR1, which also lack the SUMO-1 binding site, SUMO-1 is preferentially localized in the cytoplasm, which is associated with loss of distinct PML bodies. Recently, arsenic trioxide (ATO) was proposed as an alternative therapy for APL that was resistant to traditional therapy. Treatment of cells expressing ZNF198/FGFR1 with ATO demonstrated reduced autophosphorylation of the ZNF198/FGFR1 protein and induced apoptosis, which is not seen in cells expressing wild-type ZNF198. Overall our results suggest that the sumoylation of ZNF198 is important for PML body formation and that the abrogation of sumoylation of ZNF198 in ZNF198/FGFR1 expressing cells may be an important mechanism in cellular transformation.

Induction of the plasminogen activator inhibitor-2 in cells expressing the ZNF198/FGFR1 fusion kinase that is involved in atypical myeloproliferative disease

The ZNF198/FGFR1 fusion kinase associated with an atypical myeloproliferative disease is constitutively activated and regulates several STAT transcription factors. We used oligonucleotide microarrays to compare the gene-expression profiles between HEK-293 cells that stably express either the ZNF198/FGFR1 chimeric protein or the wild-type ZNF198 gene. Expression of the plasminogen activator inhibitor-2 (PAI-2/SERPINB2) was highly increased in cells expressing the fusion gene. Western blot analysis demonstrated that HEK-293 cells do not express PAI-2 endogenously, but in ZNF198/FGFR1-expressing cells 2 molecular forms of PAI-2, which were 47 kDa and 32 kDa, were expressed intracellularly, and a 60-kDa form was secreted. Similarly, expression of ZNF198/FGFR1 in BaF/3 mouse hematopoietic cells also induced the expression of the PAI-2 protein. Immunoprecipitation analysis revealed that both intracellular forms of PAI-2 bind to the ZNF198/FGFR1 kinase. Treatment of HEK-293 and BaF/3 cells with TNF-alpha in the presence of cycloheximide, induced apoptosis in both cases. In contrast, HEK-293 and BaF/3 cells expressing ZNF198/FGFR1 were resistant to TNF-alpha-induced apoptosis. These observations suggest that expression of the ZNF198/FGFR1 fusion gene is associated with specific PAI-2-mediated resistance to apoptosis which may contribute to the highly malignant nature of leukemic cells carrying this fusion kinase gene.

Long-term complete haematological and molecular remission after allogeneic bone marrow transplantation in a patient with a stem cell myeloproliferative disorder associated with t(8;13)(p12;q12)

A rare atypical myeloproliferative disorder (aMPD) associated with chromosomal translocations involving the short arm of chromosome 8, region p11-p12 has been described. In most patients, the cytogenetic abnormality is a t(8;13)(p12;q12) that fuses fibroblast growth factor receptor 1, the 8p12 key gene, to FIM/ZNF198 gene. Prognosis is poor with frequent evolution to acute myeloid leukaemia within 1 year of diagnosis. We report a new patient with aMPD with a t(8;13) translocation. Complete haematological, cytogenetic and molecular remission was demonstrated 39 months after allogeneic bone marrow transplantation. This is the first report to demonstrate a molecular remission in this disorder.

