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Advances in Brief |
1 Department of Genetics, University of Navarra, Pamplona, Spain; 2 Wessex Regional Genetics Laboratory, Salisbury and Human Genetics Division, University of Southampton, Southampton, United Kingdom; and 3 Haematology Service, Miguel Servet Hospital, Zaragoza, Spain
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| Introduction |
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| Materials and Methods |
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IFN (3 MU/day) was prescribed, and major hematological response was achieved. In 1995 a new painful episode of arthritis appeared that was interpreted as psoriasic arthritis because of the appearance of suggestive skin lesions. Karyotypic analysis showed persistence of t(5;14)(q35;q24) mitoses. Eosinophilia persisted, but no splenomegaly was observed. In March 1996, hematological remission was achieved again after treatment with
IFN (5 MU/day), psoriasic lesions were not observed, and
IFN administration was subsequently ceased. In 1997, moderate skin lesions were observed again with the WBC count progressively increasing, with eosinophila, basophilia, and mild splenomegaly. The patient refused
IFN and was subsequently treated with hydroxyurea (1 g/day), resulting in good hematological but not cytogenetical control. Reverse transcription (RT)-PCR for BCR-ABL was negative (15)
. In May 2002, due to the detection of PDGFRB involvement in the chromosomal rearrangement (16)
, treatment with imatinib mesylate was instigated. The initial dose of 400 mg/day was not well tolerated, and the patient decided to stop. In February 2003, imatinib (at 200 mg/day) was given again, resulting in hematological and cytogenetical remission but not complete molecular remission by RT-PCR (see below). On the basis of these data, the dose of imatinib was raised to 400 mg/day in November 2003.
FISH Analysis.
Whole chromosome painting was performed using the STAR*FISH human whole chromosome specific probes (Cambio, Cambridge, United Kingdom), with probes for chromosome 5 and 14 labeled with Cy3 and FITC, respectively. FISH analysis on bone marrow metaphases to narrow the breakpoint on 14q24 were performed with bacterial artificial chromosomes from the BACPAC Resource Center4
at Childrens Hospital Oakland Research Institute (Oakland, CA) or from the Sanger Institute Mapping Core Group5
at The Wellcome Trust Sanger Institute (Hinxton, United Kingdom). NIN gene on chromosome 14 was studied with bacterial artificial chromosomes RPCI-11 286O18 (centromeric to NIN) and RPCI 248J18 (which covers almost the whole gene). NIN clone positions were based on data provided by the University of CaliforniaSanta Cruz version hg16 (July 2003) available at the University of CaliforniaSanta Cruz Genome Browser.6
Southern Analysis of PDGFRB.
Ten µg of patient DNA and a control DNA without 5q31-q33 rearrangement were digested with HindIII, BamHI, EcoRI, and BglII, blotted using standard conditions and hybridized with an 813-bp
32P-dCTP-labeled PDGFRB intron 10 probe obtained by amplification by PCR with primers PD3-C and PD3-D (Table 1)
from normal human genomic DNA.
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DNA Cloning and Sequencing.
Fresh PCR products were cloned using the TOPO TA Cloning kit for Sequencing (Invitrogen-Life Technologies, Inc.). Colonies with recombinant plasmids containing PCR products were screened by boiling-PCR insert amplification. Positive recombinant plasmids were cultured again and plasmid DNA was extracted with QIAprep Spin Miniprep kit (Qiagen), checked again by EcoRI digestion and sequenced with ABI PRISM D-Rhodamine Terminator Cycle Sequencing kit (Applied Biosystems, Foster City, CA) in an ABI PRISM 377 DNA Sequencer (Applied Biosystems, Foster City, CA).
Computational Analysis.
Search for candidate genes in the 14q21.1-q32 chromosomal region was done using EnsMart as data retrieval tool from data held in the Ensembl database Human release 11.31.1 from March 2003 (built around the National Center for Biotechnology Information 31 assembly). Protein sequences were then analyzed using the pepcoil program from the EMBOSS Package.7
Pepcoil predicts coiled-coil regions by calculating the probability of a coiled-coil structure for windows of 28 residues through a protein sequence using the method of Lupas et al. (17)
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| Results |
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1 Mb that contains 13 RefSeq genes. Additional attempts to refine the chromosome 14 breakpoint by FISH were unsuccessful. PDGFRB translocation partner genes encode proteins with oligomerization domains (most of them coiled-coil domains), an essential feature required for the observed constitutive tyrosine kinase activity of the fusion proteins (2)
. We therefore tested each gene in the interval for their potential to encode proteins with coiled-coil domains, an analysis that resulted in three candidates for involvement in the t(5;14): SDCCAG1; SAV1 (SAlVador homologue 1 Drosophila); and NIN. SDCCAG1, the gene for a Serologically Defined Colon Cancer Antigen 1 codes for a putative nuclear protein with three coiled-coil domains. SAV1 encodes a protein which contains two WW domains and a coiled-coil region. Ninein, the product of the NIN gene, is a centrosomal protein that is predicted to consist of coiled-coils throughout most of its sequence. Its structure resembles that of another centrosomal protein, CEP110, a known fusion partner of FGFR1 in 8p11 myeloproliferative syndrome (18)
. For this reason, we considered NIN as the most likely fusion partner in the t(5;14).
