Original articlesInterphase Detection of t(4;14)(p16.3;q32.3) by In Situ Hybridization and FGFR3 Overexpression in Plasma Cell Malignancies
Introduction
Multiple myeloma (MM), plasma cell leukemia (PCL), and plasmacytoma (PCM) are neoplasms of the long-lived plasma cell [1]. In these plasma cell malignancies, chromosomal translocations most frequently involve the immunoglobulin heavy chain (IgH) gene locus at 14q32.33, which implicates it in the pathogenesis of MM via dysregulation of proto-oncogenes located at partner chromosomal loci 2, 3, 4, 5. We have previously detected this IgH translocation by means of fluorescence in situ hybridization (FISH) in approximately 70% patients with MM [6]. A large number of chromosome partners have been identified recurrently in this characteristic translocation (e.g., 11q13.3, 8q24.1, 4p16.3, 18q21.3, 16q23, 6p21.1, 7q32.1, 1q21, and 9p13) 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, three of which, 4p16.3, 11q13.3, and 16q23, are most commonly involved 1, 5. On the other hand, several partner chromosomes cannot be detected by means of conventional cytogenetic methods, for example 4p16.3 (FGFR3), 6p25.3 (IRF4), and 16q23 (c-maf). These genes are located at the terminal bands of their respective chromosomes. In addition, many housekeeping genes have been assigned to the telomeric regions which are particularly recombination-prone [16].
The t(4;14)(p16.3;q32.3) translocation has recently been identified in MM cell lines, and is associated with overexpression of the fibroblast growth factor receptor 3 gene 3, 17. Because this translocation is a subtle chromosomal abnormality involving two of the most telomeric regions detectable by molecular cytogenetic techniques, no cytogenetic data have been available for assessing the incidence of t(4;14) in patients with plasma cell malignancies. In order to clarify the incidence of t(4;14) in primary tumor of plasma cell malignancies and to evaluate possible correlations with specific manifestations of the disease, we performed G-banding, interphase FISH, and/or reverse-transcriptase polymerase chain reaction (RT-PCR) analyses on 45 patients with these malignancies. As a result, six patients were identified with both fusion between the FGFR3 and IgH genes (FGFR3/IgH fusion) and FGFR3 overexpression, one patient with FGFR3/IgH fusion, and one with FGFR3 overexpression.
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Patients and Cell Lines
The bone marrow (BM) or peripheral blood (PB) cells of 45 patients with plasma cell malignancies was studied. Forty patients had MM, two had plasmacytoma (PCM), and three had PCL. The PCM tumors were detected in the orbita and the skin in each patient. Diagnosis of PCL was based on plasmacytosis exceeding 2 × 109/L of plasma cells in PB [18]. Thirty patients were male and 15 female, and their median age was 66 years (range, 39 to 89) at diagnosis. The types of M-protein identified were IgGκ in
Cytogenetic Findings
Metaphase spreads were available for karyotypic analysis of 34 patients with MM, three with PCL, and two with PCM. Karyotypes of 14 of the patients (nos. 22–26, 28, 30, 31, 35, 39, and 42–45) were described previously 6, 9. Twenty-three patients showed normal karyotype, and 15 abnormal karyotypes, including three with 14q+ chromosome: add(14)(q32) in patient no. 26, three-way translocation of t(8;14;11)(q24;q32;q13) in no. 34, and t(11;14) in no. 43 (Table 1).
Controls
PCR products of Y6 and a phage
Discussion
Interphase DC-FISH with FGFR3 and Cγ probes detected t(4;14)(q16.3;q32.3) in seven of 45 patients with plasma cell malignancies. On the other hand, mRNA of FGFR3 gene overexpressed in seven of the 36 patients studied by RT-PCR. FISH analysis of six of these seven patients with FGFR3 overexpression showed FGFR3/IgH fusion. These results indicate that t(4;14) significantly correlates with overexpression of the FGFR3 gene. In previous molecular studies on primary tumors, t(4;14) was detected at
Acknowledgements
This work was supported in part by a grant-in-aid from the Ministry of Education, Science and Culture (10670962 and 08266109), Japan.
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