ARG tyrosine kinase activity is inhibited by STI571

The tyrosine kinase inhibitor STI571 inhibits BCR/ABL and induces hematologic remission in most patients with chronic myeloid leukemia. In addition to BCR/ABL, STI571 also inhibits v-Abl, TEL/ABL, the native platelet-derived growth factor (PDGF)beta receptor, and c-KIT, but it does not inhibit SRC family kinases, c-FMS, FLT3, the epidermal growth factor receptor, or multiple other tyrosine kinases. ARG is a widely expressed tyrosine kinase that shares substantial sequence identity with c-ABL in the kinase domain and cooperates with ABL to regulate neurulation in the developing mouse embryo. As described here, ARG has recently been implicated in the pathogenesis of leukemia as a fusion partner of TEL. A TEL/ARG fusion was constructed to determine whether ARG can be inhibited by STI571. When expressed in the factor-dependent murine hematopoietic cell line Ba/F3, the TEL/ARG protein was heavily phosphorylated on tyrosine, increased tyrosine phosphorylation of multiple cellular proteins, and induced factor-independent proliferation. The effects of STI571 on Ba/F3 cells transformed with BCR/ABL, TEL/ABL, TEL/PDGFbetaR, or TEL/ARG were then compared. STI571 inhibited tyrosine phosphorylation and cell growth of Ba/F3 cells expressing BCR/ABL, TEL/ABL, TEL/PDGFbetaR, and TEL/ARG with an IC(50) of approximately 0.5 microM in each case, but it had no effect on untransformed Ba/F3 cells growing in IL-3 or on Ba/F3 cells transformed by TEL/JAK2. Culture of TEL/ARG-transfected Ba/F3 cells with IL-3 completely prevented STI571-induced apoptosis in these cells, similar to what has been observed with BCR/ABL- or TEL/ABL-transformed cells. These results indicate that ARG is a target of the small molecule, tyrosine kinase inhibitor STI571.

ZNF198–FGFR1 transforming activity depends on a novel proline-rich ZNF198 oligomerization domain

An acquired chromosomal translocation, t(8;13)(p11;q11-12), observed in a distinctive type of stem cell leukemia/lymphoma syndrome, leads to the fusion of the 5′ portion of ZNF198 and the 3′ portion of FGFR1. ZNF198–FGFR1 fusion transcripts encode 4 to 10 zinc fingers, a proline-rich region, and the intracellular portion of the FGFR1 (fibroblast growth factor receptor 1) receptor tyrosine kinase. We demonstrate that the ZNF198 proline-rich region constitutes a novel self-association domain. When fused to the intracellular domain of FGFR1, the ZNF198 proline-rich region is sufficient to cause oligomerization, FGFR1 tyrosine kinase activation, and transformation of Ba/F3 cells to IL-3 independent growth.

ZNF198–FGFR1 transforming activity depends on a novel proline-rich ZNF198 oligomerization domain

An acquired chromosomal translocation, t(8;13)(p11;q11-12), observed in a distinctive type of stem cell leukemia/lymphoma syndrome, leads to the fusion of the 5′ portion of ZNF198 and the 3′ portion of FGFR1. ZNF198–FGFR1 fusion transcripts encode 4 to 10 zinc fingers, a proline-rich region, and the intracellular portion of the FGFR1 (fibroblast growth factor receptor 1) receptor tyrosine kinase. We demonstrate that the ZNF198 proline-rich region constitutes a novel self-association domain. When fused to the intracellular domain of FGFR1, the ZNF198 proline-rich region is sufficient to cause oligomerization, FGFR1 tyrosine kinase activation, and transformation of Ba/F3 cells to IL-3 independent growth.

Biphenotypic hematological malignancy with T-lymphoid and myeloid differentiation: association with t(3;12)(p25;q24.3). Case report and review of the literature

Biphenotypic hematological malignancies of T-lymphoid and myeloid differentiation are relatively rare and have most commonly been associated with t(8;13). However, this entity is invariably associated with eosinophilia and generally progresses to acute leukemia within a year of diagnosis. We describe a case of a biphenotypic hematological malignancy with T-lymphoid and myeloid differentiation without associated eosinophilia; however, there was an association with t(3;12)(p25;q24.3) as a sole abnormality and progression to acute leukemia within 10 months of presentation. This association with such a malignancy has not previously been described. Additional cases need to be accrued to determine the prognostic significance and clinical implications of such an association.

[The 8p11 myeloproliferative syndrome]

CLINICAL MANIFESTATIONS

The 8p11 myeloproliferative syndrome is characterized by a chronic myelogenous leukemia-like myeloid hyperplasia, marked eosinophilia and a strikingly high incidence of non-Hodgkin's lymphoma, mostly of the T-lymphoblastic subtype. After a short chronic phase of 6 to 9 months it rapidly transforms into an acute myelogenous leukemia. The median survival time is less than 12 months.