Identification of NIN-PDGFRB.
To determine whether NIN was fused to PDGFRB, we performed multiple PCR analyses on patient and control cDNAs with forward primers located in several NIN exons and reverse primers located in PDGFRB exons 12 and 14. Positive results were obtained with forward primers located toward the 3'-end of NIN, sequencing of which showed an in-frame fusion between NIN exon 28 and PDGFRB exon 12 (Fig. 2A1)
. The breakpoint was confirmed by RT-PCR with different primer combinations (data not shown) and also by amplifying the genomic breakpoint (Fig. 2A2)
. The breakpoint position is consistent with the rearranged bands observed by Southern analysis (Fig. 1)
. RT-PCR with primers PDGFRB-2b and NIN-7 showed very weak amplification of the predicted reciprocal PDGFRB-NIN fusion, the identity of which was confirmed by sequencing (Fig. 2A.3)
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Response to Imatinib Treatment.
Once the partner gene was identified, it was possible to monitor the molecular response to imatinib mesylate using an RT-PCR assay with primers NIN-8 and PDGFRB-2. Molecular detection of the fusion transcript was possible in every available sample before imatinib treatment and also in May 2002, when treatment with imatinib mesylate was started and karyotype analysis showed 91% of metaphases with the translocation. As described above, imatinib treatment was stopped but restarted in February 2003. From April 2003, the patient was found to be in cytogenetical remission (30 metaphases analyzed) but in November 2003 remained RT-PCR positive. On the basis of these data, the imatinib dose was raised to 400 mg/day in November 2003. The course of the patient is illustrated on Fig. 3
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| Discussion |
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NIN is the second centrosomal protein-encoding gene that is fused to a tyrosine kinase in myeloproliferative diseases, the first being CEP110, the partner of FGFR1 in 8p11 myeloproliferative syndrome with the t(8;9)(p12;q33) (Ref. 18
). In a typical somatic cell, the centrosome is composed of a pair of centrioles surrounded by a mass of amorphous pericentriolar material that contain complexes of
-tubulin, centrin, pericentrin, and ninein. Ninein has been demonstrated to play an important role in microtubule minus end capping, centriole positioning, anchoring, and in centrosome maturation (19)
. Ninein levels decline at metaphase and anaphase and reaccumulate at the telophase-G1 transition of the next cell cycle; consequently, it has been suggested that ninein might play a role in ensuring equal chromosome segregation before telophase/cytokinesis (19)
. However, because no additional karyotypic changes appeared over >13 years, it is unlikely that the t(5;14)-positive cells in this patient had centrosome abnormalities and genetic instability as a consequence of ninein involvement.
Six of the seven PDGFRB fusions described to date have been found in patients with chronic eosinophilic leukemia, atypical CML, or chronic myelomonocytic leukemia, with eosinophilia using being present (3) . CEV14-PDGFRB, associated with the t(5;14)(q31;p12), is the exception, having only been found as a secondary event in a patient with relapsed acute myeloid leukemia. As in the case described here, some patients also displayed skin lesions, and it is conceivable that these arise as a consequence of aberrant PDGFRB signaling because this receptor is normally involved in wound healing and repair of skin lesions. Alternatively, these skin lesions may be a consequence of eosinophilic infiltrations (3) .
Identification of patients with PDGFRB rearrangements is important because they respond well to treatment with imatinib mesylate (4, 5, 6, 7) . In these studies, patients were most commonly treated with 400 mg/day of imatinib as a standard dose, although in some cases, it was necessary to increase it (4, 5, 6, 7) . Our patient achieved hematological and cytogenetical remission with imatinib mesylate at 200 mg/day, but on finding expression of NIN-PDGFRB by single-step PCR after 6 months of treatment, the dose of imatinib was raised to 400 mg/day.
In summary, we have a described a myeloproliferative disease patient with a novel PDGFRB fusion gene, identified in part by bioinformatic techniques. Characterization of the translocation enabled the patient to be treated by signal transduction therapy and for that treatment to be tailored by monitoring the molecular response. The partner gene, NIN, is functionally related to CEP110, supporting the concept of a network of tyrosine kinases and partners giving rise to CML-like diseases (2) .
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Requests for reprints: José L. Vizmanos, Department of Genetics, School of Science, University of Navarra, E-31008 Pamplona, Spain. Phone: 34-948-425 600; Fax: 34-948-425-649; E-mail: jlvizmanos{at}unav.es
4 Internet address: http://www.chori.org/bacpac/. ![]()
5 Internet address: http://www.sanger.ac.uk/Teams/CloneRes. ![]()
6 Internet address: http://genome.ucsc.edu. ![]()
7 Internet address: http://www.hgmp.mrc.ac.uk/Software/EMBOSS/. ![]()
Received 1/15/04. Revised 2/18/04. Accepted 2/25/04.
| REFERENCES |
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