CYTOGENETICS

The leukemic cells of peripheral blood/bone marrow and the lymphoma cells have the same acquired, clonal abnormality of chromosome band 8p11 with the translocations t(8;13)(p11;q12), t(8;9)(p11;q34), and t(6;8)(q27;p11).

MOLECULAR GENETICS

The molecular cloning of these translocations has shown the fusion of three unrelated genes (ZNF198 at 13p12, FAN at 9q34 and FOP at 6q27) to the fibroblast growth factor receptor-1 (FGFR1) gene at 8p11. The complete coding sequence of the tyrosine kinase domain of FGFR1 is retained in all three fusion genes and presumably activated by sequences of the different fusion partners by dimerization.

CONCLUSION

Activation of tyrosinc kinase signal transduction pathways are of increasing interest in the pathogenesis of chronic myeloproliferative disorders and myelodysplastic syndromes. The development of tyrosine kinase inhibitors could represent a promising therapeutic tool.

Fibroblast growth factor receptor 1 is fused to FIM in stem-cell myeloproliferative disorder with t(8;13)

Chromosome 8p11-12 is the site of a recurrent breakpoint in a myeloproliferative disorder that involves lymphoid (T- or B-cell), myeloid hyperplasia and eosinophilia, and evolves toward acute leukemia. This multilineage involvement suggests the malignant transformation of a primitive hematopoietic stem cell. In this disorder, the 8p11-12 region is associated with three different partners 6q27, 9q33, and 13q12. We describe here the molecular characterization of the t(8;13) translocation that involves the FGFR1 gene from 8p12, encoding a tyrosine kinase receptor for members of the fibroblast growth factor family, and a gene from 13q12, tentatively named FIM (Fused In Myeloproliferative disorders). FIM is related to DXS6673E, a candidate gene for X-linked mental retardation in Xq13.1; this defines a gene family involved in different human pathologies. The two reciprocal fusion transcripts, FIM/FGFR1 and FGFR1/FIM are expressed in the malignant cells. The FIM/FGFR1 fusion protein contains the FIM putative zinc finger motifs and the catalytic domain of FGFR1. We show that it has a constitutive tyrosine kinase activity.

FGFR1 is fused with a novel zinc-finger gene, ZNF198, in the t(8;13) leukaemia/lymphoma syndrome

Various histological subtypes of leukaemia and lymphoma are associated with diagnostic chromosome translocations, and substantial strides have been made in determining the specific oncogenes targetted by those translocations. We report the cloning of a novel fusion oncogene associated with a unique leukaemia/lymphoma syndrome. Patients afflicted with this syndrome present with lymphoblastic lymphoma and a myeloproliferative disorder, often accompanied by pronounced peripheral eosinophilia and/or prominent eosinophilic infiltrates in the affected bone marrow, which generally progress to full-blown acute myelogenous leukaemia within a year of diagnosis. A specific chromosome translocation, t(8;13)(p11;q11-12), is found in both lymphoma and myeloid leukaemia cells from these patients, supporting bi-lineage differentiation from a transformed stem cell. We find that the 8p11 translocation breakpoints, in each of four patients, interrupt intron 8 of the fibroblast growth factor receptor 1 gene (FGFR1). These translocations are associated with aberrant transcripts in which four predicted zinc-finger domains, contributed by a novel and widely expressed chromosome-13 gene (ZNF198), are fused to the FGFR1 tyrosine-kinase domain. Transient expression studies show that the ZNF198-FGFR1 fusion transcript directs the synthesis of an approximately 87-kD polypeptide, localizing predominantly to the cytoplasm. Our studies demonstrate an FGFR1 oncogenic role and suggest a tumorigenic mechanism in which ZNF198-FGFR1 activation results from ZNF198 zinc-finger-mediated homodimerization.

Identification of a YAC spanning the translocation breakpoint t(8;22) associated with acute monocytic leukemia

Using a series of yeast artificial chromosomes (YAC) from the Bp11-12 chromosome region, we have analyzed a t(8;22) translocation present in two patients suffering from acute leukemia by using fluorescence in situ hybridization (FISH). We have identified a YAC that spans the breakpoint in both cases.